How Curved Spacetime Works | Gravity & Relativity Explainer
HTML-код
- Опубликовано: 5 сен 2024
- Einstein’s relativity, and how it relates to gravity, explained in less than 10 minutes. This video uses a type of spacetime diagram invented by the physics author Lewis Carroll Epstein in his book "Relativity Visualized," with proper time on the y-axis (also representing the null geodesic that light takes in a vacuum). Epstein diagrams are more intuitive for the layperson than Minkowski diagrams, where the null geodesics are at 45° angles. Epstein's book is available at many libraries, as well as online at archive.org/de... .
The GPS & Relativity article referenced in the video is here: www.astronomy....
A different article, by NASA, is here: www.nasa.gov/m...
Questions are welcome, but fringe-science comments - like insisting that gravity can be explained as the Earth expanding, or buoyancy, or massive photons, or "electric universe" nonsense, etc. - are not (sorry). General relativity is one of the most battle-tested theories in physics, for over 100 years now. If you think you have a better theory, go ahead and evangelize that pseudoscience in your own video.
Thank you to my Patreon supporters / edwardcurrent
I come back to this video every now and again just as a quick refresher. It really is that good.
Another vid after 3000 years yes
looking forward to the premiere on 5035
@@sailoragitate900 Hyped
This is exactly why I make sure that I'm always subscribed to Edward Current.
Checkmate, prior knowledge! 🕶️🤙
Great video with simplified explanations!
I'm thinking about getting back into making videos, and unfortunately it's because someone I used to respect (Neil deGrasse Tyson) has started making videos that give information that isn't simplified, it's simply wrong.
The two videos in question are one talking about the rocket equation, and the other about oxygen in rockets. The two main points he mentions that I have issues with are:
1) The SRBs on the shuttle/SLS burn atmospheric oxygen, and are dropped once the atmosphere is too thin because they don't get enough oxygen.
I knew in 3rd grade, January 28 1986, that the SRBs didn't burn atmospheric oxygen. I didn't know HOW they could do this, but I knew this meant that once they started burning, they wouldn't stop until the fuel ran out.
2) the heavier the payload, you'll need exponential more fuel to start. This is harder to explain in detail why it's wrong, but it's not the payload mass that leads to exponential fuel, but rather the velocity (and more specifically the delta V) required that leads to that exponential fuel. If you need double the payload mass to the same orbit (generally, the same velocity), you just double the rocket; engines, fuel and all. However, to double the fuel a rocket holds, if you double the tank size, you actually end up with less "dry" mass of tank, because the surface area of the tank decreases relative to the volume of the fuel.
Anyway, I was worried I was going to have to get Relativity involved to explain this part, but I think I can do it with simpler equations.
That's weird that NDT would claim that about SRBs. I mean, they don't exactly have an air-intake at the top, do they? My one piece of advice is, if you're going to take on a titan like him, get all of your ducks in a row, have good sources and everything. Because people are quick to go to appeal to authority and believe him instead just because he's famous. Best of luck.
@silverrahul ruclips.net/video/hRL2vidogRM/видео.html
"Those two boosters burn air"
It just goes to show you that an astrophysicist and expert in his field can be entirely clueless about something not in his field of expertise.
If earth is accelerating upward then what happens to the person on the other side of earth? If earth is pushing one person upward then should it not be going away from the person on the other side of earth?
No because neither is moving in space relative to the other. In flat spacetime, that would be correct. In curved spacetime, you need to literally, measurably accelerate to stay where you are (relative to a point on the other side of Earth, for example).
I’ve been watching these kind of relativity videos for hours, but this one explains it the most clearly!
Your original space time stretcher video was very helpful for understanding non inertial reference frames.
I LOVE your graphics. I’ve watched lots of high production value videos on this topic and I found yours to be the most intuitive by far. Thank you!
Thank you! I don't quite have the budget for a set where I can appear weightless in an astronaut suit.
Seems there is no need for that!
@@EdwardCurrentim didn't understand this moment 5:55 Why don't I want to fall? 😂😂
ما اسم الكتاب الذي اخذت منه@@EdwardCurrent
@@a.markuddr285 "Relativity Visualized"
One of the best explanations. Thank you! puts together many of your good points from previous videos in a more concise way with clean animations.
One of the clearest explanation on this topic. Good job.
Ok finally I think I get it. Time and space are the same thing. It's just so mind blowing how we're (on earth) moving along through time (or so we think) but constantly curving into space. But because mass (earth) has electromagnetic forces that repel (accelerate) us "upwards" we are pushed back into moving only through time. So electromagnetism (on earth) keeps us moving through only time... otherwise we'd end up moving only through space and time would end existing to us 🤯
Very good summary!
@@EdwardCurrent اهلا ادوارد لدي سؤال
هل حقا الكواكب تسقط في منحدرات الزمكان ام هو فقط تخيل للتوضيح؟
@@a.markuddr285 It's our most precise theory of gravity. Whether they are "really" doing that is a metaphysical question that cannot be determined scientifically.
@@EdwardCurrent thanks
Easily one of the best YT videos on relativity. Nice one Edward!
It's a good vid but it has a heavy issue: It swaps _coordinate time_ which is a coordinate difference between two events and _proper time_ which is a path length along a world line between the same events.
@@jensphiliphohmann1876 Hi Jens, I've read through your other comments about an issue related to an asymmetric doppler effect with time dilation. I'm struggling to properly grasp where the issue is based on how I'm (likely incorrectly) visualising it. The only way in which I can fit what you're saying, is to apply it directly to an acoustic doppler model, whereby the bounce of the wave hitting another object adds or removes energy depending on the relative velocity and angle of travel of the object to the direction of the incoming wave. The obvious point here is that the speed of light doesn't work in that way and always "bounces"(reemits) off an object at V=c therefore making my comparison nonsensical. Feel free to try clear up where I'm not getting it!
@@deanjdk
Please don't misunderstand me:
> _...an asymmetric doppler effect with time dilation._
Oh, no, the optical DE _were_ asymmetric _without_ that phenomenon often called time dilation, just like in acoustics just with the aether instead of air and (the speed of) light instead of (the speed of) sound.
The demand for symmetry only _brings in_ time dilation at all.
> _The obvious point here is that the speed of light doesn't work in that way and always "bounces" (reemits) off an object at V=c therefore making my comparison nonsensical._
On the contrary. Sound waves don't behave bouncing balls either but also are reflected always at the speed of sound regardless of the motion of the object which reflects them.
Let's construct a numerical example which is easy to calculate:
You consider yourself as stationary and me as approaching you at β = 0.6.
You send a signal to me with frequency f₀ and wave length λ₀, according to your clock and f'₀ and λ'₀ according to mine.
Considering the formulas f = c⁄λ and λ = c⁄f, replacing c with the respektive difference speed between signal and target, you'll calculate that your signal should hit me with frequency f₁ = c(1 + β)⁄λ₀ = f₀∙(1 + β) = 1.6∙f₀
according to your clock.
The echo will leave me with wave length
λ₂ = c(1 − β)⁄f₁ = λ₀∙(1 − β)/(1 + β) = 0.25∙λ₀.
Thus it will reach you with frequency
f₂ = f₀(1 + β)/(1 − β) = 4∙f₀
but it also interest us in comparison to f₁:
f₂ = f₁⁄(1 − β) = 2.5∙f
@jensphiliphohmann1876 I've found that the proper-time diagrams ("Epstein diagrams") are more easily grasped by the causal science enthusiast.
That was relatively interesting.
Generally a good video by a very special person.
I had the "Why isnt earth expanding then?" question for a while now, and this video finally answered it in a way that i understood.
I still don’t really get it 😢. Why isn’t earth expanding?
@@ssergium.4520The earth stops you from being inertial. It stops your free fall. By stopping your free fall, it exerts a force on you and puts you in a state of acceleration upward. Anything that resists gravity is accelerating. Anything that doesn't resist gravity is not accelerating. Free fall is non acceleration. No forces are acting on you during free fall and that's why you feel no weight during free fall.
@@ssergium.4520 In case you're still wondering, or for anyone else reading this: Earth isn't expanding because its surface is not actually moving upwards, only accelerating upwards. The key is in understanding that difference.
You and I right now are accelerating upwards (relative to the Earth's center of mass) only because the electromagnetic repulsion of whatever hard surface is beneath us is preventing us from traveling further on a straight-line geodesic through spacetime into the center of the Earth. The reason we would otherwise be doing that is because the Earth is the most massive object near us and is warping spacetime in such a way that the path of any less massive, inertial objects near it (such as us) have their paths curved toward it. This is the hardest part to visualize, because we can only physically perceive 3 dimensions, while spacetime is a 4-dimensional reality.
Think of a satellite in orbit around the Earth. It is in an inertial state, moving at a constant velocity in a straight line, but it circles the Earth because Earth curves spacetime around it which alters the trajectory of the satellite. The satellite has to be moving at the perfect velocity to move around this curvature without slipping into it or flying out of it. If the satellite were to suddenly stop its motion relative to the Earth, it would begin to "fall" towards Earth (can be pictured as slipping down into the curvature), and in order to maintain its altitude, it would have to engage some sort of thruster to accelerate away from the Earth at a constant rate.
While constantly accelerating at the correct rate, the satellite would appear to remain stationary relative to Earth's surface, no longer circling the Earth on a geodesic, but also not "falling" towards it. This is not difficult to picture or imagine, because we see it in the way a helicopter, drone or even a hummingbird can hover, constantly accelerating upwards and yet remaining motionless. The hummingbird must continuously flap its wings to hover, because in order to hover it doesn't just need to maintain a constant velocity, but a constant acceleration.
The tricky part is realizing that we, right now, are in the exact same situation, but instead of a rocket thruster or rotor blades or a hummingbird's wings maintaining our altitude above the surface, the solid surface of the Earth itself (or the floor of our room) is providing that acceleration to keep us from continuing on our otherwise perpetual motion along the curvature of spacetime.
Apologies, that was long-winded, but hopefully made some sense!
The most important part of your video is 5:17 to 6:54
You seem to be indicating that as we plot an inertial object's straight-line path on the curved spacetime diagram, the object is forced to move through space at an ever increasing rate for each second that passes (it falls).
I had never heard this explanation before. Very interesting.
Furthermore, you indicate that in order to not fall, the object cannot be a straight line path on the spacetime diagram. It has to curve upward with the diagram. In order to curve upward with the diagram, it cannot be inertial, it must be accelerating. The Earth preventing the free fall is what's causing the constant acceleration upward.
Yes, it was a big aha moment for me (originally spelled out in the book "Relativity Visualized" by Lewis Carroll Epstein).
@@EdwardCurrent Omg I have that book
@@EdwardCurrent Your explanation helped me understand general relativity better. I had not understood it like this until I saw this video. I think you did a great job here.
Thanks! That is a great little book.
@@EdwardCurrent You've earned my sub.
Wow what a treat for the new year
This was hands down one of the best explanations, but there is an opportunity to break it down further with smaller bits and slower. Thank you for your effort!
Hey Edward Current. First and glad to see his post
I love this explanation, and the fact he sounds exactly like Captain Hollister is just a bonus!
0:53 How a rocket, if traveling at the speed of light, is traveling only through space? If it starts at t = 0 sec and d = 0 meters, it must move 1 sec on the time axis to go 299792458 meters on the space axis, right? @EdwardCurrent
No -- that's as measured by someone moving at any speed other than c. For a clock on the rocket, it starts at t = 0 sec and ends at t = 0 sec, the rocket traversing any arbitrary distance in that (non-)interval of time. Note that the universe contracts in the direction of travel such that the rocket passes distance markers infinitely fast. From the perspective of the rocket, it is only traveling through space, seemingly at infinite speed. This is only true for a rocket moving at c (which is impossible if it has nonzero rest mass).
@@EdwardCurrent ( Are we talking about inertial reference frame? Perhaps, I'm not sure. But, ) what I can comprehend from your reply, is that for me (as an observer who can somehow watch the whole event) it would be like, in 1 sec, the rocket has traveled a distance which is equal to what light travels in 1 sec. But from the perspective of the rocket, it'd be like time is stopped and it is just moving through space at an infinitely faster speed (
@@EdwardCurrent If you think my knowledge isn't enough to understand the topic, please point me to some textbook/article or something. I wanna know and that'd be really...really...really helpful. And thanks for your reply.
The first part of your first reply is all correct. But...
_But even the rocket will feel the passage of time after 1 sec (according to the clock on board), isn't it?_
No. A clock moving at the speed of light never ticks. There is no "after 1 second" for that clock. It only travels through space.
Note that this is a unique situation (and physically impossible for something with mass) -- at any other speed, including .9999c, an observer will see their own clock ticking away at the normal rate. At .9999c they can travel across space much faster than 186,000 miles per second as counted on their own clock. Yet if they shine a flashlight forward, they will still measure the light as moving away at c.
This is special relativity, and I didn't spend a lot of time on it in this video. I recommend seeking out and watching a bunch of videos on special relativity.
@@EdwardCurrent Whenever I explore relativity, the part which I find most troublesome is when we talk about the light that its speed is constant in the universe and all that.... and my mind just doesn't agree and I say WHY and HOW? I'm gonna start all over again and I'll continue this conversation... it's still unfinished.
I really appreciate how you reply to your viewers' comments. Thanks for that.
I'm still lost. Do you think if I bought one of those Prayer Max 5000s it would help?
Underrated comment
Fantastic explanation.
Wow! This video finally made everything click for me. I've learned about relativity before, but until now I never had a full understanding of space-time curvature. Thanks for making these videos.
Decent explanation, though a bit too quick for me in places, such as the idea of objects moving at the speed of light not moving in time (how do they get anywhere?), and which lines exactly represented the tone dilation effect (there was a red line but that seemed to be just time passed, unclear). The real strength of this video was putting everything together in one video rather than spreading individual elements across multiple videos.
Tough to cover all of that in less than 10 minutes, but I thought I'd give it a shot. Objects at the speed of light get anywhere because they're moving through space!
@@EdwardCurrent One thing in general I find hard to wrap my head around is how an observer's perspective translates into reality. For example, if I look at a fence from an angel, it looks thinner lengthwise. But I understand that the fence hasn't actually changed. So when you use that as a way to explain how the length of things changes when travelling faster, it just doesn't make sense to me.
I understand. The distinction is that in relativity, there is no "true length"; it's only a matter of perspective. This is similar to certain observable quantities in quantum mechanics, where there is no "true spin" of an unmeasured particle, for example, but instead a superposition of all possible spins.
@@EdwardCurrent I just looked it up and I don't think this a very good explanation. Objects have a true length, which is their length at rest. If you are travelling at the same speed and in the same direction as an object (so it is stationary in your reference frame), it doesn't matter which angle you look at it from, you can still determine its length straightforwardly by basic geometry. It's only when the object speeds up relative to you that basic geometry no longer cuts it; if you do the same transformation as you would if it was at rest, it would look like it was shorter than it ought to be. And this has real effects, on how objects behave, whereas changing the angle you look at something from doesn't.
@hoagie911 "Objects have a true length, which is their length at rest" But there is no absolute state of rest. The idea of looking at a rotated view of a fence is merely a metaphor, but it works, because changing the reference frame in relativity (for example going from a rest frame to a moving frame) is a matter of rotating the spacetime graph. And the observed length of an object depends upon this angle of rotation. In relativity, the "rotation" or "perspective" I'm talking about is not a literal rotation of the optical perspective, as in the fence metaphor - it's a rotation of the space vs. time graph.
Another parallel is that relativistic rest length can be considered a maximum value of measured length, similar to how the real length of a fence is the longest it can appear to be when viewed at various angles.
May I suggest watching the first part of the video again, then ask questions if anything is still confusing you.
Amazing video!! But you stated that objects in curved space-time have to accelerate to stay still meaning that the earth is also still, but you also stated that earth accelerates towards things in the sky(rather than the objects falling,),how is that? And in other videos including this one you showed that inertial objects in the sky move towrds earth due to the curviture so in flat spacetime they only move throught time but in curved spacetime they move also through space, but where does that movement come from and at what velocity or acceleration is it?
I think the best thing I can point you to is the sequence from 6:10-6:14: The house is moving along a curved line and not moving through space. But the apple is moving along a straight line, and initially not moving through space, but later, it is moving through space. The house is accelerating (by definition) because its path is curved. But because of the curvature, it never moves through space, unlike the apple.
Excellent explanation. One of the best.
Checkmate Physics! 😉
Brilliant video - a lot better explained than what my Physics teacher did so many moons ago….
Thank you.
So, is a bobblehead is a space/time indicator?
Yes, it is. You should have a bobblehead in the car just in case you need help navigating your intertial frame of reference.
That's a great point...wish I had thought of that!
why light speed is not a 45 degree angle straight line between time and space axis?
That's how it's depicted in Minkowski spacetime diagrams, where time is coordinate time. Those diagrams are useful for many things, but I think these diagrams -- where the horizontal axis represents proper time -- are more intuitive for understanding spacetime basics. They were invented by physicist author LC Epstein for his popular book "Relativity Visualized." (Proper time is the time experienced by whatever is depicted moving through spacetime.)
No matter how many videos I watch on spacetime curvature, I still don't get it
Dude same :(
Now this is a good video.
Thank you. After several semi-successful attempts, it was satisfying to put it all together, with superior graphics.
@@EdwardCurrent Yeah this cleared up a lot of confusion. It also made the topic much easier to digest. I would love to see another video on the topic, perhaps going deeper on the subject, or even simply discussing other concepts of the theory. Your method of presenting is very effective.
I am a layman who loves physics, and have been looking into the subject for a while, yet only came across this idea that Earth is "accelerating upwards" recently. I feel like mainstream scientists do not really get into this (which is strange to me), as gravity is still commonly described as a falling force. So it's good that there are videos like yours here.
Thank you. I have some other ideas for the series, such as explaining black-hole spaghettification in terms of curved spacetime rather than gravitational force, how a bobblehead is a spacetime compass, and how magnetism emerges from special relativity (there are already several videos on that by big channels).
A lot of science communicators avoid the topic because it's hard. It creates a lot of misunderstandings that need to be addressed immediately, such as how the surface can accelerate upward without the Earth expanding. There's also the irritation of deniers posting their own theories and/or claiming that Einstein was an idiot, but Tesla was the real genius, la-dee-da.
I'd also like to get into quantum mechanics and entanglement, but that's a whole other ball of wax.
@@EdwardCurrent Great point. And all of those would be great video ideas, a bobblehead being a spacetime compass is an interesting one for sure.
One idea that I just came across is the idea that time dilation causes gravity -- a confusing notion. I recently saw this video seeking to debunk the idea, ruclips.net/video/PjT85AxTmI0/видео.html , but am now even more confused on this topic. Perhaps this is another candidate for a future video
I've seen the time-dilation-causes-gravity explanation. It's another way of demonstrating GR and it's clever, although maybe not the most intuitive for people just getting their feet wet.
Someone else showed me that Dialect video 3 weeks ago. Here's part of my reply, from below: "I would say that depiction is a less standard explanation than all the ones he claims were 'tricked,' including mine. Does he say how time dilation comes out of that model, the way I do in my video?"
Unless they're a professional physicist who teaches GR, I wouldn't advise people to be in the business of deciding which demonstrations and explanations are right and which are wrong. It's a very difficult topic and can be interpreted a number of ways that are all consistent with the mathematics, like all the different proofs of the Pythagorean theorem.
Thank you for giving some straightforward explanations that demushified some of my understanding. 🙂
Please also mention the phenomenon observed are seen by which observer
Centripetal acceleration! Thank you. I've been struggling to make sense of this for way too long
Another RUclipsr team called Dialect have actually commented on your video and they find it wrong. I'm left with confusion because I don't know which one I should believe? You or Dialect?
You'd have to be more specific. They haven't commented in these comments.
@@EdwardCurrent Here is their comments in their video called: "The TRUE Cause of Gravity in General Relativity"
ruclips.net/video/PjT85AxTmI0/видео.html
At 19:45 "who probably got it from this dude" meaning you.
Dialect's video implyies that you have all been tricked by a coordinate transformation and that what you describe is not true gravity.
I'm not trying to create a RUclips beef here, I'm just confused as to what to believe as a student or a layman for physics.
I would say that depiction is a less standard explanation than all the ones he claims were "tricked," including mine. Does he say how time dilation comes out of that model, the way I do in my video?
@@EdwardCurrent I honestly don't know!
I'm just starting to understand a little bit about Special Relativity. General Relativity even though I understand the basic consepts is really not something that I understand...
Curved spacetime is an insane concept for me (I do believe in it, I just don't understand it).
For starters, we have a 4D spacetime that is curved. But when you ask people what is it curved into they tell you all kinds of stuff just to avoid the obvious - that's its bend on some 5D thing. Because honestly I can't understand how a 4D spacetime can ever be curved withought being curved onto some 5D entity.
I understand that our understanding of the curvature is intrinsic but that either the curvature isn't really curvature or it is and there should be some 5th dimension for it to curve into...
Etc... :P
@@-_Nuke_- I think the biggest problem is that even if the mathematics all work out, curved 4D spacetime is just difficult for us to visualize. The best thing I can point you to is the spacetime diagram depicted in the video thumbnail. It's only two dimensions, but it's a "curved" version of the 2D diagram regardless. Warped or non-Euclidean might be more accurate terms.
Everybody is balanced if its center of mass passes through its base.
But in the banking of the cycle, the cycle is ultimately balanced because its center of mass is not passing through its wheels. (base)
How does a banking cycle balance?
Because of a combination of forces (or pseudo-forces, depending on the frame of reference) in different directions.
i watched so many video on spacetime but this one make me subscribe this channel
Best explanation that I have seen. I particularly like rotating the grid to demonstrate different points of reference.
This is a great visual explanation!
Caramba que explicação sensacional! Parabéns
How do we know we need to accelerate to keep up with space time curvature and not that it’s the opposite and objects at rest stay within the space time curvature and accelerating objects straighten their path in curved space?
In other words if I understood correctly, you proposed in your graphic that the house is accelerating and therefore moving with space-time curvature and the apple is moving inertially and through the grid of space-time, but how do we know it’s not the opposite and the inertial objects (that would be the house in this opposite scenario) adjust their movement to the space-time curvature and accelerating objects (the apple) are the ones that deviate their paths from the curvature of space-time?
That's what the geometry of the model tells us. To simplify a bit, measurements of path lengths across the curved surface correspond exactly to measurements of durations in time and distances in space. The calculations only work out if all free-floating/inertial objects take straight paths/geodesics across the surface.
@@EdwardCurrent understood.
Edwards upload rate has decayed exponentially to the square of the distance of the warping of SpaceTime his next video upload will be in 10 years from now
great explanation
Brilliantly explained.
Excellent! And quite different from the last EdwardCurrent video I watched :)
Hello. Great video. All good and correct! Just a quick question;
Spacetime in an accelerated frame should be curved as acceleration is the same as gravity locally.Time dilates,light bends in an accelerated frame,so Spacetime must be curved.
Is this correct? Do you agree?
No that is not correct. Spacetime curvature is is a physical fact, independent on the observer. It can not be globally transformed away. What is curved for the accelerated observer is their coordinates.
Acceleration does not cause curvature.
This can be seen by looking at the equivalence principle. It says acceleration is locally equivalent to a _uniform_ gravitational field. A globally uniform gravitational field has no curvature and can be transformed away by a change in coordinates.
Coordinates are arbitrary with no inherent physical meaning. Spacetime curvature is physically real.
@@narfwhals7843 Although, I agree that there is no REAL gravity in accelerated frames, I disagree that there is no spacetime curvature. Refer to the rotating disc of Einstein's thought experiment which gave him the idea of General Relativity and spacetime curvature.
Also, does time curve in an accelerated frame? Yes it does.
Does space curve? Yes it does. ( Bending of light)
This only implies that LOCALLY spacetime must be curved in an accelerated frame. Ohh yes, the Riemannianian tensor globally is ZERO,but not in the accelerated frame.
Please refer to the rotating disc.
@@nadirceliloglu7623 If the Riemann tensor is zero in one frame then it is zero in all frames. That is the point of a tensor. Again, the rotating observer has curved _coordinates_ and there seems to be no obvious way to use simple transformations to transform the tensor, since clock synchronization is impossible for the global rotating frame.
The Ehrenfest disc problem plays out entirely in flat Minkowski spacetime.
If you look for the Riemann tensor for the rotating disk you'll find mention of it being non-zero. But, as far as I can tell, these mentions are about a sub-manifold on the disk, not the global spacetime.
Again, real curvature is a feature of the manifold itself, not the coordinates.
The way this gave Einstein the idea of spacetime curvature was that, for the accelerated observer the geometry looks non-euclidian. From the equivalence principle this means the geometry must look non-euclidian in a gravitational field. But the global gravitational field is not observer dependent, while the accelerated coordinates are, so the gravitational field must be "real curvature".
Accelorometer app?! Gotta get that now....
Amazing
So are you saying that because of the earth orbiting the sun it creates a centripute aceleration so when and object fall the earth is going upward because of this aceleration motion?
No, Earth's gravity has nothing to do with its rotation or orbit around the sun.
@@EdwardCurrent so i do not understand so far why is the earth which accelerates and not the object who falls. Could you explain how it is pisible because you said the surface is going in the curve and goes ups😭😭😭😭😭
@@elizabethreyna8354 Explaining how curved spacetime does that is what the video is for.
@@EdwardCurrent but ho is it that earth accelerate upwards i do not get it. In your ilustration you put a surface goibg upwards while the object is in a inertial frame.
What i understood is that earth follows the curvature by its rotatibg movement like a wheel , so why the earth follows that curvature and not the apple. That make us thing earth is expanding.
I'd say if you're not understanding it via my video, maybe watch some other videos on the topic. It's not easy to understand.
Checkmate gravity
Excellent work, thank you. You're the best and most helpful.
Great explanation👍. Thank you!!!!
ah, finally. this was what i was looking for. i get this, unlike the "gradient in the flow of time" thing most youtubers were pushing.
These explanations aren't in conflict with each other. The "gradient" is part of the spacetime curvature. And in a certain coordinate system it is the relevant part of normal gravitational motion.
Veritasium mentioned Four-Acceleration being a sum of proper acceleration and a space-time curvature term. Like A = d^2x/dt^2 + curvature term. So even if the first term (coordinate acceleration) is 0 and the observer is not changing position, the Four-Acceleration can still be non-zero if space-time is curved. An observer will feel being accelerated no matter the source of the acceleration and hence will claim a force is being applied. Would be nice if you went into detail on this, if your proficience in the subject alows it of course.
That's certainly a more rigorous explanation than my diagrams. I try to keep these videos short, and limit space to one dimension for maximum accessibility.
What a passive-agressive comment.
We all know that the noodly appendages pressing down on us is what causes gravity. I read it in a religious text....soooo....CHECKMATE, ATHIEST!
Great video, thanks! At 0:48 light travels through space but not time... but light has a defined speed, meaning it travels through time too, doesn't it? Does it have to do with the shape of the reference frame... not being curved?
It travels through time for an observer not moving at c. As far as light is concerned however, it does not travel through or experience time. That is what the time axis in these diagrams is showing (known as proper time). If you could move at the speed of light, you'd cross the universe instantly, and meanwhile the universe would be Lorentz-contracted to nothing in the direction of your travel.
I can relate to how gravity affects space time with something like the Earth orbiting the Sun, as it is actually orbiting in a straight line in a curved space-time. What I don't understand is how is space-time curved in interstellar space that is far away from any strong gravitational pull, with the exception of the center of the galaxy? What if there is a spaceship traveling far away from any galaxy's gravitational pull and it accelerated to near the speed of light? What would cause the time dilation?
Interstellar space has some curvature, it just depends on what masses are closest. To use a bad analogy, you can imagine a ball rolling on an undulating landscape that controls how the ball moves. As for what causes time dilation out there, just plain old special relativity. Time dilation doesn't require gravity/spacetime curvature - relative velocity alone will do it - although gravity/spacetime curvature will also do it. For example, from Earth, those interstellar clocks will look to be running a bit faster, regardless of their velocity.
@@EdwardCurrent Thank you for the explanation Edward. I understand it. I just still don't understand why relativity works that way. I guess it must be easier to understand if you can understand the math.
Try to think of space and time as things that can trade off for each other, like a currency...in the same way you could pay for something with either all dollars or all euros, or some combination of the two. In the case of space and time, the conversion factor is 300,000 kilometers per second...300,000 kilometers of space is one second of time.
Nice video. Are you messing with our brains on purpose flipping space and time axes? 😂
I like time on the "x" axis because time is always running for you, unless you're a photon. (It should be notes that the vertical axis on these "Epstein diagrams" is represented by a 45° line on Minkowski spacetime diagrams, and shows coordinate time, vs. the proper time depicted here. I think this is more intuitive for the general public.)
Who are you and why am I here?
These nuts gottem
We're waiting for you to wake up. This is a message from the rest of us. We aren't sure how you will see this message. Please, wake up.
I am who I am
Perhaps I am you, perhaps we are all you.
If I wasn't me because my mum and dad never met, would I still be me.
@@Steven_Rowe Perhaps.
Great video. But can someone explain why it is both observers agree that a clock in a lower gravitational field ticks slower than in euclidean spacetime?
I think it's merely that the lower observer sees the higher clock ticking faster. You could also say that both observers agree that the higher clock ticks faster.
My theory of relativity is that weight increases relative to distance carried.
I'll get my coat....
especially if the destination is the kitchen... here's your coat sir.
@@kirkhamandy
The kitchen is where the cake is.
my question is how matters get mass to curve space time?
Nobody knows. It's one of the great mysteries of modern physics....
Hi thanks for the video it's exactly what i pictured when i finally understood the maths ! Great job. On your diagram with the house, should'nt the space parallels be actually vertical? Is there a reason for the house to be normal to the time curve ?
Thank you! In this representation where time is proper time (as opposed to the coordinate time of Minkowski spacetime diagram), time and space remain orthogonal. Lorentz transforms correspond to rotations of both axes rather than hyperbolic transforms. One of the reasons these "Epstein diagrams" are more intuitive for teaching basic GR concepts to the general public.
@@EdwardCurrent Hold on the diagram is distorted through Lorentz transformation?? but from which frame to which? What I understood was you could bend the grid in virtue of the derivative of the time basis vector being positive g. but the r basis vector has derivative components = ±g/c^2 ≈ 0 so I pictured the r axis to remain vertical
SR Lorentz boost just rotates the diagram for the appropriate observer and calculations are just Pythagorean (which you can glimpse right there in the Lorentz equation with the square root and the 1- (v/c)^2 and whatnot).
If you're moving horizontally, at 8:50, how are the markers 100 km apart if they are separated vertically? YOu're not moving past them are you?
I assume you mean 2:06 not 8:50? The markers are placed 100 km apart. This is what you'd measure in the limit of passing them slowly, or if you had a measuring tape that's 100 km long, at rest relative to the markers. In the graph, you're only moving horizontally if you are at rest relative to the markers, and moving only through time. Once you start to move past them, your path is a diagonal on the graph. Maybe I don't understand your question.
It seems that in the diagram, the curvature of spacetime is sort of "surrounding" the massive object, and an apple at rest in the spacetime should actually move farther from the massive object. There must be a point I misunderstood, but I can't find it out. Could anyone please explain it to me?
You can't be at rest in spacetime! You're still moving through time if you're at rest in space. That's a very important concept in relativity.
@@EdwardCurrent I mean, as 5:31 and 5:46 shows, the path of an apple at rest in space bends toward the opposite direction of the massive object. Doesn't that mean that the apple would move away from the massive object?
@@Terry-w- In the diagram at 5:46, the massive object is toward the bottom of the diagram, not the top. You'll notice that the spacetime grid is curved more strongly at the bottom.
@@EdwardCurrent Ok, I now get it, thank you very much
The space time you show at 6:10 is not curved because the two parallel geodesics like the one for the house remain parallel unlike a spere (a true curved space) where parallel geodesics meet)
Those aren't geodesics. They are accelerated worldlines. At no point in spacetime (i.e., at no event) do the top and bottom of a house meet.
Interesting.
Freeze at 6:09
You said "upward" but that is not upward... That is an arrow that points towards a direction in both space and time (since this is a spacetime diagram). Remember we have compressed all 3 dimensions of space into a single line and we are using the 4th which is time to show the curvature... So clearly - this arrow doesn't point upwards from the point of view of someone on the Earth, does it?
The "upward" arrow (and the acceleration vector) is always pointing in the space direction only. It has zero time component.
_Remember we have compressed all 3 dimensions of space into a single line_
Not really, we are just showing one dimension of space and ignoring the other two as irrelevant to this particular situation.
_and we are using the 4th which is time to show the curvature_
We are assigning the 2nd dimension of the 2D diagram to time. The curvature manifests as a change in spacetime relationships across the 2D surface - on a Euclidean surface this relationship is constant, whereas on a non-Euclidean or warped surface, spacetime rotates from one point relative to another. Curvature can also be represented as bending into a 3rd dimension (as at 5:15) but that's still a rotation as one moves across the surface.
@@EdwardCurrent
Up is relative. It depends on who makes the observation.
So, my up from Greece, is different from someone elses up, from the US for example...
For the Earth to be accelerating upwards - either the Earth has to be flat, or it can't happen...
In a flat Earth, up is the same for everyone. So then, the Earth can indeed be accelerate "upwards" and not explode.
The future - for example - is something that its the same for everyone... So maybe by "upward" you mean that the Earth is accelerating "towards the future"?
- - - -
Because if the Earth accelerates "up" - where "up" is always whatever someone will call "up" from anywhere on the Earth - then the Earth will explode!
If the Earth right now accelerates "up" towards whatever I call "up", from here in Greece... AND ALSO towards whatever you call "up", from your own country - then these are 2 different "ups"... And the only way for that to happen is for the Earth to explode!
Im sorry if my question sounds naive! But I really don't understand this...
- - - -
One thing that I could possibly understand - is to assume for a moment that the Earth really is flat...
Imagine, a flat disc.
Now assume that that flat disc is accelerating towards a direction, lets name it "a".
Now, if there is something floating in empty space and it happens to be inside the flat Earth's "a" path, then the flat disc will collide with the object... We can call that Gravity...
- - - -
If we now magically turn the spacetime around the flat disc, from a flat spacetime to a curved one... Then this disc will become a sphere...
Lets run the same experiment again! If there is something floating in empty space and it happens to be inside the Earth's "a" path, then the spherical Earth will collide with the object... We called that Gravity.
- - - -
As we can see, the sphere is now accelerating towars the same direction "a" but that direction is outside our 3 familiar dimensions...
The real question then - is where is that "a"? Because it can't be in the 3 familiar dimensions that we know. And its definitely not upwards!
- - - -
@@-_Nuke_- You seem to be missing the critical concept that in curved spacetime, you need to be accelerated (e.g. by the ground) to remain in place. Otherwise, without this acceleration you "fall." And since spacetime curvature is the same wrapping all around the Earth, at every position, you need to be accelerated in the local "up" direction in order not to start spontaneously moving toward the planet's center (falling, in the local "down" direction). In other words the North Pole and South Pole, despite being accelerated locally upward -- as can be confirmed by accelerometers in both locations -- are not moving away from each other. Maybe watch 4:23-6:08 again? Mind you, this material is counterintuitive and difficult.
@@EdwardCurrent Thank you for answering my questions :)
But I still don't understand...
Ok, assume that we have the Earth inside a curved spacetime...
Ok. Now assume that we can magically un-curve the spacetime around the Earth... From a curved one to a flat one.
Will this make the Earth take a new shape? And what will that shape be?
Will it be a flat disc? Because if that indeed happens, (you have already shown how a satelite traveling at a straight path will now travel in a circle because of spacetime curvature) then the result will be a flat disc and things not attached to it will indeed collide with the Earth as the Earth accelerates towards them...
That I can understand. Is that what will happen?
No. If for example you removed all of the material from below Earth's surface and transported it far away, then spacetime all around the surface would be virtually flat -- and the surface would still be spherical. And since spacetime is flat, the surface wouldn't collapse toward the center. It would just remain a floaty shell.
The curvature/shape of the Earth has nothing to do with the curvature of spacetime, except that very massive bodies like planets take roughly spherical shapes because of the large amounts of spacetime curvature they create, and the forces within the body reaching a stable equilibrium under those conditions.
You might want to try Veritasium's explanation for a different perspective: ruclips.net/video/XRr1kaXKBsU/видео.html
I thought of your videos & searched you up. Clicked on a video & it said 16 years ago! WTF?! That is very scary stuff, i was watching you when i was about 13 y/o or so.
What's even scarier is I was watching you 😲
These are great. Thank You
My lord Edward where are you
I miss your checkmate atheist videos
Also after watching your video i have become atheist and having existential crisis
Make video on how to counter that and find some meaning in life
And your content is amazing keep going
I've often wondered, if space and time are curved, isn't it possible that when we look at the more distant astronomical objects we are actually seeing ourselves that many lightyears in the past. Rather than the universe being an open and expanding "thing", the next layer of astronomical objects that are the same distance further out is us again, and the universe is a constrained spiraling "thing"?
I get what you are saying! It seems like you could go in one direction and get back to where you came from, like on Earth. But all available evidence indicates that at large scales, the universe generally averages out to flat, not curved. The curvature as discussed in this video only happens near massive objects, and flattens out as you move away.
Very interesting hypothesis.
@ 0:47 traveling at the speed of light is temporal because traveling requires time. Say getting from A to B requires time for example. If something moves, it requires time.
Acceleration is a deviation of a speed constant. Geodesic only refers to curves, not straight lines and straight lines do 100% exist in space time. Granted, the universe is always expanding, hence, no straight lines can exist short of in a minor measurement like finding a straight board at The Home Depot.
_If something moves, it requires time_
But it requires less time the closer it gets to c. At the limit of c, it requires zero time. Light only takes time to travel according to things (with mass) that have a reference frame.
@@EdwardCurrent I understand how time differentiates. Damn this is complicated. It does not require less time the closer time gets to C aka the speed of light, it is just that time dilates due to our human perception of time. If there was no movement at all in our universe, there would be no time. Since there is movement in our universe and minds that can clock movement because we have memories recording the movements of things traveling (what we call time), we can speculate speeds, futures, velocities, gravity, anything that has movement based upon how we as humans perceive and what we call time and movement.
Relativity has nothing more to do with than movement, memory, and position when it comes to movement in any space.
Is light the fastest that anything can move within space time? Yes! As far as we know as documented in the original Planet of the Apes movie and Monty Python's The Meaning of Life and physics as we know it today.
Time does go to zero at the speed of light as far as we as humans know, yet we can look at the light coming off a computer screen within time.
Think about this, would it require zero time to get to the speed of light? As we all know, the speed of light exists. As we all know, the speed of light takes time to reach a destination. Explain celeritas/C if equals zero.
You seem to be advancing a non-standard interpretation of relativity. In the standard version of the theory, it has nothing to do with human perception. Would it require zero time to get to the speed of light? If we're talking about light, yes, absolutely. A photon cannot exist at any other speed than c.
@@EdwardCurrent Yet the speed of light can change based on what it is traveling through, hence refraction .
@@FishHeadSalad We aren't talking about light interacting with a medium. We are talking about c, the speed of light in a vacuum. An individual isolated photon cannot move at any other speed.
Good stuff thank you
OK, but how does this explain the way the PrayerMAX 5000 works?
BTW, do you still have any left in stock? I can pay the entire 420 up front.
I think there are two mistakes here,
First: objects moving with constant velocity can have curved worldlines in spacetime diagram
Second: curved spacetime and equivalence principle are two seperate thing and shouldn't confuse with each other
Acceleration = curved path, inertial - straight/geodesic. If an object is following a geodesic, then an accelerometer on that object will always measure 0. And the equivalence principle is important in understanding how Einstein derived the concept of curved spacetime. People rightly chastised me for leaving it out of earlier videos on the topic.
@@EdwardCurrentBut isn't a geodesic a straight line on a curved surface? Straight lines on curved services aren't straight, they're curved.
@@inertiaforce7846 A straight line on a curved surface is a straight line *on that surface,* however. What happens when you drive a car across the surface of a planet and never turn left or right? Can you drive any straighter than that? You can think of a geodesic as the straightest line possible on whatever manifold that line is on.
@@EdwardCurrent Agreed. I'm still a little bit confused on other issues though. GR is really difficult to fully grasp.
Question: Static charge produces an electric field around itself. But how does a moving charge produces a magnetic field around itself?
That's actually special relativity in action. It seems unbelievable, but when electrons for example are moving, even at extremely low speeds, there is enough relativistic length contraction among them that charge densities become asymmetrical and there is a net force. That force is the "magnetic force." I started making a video on this, but there are several good ones already available; search for "magnetism relativity."
@@EdwardCurrent Thanks a lot
You are doing amazing work edward I request you to make a video
often times when I explain theory of evolution to my friend and give them evidence . they accept evidence but often it is very hard for them to comprehend how can a single prokaryotic cell can evolve to form human means if you can make video explaining why it is logical to think prokaryotic cell can evolve to humans in billions of year it will be a great help
Thank you. I find it hard to comprehend it myself, given that humans are very bad at imagining anything longer than about 100 years. There are lots of evolution videos out there - even though I have a biology degree I'm not sure I could make one that breaks through to everyone.
@@EdwardCurrent yeah thatswhy people like kam hovind say microevolution is true like darwin finches , e coli while macroevolution is false as no one seen one species turning into one another
Except that you can see it happening in the fossil record. You can't see "macroevolution" happening with our eyes during our lifetimes for the same reason you can't put a ruler on the ground and see the curvature of the Earth. An analogy that's remarkably appropriate.
@@EdwardCurrent yeah i also request you to make video on one controversial topic if you don't mind
Relation between race and intelligence with scientific point of view i have seen many white supremacist use reasoning that other people like Asian and blacks are intellectally infrior than white ,race and it is evident that all great inventions and advancement in science are done by whte man and all developed countries in are whits majority
Don't forget, Edward, time dilation works the same way as the basic Doppler effect, so time contracts for objects on approach; it dilates only as they recede.
You're referring to relativistic doppler effect. If the clock is approaching or receding, both effects are in play. As long as it isn't approaching straight-on, there should be an angle at which time dilation and relativistic doppler effect cancel, and the clock runs at "normal" speed (at least momentarily). A topic maybe worthy of its own video.
@TheRojo387
You confuse appearance with the actual thing which misleadingly still is called "time dilation" (indeed it's rather a projection of one observer's clock rate to the world line of another).
Let's take an example which is easy to calculate: We assume that we're _approaching_ each other at v⁄c =: β = 0.6 but we don't know that first. You figure it out by sending me a radio signal of frequency f₀ and measure that, f₂ of the echo.
Within your reference frame, it approaches me with wave length λ₀ = c⁄f₀ at a difference speed (not relative speed!)
c + v = c(1 + β) = 1.6∙c
which yields it hitting me with frequency
f₁ = c(1 + β)⁄λ₀ = 1.6∙f₀
according to your own clock. The echo leaves me at a difference speed c(1 − β) = 0.4∙c, rendering it's wave length to
λ₂ = c(1 − β)⁄f₁ = λ₀(1 − β)/(1 + β) = 0.25∙λ₀
which leads to the echo reaching me with
f₂ = f₀(1 + β)/(1 − β) =: K²f₀ = 4∙f₀.
You can calculate the speed by
β = (K² − 1)/(K² + 1) = ³⁄₅.
If you, at the other hand, consider me at rest, you expect the signal having first λ₁ = c(1 − β)/f₀ which leads to
f₁* = 1/(1 − β)λ₁ = f₀/(1 − β) = 2.5∙f₀,
the echo being further blueshifted by another factor 1.6 by your motion. Either way, the 2-ways DOPPLER shift is factor 4.
An asymmetric 1-way DOPPLER shift, however, would tell us who of us is at rest which contradicts the principle of relativity, thus I must measure the frequency f'₁ = K∙f₀ = 2∙f₀
which is higher than f₁ by a factor
γ := 1/√{1 − β²} = 1.25
and lower than f*₁ by 1⁄γ = 0.8.
@@jensphiliphohmann1876 Explicitly, what is the distinction between appearance and the actual thing in this case? Is relativistic doppler effect appearance and SR time dilation the actual thing? Maybe I don't understand what is asymmetric about relativistic doppler shift.
@@EdwardCurrent
The point is that the relativistic DOPPLER shift _must not_ be asymmetric _at all._
We would instead expect the effect being asymmetric _within pre- LORENTZ aether theory,_ just as this is true for the acoustic DOPPLER shift.
Assume we both believed in this, also assuming you are at rest with respect to the aether whereas I am approaching you at β=0.6. It's straightforward then to calculate that
▪︎any signal you send to me must be blueshifted by a factor 1 + β = 1.6 in terms of frequency i.e. by 1/(1 + β) = 0.625 in terms of periodic time or wavelength, and
▪︎any signal I send to you must be blueshifted by a factor 1/(1 − β) = 2.5 in terms of frequency i.e. by 1 − β = 0.4 in terms of periodic time or wavelength.
In both cases, each of us receives the echo of his own signal blueshifted by a factor
(1 + β)/(1 − β) =: K² = 2.5∙1.6 ≡ 1.6∙2.5 = 4
in terms of frequency and
K⁻² = 0.25
in terms of periodic time or wavelength. Of course, our expectations are based on old aether theory where GALILEI's finding about motion being relative to something just approximately holding for β
I still don't know what you meant by "You confuse appearance with the actual thing" (to @TheRojo387)
Now apply this to Poul Andersons Tau Zero…..
0:48 this is false.
Light travels through both space and time (it's called a light cone in space-time graphs)
What's depicted here is something moving infinitely fast, which physically doesn't exist.
1:29 rotating the graph does not equate to changing frames. Lorentz transformation is more accurately, a "tilting" of the time axis.
You're referring to a Minksowki spacetime diagram with coodrinate time (ct) on the y axis. The method used in this video (which I think is much more useful as a teaching tool) puts proper time on the y axis. Photons do not experience time (i.e., proper time) so that is why it's "infinite." This method of teaching relativity was invented by Lewis Carroll Epstein in his popular physics book Relativity Visualized.
@@EdwardCurrent oh. That makes more sense now. Feels less intuitive to me, but if it works
This is confusing. I may need an easier explanation
I don't know if you'll find one...this stuff is difficult. A lot of people liked my original gravity video though: ruclips.net/video/jlTVIMOix3I/видео.html
Very thought-provoking, I need to watch this again and again,and just when I think I grasp something, I realise there are things I don't understand.
I am thinking about Einstein's thoughr experient about observing the clock from the bus that travelled at light speed.
He said if the bus travelled at light speed the clock in Bern would stand still or it would appear to him as if it was.
Speed is distance over time, so if you were on the bus at light speed your clock would tick would tick one second and you would be 186000 miles away from the Bern clock, I think.
If after that one second the bus reversed back to Bern at light speed then another second would elapse on the bus clock, and the observable clock in Bern would start moving at twice the speed, so surely whe. You got back both clocks would have moved to seconds.
Sounds great, but then I read they have placed atomic clocks on a plane in sync with one on the ground and when the plane returned the clocks were different
I am now one second from going mad.
done forget time is relative: if I playback this video at 50% speed it takes 20mins to absorb some bentness
Does this theory means that Earth is actually flat, and only appears shperical due to spacetime cruve because of gravity?
No.
@@EdwardCurrent Well, ok.
🤯
The background music is annoying and doesn't help this!!
Where are you Edward? You havent posted since January 1 2023
Sorry! I'm waiting for AI to get better because making videos from scratch is a huge pain in the ass
@@EdwardCurrent 😂😂😂😂 you didn't need AI for all of those funny videos back in the day! Checkmate checkmate checkmate checkmate checkmate checkmate checkmate checkmate checkmate checkmate!
@@EdwardCurrent please at least do something about the trump guilty verdicts
I wish I could imagine / understand why earth is not expanding
Earth is not expanding. The reason the ground accelerates up is because freefall is non accelerated according to Einstein. The ground prevents you from being in freefall, and therefore prevents you from being non accelerated, and therefore the ground is accelerating you up by preventing you from being non accelerated.
@@inertiaforce7846 that doesn’t really mean much to me. However I did find a video by FloatHeadPhysics that nicely illustrated the curvature of time that shows that the earth can accelerate to be “still” while us, free falling objects going straight, are actually bend towards the earth so it looks like we’re falling!
The video is ruclips.net/video/OpOER8Eec2A/видео.html (the one about the illusion of gravity). I really loved it!
So, earth is pushing against it's own gravitational field, but the gravitational "force" is perfectly balanced? Kinda like the Newtonian action/reaction?
Because in stars gravity acts like this. It's a constant battle between gravity and the star that is essentially constantly exploding "outwards'.
But what on earth is generating this "away from the center " push?
It's the Van der Waals force -- electrons repelling electrons. In ordinary matter it's a lesser but analogous version of the star's explosive outward forces, and similarly in an equilibrium or stable configuration.
@@EdwardCurrent - In case of Newtonian physics we called the force going upward as Normal force. So what is the difference between Van Der Waals and normal force??
@@angadbagga9166 Good question. There's no difference. The normal force is produced on the molecular level by the van der waals force.
@@EdwardCurrent Thanks and great work on these videos. I will try to read more on Normal force as it's really interesting.
@@EdwardCurrent This concept doesn't involve the Earth physically moving upwards but rather suggests that objects fall towards the Earth because they're following a curved path in the spacetime geometry created by the Earth's mass. So, in a sense, the person jumping isn't hitting the Earth because the Earth is moving upwards, but because they are following a geodesic (a curved path in spacetime) caused by the curvature of spacetime around the Earth's mass.
> acceleration is an absolute phenomenon
No, not exactly. If everything in a given frame of reference is being accelerated at the same rate, it'd be indistinguishable from not accelerating at all. In the case of the rocket, the acceleration is felt because the rocket is acellerating first, and there is a delay between your feet being acellerated and the top of your head being accelerated, resulting in your body being stretched or squished.
I think in the first part of your comment you're referring to the "mass as the charge of gravity" way of looking at it, which I talk about in one of the videos referenced at the end. In this frame, does light go straight or curve?
@@EdwardCurrent Well, I'm not really specifying any model in particular. If we consider the simplest toy universe that can have objects with velocity and acceleration, you can only detect relative differences in acceleration. If all objects in this system were always accelerating at the same rate at the same time, to an observer inside it would appear that everything is stationary. So long as every object X's acceleration A is equal to every other object Y's acceleration at time T, it'd appear this way - even if the function f(T) = A changed wildly as T increased.
I believe this would be the case for all higher derivatives (the next one being jolt - rate of change of acceleration).
One thing that IS absolute though is angular velocity, angular acceleration, etc. These, I believe, are absolute, and you can know whether a given frame of reference is rotationally stationary.
Whether this concept of acceleration relativity extends to the real world, I'm not entirely sure. I suspect since the gravitational model from newtonian physics is less accurate at large scales, that it might not be. (In the same way that a tangental plane is only an accurate representation of a single point on a unit sphere - as you compare a larger area of a plane to a larger area of the sphere, the surface of that plane becomes a less and less accurate approximation of the sphere.)
I suspect it isn't possible to have a situation where all objects are uniformly accelerated within a given region of space. (Unless you were to have tiny thrusters attached to each unit of mass.) In order to have acceleration (in a newtonian sense) that isn't caused by propulsion, you'd need curved space - and when you have curved space, geodesic paths may not remain parallel anymore, thus their motion isn't uniform.
Then again, if you were to have a region of space that only had one curvature direction (like a ribbon that could fold but not twist) objects travelling along the ribbon could have uniform acceleration relative to objects travelling diagonally across it... perhaps?
I don't know. It's the kind of question I'd go to Physics Forums to ask (that's a great resource...for this video they helped me with the Eddington experiment...as long as you don't mind a little condescension when a question isn't worded exactly right).
Light is the ultimate accelerometer, which is why I mentioned it. If any reference frame is an accelerating or rotating one, this will show up with light curving - even in a situation that's highly contrived, like putting a tiny thruster on every particle.
@@EdwardCurrent Thanks for the interesting conversation!
Regarding forums, personally I don't like to indignify myself by engaging with people who don't respect those who are ignorant but honestly willing to learn and reciprocate that respect - unless I really need to for some specific goal. Same problem happens in StackOverflow and it is nauseating.
Sometimes I wonder if leaving the odd intentional spelling or grammar error is a good way to filter out people who are not worth your time.
i'm in a rocket accelerating at 9.8m/s/s , that would feel exactly same as standing still on earth.
So standing on earth you are accelerating upwards at 9.8m/s/s?
is yes then my velocity is constantly increasing when standing still on earth ( like in a rocket ship with a=9.8m/s/s) ?????
No because velocity is a function of time, and where spacetime is curved, acceleration (defined as any worldline other than a geodesic) doesn't equal an increase in velocity. In flat spacetime, it does.
@@EdwardCurrent how bizar you really do understand this stuff
The basics are not that difficult to understand, just counterintuitive.
sure if we exchange 'ABSENCE of EVERYTHING' with something like 'the FABRIC of SPACE' you can punch a hole in A FABRIC, or tear A FABRIC, and A FABRIC can curve. BUT A FABRIC isn't NOTHINGNESS is it?
No one said it was nothing, because it isn't.
Fantastic. Check mate, atheists!
Wait...
ONE can NOT curve or tear or punch a hole in a NOTHING if NOTHING means absence of all THINGS all MATTER.
"Nothing" still contains all of the fields of the various fundamental interactions as well as the Higgs field, without which there would be no mass. And we aren't punching tearing or a hole in it. That's a topological change. The geometric relation between space and time changes over its extent, and this is quantitatively measurable. The incredulity of armchair commenters has no bearing on these quantitative measurements.
Checkmate, classical Newtonian mechanics!
bullshit, how can acceleration be absolute when both space and time are relative? acceleration is always relative to something else
Nope, acceleration can be and always is measured the same regardless of uniform motion. You can demonstrate this on your phone with an accelerometer app - I have a video where I do this.
@@EdwardCurrent you are only able to measure acceleration gradient, if all of the atoms in an accelerometer were accelerated the same you wouldnt be able to measure it at all
@@midas01tw Physics can only deal with observables. If acceleration can't be observed by an instrument designed to measure accelerations and forces, then it's meaningless to say it's being accelerated.
Welcome back, Eddy, Current. Give it a rest, mite. No poor child can possibly understand this, in a M years, coz U don't really know, how gravity works, in 3D.
so the earth is flat, its just the eyes that are curved.
Oh, I miss "checkmate atheists" so much :)