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hey, i know u wanted to leave out insignificant information, to focus on the most important parts, but to make this example more realistic: u could let the space ship accelerate with near g , so the passenger can actually survive the flight. Then the accelerations (both away from earth and back to earth) up to near c relative to the earth frame would be taking some years. That wouldnt change much in the physics, especially not with the time dilation.
Gravitational time dilation is not just a function of the strength of the gravity. It is also a function of the distance between the two clocks, along the direction of the gravitational field. When Adam fires his rockets to turn around, there is a very large distance between his clock and Sarah's clock, hence the effect of gravitational time dilation (from Adam's point of view) due to the external gravitational field is very significant.
The Earth's gravitational field is negligible far away from the Earth. By contrast, the external gravitational field which only Adam thinks exists is present throughout the entire universe. If "h" is the distance from the Earth, and g(h) is the strength of the gravitational field, the time dilation between two clocks is the integral (from 0 to h) of g(h)dh.
@Physics Videos by Eugene Khutoryansky Adam sees Sarah's clock speed slow down because of the speed of light. It takes longer and longer to receive the information. Think of it as a slinky. When compressed, on object moves from end to end in a short amount of time. As it is being stretched out, it is taking longer to move from end to end. Has time really slowed down for Adam?
Everyone, if you liked this video, you can help more people find it in their search engine by clicking the like button and writing a comment. Also, if you haven't already seen it, two days ago I uploaded a video on gravity's effect on the flow of time. Thanks.
Everyone, although I briefly covered the Twin Paradox in my main video on Relativity, the Twin Paradox is the topic that I keep receiving by far the most number of questions on. This is why I felt I needed to do this separate video to address this issue in much more detail.
whoatemyhummus Adam would never be able to tell if he is moving. This is because it is entirely consistent with the laws of physics to have a uniform gravitational field throughout the entire universe without an object with mass to create it. The existence of objects with mass only dictates how the gravitational field varies from one point in space to another.
You are arguingby acceleration alone to explan the difference who is staynh younger. But You firgot, thta there is a solution without any acceleration phases by using 2 ships. Also- main part of the trip can be passed without accelerazion. The lenhth jf thta phase is independent of the acceleration rate. This is surely most wrong explain of twin paradox.
As a teacher, I realized that good explanations are almost always good because they are fancy. People will understand the twin paradox when you say the values of the following problem (having or not similar results). Until then, you are running away from the main point. Imagine twin A on Earth. Earth and the Star are going left with v/2. Imagine twin B in a spaceship to the right with v/2. When twin A calculates twin B to reach the Star, he reverses (and the Earth and the Star go together with him.) When twin B sees reaching the Star, he reverses too. Twin B stops a clock just after leaving the Earth, another just before reaching the Star, another just after leaving the Star, and another just before reaching the Earth. I want to know the values of those stopped clocks when they meet.
No need to invoke GR to break the symmetry. The older twin sees more redshifted light from the younger one. If you can use Matlab or Octave, try this: function ageDiff = TwinParadox(v2, v1=0, vo=0) % SYNOPSIS: Plot worldlines and time ticks for the Twin Paradox scenario % v2 is velocity of the 2nd twin in the CoM frame % v1 is velocity of the 1st twin in the CoM frame % vo is the velocity of the observer in the CoM frame v = [vo v1 v2]; worldline{1} = zigzag(0,v(1)); [ worldline{2} age1 red1 white1 blue1] = zigzag(v(2),v(1)); [ worldline{3} age2 red2 white2 blue2] = zigzag(v(3),v(1)); % Minkowski grid lines xm2 = linspace(-1,1,201); tm2 = []; for i=0:11 tm2 = [tm2; sqrt((i/10)^2+xm2.*xm2)]; endfor xm3 = tm2(:,101:201); tm3 = xm2(101:201); xm1 = -xm3; tm1 = tm3; % Lines of sight v(1) = -v(1); for i=2:3 v(i) = (v(i)+v(1))/(1+v(i)*v(1)); endfor los = {}; for i=1:3 los{i} = [[0 0]; [sign(v(i)) abs(v(i))]]; endfor % Plot results figure, hold on, grid on ageDiff = age2 - age1; title (['Twin Paradox (\DeltaT = ',num2str(ageDiff), ')']) xlabel ('Space') ylabel ('Time') xlim([-1 1]) ylim([0 1.5]) color = 'kmg'; names = {'CoM'; 'Twin #1'; 'Twin #2'}; for i=1:3 plot(worldline{i}(:,2), worldline{i}(:,1), [ color(i) ';' names{i} ' (v = ' num2str(v(i)) ');'], 'linewidth', 2); endfor for i=1:11 plot(xm1(i,:),tm1,'k-.') plot(xm2,tm2(i,:),'k-.') plot(xm3(i,:),tm3,'k-.') endfor for i=1:length(red1) plot(red1{i}(:,2), red1{i}(:,1),'r') endfor for i=1:length(red2) plot(red2{i}(:,2), red2{i}(:,1),'r') endfor for i=1:length(blue1) plot(blue1{i}(:,2), blue1{i}(:,1),'b') endfor for i=1:length(blue2) plot(blue2{i}(:,2), blue2{i}(:,1),'b') endfor for i=1:3 data = los{i}; plot(data(:,1), data(:,2), color(i), 'linewidth', 2); endfor plot(white1(:,2), white1(:,1),'k') plot(white2(:,2), white2(:,1),'k') endfunction function [ worldline age red white blue] = zigzag(v,vo) g = 1 / sqrt(1 - v^2); t = g * [0:0.1:1]; x = v * t; secondleg = find(t > 0.5); x(secondleg) = v * (1 - t(secondleg)); roundtrip = find(sign(v) * x >= 0); ticks = [t(roundtrip)' x(roundtrip)']; worldline = [[0 0]; [0.5 v * 0.5]; [1 0]]; firstleg = find(ticks(:,1) 0.5); blue = {}; for i=1:length(secondleg); j = secondleg(i); blue{i} = [[ticks(j,1) ticks(j,2)]; [ticks(j,1) + abs(ticks(j,2)) 0]]; blue{i} = boost(blue{i}, vo); endfor white = [0.5, v/2]; white = [white; [0.5 + abs(v)/2, 0]]; white = boost(white, vo); age = 1 / g; worldline = boost(worldline, vo); endfunction function [result] = boost(data, v) g = 1 / sqrt(1 - v^2); t = g * (data(:,1) - v * data(:,2)); x = g * (data(:,2) - v * data(:,1)); result = cat(2, t, x); endfunction
Nice video. Note that, since special relativity is a self-contained theory, it's also possible to resolve the twin paradox without reference to general relativity by invoking *relativity of simultaneity* in the context of the frame change experienced by the twin at the return point at large distance from earth.
The frame-change depends on who experiences acceleration. If you've established proper acceleration, the symmetry is already broken and there's already no more paradox before you even start calculating.
I have a sincere question... What if Adam's space-ship, say, hit a wall, and exhibited a perfectly elastic collision... Wouldn't the acceleration you're talking about in this video be for an infinitesimally small time? How would we explain twin paradox in this case? Thank you!
@@SamuelWesley_samwesprem ruclips.net/video/1ENkP0h8nAg/видео.html I know its a little late, but anyhow ... In Eugene's 'Gravity's effect on the flow of time in General Relativity', notice what the narrator tells us: 9:00: "Suppose we are in a region of space where the strength of the gravitational field is the same everywhere" 9:15: "Clocks that are far apart along the direction of the gravitational field will run at different speeds" 9:28: "The difference in the rates at which the two clocks run increases as we increase the distance between the two clocks along the direction of the gravitational field" 9:58: "The difference in the rates atwhich the two clocks run also increases if we increase the strength of the gravitational field" Therefore, what's essential here is two things: a) The strength of the gravitational field, say g, and b) The distance between Alice's and Bob's clocks, say D In this way we can conclude: Difference between the rates at which the clocks tick = K x g x D (for some constant K) So I think what you're asking is what happens if the turnaround is nearly infinitesimal small ... Well, then the corresponding force (felt by Bob) will make the gravitational field strength even more strong, because what counts is the amount K x g x D. In it, there's no time-dependence ...
Great video, but I'm still confused about what is different for the two people. From Adam's point of view (when he accelerates) he experiences a gravitational field for the entire universe (which cancels out with his engine thrust) which results in Sarahs clock moving really fast compared to his clock. If this is correct couldn't you also say that from Sarah's point of view a gravitational field is applied on Adam's ship which makes his clock move really fast as well...
FINALLY. For EVERY twin paradox explanation, I was always left with the same freaking question : “Well, from the traveler's point of view, he is standing still and the earth is the one accelerating mid journey. So how does he know he’s the one accelerating ?” NOW I understand ! THANK YOU 😊
We need to address this problem without involving gravity and acceleration. Assume instant acceleration so that 100%of journey is spent in constant speed. In this case it will be impossible to solve the paradox with just the two observers. They both need to be measured relative to a third reference frame, that being the universe itself. Only one of them is moving faster than the other relative to the whole universe.
how can it not violate the theory when you can clearly tell who is moving just by seeing if he or she aged. In the video, it said that they both agree about who is aging. Can someone explain?
+hieu dang you dont really know if when adam left earth if he has left a staionary object, or if the object is speeding through space towards a gravitaional field and that his rockets simply opposed this forced so that he sat still while the universe was pulled away. then upon returning, the gravitational field reversed and sucked everything the other way and his rockets again simply opposed the force to keep him still. the effects of time dont confirm who is moving, only their relative position in the 2 gravitational fields. The fields are only felt when accelerating. so if he accelerates to leave and is close to sarah, the effects on both of them should be close. when he turns to return to earth. they are far apart and the field is now behind adam. so his time will be effected much more than sarah's, because the effects of gravity on time have to do with the position along the field as it increases, just as gravity's forces is related to the distance between the two objects of mass. the effects on time are also increased with this field.
This is the best video I have seen on the clock paradox. You have to include general relativity and not just stay with special as other explanations have tried to do.
Thanks for the compliment about my video. Yes, the explanations which just stick to Special Relativity miss the whole point of what this paradox is supposed to be about.
Nice attempt to explain the paradox. Here is a simpler explanation: When the Sarah is flying away from Earth at 95% the speed of light, the radio communication is impaired because of a Doppler shift. Both sister need to tune their 1 GHz frequency to 50 MHz, which electrical engineers call carrier frequency. The AM or FM modulated signal, a slower wave which modify slightly the carrier frequency amplitude or frequency is equally slower. All embedded binary code are also streaming 20 times slower. The decoded voice of Sarah is deeper, like playing a vinyl disc or magnetic cassette in slow motion and the video are almost still pictures. A year later, Sarah turn around and come back toward Earth at 95% the speed of light, the following happen: That day, one year after their separation, Alice on Earth keep receiving the slow stream of radio at 50 MHz. She just received the video from Sarah telling how boring it is now, after 2 weeks of travel. She think her sister is crazy, talking about 2 weeks when in reality she his gone for a year and she is supposed to turn around now. Sarah also receive old news from her sister on Earth. She see the video telling her that she already miss her after two weeks of separation. However, the radio is fucked up because Sarah at the switch frequency from 50 MHz (for the 1 GHz carrier frequency) to 20 GHz. Also, the voice sound like chip monks and the videos are 20 times too fast. As the time pass between 12 month and 24 month of the total duration, the video that Sarah receive from Alice catch-up with the real time. Everything synchronize just right so that the last day of this 2 years voyage, Sarah can see a video of her sister recorded only 20 days earlier. For Alice, the second year events are a little more complicated to explain. She keep receiving outdated video on the radio station tuned at 50 MHz. Suddenly, 2 weeks before the end of the 2 years trip, the frequency jump from 50 MHz to 20 GHz. The video from Sarah describe that she now prepare to turn around. Alice think that she is crazy to announce that after 23.5 months. Then, during these last 2 weeks, Alice receive all the videos from Sarah describing that entire year where she is flying back to Earth. Finally, both sisters re-unite and they both aged by exactly 2 years. End of paradox.
I think the video focused too much on gravity and is missing an important factor which is the light. When Adam and Sarah each hold a flashlight giving each day one light impulse then the time has to slow down when they move away from each other. So the light can catch up its speed. But both will see less impulse coming in from the other side. And light is red (doppler effect). When they later approach to each other then clocks are faster to compensate the accelerated and blue light. Now each side sees more impulses coming in than sent out. Both effects don't neutralize because of the turning point. When Adam turns his ship he sees Sarahs flashlight immediately turning blue (and impulses speeding up) while Sarah will see Adams turn many years later. She sees his red signals much longer.
You say a uniform gravitational field throughout "the entire universe" is entirely consistent, but I don't see how. My understanding is that the uniform gravitational field picture is only valid locally (via the equivalence principle.) What are the equations that show a uniform, source-less field for all space?
I guessed she was thinking in the non-inertial frame of reference (the person in the rocket during the acceleration). During the acceleration in the non-inertial frame of reference, the observer in the rocket sees himself as stationary while the entire universe accelerates (uniform gravitation field) in the same direction.
This was an awesome explanation. Thank you. I'm studying physics at degree level and someone asked me about this and I couldn't figure out the resolution of the paradox. Now I know!
Scientists had two synchronized atomic clocks and put one in an airplane trip around the world. After the trip, the two clock were no longer synchronous. Sure the difference was negligible, but there still was a difference. I've also heard that "light speed" isn't the cosmic speed limit for matter, it's the speed of causality or how fast two things can "relay information" or interact and light just happens to go this fast.
Finally I get it!! Thanks... But, what if the universe is like the surface of a sphere so that going in one direction gets you back? In that case there would be no acceleration, right?... Or is it not a valid case because of the Minkowski metric doesn't apply?
The universe is hyperbolic and relatively flat actually. But in theory this is an interesting concept. The closest of a concept that you can get to this is a wormhole. I recommend Leonard susskinds lectures he explains it very clearly and simply!
if sarah(the twin left on earth) has an equally valid perception that she is the one moving away from adam her twin in the spaceship whom she assumes is standing still, why would her clock be the one to show a faster rate of time compared to adam when he gets back to earth to her? is it the distance of adam's clock from the earth's center of mass and his speed of motion that is causing adam's clock to slow down compared to sarah's.
your obvious observation falsifies relativity. in one reference frame she ages faster than him, in another he ages faster than her. there's no use trying to accept relativity, the whole thing is an exercise of mathemagical mental masturbation.
Well then it doesn't matter. You can't really compare two clocks unless they are either in the same location at the same time, or stationary relative to each other. So, if he flies off and never returns, neither of those requirements are true, so you can't really definitively say which one is older. It depends on your frame of reference at that point.
Arklius what if he traveled only far enough for minimal time dilation with a neutral observer in between earth and him who can see the faces with a supertelescope...who would look older? or, what if they both had an electric bomb strapped before he left and whomever ages faster 1st dies...who's bomb would go off?
Well the neutral observer scenario depends on a lot of variables you haven't defined, such as his position relative to Earth and the traveler, his relative velocity, the velocity of the traveler, whether you want to know what he would observe, or what he would calculate after the fact after accounting for the travel time of light, etc. The second scenario is basically saying you have two time bombs with the same timer, one flying off into space, which one goes off first? That depends on your frame of reference. Simultaneity is not absolute in relativity. Things that are simultaneous in one frame of reference are not in another, and for some events, the relative order in time they occur in can depend on your frame of reference as well.
Please consider this scenario: 2 stationary points in space, A and B, One bomb in A, one bomb in the ship. One Bomb in B. The bombs have a start button. The bombs are identical. The bomb in A and the bomb in B are synchronized to start at the same time. The experiment starts.... the ship travels from far far away and when pass the point A (traveling at constant speed) The bomb in A, B and the bomb in the ship start the count down (one stationary observer at the same distance from A and B can tell the 3 clocks start at the same time. When the ship reaches the point B at constant speed (0.9c) the pilot take a picture of his bomb and one observer in the point B take a picture of the bomb B when the ship passes B so the 2 pictures are taken at the same time because they are in the same point B. Then the ship stops turn around and return to the point B to compare the pictures. Are the pictures showing the same time? Is one bomb near to explode more than the other? The acceleration does not affect the pictures. All the pictures were taken at constant speeds. Please explain the maths for this experiment. Ty
Your scenario is a little confusing, I think you may have mistyped part of it. You say that the bomb ship arrives at point B where the pilot and observer at B take a picture. You then say it turns around and returns to point B. That doesn't really make sense. Do you mean it turns around and returns to point A?
Now I feel that I finally understood why Sarah and Adam disagree on why more time has passed for Sarah during Adam's voyage. It seems so obvious now, why didn't I get it when I watched your earlier videos? Anyway, big thanks to you Eugene, again!
***** I am glad I was able to clear that up. There were a lot of people who were having trouble understanding this, as I only had time to cover this very briefly in my main video on Relativity. Thanks.
QUESTION: What if Adam decided not to stop his ship in an environment in the middle of space that lacked gravity? What if Adam decided to stop his ship in an environment close to a planet that had a mass equal to the mass of Earth? Wouldn't this decision make it so the time of Sarah never "speeds up" from the point of view of Adam?
Both Sarah and Adam were traveling through the spacetime continuum at the same speed, Adam only traveled more in the space variable and Sarah only traveled more in the time variable.
But from Adam's perspective, Sarah traveled more in space, and he traveled more in time. Not to mention, that it doesn't sound like an explanation of physics.
Since these two things are linked, i.e. time and space. When a photon is traveling through a vacuum, we measure it's speed (c). The 299792458 meters per second. That would mean the particle is not traveling through time at all, correct?
This does not explain the paradox. From Adam's perspective you can say the same thing: Sarah traveled more in the space and he traveled more in the time variable. So he should have been older. He is not. The key is acceleration/deceleration of Adam when he is far away from Earth.
What if adam had taken a circular path? Then there is no need to fire the rockets right? Oh or does he need to fire rockets to maintain ciruclar trajectory hence centripetal acceleration makes adam think he is in orbit around a gravitational field.
The paradox is wrong from the start because it assumes that both observes a slower clock of the other. The paradox is also misleading by staying on Earth means standing still but in reality is also accelerating in spacetime and we can replace Earth with another spaceship . Imagine an empty space with only the twins and no visible reference. Then suddenly, they went far apart in opposite directions. No one would be able to tell who left, who stayed still, or if both accelerated. It is only through the comparison of their clocks where they can tell who accelerated faster.
If they would have moved in constant speeds, then you are correct. But in reality, one (or both) of them would have to accelerate, which is equivalent to putting himself in a gravitational field. So there IS a difference between them: one experiences a strong gravitational field, while the other does not.
But the person on Earth, or any planet, is subject to gravity which in itself warps space time. So yes the Earth is moving but unlike the rocket, Sarah is subject to gravity.
The earth's gravity is not very strong. The twin paradox would work the same if Sara was floating in space, because unlike velocity, acceleration/gravity is something a person feels and can measure. If Sara and Adam would float in empty space, and then suddenly Adam would accelerate, both their measurements will show that Adam accelerated, not Sara. (The same measurements can be interpreted as if Adam was in a sudden gravity field, and Sara was not). zodiacfml wrote in his comment that we can't know which one of them accelerated, but that is not true. While we can only measure our velocity relative to someone else, we can measure our acceleration/gravity even if we are flying alone in a vacuum.
I think, that there's a big flaw in some parts of SR, so it has to add GR and the acceleration, to solve this issue. Adam doesn't have to slow down during his trip to a distant star - he can for example move along a circular path and gain speed "behind" Earth, so he will move with a constant velocity all the time. We can as well exclude the planet, so there won't be no gravity involved. In such case, telling that any of twins will get older, than the other, is a direct violation of SR own rules...
I think its confusing cause adam is moving near the speed of light. and sarah isnt moving at all. So if this was playing at real speeds, adam and sarah wouldnt even see each other cause adam would be moving to fast, right?
Great point ratamacue. The video constantly makes the confusion between what one observer perceive or can tell from the other observer and what really is.
But what will happens if ADAM did NOT turn around, and just continue in straight line until he circumnavigate the entire universe (let´s say it´s a small and closed universe). If he circumnavigate the universe, he will return back to Earth, without doing any turn around and acelerating. I think this explanation actually don´t resolve the paradox...
So, if we were to run a quantum clock and shut down Adams clock before the acceleration back and the information was instantly transported. It would disprove what they're saying and you'd realize that the effect was not due to "gravity". China launched the rocket 2 days ago and they're about to test this. Einstein was wrong.
thanks for the video. I have a question: Suppose Adam is not alone in the ship, and his travel takes (T0) time to reach the 0.9 speed of light and then he travels 10 years (T1) at constant speed... At the exact time (T0) (when he is at constant speed. I have a stationary base in the path previously arranged for the experiment ) his first child is born in the chip, take a picture and leave it in the stationary base when he passes without stopping. In the same base I take a picture to an other child born the same day (each pict show a new born baby). Then 5 years later of his traveling at constant speed he takes a new picture of his 5 years old son and leaves it again in a new stationary base (the de-acceleration of the picture does not affect the age of the person on it... or yes?). If we compare the picture of the child in the stationary base taken at the same time that the ship passes the 2nd base at constant speed with the 2nd picture of the traveling baby... who is older? why? all the pictures occur in a time interval (T1) with everybody at constant speeds. thanks a LOT PD: I want to see the maths from both sides
Amazing approach to the explanation explanation , what puzzles me is that 2 different explanations from 2 different viewpoints attribute to the same result.
There is one slight bit of this I don't quite understand. It has to do with reconciling the two frames. From the perspective of the twin on Earth, time dilation for the astronaut piles up along all three segments of the trip - a certain and same amount for the trip out and back and then very heavily during the turn around (a + B + c). But from the perspective of the astronaut, the trip out and back essentially subtract from his overall time dilation against the swamping amount of the turnaround (B - a - c). So to me they would largely agree with each other, except that from the astronaut point of view, the time dilation affect overall would have been slightly less than what the twin on Earth would estimate. It seems like they should exactly match.
From the perspective of the twin on Earth, the time dilation during the turnaround is negligible, and almost all the time dilation was due to segments (a) and (c). Keep in mind, from the point of view of the twin on Earth, this extra gravitational field never existed.
I don’t understand how someone “believes” gravity is effecting them and that Sarah is accelerating towards him. He KNOWS he’s the one who left, who accelerated away, and gravity exists due to massive objects, so no one could plausibly “believe” it’s slowing them down if there is no mass actually doing it. I’m so confused.... :/ Any help?
I think, that there's a big flaw in some parts of SR, so it has to add GR and the acceleration, to solve this issue. Adam doesn't have to slow down during his trip to a distant star - he can for example move along a circular path and gain speed "behind" Earth, so he will move with a constant velocity all the time. We can as well exclude the planet, so there won't be no gravity involved. In such case, telling that any of twins will get older, than the other, is a direct violation of SR own rules...
as soon as instantaneous communication will be established, e.g. via means of quantum entanglement, this discussion will get a truer and more easily understandable direction
I finally understand why planet gravity does not make the deep universe run super fast. Gravity diminishes with distance, and it is acceleration over the distance that matters which only to the spaceship view is the same into infinity.
Nice, but the problem can be reformulated without acceleration by giving Adam an initial velocity and adding a 3rd observer (Bob) with equal and opposite velocity at the turn-around point. Bob and Adam can compare clocks as they pass at the halfway point. The paradox can only be resolved if you know how each observer moves with respect to their combined centre of mass. (We are presumably talking about flat spacetime so we can ignore the Earth and the rest of the universe.) The speed of time is evidently maximal in the centre of mass reference frame. Clocks run more slowly in all other frames.
What if Adam performs the "accelerations" without any g-forces by employing gravitomagnetic effects of a rotating torus? ( Referring to your video on GEM, by rotating a mass torus in a "smoke ring manner" one can induce a gravitational field.)
Ok but what if there was a human thats a long as 1 lightyear, and then he observed these twins doing the twin paradox experiment, how would time pass for him?
I suspect that when Adam fires his rocket engines he isn't going to believe that a gravitational field suddenly appeared from nowhere. He'll realize he is accelerating. Good explanation though. In fact, the best I've seen. Some of the others talk about "rotating in time" which is confusing to me. What does rotating in time even mean?
What would cause that gravitational field from Adam's point of view? In classical physics, gravity is caused by masses and thus is a real force. If someone detects the effects of a fictitious force (i.e. a force which is not caused by anything in particular) then they can know for sure they are accelerating and hence moving. Is it different in General Relativity? I mean, is somehow the gravitational field Adam feels different from the gravitational field of the earth?
Wurtt Mapper well, "gravity" isn't really a "real" force, precisely because it has the same exact effects on velocity and spacetime flow as acceleration does. Gravity and acceleration are essentially the same thing
What if the universe is closed, like surface of the earth? If two twins travel in opposite direction at constant velocity, but eventually meet up again, will one be younger than the other?
Relative motion between a stationary and moving object creats an illusion for moving object as if stationary object is moving. To find out which object is stationary and which is moving we need to check motion relative to space. Relativistic effects are restricted to object moving relative to space.
There does not exist an ultimate frame of reference, which we call space. There also does not exist an ultimate moment termed "now." All of these depend on frames of reference.
Light travels in its own frame of reference. The time-dilation, fewer clock cycles, is only occurring in the clock's frame of reference. The clock's cesium-133 atom is being energized by a constant power source. The cells of your body are energized by the circulatory system. Heart rate increases as the applied force increases. Your cells are using more energy in a high g-force environment. Not less. Not only that, the clock's cesium-133 atom is being chilled to absolute zero while the observer's are at room temperature. There is no correlation between the clock's readout and the observer's biological processes. They are in separate frames of reference.
But there is still some trouble left in my understanding, 1. Einstein's theory is based on one point that you can't do experiment to identify who is in velocity. However, you say that the twin in the spaceship is experiencing the gravitational field. Gravitational fields do converge to a point. But the objects in different points inside the spaceship do not converge. So experimenting inside the spaceship would reveal it is gravity or acceleration. I am assuming that the spaceship is big enough to be sensitive enough to the convergence experiment. 2. Wat about the case where the spaceship has stopped accelerating. For e.g the spaceship accelerates only for a very short period of time in the entire journey time like 1%. Once the acceleration stops then no gravitational field will be experienced in the spaceship. However the majority of the time dilation experienced by the twin in the spaceship is due to its velocity and not sure to acceleration. Having the acceleration for a short period of time, how will it account for the time dilation for the entire trip?
+Saran Paramanantham, gravitational fields do not necessarily have to converge on a point. Having a uniform gravitational field throughout the entire universe is consistent with the laws of physics. Objects with mass only determine how the gravitational field varies from one point to another, but there is nothing preventing a uniform gravitational field from being present everywhere added to these variations. In reply to your other question, during the 1% of the trip when the acceleration occurs, the effect on the difference in the rates of the two clocks is so great that it more than compensates for the remaining 99% of the journey.
Don't you think you are missing something? Imagine that the spaceship accelerated to near speed of light in 3 months from an external observer's point of view in both the directions of the journey? So the acceleration happened only for a total of 6 months from extremal observer's point of view. This can't account for 4 years of time dilation. Moreover time dilation takes the velocity component and not acceleration. What would the twin in the spaceship think during the period of constant velocity of the spaceship with the earth approaching him or moving away from him?
Do you think a light photon accelerates in order for it to not experience time? Acceleration merely transports an object from one position in time dimension to another. But wat matters is that how long was the spaceship in that near speed of light velocity. Of course acceleration matters but it matters only because it comes with a velocity.
+Eugene Khutoryansky With regards to the universal gravitational field without convergence, please state how that is a possible to become practical? I agree that gravity to be almost equivalent to accelerated reference frame but there is definitely a difference between these 2, that difference is convergence. Gravity being an effect due to the spacetime distortion produced by the presence of mass/enerygy and every mass/energy should have a center for its gravity hence convergence can't be avoided. The convergence only can be reduced but not made zero. May be this minor difference is what is playing a bigger role in the mystery of velocity of stars remaining constant even if the distance increases from its center. May be I am wrong. It could be possible that General relativity is a better approximation of Newtonian Gravity but not the perfect theory of Gravity.
The Distributed, Synchronised, Clocks Problem. Setup a line, or grid, of clocks at, say, 1 light second intervals in an Inertial Frame. Allow them to pulse a light source on the clocks at 1 second intervals. Now all clocks will be able to show the same 'frame time', after allowing for the distance between them that light takes to travel in the frame. This is the way we synchronised distributed clocks on Earth today, though at closer than 1 light second intervals of course. Now try and create a second, otherwise identical, Inertial Frame and give it some relative velocity between the two frames of v. Any pulses of light created at any common point in both frames must propagate though both frames at c regardless of any relative velocity between them. A Problem.
Does this mean that all accelerated motion will involve this "pseudo-gravitational" force and consequent time effects? In other words, can we still discuss accelerated motion in terms on special relativity alone?
There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened. -- Douglas Adams, "The Hitchhiker's Guide to the Galaxy" series.
Mindblowing! Great video on the topic, helped clear things up for me. Also, what are the songs used in this video? You always have the best music choice.
Goomy Smash Thanks for the compliment, and I am glad that it helped clear things up. In reply to your question, the song is from the free RUclips audio library, and it is called "1812_Overture_by_Tchaikosvky".
Even if the gravitational field is causing Sarah's time to flow much faster than him, but Sarah is also moving faster and therefore the time will also run slower. How does this work now?
mill tanyanun In this case, the effect of the gravitational field is far more than overcoming the effect of Sarah moving fast. Although Sarah's motion causes her clock to move slower, the gravitational field is causing her clock to move much, much faster, and in this case, the effect of the gravitational field wins out.
From Adam's point of view, when he fires his rockets, it's Sarah who is accelerating towards him. Why is it Adam is the only one who feels the effects of the artificial gravitation? I'm sure it has something to do with the application of force but I can't quite wrap my head around it.
It is only Adam that believes that this external gravitational field exists. This field does not exist from Sarah's perspective. I explain this in detail in my video at ruclips.net/video/1ENkP0h8nAg/видео.html
why does there have to be a twist (different perspectives) in twin paradox?Couldn't Adam simply always see the time on earth pass faster?Is it because he then would know that he is the 1 moving and would violate einstein's principle and cause entire theory of relativity to collapse? If Adam notices that he needs to spend infinite amount of energy in order to go faster,couldnt he conclude that its his spaceship that is moving with the speed of light, rather then the earth?
I love your videos! Keep them coming! As well as, what if the universe is a sphere, and there for he never had to turn around, and completely went around the universe never turning his rockets the other way. Would that change anything? Thanks!
are there any published papers that support this explanation of the paradox? I'm doing a paper with a new look on the twin's paradox that shares some similarities with this video.
I am a bit puzzled on the idea of time. That say if there are two objects, which are non living things. So, whether one object stand still and the other is traveling at the speed of light, is there any significance difference if we apply time on this case? I rather believe that time in this instance will only apply to two living things. If we are refering to 2 rocks, will the speed of 1 rock cuses any significant differences to the other? Whether any one rock travels at the speed of light, if the other stand still rock cannot appear to be affected, then, what is the meaning of time to the 2? If gravity is the curvature of time and space, then if the two items are put in a vacuum, without any external force, can the curvature works? That is, we have to explain, how come in a lab with no gravity, we can float. If the space time curvature is present everywhere, by right the gravitational field should apply, regardless of circumstances. Sorry, I may mistaken Theory of Relativity. So, I appreciate correction.
I can't understand the end when it says both can belive that they were standing still during the entire journey. For Sarah perspective that makes sense, but for Adam when he turned his ship and the rockets were fired he experienced acceleration/gravity. I thought that as soon as you experience an acceleration/gravity you couldn't claim to be standing still.
From Adam's point of view, the force from his rockets exactly balanced the "force" from the gravitational field, thereby causing his spaceship to remain standing still.
Using phrases such as "Adam will believe" and "Adam's point of view" is not good - it will leave those who don't know Physics with the impression that time dilation and length contractions are just illusions. In any case, the twin paradox can be resolved using on SR - no need to invoke GR.
Indeed. It really is best to define those terms more succinctly before launching into the explanation. :-) And, yeah. Use GR... or use SR with acceleration. The picture is the same... only the terminology changes! :-)
οκ nice explanation buy what if adam circles the earth at near the speed of light for some years?then, in adam's point of view, the earth spins around him at nearly the speed of light for years and never goes far away of him and his spaceship. So, when the earth finally stops and he returns he must expect to find sarah young while he is an old man.on the other hand , in sarah's point of view ,adam were circling the earth for years at near the speed of light so he must be young when he returns while she is an old woman.can you explain this paradox?
........ Wait, doesn't that mean that a theoretical Alcubierre Warp Drive still violates Relativity even at subluminal speeds (disregard the superluminal ones for obvious reasons) since the passangers of the ship wouldn't feel any acceleration at all and thus making us go back to square one with this paradox?
People will understand the twin paradox when you say the values of the following problem (having or not similar results). Imagine twin A on Earth. Earth and the Star (speaking about abstract points fixed in a system) are going left with u/2. Imagine twin B in a spaceship to the right with u/2 só that they have a relative velocity v. When twin A calculates twin B to reach the Star, he reverses (and the Earth and the Star go together with him.) When twin B sees reaching the Star, he reverses too. Twin B stops a clock just after leaving the Earth, another just before reaching the Star, another just after leaving the Star, and another just before reaching the Earth. Twin A also stops one clock just after leaving Twin B, another one just before reversing, another one just after reversing, and another one when they meet. The values of those stopped clocks should be compared with the respective ones of the classical twin paradox, in which only twin B reverses.
So does this distance-between-clocks-in-gravity effect occur in any circumstance? If we have Sarah on Earth, Adam orbiting at near-light-speed around black hole A, and another guy named Josh orbiting similarly around black hole B, but B is twice as far away from Earth as A, then when both Adam and Josh return to Earth to compare clocks, will Josh be even younger than Adam?
Let's say, it take 100 years for Adam to go and return in Sarah's point of view, but it's a small amount of time for Adam. Let's imagine a Worm Hole at the furthest point Adam get to, linking that point to Earth. Adam would reach that Worm Hole 50 years after his take-off in Sarah's pov. But in his pov, Sarah's time hasn't passed (much). If he used the Worm Hole, what would happen? Would he return to a old Sarah or the young Sarah? What about the old Sarah seeing Adam enter the worm hole? Would he return (to old Sarah) or disappear (to young Sarah)? Or, from Sarah's pov, Adam would take off, then immediately appear out from the Worm Hole. But there would be still another forever-young Adam moving toward the Worm Hole and would reach it in 50 years.
What if Adam was really just Sara the whole time ? and JFK was never assassinated when he jumps into the black hole from which he gets out of using 'Ludicrous' speed ?
If the wormhole is not inside Adam's vehicle then Adam returns to an older(About 50 yrs) Sarah. If the wormhole is inside his vehicle i.e. travelling with Adam (I have no idea how!) then Adam returns to young Sarah i.e. the wormhole is now a time machine, which happens only if Adam somehow manages to enter and exit the wormhole without feeling any acceleration. However in the first case the result only applies if Adam attempts to stop and measure Sarah's age, otherwise if he somehow measures Sarah's age while moving at const. velocity Sarah will still appear young. From Sarah's pov : In the first case Adam takes 50 years to reach wormhole. He then instantly reaches Sarah. In the second case Adam's vehicle takes off and Sarah can see an Adam riding his vehicle for 50 years. But right after the start of the journey another Adam pops out of the wormhole at Sarah's location. Notice that now, for 50 years Sarah is going to see two Adams - one at earth and another at the ship. This case is actually briefly discussed by Kip Thorne in one of his books on relativity and gravitation and black holes and stuff. All this however is purely speculative.
In the main Relativity video, it was stated that objects moving close to the speed of light have greater mass. Even without the mass increase, the Universe has more mass than Adam's ship, so how does a rocket with enough force to accelerate a spaceship close to the speed of light end up accelerating the Universe instead?
+Garrett Thomas, the rocket does not accelerate the Universe. The gravitational field accelerates the Universe. From Adam's perspective, the rocket balances out the force of the gravitational field, causing his ship to stay in one place, while the rest of the Universe is accelerates.
Eugene Khutoryansky Then what causes the gravitational field? Surely no object is massive enough to accelerate the Universe to the speed of light that quickly.
I am from India, you are requested to put Hindi subtitles in the caption. I will be grateful to you Satyendra Singh Bhadauria alias Vitarag from India. 🌹
What if both Adam and Sarah are orbiting a black hole/neutron star in separate ships in opposite directions and periodically passing by each other? What would they see? I mean their frames of reference are sort of inertial, and their relative speeds are quite high as well. They never fire their engines yet they can regularly see each other from a short distance.
In short, dude, what is the conclusion? All these relative stuff we all knew since the first film of Star Wars or Star Trek. Give finaly your points of view about where can we use the principles?
Excuse me, it might be a dumb question, but in this case, how can distance have anything to do with time dilation, when the gravity of acceleration that affects Adam doesn't affect Sarah at all? My intuition tells me, that at both acceleration phases, Adam's clock will slow down the same amount relative to Sarah's... Once again, sorry if this question doesn't make sense.
The extra gravitational field only exists from Adam's perspective. It does not exist from the perspective of anyone outside his spaceship . I cover this in detail in my video "Gravity's effect on the flow of time in General Relativity" at the following link ruclips.net/video/1ENkP0h8nAg/видео.html
so lets so that the distance that adam travels before turning is L, then if adam travels at near the speed of light through a distance of L then stops. Then sara moves at near the speed of light to that same location, will sara be have experienced more time than adam, or do they experience the same time? because sara accelerates twice, first from earth, then her deceleration at L, but so does adam. So they must experience the same change in time right?
+ligase75, Quantum Entanglement does not allow for meaningful communication. I go into detail about this in my video titled "Quantum Entanglement, Bell Inequality, EPR paradox".
Panda Pandemic Thanks for the compliment about the video. I discussed how gravitational acceleration is the result of how mass creates a curvature in Space-Time in my "Laws of Motion" video and in my "Einstein's Theory of a Relativity" video, but yes, I can make another video which goes into this topic into much more detail. I'll put this on my list of topics for future videos. Thanks.
Distance as a Time Delay is not the same as Time itself. Differences in Distance do not affect Time, only any delays that are observed between remote sites and local ones.
if two entities are somehow connected by a string or even their gravitational pull, circling around their center of mass, how are the relations gonna be between them or between each of them and the midpoint? Is the consequence, that the core of e.g a fast spinning neutron star is older than its shell? Or even is earths core? Any thoughts?
To an observer stationary in the centre, each of the circling entities would be time slowed. From the point of view of each of these entities, the centre would be correspondingly time hasted! This is because, while a circling entity sees the centre as moving (and hence time slowed because of its motion), it is also accelerating towards the centre (to remain traveling in a circle) so it also adds an additional effect that speeds up the centre's time flow. The net result is that the centre's time flows faster.
What if Sarah is on a stationary rocket ship in space with very little gravitational pull and Adam passes a point ( on the other side of the Universe ) in space already going near the speed of light ! Then which one of them will have aged and which of them will not ?
It seems to me that the video is trying to explain something that already has an explanation within special relativity using a hypothesis that is known to be false, that is, to suppose that there is a uniform gravitational field throughout the universe in the opposite direction of the spacecraft's motion.
Nevertheless, while the rocket turns and accelerates, apart from the spaceship and Adam themselves, the earth and Sara are accelerating too. Therefore, Sara should be affected by the gravitational force too. Moreover, what's the accurate meaning of 'along the direction of the gravitation field'?
+Michael Cheung They all feel the same gravitational field, yes. But Adam is 'deeper' into the gravitational field and thus his clock runs slower than Sarahs. On the other hand, at the initial take off, both Adam and Sara are at approximately the same depth in the gravitational field and thus their clocks run at approximately the same speed up until Adam's speed increases close to c.
@@EugeneKhutoryanskynice fantasy universe you got here. Great science fiction stuff. You shouldn't be peddling it as reality though. Your so-called time-dilation, looking at each other's clocks, is merely informational. In fact, the observer is not even in the same Time frame of reference as the clock. Check the engineering specs on the atomic clock. You will see that the cesium-133 atom is being chilled to absolute zero. Are Sarah's atoms being chilled? Adams? You are comparing apples to oranges and coming up with lemons.
Hey Eugene, can we assume the travelling twin is in constant acceleration and attribute that to a gravitational force? How would that effect the experiment? Would the travelling twin still age less? Is the turn around necessary for the two to age differently?
I am not sure I understand your question. If the question is if Adam can be in constant acceleration from the time he left to the time he returned, then yes, Adam can attribute all the effects to an external gravitational field, and he will still have aged less than Sarah when he returns.
@EugeneKhutoryansky I'm trying to think of a hypothetical where the travelling twin is accelerated in a different path. For instance in this video he leaves and comes back to Earth. But what if he was simply sitting in some machine that accelerated him forward and back or in circles while still on Earth. Would his age still decrease relative to those around him?
Newton's law of motion, F=ma. Force equals Acceleration. The accelerating rocketship also accelerates the astronaut in time as evidenced by an accelerated heart rate and a shorter lifespan. The traveling twin will be the same age as the stationary twin as evidenced by the synchronized clock experiments showing no difference in the amount of energy the clocks used. The clock and the observer are in different frames of reference. Its like putting a banana on the counter and one in the freezer. It's like putting a plant under a growlight and one in natural sunlight. Atomic clocks are designed specifically to prevent the caesium-133 atom from being accelerated in time when a force is applied.
I thought the Twins Paradox was that when I see two twins together they can be like an 8 each (=16), but when I just see one of them she's really like a 6.
I'm confused about one part. When he turns around and begins accelerating, he can not distinguish this from a gravitational field, and therefore sees her time as moving faster than his. However, doesn't Sarah also see him as being very far along the Earth's gravitational field, and should therefore see his time as moving faster than hers (for argument's sake lets say he accelerates by 9.8m/s^2 to keep the situation roughly symmetrical)? If the fact that he is moving near the speed of light makes up for this, then shouldn't the same apply to Adam, who sees her moving away from him?
The gravitational field due to the Earth drops off to almost zero far away from the Earth. By contrast, the extra gravitational field that Adam believes exists has constant strength throughout the entire Universe. It is the sum (integral) of the gravitational field throughout the entire distance between Adam and Sarah that accounts for the difference in the rates at which their clocks run. Hence, the contribution from the gravitational field of the Earth is negligible. But, since there is a large distance between Adam and Sarah, the constant gravitational field that Adam believes exists has a major impact on the difference between the two clocks.
@@EugeneKhutoryansky Thank you for the answer. I have so many questions and I understand it's not possible to go much further here without mathematical rigor, but there is still something which doesn't sit right with me. If an observer can't tell the difference between a gravitational field and acceleration, then I assume the only way Sarah knows the gravitational field of Earth is not affecting Adam in deep space is because she sees he's not accelerating. Likewise, he assumes gravity is uniform everywhere because he sees everything in Sarah's direction as accelerating towards him without drop off. However, when he accelerates towards Sarah, does he not look like he's in a gravitational field to her? How can she know, without apriori knowledge of the nature of the gravitational field she's in, that Adam isn't accelerating due to gravity? Or is it because it's only him accelerating and not the rest of the universe?
Both Adam and Sarah know the details of the gravitational field that is created by the Earth, because they know how much mass the Earth has, and they know that the strength of the Earth's gravitational field gets weaker further away from the Earth. What they don't know is whether or not there is an extra uniform gravitational field throughout the entire Universe. This is because everything in the Universe would accelerate at the same rate, and hence there is no experiment that could be performed to determine if this extra gravitational field exists. But, both Adam and Sarah know that Adam is firing his rockets, and that the rockets are exerting a force on his spaceship. If this extra gravitational field exists, it would be cancelling out the force from his rockets, causing his ship to stay in the same place.
Something seems wrong. If the pilot ever sees earthtime move faster, then that means he is receiving light from earth faster than the constant speed of light, which isn't possible, right?
+AngelEyes986 he isn't moving at the speed of light since that would be impossible he is moving close to the speed of light so in theory he could see sarah's clock but looking at each others clocks is here so people could understand this better, because that is happening wheather adam sees it or not
+Lovro Dulibić I never said how fast he was going. I was stating that light is constant, so you couldn't see things at a faster or slower rate. But this was over a month ago. I've since researched a ton on relativity and understand it very well now. Basically its actually possible to see someone age slower or faster. Light will still remain constant. The object will either age faster or slower, or the object will flatten or elongate it's shape depending on velocities. Basically space and time are the same thing and it will warp one way or the other so light can remain constant.
TheAirpirate28 In Russian, the "Kh" sound is signified by a single letter, and there is no equivalent sounding letter in the English language, so "Kh" is the closest translation. Thanks for the compliment about the video.
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hey, i know u wanted to leave out insignificant information, to focus on the most important parts, but to make this example more realistic: u could let the space ship accelerate with near g , so the passenger can actually survive the flight. Then the accelerations (both away from earth and back to earth) up to near c relative to the earth frame would be taking some years. That wouldnt change much in the physics, especially not with the time dilation.
Gravitational time dilation is not just a function of the strength of the gravity. It is also a function of the distance between the two clocks, along the direction of the gravitational field. When Adam fires his rockets to turn around, there is a very large distance between his clock and Sarah's clock, hence the effect of gravitational time dilation (from Adam's point of view) due to the external gravitational field is very significant.
The Earth's gravitational field is negligible far away from the Earth. By contrast, the external gravitational field which only Adam thinks exists is present throughout the entire universe. If "h" is the distance from the Earth, and g(h) is the strength of the gravitational field, the time dilation between two clocks is the integral (from 0 to h) of g(h)dh.
I am simply explaining what Einstein's General Theory of Relativity says about this. You are welcome to disagree with his theory.
@Physics Videos by Eugene Khutoryansky Adam sees Sarah's clock speed slow down because of the speed of light. It takes longer and longer to receive the information. Think of it as a slinky. When compressed, on object moves from end to end in a short amount of time. As it is being stretched out, it is taking longer to move from end to end. Has time really slowed down for Adam?
Everyone, if you liked this video, you can help more people find it in their search engine by clicking the like button and writing a comment. Also, if you haven't already seen it, two days ago I uploaded a video on gravity's effect on the flow of time. Thanks.
Everyone, although I briefly covered the Twin Paradox in my main video on Relativity, the Twin Paradox is the topic that I keep receiving by far the most number of questions on. This is why I felt I needed to do this separate video to address this issue in much more detail.
Lots more videos are coming very soon.
***** Thank you! That's nice to hear.
Eugene Khutoryansky Hi Eugene. If Adam could detect Gravitons while accelerating towards earth could he be able to tell if it's him moving or not?
whoatemyhummus Adam would never be able to tell if he is moving. This is because it is entirely consistent with the laws of physics to have a uniform gravitational field throughout the entire universe without an object with mass to create it. The existence of objects with mass only dictates how the gravitational field varies from one point in space to another.
This is the only best explanation of twin paradox that I have ever read. This topic had always troubled me but not anymore. Thank you!
+Saran Paramanantham, I am glad that you liked my video that much. Thanks.
You are arguingby acceleration alone to explan the difference who is staynh younger. But You firgot, thta there is a solution without any acceleration phases by using 2 ships. Also- main part of the trip can be passed without accelerazion. The lenhth jf thta phase is independent of the acceleration rate. This is surely most wrong explain of twin paradox.
As a teacher, I realized that good explanations are almost always good because they are fancy.
People will understand the twin paradox when you say the values of the following problem (having or not similar results). Until then, you are running away from the main point.
Imagine twin A on Earth. Earth and the Star are going left with v/2. Imagine twin B in a spaceship to the right with v/2. When twin A calculates twin B to reach the Star, he reverses (and the Earth and the Star go together with him.) When twin B sees reaching the Star, he reverses too. Twin B stops a clock just after leaving the Earth, another just before reaching the Star, another just after leaving the Star, and another just before reaching the Earth. I want to know the values of those stopped clocks when they meet.
No need to invoke GR to break the symmetry. The older twin sees more redshifted light from the younger one. If you can use Matlab or Octave, try this:
function ageDiff = TwinParadox(v2, v1=0, vo=0)
% SYNOPSIS: Plot worldlines and time ticks for the Twin Paradox scenario
% v2 is velocity of the 2nd twin in the CoM frame
% v1 is velocity of the 1st twin in the CoM frame
% vo is the velocity of the observer in the CoM frame
v = [vo v1 v2];
worldline{1} = zigzag(0,v(1));
[ worldline{2} age1 red1 white1 blue1] = zigzag(v(2),v(1));
[ worldline{3} age2 red2 white2 blue2] = zigzag(v(3),v(1));
% Minkowski grid lines
xm2 = linspace(-1,1,201);
tm2 = [];
for i=0:11
tm2 = [tm2; sqrt((i/10)^2+xm2.*xm2)];
endfor
xm3 = tm2(:,101:201);
tm3 = xm2(101:201);
xm1 = -xm3;
tm1 = tm3;
% Lines of sight
v(1) = -v(1);
for i=2:3
v(i) = (v(i)+v(1))/(1+v(i)*v(1));
endfor
los = {};
for i=1:3
los{i} = [[0 0]; [sign(v(i)) abs(v(i))]];
endfor
% Plot results
figure, hold on, grid on
ageDiff = age2 - age1;
title (['Twin Paradox (\DeltaT = ',num2str(ageDiff), ')'])
xlabel ('Space')
ylabel ('Time')
xlim([-1 1])
ylim([0 1.5])
color = 'kmg';
names = {'CoM'; 'Twin #1'; 'Twin #2'};
for i=1:3
plot(worldline{i}(:,2), worldline{i}(:,1),
[ color(i) ';' names{i} ' (v = ' num2str(v(i)) ');'],
'linewidth', 2);
endfor
for i=1:11
plot(xm1(i,:),tm1,'k-.')
plot(xm2,tm2(i,:),'k-.')
plot(xm3(i,:),tm3,'k-.')
endfor
for i=1:length(red1)
plot(red1{i}(:,2), red1{i}(:,1),'r')
endfor
for i=1:length(red2)
plot(red2{i}(:,2), red2{i}(:,1),'r')
endfor
for i=1:length(blue1)
plot(blue1{i}(:,2), blue1{i}(:,1),'b')
endfor
for i=1:length(blue2)
plot(blue2{i}(:,2), blue2{i}(:,1),'b')
endfor
for i=1:3
data = los{i};
plot(data(:,1), data(:,2), color(i), 'linewidth', 2);
endfor
plot(white1(:,2), white1(:,1),'k')
plot(white2(:,2), white2(:,1),'k')
endfunction
function [ worldline age red white blue] = zigzag(v,vo)
g = 1 / sqrt(1 - v^2);
t = g * [0:0.1:1];
x = v * t;
secondleg = find(t > 0.5);
x(secondleg) = v * (1 - t(secondleg));
roundtrip = find(sign(v) * x >= 0);
ticks = [t(roundtrip)' x(roundtrip)'];
worldline = [[0 0]; [0.5 v * 0.5]; [1 0]];
firstleg = find(ticks(:,1) 0.5);
blue = {};
for i=1:length(secondleg);
j = secondleg(i);
blue{i} = [[ticks(j,1) ticks(j,2)]; [ticks(j,1) + abs(ticks(j,2)) 0]];
blue{i} = boost(blue{i}, vo);
endfor
white = [0.5, v/2];
white = [white; [0.5 + abs(v)/2, 0]];
white = boost(white, vo);
age = 1 / g;
worldline = boost(worldline, vo);
endfunction
function [result] = boost(data, v)
g = 1 / sqrt(1 - v^2);
t = g * (data(:,1) - v * data(:,2));
x = g * (data(:,2) - v * data(:,1));
result = cat(2, t, x);
endfunction
Nice video. Note that, since special relativity is a self-contained theory, it's also possible to resolve the twin paradox without reference to general relativity by invoking *relativity of simultaneity* in the context of the frame change experienced by the twin at the return point at large distance from earth.
You are right. This is what I showed in a video I posted. ruclips.net/video/mZByVMQpdAI/видео.html
The frame-change depends on who experiences acceleration.
If you've established proper acceleration, the symmetry is already broken and there's already no more paradox before you even start calculating.
I love your videos! Also, the music includes some of my classical favorites :)
Thank you! I had this question in my mind for so long and you explained it in such an elegant way
+Hamid Ghorbanbeigi, Glad I was able to help. Thanks.
I have a sincere question... What if Adam's space-ship, say, hit a wall, and exhibited a perfectly elastic collision... Wouldn't the acceleration you're talking about in this video be for an infinitesimally small time? How would we explain twin paradox in this case? Thank you!
@@SamuelWesley_samwesprem
ruclips.net/video/1ENkP0h8nAg/видео.html
I know its a little late, but anyhow ...
In Eugene's 'Gravity's effect on the flow of time in General Relativity', notice what the narrator tells us:
9:00: "Suppose we are in a region of space where the strength of the
gravitational field is the same everywhere"
9:15: "Clocks that are far apart along the direction of the gravitational field
will run at different speeds"
9:28: "The difference in the rates at which the two clocks run increases as we increase
the distance between the two clocks along the direction of the gravitational field"
9:58: "The difference in the rates atwhich the two clocks run also increases
if we increase the strength of the gravitational field"
Therefore, what's essential here is two things:
a) The strength of the gravitational field, say g, and
b) The distance between Alice's and Bob's clocks, say D
In this way we can conclude:
Difference between the rates at which the clocks tick = K x g x D (for some constant K)
So I think what you're asking is what happens if the turnaround is nearly infinitesimal small ...
Well, then the corresponding force (felt by Bob) will make the gravitational field strength even more strong, because what counts is the amount K x g x D. In it, there's no time-dependence ...
Adam shouldn't leave Sarah :(
His sister. He went to find another woman.
Neme Dinner and a movie with Sarah :)
Come back adam! Before it is too late!
wrr, doens't matter
'xD
Great video, but I'm still confused about what is different for the two people. From Adam's point of view (when he accelerates) he experiences a gravitational field for the entire universe (which cancels out with his engine thrust) which results in Sarahs clock moving really fast compared to his clock. If this is correct couldn't you also say that from Sarah's point of view a gravitational field is applied on Adam's ship which makes his clock move really fast as well...
Sarah does not believe this gravitational field exists, because this is what is necessary for her to believe that she is standing still.
Eugene, you are the best teacher of theoretical physics in RUclips. Hands down.
+The Tiger Koley, thanks for the compliment.
FINALLY. For EVERY twin paradox explanation, I was always left with the same freaking question :
“Well, from the traveler's point of view, he is standing still and the earth is the one accelerating mid journey. So how does he know he’s the one accelerating ?” NOW I understand !
THANK YOU 😊
Thanks.
We need to address this problem without involving gravity and acceleration. Assume instant acceleration so that 100%of journey is spent in constant speed. In this case it will be impossible to solve the paradox with just the two observers. They both need to be measured relative to a third reference frame, that being the universe itself. Only one of them is moving faster than the other relative to the whole universe.
how can it not violate the theory when you can clearly tell who is moving just by seeing if he or she aged. In the video, it said that they both agree about who is aging. Can someone explain?
+hieu dang you dont really know if when adam left earth if he has left a staionary object, or if the object is speeding through space towards a gravitaional field and that his rockets simply opposed this forced so that he sat still while the universe was pulled away. then upon returning, the gravitational field reversed and sucked everything the other way and his rockets again simply opposed the force to keep him still. the effects of time dont confirm who is moving, only their relative position in the 2 gravitational fields.
The fields are only felt when accelerating. so if he accelerates to leave and is close to sarah, the effects on both of them should be close. when he turns to return to earth. they are far apart and the field is now behind adam. so his time will be effected much more than sarah's, because the effects of gravity on time have to do with the position along the field as it increases, just as gravity's forces is related to the distance between the two objects of mass. the effects on time are also increased with this field.
This is the best video I have seen on the clock paradox. You have to include general relativity and not just stay with special as other explanations have tried to do.
Thanks for the compliment about my video. Yes, the explanations which just stick to Special Relativity miss the whole point of what this paradox is supposed to be about.
You can explain the paradox in Special Relativity if you are careful to show why you are applying a specific Lorentz Boost... but they never do. :-)
Nice attempt to explain the paradox. Here is a simpler explanation:
When the Sarah is flying away from Earth at 95% the speed of light, the radio communication is impaired because of a Doppler shift. Both sister need to tune their 1 GHz frequency to 50 MHz, which electrical engineers call carrier frequency.
The AM or FM modulated signal, a slower wave which modify slightly the carrier frequency amplitude or frequency is equally slower. All embedded binary code are also streaming 20 times slower.
The decoded voice of Sarah is deeper, like playing a vinyl disc or magnetic cassette in slow motion and the video are almost still pictures.
A year later, Sarah turn around and come back toward Earth at 95% the speed of light, the following happen:
That day, one year after their separation, Alice on Earth keep receiving the slow stream of radio at 50 MHz. She just received the video from Sarah telling how boring it is now, after 2 weeks of travel. She think her sister is crazy, talking about 2 weeks when in reality she his gone for a year and she is supposed to turn around now.
Sarah also receive old news from her sister on Earth. She see the video telling her that she already miss her after two weeks of separation. However, the radio is fucked up because Sarah at the switch frequency from 50 MHz (for the 1 GHz carrier frequency) to 20 GHz. Also, the voice sound like chip monks and the videos are 20 times too fast.
As the time pass between 12 month and 24 month of the total duration, the video that Sarah receive from Alice catch-up with the real time. Everything synchronize just right so that the last day of this 2 years voyage, Sarah can see a video of her sister recorded only 20 days earlier.
For Alice, the second year events are a little more complicated to explain. She keep receiving outdated video on the radio station tuned at 50 MHz. Suddenly, 2 weeks before the end of the 2 years trip, the frequency jump from 50 MHz to 20 GHz. The video from Sarah describe that she now prepare to turn around. Alice think that she is crazy to announce that after 23.5 months. Then, during these last 2 weeks, Alice receive all the videos from Sarah describing that entire year where she is flying back to Earth.
Finally, both sisters re-unite and they both aged by exactly 2 years. End of paradox.
Christian Gingras this is the best explanation I have read so far. Thank you.
I think the video focused too much on gravity and is missing an important factor which is the light. When Adam and Sarah each hold a flashlight giving each day one light impulse then the time has to slow down when they move away from each other. So the light can catch up its speed. But both will see less impulse coming in from the other side. And light is red (doppler effect). When they later approach to each other then clocks are faster to compensate the accelerated and blue light. Now each side sees more impulses coming in than sent out.
Both effects don't neutralize because of the turning point. When Adam turns his ship he sees Sarahs flashlight immediately turning blue (and impulses speeding up) while Sarah will see Adams turn many years later. She sees his red signals much longer.
You say a uniform gravitational field throughout "the entire universe" is entirely consistent, but I don't see how. My understanding is that the uniform gravitational field picture is only valid locally (via the equivalence principle.) What are the equations that show a uniform, source-less field for all space?
I guessed she was thinking in the non-inertial frame of reference (the person in the rocket during the acceleration). During the acceleration in the non-inertial frame of reference, the observer in the rocket sees himself as stationary while the entire universe accelerates (uniform gravitation field) in the same direction.
sarah is really hot...
+Robert Graham But she's old now.
Wilma or Betty kind of thing?
hmm...
wrr
no she is on the groenland
This was an awesome explanation. Thank you. I'm studying physics at degree level and someone asked me about this and I couldn't figure out the resolution of the paradox. Now I know!
+somethingness, thanks for the compliment, and I am glad that my video was helpful.
Scientists had two synchronized atomic clocks and put one in an airplane trip around the world. After the trip, the two clock were no longer synchronous. Sure the difference was negligible, but there still was a difference.
I've also heard that "light speed" isn't the cosmic speed limit for matter, it's the speed of causality or how fast two things can "relay information" or interact and light just happens to go this fast.
Adam isn't looking at Sarah's clock... unless he's gay
oh...! yea!
He's gay. Now focus.
Finally I get it!! Thanks...
But, what if the universe is like the surface of a sphere so that going in one direction gets you back? In that case there would be no acceleration, right?... Or is it not a valid case because of the Minkowski metric doesn't apply?
The universe is hyperbolic and relatively flat actually. But in theory this is an interesting concept. The closest of a concept that you can get to this is a wormhole. I recommend Leonard susskinds lectures he explains it very clearly and simply!
if sarah(the twin left on earth) has an equally valid perception that she is the one moving away from adam her twin in the spaceship whom she assumes is standing still, why would her clock be the one to show a faster rate of time compared to adam when he gets back to earth to her? is it the distance of adam's clock from the earth's center of mass and his speed of motion that is causing adam's clock to slow down compared to sarah's.
your obvious observation falsifies relativity. in one reference frame she ages faster than him, in another he ages faster than her. there's no use trying to accept relativity, the whole thing is an exercise of mathemagical mental masturbation.
If only Einstein and every reputable scientist in the past century could have read this youtube comment and realized how foolish they were!
What if Adam won't turn around or accelerate?
Well then it doesn't matter. You can't really compare two clocks unless they are either in the same location at the same time, or stationary relative to each other. So, if he flies off and never returns, neither of those requirements are true, so you can't really definitively say which one is older. It depends on your frame of reference at that point.
Arklius what if he traveled only far enough for minimal time dilation with a neutral observer in between earth and him who can see the faces with a supertelescope...who would look older?
or, what if they both had an electric bomb strapped before he left and whomever ages faster 1st dies...who's bomb would go off?
Well the neutral observer scenario depends on a lot of variables you haven't defined, such as his position relative to Earth and the traveler, his relative velocity, the velocity of the traveler, whether you want to know what he would observe, or what he would calculate after the fact after accounting for the travel time of light, etc.
The second scenario is basically saying you have two time bombs with the same timer, one flying off into space, which one goes off first? That depends on your frame of reference. Simultaneity is not absolute in relativity. Things that are simultaneous in one frame of reference are not in another, and for some events, the relative order in time they occur in can depend on your frame of reference as well.
Please consider this scenario: 2 stationary points in space, A and B, One bomb in A, one bomb in the ship. One Bomb in B. The bombs have a start button. The bombs are identical. The bomb in A and the bomb in B are synchronized to start at the same time. The experiment starts.... the ship travels from far far away and when pass the point A (traveling at constant speed) The bomb in A, B and the bomb in the ship start the count down (one stationary observer at the same distance from A and B can tell the 3 clocks start at the same time. When the ship reaches the point B at constant speed (0.9c) the pilot take a picture of his bomb and one observer in the point B take a picture of the bomb B when the ship passes B so the 2 pictures are taken at the same time because they are in the same point B. Then the ship stops turn around and return to the point B to compare the pictures. Are the pictures showing the same time? Is one bomb near to explode more than the other? The acceleration does not affect the pictures. All the pictures were taken at constant speeds. Please explain the maths for this experiment. Ty
Your scenario is a little confusing, I think you may have mistyped part of it. You say that the bomb ship arrives at point B where the pilot and observer at B take a picture. You then say it turns around and returns to point B. That doesn't really make sense. Do you mean it turns around and returns to point A?
How does adam's body know that he was moving at speed of light... so we will also age same as sarah
Now I feel that I finally understood why Sarah and Adam disagree on why more time has passed for Sarah during Adam's voyage. It seems so obvious now, why didn't I get it when I watched your earlier videos? Anyway, big thanks to you Eugene, again!
***** I am glad I was able to clear that up. There were a lot of people who were having trouble understanding this, as I only had time to cover this very briefly in my main video on Relativity. Thanks.
QUESTION: What if Adam decided not to stop his ship in an environment in the middle of space that lacked gravity? What if Adam decided to stop his ship in an environment close to a planet that had a mass equal to the mass of Earth? Wouldn't this decision make it so the time of Sarah never "speeds up" from the point of view of Adam?
Eugene, can you specifically make one video based on Higgs Field and Higgs Boson? Many thanks :)
Both Sarah and Adam were traveling through the spacetime continuum at the same speed, Adam only traveled more in the space variable and Sarah only traveled more in the time variable.
+whoatemyhummus Thanks that cleared up a lot of things
But from Adam's perspective, Sarah traveled more in space, and he traveled more in time.
Not to mention, that it doesn't sound like an explanation of physics.
Since these two things are linked, i.e. time and space. When a photon is traveling through a vacuum, we measure it's speed (c). The 299792458 meters per second. That would mean the particle is not traveling through time at all, correct?
According to relativity, photon's "time" stands still indeed.
This does not explain the paradox. From Adam's perspective you can say the same thing: Sarah traveled more in the space and he traveled more in the time variable. So he should have been older. He is not. The key is acceleration/deceleration of Adam when he is far away from Earth.
What if adam had taken a circular path? Then there is no need to fire the rockets right? Oh or does he need to fire rockets to maintain ciruclar trajectory hence centripetal acceleration makes adam think he is in orbit around a gravitational field.
from sarah's view gravitational field is acting on adam.... means adam is been pull by the earth... so, adam clock will move faster than her!!!!???
The paradox is wrong from the start because it assumes that both observes a slower clock of the other. The paradox is also misleading by staying on Earth means standing still but in reality is also accelerating in spacetime and we can replace Earth with another spaceship . Imagine an empty space with only the twins and no visible reference. Then suddenly, they went far apart in opposite directions. No one would be able to tell who left, who stayed still, or if both accelerated. It is only through the comparison of their clocks where they can tell who accelerated faster.
If they would have moved in constant speeds, then you are correct. But in reality, one (or both) of them would have to accelerate, which is equivalent to putting himself in a gravitational field. So there IS a difference between them: one experiences a strong gravitational field, while the other does not.
But the person on Earth, or any planet, is subject to gravity which in itself warps space time. So yes the Earth is moving but unlike the rocket, Sarah is subject to gravity.
The earth's gravity is not very strong. The twin paradox would work the same if Sara was floating in space, because unlike velocity, acceleration/gravity is something a person feels and can measure. If Sara and Adam would float in empty space, and then suddenly Adam would accelerate, both their measurements will show that Adam accelerated, not Sara. (The same measurements can be interpreted as if Adam was in a sudden gravity field, and Sara was not). zodiacfml wrote in his comment that we can't know which one of them accelerated, but that is not true. While we can only measure our velocity relative to someone else, we can measure our acceleration/gravity even if we are flying alone in a vacuum.
I think, that there's a big flaw in some parts of SR, so it has to add GR and the acceleration, to solve this issue. Adam doesn't have to slow down during his trip to a distant star - he can for example move along a circular path and gain speed "behind" Earth, so he will move with a constant velocity all the time. We can as well exclude the planet, so there won't be no gravity involved. In such case, telling that any of twins will get older, than the other, is a direct violation of SR own rules...
Astral Traveler, moving in a circular path requires continuous acceleration, therefore you cannot talk about it in terms of SR alone.
I think its confusing cause adam is moving near the speed of light. and sarah isnt moving at all. So if this was playing at real speeds, adam and sarah wouldnt even see each other cause adam would be moving to fast, right?
This is simply outstanding. I have never seen an explanation so clear, simple and complete.
Thanks for the compliment. I am glad you liked my explanation.
What do you mean when you speak of an observer's "beliefs"?
Not religious, but an opinion.
Great point ratamacue. The video constantly makes the confusion between what one observer perceive or can tell from the other observer and what really is.
But what will happens if ADAM did NOT turn around, and just continue in straight line until he circumnavigate the entire universe (let´s say it´s a small and closed universe). If he circumnavigate the universe, he will return back to Earth, without doing any turn around and acelerating.
I think this explanation actually don´t resolve the paradox...
So, if we were to run a quantum clock and shut down Adams clock before the acceleration back and the information was instantly transported. It would disprove what they're saying and you'd realize that the effect was not due to "gravity". China launched the rocket 2 days ago and they're about to test this. Einstein was wrong.
thanks for the video. I have a question: Suppose Adam is not alone in the ship, and his travel takes (T0) time to reach the 0.9 speed of light and then he travels 10 years (T1) at constant speed... At the exact time (T0) (when he is at constant speed. I have a stationary base in the path previously arranged for the experiment ) his first child is born in the chip, take a picture and leave it in the stationary base when he passes without stopping. In the same base I take a picture to an other child born the same day (each pict show a new born baby). Then 5 years later of his traveling at constant speed he takes a new picture of his 5 years old son and leaves it again in a new stationary base (the de-acceleration of the picture does not affect the age of the person on it... or yes?). If we compare the picture of the child in the stationary base taken at the same time that the ship passes the 2nd base at constant speed with the 2nd picture of the traveling baby... who is older? why? all the pictures occur in a time interval (T1) with everybody at constant speeds.
thanks a LOT
PD: I want to see the maths from both sides
Amazing approach to the explanation explanation , what puzzles me is that 2 different explanations from 2 different viewpoints attribute to the same result.
There is one slight bit of this I don't quite understand. It has to do with reconciling the two frames. From the perspective of the twin on Earth, time dilation for the astronaut piles up along all three segments of the trip - a certain and same amount for the trip out and back and then very heavily during the turn around (a + B + c). But from the perspective of the astronaut, the trip out and back essentially subtract from his overall time dilation against the swamping amount of the turnaround (B - a - c). So to me they would largely agree with each other, except that from the astronaut point of view, the time dilation affect overall would have been slightly less than what the twin on Earth would estimate. It seems like they should exactly match.
From the perspective of the twin on Earth, the time dilation during the turnaround is negligible, and almost all the time dilation was due to segments (a) and (c). Keep in mind, from the point of view of the twin on Earth, this extra gravitational field never existed.
I don’t understand how someone “believes” gravity is effecting them and that Sarah is accelerating towards him. He KNOWS he’s the one who left, who accelerated away, and gravity exists due to massive objects, so no one could plausibly “believe” it’s slowing them down if there is no mass actually doing it. I’m so confused.... :/ Any help?
Ok, but what about the 2 spaceships flying in different direction version of this paradox?
I think, that there's a big flaw in some parts of SR, so it has to add GR and the acceleration, to solve this issue. Adam doesn't have to slow down during his trip to a distant star - he can for example move along a circular path and gain speed "behind" Earth, so he will move with a constant velocity all the time. We can as well exclude the planet, so there won't be no gravity involved. In such case, telling that any of twins will get older, than the other, is a direct violation of SR own rules...
as soon as instantaneous communication will be established, e.g. via means of quantum entanglement, this discussion will get a truer and more easily understandable direction
I finally understand why planet gravity does not make the deep universe run super fast. Gravity diminishes with distance, and it is acceleration over the distance that matters which only to the spaceship view is the same into infinity.
Thanks again Eugene for another great video, its been exciting to see so many come out in such a short amount of time!
blake301987 Thanks for the compliment, and I am glad you liked the video. Many more videos are coming very soon.
Nice, but the problem can be reformulated without acceleration by giving Adam an initial velocity and adding a 3rd observer (Bob) with equal and opposite velocity at the turn-around point. Bob and Adam can compare clocks as they pass at the halfway point. The paradox can only be resolved if you know how each observer moves with respect to their combined centre of mass. (We are presumably talking about flat spacetime so we can ignore the Earth and the rest of the universe.) The speed of time is evidently maximal in the centre of mass reference frame. Clocks run more slowly in all other frames.
What if Adam performs the "accelerations" without any g-forces by employing gravitomagnetic effects of a rotating torus? ( Referring to your video on GEM, by rotating a mass torus in a "smoke ring manner" one can induce a gravitational field.)
Ok but what if there was a human thats a long as 1 lightyear, and then he observed these twins doing the twin paradox experiment, how would time pass for him?
I suspect that when Adam fires his rocket engines he isn't going to believe that a gravitational field suddenly appeared from nowhere. He'll realize he is accelerating. Good explanation though. In fact, the best I've seen. Some of the others talk about "rotating in time" which is confusing to me. What does rotating in time even mean?
What would cause that gravitational field from Adam's point of view? In classical physics, gravity is caused by masses and thus is a real force. If someone detects the effects of a fictitious force (i.e. a force which is not caused by anything in particular) then they can know for sure they are accelerating and hence moving.
Is it different in General Relativity? I mean, is somehow the gravitational field Adam feels different from the gravitational field of the earth?
Wurtt Mapper well, "gravity" isn't really a "real" force, precisely because it has the same exact effects on velocity and spacetime flow as acceleration does. Gravity and acceleration are essentially the same thing
This clarified all the confusion I had. Thanks!
MrCristie1 Thanks. That was what I was hoping for, as there seems to be a lot of confusion about this topic.
What if the universe is closed, like surface of the earth? If two twins travel in opposite direction at constant velocity, but eventually meet up again, will one be younger than the other?
Relative motion between a stationary and moving object creats an illusion for moving object as if stationary object is moving. To find out which object is stationary and which is moving we need to check motion relative to space. Relativistic effects are restricted to object moving relative to space.
There does not exist an ultimate frame of reference, which we call space. There also does not exist an ultimate moment termed "now." All of these depend on frames of reference.
Light travels in its own frame of reference. The time-dilation, fewer clock cycles, is only occurring in the clock's frame of reference.
The clock's cesium-133 atom is being energized by a constant power source. The cells of your body are energized by the circulatory system. Heart rate increases as the applied force increases. Your cells are using more energy in a high g-force environment. Not less. Not only that, the clock's cesium-133 atom is being chilled to absolute zero while the observer's are at room temperature. There is no correlation between the clock's readout and the observer's biological processes. They are in separate frames of reference.
But there is still some trouble left in my understanding,
1. Einstein's theory is based on one point that you can't do experiment to identify who is in velocity. However, you say that the twin in the spaceship is experiencing the gravitational field. Gravitational fields do converge to a point. But the objects in different points inside the spaceship do not converge. So experimenting inside the spaceship would reveal it is gravity or acceleration. I am assuming that the spaceship is big enough to be sensitive enough to the convergence experiment.
2. Wat about the case where the spaceship has stopped accelerating. For e.g the spaceship accelerates only for a very short period of time in the entire journey time like 1%. Once the acceleration stops then no gravitational field will be experienced in the spaceship. However the majority of the time dilation experienced by the twin in the spaceship is due to its velocity and not sure to acceleration. Having the acceleration for a short period of time, how will it account for the time dilation for the entire trip?
+Saran Paramanantham, gravitational fields do not necessarily have to converge on a point. Having a uniform gravitational field throughout the entire universe is consistent with the laws of physics. Objects with mass only determine how the gravitational field varies from one point to another, but there is nothing preventing a uniform gravitational field from being present everywhere added to these variations. In reply to your other question, during the 1% of the trip when the acceleration occurs, the effect on the difference in the rates of the two clocks is so great that it more than compensates for the remaining 99% of the journey.
Don't you think you are missing something? Imagine that the spaceship accelerated to near speed of light in 3 months from an external observer's point of view in both the directions of the journey? So the acceleration happened only for a total of 6 months from extremal observer's point of view. This can't account for 4 years of time dilation. Moreover time dilation takes the velocity component and not acceleration. What would the twin in the spaceship think during the period of constant velocity of the spaceship with the earth approaching him or moving away from him?
Do you think a light photon accelerates in order for it to not experience time? Acceleration merely transports an object from one position in time dimension to another. But wat matters is that how long was the spaceship in that near speed of light velocity. Of course acceleration matters but it matters only because it comes with a velocity.
+Eugene Khutoryansky With regards to the universal gravitational field without convergence, please state how that is a possible to become practical? I agree that gravity to be almost equivalent to accelerated reference frame but there is definitely a difference between these 2, that difference is convergence. Gravity being an effect due to the spacetime distortion produced by the presence of mass/enerygy and every mass/energy should have a center for its gravity hence convergence can't be avoided. The convergence only can be reduced but not made zero. May be this minor difference is what is playing a bigger role in the mystery of velocity of stars remaining constant even if the distance increases from its center. May be I am wrong. It could be possible that General relativity is a better approximation of Newtonian Gravity but not the perfect theory of Gravity.
+Eugene Khutoryansky I would be glad to hear a response from you on my other questions.
soo many videos lately, and all high quality, keep it up :D
julius groenjes Thanks. I am glad that you feel that all the videos are high quality.
The Distributed, Synchronised, Clocks Problem.
Setup a line, or grid, of clocks at, say, 1 light second intervals in an Inertial Frame. Allow them to pulse a light source on the clocks at 1 second intervals.
Now all clocks will be able to show the same 'frame time', after allowing for the distance between them that light takes to travel in the frame.
This is the way we synchronised distributed clocks on Earth today, though at closer than 1 light second intervals of course.
Now try and create a second, otherwise identical, Inertial Frame and give it some relative velocity between the two frames of v.
Any pulses of light created at any common point in both frames must propagate though both frames at c regardless of any relative velocity between them.
A Problem.
Does this mean that all accelerated motion will involve this "pseudo-gravitational" force and consequent time effects? In other words, can we still discuss accelerated motion in terms on special relativity alone?
The effects at short (on galactic scale) distances is very small.
There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.
-- Douglas Adams, "The Hitchhiker's Guide to the Galaxy" series.
Mindblowing! Great video on the topic, helped clear things up for me. Also, what are the songs used in this video? You always have the best music choice.
Goomy Smash Thanks for the compliment, and I am glad that it helped clear things up. In reply to your question, the song is from the free RUclips audio library, and it is called "1812_Overture_by_Tchaikosvky".
Goomy Smash You're not familiar with Tchaikovsky? Well, you've got a ride ahead of you.
Even if the gravitational field is causing Sarah's time to flow much faster than him, but Sarah is also moving faster and therefore the time will also run slower. How does this work now?
mill tanyanun In this case, the effect of the gravitational field is far more than overcoming the effect of Sarah moving fast. Although Sarah's motion causes her clock to move slower, the gravitational field is causing her clock to move much, much faster, and in this case, the effect of the gravitational field wins out.
From Adam's point of view, when he fires his rockets, it's Sarah who is accelerating towards him. Why is it Adam is the only one who feels the effects of the artificial gravitation? I'm sure it has something to do with the application of force but I can't quite wrap my head around it.
It is only Adam that believes that this external gravitational field exists. This field does not exist from Sarah's perspective. I explain this in detail in my video at ruclips.net/video/1ENkP0h8nAg/видео.html
Great explanation, but too slow. Too much waiting for the next sentence or point. First time I've heard it explained this way. Cool.
Awesome! Thanks for all of the videos about gravitation!
electrocat1 I am glad you like them. Thanks.
why does there have to be a twist (different perspectives) in twin paradox?Couldn't Adam simply always see the time on earth pass faster?Is it because he then would know that he is the 1 moving and would violate einstein's principle and cause entire theory of relativity to collapse? If Adam notices that he needs to spend infinite amount of energy in order to go faster,couldnt he conclude that its his spaceship that is moving with the speed of light, rather then the earth?
I love your videos! Keep them coming! As well as, what if the universe is a sphere, and there for he never had to turn around, and completely went around the universe never turning his rockets the other way. Would that change anything? Thanks!
are there any published papers that support this explanation of the paradox? I'm doing a paper with a new look on the twin's paradox that shares some similarities with this video.
I am a bit puzzled on the idea of time. That say if there are two objects, which are non living things. So, whether one object stand still and the other is traveling at the speed of light, is there any significance difference if we apply time on this case? I rather believe that time in this instance will only apply to two living things. If we are refering to 2 rocks, will the speed of 1 rock cuses any significant differences to the other? Whether any one rock travels at the speed of light, if the other stand still rock cannot appear to be affected, then, what is the meaning of time to the 2? If gravity is the curvature of time and space, then if the two items are put in a vacuum, without any external force, can the curvature works? That is, we have to explain, how come in a lab with no gravity, we can float. If the space time curvature is present everywhere, by right the gravitational field should apply, regardless of circumstances. Sorry, I may mistaken Theory of Relativity. So, I appreciate correction.
I can't understand the end when it says both can belive that they were standing still during the entire journey. For Sarah perspective that makes sense, but for Adam when he turned his ship and the rockets were fired he experienced acceleration/gravity. I thought that as soon as you experience an acceleration/gravity you couldn't claim to be standing still.
From Adam's point of view, the force from his rockets exactly balanced the "force" from the gravitational field, thereby causing his spaceship to remain standing still.
Why would Adam think the earth is racing towards him whe he's the one driving the rocket back to earth?
Using phrases such as "Adam will believe" and "Adam's point of view" is not good - it will leave those who don't know Physics with the impression that time dilation and length contractions are just illusions.
In any case, the twin paradox can be resolved using on SR - no need to invoke GR.
Indeed. It really is best to define those terms more succinctly before launching into the explanation. :-)
And, yeah. Use GR... or use SR with acceleration. The picture is the same... only the terminology changes! :-)
οκ nice explanation buy what if adam circles the earth at near the speed of light for some years?then, in adam's point of view, the earth spins around him at nearly the speed of light for years and never goes far away of him and his spaceship. So, when the earth finally stops and he returns he must expect to find sarah young while he is an old man.on the other hand , in sarah's point of view ,adam were circling the earth for years at near the speed of light so he must be young when he returns while she is an old woman.can you explain this paradox?
Don't Adam's acceleration and breaking effects cancel each other?
........ Wait, doesn't that mean that a theoretical Alcubierre Warp Drive still violates Relativity even at subluminal speeds (disregard the superluminal ones for obvious reasons) since the passangers of the ship wouldn't feel any acceleration at all and thus making us go back to square one with this paradox?
People will understand the twin paradox when you say the values of the following problem (having or not similar results).
Imagine twin A on Earth. Earth and the Star (speaking about abstract points fixed in a system) are going left with u/2. Imagine twin B in a spaceship to the right with u/2 só that they have a relative velocity v. When twin A calculates twin B to reach the Star, he reverses (and the Earth and the Star go together with him.) When twin B sees reaching the Star, he reverses too. Twin B stops a clock just after leaving the Earth, another just before reaching the Star, another just after leaving the Star, and another just before reaching the Earth. Twin A also stops one clock just after leaving Twin B, another one just before reversing, another one just after reversing, and another one when they meet.
The values of those stopped clocks should be compared with the respective ones of the classical twin paradox, in which only twin B reverses.
So does this distance-between-clocks-in-gravity effect occur in any circumstance?
If we have Sarah on Earth, Adam orbiting at near-light-speed around black hole A, and another guy named Josh orbiting similarly around black hole B, but B is twice as far away from Earth as A, then when both Adam and Josh return to Earth to compare clocks, will Josh be even younger than Adam?
Let's say, it take 100 years for Adam to go and return in Sarah's point of view, but it's a small amount of time for Adam.
Let's imagine a Worm Hole at the furthest point Adam get to, linking that point to Earth. Adam would reach that Worm Hole 50 years after his take-off in Sarah's pov. But in his pov, Sarah's time hasn't passed (much). If he used the Worm Hole, what would happen? Would he return to a old Sarah or the young Sarah? What about the old Sarah seeing Adam enter the worm hole? Would he return (to old Sarah) or disappear (to young Sarah)? Or, from Sarah's pov, Adam would take off, then immediately appear out from the Worm Hole. But there would be still another forever-young Adam moving toward the Worm Hole and would reach it in 50 years.
What if Adam was really just Sara the whole time ? and JFK was never assassinated when he jumps into the black hole from which he gets out of using 'Ludicrous' speed ?
If the wormhole is not inside Adam's vehicle then Adam returns to an older(About 50 yrs) Sarah. If the wormhole is inside his vehicle i.e. travelling with Adam (I have no idea how!) then Adam returns to young Sarah i.e. the wormhole is now a time machine, which happens only if Adam somehow manages to enter and exit the wormhole without feeling any acceleration. However in the first case the result only applies if Adam attempts to stop and measure Sarah's age, otherwise if he somehow measures Sarah's age while moving at const. velocity Sarah will still appear young. From Sarah's pov : In the first case Adam takes 50 years to reach wormhole. He then instantly reaches Sarah. In the second case Adam's vehicle takes off and Sarah can see an Adam riding his vehicle for 50 years. But right after the start of the journey another Adam pops out of the wormhole at Sarah's location. Notice that now, for 50 years Sarah is going to see two Adams - one at earth and another at the ship. This case is actually briefly discussed by Kip Thorne in one of his books on relativity and gravitation and black holes and stuff. All this however is purely speculative.
In the main Relativity video, it was stated that objects moving close to the speed of light have greater mass.
Even without the mass increase, the Universe has more mass than Adam's ship, so how does a rocket with enough force to accelerate a spaceship close to the speed of light end up accelerating the Universe instead?
+Garrett Thomas, the rocket does not accelerate the Universe. The gravitational field accelerates the Universe. From Adam's perspective, the rocket balances out the force of the gravitational field, causing his ship to stay in one place, while the rest of the Universe is accelerates.
Eugene Khutoryansky
Then what causes the gravitational field? Surely no object is massive enough to accelerate the Universe to the speed of light that quickly.
I am from India, you are requested to put Hindi subtitles in the caption. I will be grateful to you Satyendra Singh Bhadauria alias Vitarag from India. 🌹
What if both Adam and Sarah are orbiting a black hole/neutron star in separate ships in opposite directions and periodically passing by each other? What would they see? I mean their frames of reference are sort of inertial, and their relative speeds are quite high as well. They never fire their engines yet they can regularly see each other from a short distance.
In short, dude, what is the conclusion? All these relative stuff we all knew since the first film of Star Wars or Star Trek. Give finaly your points of view about where can we use the principles?
How about if Adam never stopped and used a closed loop path to return to his point of departure?
Traveling in a loop still requires acceleration. For example, traveling in a circle requires acceleration towards the center of the circle.
Excuse me, it might be a dumb question, but in this case, how can distance have anything to do with time dilation, when the gravity of acceleration that affects Adam doesn't affect Sarah at all? My intuition tells me, that at both acceleration phases, Adam's clock will slow down the same amount relative to Sarah's... Once again, sorry if this question doesn't make sense.
The extra gravitational field only exists from Adam's perspective. It does not exist from the perspective of anyone outside his spaceship . I cover this in detail in my video "Gravity's effect on the flow of time in General Relativity" at the following link ruclips.net/video/1ENkP0h8nAg/видео.html
so lets so that the distance that adam travels before turning is L, then if adam travels at near the speed of light through a distance of L then stops. Then sara moves at near the speed of light to that same location, will sara be have experienced more time than adam, or do they experience the same time? because sara accelerates twice, first from earth, then her deceleration at L, but so does adam. So they must experience the same change in time right?
Great video! I tought I already understood the twin paradox, but this explanation is awesome! Thanks again, Eugene and Kira!
Thanks. Glad you liked my explanation.
What would happen if Adam and Sarah had quantum entangled communication devices? How would they perceive the conversation?
+ligase75, Quantum Entanglement does not allow for meaningful communication. I go into detail about this in my video titled "Quantum Entanglement, Bell Inequality, EPR paradox".
Fantastic video! Eugene, can you please explain what causes gravitational acceleration in General Relativity?
Panda Pandemic Thanks for the compliment about the video. I discussed how gravitational acceleration is the result of how mass creates a curvature in Space-Time in my "Laws of Motion" video and in my "Einstein's Theory of a Relativity" video, but yes, I can make another video which goes into this topic into much more detail. I'll put this on my list of topics for future videos. Thanks.
Distance as a Time Delay is not the same as Time itself. Differences in Distance do not affect Time, only any delays that are observed between remote sites and local ones.
Thanks a lot. This video (almost) solved doubts I've had for years
if two entities are somehow connected by a string or even their gravitational pull, circling around their center of mass, how are the relations gonna be between them or between each of them and the midpoint? Is the consequence, that the core of e.g a fast spinning neutron star is older than its shell? Or even is earths core? Any thoughts?
To an observer stationary in the centre, each of the circling entities would be time slowed. From the point of view of each of these entities, the centre would be correspondingly time hasted!
This is because, while a circling entity sees the centre as moving (and hence time slowed because of its motion), it is also accelerating towards the centre (to remain traveling in a circle) so it also adds an additional effect that speeds up the centre's time flow. The net result is that the centre's time flows faster.
What if Sarah is on a stationary rocket ship in space with very little gravitational pull and Adam passes a point ( on the other side of the Universe ) in space already going near the speed of light !
Then which one of them will have aged and which of them will not ?
It seems to me that the video is trying to explain something that already has an explanation within special relativity using a hypothesis that is known to be false, that is, to suppose that there is a uniform gravitational field throughout the universe in the opposite direction of the spacecraft's motion.
Nevertheless, while the rocket turns and accelerates, apart from the spaceship and Adam themselves, the earth and Sara are accelerating too. Therefore, Sara should be affected by the gravitational force too. Moreover, what's the accurate meaning of 'along the direction of the gravitation field'?
+Michael Cheung
They all feel the same gravitational field, yes. But Adam is 'deeper' into the gravitational field and thus his clock runs slower than Sarahs. On the other hand, at the initial take off, both Adam and Sara are at approximately the same depth in the gravitational field and thus their clocks run at approximately the same speed up until Adam's speed increases close to c.
So all that difference in age would only occur when Adam's ship turn and start accelerating towards her, right?
Yes, Adam would see Sarah's clock running faster only when he is accelerating towards her.
@@EugeneKhutoryanskynice fantasy universe you got here. Great science fiction stuff.
You shouldn't be peddling it as reality though.
Your so-called time-dilation, looking at each other's clocks, is merely informational.
In fact, the observer is not even in the same Time frame of reference as the clock. Check the engineering specs on the atomic clock. You will see that the cesium-133 atom is being chilled to absolute zero. Are Sarah's atoms being chilled? Adams?
You are comparing apples to oranges and coming up with lemons.
Hey Eugene, can we assume the travelling twin is in constant acceleration and attribute that to a gravitational force? How would that effect the experiment? Would the travelling twin still age less? Is the turn around necessary for the two to age differently?
I am not sure I understand your question. If the question is if Adam can be in constant acceleration from the time he left to the time he returned, then yes, Adam can attribute all the effects to an external gravitational field, and he will still have aged less than Sarah when he returns.
@EugeneKhutoryansky I'm trying to think of a hypothetical where the travelling twin is accelerated in a different path. For instance in this video he leaves and comes back to Earth. But what if he was simply sitting in some machine that accelerated him forward and back or in circles while still on Earth. Would his age still decrease relative to those around him?
Yes. Moving in a circle requires a constant acceleration towards the center of the circle.
Newton's law of motion, F=ma. Force equals Acceleration. The accelerating rocketship also accelerates the astronaut in time as evidenced by an accelerated heart rate and a shorter lifespan. The traveling twin will be the same age as the stationary twin as evidenced by the synchronized clock experiments showing no difference in the amount of energy the clocks used.
The clock and the observer are in different frames of reference. Its like putting a banana on the counter and one in the freezer. It's like putting a plant under a growlight and one in natural sunlight.
Atomic clocks are designed specifically to prevent the caesium-133 atom from being accelerated in time when a force is applied.
I thought the Twins Paradox was that when I see two twins together they can be like an 8 each (=16), but when I just see one of them she's really like a 6.
Best twin paradox ever explained
I'm confused about one part. When he turns around and begins accelerating, he can not distinguish this from a gravitational field, and therefore sees her time as moving faster than his. However, doesn't Sarah also see him as being very far along the Earth's gravitational field, and should therefore see his time as moving faster than hers (for argument's sake lets say he accelerates by 9.8m/s^2 to keep the situation roughly symmetrical)? If the fact that he is moving near the speed of light makes up for this, then shouldn't the same apply to Adam, who sees her moving away from him?
The gravitational field due to the Earth drops off to almost zero far away from the Earth. By contrast, the extra gravitational field that Adam believes exists has constant strength throughout the entire Universe. It is the sum (integral) of the gravitational field throughout the entire distance between Adam and Sarah that accounts for the difference in the rates at which their clocks run. Hence, the contribution from the gravitational field of the Earth is negligible. But, since there is a large distance between Adam and Sarah, the constant gravitational field that Adam believes exists has a major impact on the difference between the two clocks.
@@EugeneKhutoryansky Thank you for the answer. I have so many questions and I understand it's not possible to go much further here without mathematical rigor, but there is still something which doesn't sit right with me. If an observer can't tell the difference between a gravitational field and acceleration, then I assume the only way Sarah knows the gravitational field of Earth is not affecting Adam in deep space is because she sees he's not accelerating. Likewise, he assumes gravity is uniform everywhere because he sees everything in Sarah's direction as accelerating towards him without drop off.
However, when he accelerates towards Sarah, does he not look like he's in a gravitational field to her? How can she know, without apriori knowledge of the nature of the gravitational field she's in, that Adam isn't accelerating due to gravity? Or is it because it's only him accelerating and not the rest of the universe?
Both Adam and Sarah know the details of the gravitational field that is created by the Earth, because they know how much mass the Earth has, and they know that the strength of the Earth's gravitational field gets weaker further away from the Earth. What they don't know is whether or not there is an extra uniform gravitational field throughout the entire Universe. This is because everything in the Universe would accelerate at the same rate, and hence there is no experiment that could be performed to determine if this extra gravitational field exists. But, both Adam and Sarah know that Adam is firing his rockets, and that the rockets are exerting a force on his spaceship. If this extra gravitational field exists, it would be cancelling out the force from his rockets, causing his ship to stay in the same place.
Something seems wrong. If the pilot ever sees earthtime move faster, then that means he is receiving light from earth faster than the constant speed of light, which isn't possible, right?
+AngelEyes986 he isn't moving at the speed of light since that would be impossible he is moving close to the speed of light so in theory he could see sarah's clock but looking at each others clocks is here so people could understand this better, because that is happening wheather adam sees it or not
+Lovro Dulibić I never said how fast he was going. I was stating that light is constant, so you couldn't see things at a faster or slower rate.
But this was over a month ago. I've since researched a ton on relativity and understand it very well now. Basically its actually possible to see someone age slower or faster. Light will still remain constant. The object will either age faster or slower, or the object will flatten or elongate it's shape depending on velocities. Basically space and time are the same thing and it will warp one way or the other so light can remain constant.
Nice animations..
Nice narrations..
Again easy-to-comprehend..
But i have a question:
How is "Khutoryansky" pronounced ? :)
TheAirpirate28 In Russian, the "Kh" sound is signified by a single letter, and there is no equivalent sounding letter in the English language, so "Kh" is the closest translation. Thanks for the compliment about the video.