Well, I find the video has a long introduction and then finishes off a bit too short with the conclusion that the moving person exists in two reference frames, period. That part, the meat of the paradox, should have been better explained.
I agree, in fact, I didn't understand what he meant. Could you please explain? Doesn't seem to make any sense, I would simply say that we have 3 frames and each of the frames is at rest in relation to one of the observers.
Yes, it really needed to circle back at 12:25 and expand on what those two very brief bullet points mean rather than just declaring it solved as I bet many missed it and quite a few may not get it on reviewing.
Like others here, I don't see the explanation. I hear "two frames of reference" but I can't connect that observation to an explanation I can grasp. It's like you ran out of time.
@@BinuJasim The stationary person does not *measure* time for the moving person. But she can *calculate* how much time should be passing for the moving person.
I'm sorry but you went all detail with the easy and well understood part, explaining it like we would to a 5th grader, and then just conclude in literally 5 seconds that since the observers B and C are not in one single reference frame (wich could have been explained as well as the rest was) this is the proof for the paradox not being a paradox. While I'm sure this is correct, and not wanting to tell you how to make your videos, this last part ,with no explanation at all to support or motivate your conclusion, didn't really prove anything to me. Still, it did provide for a starting point for me to dwelve deeper into, so thanks for that.
@@Guoenyi it's still a paradox, even if it's resolved. If you work in minkowski space(M4), there is no paradox because M4 is manifestly self-consistent.
This is a horrible example. Think about it guys. Dr. Lincon's example of A being stationary and C and B moving is the SAME as B being stationary and A and C are moving in the same direction (A away from B and C towards B), but C is merely 2x faster than A in the same direction while B is really stationary! The other probability is C is stationary and it's B and A moving towards C, but B moving at 2x the velocity of A, which in this 3rd scenario C is really stationary! To all observers, in all scenarios it would look identical and no one would be able to tell who's really doing the moving! Horrible example. The real reason is the person leaving Earth did the acceleration near the speed of light. That's the same as moving near a black hole and feeling the "acceleration" or the gravity well of the black hole (which relativity tells us gravity is just another form of acceleration and vice versa). Any person moving near a black hole would have their time slowed down, relative to an outside observer.
It's because the distance to the star looks different for the traveler than it does for the non-traveler. The difference in the distance occurs because the speed of light is always the same, if you're moving toward the light source or away from it. Bingo! I majored in physics at the university of michigan. I went to every single physics professor for an explanation, none of them had one so i switched to math.
I believe that there is an error in 10:25. According to observe C's perspective: the x co-ordinate (position) of event 1 would be -2yl, the x co-ordinate (length) of event 2 would be 0 and the x co-ordinate (length) of event 3 would be again 0. This is because the events' positions are relative to the perspective of C. It can also be supported by the x co-ordinates of the 3 events according to observer A and B's perspective since in the video the x co-ordinates of both perspectives are relative to the observer (i.e. for observer B event 2's x co-ordinate is considered to be 0 as the observer B and event 2 are on the same position). According to example I wrote in parenthesis, the x co-ordinate of event 2 for observer c would also be 0 as observer B and C are on the same position as well as event 2. However, this does not effect the conclusion reached. Please reply me either you believe I am right or explain my mistake.
I'm having a serious problem with this explanation. I get the idea that it's a question of which clock you're using as a reference but nothing shown shows why Ron's choice of his clock as the 'stationary' one is not the same as Don choosing his clock as the 'stationary' one. It's like somewhere in there, there's an assumption of which one is really stationary when in fact, once you exclude acceleration as a factor (which you do), then neither is a preferred frame. Even though it looks like it's solved the mystery - throughout the entire discussion, A is referred to as being 'the stationary person'.. but that's literally the thing we're trying not to say. Take all the math done and flip the contexts and they apply equally well and give exactly the same results relative to each viewer, except you're swapping A and B. That's the problem with this video - it shows the math from the 'stationary' person's view - but not from the 'moving' person's view in the perspective of his being the stationary person. Oh.. one other thought. In another video, you explain that the reason there is time dilation at all is a consequence of the fact that we're *always* travelling at the speed of light. Assuming we're just talking about one spatial axis, x, and one temporal axis, t - the vector must always be a unit vector... so at rest, it points entirely along the time axis and represents 1 second per second. As you change velocities (and I'm avoid saying acceleration intentionally because it's the velocity that causes it, not the acceleration) the unit vector rotates until you hit the speed of light where all of the vector lies in the x axis and there's no vector in t - ie no time movement. It seems like you're offering two different explanations for dilation. Keep in mind, I'm not saying you're wrong - you know way more than I could hope to about the subject.. I'm just suggesting that this explanation could be better.
No, it wouldn't show a paradox if you flipped the referential (just give it a try). Point is that all used referential in the video are inertia ones. A is not jumping to any other inertia referential, and you can't make a valid Lorentz transform that would show such a behavior, because in all other inertia frames, A is an inertia frame (constant velocity).
@@ThomasKundera Consider the spaceship reference frame A, consider the stationary person reference frame B and C except with the negative of the velocities used in the example. Perform all of the same calculations. Why would it be wrong to do this?
@@lukecasey2830 : _"consider the stationary person reference frame B and C "_ B is stationary, C is stationary. But (B and C) are not. So you can't make a computation assuming (B and C) is an inertia frame of reference (as you can do in A, as A is one).
@@ThomasKundera But we are not considering the stationary person as stationary when viewed from the spaceship's frame of reference. We use two frames of reference to describe the space ship, I do not see why we couldnt in return use two reference frames to describe the stationary person when considering the moving space ship as stationary. How do we even know the space ship is moving and not everything around it? The fact that it isnt expending fuel and accelerating, therefor not losing mass, leads to the conclusion that we dont know if the spaceship is moving or the stationary person (ignore that fact that we are callling the stationary person stationary, what we call the person is beside the point). Can you explain to me how we know the spaceship is moving, not everything around it, and how we know we must use 2 reference frames to only describe the spaceships movement? Please I am trying to figure this out but I cant. I know I am wrong and that I am not understanding something
@@lukecasey2830 : You can take any of A, B or C as "stationary". But, again, B then C is not. _" I do not see why we couldnt in return use two reference frames to describe the stationary person"_ Because if you need more than one frame, then it's not stationary, by any reference.
Sorry but you haven't done any actual explaining. Yes, you've set up a thought experiment with a departing and returning frame of reference that does without acceleration. You then arrive around 11:59 at "Duration(moving) = Duration(stationary)/gamma". But this is equally "paradoxical" as the original problem, because "moving" and "stationary" are still relative. You would actually need to show explicitly that the results are consistent if B or C were considered stationary AND independent of which clocks you use to measure the time between the different events. I'm sure it'll all work out but it seems awfully complex (involving relativity of simultaneity) and is definitely not obvious.
You need the relativity of simultaneity to fully explain why things are different for A and C. It's taken care of by the vx/c2 term in the Lorentz transformation for time, but unfortunately Don Lincoln didn't talk about it. Either he doesn't know it, or stayed silent on it by intention and just was focusing on the math.
@@NeedsEvidence I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations
Best comment. The video doesn,t explain the paradox. When he shows the (x,t) coordinates from B and C perspectives it,s not true. In fact, are the B and C (x,t) coordinates from A perspective. As you say, he should do the same calculations using the perspective of B and C and check that the results are consistent relative to A perspective. In addition there is a mistake on the (x,t)II,C coordinate maths, he shows x = gamma*L but it,s x = 2*gamma*L
I came to the SAME conclusions. This example of A being stationary can be said that C or B are also stationary and it's the other two moving! The real answer is the acceleration part. When you accelerate near the speed of light, Einstein tell us it's the same as being close to the gravitational effects of a black hole. GRAVITY and ACCELERATION are the same! Time slows down near the gravitational effects of a black hole, which would accelerate you near the speed of light to the event horizon! That is the real answer. Dr. Lincoln is correct on many things, but he's clearly wrong on this one.
I'm 67 and retired, but WHY could I not have had a Prof like you in University. You make complex things so understandably easy. Please keep teaching our hungry minds. Thank you Sir ! ! !
It is still a paradox. A is at one location as he said which explains his reference of movement is that "location" which is independent from the observers, which also decides that A is stationary there are three stationary "locations". But these locations don't exist in real space-time and the only reference is one of the three observers, which is why we do not know who is actually stationary. If you still don't understand let us say location 1 is the earth. Unless you think earth is stationary we don't know who is moving. Or we don't know if earth is always at that stationary "location" but never moves. Or thinks there is a stationary ether in which there is a location 1
This is unfortunately not correct! You are changing the entire scenario by inteiducing a third twin,second spaceship! Also, you are removing acceleration completely. How can you? Not possible! Have you read Einstein's solutiin to the Twin Paradox as mentioned in his 1918 documents? He explicitly states that acceleration of the travelli ng twin causes non- reciprocal time dilation which makes the travell8ng twin to be younger. Easy! Also, you can easily deduce this from the worldlines of the stay at home twin and the travelling twin. Whose wordline is shorter? The travellung twin's worldline. So, he remains younger. Why are you complicating it Mr. FERMILAB? 😊
Consider this, the earth moves ( rotation and revolution) yet we feel we are stationary. That's because we are in the same reference frame where everything on earth is moving. Now consider A to be on earth. A is stationary within this reference frame earth. Now B and C have different reference frames each. One when they start their journey ( Earth for B and 2L for C) and when they pass each other ( L for B and C both) and when they end their journey ( 2L for B amd earth for C). Thus these two people have different reference frames therefore there must have been some movement to change those reference frames. Therefore its concluded that B and C were moving and not A. All in all, the paradox arises with the question who exactly is moving. Now since it gets clear that B and C are moving and not A, the paradox gets solved
@@trsomas They are both moving relative to. A. So we can say B is stationary and A and C are moving relative to each other. I belive he should have done that calculation too to convince most people.
@@jaimeduncan6167 The problem that I have with this explanation is that in the original paradox, B and C are both represented by one person that never moves relative to himself, so what does this explanation have to do with explaining the original paradox?
@@trsomas And A and C are moving relative to each other and A and B are moving relative to each other. I sense poppycock here. They are all inertial systems and the Lorenz transformation can be applied equally in all permutiations.
"When we start the experiment, all 3 observers start a stopwatch." This sentence contains the idea of "simultaneously". Problem is, simultaneous in whose reference frame?
That's an excellent point Don Lincoln failed to address. It is the vx/c2 term in the Lorentz transformation that takes care of the relativity of simultaneity. In fact, C's "now-slice" corresponds to a future moment of A, and it is for this reason that A sees more time passing than C when C reaches A.
The end of the video was the most critical part to helping people understand why the twin paradox is not a paradox. In my opinion, you failed that task. You hinted at the answer, but you did not clearly spell it out for people who do not understand. (Also, as I understand it, you synthetically created a jump discontinuity, which is equivalent to an "instantaneous" "infinite" acceleration. If true, the example fails to illustrate your point.) At any rate, the animations and video editing were boss.
glad, I'm not the only one to recognize this... Sometimes he prolongs certain passages unnecessarily, almost putting the audience to sleep, and then when the final conclusion is due, he just leaves it up to the listener to spell it out in their minds... His pedagogical style is as discontinuous as his frame jumping that supposedly got rid of "acceleration" / change in direction issues. (which it didn't)
James Wilson SOOO?? Why the heck wouldn’t you explain it if you understand it so well????! You take the time to write all that (which was a little unncessary considering that you first phrase was enough) and you don’t even explain what that hint means?!? So why even bother stating all that? What’s your line of reasoning? It seems to me as if you are not using your head at all.
"jump discontinuity"? What is that, and How? Where? Seems to me that B was in constant motion towards +v and C was in constant motion towards -v. All they did was pass information. How is that a "jump discontinuity"?
I found this version to be better than the version without equations. It would have been more clear if Dr. Lincoln had explained what he meant by "the moving observers existed in two [frames of reference]". When he said that, he meant that the moving observers existed in two _separate_ frames of reference. Thus, he debunks the notion that the acceleration explanation for earthbound Don being older than astronaut Ron. So, the twin paradox isn't a paradox. It's just a conundrum ... and the conundrum isn't explained by acceleration, but by the Lorenz transform equations.
I don't get how is it possible that we have one non-moving observer and two moving observers. Aren't all observers non-moving (according to themselves, of course) by definition? Considering B and C as moving isn't in fact still viewing the situation only from A's perspective? And how is it justified, considering that we have to prove that «Ron is younger» with every system of reference? So, for A, the velocities of A, B and C are: 0, v, -v; for B, they are: -v, 0, -2v; and for C: v, 2v, 0. Therefore, the order of the magnitude also changes: A: a
That doesn't make any sense. Although I'm willing to admit to being wrong, all observers should exist for everyone else and everyone can measure everyone moving. I'm willing to admit to not getting it, but it doesn't prove it to me. Maybe it's because I'm a humanities guy.
One person stays in the same inertial frame of reference throughout and the other shifts from one inertial frame to another. ruclips.net/video/JPCDKta2LVE/видео.html
@@trsomas I'm a believer that time is a universal constant. Who cares what speed or acceleration you are at.... A lightyear still takes you a year to travel at lightspeed...
And don't get me started on the "observer" bullshit. They see light at light speed. I believe that relativity is something people got confused into believing because of all the variables and confusing names for variables like "light-year". It's a measurement of DISTANCE. It's how far light gets after 1 year of traveling. In all these experiments, they treat travelling a light year at light-speed like it's instantaneous. STILL TAKES A FUCKN YEAR.
You are only talking about Special Relativity. Relative acceleration does play a role in General Relativity, where a single non-inertial reference frame is allowed for the spaceship’s entire journey. The person in the spaceship can believe that he is standing still by believing that there is a gravitational field present throughout all of space, and that gravitational time dilation is what causes him to be older than his twin.
Well, if the acceleration is only about 1 g, the time dilation due to acceleration will be tiny---it would be comparable to the time dilation we experience by sitting on the Earth, which is not much! So GR adds some (very small) correction, but doesn't change the main picture.
The issue with using general relativity is that spacetime does not curve due to acceleration, and so gravitational time dilation is not a factor in the paradox.
stecordas uh....isn't it impossible for an occupant to determine the difference between acceleration and gravity? who says BOTH don't cause curving of spacetime?
AirPlayRule For the same reason centrifugal force is not a real force; apparent force is an illusion of your finite senses. The universe doesn't care what your brain is falsely interpreting, it cares what your bundle of atoms are actually doing in -dimensional spacetime.
I have to disagree with you here. This video is not about the twin paradox, but about time dilation. I don't know why people often get confused between these two concepts. Time dilation is saying that proper time always shorter than coordinate time in a Lorentz transformation, but this is not a problem since you need 2 synchronized observers to measure the coordinate time but simultaneity is not absolute for all inertia observers. However, the twin paradox is comparing the proper time between two observers, which are stationary with respect to themselves. Your explanation is not strictly valid because you implicitly assume there is one stationary reference frame and the other observer changes his reference frame with respect to the stationary observer. But in that case, why can't we say the second observer is stationary and the first observer changes his reference frame with respect to the second observer? I mean how do you even justify which twin is your observer A in 6:27? You cannot simply say just because the twin is on Earth then he is not moving. The main reason that leads to the twin paradox is that special relativity treats systems with relative acceleration asymmetrically. That is, the laws of physics under special relativity are not invariant under a transformation involving accelaration. Besides that, Newton's law of gravity is incompatible with special relativity, in other words it is not Lorentz covariant. These two problems bothered Einstein for quite a while. But ultimately he realized that these two problems are strongly related to each other via the equivalent principle. So despite that twin paradox can be solved in the framework of special relativity, even without mentioning acceleration (equivalently treat it as infinite and instantaneous) using the spacetime diagram. It does not answer the most fundamental question of this problem: when, how and why does the symmetry between two reference frames break down, does it mean physics has a preferred frame of reference? Einstein answered all these questions in 1915-1916 by the introduction of general relativity, where we see the laws of physics (gravity and classical electromagnetism) are invariant for frames of reference. Until then, special relativity is only a special case of a more general theory of relativity.
@silverrahul The example he used does not resolve twin paradox. It is just time dilation. To resolve twin paradox, the two systems must synchronize their clocks in the first place and compare the time elapsed when they rejoin. This process does not involve a third observer, this is why his argument is invalid.
@silverrahul Did you see the problem here? The reason that leads to this asymmetry is that one observer is assumed to occupy two reference frames during his journey. Despite B sync his clock with A and C sync his clock with B, then finally A and C compare their time, leading A to believe that B is younger than him. However, B does not agree with this statement. Since C is moving away from B, B would see the clock of C is running slower than his clock after their synchronization in the middle, leading B to think that he is still older than A. This restores the paradox.
@silverrahul Are we still talking about the same problem here? I think you are the one who gets confused. I only assert one claim. "This video does not resolve the twin paradox." I can say this for sure because he transformed the twin paradox into a different problem. At the end, he states that "Non-moving observer (Earth twin) existed in one frame while the moving observers (correspond to Space twin during outbound and inbound respectively) existed in two frames. This is the answer to the twin paradox. " Only if we make this assumption, then the example of the A, B, and C observers would be valid. The space twin has to agree that he is the one who switches from B frame to C frame during his journey. However, this claim is not justified. How can you prove that the Space twin existed in two frames while the Earth twin only existed in one frame? Answer my last question.
@silverrahul First of all, by "one observer in two frames" I meant the space twin, not A, B, or C. Furthermore, he did transform the problem into a different (and not equivalent) problem. There are only 2 observers in the original twin paradox while he formulated the problem involving 3 distinct observers. Maybe my math sucks, perhaps 2 is somehow equal to 3. Regarding your last argument, you claim that the space twin existed in two frames because he is the one who fires his rocket and goes back. By making this premise, you already put yourselves in the reference frame of A. What if the space twin insisted that despite firing his rocket, he is the one who stays stationary (with respect to himself) and the Earth twin is the one who travels away from him then turns back around and rejoins him? In simpler words, simply use the argument in the video but now swap the Space twin and Earth twin. That is, the space twin now changed to A, while the Earth twin is represented by B and C during outbound and inbound respectively. Then you will see the paradox still persists.
@silverrahul You see, he formulated the problem in such a way that it requires an intermediate observer to compare whether the Space twin or the Earth twin is younger. But then there is no direct comparison of time elapsed between the two twins anymore, so the problem has changed. On the other hand, I am happy that you finally brought out the concept of proper acceleration and inertial frame. This affirms my claim in the first place: "The video does not resolve the twin paradox." Because it does not state the key event that breaks the symmetry between the twins. That is, the Space twin did not remain in a single inertia frame of reference the whole time but the Earth twin did. This is the real resolution of the twin paradox.
As a teacher of A-level Physics I found this video interesting, especially as the textbook we supply to our students gives the acceleration & deceleration solution. A past exam question (AQA exam board) explained it by saying the rocket twin was in a non-inertial frame of reference.
The twins paradox exists in inertial frames without doing the introduction of a new reference frame C. Just imagine twin A is in a high circular orbit, and twin B is in an eccentric orbit that tangentially intersects A’s circular orbit. No rockets, no thrust, no acceleration, no non-inertial frame nonsense. We know high orbits experience time slower than low orbits. GPS satellites lose 1ns per 1s compared with us surface dwellers. But how does the twin B know it’s in a low orbit when it’s in an inertial frame? Orbits are just free-fall, and are inertial frames.
@@hdthorcircular orbits are non intertidal. They experience constant acceleration. But I agree with you that the acceleration is not needed for the paradox to occur.
The solution with acceleration is the solutiin given by Albert Einstein in 1918. You can not solve it without acceleration as the travelling twin must change refence feames through acceleration and deceleration!!
@@hardkraft6894 An object in free fall does not experience acceleration. If you jump of a building you feel no forces until you hit the ground. When standing on the ground you feel the earth pushing you up from your feet. So on the surface of the earth is a non-inertial frame. The moon is in an inertial frame. So if you see an object dropped off a building while you are standing on the ground, you will calculate that it's speed is increasing relative to you and you might say it is accelerating but it is you that is feeling the upward force not the object. So from the objects point of view you are accelerating upward. This is like the equivalence principle that Einstein used at the start of General Relativity. If you are standing at the engine end of a rocket and it is accelerating, you feel a force on your feet pushing you up. When you hit the gas in your car, your seat pushed on your back to accelerate you forward. So if you equate gravity with other forces that accelerate you , just standing on the ground is as if you are accelerating up.
6:35 I don't understand how A and B could agree where C is "now" if A and B are moving relative to each other and have different perspective what "now" is in point 3.
Ehm psychology is about different states of brains, which are electrical currents within a specific kind of very physical object. That's physics, but instead of trying to go the natural scientific way (like it's today done by trying to map the individual connectome), people just made up some pseudoscience and termed it "psychology". Social "sciences" are about behaviors of humans. Humans are typical animals. Biology is in principle just the result of biochemistry/molecular biology and that's just chemistry, which is in first approximation nothing else than the physics of the outer valence shell electrons. Everything is natural sciences and in the end physics. Exactly that's why social sciences have such a bad reputation among educated people. And of course because hey rely more on citation and who said what, than on observation, thus perverting the scientific method.
Philip Berthiaume Hawking had no true knowledge about the universe. The universe is much, much more complicated than Hawking could ever imagine. Do you know where is Hawking now?
Right. Also, the only way for Ron to switch from frame B to frame C (when they meet at position 2) is by experiencing acceleration... and if I neglected that idea, I would be entitled to apply the same argument to the motion of Don relative to Ron (rather than the motion of Ron relative to Don), and I would reach exactly the opposite conclusion, using the same formulas.
It is funny how the Einsteinists - the paradox "explanators" bring the human fillings into consideration. Now you have to fill the acceleration - this switches you from frame to another frame, you are only stationary when you don't fill acceleration :) Where it is in Einstein's equations?This is why the theory is crap.
The theory is definitely not crap, because it is used it many, many times to explain real observations to high degree of precision, where classical kinematics has failed completely. It is not intuitive, and not even required at low relative speeds, so you should be good to go in most of the experiences that we, as humans, deal with..
I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations
I may have missed something here, but in the (x,t) coords for event II for observers B and C there seems to be an inconsistency. Specifically, the location (x) for B is given as 0, but for C is yL (I use y for gamma so it is easier to type). It seems to me that B should be -yL. If not, then C should also be 0, not yL.
Although X coordinate is not used for the demonstration of the time dilation, I think it is useful to work out what happened to it. E.g C takes part in all three events, so X for it is always 0.
@@alexotenko6597 good point. why is every missing this? If i am right, then if you look at 10:14 to 10:32, those equations location are all considering "X" from A's perspective only. Then shouldn't we write equations from B's and C's perspective where X is always 0 from B's perspective and X is always 0 from C's perspective. Then no body is aging faster?
Since A, B and C were not accelerating, they were moving (parting away or coming closer) steadily with respect to one another by exactly the same amount. Since there is no "Stationary" frame of reference, all three would think that other two inertially moving persons are aging younger by exactly the same amount(e.g. 6 years). A would think B and C are younger by 6 year, B will think A and C are younger by 6 years, and C would think A an B are younger by 6 year. It is understandable why the presenter abruptly cut off the video by just mentioning: it is because to ONE frame vs TWO or THREE frames -- instead of steadfastly reasoning why A would grow older by 6 years from others perspective while others would remain younger despite same relative motion! He could have plugged numbers in those equations that are 100% same for all three and prove why just one of those three symmetrical equations would magically yield no time dilation!
?? On to the CORRECTION in 10:32, shouldn't the location of event II for observer C be 0, not 2yL? If so, C's locations for events I and III should be 2yL and 0 respectively (not the other way around).
5 лет назад
Right, almost. Notice that C overlaps A at event III. That means x should be 0 from C's perspective for that event.
This is because two different observers, each moving at different velocities, perceive simultaneous events differently, implying that they possess distinct planes of simultaneity. Consequently, the Lorentz transform factors in the velocity's sign.
Excellent explanation! I noticed there is a mistake for the perspective of the referential frame of observer "C" for event II, where instead of position γL should be 2γl. After struggling with the problem, I saw you already have made the correction. I think it is important to highlight that the origin of three frames started together at the event I. There is an asymmetry to explain the paradox. While observer "A" measures the difference between events in two clocks at rest where these events happened (B-A) and (C-B), each one of the observers "B" and "C" measures the interval of time on their own clocks attached with their bodies. The second intervals are proper times, related to the interval of time measured by "A" for dilation time expression: each time interval for A equals γ multiplied by each proper time interval .for B and C. If we begin with the interval measured by observer "A", we have to subtract the quantity of xv/c² for event B and add the quantity xv/c² for event C because the clocks are advanced in the direction of motion and delayed in the opposite direction by these terms according to relativity of simultaneity . After that, we have the interval of time passed in only one clock in the frame of observer "A" and we must multiply it by γ to obtain the interval for observers "B" and "C". In other words, the origin of asymmetry is the relativity of simultaneity expressed in Lorentz Transformation. Each one observer can claim the other clock is slower, and each one observer can consider moving in the direction of future of the other reference frame as expected by symmetry.
My conclusion from your complicated response here is that the video fails to give a clear explanation. It is completely expected that for A the first interval travelled by B from its passing by A until passing by C and subsequently the second interval travelled by C from its passing by B until its passing by A are of the same duration, namely the duration for A between B passing by A and C passing by, divided by 2γ (two gamma). This, however, does NOT explain why A cannot be seen by B to age much less.
Two questions then. 1) What part of the equation dealt with the delay of causality (light) it takes to get from 2l to person A? 2) You said person A only has one reference frame. However, In the twin paradox don was on a planet. Which is moving there for he also has multiple frames of reference. In fact. If everything is retaliative then counting the frames of reference is a paradox as they can be flipped. Inertia is still the only thing that separates them irrespective if you can work it out after the change in velocity or not. What have I missed? Example of my thinking based on your experiment. Let's slow things down to very (VERY) small numbers. put the two in cars going 100km/h. It was the previous acceleration that changed person c to 100km/h. So he is the one changing frames. You can see it based on the 100km/h but it's still the acceleration that caused it.
An assumption has been made that the planet is in an inertial frame. This means we assume that the proper acceleration of the planet is negligible. If you do not want to make that approximation, then instead of a planet, assume that Don stays at rest in some inertial frame of reference.
I sort of "get" this, but I also agree with brixomatic about "long introduction" and "bit too short with the conclusion". Do another video please to follow up this one! Three specific comments on this video: (1) I would like to see some sort of comparison of what each of the observers (A, B and C) experience, as I would like to see everything being consistent for observers when they are momentarily at the same point, 1 and 2. (2)I am slightly concerned about how the points 1, 2 and 3 are observed by ANY observer. Is it required that there is a NOW point for 1, 2 and 3 (in at least some observers view) when this all starts? Perhaps, if so, the NOW, or "start time" at 1, 2 and 3 can be called by "you", the passive 4th observer of this situation, in the same inertial frame as 1, 2 and 3. However, for that to be the case 1, 2 and 3 would have to be equidistant from you - and that puts them on a spherical surface. That means that B and C are accelerating when they are moving! (Although I can see the "local" time at location 2 could be irrelevant, in which case it can be on a straight line between 1 and 3.) (3)This video explanation shows that acceleration is not required to resolve the theoretical paradox but it does not mention any additional effect that acceleration might have should it occur. In a real twin paradox experiment, acceleration would have to occur. And, since acceleration is equivalent to a gravitational field (in which clocks run slow), additional effects of acceleration in a real situation should at least get a mention in this video.
I understood everything up until 10:12. I can't figure out how you solve for any of those positions for B or C. Nor, for that matter, why C starts at (0,0). C starts at (2L, 0), from all perspectives, does it not?
That's not where C starts, you're looking at Event 1, which is the "event" of B leaving Earth. That event has the same position in all reference frames because it was chosen at the origin (0,0), and the Lorentz Transform preserves zero.
@@ericchasseur3904 Thanks for replying to my old comment. Coming back to this, rewatching that part of the video, I understood my confusion, and I understood ANGRY's reply, which I originally did not. Thx yall.
A point of possible confusion with this is at 8:07 where the statement is made that you can work out how you can get from 1 to 2 and back to 1 again without any acceleration. This is true for non-massive quantities, and it actually would take an infinite, impossible acceleration at position 2 to accomplish this with anything that has mass. You have shown that you can get information from 1 to 2 and back again this way, but not an observer or clock. If you compare the clocks of observers B and C and the "end" of the experiment, there is no difference. This example should be re-presented in a physically realistic point of view from observers starting from a common space-time point. Mixing observers that are in different frames from the start might create confusion and is not the essence of twin "paradox" since the starting point has two opposing frames that are not twins.
Rafael Cacilhas No, because B started at position 1, where A is. The light would be coming from the midpoint, position 2, and reach position 1, where A and B are, and position 3, where C is, at the same time, signaling person B at position 1, and person C at position 3, to start moving, while person A remains at position 1.
@@wr2382No this doesn’t work. Person A and person C will not agree that they started their clocks at the same moment. Their reference frames are different and clocks will not be synchronized with each other and would claim the other person started their clock at the wrong moment. I mean also, person C will get the light before person A since person C is going to meet the light partway (according to the view that person A is at rest).
The original version of the experiment involves only 2 observers, in the explanation it involves 3 observers. Observers B and C see a shorter distance due to Lorentz contraction of length. But for the original version of the paradox, Ron and Don started and ended in the same inertial frame (one can forget about the earth which confuses the issue as it creates a non-inertial frame), it seems that the explanation does not deal with the original paradox. (Sorry, I am not a professional physicist.)
You're right, but the purpose of this scenario is to show how the result of the original scenario can be replicated without relying on acceleration. The point is that while acceleration is a relevant detail in the solution to the twin paradox, it is not the proximal cause of the differential aging.
@@Arkalius80 Acceleration is the primary cause of the ageing though, since the special relativistic component only deals with the perception of time from a distance of objects at different velocity, not the fundamental nature of matter being energy in motion, which is general relativity, this problem is asking the question why are they different ages upon being reunited, which turns out to be how many relativistic rotations they ended up making and why they are different. Turns out the simple point is that matter is only in motion in relation to it's inertia, which is not a euclidean frame, it's actually represented by a matter distribution surrounding an object, using Newton's every action has an equal and opposite reaction, the sum of action and it's inertia are zero. In relativity, even the frame is projected at the speed of light, because no causal influence can happen without time, it takes time to project the frame and so an object's inertia is more influenced by matter that is closer to it. The twin paradox is dealing with the matter ageing differently when an object is accelerating in relation to it's own surrounding inertia, it experiences slower time because the electrons spinning inside the accelerated matter are limited to travel no faster than light speed, the matter slows it's internal rotations compared to the matter that makes up it's inertia. The twin paradox is all to do with it being matter that is ageing differently and general relativity solves it, special relativity is going to have to resolve crossed frames to assign a rest point and then ask relevant questions only, since asking a question must have an observer. It's a general relativity problem, like solving kinetic motion using energy equations, using special relativistic time dilation and length contraction only explain appearances from different perspectives, it doesn't deal with root of the question.
@@Arkalius80That's 100% wrong. It's solely about acceleration. Acceleration is what leads to the phenomenon of one twin aging less. If they accelerated the same, they would have aged the same.
Nice video, but it seems that the resolution of this paradox still requires acceleration. Without acceleration, each twin will perceive the other as younger; the resolution requires a real comparison, and you at least need one of them to accelerate to the frame of the other in order to do that - no matter how many twins you have.
I don't understand something here. The only way the spaceship twin can avoid acceleration is to be going at the close to the speed of light when she leaves earth. That is the spaceship sister flys pass her twin sister on earth as she is flying on her way to the star at close a speed of light. But how does she coordinate her clock with her twin's clock? She must include her speed in determining if the two clocks are synchronous. In fact the sister on earth will see her twin sister's clock on the spaceship moving very slow. The sister on the spaceship will also see her sister's clock on earth moving very slow. Provided neither sister slams on the brakes and undergoes gravity, or what looks like gravity, than neither sister will ever know the age of the other sister because a signal traveling at the speed of light to show the time on the clocks will always be lagging behind the spaceship traveling at close to the speed of light. And it will take this considerable time to catch up with the spaceship. I think Einstein is very careful to state that for two clocks to be determined to be synchronous they must be checked where both clocks are close to each other and in the same frame of reference. But how can the twin sisters clocks be in the same frame of reference or close to each other if one is moving away from or toward the other at the speed of light. This is of considerable error if the third sister, L2, is making her observation from a star 4 light-years away from the sister resting on the planet. Which is to say you do not make the problem any easier to understand by eliminating the acceleration. You just move the complexications to determining what do you mean by saying all 3 sisters, the one on the planet, the one moving away from the planet and the one moving towards the plant are all the same age (clocks are synchronous) at the start of the experiment. Note this is not a trivial acceleration, or gravitational pull, to go from zero to 0.999c to zero to 0.999c to zero in 4 months. No such spaceship exist or can be built if relativity is correct. Provided all three sisters are the same age, that is the clocks are synchronous at the start of the experiment, and no sister undergoes acceleration then the experiment is impossible to conduct. This paradox looks a little like a perpetual motion machine where it works only if you ignore the details. You could say OK all three sisters are to start the experiment from earth at the same time. One sister remains on earth, one flies away to turn around and fly past earth on her way to the star and one flies to the star to turn around and fly back past the earth. The problem is all three sisters will be starting the experiment at different ages and be in different frames of reference. And when the experiment is completed all will be of different ages. But no paradox because you can not compare each sisters space-time travel or synchronize the experiment start.
I think the resolution is incomplete. Three quarters done, to be precise. It has been explained how much time passes on the spaceship according to an observer on earth as well as on the spaceship(s). So far, so good. The time that passes on earth during this ordeal, according to the observer on earth, has also been noted. But how much time passes on earth according to the observer(s) on the spaceship(s), and how that matches with the aforementioned interval (time passed on earth according to observer on earth), has not been explained. This, according to me, is the heart of this paradox, which is also the most difficult part to resolve without considering accelerated frame.
5 лет назад
Exactly, that is what is missing! I think the explanation is the issue of simultaneousness. Two observers can only compare clocks when they are at the same position. That is the whole idea of the set-up. The problem you mention is that B should observe A's clock moving slower. This would give a conflicting result, from B's reference when reaching event II. I think the explanation here is that B can't compare clocks with A at event II because they are not at the same position.
A perfectly symmetric scenario is described? B and C are absolutely symmetric. That being said, I understand it all and it doesn't resolve the twin paradox. You have to incorporate the asymmetry, and it is due to acceleration. Acceleration is outside the scope of special relativity and violates the assumptions of both SR and the Lorentz transformations. The twin that experiences acceleration is not even remotely allowed to say she's stationary within the context of SR or Lorentz. This is a part of the assumptions of the theory. You can pseudo-analyze non-inertial frames within the context of SR, but it is a logical violation of assumption. I of course follow your arguments, but they are mathematically, formally inconsistent when applied to the departing and returning twin. A better resolution is required. In the purely SR case, "outliving your enemies" can be achieved by relative velocity, but you have to have differential acceleration to get there and back. There is no denying that. To say that it is all velocity is denying the derivative. All things considered, this is an excellent video and among the best presentations on this topic I've seen. The bottom line is that if a departing and returning traveler and twin experience different accelerations, they will have different times upon reuniting. If they experience identical accelerations, well, they will have identical times. This post will likely be deleted by remote observer with faster clock, but I encourage you to read before.
yes, inconsistent, that's the word. the setup is fundamentally different from the twin paradox experiment, it's a different scenario. any proof that the result can be applied to the twin paradox??
@@karejonsson8264 The "gravitational" time dilation due to acceleration is a factor of the distance between the clocks, which indirectly depends on the duration.
It appears it wasnt just me left thinking 'but... acceleration is what changes your reference frame. So isnt this rather semantic?' but Im inclined to believe that when an experts explanation doesnt add up to me that I must be missing something. So I was considering the scenario of the twins being in a small spherical universe where one starts off and arrives back by going all the way round that universe without accelerating. Im not sure how difficult a problem that would be to solve, if it needs some heady general relativity or not, but perhaps in this case and other parts of general relativity it could make for a more substantive distinction between the two ways of thinking about this? Edit: I wouldnt mind hearing other possible suggestions. I have to say Im kind of confused by what incite hes really getting at here.
Yes acceleration changes reference frame but the way some RUclips videos give explanation based on acceleration is wrong. They say that the travelling twin is accelerating, so his clock will tick slower. The correct way is to use general theory of relativity from travelling twin's frame of reference and argue that the stationary twin's clock will tick faster. See this video for more detail. ruclips.net/video/JPCDKta2LVE/видео.html
@@abdullahbinjahed6900 According to the paradox, if we use time dilation from A's frame, we find B is younger and if we use time dilation in B's frame, we find A is younger. We should be able to resolve the paradox by pointing out where time dilation has been used wrongly in the paradox. The answer is that the astronaut uses time dilation formula form two different inertial frames and he does not account for changing from one inertial frame to another. This is where time dilation has been used wrongly in the paradox. Acceleration only serves the purpose of changing the inertial frame of reference.
@@trsomas say ... a round universe with nothing in it ... now you and me popped up in existence and travel in different directions at a constant velocity ... because the universe is round we will meet again without even changing our direction ... so ... now tell me ... what's the solution ?
I'm quite disappointed with this "real" explanation. Isn't "frame jumping" just acceleration? I find the difference only semantic. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any person with any relevant credentials claiming this.
No, they are not the same - acceleration is real and frame jumping is a shell game. Einstein used acceleration in his paradox resolution in 1918. This doesn't.
+Chenfeng It's wrong to say that time dilation happens only during acceleration, but it's not wrong to say that it happens because of acceleration. Go back to the real twin paradox (not one without twins that is shown here). If there is no differential acceleration, there is no differential time, period. This is, by accepted definitions of the term, a causal relation between differential acceleration and differential time dilation.
What if there is a theoretical person A travelling at a constant velocity to infinity, and a variable twin B that just exists in V = 0 - wouldn't that person A age slower, without any change in velocity? If person A was born into the shape-ship already in motion. Of course this is no possible in the Twin example (no one would return to earth here), but just a theoretical example doesn't till still hold true? Especially if you had theoretical person C at the opposite end of the distance from person A, also in motion travelling to the direction of A.
Chenfeng Bao But that is pretty much the same thing that happens when you go to a point a distance L appart from a stationary observer, and then back again. You change the direction of your velocity when you turn and go back. The only difference between observer B and observer C is that their velocity has opposite directions. So "jumping" from frame B to frame C is equivalent to just "suddenly" turn and go in the opposite direction without accelerating. Of course, this is physically impossible, because you have to accelerate to do so, but this shows that if it was possible, or if you can do something similar to it, then special relativity would still work.
Felis Super You could assume a constant speed, but smooth change in direction (curve) until B's velocity vector is pointing right back at A, if you truly want to make the example "realistic"... But since it is just a thought experiment, there's no need for that! The point is, that a change in direction (no matter how realistic) will always break the (relativity-) symmetry between A and B. When linear motions are involved, all frames of reference are equally valid. But as soon as one of the two observers changes direction (or speed), it will know! (forces etc.). If we truly cared about a realistic change in speed that much, we should also include the traveling twin's acceleration from earth into space to begin with, which is not possible to be instantaneous either....If the creator of this video actually tried to get rid of "change in direction" by introducing new observers, complicating the thought experiment, he should also have introduced a new observer D in order to get rid of the take off discontinuity in velocity, although I guess making B just fly by earth (observer A) while exchanging time information would've sufficed.
At 10:23 the video shows that the value of x for the event II in the observer C's perspective is γL, but I got 2γL. (My results for all the other values correspond with your solution.) Is there an error in the video? If not, how did you get γL?
Kirsti Sunde Midttun, you just put *v* with the correct sign. The sign depends on the direction of A moving relative to the observer. As far as Observer B is concerned, Observer A is moving with a velocity *-v* (A is moving left relative to B), whereas Observer C sees Observer A moving with a velocity *+v* (A is moving right relative to C).
One thing is not clear to me in this case. Can you define the three events? Since they are far away from each other (at least A and C, and C happens to be moving), so they could not agree on a specific time when an event happens, right?
They will not agree on whether the events are simultaneous with each other or not, but they will agree on what the person at the event's clock reads as they pass it.
@@Arkalius80 But the important question is how do you know that observer C started his stopwatch "at the same time" observers A and B started theirs? If the starting of all three watches is not a "simultaneous" event, their relative readings are essentially meaningless. And special relativity owes its origins to deep thought into what, exactly, "simultaneous" actually means when events take place in different locations.
indeed, no need for that. that would drown us in the complications of simultaneity. they actually don't start moving because they move eternally, no acceleration allowed. you can imagine that there's an infinite stream of travellers C and this experiment looks at the one guy who meets traveller B at the middle point #2.
Yes with a light signal. If you look at a spacetime diagram, light will always move at a 45 degree angle regardless of the speed of the other reference frame. So you can send a light signal to another observer and he starts his clock when the light signal hits him. It's reflected off a surface and send back to the original observer. If you take the total time elapsed for the first observer and divide it by two, you know how long it took for the light to reach the second observer so you then how much to delay your clock for proper calibration
Help from a physicist please: Don says that there is no acceleration in the case of the twin paradox - but isn't the transition from one reference frame to another what acceleration is? Where am I going wrong here?
+Theo Philus Yer not wrong: describing the motion via 'clock swapping' still requires gluing together different inertial frames comoving with actual observers - i.e., acceleration
"His example shows that the acceleration isn't relevant" But, by definition, the twin paradox REQUIRES that Observer B travel to Alpha Centauri AND return. The ONLY way Observer B can return is by transitioning to Observer C's reference frame at Alpha Centauri. And the ONLY way Observer B can do this is by accelerating from v to -v at Alpha Centauri. Without this acceleration, Observer B continues to travel away from Observer A so (1) there is no twin paradox, and (2) the thought experiment is only 2 separate examples of time dilation added together. The twin paradox requires that the twins MEET in the future to compare ages side by side. Bottom line: 2 twins start and end in the same place. Which twin is younger? The twin who traveled and who experienced the acceleration.
ScienceNinjaDude But can't we set the rocket person as the stationary frame and say Earth is the frame that's moving out and back? That's using the same treatment with two different frames for the Earth "frame". I guess what I'm trying to say is, why is the rocket the one with 2 frames? Why isn't Earth the one with two frames?
I agree. Whether it's "acceleration" or "frame jumping" is just a semantic difference. I don't find any deep meaningful difference between the two explanations. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any people with any relevant credential claiming this. Credential: PhD student in physics.
ok.. if the 3 events from A's POV are (0,0); (L, L/v), and (0, 2L/v), then why arent the same 3 events from B's POV: (0,0), (0, L/v), and (-2L, 2L/v) ? Why do they have y (gamma factor) in their perspective? If you are factoring gamma in "B and C's POV", Basically you are taking only A's POV under the names B's POV and C's POV! Can you explain this?
Exactly! An equally valid interpretation for A is (0,0), (L,vL), (0, 2vL). SR cannot distinguish between those two cases. There is a tacit assumption that (to a very good approximation) A resides in the centre of mass reference frame throughout the entire affair.
What I don't understand is why don't we just make the speed of light our zero point/ the point of reference, since it's constant. Everything else is moving relatively to it.
(1) I thought an event was a point in spacetime. But your Event I for A and B is located at a different point in space than Event I for C. (2) If instead of a thought experiment you tried to carry out this experiment for real, how would you do it without accelerations? How do B and C reach v and -v in the first place. (3) It is a paradox. It's not a contradiction. It has a rational explanation. But it is still paradoxical. (4) The maths works out, but you are still not explaining what it is that causes the aging of one twin to slow down. I'm still left with the suspicion that the initial acceleration shifts the travelling twin into another timeframe. I'm not saying that the dilation occurs during the acceleration, but without any acceleration there would be no time dilation. From this it seems to follow that acceleration is central to the effect.
Coordinates are just labels, like address of a house. Different frames of reference can assign different coordinates to the same point in spacetime. For observer A his position has coordinate 0 and C has coordinate 2L. For C it's different, C is at 0 and A is at -2L. Different frames of reference assign different coordinates.
@@thedeemon but then event 2 for A would also be 0 (we took it L). An event is a specific set of 4 coordinates, so event 1 should be at (0,0,0,0) for A's and B's frames and (L',0,0,0) for C's frame
excellent comments Brendan! ad 2 and 1: I'd do no synced start, just the encounters must happen in the order AB then BC then CA. The velocity is gained and settled before the encounters, so B and C appear as flying eternally. However, C must now additionaly note down also the coordinate of the encounter with A, not just A's clock, which might mean an equal complication so I'm affraid that I'm just shifting the difficulty around. Regarding your point 4, yes, I'm totally with you: if switching the frame on the turn-arround (emulated here by the BC encounter) causes a jump in simultaneity then why not the departure/arrival switches?! My explanation is that the the switch happens when the twins are at the same spot so no alternate simultaneity is possible. And here the SR reasoning departs from the reality because if the realistic acceleration happens over some time interval it also happens along a certain spatial interval, twins not at the same spot anymore - and here the expected shifts in simultaneity can already occur.
I found both of Dr. Lincoln’s clips on this subject helpful. His thought experiment is not quite the same as the traveling twins thought experiment, but his experiment is successful in its own right in showing that acceleration is not key to resolving the twins paradox. For me, the essential point is this. The experiences of the two twins are not equivalent, because one involves motion of the twin with respect to his cosmic (space time) background, and the other does not. You can argue that, from his point of view, the spaceship twin has remained motionless while the Earth, and indeed the entire cosmos surrounding the Earth, have rushed away and back again. But in that scenario, from the point of view of the spaceship twin, the earthbound twin is moving along with his cosmic background; he is not moving WITHIN it. In contrast, from the point of view of the earthbound twin, the spaceship twin is moving within his cosmic background, with corresponding time dilation effects. That, I think, is the essential point. The seeming “paradox” arises because it is difficult for us to set up and explain the different frames of reference involved and how they relate to each other.
Like i'm driving in my car and all of a sudden i slam the brakes then i see the car in front of me accelerate away from me and the harder i slam the brakes the harder the car in front of me accelerates away from me. But of course the other car can say the same about me but it was really me slamming the brakes so there's no paradox.
@@SpongeWorthy76 Yeah but it's a bit the same idea, i was decellerating not the car in front of me who was just driving at a constant speed wrt the road.
Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice. On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy. Brian Greene has a marvelous "now" timeslice visual: ruclips.net/video/idsw99SSwKc/видео.html
You're 100% wrong. The entire point of relativity is that there is no special "space time background". Videos like this are so harmful, because their nonsense basically implies your misunderstanding. No: what breaks the symmetry is acceleration. It doesn't matter what the rest of the stars and galaxies do at all.
Interestingly enough, Einstein himself stated that the acceleration was the only possible explanation. Which of course it is. It's a lot easier to think about this if you start with the twins on board two different spaceships (rather than one being on the earth, which tends to make people automatically think of it as "immobile" while the spaceship is "moving" - but why?). It is impossible in special relativity to get rid of the symmetry issue the two reference frames, because it only deals with inertial (that is, non-accelerated) frames. Acceleration is what makes the difference. Just like Einstein said.
Acceleration is the cause of the fact that one twin is stationary in two different inertial frames while the other only in one. The acceleration isn't the proximal cause, the different reference frames is. So it is correct to say the acceleration is important, but to focus too strongly on it would be misleading, suggesting that acceleration is necessary to produce this kind of result in general.
We can explain using acceleration also. We use general theory of relativity in travelling observer's frame of reference and argue that the stationary observer's clock will be faster. But it is possible to resolve the paradox purely by using special theory of relativity. ruclips.net/video/JPCDKta2LVE/видео.html
Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice. On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy. Brian Greene has a marvelous "now" timeslice visual: ruclips.net/video/idsw99SSwKc/видео.html
I am working through the Lorentz calculations to understand the work. Am I mistaken in thinking the space coordinate for observer c looking at event 2 should be 2yL (where y is gamma). I'm getting y(L+vL/v) which isn't working out to yL. :(
The solution to the paradox is that the one who is moving will experience a slowing of time. If something about the situation tells you who is actually moving, then you will know who is experiencing slower time. In the original paradox, the one who travels around the star is obviously the one moving. This is so because he decelerates (or accelerated, it doesn't matter which). In the example given, we don't know with absolute certainty who is moving. And we don't have actual proof of who is experiencing slower time. We are just having the characters hold up cards based on our assumed Lorentzian calculations. If you performed this experiment assuming that A were moving, you would apply the Lorentzian calculations to her and get a similar result. But you are assuming who is moving. The fact is, there is a multiverse going on in special relativity: the reference frames in some ways don't communicate. They are islands unto themselves. It is only when symmetry is broken and the one who is truly moving is revealed that we know who experiences the various strange happenings of special relativity.
This was a bid hard to understand. The best explanation I ever heard was in the video "Raumzeitdiagramme und Zwillingsparadoxon • Aristoteles ⯈ Stringtheorie (16) | Josef M. Gaßner" (german) using Minkowski diagrams. Especially about the 26:00 mark was the breakthrough for me. Its totally obvious seeing this. Good video however, as always :)
If you haven't seen the videos (4) he references to preface this one, I recommend them like he does. They give the proper background to explain the problem he poses here . Plus you get to see him rollen past the haters in a sweet Corvette.
+Daniel Nogueira Leitão This video is wrong in saying the twin paradox has nothing to do with acceleration, although its own explanation itself isn't wrong. Just different semantics, different emphasis.
@@DanielNogueiraLeitao She says that you cannot treat an inertial frame the same as a non-inertial frame. The "paradox" arises when the same treatment is applied to both frames. That's not a causal attribution. It's a statement about the proper mathematics needed to compare the intervals traversed by the two paths connecting the two events. They will not be equal in the general case, and in particular, cannot be equal when one is a unique geodesic and the other is not a geodesic.
I'm confused. At about 10:24 the video shows the coordinates of the three events in C's reference frame. However, C was present at events II and III, and is at rest in her own frame, so the _x_ coordinates for those events should be the same, just as A's are for events I and III. However, the _x_ for event II is γL while the _x_ for event III is 2γL. What is going on? Why are these two coordinates different?
Time is the same for him as for his fuel (so: 4 months). But: To get to his speed he needs a lot of energy to accelerate. Once his velocity near c is reached, I assume his fuel-cost-efficiency is pretty neat, if he never wants to stop again.
no fuel needed, Ron does not accelerate in this experiment! Instead, Ron got schizophrenic, he's now Ron b and Ron c, new approach to interstellar travels, you become two (sorry I'm being sarcastic at the faulty setup of the experiment)
Good question. He'll need enough fuel to accelerate to .99c, then to decelerate to go around alpha centauri, then to accelerate back up to .99c again, and then finally to decelerate to 0 back at earth. He wouldn't use any fuel during the parts of the trip at constant speed. So, no idea...
sir, suppose both Ron and Don are not familiar with STR & time dilation. Now Ron knows it will take him atleast 4yrs to reach the star since his ship travels at 0.99C. But due to time dilation he realizes he has reached in merely 22 mnts. So he decides to crosscheck his speed and finds out he must be travelling at 2.2C to cover 4 light years in 22 mnts. How is this possible,please explain?
For Ron, the distance to reach the star was a bit more then 22 lightmonths, or 1.83 ly. Travelling at high speed shortens distances too. Accelerating warps the space around you. I advice you to check this game: Velocity Raptor. It shows you what would happen if the light speed was ridiculously low. (featured on Vsauce's channel DONG) testtubegames.com/velocityraptor.html
Distances are relative. A lightyear isnt any more absolute than a mile or a foot. Remember light is moving at c in both reference frames. So a lightyear measured by Ron is much longer than a lightyear measured by Don.
I’d like to see you do a video that incorporates the apparent simultaneity into resolving this paradox. As you change frames of reference, what is considered “now” changes. In imagining how the two twins perceive the flow of time, it’s like when the moving twin turns around, his “now” for the other twin changes. At a constant velocity, both would see their own “now” going further into the other’s past. When the one turns around the frame of reference changes so much that the moving twin see’s the apparent “now” jump so far into the other’s future that he can still see the other aging slower with time dilation during the entire trip, but arrives back home finding the stationary twin has aged considerably more than himself. Like Brian Greene talks about “now slices” in this clip: ruclips.net/video/MO_Q_f1WgQI/видео.html
I don't get this, 'In imagining how the two twins perceive the flow of time' what do you mean by this? And what is 'now' ? You can only have the same now if together, otherwise I'm not sure what you mean by 'now'? I have seen other people talk about 'now' in Relativity related scenarios, but don't grasp it, because 'now' is only relevant to me now, or to someone else, somewhere else, which is somewhen else (not local). They are not linked, unless very local like a telephone call.
@@jonathanbyers791 It's like trying to keep a clock that shows your own time, and one that will show the other's time and match their clock when you get back together. You can send messages between each other to keep up to date. But if the message came from a light year away, it makes a big difference if your inertial frame of reference is moving toward them, or away from them. That inertial frame has been moving in that direction at a constant velocity for a whole year since the message was sent. www.staskoagency.com/wp-content/uploads/2016/12/b8258-oldnewsroom.jpeg
At 5:32, the equations are ambiguous, without clear specification of the (x2,t2) and (x1,t1) coordinates. The Lorentz transform equations are often written with a - sign inside the bracket where (x2,t2) is the coordinate of an event occurring in an initially co-aligned system moving at constant velocity, relative to another "fixed" observer who logs (x1,t1) for the same event. It's OK to downplay the math for such a wide audience but not OK to the point of spawning confusion. Physics is not pure algebra - the symbols all have physical meaning! Having criticized this omission, I still do appreciate the intuitive explanation of the twin non-paradox using A, B, and C observers.
How was t(II, B) calculated at 10:20? Why would there be a factor of 1/gamma, if the time interval between events I and II is a proper time interval for Observer B?
@silverrahul Ah, of course! I got mixed up both with the definition of proper time and when trying to use the Lorentz transformation equation. The latter method requires much more complicated algebra, but I just verified that it does work. Thanks!
Dr Don's footage is a load of krapp. A gedanken. In deep outer space spaceship A passes close by spaceship B. Both facing in opposite directions. During the very brief time that they are very near, A sees that B's giant sized clock is ticking slower than A's, whilst B sees that A's giant sized clock is ticking slower than B's (according to STR). A paradox. And no accelerations involved. Another gedanken. The identical spaceships each have 2 antennas (at front & at back). Each ship has an identical clock midway tween their own antennas & connected to their own antennas. Whilst passing, Ship A senses/sees that... (1) The 2 front antennas touch. (2) Later, the front touches the back. (3) Later, the back touches the front (because Ship B appears shorter to A). (4) Later the back touches the back. Ship B senses/sees the same as Ship A, but in a reciprocal way (because Ship A appears shorter to B). Hence here above we have the paradox that each Ship reckons that it is longer than the other. Plus if we compare the 2 sets of recorded timings of the four events we find a version of the twins paradox. A double paradox. The truth is that STR does not assign any real or true or absolute values to any lengths or times, all lengths & times are relative. Hence there is no need to try to wriggle out of any paradox. STR is what it is. I had a look at the youtube re the effect of position/location. It looks silly to me. If true that location is important then using the same speeds & accelerations but changing the location of one or more of the 3 observers must change the ages. Nope -- & anyhow thats not what Einstein ever said. But GTR does include a simple effect of gravity on clocks, where v in the equation for gamma is the escape velocity for the gravitating body in question. Actually i very much like that bit of Einstein's theory, his one contribution to science. Although the effect is not due to gravity (ie acceleration), it is due to the nearness of mass (but i wont go into that here). So when Dr Don says that acceleration has of itself no direct effect on apparent ticking (& apparent length) he is correct (unless i have misunderstood his meaning). I often see comments that the twin sitting on Earth experiences an acceleration (ie g), whilst the twin in the spaceship experiences his own acceleration (which sometimes in some youtube footages happens to be g). And the comments say that both twins suffer the same time dilation due to acceleration (ie if they have the same g). This is correct, ie it accords with STR/GTR (but of course we then need to add the effect of relative speed). But in (my Aetherian) reality the twin on Earth suffers ticking dilation due to the nearness of mass (not due to gravity), whilst the twin in the spaceship suffers no such ticking dilation because she is not near mass, & because acceleration does not directly affect ticking (it has an indirect effect in that it affects relative speed).
@silverrahul I think that it was Langevin that first described the twins paradox, & the stationary twin sat on Earth for 1 year, whilst the spaceship twin took 100 years to reach a star, then ditto coming back, giving 2 years versus 200 years. That was in say 1911 or at least before GTR in 1916. But Einstein himself used GTR to try to explain away the paradox. Dr Don dismisses acceleration, & invokes the full Lorentz transform which includes position/location rather than just velocity or speed. However Dr Don's explanation in no way actually addresses the paradox, & only introduces further complexity, & adds to the wide spectrum of supposed answers (there were about 10 different supposed explanations)(more if we add the more exotic & bizarre) (now we can add Dr Don's novel extra one). I wonder what Nick Percival would say.
@silverrahul When using STR only u get the paradox (the other twin appears to age more slowly). Scientists fall into 2 camps, (1) thems that say that it is only an observed effect, not real, & is ok, & in no way hurts STR, & (2) thems that adopt a (supposed) solution that says that when the true actual real effect is calculated there is no paradox (they all say that the spaceship twin is always younger). Both (1) & (2) are wrong. (1)'s are correct that it is only an observed effect, not real, but they are wrong to say that it doesnt hurt STR. (2)'s are wrong because there is no possible solution that uses STR or GTR or a mix. All of their supposed solutions are wrong because of errors & omissions. Plus we have lots of contradictory versions of the supposed reality. Where do u sit??
@silverrahul If we use STR we get the paradox, ie each sees the other as being younger. If we use a mix of STR & GTR i doubt that there is a method that results in a younger spaceship twin in every case (hence every proposed possible method to date fails). My reading of GTR tells me that the Earthly twin suffers time dilation due to Earth's g (here we insert the Earth's escape velocity of 11.2 km/s into v in the standard Einsteinian equation to get the gamma)(the gamma is the time dilation). And the spaceship twin suffers time dilation due to her acceleration & then deceleration & then acceleration & finally deceleration (here we calculate the 4 pseudo escape velocities for a 4 bodies having those 4 accel/decel/accel/decel & we insert those 4 v's into the equation to get the 4 gammas). And the resulting GTR time dilation is added to the STR time dilation. But Dr Don would tell us that we need to use the full Einsteinian STR transform for the STR time dilation (which he calls the Lorentz transform), ie that we need to include an STR term for the location (along the xx axis) of the spaceship, & Dr Don would tell us that we need not worry about any real g or pseudo g's or pseudo escape velocities etc related to GTR. But an aetheric analysis doesnt ever suffer from a contradiction. The Earthly twin can sometimes be younger & the spaceship twin can sometimes be younger, depending on the exact case. The aetheric analysis always uses the absolute frame, ie the preferred frame, ie the frame where the aetherwind is zero km/s. The absolute/actual/true/real ticking dilation is calculated separately for each twin, where the v in the gamma is the aetherwind felt by each twin. Rather than having an Einsteinian relativity where each (supposedly stationary) twin sees an apparent/perceived/observed ticking dilation for the other (supposedly moving) twin, we have an Aetherian relativity where an observer truly stationary in the absolute frame (where the aetherwind is zero km/s) sees/observes/measures the true ticking dilation for each (truly moving) twin. The Aetherian relativity gives goodish numbers but is difficult to work with (firstly u need to know the values of the 2 aetherwind(s)). The Einsteinian relativity gives goodish numbers in some cases & bad numbers in most cases but is easy to work with (all u need is the relative velocity)(no complicated aetherwind needed). In addition the aetherwind varies with location, & with time of day, & with time of year. And with orientation. Difficult. Things were simpler in the oldendays. Aetherists believed that the aether was dragged along by the Earth. Hence if one twin was stationary on Earth then the 2 relativities (Einsteinian & Lorentzian) gave the same numbers. But in the modern era we have neoLorentz relativity, where the aether is free-range, much more complicated.
@silverrahul Yes STR discards any aether, ie any preferred frame, ie any privileged observer, ie any real speed or real length or real time (length & time are relative, ie observed, ie not real). Hence in a sense the Twins Paradox is not a contradiction, hence STR is a little or a lot useful & not useless. This is in a way correct, but i say that STR nowadays gives numbers that are not useful, ie not accurate enough for modern use. And as experiments & usage gets more & more accurate & exacting the stupidity of STR will get more & more obvious, & the present Einsteinian Dark Age of science will end. For the times they are a-changin'. And neoLorentz relativity will too be found to be imperfect. The best relativity is my own, which is a mix of neoLorentz (corrected for a number of errors that i have identified) & Einsteinian (i include a GTR term related to Shapiro Delay)(ie due to the slowing of light near mass). I could name it neo-FitzGerald-Larmor-Einstein-Relativity (nFLER). FitzGerald being the father of length contraction (or change in size & shape). Larmor giving us the first goodish derivation of ticking dilation (at the atomic level at least). Einstein predicting the slowing of light near mass (but using false premises). And me myself i show how to put them all together plus i introduce say 6 needed corrections to the equations for the gammas (particularly for ticking dilation). Time will tell if i am correct, or at least better/best (pun intended). Re the ins & outs of the Twins Paradox u should read what Nick Percival has written. Plus he has some youtube footage under Nick of Time. And i will repeat my comment of 2 days ago, quoting some of Nick's wordage (or it might have been Kelly or Dingle) (which u obviously have not seen) in a separate reply in a few minutes.
@silverrahul Kelly said that many years ago Dingle said that Einstein wrote that steady speed slowed a clock, but that acceleration/deceleration fasted a clock .................................................. 5. Even more of an embarrassment is the completely incorrect and bizarre bluff of Einstein in Naturwissenschaften (6th year, Heft 48, page 697-712, 1918) concerning the Twin Paradox. I challenge you to quote this nonsense and debunk it! Einstein was challenged concerning the one-sided aging of the twins, who are in relative motion. He postulated, in an article in Naturwissenschaften, that the speeding up of a moving clock in the deceleration/acceleration phase was exactly twice the slowing down that is occasioned in the steady-speed state. This is quoted in translation in Dingle¹s book (p. 194). In a supposed discussion between a skeptic and a relativist, the skeptic raises the paradox of the two clocks (U1 and U2), each supposed to be running slower than the other. The supposed 'proof¹ of one-sided aging has been buried in the archives. It is surely another huge embarrassment to adherents of Relativity Theory. I have never seen it even partially quoted in the past 20 years, since Dingle quoted it (pages 192-201 of his book ³Science at the Crossroads", nor in the previous 50 years. Why, oh why? Einstein actually pretends that the whole paradox is explained by the following statement (referring to the acceleration and deceleration phase as causing 'advancement' or lessening of age): "Calculation shows that the consequent advancement amounts to exactly twice as much as the retardation during stages 2 and 4. This completely clears up the paradox which you have propounded." (page 669 Columns 1 & 2 of Natürwissenschaften). Phases 2 and 4 are the steady uniform motion phases going out and then back. I love the phrase ‘calculation shows’. What calculation? Be wary of any such evasive statement. Young’s "University Physics" on the Twin Paradox says "Careful analysis shows", but carefully avoids saying how this is done! Let us consider this question. On the journey of a twin, who goes off, and then turns around and comes back again, the acceleration phase can be of any duration and magnitude, and the deceleration phase can be likewise; also the return journey could have entirely different acceleration and deceleration from the outward journey. So, we cannot say that the magnitude of any effect would exactly balance out the slowing that is supposed to happen during the (arbitrarily chosen) steady-state phase. As an example, we could have the steady state phases going out and back each of duration 1000 years, while the deceleration/acceleration, which reverses the motion, could take 1/100 second. How could the slowing that took place over 2000 years be magically exactly balanced by a quickening that takes place in our arbitrarily chosen 1/100 second! An alternative example could have the steady state out-and-back taking 1/100 second, and the acceleration and deceleration part taking 1000 years. Also, the outward acceleration and deceleration could be 10,000 times greater (or less) than those on the return journey! It is arrant nonsense to suggest that the two always balance exactly, no matter what the duration of the steady state phase, or the acceleration phases. What a blatant crooked swindle! But, this must be quoted when debating this paradox. Why pretend that Einstein did not say that? I dare any proponent of S.R to mention this statement by Einstein. He was challenged to explain the paradox, and this was his considered published reply (after a 7 year delay from when it was mentioned by Langevin). He occluded the supposed balancing of the steady state, and the acceleration & deceleration phases, with convoluted applications of imaginary gravitational fields acting upon the twins! You imply that a correct 'explanation' is in almost all relativity textbooks. I have, so far, collected 54 different so-called 'explanations' (up to Summer 1999), published in mainstream physics journals (all suitably peer reviewed!) and textbooks, and each implies that most of the others are wrong!!! These so-called explanations are broken down as follows: 8 say it is inexplicable, and causes a huge problem for Relativity (among these is Essen the inventor of the cesium clock); 4 say the differential aging is all caused solely during the acceleration & deceleration phases (this includes Langevin, Bondi, Rindler and a standard 1990's textbook); 9 say the acceleration has nothing whatever to do with the explanation; 3 say that General Relativity has nothing to do with the explanation; 4 say that General Relativity gives the sole explanation; 2 say jumping from one Inertial Frame to another explains the paradox. Other more exotic and bizarre explanations make up the rest. So, it as all very simple, and the correct explanation is to be seen in every standard text? Like hell it is! Møller's widely used text "The Theory of Relativity" had to admit that its original explanation was not correct. In later editions it concocts a mass that suddenly goes from + to - for a twin! That must be an interesting experience! ŒBizarre¹ is the word for that. Umberto Bartocci has yet another explanation (if this has been published, it can be counted as number 55) viz: that the path of one of the clocks is 'geodesic, the other definitively not". He claims that "the 'postulate of relativity' either special or general, never asserts that supposed complete symmetry between the two clocks". I claim that Einstein said just that in his 1922 book (see above). Also, in relation to this paradox why not also quote another simple objection; if the twins never met again, and just start by passing each other at high speed and exchange photographs, and after 30 years of each others own recorded 'time' take another photograph and post that to the other twin?. This is the simple set-up that is very carefully avoided in the debate. Or what of the "Peter would be dead and Paul alive on the one hand, while Paul would be dead and Peter alive on the other hand" problem set by Lovejoy in 1931. We have Peter both dead and alive, and also Paul both dead and alive! Why, oh why, do so many adherents of S.R. adopt a lofty condescending attitude on this problem, as if everyone else was stupid, and ‘dead from the neck up’?
Acceleration isn‘t the cause! That cannot be stressed enough, as it is such a widespread misconception! So thanks a lot for that superb video on this topic, Dr. Lincoln!
It _is_ ; check out my comment on why. The contrived 'two frames' conclusion here, though seemingly getting rid of acceleration, doesn't do so because it requires swapping a _global_ chart for an _atlas_ of _local_ ones to describe the motion. This is a technicality of diff geo, that relates to things like the stereographic projection, but it's at the heart of the equivalence principle: local inertial motion = acceleration = gravity
I feel like it's important to say acceleration isn't the proximal cause. It is, however, important in the scenario. The proximal cause is the fact that the traveling twin exists in more than one inertial frame of reference on his trip. The reason he does this (in the classical twin paradox) is because he must accelerate to turn around. So it would be wrong to say the answer has nothing to do with acceleration. However, it would also be inaccurate to focus on the acceleration itself rather than its result.
Arkalius80 There is also the case of the identically accelerated twins. Here both twins undergo identical acceleration, yet one ends up older. See for example www.researchgate.net/publication/241349452_The_case_of_the_identically_accelerated_twins
Right - why do physicists propose to tell you that there is really no "twin paradox" at all but then when they try to prove it, their example has a traveling twin who never returns to earth? In the tradition of 7 fictitious dimensions I can sell you and a host of super symmetric particles that will be detected any minute now (just you wait!) you will have to believe your twin brother is younger than you even though you will never see him again because they sent him away for life. Watch my rebuttal video to Brian Greene's explanation.
I have a notepad full of scribbles which give a very impressive look to my total failure to perform the transformation. I'm not even sure how the additional reference frame solves the paradox. Still, there's nothing better than having something you firmly believed shown to be completely wrong and I'm not beaten yet. Back to my scribbling I go...
So A's perspective is good old Galileo: Ai. x=0, t=0 Aii. x=L, t=L/v Aiii. x=0, t=2L/v Let's focus on the spacial transformation and employ x2=y(x1 + vt1) Bi. x= It's very obvious B is where the event is happening so x=0 from his perspective. So the maths should be easy and we can confirm we get the right number. We need the x transformation: x2=y(0 + v*0) Great, we get x=0. Quick check for t: t2 = y(t1 + v/c^2 * x1) so y(0 + v/v^2 * 0) = 0. Ok good, zero again. Bi. x=0, t=0 For Bii, the right answer is also obvious but let's do it. First question, it's t1 (so A's then and t=L/v) but whose v?? Is it from A's perspective (so positive) or B's (negative)? It must be A's because the whole point is to calculate B's from A's. Second question, is x1 A's perspective on its own distance to the event or A's perspective on B's distance? I'll try the former: x2 = y(L + v*L/v) so yL. That is not zero. The latter then: x means A's opinion on the distance between B and the event. Jesus... ok. y(0 + v * 1/v) so y(0 + 0). Mmm. I'm getting zero but I'm not convinced. Let's skip ahead to the end to x on the third event for C which isn't zero: Ciii. x=y(2 + v*2/v)=y(2L) - is that the same as your answer 2yL?? I have no idea... I wish I had a working example with velocities and times to check my answers... I have no idea if I'm doing it completely wrong or if these are valid answers... Given this, I think the latter isn't the likeliest option! If anyone wishes to point out my abject stupidity then I'd be grateful!! :-)
I got lost at the same place, this guy does not explain or defines half of the things he writes, it is very hard to follow him and understand what he tries to say. I assume constant V (capital) is the speed to the right and -V the speed to the left for the guys in the example. In the Lorenz transformations, there is a lowercase v, which is a variable. For case II, you have as seen from A (x,t) = (L, L/V). So when you replace in the Lorenz transform for the position, you get: x' = gamma (L + v * L/V). Then what is v in this formula? I guess it is the speed of A seen from B, because that is what matches his result: x' = gamma (L + -V*L/V) = gamma (L-L) = gamma * 0 = 0. An then for the Lorenz transformation for time: t' = gamma ( L/V + -V*L/c^2) = L * gamma * (1/V - V/c^2) = > (multiplying by V on both sides) => t'*V = L * gamma * (1/V - V/c^2) * V = L * gamma * (V/V - V^2/c^2) = L * gamma (1 - v^2/c^2) = (hmmm that looks familiar!) = L * gamma / gamma^2 = L/gamma => t' = L/(V * gamma). Oh crap, I just got this one trying to show where I got stuck, I promise! :)
For some reason he actually has the inverse Lorentz boost written in the video, which means you need the velocity from B's perspective (negative for B, positive for C). Normally the Lorentz boost is written from A's perspective and the equations have negative signs. There also appears to be a typo in the results, for Cii it should be x = 2 * γ * L I hope that helps.
He just posted a follow-up to this. Showing how his explanation is equivalent to Sabine Hossenfelder's. Hossenfelder insists repeatedly that acceleration is the only thing that can be measured, not velocity. I can see the equivalence he makes here, but it ultimately means that it is acceleration that is the cause.
This proves that the reference frame of the accelerated traveler coincides with those two reference frames in part of her trip. Of course, the acceleration accounts for the difference in age for the twins, simply you can calculate that difference without accelerating frame, but you don't explain it without the accelerated part of the trip.
what if the acceleration is instant? Then is takes 0 time in Ron's frame, and 0 time in Don's frame. How does something that last ZERO seconds in ALL frames account for aging in locations that are not casually connected to the accelerating frame?
@@dodgsonlluis well if you want to really understand why the twin paradox is paradoxical, you need to stop worrying about acceleration and understand what happens when something that takes zero time in all restframes causes a time paradox. Regarding proper time on world lines...that's a manifestly covariant formulation so there no paradox to begin with, SR is self consistent.
I gather from this video that acceleration myth has been busted. Youthfulness is proportional solely to the number of reference frames, whatever the method of counting those frames is. Now, why did physics design such an awkward thought experiment 100 years ago, full of unnecessary circumstances? No wonder it lead to the myth. Studying this newest explanation (by the way, it's somewhat hard to grasp when sitting here looking at the explanation from the fourth reference frame, looking at paradox that cancels out with another paradox sort of stuff) I can't help looking for simpler explanation. Perhaps some explanation along the lines on how one gets minimum youthfulness in absolute zero temperature environment and every moving beyond that then increases youthfulness, up to a photon in vacuum that doesn't age at all. Something simpler that is. The slippery relativistics make my head spin.
See what you think of this: ruclips.net/video/rrZC0Bl6NDY/видео.html Rather than describe the math, I've put everything into mathematica, and actually make IT do all the calculations to perform the Lorentz Transformation on the spacetime diagram over the course of the traveling twin's journey.
Your animation is a brilliant head spinner, Jonathan. I like it, it has all the necessary details I think. Of course, I'm just a layman looking for a word that would best describe what makes one twin younger and not the other. All the videos I find have always somehow preestablished that the traveler will come out younger, but what if for example the Earth was really massive, so that the twin on Earth would spend his time in a considerable gravitational free fall, while the traveler would have an easy ride. Could there then be a situation when the earthling comes out younger?
Are you saying that the explanation is that the traveler goes through more reference frames (space "slices") than the non-traveler and that's why he ages less (experiences more space but less time)? That sounds much more clear to me than Dr. Lincolns' explanation. Thank you very much.
Acceleration is NOT a myth. No myth busted here. An instantaneous acceleration of the Twin Paradox rocket occurs at the point of turnaround but is completely ignored by the flawed proposed "two frames of reference" assertion in this video. See my posted comment for more.
I believe there is one small error at 10:36. These relations would be correct for a reference frame starting at point 1 stationary with respect to the observer C. However, because the observer C starts from a different place, the transform relations should be different. It doesn't change the conclusions though.
5 лет назад+1
Right, observer C shouldn't have event I at (0,0). That would mean that all three observers start at the same time and position. Also, observer C is at event II and III, meaning x must be 0 from her perspective for those events.
Isn't it according to the traveler that the earth observer is the one who switched between two different frames of reference, and hence, symmetry persists?
This is GENIUS! It's like I have just had my decade-long storage of nagging thoughts+lingering questions+half-baked answers suddenly decluttered in 13 mins. Dr Lincoln, you totally rock like the new opening background music of this series. :)
Hello, i didn't went deep on the math part, so maybe i missed something, but please explain me this. So, the distant star is 4 light-years away, however when the twin that travel there when he returns back to earth in his clock it just passed 4 months? Like that is very strange to me because i think that before one the twins leaves the earth both agree that the star is 4 light years away, even after the twin arrives the star he would look back to earth again and say that the earth is again 4 light years away, however in his clock it will just take 2 months to return to earth. I am not getting that part.
It seems to me that saying that observer A has been all along in the same reference frame presupposes it was A who stayed at rest and this takes us back to the paradox. This is no real explanation unless there is a preferred reference frame. But would that not put SR into question? If there is a preferred reference frame, it should be there for accelerating as well as for inertial movement.
To Dr. Don Lincoln and Fermilab: I like that you have experimented with a changed scenario to try to finally end the twin paradox of the special theory of relativity. But I got completely lost at the end of the video. I think that such an important theory experiment should be well worth the added time to end the video with a detailed explanation. My theory, matter theory, explains the same observables as the special theory of relativity, but differently, and without any paradoxes. If you are interested, you can view my video, “You’ve Learned Relativity Theory”, which challenges anyone’s understanding of relativity theory. I am curious to learn what you think of this video. You can find my videos using the search keywords: matter theory marostica.
A crucial point in the derivation is that the vx/c2 term in the Lorentz transformation expresses the effect of relativity of simultaneity. In C's frame of reference, the now-slice (the space-time points corresponding to t_C=0) is tilted such that it intercepts A's position at a *future* moment. A sees B's and C's clock time dilated by the same gamma factor as B and C see A's clock (total symmetry here), but when C starts moving towards A, C's "now" already corresponds to A's future (which is only possible when you compare times at different locations, a point Don Lincoln mentioned). That's why A sees more time passing as C crosses A than it took B to meet C halfway and C to reach A.
Actually this video does not do anything else than divides the traveler twin's path in two sections. Although it is true that the time difference in the end depends on the length of the uniform motion of the travel, it is actually the acceleration part (or the change of the reference frame of the moving twin) that causes a shift of simultaneity for the moving twin. Until that does not happen, there will be no twin paradox, just a usual symmetrical case of time dilation.
In the scenario with the twins, isn't acceleration crucial to allowing the traveling twin to turn around, and therefore to change reference frames? Meaning that while it might not be responsible for all of the time dilation, acceleration is the only thing that allows the twin to return at all, hence making it "responsible"? Or do people also imply that it is the only contributor to the time dilation (shown here to be incorrect)? Also, is there another way the twin could return without accelerating, say in some kind of orbit?
So at 10:25 shouldn't observer C see event II and even III happening at location 0 from her perspective? I feel like the difference here is that with respect to A everything is moving at speed V. Both B and C perceive one thing moving at 2v/(1+(v/c)^2) {more than v} and another thing moving at V. The faster things look to you the more your time dilates corect? If in our twin paradox there were other objects moving in a pattern locked with Rons "motion" then wouldn't Don be the one whos clock runs slow. Like in the example if it weren't for observer C then A and B would be indistinguishable. If in the example if observer C started to the left and was moving to the right at 2v/(1+(v/c)^2) then it would be observer B who's clock would run faster than As. If you are comparing clocks of A and B you will get different answers depending on what C does. Is it the relationship with C that defines how the clocks with A and B run? Is Proxima Centauri observer C in the paradox?
At 9:40 how do we get x Co-ordinat as 0 in 3rd event. If they are traveling in straight line then it must be 2L and also at 10:15 the x Co-ordinat of event 2 is 0 but how?! . If anyone have a explanation please explain.
Those are the times spent traveling those paths. It doesn't matter who measured them. In the scenario with only one traveling observer this observer occupies many different frames and the time they measure is the sum of the times spent in each frame.
Can't seem to find a consistency between A's, B's and C's perspective at 9:45 for the x-coordinate: For A's perspective, it seems like its about A's perspective on the movement from location 1-2-1 For B's perspective, it seems like its about B's perspective on the movement from location 1-2-1 (consistent with A's perspective above) BUT For C's perspective, it seems like its about A's movement towards C or vice versa. For the velocity: For A's perspective, it is the entire 1-2-1 trip For B's perspective, like A is moving away from B, as B moves from 1 to 3 (INconsistent with x above) For C's perspective, it is A moving towards C from 1 to 3 (consistent with x above) Can you please correct my understanding, if it is wrong? Can you also show how to derive C's perspective of time on event II from the lorentz transform and B's perspective of time on Event II as well?
10:36 I believe that choosing A's and B's startup position as C's X=0 was not so happy choice, but you can just substract 2ɣL from everything to be more consistent - that everybody's X=0 from their own perspective (which is true for A and B but not selected so for C). EDIT: There actually is an error in xc2, must be xc2=xc3 because C is there in both events. I find nothing wrong with velocity, B starts where A is (xb1=0), then meets C (xb2=0) then sees C meeting A (xb3=-2ɣL, va=-2ɣL/(2ɣL/v)=-v) Hint: Try calculating WHEN C leaves its star from B's perspective ;) (and when B leaves earth from C's perspective)
Yes it is confusing, as said in my comment made on 9-nov-2018 (please read it; it should help). The whole point is to see the difference when clocks are compared on earth (location 1, or equivalently A's location). So the Obs.B's perspective and Obs.C's perspective slides show the Lorentz-transformed values when Obs.A's perspective values are used in the Lorentz formulas. Please also bear in mind there is a typo in the displayed x(II,C) value, as stated in the video summary text.
I think I see an error in presentation. Around elapsed time 10:14. For Event III scene from Frame B, the time you write is "2 gamma L /v." I believe the correct time "(2 L) / ( gamma v )."
I don't understand. The only reason why we know we need to describe the space ship with two reference frames is because we know it is moving. If we observed this situation from the space ship's point of view and considered the stationary person as moving away and towards the space ship again, we would also need to use 2 reference frames to describe the stationary person from the space ship's point of view. I think my question is "how do we know what is moving and what isn't". Is it because the ship is expending fuel that we know that it is moving? But it isn't, because it isn't accelerating. If the ship stayed at the star, would there still be an age difference? Because at that point, even if we considered the space ship to be moving, we would only need one reference frame to describe its movement relative to the stationary person. I have a lot of questions and I cant find the answers to them. If anyone has any insights, please help. Edit: I think the question I am most baffled about is "Why do we know the movement of the space ship (and definitely not the movement of stationary observer when observed from the space ship) requires two reference frames?"
The spaceship experiences some real force. So it does not remain in the same frame of reference. Note that real force does not depend on frame of reference. ruclips.net/video/JPCDKta2LVE/видео.html
I am confused. So, acceleration has nothing to do with it. Richard Feynman, one of the greatest physicists that ever lived, writes in Chapter 16 of his lectures, quote: "... the man who has felt the accelerations, who has seen things fall against the walls, and so on, is the one who would be the younger; that is the difference between them in an “absolute” sense, and it is certainly correct."
Acceleration is what breaks the symmetry, but it is the uniform motion where the time dilation happens for Ron. For Don there is a speed up when Ron turns around. The other thing to keep in mind is that Don can use SR because he never undergoes acceleration. Ron can't use SR because he does. You can integrate Ron's proper time (the time in his system) over the trip (see the first relativity chapter in J.D. Jackson, _Classical Electrodynamics_ for the actual integral).
Can you make a different twin paradox example using A, B, and C experiencing different gravity? Maybe all three are stationary to all observers. Then a black hole moves through the single frame of reference, with A, B, and C at different distances from the black hole. The gravity of the black hole attracts the three observers A, B, and C. Normally this would make the observers closest to the black hole appear to move faster, relative to a fourth observer. But remember in this example all three appear stationary to all observers. So for example, if A is closest to the black hole, A must accelerate away from the black just enough to have no apparent motion relative to itself or any other observers. The same for B and C, although they will require less acceleration to appear stationary because they are farther away from the black hole. After the black hole passes, all observers agree to have observed no motion. However, observer A will have experienced the less time than B and C.
So the answer to the question at 4:15 is: the thing that makes they experience differently is a simple fact that one didn't left the Earth (he was in frame 1 all the time) and another one did and return to the Earth (he was in 2 frames). So there is difference no matter who is stationary observer or if there is acceleration or not.
I do not understand this explanation. In the proposed experiment it is assumed that B and C will meet at location II. For that they have to start from their locations simultaneously. However it is not possible because in special relativity different observer's clocks cannot be synchronized in principle so there is no notion of "simultaneity" as soon as the 2 events are not co-located. To me this explanation is not any better than the "acceleration" one. Sorry.
@silverrahul That is true. You need to think or a sea of clocks at any point in space. You can set them going instantaneously to be your "big brother" on what subseqently happens.
Good explanation. Some side notes: If observer A is truly stationary, the observers B and C clocks will show the same interval times. However, if A is moving, then the intervals shown on observer B & C clocks will be different by an amount dependent on the absolute speed of A. This provides a theoretical means of determining absolute velocity for any observer. This too shows there is no paradox. While each observer has a self-consistent relativistic frame of reference and can locally consider that he is stationary within that frame of reference, comparing the clock intervals from A, B, & C can reveal which one is moving slowest, or not at all, from a hypothetical absolute frame of “stationary”. Of course, the precision of the clocks and measured speeds would be essential to determining that “absolute” reference frame with precision.
You should explain why the Lorentz equations were not used for Obs A. And I guess that's because Obs A sees the distance L as static, not in relative motion. As you said, "remember that location 2 is a distance L away from observer A". Obs B and C do see distances between events as contracting. In the Lorentz transform, both x2 and t2 are related to both x1 and t1, so space and time are connected so to speak. I think "length contraction" is an easier way to see why there is no paradox.
Ok.. but can't C just use a difference reference point and claim that it is A that sees a contracting distance and not C? I'm still confused. It seems to me that the end of the video just did some hand waving and didn't explain the crucial point.
The thought experiment doesn’t clearly factor out acceleration, because it seems ‘B’ and ‘C’ are stopped and only start moving when the experiment begins. If both are ALREADY in constant motion, and ‘B’ passes ‘A’ at time zero, and ‘C’ passes location ‘3’ at time zero, then no one is EVER accelerating. And, FWIW, I was surprised there was no mention of how a traveler - whose clock seems perfectly normal to them - can make the trip in such a short time: Because the distance appears much shorter since the traveler perceives space moving past them.
Hi Dr. Lincoln! I'm the guy who met you at O'Hare yesterday. Thanks for giving me 5 minutes of your time and sorry I had to run, I had a certain space and time to be at.
Well, I find the video has a long introduction and then finishes off a bit too short with the conclusion that the moving person exists in two reference frames, period. That part, the meat of the paradox, should have been better explained.
I agree, in fact, I didn't understand what he meant. Could you please explain? Doesn't seem to make any sense, I would simply say that we have 3 frames and each of the frames is at rest in relation to one of the observers.
Yes, it really needed to circle back at 12:25 and expand on what those two very brief bullet points mean rather than just declaring it solved as I bet many missed it and quite a few may not get it on reviewing.
Yeah, that part I don't understand at all.
Agreed
I totally agree.
Like others here, I don't see the explanation. I hear "two frames of reference" but I can't connect that observation to an explanation I can grasp. It's like you ran out of time.
See if this explanation is clear. ruclips.net/video/JPCDKta2LVE/видео.html
yeah. if this video was 1322 or longer then the universe would have died then and there so... he did what he had to do
I think this one is a better explanation: ruclips.net/video/0iJZ_QGMLD0/видео.html
@@renedekker9806 No, it's factually mistaken, I guess. How can the stationary person measure time for the moving person. Then it will be 10s only!
@@BinuJasim The stationary person does not *measure* time for the moving person. But she can *calculate* how much time should be passing for the moving person.
I'm sorry but you went all detail with the easy and well understood part, explaining it like we would to a 5th grader, and then just conclude in literally 5 seconds that since the observers B and C are not in one single reference frame (wich could have been explained as well as the rest was) this is the proof for the paradox not being a paradox. While I'm sure this is correct, and not wanting to tell you how to make your videos, this last part ,with no explanation at all to support or motivate your conclusion, didn't really prove anything to me.
Still, it did provide for a starting point for me to dwelve deeper into, so thanks for that.
His solution was very good, for debunking the "acceleration" theory. But did not really explain why the paradox is not a paradox.
@@Guoenyi it's still a paradox, even if it's resolved. If you work in minkowski space(M4), there is no paradox because M4 is manifestly self-consistent.
This is a horrible example. Think about it guys. Dr. Lincon's example of A being stationary and C and B moving is the SAME as B being stationary and A and C are moving in the same direction (A away from B and C towards B), but C is merely 2x faster than A in the same direction while B is really stationary! The other probability is C is stationary and it's B and A moving towards C, but B moving at 2x the velocity of A, which in this 3rd scenario C is really stationary! To all observers, in all scenarios it would look identical and no one would be able to tell who's really doing the moving! Horrible example. The real reason is the person leaving Earth did the acceleration near the speed of light. That's the same as moving near a black hole and feeling the "acceleration" or the gravity well of the black hole (which relativity tells us gravity is just another form of acceleration and vice versa). Any person moving near a black hole would have their time slowed down, relative to an outside observer.
@@BD-np6bv If you think |v_C| = 2|v_A| in B's reference frame, you don't understand relativity.
It's because the distance to the star looks different for the traveler than it does for the non-traveler. The difference in the distance occurs because the speed of light is always the same, if you're moving toward the light source or away from it. Bingo! I majored in physics at the university of michigan. I went to every single physics professor for an explanation, none of them had one so i switched to math.
Please make a sequel, the "conclusion" needs more explanation.
Hahahaha, I was waiting until the end to see the final answer... Then he says "and that's why!"
Like... what?
That's from your perspective
Pro tip: you can watch series on flixzone. I've been using them for watching lots of of movies lately.
@Jeremias Cristian Yup, have been watching on flixzone} for years myself =)
@@LuisSierra42No, the video is complete nonsense, because it just assumes the conclusion.
I believe that there is an error in 10:25. According to observe C's perspective: the x co-ordinate (position) of event 1 would be -2yl, the x co-ordinate (length) of event 2 would be 0 and the x co-ordinate (length) of event 3 would be again 0. This is because the events' positions are relative to the perspective of C. It can also be supported by the x co-ordinates of the 3 events according to observer A and B's perspective since in the video the x co-ordinates of both perspectives are relative to the observer (i.e. for observer B event 2's x co-ordinate is considered to be 0 as the observer B and event 2 are on the same position). According to example I wrote in parenthesis, the x co-ordinate of event 2 for observer c would also be 0 as observer B and C are on the same position as well as event 2. However, this does not effect the conclusion reached. Please reply me either you believe I am right or explain my mistake.
anche io vedo un errore ☹️
I'm having a serious problem with this explanation. I get the idea that it's a question of which clock you're using as a reference but nothing shown shows why Ron's choice of his clock as the 'stationary' one is not the same as Don choosing his clock as the 'stationary' one. It's like somewhere in there, there's an assumption of which one is really stationary when in fact, once you exclude acceleration as a factor (which you do), then neither is a preferred frame.
Even though it looks like it's solved the mystery - throughout the entire discussion, A is referred to as being 'the stationary person'.. but that's literally the thing we're trying not to say. Take all the math done and flip the contexts and they apply equally well and give exactly the same results relative to each viewer, except you're swapping A and B.
That's the problem with this video - it shows the math from the 'stationary' person's view - but not from the 'moving' person's view in the perspective of his being the stationary person.
Oh.. one other thought. In another video, you explain that the reason there is time dilation at all is a consequence of the fact that we're *always* travelling at the speed of light. Assuming we're just talking about one spatial axis, x, and one temporal axis, t - the vector must always be a unit vector... so at rest, it points entirely along the time axis and represents 1 second per second. As you change velocities (and I'm avoid saying acceleration intentionally because it's the velocity that causes it, not the acceleration) the unit vector rotates until you hit the speed of light where all of the vector lies in the x axis and there's no vector in t - ie no time movement.
It seems like you're offering two different explanations for dilation.
Keep in mind, I'm not saying you're wrong - you know way more than I could hope to about the subject.. I'm just suggesting that this explanation could be better.
No, it wouldn't show a paradox if you flipped the referential (just give it a try).
Point is that all used referential in the video are inertia ones.
A is not jumping to any other inertia referential, and you can't make a valid Lorentz transform that would show such a behavior, because in all other inertia frames, A is an inertia frame (constant velocity).
@@ThomasKundera Consider the spaceship reference frame A, consider the stationary person reference frame B and C except with the negative of the velocities used in the example. Perform all of the same calculations. Why would it be wrong to do this?
@@lukecasey2830 : _"consider the stationary person reference frame B and C "_
B is stationary, C is stationary.
But (B and C) are not.
So you can't make a computation assuming (B and C) is an inertia frame of reference (as you can do in A, as A is one).
@@ThomasKundera But we are not considering the stationary person as stationary when viewed from the spaceship's frame of reference. We use two frames of reference to describe the space ship, I do not see why we couldnt in return use two reference frames to describe the stationary person when considering the moving space ship as stationary. How do we even know the space ship is moving and not everything around it? The fact that it isnt expending fuel and accelerating, therefor not losing mass, leads to the conclusion that we dont know if the spaceship is moving or the stationary person (ignore that fact that we are callling the stationary person stationary, what we call the person is beside the point). Can you explain to me how we know the spaceship is moving, not everything around it, and how we know we must use 2 reference frames to only describe the spaceships movement? Please I am trying to figure this out but I cant. I know I am wrong and that I am not understanding something
@@lukecasey2830 : You can take any of A, B or C as "stationary".
But, again, B then C is not.
_" I do not see why we couldnt in return use two reference frames to describe the stationary person"_
Because if you need more than one frame, then it's not stationary, by any reference.
Sorry but you haven't done any actual explaining. Yes, you've set up a thought experiment with a departing and returning frame of reference that does without acceleration. You then arrive around 11:59 at "Duration(moving) = Duration(stationary)/gamma". But this is equally "paradoxical" as the original problem, because "moving" and "stationary" are still relative. You would actually need to show explicitly that the results are consistent if B or C were considered stationary AND independent of which clocks you use to measure the time between the different events. I'm sure it'll all work out but it seems awfully complex (involving relativity of simultaneity) and is definitely not obvious.
I have found none that explains it from both perspectives so far
You need the relativity of simultaneity to fully explain why things are different for A and C. It's taken care of by the vx/c2 term in the Lorentz transformation for time, but unfortunately Don Lincoln didn't talk about it. Either he doesn't know it, or stayed silent on it by intention and just was focusing on the math.
@@NeedsEvidence I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations
Best comment. The video doesn,t explain the paradox. When he shows the (x,t) coordinates from B and C perspectives it,s not true. In fact, are the B and C (x,t) coordinates from A perspective. As you say, he should do the same calculations using the perspective of B and C and check that the results are consistent relative to A perspective. In addition there is a mistake on the (x,t)II,C coordinate maths, he shows x = gamma*L but it,s x = 2*gamma*L
I came to the SAME conclusions. This example of A being stationary can be said that C or B are also stationary and it's the other two moving! The real answer is the acceleration part. When you accelerate near the speed of light, Einstein tell us it's the same as being close to the gravitational effects of a black hole. GRAVITY and ACCELERATION are the same! Time slows down near the gravitational effects of a black hole, which would accelerate you near the speed of light to the event horizon! That is the real answer. Dr. Lincoln is correct on many things, but he's clearly wrong on this one.
I'm 67 and retired, but WHY could I not have had a Prof like you in University. You make complex things so understandably easy. Please keep teaching our hungry minds. Thank you Sir ! ! !
It is still a paradox. A is at one location as he said which explains his reference of movement is that "location" which is independent from the observers, which also decides that A is stationary there are three stationary "locations". But these locations don't exist in real space-time and the only reference is one of the three observers, which is why we do not know who is actually stationary. If you still don't understand let us say location 1 is the earth. Unless you think earth is stationary we don't know who is moving. Or we don't know if earth is always at that stationary "location" but never moves. Or thinks there is a stationary ether in which there is a location 1
This is unfortunately not correct! You are changing the entire scenario by inteiducing a third twin,second spaceship! Also, you are removing acceleration completely. How can you?
Not possible!
Have you read Einstein's solutiin to the Twin Paradox as mentioned in his 1918 documents?
He explicitly states that acceleration of the travelli
ng twin causes non- reciprocal time dilation which makes the travell8ng twin to be younger. Easy!
Also, you can easily deduce this from the worldlines of the stay at home twin and the travelling twin.
Whose wordline is shorter? The travellung twin's worldline. So, he remains younger.
Why are you complicating it Mr. FERMILAB? 😊
Now you’re 73!
@@519stream3 There is no paradox, as rigorously proven in this tutorial: ruclips.net/video/Dy8fC2eVOeA/видео.html
I still don't get it. What did he mean by "Observer A exists in only one reference frame but observers B and C exist in 2"?
B and C are moving relative to each other. So they are in different inertial frames.
Consider this, the earth moves ( rotation and revolution) yet we feel we are stationary. That's because we are in the same reference frame where everything on earth is moving. Now consider A to be on earth. A is stationary within this reference frame earth. Now B and C have different reference frames each. One when they start their journey ( Earth for B and 2L for C) and when they pass each other ( L for B and C both) and when they end their journey ( 2L for B amd earth for C). Thus these two people have different reference frames therefore there must have been some movement to change those reference frames. Therefore its concluded that B and C were moving and not A. All in all, the paradox arises with the question who exactly is moving. Now since it gets clear that B and C are moving and not A, the paradox gets solved
@@trsomas They are both moving relative to. A. So we can say B is stationary and A and C are moving relative to each other. I belive he should have done that calculation too to convince most people.
@@jaimeduncan6167 The problem that I have with this explanation is that in the original paradox, B and C are both represented by one person that never moves relative to himself, so what does this explanation have to do with explaining the original paradox?
@@trsomas And A and C are moving relative to each other and A and B are moving relative to each other. I sense poppycock here. They are all inertial systems and the Lorenz transformation can be applied equally in all permutiations.
"When we start the experiment, all 3 observers start a stopwatch." This sentence contains the idea of "simultaneously". Problem is, simultaneous in whose reference frame?
Imagine someone at location B sending a signal to A and C at the same time. When the observers receive the signal they start their stopwatches.
T=0 for all of them.
That's an excellent point Don Lincoln failed to address. It is the vx/c2 term in the Lorentz transformation that takes care of the relativity of simultaneity. In fact, C's "now-slice" corresponds to a future moment of A, and it is for this reason that A sees more time passing than C when C reaches A.
@@xw591 That is what I noticed at the start, but how do you synchronize the clocks ? How do you measure the lengths to know where the center point is.
@@jeffbguarino dunno im a mathematician
The end of the video was the most critical part to helping people understand why the twin paradox is not a paradox. In my opinion, you failed that task. You hinted at the answer, but you did not clearly spell it out for people who do not understand. (Also, as I understand it, you synthetically created a jump discontinuity, which is equivalent to an "instantaneous" "infinite" acceleration. If true, the example fails to illustrate your point.) At any rate, the animations and video editing were boss.
glad, I'm not the only one to recognize this... Sometimes he prolongs certain passages unnecessarily, almost putting the audience to sleep, and then when the final conclusion is due, he just leaves it up to the listener to spell it out in their minds... His pedagogical style is as discontinuous as his frame jumping that supposedly got rid of "acceleration" / change in direction issues. (which it didn't)
That's like almost every Physics lecture, starts slow, expands on the simple stuff, and then brushes over the difficult part before you realize it.
James Wilson SOOO?? Why the heck wouldn’t you explain it if you understand it so well????! You take the time to write all that (which was a little unncessary considering that you first phrase was enough) and you don’t even explain what that hint means?!? So why even bother stating all that? What’s your line of reasoning? It seems to me as if you are not using your head at all.
"jump discontinuity"? What is that, and How? Where? Seems to me that B was in constant motion towards +v and C was in constant motion towards -v. All they did was pass information. How is that a "jump discontinuity"?
B, and C were already moving, dont think they stoped and accelerated, just that they passed the info every intersection
Some people just have a knack at breaking down complex problems to smaller, more complex problems that are even harder to understand.
I found this version to be better than the version without equations.
It would have been more clear if Dr. Lincoln had explained what he meant by "the moving observers existed in two [frames of reference]". When he said that, he meant that the moving observers existed in two _separate_ frames of reference. Thus, he debunks the notion that the acceleration explanation for earthbound Don being older than astronaut Ron.
So, the twin paradox isn't a paradox. It's just a conundrum ... and the conundrum isn't explained by acceleration, but by the Lorenz transform equations.
I don't get how is it possible that we have one non-moving observer and two moving observers. Aren't all observers non-moving (according to themselves, of course) by definition? Considering B and C as moving isn't in fact still viewing the situation only from A's perspective? And how is it justified, considering that we have to prove that «Ron is younger» with every system of reference?
So, for A, the velocities of A, B and C are: 0, v, -v;
for B, they are: -v, 0, -2v;
and for C: v, 2v, 0.
Therefore, the order of the magnitude also changes:
A: a
That doesn't make any sense.
Although I'm willing to admit to being wrong, all observers should exist for everyone else and everyone can measure everyone moving.
I'm willing to admit to not getting it, but it doesn't prove it to me. Maybe it's because I'm a humanities guy.
Can you explain what you mean by the second sentence? I don't quite understand what it is that you don't understand, otherwise I can try to help out.
One person stays in the same inertial frame of reference throughout and the other shifts from one inertial frame to another. ruclips.net/video/JPCDKta2LVE/видео.html
@@trsomas I'm a believer that time is a universal constant. Who cares what speed or acceleration you are at.... A lightyear still takes you a year to travel at lightspeed...
And don't get me started on the "observer" bullshit. They see light at light speed. I believe that relativity is something people got confused into believing because of all the variables and confusing names for variables like "light-year". It's a measurement of DISTANCE. It's how far light gets after 1 year of traveling. In all these experiments, they treat travelling a light year at light-speed like it's instantaneous. STILL TAKES A FUCKN YEAR.
@@xwarslayerx You don't really know what you're talking about, sorry.
You are only talking about Special Relativity. Relative acceleration does play a role in General Relativity, where a single non-inertial reference frame is allowed for the spaceship’s entire journey. The person in the spaceship can believe that he is standing still by believing that there is a gravitational field present throughout all of space, and that gravitational time dilation is what causes him to be older than his twin.
I agree. Pure Inertial frames are too simplistic subsets of reality!
Well, if the acceleration is only about 1 g, the time dilation due to acceleration will be tiny---it would be comparable to the time dilation we experience by sitting on the Earth, which is not much! So GR adds some (very small) correction, but doesn't change the main picture.
The issue with using general relativity is that spacetime does not curve due to acceleration, and so gravitational time dilation is not a factor in the paradox.
stecordas uh....isn't it impossible for an occupant to determine the difference between acceleration and gravity? who says BOTH don't cause curving of spacetime?
AirPlayRule For the same reason centrifugal force is not a real force; apparent force is an illusion of your finite senses. The universe doesn't care what your brain is falsely interpreting, it cares what your bundle of atoms are actually doing in -dimensional spacetime.
I have to disagree with you here. This video is not about the twin paradox, but about time dilation. I don't know why people often get confused between these two concepts. Time dilation is saying that proper time always shorter than coordinate time in a Lorentz transformation, but this is not a problem since you need 2 synchronized observers to measure the coordinate time but simultaneity is not absolute for all inertia observers. However, the twin paradox is comparing the proper time between two observers, which are stationary with respect to themselves. Your explanation is not strictly valid because you implicitly assume there is one stationary reference frame and the other observer changes his reference frame with respect to the stationary observer. But in that case, why can't we say the second observer is stationary and the first observer changes his reference frame with respect to the second observer? I mean how do you even justify which twin is your observer A in 6:27? You cannot simply say just because the twin is on Earth then he is not moving. The main reason that leads to the twin paradox is that special relativity treats systems with relative acceleration asymmetrically. That is, the laws of physics under special relativity are not invariant under a transformation involving accelaration. Besides that, Newton's law of gravity is incompatible with special relativity, in other words it is not Lorentz covariant. These two problems bothered Einstein for quite a while. But ultimately he realized that these two problems are strongly related to each other via the equivalent principle. So despite that twin paradox can be solved in the framework of special relativity, even without mentioning acceleration (equivalently treat it as infinite and instantaneous) using the spacetime diagram. It does not answer the most fundamental question of this problem: when, how and why does the symmetry between two reference frames break down, does it mean physics has a preferred frame of reference? Einstein answered all these questions in 1915-1916 by the introduction of general relativity, where we see the laws of physics (gravity and classical electromagnetism) are invariant for frames of reference. Until then, special relativity is only a special case of a more general theory of relativity.
@silverrahul The example he used does not resolve twin paradox. It is just time dilation. To resolve twin paradox, the two systems must synchronize their clocks in the first place and compare the time elapsed when they rejoin. This process does not involve a third observer, this is why his argument is invalid.
@silverrahul Did you see the problem here? The reason that leads to this asymmetry is that one observer is assumed to occupy two reference frames during his journey. Despite B sync his clock with A and C sync his clock with B, then finally A and C compare their time, leading A to believe that B is younger than him. However, B does not agree with this statement. Since C is moving away from B, B would see the clock of C is running slower than his clock after their synchronization in the middle, leading B to think that he is still older than A. This restores the paradox.
@silverrahul Are we still talking about the same problem here? I think you are the one who gets confused. I only assert one claim. "This video does not resolve the twin paradox." I can say this for sure because he transformed the twin paradox into a different problem. At the end, he states that "Non-moving observer (Earth twin) existed in one frame while the moving observers (correspond to Space twin during outbound and inbound respectively) existed in two frames. This is the answer to the twin paradox. " Only if we make this assumption, then the example of the A, B, and C observers would be valid. The space twin has to agree that he is the one who switches from B frame to C frame during his journey. However, this claim is not justified. How can you prove that the Space twin existed in two frames while the Earth twin only existed in one frame? Answer my last question.
@silverrahul First of all, by "one observer in two frames" I meant the space twin, not A, B, or C. Furthermore, he did transform the problem into a different (and not equivalent) problem. There are only 2 observers in the original twin paradox while he formulated the problem involving 3 distinct observers. Maybe my math sucks, perhaps 2 is somehow equal to 3. Regarding your last argument, you claim that the space twin existed in two frames because he is the one who fires his rocket and goes back. By making this premise, you already put yourselves in the reference frame of A. What if the space twin insisted that despite firing his rocket, he is the one who stays stationary (with respect to himself) and the Earth twin is the one who travels away from him then turns back around and rejoins him? In simpler words, simply use the argument in the video but now swap the Space twin and Earth twin. That is, the space twin now changed to A, while the Earth twin is represented by B and C during outbound and inbound respectively. Then you will see the paradox still persists.
@silverrahul You see, he formulated the problem in such a way that it requires an intermediate observer to compare whether the Space twin or the Earth twin is younger. But then there is no direct comparison of time elapsed between the two twins anymore, so the problem has changed. On the other hand, I am happy that you finally brought out the concept of proper acceleration and inertial frame. This affirms my claim in the first place: "The video does not resolve the twin paradox." Because it does not state the key event that breaks the symmetry between the twins. That is, the Space twin did not remain in a single inertia frame of reference the whole time but the Earth twin did. This is the real resolution of the twin paradox.
As a teacher of A-level Physics I found this video interesting, especially as the textbook we supply to our students gives the acceleration & deceleration solution. A past exam question (AQA exam board) explained it by saying the rocket twin was in a non-inertial frame of reference.
The twins paradox exists in inertial frames without doing the introduction of a new reference frame C.
Just imagine twin A is in a high circular orbit, and twin B is in an eccentric orbit that tangentially intersects A’s circular orbit. No rockets, no thrust, no acceleration, no non-inertial frame nonsense.
We know high orbits experience time slower than low orbits. GPS satellites lose 1ns per 1s compared with us surface dwellers. But how does the twin B know it’s in a low orbit when it’s in an inertial frame? Orbits are just free-fall, and are inertial frames.
@@hdthor in special relativity, spacetime is flat, so a circular or elliptical orbit would require acceleration.
@@hdthorcircular orbits are non intertidal. They experience constant acceleration.
But I agree with you that the acceleration is not needed for the paradox to occur.
The solution with acceleration is the solutiin given by Albert Einstein in 1918. You can not solve it without acceleration as the travelling twin must change refence feames through acceleration and deceleration!!
@@hardkraft6894 An object in free fall does not experience acceleration. If you jump of a building you feel no forces until you hit the ground. When standing on the ground you feel the earth pushing you up from your feet. So on the surface of the earth is a non-inertial frame. The moon is in an inertial frame. So if you see an object dropped off a building while you are standing on the ground, you will calculate that it's speed is increasing relative to you and you might say it is accelerating but it is you that is feeling the upward force not the object. So from the objects point of view you are accelerating upward. This is like the equivalence principle that Einstein used at the start of General Relativity. If you are standing at the engine end of a rocket and it is accelerating, you feel a force on your feet pushing you up. When you hit the gas in your car, your seat pushed on your back to accelerate you forward. So if you equate gravity with other forces that accelerate you , just standing on the ground is as if you are accelerating up.
6:35 I don't understand how A and B could agree where C is "now" if A and B are moving relative to each other and have different perspective what "now" is in point 3.
'Physics is everything', it truly is. (Edit) We shall miss you Dr Hawking. 18-03-14, a triumph we had you so long and sad loss.
Psychology, Social sciences, consciousness anyone? That has nothig to do with physics, but is still very real.
Ehm psychology is about different states of brains, which are electrical currents within a specific kind of very physical object. That's physics, but instead of trying to go the natural scientific way (like it's today done by trying to map the individual connectome), people just made up some pseudoscience and termed it "psychology".
Social "sciences" are about behaviors of humans. Humans are typical animals. Biology is in principle just the result of biochemistry/molecular biology and that's just chemistry, which is in first approximation nothing else than the physics of the outer valence shell electrons. Everything is natural sciences and in the end physics.
Exactly that's why social sciences have such a bad reputation among educated people. And of course because hey rely more on citation and who said what, than on observation, thus perverting the scientific method.
Ronald de Rooij What he meant is that physics is the most fundamental of the sciences. All arrows of explanation trace back to physics.
Hawking is as fake as Einstein's gravity
Philip Berthiaume Hawking had no true knowledge about the universe. The universe is much, much more complicated than Hawking could ever imagine. Do you know where is Hawking now?
This has generated a massive amount of confusion. I think you need to use space-time diagrams.
Right. Also, the only way for Ron to switch from frame B to frame C (when they meet at position 2) is by experiencing acceleration... and if I neglected that idea, I would be entitled to apply the same argument to the motion of Don relative to Ron (rather than the motion of Ron relative to Don), and I would reach exactly the opposite conclusion, using the same formulas.
It is funny how the Einsteinists - the paradox "explanators" bring the human fillings into consideration. Now you have to fill the acceleration - this switches you from frame to another frame, you are only stationary when you don't fill acceleration :) Where it is in Einstein's equations?This is why the theory is crap.
The theory is definitely not crap, because it is used it many, many times to explain real observations to high degree of precision, where classical kinematics has failed completely. It is not intuitive, and not even required at low relative speeds, so you should be good to go in most of the experiences that we, as humans, deal with..
@@marianskodowski8337 Acceleration is dealt with in general relativity.
I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations
I may have missed something here, but in the (x,t) coords for event II for observers B and C there seems to be an inconsistency. Specifically, the location (x) for B is given as 0, but for C is yL (I use y for gamma so it is easier to type). It seems to me that B should be -yL. If not, then C should also be 0, not yL.
Although X coordinate is not used for the demonstration of the time dilation, I think it is useful to work out what happened to it. E.g C takes part in all three events, so X for it is always 0.
@@alexotenko6597 good point. why is every missing this? If i am right, then if you look at 10:14 to 10:32, those equations location are all considering "X" from A's perspective only. Then shouldn't we write equations from B's and C's perspective where X is always 0 from B's perspective and X is always 0 from C's perspective. Then no body is aging faster?
Since A, B and C were not accelerating, they were moving (parting away or coming closer) steadily with respect to one another by exactly the same amount. Since there is no "Stationary" frame of reference, all three would think that other two inertially moving persons are aging younger by exactly the same amount(e.g. 6 years). A would think B and C are younger by 6 year, B will think A and C are younger by 6 years, and C would think A an B are younger by 6 year. It is understandable why the presenter abruptly cut off the video by just mentioning: it is because to ONE frame vs TWO or THREE frames -- instead of steadfastly reasoning why A would grow older by 6 years from others perspective while others would remain younger despite same relative motion! He could have plugged numbers in those equations that are 100% same for all three and prove why just one of those three symmetrical equations would magically yield no time dilation!
?? On to the CORRECTION in 10:32, shouldn't the location of event II for observer C be 0, not 2yL? If so, C's locations for events I and III should be 2yL and 0 respectively (not the other way around).
Right, almost. Notice that C overlaps A at event III. That means x should be 0 from C's perspective for that event.
Why should the formula for event II for obs. A 9:28 and obs. B 10:16 be any different, while their movement is completely reciprocal?
This is because two different observers, each moving at different velocities, perceive simultaneous events differently, implying that they possess distinct planes of simultaneity. Consequently, the Lorentz transform factors in the velocity's sign.
Excellent explanation! I noticed there is a mistake for the perspective of the referential frame of observer "C" for event II, where instead of position γL should be 2γl. After struggling with the problem, I saw you already have made the correction. I think it is important to highlight that the origin of three frames started together at the event I. There is an asymmetry to explain the paradox. While observer "A" measures the difference between events in two clocks at rest where these events happened (B-A) and (C-B), each one of the observers "B" and "C" measures the interval of time on their own clocks attached with their bodies. The second intervals are proper times, related to the interval of time measured by "A" for dilation time expression: each time interval for A equals γ multiplied by each proper time interval .for B and C. If we begin with the interval measured by observer "A", we have to subtract the quantity of xv/c² for event B and add the quantity xv/c² for event C because the clocks are advanced in the direction of motion and delayed in the opposite direction by these terms according to relativity of simultaneity . After that, we have the interval of time passed in only one clock in the frame of observer "A" and we must multiply it by γ to obtain the interval for observers "B" and "C". In other words, the origin of asymmetry is the relativity of simultaneity expressed in Lorentz Transformation. Each one observer can claim the other clock is slower, and each one observer can consider moving in the direction of future of the other reference frame as expected by symmetry.
My conclusion from your complicated response here is that the video fails to give a clear explanation. It is completely expected that for A the first interval travelled by B from its passing by A until passing by C and subsequently the second interval travelled by C from its passing by B until its passing by A are of the same duration, namely the duration for A between B passing by A and C passing by, divided by 2γ (two gamma). This, however, does NOT explain why A cannot be seen by B to age much less.
Excellent? Are you kidding me? You are probably not a Physicist.
Dialect's video is full of flaws. The presentation is excellent, not the content.
@@benheideveld4617 exactly. The video is full of flaws.
Two questions then.
1) What part of the equation dealt with the delay of causality (light) it takes to get from 2l to person A?
2) You said person A only has one reference frame. However, In the twin paradox don was on a planet. Which is moving there for he also has multiple frames of reference. In fact. If everything is retaliative then counting the frames of reference is a paradox as they can be flipped. Inertia is still the only thing that separates them irrespective if you can work it out after the change in velocity or not. What have I missed?
Example of my thinking based on your experiment.
Let's slow things down to very (VERY) small numbers. put the two in cars going 100km/h. It was the previous acceleration that changed person c to 100km/h. So he is the one changing frames. You can see it based on the 100km/h but it's still the acceleration that caused it.
An assumption has been made that the planet is in an inertial frame. This means we assume that the proper acceleration of the planet is negligible. If you do not want to make that approximation, then instead of a planet, assume that Don stays at rest in some inertial frame of reference.
I sort of "get" this, but I also agree with brixomatic about "long introduction" and "bit too short with the conclusion". Do another video please to follow up this one! Three specific comments on this video:
(1) I would like to see some sort of comparison of what each of the observers (A, B and C) experience, as I would like to see everything being consistent for observers when they are momentarily at the same point, 1 and 2.
(2)I am slightly concerned about how the points 1, 2 and 3 are observed by ANY observer. Is it required that there is a NOW point for 1, 2 and 3 (in at least some observers view) when this all starts? Perhaps, if so, the NOW, or "start time" at 1, 2 and 3 can be called by "you", the passive 4th observer of this situation, in the same inertial frame as 1, 2 and 3. However, for that to be the case 1, 2 and 3 would have to be equidistant from you - and that puts them on a spherical surface. That means that B and C are accelerating when they are moving! (Although I can see the "local" time at location 2 could be irrelevant, in which case it can be on a straight line between 1 and 3.)
(3)This video explanation shows that acceleration is not required to resolve the theoretical paradox but it does not mention any additional effect that acceleration might have should it occur. In a real twin paradox experiment, acceleration would have to occur. And, since acceleration is equivalent to a gravitational field (in which clocks run slow), additional effects of acceleration in a real situation should at least get a mention in this video.
I understood everything up until 10:12. I can't figure out how you solve for any of those positions for B or C. Nor, for that matter, why C starts at (0,0). C starts at (2L, 0), from all perspectives, does it not?
That's not where C starts, you're looking at Event 1, which is the "event" of B leaving Earth. That event has the same position in all reference frames because it was chosen at the origin (0,0), and the Lorentz Transform preserves zero.
These are not positions, these are deltas of distances (delta x's). We compare differential of distances between different observers.
@@ericchasseur3904 Thanks for replying to my old comment. Coming back to this, rewatching that part of the video, I understood my confusion, and I understood ANGRY's reply, which I originally did not. Thx yall.
@@ANGRYpooCHUCKER Ah, good clarification.
A point of possible confusion with this is at 8:07 where the statement is made that you can work out how you can get from 1 to 2 and back to 1 again without any acceleration. This is true for non-massive quantities, and it actually would take an infinite, impossible acceleration at position 2 to accomplish this with anything that has mass. You have shown that you can get information from 1 to 2 and back again this way, but not an observer or clock. If you compare the clocks of observers B and C and the "end" of the experiment, there is no difference. This example should be re-presented in a physically realistic point of view from observers starting from a common space-time point. Mixing observers that are in different frames from the start might create confusion and is not the essence of twin "paradox" since the starting point has two opposing frames that are not twins.
How do you get them (A,B,C) to all start stopwatches at the same time?
Easy.
1. Put a light at the mid-point.
2. Turn the light on.
3. A, B and C start their stopwatches when the light reaches them.
If you do this then B will start his watch L/c seconds before the others, since he IS at midpoint.
Rafael Cacilhas No, because B started at position 1, where A is. The light would be coming from the midpoint, position 2, and reach position 1, where A and B are, and position 3, where C is, at the same time, signaling person B at position 1, and person C at position 3, to start moving, while person A remains at position 1.
Quantum Telepathy...
@@wr2382No this doesn’t work. Person A and person C will not agree that they started their clocks at the same moment. Their reference frames are different and clocks will not be synchronized with each other and would claim the other person started their clock at the wrong moment.
I mean also, person C will get the light before person A since person C is going to meet the light partway (according to the view that person A is at rest).
The original version of the experiment involves only 2 observers, in the explanation it involves 3 observers. Observers B and C see a shorter distance due to Lorentz contraction of length. But for the original version of the paradox, Ron and Don started and ended in the same inertial frame (one can forget about the earth which confuses the issue as it creates a non-inertial frame), it seems that the explanation does not deal with the original paradox. (Sorry, I am not a professional physicist.)
You're right, but the purpose of this scenario is to show how the result of the original scenario can be replicated without relying on acceleration. The point is that while acceleration is a relevant detail in the solution to the twin paradox, it is not the proximal cause of the differential aging.
@@Arkalius80 Acceleration is the primary cause of the ageing though, since the special relativistic component only deals with the perception of time from a distance of objects at different velocity, not the fundamental nature of matter being energy in motion, which is general relativity, this problem is asking the question why are they different ages upon being reunited, which turns out to be how many relativistic rotations they ended up making and why they are different. Turns out the simple point is that matter is only in motion in relation to it's inertia, which is not a euclidean frame, it's actually represented by a matter distribution surrounding an object, using Newton's every action has an equal and opposite reaction, the sum of action and it's inertia are zero. In relativity, even the frame is projected at the speed of light, because no causal influence can happen without time, it takes time to project the frame and so an object's inertia is more influenced by matter that is closer to it. The twin paradox is dealing with the matter ageing differently when an object is accelerating in relation to it's own surrounding inertia, it experiences slower time because the electrons spinning inside the accelerated matter are limited to travel no faster than light speed, the matter slows it's internal rotations compared to the matter that makes up it's inertia. The twin paradox is all to do with it being matter that is ageing differently and general relativity solves it, special relativity is going to have to resolve crossed frames to assign a rest point and then ask relevant questions only, since asking a question must have an observer. It's a general relativity problem, like solving kinetic motion using energy equations, using special relativistic time dilation and length contraction only explain appearances from different perspectives, it doesn't deal with root of the question.
@@Arkalius80That's 100% wrong.
It's solely about acceleration. Acceleration is what leads to the phenomenon of one twin aging less. If they accelerated the same, they would have aged the same.
Nice video, but it seems that the resolution of this paradox still requires acceleration. Without acceleration, each twin will perceive the other as younger; the resolution requires a real comparison, and you at least need one of them to accelerate to the frame of the other in order to do that - no matter how many twins you have.
I don't understand something here. The only way the spaceship twin can avoid acceleration is to be going at the close to the speed of light when she leaves earth. That is the spaceship sister flys pass her twin sister on earth as she is flying on her way to the star at close a speed of light. But how does she coordinate her clock with her twin's clock? She must include her speed in determining if the two clocks are synchronous. In fact the sister on earth will see her twin sister's clock on the spaceship moving very slow. The sister on the spaceship will also see her sister's clock on earth moving very slow. Provided neither sister slams on the brakes and undergoes gravity, or what looks like gravity, than neither sister will ever know the age of the other sister because a signal traveling at the speed of light to show the time on the clocks will always be lagging behind the spaceship traveling at close to the speed of light. And it will take this considerable time to catch up with the spaceship.
I think Einstein is very careful to state that for two clocks to be determined to be synchronous they must be checked where both clocks are close to each other and in the same frame of reference. But how can the twin sisters clocks be in the same frame of reference or close to each other if one is moving away from or toward the other at the speed of light. This is of considerable error if the third sister, L2, is making her observation from a star 4 light-years away from the sister resting on the planet. Which is to say you do not make the problem any easier to understand by eliminating the acceleration. You just move the complexications to determining what do you mean by saying all 3 sisters, the one on the planet, the one moving away from the planet and the one moving towards the plant are all the same age (clocks are synchronous) at the start of the experiment.
Note this is not a trivial acceleration, or gravitational pull, to go from zero to 0.999c to zero to 0.999c to zero in 4 months. No such spaceship exist or can be built if relativity is correct.
Provided all three sisters are the same age, that is the clocks are synchronous at the start of the experiment, and no sister undergoes acceleration then the experiment is impossible to conduct. This paradox looks a little like a perpetual motion machine where it works only if you ignore the details.
You could say OK all three sisters are to start the experiment from earth at the same time. One sister remains on earth, one flies away to turn around and fly past earth on her way to the star and one flies to the star to turn around and fly back past the earth. The problem is all three sisters will be starting the experiment at different ages and be in different frames of reference. And when the experiment is completed all will be of different ages. But no paradox because you can not compare each sisters space-time travel or synchronize the experiment start.
I think the resolution is incomplete. Three quarters done, to be precise. It has been explained how much time passes on the spaceship according to an observer on earth as well as on the spaceship(s). So far, so good. The time that passes on earth during this ordeal, according to the observer on earth, has also been noted. But how much time passes on earth according to the observer(s) on the spaceship(s), and how that matches with the aforementioned interval (time passed on earth according to observer on earth), has not been explained. This, according to me, is the heart of this paradox, which is also the most difficult part to resolve without considering accelerated frame.
Exactly, that is what is missing!
I think the explanation is the issue of simultaneousness. Two observers can only compare clocks when they are at the same position. That is the whole idea of the set-up.
The problem you mention is that B should observe A's clock moving slower. This would give a conflicting result, from B's reference when reaching event II. I think the explanation here is that B can't compare clocks with A at event II because they are not at the same position.
A perfectly symmetric scenario is described? B and C are absolutely symmetric. That being said, I understand it all and it doesn't resolve the twin paradox. You have to incorporate the asymmetry, and it is due to acceleration. Acceleration is outside the scope of special relativity and violates the assumptions of both SR and the Lorentz transformations. The twin that experiences acceleration is not even remotely allowed to say she's stationary within the context of SR or Lorentz. This is a part of the assumptions of the theory. You can pseudo-analyze non-inertial frames within the context of SR, but it is a logical violation of assumption. I of course follow your arguments, but they are mathematically, formally inconsistent when applied to the departing and returning twin. A better resolution is required. In the purely SR case, "outliving your enemies" can be achieved by relative velocity, but you have to have differential acceleration to get there and back. There is no denying that. To say that it is all velocity is denying the derivative. All things considered, this is an excellent video and among the best presentations on this topic I've seen. The bottom line is that if a departing and returning traveler and twin experience different accelerations, they will have different times upon reuniting. If they experience identical accelerations, well, they will have identical times. This post will likely be deleted by remote observer with faster clock, but I encourage you to read before.
If acceleration was the thing the duration of the flight would not matter but thats incorrect.
yes, inconsistent, that's the word. the setup is fundamentally different from the twin paradox experiment, it's a different scenario. any proof that the result can be applied to the twin paradox??
@@karejonsson8264 The "gravitational" time dilation due to acceleration is a factor of the distance between the clocks, which indirectly depends on the duration.
It appears it wasnt just me left thinking 'but... acceleration is what changes your reference frame. So isnt this rather semantic?' but Im inclined to believe that when an experts explanation doesnt add up to me that I must be missing something.
So I was considering the scenario of the twins being in a small spherical universe where one starts off and arrives back by going all the way round that universe without accelerating. Im not sure how difficult a problem that would be to solve, if it needs some heady general relativity or not, but perhaps in this case and other parts of general relativity it could make for a more substantive distinction between the two ways of thinking about this?
Edit: I wouldnt mind hearing other possible suggestions. I have to say Im kind of confused by what incite hes really getting at here.
Yes acceleration changes reference frame but the way some RUclips videos give explanation based on acceleration is wrong. They say that the travelling twin is accelerating, so his clock will tick slower. The correct way is to use general theory of relativity from travelling twin's frame of reference and argue that the stationary twin's clock will tick faster. See this video for more detail. ruclips.net/video/JPCDKta2LVE/видео.html
However, the problem can be resolved without considering the value of acceleration and simply by using special theory of relativity.
@@trsomas that's what i want to know .... acceleration doesn't solve the Paradox
@@abdullahbinjahed6900 According to the paradox, if we use time dilation from A's frame, we find B is younger and if we use time dilation in B's frame, we find A is younger. We should be able to resolve the paradox by pointing out where time dilation has been used wrongly in the paradox. The answer is that the astronaut uses time dilation formula form two different inertial frames and he does not account for changing from one inertial frame to another. This is where time dilation has been used wrongly in the paradox. Acceleration only serves the purpose of changing the inertial frame of reference.
@@trsomas say ... a round universe with nothing in it ... now you and me popped up in existence and travel in different directions at a constant velocity ... because the universe is round we will meet again without even changing our direction ... so ... now tell me ... what's the solution ?
I'm quite disappointed with this "real" explanation. Isn't "frame jumping" just acceleration? I find the difference only semantic. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any person with any relevant credentials claiming this.
No, they are not the same - acceleration is real and frame jumping is a shell game. Einstein used acceleration in his paradox resolution in 1918. This doesn't.
+Chenfeng It's wrong to say that time dilation happens only during acceleration, but it's not wrong to say that it happens because of acceleration. Go back to the real twin paradox (not one without twins that is shown here). If there is no differential acceleration, there is no differential time, period. This is, by accepted definitions of the term, a causal relation between differential acceleration and differential time dilation.
What if there is a theoretical person A travelling at a constant velocity to infinity, and a variable twin B that just exists in V = 0 - wouldn't that person A age slower, without any change in velocity? If person A was born into the shape-ship already in motion. Of course this is no possible in the Twin example (no one would return to earth here), but just a theoretical example doesn't till still hold true? Especially if you had theoretical person C at the opposite end of the distance from person A, also in motion travelling to the direction of A.
Chenfeng Bao But that is pretty much the same thing that happens when you go to a point a distance L appart from a stationary observer, and then back again. You change the direction of your velocity when you turn and go back. The only difference between observer B and observer C is that their velocity has opposite directions. So "jumping" from frame B to frame C is equivalent to just "suddenly" turn and go in the opposite direction without accelerating. Of course, this is physically impossible, because you have to accelerate to do so, but this shows that if it was possible, or if you can do something similar to it, then special relativity would still work.
Felis Super You could assume a constant speed, but smooth change in direction (curve) until B's velocity vector is pointing right back at A, if you truly want to make the example "realistic"... But since it is just a thought experiment, there's no need for that! The point is, that a change in direction (no matter how realistic) will always break the (relativity-) symmetry between A and B. When linear motions are involved, all frames of reference are equally valid. But as soon as one of the two observers changes direction (or speed), it will know! (forces etc.).
If we truly cared about a realistic change in speed that much, we should also include the traveling twin's acceleration from earth into space to begin with, which is not possible to be instantaneous either....If the creator of this video actually tried to get rid of "change in direction" by introducing new observers, complicating the thought experiment, he should also have introduced a new observer D in order to get rid of the take off discontinuity in velocity, although I guess making B just fly by earth (observer A) while exchanging time information would've sufficed.
At 10:23 the video shows that the value of x for the event II in the observer C's perspective is γL, but I got 2γL. (My results for all the other values correspond with your solution.)
Is there an error in the video? If not, how did you get γL?
I cant figure out how to find v in the Lorentz Transforms, can you tell me how I do that? I dont know what to put in for v
Kirsti Sunde Midttun, you just put *v* with the correct sign. The sign depends on the direction of A moving relative to the observer. As far as Observer B is concerned, Observer A is moving with a velocity *-v* (A is moving left relative to B), whereas Observer C sees Observer A moving with a velocity *+v* (A is moving right relative to C).
@elio817 this is for sure a mistake, I come to the same conclusion as yours.
One thing is not clear to me in this case. Can you define the three events? Since they are far away from each other (at least A and C, and C happens to be moving), so they could not agree on a specific time when an event happens, right?
They will not agree on whether the events are simultaneous with each other or not, but they will agree on what the person at the event's clock reads as they pass it.
@@Arkalius80 But the important question is how do you know that observer C started his stopwatch "at the same time" observers A and B started theirs? If the starting of all three watches is not a "simultaneous" event, their relative readings are essentially meaningless. And special relativity owes its origins to deep thought into what, exactly, "simultaneous" actually means when events take place in different locations.
Splitting Ron into B and C to get rid of accellerations could have been mentioned more explicitly, Still a neat explanation!
How do they synchronize to start moving at the same time? Send a lightbeam as signal?
It doesn't matter. It is a thought experiment. It would be hard to organize, but theoretically possible and hence the math can just be applied.
indeed, no need for that. that would drown us in the complications of simultaneity. they actually don't start moving because they move eternally, no acceleration allowed. you can imagine that there's an infinite stream of travellers C and this experiment looks at the one guy who meets traveller B at the middle point #2.
Yes with a light signal. If you look at a spacetime diagram, light will always move at a 45 degree angle regardless of the speed of the other reference frame. So you can send a light signal to another observer and he starts his clock when the light signal hits him. It's reflected off a surface and send back to the original observer. If you take the total time elapsed for the first observer and divide it by two, you know how long it took for the light to reach the second observer so you then how much to delay your clock for proper calibration
Help from a physicist please: Don says that there is no acceleration in the case of the twin paradox - but isn't the transition from one reference frame to another what acceleration is? Where am I going wrong here?
Don's example still confuses me (though it is new to me, I must confess). In the twins case, the two twins A & B part company then rejoin.
+Theo Philus Yer not wrong: describing the motion via 'clock swapping' still requires gluing together different inertial frames comoving with actual observers - i.e., acceleration
"His example shows that the acceleration isn't relevant"
But, by definition, the twin paradox REQUIRES that Observer B travel to Alpha Centauri AND return. The ONLY way Observer B can return is by transitioning to Observer C's reference frame at Alpha Centauri. And the ONLY way Observer B can do this is by accelerating from v to -v at Alpha Centauri.
Without this acceleration, Observer B continues to travel away from Observer A so (1) there is no twin paradox, and (2) the thought experiment is only 2 separate examples of time dilation added together. The twin paradox requires that the twins MEET in the future to compare ages side by side.
Bottom line: 2 twins start and end in the same place. Which twin is younger? The twin who traveled and who experienced the acceleration.
ScienceNinjaDude But can't we set the rocket person as the stationary frame and say Earth is the frame that's moving out and back? That's using the same treatment with two different frames for the Earth "frame".
I guess what I'm trying to say is, why is the rocket the one with 2 frames? Why isn't Earth the one with two frames?
I agree. Whether it's "acceleration" or "frame jumping" is just a semantic difference. I don't find any deep meaningful difference between the two explanations. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any people with any relevant credential claiming this. Credential: PhD student in physics.
ok.. if the 3 events from A's POV are (0,0); (L, L/v), and (0, 2L/v), then why arent the same 3 events from B's POV: (0,0), (0, L/v), and (-2L, 2L/v) ? Why do they have y (gamma factor) in their perspective?
If you are factoring gamma in "B and C's POV", Basically you are taking only A's POV under the names B's POV and C's POV! Can you explain this?
Exactly! An equally valid interpretation for A is (0,0), (L,vL), (0, 2vL). SR cannot distinguish between those two cases. There is a tacit assumption that (to a very good approximation) A resides in the centre of mass reference frame throughout the entire affair.
What I don't understand is why don't we just make the speed of light our zero point/ the point of reference, since it's constant. Everything else is moving relatively to it.
(1) I thought an event was a point in spacetime. But your Event I for A and B is located at a different point in space than Event I for C.
(2) If instead of a thought experiment you tried to carry out this experiment for real, how would you do it without accelerations? How do B and C reach v and -v in the first place.
(3) It is a paradox. It's not a contradiction. It has a rational explanation. But it is still paradoxical.
(4) The maths works out, but you are still not explaining what it is that causes the aging of one twin to slow down. I'm still left with the suspicion that the initial acceleration shifts the travelling twin into another timeframe. I'm not saying that the dilation occurs during the acceleration, but without any acceleration there would be no time dilation. From this it seems to follow that acceleration is central to the effect.
Coordinates are just labels, like address of a house. Different frames of reference can assign different coordinates to the same point in spacetime. For observer A his position has coordinate 0 and C has coordinate 2L. For C it's different, C is at 0 and A is at -2L. Different frames of reference assign different coordinates.
@@thedeemon but then event 2 for A would also be 0 (we took it L). An event is a specific set of 4 coordinates, so event 1 should be at (0,0,0,0) for A's and B's frames and (L',0,0,0) for C's frame
excellent comments Brendan! ad 2 and 1: I'd do no synced start, just the encounters must happen in the order AB then BC then CA. The velocity is gained and settled before the encounters, so B and C appear as flying eternally. However, C must now additionaly note down also the coordinate of the encounter with A, not just A's clock, which might mean an equal complication so I'm affraid that I'm just shifting the difficulty around.
Regarding your point 4, yes, I'm totally with you: if switching the frame on the turn-arround (emulated here by the BC encounter) causes a jump in simultaneity then why not the departure/arrival switches?! My explanation is that the the switch happens when the twins are at the same spot so no alternate simultaneity is possible. And here the SR reasoning departs from the reality because if the realistic acceleration happens over some time interval it also happens along a certain spatial interval, twins not at the same spot anymore - and here the expected shifts in simultaneity can already occur.
I found both of Dr. Lincoln’s clips on this subject helpful. His thought experiment is not quite the same as the traveling twins thought experiment, but his experiment is successful in its own right in showing that acceleration is not key to resolving the twins paradox.
For me, the essential point is this. The experiences of the two twins are not equivalent, because one involves motion of the twin with respect to his cosmic (space time) background, and the other does not. You can argue that, from his point of view, the spaceship twin has remained motionless while the Earth, and indeed the entire cosmos surrounding the Earth, have rushed away and back again. But in that scenario, from the point of view of the spaceship twin, the earthbound twin is moving along with his cosmic background; he is not moving WITHIN it. In contrast, from the point of view of the earthbound twin, the spaceship twin is moving within his cosmic background, with corresponding time dilation effects.
That, I think, is the essential point. The seeming “paradox” arises because it is difficult for us to set up and explain the different frames of reference involved and how they relate to each other.
Like i'm driving in my car and all of a sudden i slam the brakes then i see the car in front of me accelerate away from me and the harder i slam the brakes the harder the car in front of me accelerates away from me.
But of course the other car can say the same about me but it was really me slamming the brakes so there's no paradox.
@@ernestschoenmakers8181 you've described an (de)acceleration scenario
@@SpongeWorthy76 Yeah but it's a bit the same idea, i was decellerating not the car in front of me who was just driving at a constant speed wrt the road.
Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice.
On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy.
Brian Greene has a marvelous "now" timeslice visual:
ruclips.net/video/idsw99SSwKc/видео.html
You're 100% wrong.
The entire point of relativity is that there is no special "space time background". Videos like this are so harmful, because their nonsense basically implies your misunderstanding.
No: what breaks the symmetry is acceleration. It doesn't matter what the rest of the stars and galaxies do at all.
Interestingly enough, Einstein himself stated that the acceleration was the only possible explanation. Which of course it is. It's a lot easier to think about this if you start with the twins on board two different spaceships (rather than one being on the earth, which tends to make people automatically think of it as "immobile" while the spaceship is "moving" - but why?). It is impossible in special relativity to get rid of the symmetry issue the two reference frames, because it only deals with inertial (that is, non-accelerated) frames. Acceleration is what makes the difference. Just like Einstein said.
Acceleration is the cause of the fact that one twin is stationary in two different inertial frames while the other only in one. The acceleration isn't the proximal cause, the different reference frames is. So it is correct to say the acceleration is important, but to focus too strongly on it would be misleading, suggesting that acceleration is necessary to produce this kind of result in general.
We can explain using acceleration also. We use general theory of relativity in travelling observer's frame of reference and argue that the stationary observer's clock will be faster. But it is possible to resolve the paradox purely by using special theory of relativity. ruclips.net/video/JPCDKta2LVE/видео.html
Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice.
On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy.
Brian Greene has a marvelous "now" timeslice visual:
ruclips.net/video/idsw99SSwKc/видео.html
I am working through the Lorentz calculations to understand the work. Am I mistaken in thinking the space coordinate for observer c looking at event 2 should be 2yL (where y is gamma). I'm getting y(L+vL/v) which isn't working out to yL. :(
Nevermind I didn't read the correction. Man that would have saved me a few minutes of frustration.
@@minhtrinh5003 indeed, 2 y L is correct.
The solution to the paradox is that the one who is moving will experience a slowing of time. If something about the situation tells you who is actually moving, then you will know who is experiencing slower time. In the original paradox, the one who travels around the star is obviously the one moving. This is so because he decelerates (or accelerated, it doesn't matter which). In the example given, we don't know with absolute certainty who is moving. And we don't have actual proof of who is experiencing slower time. We are just having the characters hold up cards based on our assumed Lorentzian calculations. If you performed this experiment assuming that A were moving, you would apply the Lorentzian calculations to her and get a similar result. But you are assuming who is moving. The fact is, there is a multiverse going on in special relativity: the reference frames in some ways don't communicate. They are islands unto themselves. It is only when symmetry is broken and the one who is truly moving is revealed that we know who experiences the various strange happenings of special relativity.
This was a bid hard to understand.
The best explanation I ever heard was in the video "Raumzeitdiagramme und Zwillingsparadoxon • Aristoteles ⯈ Stringtheorie (16) | Josef M. Gaßner" (german) using Minkowski diagrams. Especially about the 26:00 mark was the breakthrough for me. Its totally obvious seeing this.
Good video however, as always :)
Also MP, and das Wiki :D
Gonna have to study this video for a while, but gaining clarity about the "paradox" will be more than worth the effort! Thanks, Don!!!
If you haven't seen the videos (4) he references to preface this one, I recommend them like he does. They give the proper background to explain the problem he poses here . Plus you get to see him rollen past the haters in a sweet Corvette.
I am not so sure.
PhysicsGirl also has a great video about it, which is less deep, but more understandable for casuals.
I mean it is not accurate, but it definitely helps if we understand that one, before listening to this one.
The problem is PhysicsGirl attributes time dilation to acceleration, whereas this video says it has nothing to do with it.
+Daniel Nogueira Leitão This video is wrong in saying the twin paradox has nothing to do with acceleration, although its own explanation itself isn't wrong. Just different semantics, different emphasis.
@@DanielNogueiraLeitao She says that you cannot treat an inertial frame the same as a non-inertial frame. The "paradox" arises when the same treatment is applied to both frames.
That's not a causal attribution. It's a statement about the proper mathematics needed to compare the intervals traversed by the two paths connecting the two events. They will not be equal in the general case, and in particular, cannot be equal when one is a unique geodesic and the other is not a geodesic.
Help me out here.
What are the two reference frames he is referring to at the end?
A stationary one and a moving one?
I'm confused. At about 10:24 the video shows the coordinates of the three events in C's reference frame. However, C was present at events II and III, and is at rest in her own frame, so the _x_ coordinates for those events should be the same, just as A's are for events I and III. However, the _x_ for event II is γL while the _x_ for event III is 2γL. What is going on? Why are these two coordinates different?
They made a typo. The correct value of x for the event II in the observer C's perspective is 2γL. Check the description of the video :)
Thanks. I actually figured it out myself. Eventually.
Ron needs to fly 8 lightyears and it will take him 4 months. Does he need 8 years worth of fuel on the spaceship or 4 months?
Time is the same for him as for his fuel (so: 4 months). But: To get to his speed he needs a lot of energy to accelerate. Once his velocity near c is reached, I assume his fuel-cost-efficiency is pretty neat, if he never wants to stop again.
no fuel needed, Ron does not accelerate in this experiment! Instead, Ron got schizophrenic, he's now Ron b and Ron c, new approach to interstellar travels, you become two (sorry I'm being sarcastic at the faulty setup of the experiment)
Good question.
He'll need enough fuel to accelerate to .99c, then to decelerate to go around alpha centauri, then to accelerate back up to .99c again, and then finally to decelerate to 0 back at earth. He wouldn't use any fuel during the parts of the trip at constant speed. So, no idea...
I'm not sure if you meant to, but you've stumbled across a VERY interesting 'philosophical' question. :D
Lets give it a twist: does he need oxygen and food supply for 4 months or 8 years? I think its for 8 years, but I might be wrong
sir, suppose both Ron and Don are not familiar with STR & time dilation. Now Ron knows it will take him atleast 4yrs to reach the star since his ship travels at 0.99C. But due to time dilation he realizes he has reached in merely 22 mnts. So he decides to crosscheck his speed and finds out he must be travelling at 2.2C to cover 4 light years in 22 mnts. How is this possible,please explain?
length contraction?
For Ron, the distance to reach the star was a bit more then 22 lightmonths, or 1.83 ly.
Travelling at high speed shortens distances too.
Accelerating warps the space around you. I advice you to check this game: Velocity Raptor.
It shows you what would happen if the light speed was ridiculously low. (featured on Vsauce's channel DONG)
testtubegames.com/velocityraptor.html
Aashish Hegde the distance is dilated as well.
Distances are relative. A lightyear isnt any more absolute than a mile or a foot. Remember light is moving at c in both reference frames. So a lightyear measured by Ron is much longer than a lightyear measured by Don.
Ron forgot about length contraction.
I’d like to see you do a video that incorporates the apparent simultaneity into resolving this paradox.
As you change frames of reference, what is considered “now” changes. In imagining how the two twins perceive the flow of time, it’s like when the moving twin turns around, his “now” for the other twin changes. At a constant velocity, both would see their own “now” going further into the other’s past. When the one turns around the frame of reference changes so much that the moving twin see’s the apparent “now” jump so far into the other’s future that he can still see the other aging slower with time dilation during the entire trip, but arrives back home finding the stationary twin has aged considerably more than himself.
Like Brian Greene talks about “now slices” in this clip: ruclips.net/video/MO_Q_f1WgQI/видео.html
I don't get this, 'In imagining how the two twins perceive the flow of time' what do you mean by this? And what is 'now' ? You can only have the same now if together, otherwise I'm not sure what you mean by 'now'? I have seen other people talk about 'now' in Relativity related scenarios, but don't grasp it, because 'now' is only relevant to me now, or to someone else, somewhere else, which is somewhen else (not local). They are not linked, unless very local like a telephone call.
@@jonathanbyers791 It's like trying to keep a clock that shows your own time, and one that will show the other's time and match their clock when you get back together. You can send messages between each other to keep up to date. But if the message came from a light year away, it makes a big difference if your inertial frame of reference is moving toward them, or away from them. That inertial frame has been moving in that direction at a constant velocity for a whole year since the message was sent. www.staskoagency.com/wp-content/uploads/2016/12/b8258-oldnewsroom.jpeg
At 5:32, the equations are ambiguous, without clear specification of the (x2,t2) and (x1,t1) coordinates. The Lorentz transform equations are often written with a - sign inside the bracket where (x2,t2) is the coordinate of an event occurring in an initially co-aligned system moving at constant velocity, relative to another "fixed" observer who logs (x1,t1) for the same event. It's OK to downplay the math for such a wide audience but not OK to the point of spawning confusion. Physics is not pure algebra - the symbols all have physical meaning! Having criticized this omission, I still do appreciate the intuitive explanation of the twin non-paradox using A, B, and C observers.
4:04 the description of the problem is not quite correct. They are not the same as only one of them is going to experience acceleration.
Wrong, they will both experience the same relative acceleration, although one may 'feel' the acceleration more due to relative conditions.
Ohhh no, I did not understand the point with the 2 frames .. and that was key... :-(
I really like how you match your t-shirts with the video content 😃😃
"I'll pause for a moment so you can look at them..."
LOLOLOLOL!!!
How was t(II, B) calculated at 10:20? Why would there be a factor of 1/gamma, if the time interval between events I and II is a proper time interval for Observer B?
@silverrahul Ah, of course! I got mixed up both with the definition of proper time and when trying to use the Lorentz transformation equation. The latter method requires much more complicated algebra, but I just verified that it does work. Thanks!
Dr Don's footage is a load of krapp.
A gedanken. In deep outer space spaceship A passes close by spaceship B. Both facing in opposite directions.
During the very brief time that they are very near, A sees that B's giant sized clock is ticking slower than A's, whilst B sees that A's giant sized clock is ticking slower than B's (according to STR). A paradox. And no accelerations involved.
Another gedanken. The identical spaceships each have 2 antennas (at front & at back).
Each ship has an identical clock midway tween their own antennas & connected to their own antennas.
Whilst passing, Ship A senses/sees that...
(1) The 2 front antennas touch.
(2) Later, the front touches the back.
(3) Later, the back touches the front (because Ship B appears shorter to A).
(4) Later the back touches the back.
Ship B senses/sees the same as Ship A, but in a reciprocal way (because Ship A appears shorter to B).
Hence here above we have the paradox that each Ship reckons that it is longer than the other.
Plus if we compare the 2 sets of recorded timings of the four events we find a version of the twins paradox.
A double paradox.
The truth is that STR does not assign any real or true or absolute values to any lengths or times, all lengths & times are relative. Hence there is no need to try to wriggle out of any paradox. STR is what it is.
I had a look at the youtube re the effect of position/location. It looks silly to me. If true that location is important then using the same speeds & accelerations but changing the location of one or more of the 3 observers must change the ages. Nope -- & anyhow thats not what Einstein ever said.
But GTR does include a simple effect of gravity on clocks, where v in the equation for gamma is the escape velocity for the gravitating body in question. Actually i very much like that bit of Einstein's theory, his one contribution to science. Although the effect is not due to gravity (ie acceleration), it is due to the nearness of mass (but i wont go into that here).
So when Dr Don says that acceleration has of itself no direct effect on apparent ticking (& apparent length) he is correct (unless i have misunderstood his meaning).
I often see comments that the twin sitting on Earth experiences an acceleration (ie g), whilst the twin in the spaceship experiences his own acceleration (which sometimes in some youtube footages happens to be g). And the comments say that both twins suffer the same time dilation due to acceleration (ie if they have the same g). This is correct, ie it accords with STR/GTR (but of course we then need to add the effect of relative speed).
But in (my Aetherian) reality the twin on Earth suffers ticking dilation due to the nearness of mass (not due to gravity), whilst the twin in the spaceship suffers no such ticking dilation because she is not near mass, & because acceleration does not directly affect ticking (it has an indirect effect in that it affects relative speed).
@silverrahul I think that it was Langevin that first described the twins paradox, & the stationary twin sat on Earth for 1 year, whilst the spaceship twin took 100 years to reach a star, then ditto coming back, giving 2 years versus 200 years. That was in say 1911 or at least before GTR in 1916.
But Einstein himself used GTR to try to explain away the paradox.
Dr Don dismisses acceleration, & invokes the full Lorentz transform which includes position/location rather than just velocity or speed.
However Dr Don's explanation in no way actually addresses the paradox, & only introduces further complexity, & adds to the wide spectrum of supposed answers (there were about 10 different supposed explanations)(more if we add the more exotic & bizarre) (now we can add Dr Don's novel extra one). I wonder what Nick Percival would say.
@silverrahul When using STR only u get the paradox (the other twin appears to age more slowly). Scientists fall into 2 camps,
(1) thems that say that it is only an observed effect, not real, & is ok, & in no way hurts STR, &
(2) thems that adopt a (supposed) solution that says that when the true actual real effect is calculated there is no paradox (they all say that the spaceship twin is always younger).
Both (1) & (2) are wrong.
(1)'s are correct that it is only an observed effect, not real, but they are wrong to say that it doesnt hurt STR.
(2)'s are wrong because there is no possible solution that uses STR or GTR or a mix. All of their supposed solutions are wrong because of errors & omissions. Plus we have lots of contradictory versions of the supposed reality.
Where do u sit??
@silverrahul If we use STR we get the paradox, ie each sees the other as being younger.
If we use a mix of STR & GTR i doubt that there is a method that results in a younger spaceship twin in every case (hence every proposed possible method to date fails).
My reading of GTR tells me that the Earthly twin suffers time dilation due to Earth's g (here we insert the Earth's escape velocity of 11.2 km/s into v in the standard Einsteinian equation to get the gamma)(the gamma is the time dilation). And the spaceship twin suffers time dilation due to her acceleration & then deceleration & then acceleration & finally deceleration (here we calculate the 4 pseudo escape velocities for a 4 bodies having those 4 accel/decel/accel/decel & we insert those 4 v's into the equation to get the 4 gammas). And the resulting GTR time dilation is added to the STR time dilation.
But Dr Don would tell us that we need to use the full Einsteinian STR transform for the STR time dilation (which he calls the Lorentz transform), ie that we need to include an STR term for the location (along the xx axis) of the spaceship, & Dr Don would tell us that we need not worry about any real g or pseudo g's or pseudo escape velocities etc related to GTR.
But an aetheric analysis doesnt ever suffer from a contradiction. The Earthly twin can sometimes be younger & the spaceship twin can sometimes be younger, depending on the exact case. The aetheric analysis always uses the absolute frame, ie the preferred frame, ie the frame where the aetherwind is zero km/s. The absolute/actual/true/real ticking dilation is calculated separately for each twin, where the v in the gamma is the aetherwind felt by each twin. Rather than having an Einsteinian relativity where each (supposedly stationary) twin sees an apparent/perceived/observed ticking dilation for the other (supposedly moving) twin, we have an Aetherian relativity where an observer truly stationary in the absolute frame (where the aetherwind is zero km/s) sees/observes/measures the true ticking dilation for each (truly moving) twin.
The Aetherian relativity gives goodish numbers but is difficult to work with (firstly u need to know the values of the 2 aetherwind(s)). The Einsteinian relativity gives goodish numbers in some cases & bad numbers in most cases but is easy to work with (all u need is the relative velocity)(no complicated aetherwind needed).
In addition the aetherwind varies with location, & with time of day, & with time of year. And with orientation. Difficult.
Things were simpler in the oldendays. Aetherists believed that the aether was dragged along by the Earth. Hence if one twin was stationary on Earth then the 2 relativities (Einsteinian & Lorentzian) gave the same numbers. But in the modern era we have neoLorentz relativity, where the aether is free-range, much more complicated.
@silverrahul Yes STR discards any aether, ie any preferred frame, ie any privileged observer, ie any real speed or real length or real time (length & time are relative, ie observed, ie not real). Hence in a sense the Twins Paradox is not a contradiction, hence STR is a little or a lot useful & not useless.
This is in a way correct, but i say that STR nowadays gives numbers that are not useful, ie not accurate enough for modern use. And as experiments & usage gets more & more accurate & exacting the stupidity of STR will get more & more obvious, & the present Einsteinian Dark Age of science will end. For the times they are a-changin'. And neoLorentz relativity will too be found to be imperfect.
The best relativity is my own, which is a mix of neoLorentz (corrected for a number of errors that i have identified) & Einsteinian (i include a GTR term related to Shapiro Delay)(ie due to the slowing of light near mass). I could name it neo-FitzGerald-Larmor-Einstein-Relativity (nFLER). FitzGerald being the father of length contraction (or change in size & shape). Larmor giving us the first goodish derivation of ticking dilation (at the atomic level at least). Einstein predicting the slowing of light near mass (but using false premises). And me myself i show how to put them all together plus i introduce say 6 needed corrections to the equations for the gammas (particularly for ticking dilation). Time will tell if i am correct, or at least better/best (pun intended).
Re the ins & outs of the Twins Paradox u should read what Nick Percival has written. Plus he has some youtube footage under Nick of Time.
And i will repeat my comment of 2 days ago, quoting some of Nick's wordage (or it might have been Kelly or Dingle) (which u obviously have not seen) in a separate reply in a few minutes.
@silverrahul Kelly said that many years ago Dingle said that Einstein wrote that steady speed slowed a clock, but that acceleration/deceleration fasted a clock ..................................................
5. Even more of an embarrassment is the completely incorrect and bizarre bluff of Einstein in Naturwissenschaften (6th year, Heft 48, page 697-712, 1918) concerning the Twin Paradox. I challenge you to quote this nonsense and debunk it! Einstein was challenged concerning the one-sided aging of the twins, who are in relative motion. He postulated, in an article in Naturwissenschaften, that the speeding up of a moving clock in the deceleration/acceleration phase was exactly twice the slowing down that is occasioned in the steady-speed state. This is quoted in translation in Dingle¹s book (p. 194). In a supposed discussion between a skeptic and a relativist, the skeptic raises the paradox of the two clocks (U1 and U2), each supposed to be running slower than the other. The supposed 'proof¹ of one-sided aging has been buried in the archives. It is surely another huge embarrassment to adherents of Relativity Theory. I have never seen it even partially quoted in the past 20 years, since Dingle quoted it (pages 192-201 of his book ³Science at the Crossroads", nor in the previous 50 years. Why, oh why? Einstein actually pretends that the whole paradox is explained by the following statement (referring to the acceleration and deceleration phase as causing 'advancement' or lessening of age):
"Calculation shows that the consequent advancement amounts to exactly twice as much as the retardation during stages 2 and 4. This completely clears up the paradox which you have propounded." (page 669 Columns 1 & 2 of Natürwissenschaften).
Phases 2 and 4 are the steady uniform motion phases going out and then back. I love the phrase ‘calculation shows’. What calculation? Be wary of any such evasive statement. Young’s "University Physics" on the Twin Paradox says "Careful analysis shows", but carefully avoids saying how this is done!
Let us consider this question. On the journey of a twin, who goes off, and then turns around and comes back again, the acceleration phase can be of any duration and magnitude, and the deceleration phase can be likewise; also the return journey could have entirely different acceleration and deceleration from the outward journey. So, we cannot say that the magnitude of any effect would exactly balance out the slowing that is supposed to happen during the (arbitrarily chosen) steady-state phase. As an example, we could have the steady state phases going out and back each of duration 1000 years, while the deceleration/acceleration, which reverses the motion, could take 1/100 second. How could the slowing that took place over 2000 years be magically exactly balanced by a quickening that takes place in our arbitrarily chosen 1/100 second! An alternative example could have the steady state out-and-back taking 1/100 second, and the acceleration and deceleration part taking 1000 years. Also, the outward acceleration and deceleration could be 10,000 times greater (or less) than those on the return journey!
It is arrant nonsense to suggest that the two always balance exactly, no matter what the duration of the steady state phase, or the acceleration phases. What a blatant crooked swindle! But, this must be quoted when debating this paradox. Why pretend that Einstein did not say that? I dare any proponent of S.R to mention this statement by Einstein. He was challenged to explain the paradox, and this was his considered published reply (after a 7 year delay from when it was mentioned by Langevin). He occluded the supposed balancing of the steady state, and the acceleration & deceleration phases, with convoluted applications of imaginary gravitational fields acting upon the twins!
You imply that a correct 'explanation' is in almost all relativity textbooks. I have, so far, collected 54 different so-called 'explanations' (up to Summer 1999), published in mainstream physics journals (all suitably peer reviewed!) and textbooks, and each implies that most of the others are wrong!!! These so-called explanations are broken down as follows: 8 say it is inexplicable, and causes a huge problem for Relativity (among these is Essen the inventor of the cesium clock); 4 say the differential aging is all caused solely during the acceleration & deceleration phases (this includes Langevin, Bondi, Rindler and a standard 1990's textbook); 9 say the acceleration has nothing whatever to do with the explanation; 3 say that General Relativity has nothing to do with the explanation; 4 say that General Relativity gives the sole explanation; 2 say jumping from one Inertial Frame to another explains the paradox. Other more exotic and bizarre explanations make up the rest. So, it as all very simple, and the correct explanation is to be seen in every standard text? Like hell it is!
Møller's widely used text "The Theory of Relativity" had to admit that its original explanation was not correct. In later editions it concocts a mass that suddenly goes from + to - for a twin! That must be an interesting experience! ŒBizarre¹ is the word for that.
Umberto Bartocci has yet another explanation (if this has been published, it can be counted as number 55) viz: that the path of one of the clocks is 'geodesic, the other definitively not". He claims that "the 'postulate of relativity' either special or general, never asserts that supposed complete symmetry between the two clocks". I claim that Einstein said just that in his 1922 book (see above).
Also, in relation to this paradox why not also quote another simple objection; if the twins never met again, and just start by passing each other at high speed and exchange photographs, and after 30 years of each others own recorded 'time' take another photograph and post that to the other twin?. This is the simple set-up that is very carefully avoided in the debate. Or what of the "Peter would be dead and Paul alive on the one hand, while Paul would be dead and Peter alive on the other hand" problem set by Lovejoy in 1931. We have Peter both dead and alive, and also Paul both dead and alive! Why, oh why, do so many adherents of S.R. adopt a lofty condescending attitude on this problem, as if everyone else was stupid, and ‘dead from the neck up’?
Acceleration isn‘t the cause! That cannot be stressed enough, as it is such a widespread misconception! So thanks a lot for that superb video on this topic, Dr. Lincoln!
It _is_ ; check out my comment on why. The contrived 'two frames' conclusion here, though seemingly getting rid of acceleration, doesn't do so because it requires swapping a _global_ chart for an _atlas_ of _local_ ones to describe the motion. This is a technicality of diff geo, that relates to things like the stereographic projection, but it's at the heart of the equivalence principle: local inertial motion = acceleration = gravity
No relative acceleration, no clock difference. This passes many tests of causality. Define cause?
I feel like it's important to say acceleration isn't the proximal cause. It is, however, important in the scenario. The proximal cause is the fact that the traveling twin exists in more than one inertial frame of reference on his trip. The reason he does this (in the classical twin paradox) is because he must accelerate to turn around. So it would be wrong to say the answer has nothing to do with acceleration. However, it would also be inaccurate to focus on the acceleration itself rather than its result.
Arkalius80 There is also the case of the identically accelerated twins. Here both twins undergo identical acceleration, yet one ends up older. See for example www.researchgate.net/publication/241349452_The_case_of_the_identically_accelerated_twins
onehit pick That’s wrong. See the case of the identically accelerated twins.
So to solve the Twin Paradox you actually need a triplet?
Right - why do physicists propose to tell you that there is really no "twin paradox" at all but then when they try to prove it, their example has a traveling twin who never returns to earth? In the tradition of 7 fictitious dimensions I can sell you and a host of super symmetric particles that will be detected any minute now (just you wait!) you will have to believe your twin brother is younger than you even though you will never see him again because they sent him away for life. Watch my rebuttal video to Brian Greene's explanation.
I have a notepad full of scribbles which give a very impressive look to my total failure to perform the transformation. I'm not even sure how the additional reference frame solves the paradox.
Still, there's nothing better than having something you firmly believed shown to be completely wrong and I'm not beaten yet. Back to my scribbling I go...
So A's perspective is good old Galileo:
Ai. x=0, t=0
Aii. x=L, t=L/v
Aiii. x=0, t=2L/v
Let's focus on the spacial transformation and employ x2=y(x1 + vt1)
Bi. x=
It's very obvious B is where the event is happening so x=0 from his perspective. So the maths should be easy and we can confirm we get the right number. We need the x transformation: x2=y(0 + v*0) Great, we get x=0. Quick check for t: t2 = y(t1 + v/c^2 * x1) so y(0 + v/v^2 * 0) = 0. Ok good, zero again.
Bi. x=0, t=0
For Bii, the right answer is also obvious but let's do it. First question, it's t1 (so A's then and t=L/v) but whose v?? Is it from A's perspective (so positive) or B's (negative)? It must be A's because the whole point is to calculate B's from A's. Second question, is x1 A's perspective on its own distance to the event or A's perspective on B's distance? I'll try the former: x2 = y(L + v*L/v) so yL. That is not zero. The latter then: x means A's opinion on the distance between B and the event. Jesus... ok. y(0 + v * 1/v) so y(0 + 0). Mmm. I'm getting zero but I'm not convinced. Let's skip ahead to the end to x on the third event for C which isn't zero:
Ciii. x=y(2 + v*2/v)=y(2L) - is that the same as your answer 2yL?? I have no idea... I wish I had a working example with velocities and times to check my answers...
I have no idea if I'm doing it completely wrong or if these are valid answers... Given this, I think the latter isn't the likeliest option! If anyone wishes to point out my abject stupidity then I'd be grateful!! :-)
I got lost at the same place, this guy does not explain or defines half of the things he writes, it is very hard to follow him and understand what he tries to say.
I assume constant V (capital) is the speed to the right and -V the speed to the left for the guys in the example. In the Lorenz transformations, there is a lowercase v, which is a variable.
For case II, you have as seen from A (x,t) = (L, L/V). So when you replace in the Lorenz transform for the position, you get: x' = gamma (L + v * L/V). Then what is v in this formula? I guess it is the speed of A seen from B, because that is what matches his result: x' = gamma (L + -V*L/V) = gamma (L-L) = gamma * 0 = 0.
An then for the Lorenz transformation for time: t' = gamma ( L/V + -V*L/c^2) = L * gamma * (1/V - V/c^2) = > (multiplying by V on both sides) => t'*V = L * gamma * (1/V - V/c^2) * V = L * gamma * (V/V - V^2/c^2) = L * gamma (1 - v^2/c^2) = (hmmm that looks familiar!) = L * gamma / gamma^2 = L/gamma => t' = L/(V * gamma). Oh crap, I just got this one trying to show where I got stuck, I promise! :)
For some reason he actually has the inverse Lorentz boost written in the video, which means you need the velocity from B's perspective (negative for B, positive for C). Normally the Lorentz boost is written from A's perspective and the equations have negative signs.
There also appears to be a typo in the results, for Cii it should be x = 2 * γ * L
I hope that helps.
12:14
How is this difference any different than acceleration?
What is switching reference frames if not acceleration?
He just posted a follow-up to this. Showing how his explanation is equivalent to Sabine Hossenfelder's. Hossenfelder insists repeatedly that acceleration is the only thing that can be measured, not velocity. I can see the equivalence he makes here, but it ultimately means that it is acceleration that is the cause.
This proves that the reference frame of the accelerated traveler coincides with those two reference frames in part of her trip. Of course, the acceleration accounts for the difference in age for the twins, simply you can calculate that difference without accelerating frame, but you don't explain it without the accelerated part of the trip.
what if the acceleration is instant? Then is takes 0 time in Ron's frame, and 0 time in Don's frame. How does something that last ZERO seconds in ALL frames account for aging in locations that are not casually connected to the accelerating frame?
@@DrDeuteron I cannot integrate an infinite acceleration to get the proper time. Fortunately, that is a physically impossible situation.
@@dodgsonlluis there is no time. Zero proper time passes for Don, and zero proper time passes for Ron. That's why there's a paradox.
@@DrDeuteron There is nothing like infinite acceleration. You can find in the web an accelerated travel to calculate the proper time of the traveler.
@@dodgsonlluis well if you want to really understand why the twin paradox is paradoxical, you need to stop worrying about acceleration and understand what happens when something that takes zero time in all restframes causes a time paradox.
Regarding proper time on world lines...that's a manifestly covariant formulation so there no paradox to begin with, SR is self consistent.
I gather from this video that acceleration myth has been busted. Youthfulness is proportional solely to the number of reference frames, whatever the method of counting those frames is. Now, why did physics design such an awkward thought experiment 100 years ago, full of unnecessary circumstances? No wonder it lead to the myth.
Studying this newest explanation (by the way, it's somewhat hard to grasp when sitting here looking at the explanation from the fourth reference frame, looking at paradox that cancels out with another paradox sort of stuff) I can't help looking for simpler explanation. Perhaps some explanation along the lines on how one gets minimum youthfulness in absolute zero temperature environment and every moving beyond that then increases youthfulness, up to a photon in vacuum that doesn't age at all. Something simpler that is. The slippery relativistics make my head spin.
See what you think of this: ruclips.net/video/rrZC0Bl6NDY/видео.html
Rather than describe the math, I've put everything into mathematica, and actually make IT do all the calculations to perform the Lorentz Transformation on the spacetime diagram over the course of the traveling twin's journey.
Your animation is a brilliant head spinner, Jonathan. I like it, it has all the necessary details I think. Of course, I'm just a layman looking for a word that would best describe what makes one twin younger and not the other.
All the videos I find have always somehow preestablished that the traveler will come out younger, but what if for example the Earth was really massive, so that the twin on Earth would spend his time in a considerable gravitational free fall, while the traveler would have an easy ride. Could there then be a situation when the earthling comes out younger?
Are you saying that the explanation is that the traveler goes through more reference frames (space "slices") than the non-traveler and that's why he ages less (experiences more space but less time)? That sounds much more clear to me than Dr. Lincolns' explanation. Thank you very much.
Acceleration is NOT a myth. No myth busted here. An instantaneous acceleration of the Twin Paradox rocket occurs at the point of turnaround but is completely ignored by the flawed proposed "two frames of reference" assertion in this video. See my posted comment for more.
Dr. Don Lincoln... my guy! :D
9:39 why position of observer A is L in event II? Wasn't observer A always in position 1 all the time according to it's own frame of reference?
I believe there is one small error at 10:36. These relations would be correct for a reference frame starting at point 1 stationary with respect to the observer C. However, because the observer C starts from a different place, the transform relations should be different. It doesn't change the conclusions though.
Right, observer C shouldn't have event I at (0,0). That would mean that all three observers start at the same time and position.
Also, observer C is at event II and III, meaning x must be 0 from her perspective for those events.
Isn't it according to the traveler that the earth observer is the one who switched between two different frames of reference, and hence, symmetry persists?
This is GENIUS!
It's like I have just had my decade-long storage of nagging thoughts+lingering questions+half-baked answers suddenly decluttered in 13 mins.
Dr Lincoln, you totally rock like the new opening background music of this series. :)
Hello, i didn't went deep on the math part, so maybe i missed something, but please explain me this. So, the distant star is 4 light-years away, however when the twin that travel there when he returns back to earth in his clock it just passed 4 months? Like that is very strange to me because i think that before one the twins leaves the earth both agree that the star is 4 light years away, even after the twin arrives the star he would look back to earth again and say that the earth is again 4 light years away, however in his clock it will just take 2 months to return to earth. I am not getting that part.
It seems to me that saying that observer A has been all along in the same reference frame presupposes it was A who stayed at rest and this takes us back to the paradox. This is no real explanation unless there is a preferred reference frame. But would that not put SR into question? If there is a preferred reference frame, it should be there for accelerating as well as for inertial movement.
To Dr. Don Lincoln and Fermilab: I like that you have experimented with a changed scenario to try to finally end the twin paradox of the special theory of relativity. But I got completely lost at the end of the video. I think that such an important theory experiment should be well worth the added time to end the video with a detailed explanation. My theory, matter theory, explains the same observables as the special theory of relativity, but differently, and without any paradoxes. If you are interested, you can view my video, “You’ve Learned Relativity Theory”, which challenges anyone’s understanding of relativity theory. I am curious to learn what you think of this video. You can find my videos using the search keywords: matter theory marostica.
A crucial point in the derivation is that the vx/c2 term in the Lorentz transformation expresses the effect of relativity of simultaneity. In C's frame of reference, the now-slice (the space-time points corresponding to t_C=0) is tilted such that it intercepts A's position at a *future* moment. A sees B's and C's clock time dilated by the same gamma factor as B and C see A's clock (total symmetry here), but when C starts moving towards A, C's "now" already corresponds to A's future (which is only possible when you compare times at different locations, a point Don Lincoln mentioned). That's why A sees more time passing as C crosses A than it took B to meet C halfway and C to reach A.
Actually this video does not do anything else than divides the traveler twin's path in two sections. Although it is true that the time difference in the end depends on the length of the uniform motion of the travel, it is actually the acceleration part (or the change of the reference frame of the moving twin) that causes a shift of simultaneity for the moving twin. Until that does not happen, there will be no twin paradox, just a usual symmetrical case of time dilation.
"Until that does not happen,"...what does that mean? There is no acceleration. No one accelerates.
In the scenario with the twins, isn't acceleration crucial to allowing the traveling twin to turn around, and therefore to change reference frames? Meaning that while it might not be responsible for all of the time dilation, acceleration is the only thing that allows the twin to return at all, hence making it "responsible"? Or do people also imply that it is the only contributor to the time dilation (shown here to be incorrect)? Also, is there another way the twin could return without accelerating, say in some kind of orbit?
So at 10:25 shouldn't observer C see event II and even III happening at location 0 from her perspective?
I feel like the difference here is that with respect to A everything is moving at speed V.
Both B and C perceive one thing moving at 2v/(1+(v/c)^2) {more than v} and another thing moving at V. The faster things look to you the more your time dilates corect?
If in our twin paradox there were other objects moving in a pattern locked with Rons "motion" then wouldn't Don be the one whos clock runs slow.
Like in the example if it weren't for observer C then A and B would be indistinguishable.
If in the example if observer C started to the left and was moving to the right at 2v/(1+(v/c)^2) then it would be observer B who's clock would run faster than As.
If you are comparing clocks of A and B you will get different answers depending on what C does.
Is it the relationship with C that defines how the clocks with A and B run? Is Proxima Centauri observer C in the paradox?
At 9:40 how do we get x Co-ordinat as 0 in 3rd event. If they are traveling in straight line then it must be 2L and also at 10:15 the x Co-ordinat of event 2 is 0 but how?! .
If anyone have a explanation please explain.
But how do we justify simple addition of two times from two different frames? Outgoing time was in frame B while Return time was in frame C.
Those are the times spent traveling those paths. It doesn't matter who measured them.
In the scenario with only one traveling observer this observer occupies many different frames and the time they measure is the sum of the times spent in each frame.
@@narfwhals7843 thank you I do see it now.
Can't seem to find a consistency between A's, B's and C's perspective at 9:45 for the x-coordinate:
For A's perspective, it seems like its about A's perspective on the movement from location 1-2-1
For B's perspective, it seems like its about B's perspective on the movement from location 1-2-1 (consistent with A's perspective above) BUT
For C's perspective, it seems like its about A's movement towards C or vice versa.
For the velocity:
For A's perspective, it is the entire 1-2-1 trip
For B's perspective, like A is moving away from B, as B moves from 1 to 3 (INconsistent with x above)
For C's perspective, it is A moving towards C from 1 to 3 (consistent with x above)
Can you please correct my understanding, if it is wrong?
Can you also show how to derive C's perspective of time on event II from the lorentz transform and B's perspective of time on Event II as well?
10:36 I believe that choosing A's and B's startup position as C's X=0 was not so happy choice, but you can just substract 2ɣL from everything to be more consistent - that everybody's X=0 from their own perspective (which is true for A and B but not selected so for C). EDIT: There actually is an error in xc2, must be xc2=xc3 because C is there in both events.
I find nothing wrong with velocity, B starts where A is (xb1=0), then meets C (xb2=0) then sees C meeting A (xb3=-2ɣL, va=-2ɣL/(2ɣL/v)=-v)
Hint: Try calculating WHEN C leaves its star from B's perspective ;) (and when B leaves earth from C's perspective)
Yes it is confusing, as said in my comment made on 9-nov-2018 (please read it; it should help). The whole point is to see the difference when clocks are compared on earth (location 1, or equivalently A's location). So the Obs.B's perspective and Obs.C's perspective slides show the Lorentz-transformed values when Obs.A's perspective values are used in the Lorentz formulas. Please also bear in mind there is a typo in the displayed x(II,C) value, as stated in the video summary text.
I think I see an error in presentation. Around elapsed time 10:14. For Event III scene from Frame B, the time you write is "2 gamma L /v." I believe the correct time "(2 L) / ( gamma v )."
I don't understand. The only reason why we know we need to describe the space ship with two reference frames is because we know it is moving. If we observed this situation from the space ship's point of view and considered the stationary person as moving away and towards the space ship again, we would also need to use 2 reference frames to describe the stationary person from the space ship's point of view. I think my question is "how do we know what is moving and what isn't". Is it because the ship is expending fuel that we know that it is moving? But it isn't, because it isn't accelerating. If the ship stayed at the star, would there still be an age difference? Because at that point, even if we considered the space ship to be moving, we would only need one reference frame to describe its movement relative to the stationary person. I have a lot of questions and I cant find the answers to them. If anyone has any insights, please help.
Edit: I think the question I am most baffled about is "Why do we know the movement of the space ship (and definitely not the movement of stationary observer when observed from the space ship) requires two reference frames?"
The spaceship experiences some real force. So it does not remain in the same frame of reference. Note that real force does not depend on frame of reference. ruclips.net/video/JPCDKta2LVE/видео.html
I am confused. So, acceleration has nothing to do with it. Richard Feynman, one of the greatest physicists that ever lived, writes in Chapter 16 of his lectures, quote: "... the man who has felt the accelerations, who has seen things fall against the walls, and so on, is the one who would be the younger; that is the difference between them in an “absolute” sense, and it is certainly correct."
Acceleration is what breaks the symmetry, but it is the uniform motion where the time dilation happens for Ron. For Don there is a speed up when Ron turns around. The other thing to keep in mind is that Don can use SR because he never undergoes acceleration. Ron can't use SR because he does. You can integrate Ron's proper time (the time in his system) over the trip (see the first relativity chapter in J.D. Jackson, _Classical Electrodynamics_ for the actual integral).
Can you make a different twin paradox example using A, B, and C experiencing different gravity? Maybe all three are stationary to all observers. Then a black hole moves through the single frame of reference, with A, B, and C at different distances from the black hole.
The gravity of the black hole attracts the three observers A, B, and C. Normally this would make the observers closest to the black hole appear to move faster, relative to a fourth observer. But remember in this example all three appear stationary to all observers. So for example, if A is closest to the black hole, A must accelerate away from the black just enough to have no apparent motion relative to itself or any other observers. The same for B and C, although they will require less acceleration to appear stationary because they are farther away from the black hole.
After the black hole passes, all observers agree to have observed no motion. However, observer A will have experienced the less time than B and C.
So the answer to the question at 4:15 is: the thing that makes they experience differently is a simple fact that one didn't left the Earth (he was in frame 1 all the time) and another one did and return to the Earth (he was in 2 frames). So there is difference no matter who is stationary observer or if there is acceleration or not.
I do not understand this explanation. In the proposed experiment it is assumed that B and C will meet at location II. For that they have to start from their locations simultaneously. However it is not possible because in special relativity different observer's clocks cannot be synchronized in principle so there is no notion of "simultaneity" as soon as the 2 events are not co-located. To me this explanation is not any better than the "acceleration" one. Sorry.
@silverrahul That is true. You need to think or a sea of clocks at any point in space. You can set them going instantaneously to be your "big brother" on what subseqently happens.
Good explanation. Some side notes:
If observer A is truly stationary, the observers B and C clocks will show the same interval times. However, if A is moving, then the intervals shown on observer B & C clocks will be different by an amount dependent on the absolute speed of A. This provides a theoretical means of determining absolute velocity for any observer. This too shows there is no paradox.
While each observer has a self-consistent relativistic frame of reference and can locally consider that he is stationary within that frame of reference, comparing the clock intervals from A, B, & C can reveal which one is moving slowest, or not at all, from a hypothetical absolute frame of “stationary”. Of course, the precision of the clocks and measured speeds would be essential to determining that “absolute” reference frame with precision.
You should explain why the Lorentz equations were not used for Obs A. And I guess that's because Obs A sees the distance L as static, not in relative motion. As you said, "remember that location 2 is a distance L away from observer A". Obs B and C do see distances between events as contracting. In the Lorentz transform, both x2 and t2 are related to both x1 and t1, so space and time are connected so to speak. I think "length contraction" is an easier way to see why there is no paradox.
Ok.. but can't C just use a difference reference point and claim that it is A that sees a contracting distance and not C?
I'm still confused. It seems to me that the end of the video just did some hand waving and didn't explain the crucial point.
Does this mean that a closed universe cannot exist, since the person leaving earth would remain in a single reference frame throughout the journey?
What prompts the definition of a new reference frame (for the returning spaceship)?
Different velocity.
First error is : x'=g(x+vt). The correct one is x'=g(x-vt), so is for t'=g(t-vx/c^2)
A 13 minute long video with a brief 5 second explanation at 12:20. Can you make the next video all about those 5 seconds please
The thought experiment doesn’t clearly factor out acceleration, because it seems ‘B’ and ‘C’ are stopped and only start moving when the experiment begins. If both are ALREADY in constant motion, and ‘B’ passes ‘A’ at time zero, and ‘C’ passes location ‘3’ at time zero, then no one is EVER accelerating. And, FWIW, I was surprised there was no mention of how a traveler - whose clock seems perfectly normal to them - can make the trip in such a short time: Because the distance appears much shorter since the traveler perceives space moving past them.
At 10:14 and 10:24 the time coordinate values for event II is same.dont let the later one intimidate u.
Hi Dr. Lincoln! I'm the guy who met you at O'Hare yesterday. Thanks for giving me 5 minutes of your time and sorry I had to run, I had a certain space and time to be at.