Please make a sequel, the "conclusion" needs more explanation.

@pedroadonish

3 жыл бұрын

Hahahaha, I was waiting until the end to see the final answer... Then he says "and that's why!" Like... what?

@LuisSierra42

3 жыл бұрын

That's from your perspective

@jeremiascristian521

3 жыл бұрын

Pro tip: you can watch series on flixzone. I've been using them for watching lots of of movies lately.

@blakematthew6880

3 жыл бұрын

@Jeremias Cristian Yup, have been watching on flixzone} for years myself =)

Well, I find the video has a long introduction and then finishes off a bit too short with the conclusion that the moving person exists in two reference frames, period. That part, the meat of the paradox, should have been better explained.

@ericlobatograef5186

6 жыл бұрын

I agree, in fact, I didn't understand what he meant. Could you please explain? Doesn't seem to make any sense, I would simply say that we have 3 frames and each of the frames is at rest in relation to one of the observers.

@protocol6

6 жыл бұрын

Yes, it really needed to circle back at 12:25 and expand on what those two very brief bullet points mean rather than just declaring it solved as I bet many missed it and quite a few may not get it on reviewing.

@LarsStokholm

6 жыл бұрын

Yeah, that part I don't understand at all.

@billg.7909

6 жыл бұрын

Agreed

@DanielNogueiraLeitao

6 жыл бұрын

I totally agree.

Like others here, I don't see the explanation. I hear "two frames of reference" but I can't connect that observation to an explanation I can grasp. It's like you ran out of time.

@trsomas

4 жыл бұрын

See if this explanation is clear. kzread.info/dash/bejne/fIR3pq2tkZWyhqg.html

@penguindragon0155

4 жыл бұрын

yeah. if this video was 1322 or longer then the universe would have died then and there so... he did what he had to do

@renedekker9806

4 жыл бұрын

I think this one is a better explanation: kzread.info/dash/bejne/Yp1-vMGKd7CydJM.html

@BinuJasim

4 жыл бұрын

@@renedekker9806 No, it's factually mistaken, I guess. How can the stationary person measure time for the moving person. Then it will be 10s only!

@renedekker9806

4 жыл бұрын

@@BinuJasim The stationary person does not *measure* time for the moving person. But she can *calculate* how much time should be passing for the moving person.

I'm sorry but you went all detail with the easy and well understood part, explaining it like we would to a 5th grader, and then just conclude in literally 5 seconds that since the observers B and C are not in one single reference frame (wich could have been explained as well as the rest was) this is the proof for the paradox not being a paradox. While I'm sure this is correct, and not wanting to tell you how to make your videos, this last part ,with no explanation at all to support or motivate your conclusion, didn't really prove anything to me. Still, it did provide for a starting point for me to dwelve deeper into, so thanks for that.

@Guoenyi

2 жыл бұрын

His solution was very good, for debunking the "acceleration" theory. But did not really explain why the paradox is not a paradox.

@DrDeuteron

2 жыл бұрын

@@Guoenyi it's still a paradox, even if it's resolved. If you work in minkowski space(M4), there is no paradox because M4 is manifestly self-consistent.

@BD-np6bv

2 жыл бұрын

This is a horrible example. Think about it guys. Dr. Lincon's example of A being stationary and C and B moving is the SAME as B being stationary and A and C are moving in the same direction (A away from B and C towards B), but C is merely 2x faster than A in the same direction while B is really stationary! The other probability is C is stationary and it's B and A moving towards C, but B moving at 2x the velocity of A, which in this 3rd scenario C is really stationary! To all observers, in all scenarios it would look identical and no one would be able to tell who's really doing the moving! Horrible example. The real reason is the person leaving Earth did the acceleration near the speed of light. That's the same as moving near a black hole and feeling the "acceleration" or the gravity well of the black hole (which relativity tells us gravity is just another form of acceleration and vice versa). Any person moving near a black hole would have their time slowed down, relative to an outside observer.

@DrDeuteron

2 жыл бұрын

@@BD-np6bv If you think |v_C| = 2|v_A| in B's reference frame, you don't understand relativity.

@GrowlinWillie

2 жыл бұрын

It's because the distance to the star looks different for the traveler than it does for the non-traveler. The difference in the distance occurs because the speed of light is always the same, if you're moving toward the light source or away from it. Bingo! I majored in physics at the university of michigan. I went to every single physics professor for an explanation, none of them had one so i switched to math.

I'm 67 and retired, but WHY could I not have had a Prof like you in University. You make complex things so understandably easy. Please keep teaching our hungry minds. Thank you Sir ! ! !

@519stream3

6 ай бұрын

It is still a paradox. A is at one location as he said which explains his reference of movement is that "location" which is independent from the observers, which also decides that A is stationary there are three stationary "locations". But these locations don't exist in real space-time and the only reference is one of the three observers, which is why we do not know who is actually stationary. If you still don't understand let us say location 1 is the earth. Unless you think earth is stationary we don't know who is moving. Or we don't know if earth is always at that stationary "location" but never moves. Or thinks there is a stationary ether in which there is a location 1

@nadirceliloglu397

5 ай бұрын

This is unfortunately not correct! You are changing the entire scenario by inteiducing a third twin,second spaceship! Also, you are removing acceleration completely. How can you? Not possible! Have you read Einstein's solutiin to the Twin Paradox as mentioned in his 1918 documents? He explicitly states that acceleration of the travelli ng twin causes non- reciprocal time dilation which makes the travell8ng twin to be younger. Easy! Also, you can easily deduce this from the worldlines of the stay at home twin and the travelling twin. Whose wordline is shorter? The travellung twin's worldline. So, he remains younger. Why are you complicating it Mr. FERMILAB? 😊

@luciustarquiniuspriscus1408

2 ай бұрын

Because you need to get a degree in 4 years.

I'm having a serious problem with this explanation. I get the idea that it's a question of which clock you're using as a reference but nothing shown shows why Ron's choice of his clock as the 'stationary' one is not the same as Don choosing his clock as the 'stationary' one. It's like somewhere in there, there's an assumption of which one is really stationary when in fact, once you exclude acceleration as a factor (which you do), then neither is a preferred frame. Even though it looks like it's solved the mystery - throughout the entire discussion, A is referred to as being 'the stationary person'.. but that's literally the thing we're trying not to say. Take all the math done and flip the contexts and they apply equally well and give exactly the same results relative to each viewer, except you're swapping A and B. That's the problem with this video - it shows the math from the 'stationary' person's view - but not from the 'moving' person's view in the perspective of his being the stationary person. Oh.. one other thought. In another video, you explain that the reason there is time dilation at all is a consequence of the fact that we're *always* travelling at the speed of light. Assuming we're just talking about one spatial axis, x, and one temporal axis, t - the vector must always be a unit vector... so at rest, it points entirely along the time axis and represents 1 second per second. As you change velocities (and I'm avoid saying acceleration intentionally because it's the velocity that causes it, not the acceleration) the unit vector rotates until you hit the speed of light where all of the vector lies in the x axis and there's no vector in t - ie no time movement. It seems like you're offering two different explanations for dilation. Keep in mind, I'm not saying you're wrong - you know way more than I could hope to about the subject.. I'm just suggesting that this explanation could be better.

@ThomasKundera

5 жыл бұрын

No, it wouldn't show a paradox if you flipped the referential (just give it a try). Point is that all used referential in the video are inertia ones. A is not jumping to any other inertia referential, and you can't make a valid Lorentz transform that would show such a behavior, because in all other inertia frames, A is an inertia frame (constant velocity).

@lukecasey2830

5 жыл бұрын

​@@ThomasKundera Consider the spaceship reference frame A, consider the stationary person reference frame B and C except with the negative of the velocities used in the example. Perform all of the same calculations. Why would it be wrong to do this?

@ThomasKundera

5 жыл бұрын

@@lukecasey2830 : _"consider the stationary person reference frame B and C "_ B is stationary, C is stationary. But (B and C) are not. So you can't make a computation assuming (B and C) is an inertia frame of reference (as you can do in A, as A is one).

@lukecasey2830

5 жыл бұрын

@@ThomasKundera But we are not considering the stationary person as stationary when viewed from the spaceship's frame of reference. We use two frames of reference to describe the space ship, I do not see why we couldnt in return use two reference frames to describe the stationary person when considering the moving space ship as stationary. How do we even know the space ship is moving and not everything around it? The fact that it isnt expending fuel and accelerating, therefor not losing mass, leads to the conclusion that we dont know if the spaceship is moving or the stationary person (ignore that fact that we are callling the stationary person stationary, what we call the person is beside the point). Can you explain to me how we know the spaceship is moving, not everything around it, and how we know we must use 2 reference frames to only describe the spaceships movement? Please I am trying to figure this out but I cant. I know I am wrong and that I am not understanding something

@ThomasKundera

5 жыл бұрын

@@lukecasey2830 : You can take any of A, B or C as "stationary". But, again, B then C is not. _" I do not see why we couldnt in return use two reference frames to describe the stationary person"_ Because if you need more than one frame, then it's not stationary, by any reference.

I believe that there is an error in 10:25. According to observe C's perspective: the x co-ordinate (position) of event 1 would be -2yl, the x co-ordinate (length) of event 2 would be 0 and the x co-ordinate (length) of event 3 would be again 0. This is because the events' positions are relative to the perspective of C. It can also be supported by the x co-ordinates of the 3 events according to observer A and B's perspective since in the video the x co-ordinates of both perspectives are relative to the observer (i.e. for observer B event 2's x co-ordinate is considered to be 0 as the observer B and event 2 are on the same position). According to example I wrote in parenthesis, the x co-ordinate of event 2 for observer c would also be 0 as observer B and C are on the same position as well as event 2. However, this does not effect the conclusion reached. Please reply me either you believe I am right or explain my mistake.

@camillomarchesi6050

Жыл бұрын

anche io vedo un errore ☹️

I found this version to be better than the version without equations. It would have been more clear if Dr. Lincoln had explained what he meant by "the moving observers existed in two [frames of reference]". When he said that, he meant that the moving observers existed in two _separate_ frames of reference. Thus, he debunks the notion that the acceleration explanation for earthbound Don being older than astronaut Ron. So, the twin paradox isn't a paradox. It's just a conundrum ... and the conundrum isn't explained by acceleration, but by the Lorenz transform equations.

Some people just have a knack at breaking down complex problems to smaller, more complex problems that are even harder to understand.

I still don't get it. What did he mean by "Observer A exists in only one reference frame but observers B and C exist in 2"?

@trsomas

4 жыл бұрын

B and C are moving relative to each other. So they are in different inertial frames.

@cvasticamuc

4 жыл бұрын

Consider this, the earth moves ( rotation and revolution) yet we feel we are stationary. That's because we are in the same reference frame where everything on earth is moving. Now consider A to be on earth. A is stationary within this reference frame earth. Now B and C have different reference frames each. One when they start their journey ( Earth for B and 2L for C) and when they pass each other ( L for B and C both) and when they end their journey ( 2L for B amd earth for C). Thus these two people have different reference frames therefore there must have been some movement to change those reference frames. Therefore its concluded that B and C were moving and not A. All in all, the paradox arises with the question who exactly is moving. Now since it gets clear that B and C are moving and not A, the paradox gets solved

@jaimeduncan6167

3 жыл бұрын

@@trsomas They are both moving relative to. A. So we can say B is stationary and A and C are moving relative to each other. I belive he should have done that calculation too to convince most people.

@Spironic

3 жыл бұрын

@@jaimeduncan6167 The problem that I have with this explanation is that in the original paradox, B and C are both represented by one person that never moves relative to himself, so what does this explanation have to do with explaining the original paradox?

@wideseen

2 жыл бұрын

@@trsomas And A and C are moving relative to each other and A and B are moving relative to each other. I sense poppycock here. They are all inertial systems and the Lorenz transformation can be applied equally in all permutiations.

This is GENIUS! It's like I have just had my decade-long storage of nagging thoughts+lingering questions+half-baked answers suddenly decluttered in 13 mins. Dr Lincoln, you totally rock like the new opening background music of this series. :)

@MrGriff305

Жыл бұрын

He didn't explain the original scenario.

@mrboombastic8369

Жыл бұрын

Hello, i didn't went deep on the math part, so maybe i missed something, but please explain me this. So, the distant star is 4 light-years away, however when the twin that travel there when he returns back to earth in his clock it just passed 4 months? Like that is very strange to me because i think that before one the twins leaves the earth both agree that the star is 4 light years away, even after the twin arrives the star he would look back to earth again and say that the earth is again 4 light years away, however in his clock it will just take 2 months to return to earth. I am not getting that part.

As a teacher of A-level Physics I found this video interesting, especially as the textbook we supply to our students gives the acceleration & deceleration solution. A past exam question (AQA exam board) explained it by saying the rocket twin was in a non-inertial frame of reference.

@TheLazyVideo

Жыл бұрын

The twins paradox exists in inertial frames without doing the introduction of a new reference frame C. Just imagine twin A is in a high circular orbit, and twin B is in an eccentric orbit that tangentially intersects A’s circular orbit. No rockets, no thrust, no acceleration, no non-inertial frame nonsense. We know high orbits experience time slower than low orbits. GPS satellites lose 1ns per 1s compared with us surface dwellers. But how does the twin B know it’s in a low orbit when it’s in an inertial frame? Orbits are just free-fall, and are inertial frames.

@montagdp

Жыл бұрын

@@TheLazyVideo in special relativity, spacetime is flat, so a circular or elliptical orbit would require acceleration.

@hardkraft6894

11 ай бұрын

​@@TheLazyVideocircular orbits are non intertidal. They experience constant acceleration. But I agree with you that the acceleration is not needed for the paradox to occur.

@nadirceliloglu397

5 ай бұрын

The solution with acceleration is the solutiin given by Albert Einstein in 1918. You can not solve it without acceleration as the travelling twin must change refence feames through acceleration and deceleration!!

@jeffbguarino

2 ай бұрын

@@hardkraft6894 An object in free fall does not experience acceleration. If you jump of a building you feel no forces until you hit the ground. When standing on the ground you feel the earth pushing you up from your feet. So on the surface of the earth is a non-inertial frame. The moon is in an inertial frame. So if you see an object dropped off a building while you are standing on the ground, you will calculate that it's speed is increasing relative to you and you might say it is accelerating but it is you that is feeling the upward force not the object. So from the objects point of view you are accelerating upward. This is like the equivalence principle that Einstein used at the start of General Relativity. If you are standing at the engine end of a rocket and it is accelerating, you feel a force on your feet pushing you up. When you hit the gas in your car, your seat pushed on your back to accelerate you forward. So if you equate gravity with other forces that accelerate you , just standing on the ground is as if you are accelerating up.

"When we start the experiment, all 3 observers start a stopwatch." This sentence contains the idea of "simultaneously". Problem is, simultaneous in whose reference frame?

@BluesManPeich

4 жыл бұрын

Imagine someone at location B sending a signal to A and C at the same time. When the observers receive the signal they start their stopwatches.

@xw591

4 жыл бұрын

T=0 for all of them.

@NeedsEvidence

4 жыл бұрын

That's an excellent point Don Lincoln failed to address. It is the vx/c2 term in the Lorentz transformation that takes care of the relativity of simultaneity. In fact, C's "now-slice" corresponds to a future moment of A, and it is for this reason that A sees more time passing than C when C reaches A.

@jeffbguarino

2 ай бұрын

@@xw591 That is what I noticed at the start, but how do you synchronize the clocks ? How do you measure the lengths to know where the center point is.

@xw591

Ай бұрын

@@jeffbguarino dunno im a mathematician

Sorry but you haven't done any actual explaining. Yes, you've set up a thought experiment with a departing and returning frame of reference that does without acceleration. You then arrive around 11:59 at "Duration(moving) = Duration(stationary)/gamma". But this is equally "paradoxical" as the original problem, because "moving" and "stationary" are still relative. You would actually need to show explicitly that the results are consistent if B or C were considered stationary AND independent of which clocks you use to measure the time between the different events. I'm sure it'll all work out but it seems awfully complex (involving relativity of simultaneity) and is definitely not obvious.

@fuseteam

4 жыл бұрын

I have found none that explains it from both perspectives so far

@NeedsEvidence

4 жыл бұрын

You need the relativity of simultaneity to fully explain why things are different for A and C. It's taken care of by the vx/c2 term in the Lorentz transformation for time, but unfortunately Don Lincoln didn't talk about it. Either he doesn't know it, or stayed silent on it by intention and just was focusing on the math.

@ricomartinez458

4 жыл бұрын

@@NeedsEvidence I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations

@stoner4683

3 жыл бұрын

Best comment. The video doesn,t explain the paradox. When he shows the (x,t) coordinates from B and C perspectives it,s not true. In fact, are the B and C (x,t) coordinates from A perspective. As you say, he should do the same calculations using the perspective of B and C and check that the results are consistent relative to A perspective. In addition there is a mistake on the (x,t)II,C coordinate maths, he shows x = gamma*L but it,s x = 2*gamma*L

@BD-np6bv

2 жыл бұрын

I came to the SAME conclusions. This example of A being stationary can be said that C or B are also stationary and it's the other two moving! The real answer is the acceleration part. When you accelerate near the speed of light, Einstein tell us it's the same as being close to the gravitational effects of a black hole. GRAVITY and ACCELERATION are the same! Time slows down near the gravitational effects of a black hole, which would accelerate you near the speed of light to the event horizon! That is the real answer. Dr. Lincoln is correct on many things, but he's clearly wrong on this one.

'Physics is everything', it truly is. (Edit) We shall miss you Dr Hawking. 18-03-14, a triumph we had you so long and sad loss.

@ronaldderooij1774

6 жыл бұрын

Psychology, Social sciences, consciousness anyone? That has nothig to do with physics, but is still very real.

@frankschneider6156

6 жыл бұрын

Ehm psychology is about different states of brains, which are electrical currents within a specific kind of very physical object. That's physics, but instead of trying to go the natural scientific way (like it's today done by trying to map the individual connectome), people just made up some pseudoscience and termed it "psychology". Social "sciences" are about behaviors of humans. Humans are typical animals. Biology is in principle just the result of biochemistry/molecular biology and that's just chemistry, which is in first approximation nothing else than the physics of the outer valence shell electrons. Everything is natural sciences and in the end physics. Exactly that's why social sciences have such a bad reputation among educated people. And of course because hey rely more on citation and who said what, than on observation, thus perverting the scientific method.

@tuele4302

6 жыл бұрын

Ronald de Rooij What he meant is that physics is the most fundamental of the sciences. All arrows of explanation trace back to physics.

@ahitler5592

6 жыл бұрын

Hawking is as fake as Einstein's gravity

@Crazytesseract

5 жыл бұрын

Philip Berthiaume Hawking had no true knowledge about the universe. The universe is much, much more complicated than Hawking could ever imagine. Do you know where is Hawking now?

Excellent explanation! I noticed there is a mistake for the perspective of the referential frame of observer "C" for event II, where instead of position γL should be 2γl. After struggling with the problem, I saw you already have made the correction. I think it is important to highlight that the origin of three frames started together at the event I. There is an asymmetry to explain the paradox. While observer "A" measures the difference between events in two clocks at rest where these events happened (B-A) and (C-B), each one of the observers "B" and "C" measures the interval of time on their own clocks attached with their bodies. The second intervals are proper times, related to the interval of time measured by "A" for dilation time expression: each time interval for A equals γ multiplied by each proper time interval .for B and C. If we begin with the interval measured by observer "A", we have to subtract the quantity of xv/c² for event B and add the quantity xv/c² for event C because the clocks are advanced in the direction of motion and delayed in the opposite direction by these terms according to relativity of simultaneity . After that, we have the interval of time passed in only one clock in the frame of observer "A" and we must multiply it by γ to obtain the interval for observers "B" and "C". In other words, the origin of asymmetry is the relativity of simultaneity expressed in Lorentz Transformation. Each one observer can claim the other clock is slower, and each one observer can consider moving in the direction of future of the other reference frame as expected by symmetry.

@benheideveld4617

Жыл бұрын

My conclusion from your complicated response here is that the video fails to give a clear explanation. It is completely expected that for A the first interval travelled by B from its passing by A until passing by C and subsequently the second interval travelled by C from its passing by B until its passing by A are of the same duration, namely the duration for A between B passing by A and C passing by, divided by 2γ (two gamma). This, however, does NOT explain why A cannot be seen by B to age much less.

@nadirceliloglu397

5 ай бұрын

Excellent? Are you kidding me? You are probably not a Physicist. Dialect's video is full of flaws. The presentation is excellent, not the content.

@nadirceliloglu397

5 ай бұрын

@@benheideveld4617 exactly. The video is full of flaws.

Since A, B and C were not accelerating, they were moving (parting away or coming closer) steadily with respect to one another by exactly the same amount. Since there is no "Stationary" frame of reference, all three would think that other two inertially moving persons are aging younger by exactly the same amount(e.g. 6 years). A would think B and C are younger by 6 year, B will think A and C are younger by 6 years, and C would think A an B are younger by 6 year. It is understandable why the presenter abruptly cut off the video by just mentioning: it is because to ONE frame vs TWO or THREE frames -- instead of steadfastly reasoning why A would grow older by 6 years from others perspective while others would remain younger despite same relative motion! He could have plugged numbers in those equations that are 100% same for all three and prove why just one of those three symmetrical equations would magically yield no time dilation!

Two questions then. 1) What part of the equation dealt with the delay of causality (light) it takes to get from 2l to person A? 2) You said person A only has one reference frame. However, In the twin paradox don was on a planet. Which is moving there for he also has multiple frames of reference. In fact. If everything is retaliative then counting the frames of reference is a paradox as they can be flipped. Inertia is still the only thing that separates them irrespective if you can work it out after the change in velocity or not. What have I missed? Example of my thinking based on your experiment. Let's slow things down to very (VERY) small numbers. put the two in cars going 100km/h. It was the previous acceleration that changed person c to 100km/h. So he is the one changing frames. You can see it based on the 100km/h but it's still the acceleration that caused it.

@trsomas

4 жыл бұрын

An assumption has been made that the planet is in an inertial frame. This means we assume that the proper acceleration of the planet is negligible. If you do not want to make that approximation, then instead of a planet, assume that Don stays at rest in some inertial frame of reference.

Thank you for answering my statement from your last video. You really cleared up my question of 'whom is stationary'. Absolutely BEAUTIFUL!!!

This is excellent Don. Once again you have nicely simplified what normally confuses

@nadirceliloglu397

5 ай бұрын

This is unfortunately not correct Don! You are changing the entire scenario by inteiducing a third twin,second spaceship! Also, you are removing acceleration completely. How can you? Not possible! Have you read Einstein's solutiin to the Twin Paradox as mentioned in his 1918 documents? He explicitly states that acceleration of the travelli ng twin causes non- reciprocal time dilation which makes the travell8ng twin to be younger. Easy! Also, you can easily deduce this from the worldlines of the stay at home twin and the travelling twin. Whose wordline is shorter? The travellung twin's worldline. So, he remains younger. Why are you complicating it Mr. FERMILAB? 😊

I may have missed something here, but in the (x,t) coords for event II for observers B and C there seems to be an inconsistency. Specifically, the location (x) for B is given as 0, but for C is yL (I use y for gamma so it is easier to type). It seems to me that B should be -yL. If not, then C should also be 0, not yL.

@alexotenko6597

9 ай бұрын

Although X coordinate is not used for the demonstration of the time dilation, I think it is useful to work out what happened to it. E.g C takes part in all three events, so X for it is always 0.

@SuryaPrakash-je5qo

8 ай бұрын

@@alexotenko6597 good point. why is every missing this? If i am right, then if you look at 10:14 to 10:32, those equations location are all considering "X" from A's perspective only. Then shouldn't we write equations from B's and C's perspective where X is always 0 from B's perspective and X is always 0 from C's perspective. Then no body is aging faster?

I really like how you match your t-shirts with the video content 😃😃

I have heard of the twin paradox a million times and only this video has ever made me see why it is both a paradox and not one. I don't think that has ever been properly explained to me before. Thank you.

@chrlpolk

Жыл бұрын

The real paradox is in the speed of light, which remains constant regardless of frame. Those within a gravitational field, and those outside, will both experience light at the same speed. Therefore, light is simultaneously traveling in multiple speeds according to multiple timeframes, all of which experience light moving at the constant speed according to their timeframe!

A crucial point in the derivation is that the vx/c2 term in the Lorentz transformation expresses the effect of relativity of simultaneity. In C's frame of reference, the now-slice (the space-time points corresponding to t_C=0) is tilted such that it intercepts A's position at a *future* moment. A sees B's and C's clock time dilated by the same gamma factor as B and C see A's clock (total symmetry here), but when C starts moving towards A, C's "now" already corresponds to A's future (which is only possible when you compare times at different locations, a point Don Lincoln mentioned). That's why A sees more time passing as C crosses A than it took B to meet C halfway and C to reach A.

That doesn't make any sense. Although I'm willing to admit to being wrong, all observers should exist for everyone else and everyone can measure everyone moving. I'm willing to admit to not getting it, but it doesn't prove it to me. Maybe it's because I'm a humanities guy.

@alexvolkov223

6 жыл бұрын

Can you explain what you mean by the second sentence? I don't quite understand what it is that you don't understand, otherwise I can try to help out.

@trsomas

4 жыл бұрын

One person stays in the same inertial frame of reference throughout and the other shifts from one inertial frame to another. kzread.info/dash/bejne/fIR3pq2tkZWyhqg.html

@xwarslayerx

4 жыл бұрын

@@trsomas I'm a believer that time is a universal constant. Who cares what speed or acceleration you are at.... A lightyear still takes you a year to travel at lightspeed...

@xwarslayerx

4 жыл бұрын

And don't get me started on the "observer" bullshit. They see light at light speed. I believe that relativity is something people got confused into believing because of all the variables and confusing names for variables like "light-year". It's a measurement of DISTANCE. It's how far light gets after 1 year of traveling. In all these experiments, they treat travelling a light year at light-speed like it's instantaneous. STILL TAKES A FUCKN YEAR.

@Catmomila

4 жыл бұрын

@@xwarslayerx You don't really know what you're talking about, sorry.

The end of the video was the most critical part to helping people understand why the twin paradox is not a paradox. In my opinion, you failed that task. You hinted at the answer, but you did not clearly spell it out for people who do not understand. (Also, as I understand it, you synthetically created a jump discontinuity, which is equivalent to an "instantaneous" "infinite" acceleration. If true, the example fails to illustrate your point.) At any rate, the animations and video editing were boss.

@parityviolation968

5 жыл бұрын

glad, I'm not the only one to recognize this... Sometimes he prolongs certain passages unnecessarily, almost putting the audience to sleep, and then when the final conclusion is due, he just leaves it up to the listener to spell it out in their minds... His pedagogical style is as discontinuous as his frame jumping that supposedly got rid of "acceleration" / change in direction issues. (which it didn't)

@maythesciencebewithyou

5 жыл бұрын

That's like almost every Physics lecture, starts slow, expands on the simple stuff, and then brushes over the difficult part before you realize it.

@KevinS47

5 жыл бұрын

James Wilson SOOO?? Why the heck wouldn’t you explain it if you understand it so well????! You take the time to write all that (which was a little unncessary considering that you first phrase was enough) and you don’t even explain what that hint means?!? So why even bother stating all that? What’s your line of reasoning? It seems to me as if you are not using your head at all.

@RME76048

5 жыл бұрын

"jump discontinuity"? What is that, and How? Where? Seems to me that B was in constant motion towards +v and C was in constant motion towards -v. All they did was pass information. How is that a "jump discontinuity"?

@omarcarrero3623

5 жыл бұрын

B, and C were already moving, dont think they stoped and accelerated, just that they passed the info every intersection

I agree with all comments about how the crucial thing was done with in 10 secs. A full video about that would be more than motivated. I am very fond of all the Fermi lab videos including this one. I have tried so hard to understand this. Here is a triplet scenario A, B and C sit in a rocket each. At some moment B and C sets of to Alpha Centurion at 0.999c. At Alpha Centurion C accelerates backwards and stops on the planet. A calculates a lower timespeed for B & C when they set of. B calculates a lower timespeed for C than his own at Alpha Centurion. Since A and C are at constant distance A = C (timespeeds) but at the same time A > B > C. Please help.

@jonathanbyers791

8 ай бұрын

By Accelerates backwards, do you mean Decelerate? What does timespeed mean? If A, B, C are people what does A>B>C Mean?

Some stuff are real hard to grasp yet i'm always coming backs for this guy because the way he speaks is just soothing enough to calm the anxiety i get from not understanding shit.

I sort of "get" this, but I also agree with brixomatic about "long introduction" and "bit too short with the conclusion". Do another video please to follow up this one! Three specific comments on this video: (1) I would like to see some sort of comparison of what each of the observers (A, B and C) experience, as I would like to see everything being consistent for observers when they are momentarily at the same point, 1 and 2. (2)I am slightly concerned about how the points 1, 2 and 3 are observed by ANY observer. Is it required that there is a NOW point for 1, 2 and 3 (in at least some observers view) when this all starts? Perhaps, if so, the NOW, or "start time" at 1, 2 and 3 can be called by "you", the passive 4th observer of this situation, in the same inertial frame as 1, 2 and 3. However, for that to be the case 1, 2 and 3 would have to be equidistant from you - and that puts them on a spherical surface. That means that B and C are accelerating when they are moving! (Although I can see the "local" time at location 2 could be irrelevant, in which case it can be on a straight line between 1 and 3.) (3)This video explanation shows that acceleration is not required to resolve the theoretical paradox but it does not mention any additional effect that acceleration might have should it occur. In a real twin paradox experiment, acceleration would have to occur. And, since acceleration is equivalent to a gravitational field (in which clocks run slow), additional effects of acceleration in a real situation should at least get a mention in this video.

This has generated a massive amount of confusion. I think you need to use space-time diagrams.

@Paolo_De_Leva

6 жыл бұрын

Right. Also, the only way for Ron to switch from frame B to frame C (when they meet at position 2) is by experiencing acceleration... and if I neglected that idea, I would be entitled to apply the same argument to the motion of Don relative to Ron (rather than the motion of Ron relative to Don), and I would reach exactly the opposite conclusion, using the same formulas.

@marianskodowski8337

6 жыл бұрын

It is funny how the Einsteinists - the paradox "explanators" bring the human fillings into consideration. Now you have to fill the acceleration - this switches you from frame to another frame, you are only stationary when you don't fill acceleration :) Where it is in Einstein's equations?This is why the theory is crap.

@onehitpick9758

6 жыл бұрын

The theory is definitely not crap, because it is used it many, many times to explain real observations to high degree of precision, where classical kinematics has failed completely. It is not intuitive, and not even required at low relative speeds, so you should be good to go in most of the experiences that we, as humans, deal with..

@mr.h4267

4 жыл бұрын

@@marianskodowski8337 Acceleration is dealt with in general relativity.

@ricomartinez458

4 жыл бұрын

I have watched many of his videos and have to say that this guy really doesn't know how to explain it in a simple way. He unnecessarily makes things complicated. As albert einstein said "if you can't explain it simply, you don't understand well enough". I would recommend listening to "Physics girl", she explains 10 times better than him and gives crystal clear explanations

I don't get how is it possible that we have one non-moving observer and two moving observers. Aren't all observers non-moving (according to themselves, of course) by definition? Considering B and C as moving isn't in fact still viewing the situation only from A's perspective? And how is it justified, considering that we have to prove that «Ron is younger» with every system of reference? So, for A, the velocities of A, B and C are: 0, v, -v; for B, they are: -v, 0, -2v; and for C: v, 2v, 0. Therefore, the order of the magnitude also changes: A: a

@silverrahul

10 ай бұрын

" _Considering B and C as moving isn't in fact still viewing the situation only from A's perspective? And how is it justified, considering that we have to prove that «Ron is younger» with every system of reference_ " He calculates the space and time coordinates of those events using A's perspective and then uses lorentz transforms to calculcate the coordinates for those events in B and C's perspectives. " So, for A, the velocities of A, B and C are: 0, v, -v; for B, they are: -v, 0, -2v; and for C: v, 2v, 0. " these are not correct. You are using newtonian velocity addition. You have to use relativistic velocity addition.

THANK YOU! I'm so glad that someone finally stated this clearly. I've heard SO MANY people who do not really understand the "Paradox" part of this whole thing. It took me a while to understand it myself because of the horrible explanations that have been given...

@mrboombastic8369

Жыл бұрын

I don't think this explanation serves because seriouslly all that math just enrolls on the starter problem. Because you can do that math all the way around, because if you assume that Observer C is the stationary element than it will be A to move towards the C. The stationary/moving argument just works if you take some reference in consideration. Because all the objects in the Universe are moving and stationary at the same time dependkng on the reference. What if the Observers A and B started at location 2 and went opposite directions and came back? Wich would return younger? All that math doesn't make sense to me.

@MrCmon113

10 ай бұрын

@@mrboombastic8369 All of his math is completely irrelevant, because he chose to replace one of the twins with two spaceships going in opposite directions. Why not the other one? It completely begs the question.

The original version of the experiment involves only 2 observers, in the explanation it involves 3 observers. Observers B and C see a shorter distance due to Lorentz contraction of length. But for the original version of the paradox, Ron and Don started and ended in the same inertial frame (one can forget about the earth which confuses the issue as it creates a non-inertial frame), it seems that the explanation does not deal with the original paradox. (Sorry, I am not a professional physicist.)

@Arkalius80

6 жыл бұрын

You're right, but the purpose of this scenario is to show how the result of the original scenario can be replicated without relying on acceleration. The point is that while acceleration is a relevant detail in the solution to the twin paradox, it is not the proximal cause of the differential aging.

@saxtant

4 ай бұрын

@@Arkalius80 Acceleration is the primary cause of the ageing though, since the special relativistic component only deals with the perception of time from a distance of objects at different velocity, not the fundamental nature of matter being energy in motion, which is general relativity, this problem is asking the question why are they different ages upon being reunited, which turns out to be how many relativistic rotations they ended up making and why they are different. Turns out the simple point is that matter is only in motion in relation to it's inertia, which is not a euclidean frame, it's actually represented by a matter distribution surrounding an object, using Newton's every action has an equal and opposite reaction, the sum of action and it's inertia are zero. In relativity, even the frame is projected at the speed of light, because no causal influence can happen without time, it takes time to project the frame and so an object's inertia is more influenced by matter that is closer to it. The twin paradox is dealing with the matter ageing differently when an object is accelerating in relation to it's own surrounding inertia, it experiences slower time because the electrons spinning inside the accelerated matter are limited to travel no faster than light speed, the matter slows it's internal rotations compared to the matter that makes up it's inertia. The twin paradox is all to do with it being matter that is ageing differently and general relativity solves it, special relativity is going to have to resolve crossed frames to assign a rest point and then ask relevant questions only, since asking a question must have an observer. It's a general relativity problem, like solving kinetic motion using energy equations, using special relativistic time dilation and length contraction only explain appearances from different perspectives, it doesn't deal with root of the question.

Splitting Ron into B and C to get rid of accellerations could have been mentioned more explicitly, Still a neat explanation!

As a retired engineer and a wantabe physicist I love watching these videos. As a engineer I was typically assigned tasks that ultimately required a number. And if I was lucky I would find an equation (generated by some one much smarter than myself) that I could use to produce that number. So I am not sure why Dr Lincoln is reluctant to show equations. I am going to try and work through the math for this twin paradox. It might be nice if Dr. Lincoln worked a few specific examples or perhaps pose problem and for us to solve and give the answer in the next video.

Thanks for doing another video explaining it with more detail.

Gonna have to study this video for a while, but gaining clarity about the "paradox" will be more than worth the effort! Thanks, Don!!!

@a.b.5772

6 жыл бұрын

If you haven't seen the videos (4) he references to preface this one, I recommend them like he does. They give the proper background to explain the problem he poses here . Plus you get to see him rollen past the haters in a sweet Corvette.

@schweinehundbullshit9176

Жыл бұрын

I am not so sure.

Nice video, but it seems that the resolution of this paradox still requires acceleration. Without acceleration, each twin will perceive the other as younger; the resolution requires a real comparison, and you at least need one of them to accelerate to the frame of the other in order to do that - no matter how many twins you have.

The youtube series of Fermilab is by far the best I've ever seen among popular physics explanations. But I'm still trying to wrap my head around this one. If I understand it at least partially, then the apparent paradox from the original 'twin paradox' (with Ron and Don) stems from the fact that Ron _returns_ to Don and thus to Don's reference frame. Is this correct? Would thus the following be correct: Let's say, instead of Ron _returning_ to Earth, Don _follows_ Ron to Alpha Centauri. That is, once Ron reaches Alpha Centauri, Don starts from Earth and upon reuniting with his twin, they find out that now _Don_ is the younger one. (Though maybe that is problematic to say: what would "once Ron reaches Alpha Centauri" mean in this context from Don's perspective?)

@nadirceliloglu397

7 ай бұрын

I disagree. It is not the best as it provides incomplete and wrong interpretations which does not agree with Physics. Take the twin Paradox for example.

You are a great video personality mr Lincoln. Keep these videos coming please!!!!!!!!!!

I’d like to see you do a video that incorporates the apparent simultaneity into resolving this paradox. As you change frames of reference, what is considered “now” changes. In imagining how the two twins perceive the flow of time, it’s like when the moving twin turns around, his “now” for the other twin changes. At a constant velocity, both would see their own “now” going further into the other’s past. When the one turns around the frame of reference changes so much that the moving twin see’s the apparent “now” jump so far into the other’s future that he can still see the other aging slower with time dilation during the entire trip, but arrives back home finding the stationary twin has aged considerably more than himself. Like Brian Greene talks about “now slices” in this clip: kzread.info/dash/bejne/f4OTs8GfYbrNgaw.html

@jonathanbyers791

8 ай бұрын

I don't get this, 'In imagining how the two twins perceive the flow of time' what do you mean by this? And what is 'now' ? You can only have the same now if together, otherwise I'm not sure what you mean by 'now'? I have seen other people talk about 'now' in Relativity related scenarios, but don't grasp it, because 'now' is only relevant to me now, or to someone else, somewhere else, which is somewhen else (not local). They are not linked, unless very local like a telephone call.

@kemptonka

8 ай бұрын

@@jonathanbyers791 It's like trying to keep a clock that shows your own time, and one that will show the other's time and match their clock when you get back together. You can send messages between each other to keep up to date. But if the message came from a light year away, it makes a big difference if your inertial frame of reference is moving toward them, or away from them. That inertial frame has been moving in that direction at a constant velocity for a whole year since the message was sent. www.staskoagency.com/wp-content/uploads/2016/12/b8258-oldnewsroom.jpeg

I found both of Dr. Lincoln’s clips on this subject helpful. His thought experiment is not quite the same as the traveling twins thought experiment, but his experiment is successful in its own right in showing that acceleration is not key to resolving the twins paradox. For me, the essential point is this. The experiences of the two twins are not equivalent, because one involves motion of the twin with respect to his cosmic (space time) background, and the other does not. You can argue that, from his point of view, the spaceship twin has remained motionless while the Earth, and indeed the entire cosmos surrounding the Earth, have rushed away and back again. But in that scenario, from the point of view of the spaceship twin, the earthbound twin is moving along with his cosmic background; he is not moving WITHIN it. In contrast, from the point of view of the earthbound twin, the spaceship twin is moving within his cosmic background, with corresponding time dilation effects. That, I think, is the essential point. The seeming “paradox” arises because it is difficult for us to set up and explain the different frames of reference involved and how they relate to each other.

@ernestschoenmakers8181

Жыл бұрын

Like i'm driving in my car and all of a sudden i slam the brakes then i see the car in front of me accelerate away from me and the harder i slam the brakes the harder the car in front of me accelerates away from me. But of course the other car can say the same about me but it was really me slamming the brakes so there's no paradox.

@SpongeWorthy76

Жыл бұрын

@@ernestschoenmakers8181 you've described an (de)acceleration scenario

@ernestschoenmakers8181

Жыл бұрын

@@SpongeWorthy76 Yeah but it's a bit the same idea, i was decellerating not the car in front of me who was just driving at a constant speed wrt the road.

@russellstephan6844

Жыл бұрын

Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice. On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy. Brian Greene has a marvelous "now" timeslice visual: kzread.info/dash/bejne/m5in2Ztyg7bde8Y.html

I would have liked you to have spoken about the time gravity relationship, and that position and velocity can be seen as being relative to centres of gravity, such as stars and planets at this level. Any chance of a video on this?

Nice! I've heard the acceleration explanation many times.

@thedeemon

6 жыл бұрын

It's not that wrong if you remember that in special relativity acceleration means change of reference frame. And in general relativity you can describe the same experiment without changing reference frames, just using acceleration and gravitational time dilation. Those are just different approaches to describe the same thing.

PhysicsGirl also has a great video about it, which is less deep, but more understandable for casuals.

@juzoli

6 жыл бұрын

I mean it is not accurate, but it definitely helps if we understand that one, before listening to this one.

@DanielNogueiraLeitao

6 жыл бұрын

The problem is PhysicsGirl attributes time dilation to acceleration, whereas this video says it has nothing to do with it.

@ChenfengBao

6 жыл бұрын

+Daniel Nogueira Leitão This video is wrong in saying the twin paradox has nothing to do with acceleration, although its own explanation itself isn't wrong. Just different semantics, different emphasis.

@rsm3t

2 жыл бұрын

@@DanielNogueiraLeitao She says that you cannot treat an inertial frame the same as a non-inertial frame. The "paradox" arises when the same treatment is applied to both frames. That's not a causal attribution. It's a statement about the proper mathematics needed to compare the intervals traversed by the two paths connecting the two events. They will not be equal in the general case, and in particular, cannot be equal when one is a unique geodesic and the other is not a geodesic.

It appears it wasnt just me left thinking 'but... acceleration is what changes your reference frame. So isnt this rather semantic?' but Im inclined to believe that when an experts explanation doesnt add up to me that I must be missing something. So I was considering the scenario of the twins being in a small spherical universe where one starts off and arrives back by going all the way round that universe without accelerating. Im not sure how difficult a problem that would be to solve, if it needs some heady general relativity or not, but perhaps in this case and other parts of general relativity it could make for a more substantive distinction between the two ways of thinking about this? Edit: I wouldnt mind hearing other possible suggestions. I have to say Im kind of confused by what incite hes really getting at here.

@trsomas

4 жыл бұрын

Yes acceleration changes reference frame but the way some KZread videos give explanation based on acceleration is wrong. They say that the travelling twin is accelerating, so his clock will tick slower. The correct way is to use general theory of relativity from travelling twin's frame of reference and argue that the stationary twin's clock will tick faster. See this video for more detail. kzread.info/dash/bejne/fIR3pq2tkZWyhqg.html

@trsomas

4 жыл бұрын

However, the problem can be resolved without considering the value of acceleration and simply by using special theory of relativity.

@abdullahbinjahed6900

4 жыл бұрын

@@trsomas that's what i want to know .... acceleration doesn't solve the Paradox

@trsomas

4 жыл бұрын

​@@abdullahbinjahed6900 According to the paradox, if we use time dilation from A's frame, we find B is younger and if we use time dilation in B's frame, we find A is younger. We should be able to resolve the paradox by pointing out where time dilation has been used wrongly in the paradox. The answer is that the astronaut uses time dilation formula form two different inertial frames and he does not account for changing from one inertial frame to another. This is where time dilation has been used wrongly in the paradox. Acceleration only serves the purpose of changing the inertial frame of reference.

@abdullahbinjahed6900

4 жыл бұрын

@@trsomas say ... a round universe with nothing in it ... now you and me popped up in existence and travel in different directions at a constant velocity ... because the universe is round we will meet again without even changing our direction ... so ... now tell me ... what's the solution ?

I am grateful for these clear and sure explanations.

Good explanation. Some side notes: If observer A is truly stationary, the observers B and C clocks will show the same interval times. However, if A is moving, then the intervals shown on observer B & C clocks will be different by an amount dependent on the absolute speed of A. This provides a theoretical means of determining absolute velocity for any observer. This too shows there is no paradox. While each observer has a self-consistent relativistic frame of reference and can locally consider that he is stationary within that frame of reference, comparing the clock intervals from A, B, & C can reveal which one is moving slowest, or not at all, from a hypothetical absolute frame of “stationary”. Of course, the precision of the clocks and measured speeds would be essential to determining that “absolute” reference frame with precision.

@silverrahul

Жыл бұрын

what do you mean by the absolute reference frame ?

This was a bid hard to understand. The best explanation I ever heard was in the video "Raumzeitdiagramme und Zwillingsparadoxon • Aristoteles ⯈ Stringtheorie (16) | Josef M. Gaßner" (german) using Minkowski diagrams. Especially about the 26:00 mark was the breakthrough for me. Its totally obvious seeing this. Good video however, as always :)

@thstroyur

6 жыл бұрын

Also MP, and das Wiki :D

How do you get them (A,B,C) to all start stopwatches at the same time?

@wr2382

5 жыл бұрын

Easy. 1. Put a light at the mid-point. 2. Turn the light on. 3. A, B and C start their stopwatches when the light reaches them.

@FaelCacilhas

5 жыл бұрын

If you do this then B will start his watch L/c seconds before the others, since he IS at midpoint.

@The_Sandcrawler

5 жыл бұрын

Rafael Cacilhas No, because B started at position 1, where A is. The light would be coming from the midpoint, position 2, and reach position 1, where A and B are, and position 3, where C is, at the same time, signaling person B at position 1, and person C at position 3, to start moving, while person A remains at position 1.

@hanxhancocks1727

5 жыл бұрын

Quantum Telepathy...

@WeAreShowboat

10 ай бұрын

⁠@@wr2382No this doesn’t work. Person A and person C will not agree that they started their clocks at the same moment. Their reference frames are different and clocks will not be synchronized with each other and would claim the other person started their clock at the wrong moment. I mean also, person C will get the light before person A since person C is going to meet the light partway (according to the view that person A is at rest).

That was great! Thanks, Also thanks for including the equations. That helped.

This is an excellent video. I am 71 and could follow every step of the way. I checked all the co-ordinates for the there event for the three observers and they were bang on. This sort of thing should be taught at A level physics or maths. Relativity is a fascinating subject. How about a lucid lecture on General Relativity? I note that many still don't get the message that acceleration is not the cause of the paradox. Think of it this way if acceleration were the cause then the duration of the trip would have no bearing on their relative ageing processes.

@firdacz

5 жыл бұрын

But I still believe acceleration is the cause, because the perception of WHEN the twin launched from earth changes rapidly during the acceleration. If acceleration was not the correct answer then why you could not use B+C frames to create paradox? You could and you would have a paradox again. You cannot switch frames like that because you would have to transform the whole scenery the same way acceleration does.

@roblouw1344

4 жыл бұрын

@@firdacz Acceleration cannot possibly be the explanation. If the journey distance were doubled then by implication if acceleration were the explanation the time dilation would be identical to the original journey. This is not the case. The longer the journey the greater the time difference would be. There would be no additional acceleration needed to travel the extra distance.

A perfectly symmetric scenario is described? B and C are absolutely symmetric. That being said, I understand it all and it doesn't resolve the twin paradox. You have to incorporate the asymmetry, and it is due to acceleration. Acceleration is outside the scope of special relativity and violates the assumptions of both SR and the Lorentz transformations. The twin that experiences acceleration is not even remotely allowed to say she's stationary within the context of SR or Lorentz. This is a part of the assumptions of the theory. You can pseudo-analyze non-inertial frames within the context of SR, but it is a logical violation of assumption. I of course follow your arguments, but they are mathematically, formally inconsistent when applied to the departing and returning twin. A better resolution is required. In the purely SR case, "outliving your enemies" can be achieved by relative velocity, but you have to have differential acceleration to get there and back. There is no denying that. To say that it is all velocity is denying the derivative. All things considered, this is an excellent video and among the best presentations on this topic I've seen. The bottom line is that if a departing and returning traveler and twin experience different accelerations, they will have different times upon reuniting. If they experience identical accelerations, well, they will have identical times. This post will likely be deleted by remote observer with faster clock, but I encourage you to read before.

@karejonsson8264

5 жыл бұрын

If acceleration was the thing the duration of the flight would not matter but thats incorrect.

@pavelmalena1154

5 жыл бұрын

yes, inconsistent, that's the word. the setup is fundamentally different from the twin paradox experiment, it's a different scenario. any proof that the result can be applied to the twin paradox??

@alanjones4358

5 жыл бұрын

@@karejonsson8264 The "gravitational" time dilation due to acceleration is a factor of the distance between the clocks, which indirectly depends on the duration.

How do they synchronize to start moving at the same time? Send a lightbeam as signal?

@Ranoake

6 жыл бұрын

It doesn't matter. It is a thought experiment. It would be hard to organize, but theoretically possible and hence the math can just be applied.

@pavelmalena1154

5 жыл бұрын

indeed, no need for that. that would drown us in the complications of simultaneity. they actually don't start moving because they move eternally, no acceleration allowed. you can imagine that there's an infinite stream of travellers C and this experiment looks at the one guy who meets traveller B at the middle point #2.

@ericl8743

5 жыл бұрын

Yes with a light signal. If you look at a spacetime diagram, light will always move at a 45 degree angle regardless of the speed of the other reference frame. So you can send a light signal to another observer and he starts his clock when the light signal hits him. It's reflected off a surface and send back to the original observer. If you take the total time elapsed for the first observer and divide it by two, you know how long it took for the light to reach the second observer so you then how much to delay your clock for proper calibration

Wow, Dr. L! That was brilliantly explained

Awesome video and explanation. Like always.., Thank you!

(1) I thought an event was a point in spacetime. But your Event I for A and B is located at a different point in space than Event I for C. (2) If instead of a thought experiment you tried to carry out this experiment for real, how would you do it without accelerations? How do B and C reach v and -v in the first place. (3) It is a paradox. It's not a contradiction. It has a rational explanation. But it is still paradoxical. (4) The maths works out, but you are still not explaining what it is that causes the aging of one twin to slow down. I'm still left with the suspicion that the initial acceleration shifts the travelling twin into another timeframe. I'm not saying that the dilation occurs during the acceleration, but without any acceleration there would be no time dilation. From this it seems to follow that acceleration is central to the effect.

@thedeemon

6 жыл бұрын

Coordinates are just labels, like address of a house. Different frames of reference can assign different coordinates to the same point in spacetime. For observer A his position has coordinate 0 and C has coordinate 2L. For C it's different, C is at 0 and A is at -2L. Different frames of reference assign different coordinates.

@maulikparekh776

5 жыл бұрын

@@thedeemon but then event 2 for A would also be 0 (we took it L). An event is a specific set of 4 coordinates, so event 1 should be at (0,0,0,0) for A's and B's frames and (L',0,0,0) for C's frame

@pavelmalena1154

5 жыл бұрын

excellent comments Brendan! ad 2 and 1: I'd do no synced start, just the encounters must happen in the order AB then BC then CA. The velocity is gained and settled before the encounters, so B and C appear as flying eternally. However, C must now additionaly note down also the coordinate of the encounter with A, not just A's clock, which might mean an equal complication so I'm affraid that I'm just shifting the difficulty around. Regarding your point 4, yes, I'm totally with you: if switching the frame on the turn-arround (emulated here by the BC encounter) causes a jump in simultaneity then why not the departure/arrival switches?! My explanation is that the the switch happens when the twins are at the same spot so no alternate simultaneity is possible. And here the SR reasoning departs from the reality because if the realistic acceleration happens over some time interval it also happens along a certain spatial interval, twins not at the same spot anymore - and here the expected shifts in simultaneity can already occur.

Ohhh no, I did not understand the point with the 2 frames .. and that was key... :-(

Thanks for the celar di planation! You solved a problem i had! In the referente of the moving twin is the stationary twin that accelerates! So i didn’t get a difference between the two!

Genuine explanation! Your guidance saved me a lot of hours thinking :-) One remark, typo?: I think the basic form of the Lorentz transformations should be with "minus".

Interestingly enough, Einstein himself stated that the acceleration was the only possible explanation. Which of course it is. It's a lot easier to think about this if you start with the twins on board two different spaceships (rather than one being on the earth, which tends to make people automatically think of it as "immobile" while the spaceship is "moving" - but why?). It is impossible in special relativity to get rid of the symmetry issue the two reference frames, because it only deals with inertial (that is, non-accelerated) frames. Acceleration is what makes the difference. Just like Einstein said.

@Arkalius80

6 жыл бұрын

Acceleration is the cause of the fact that one twin is stationary in two different inertial frames while the other only in one. The acceleration isn't the proximal cause, the different reference frames is. So it is correct to say the acceleration is important, but to focus too strongly on it would be misleading, suggesting that acceleration is necessary to produce this kind of result in general.

@trsomas

4 жыл бұрын

We can explain using acceleration also. We use general theory of relativity in travelling observer's frame of reference and argue that the stationary observer's clock will be faster. But it is possible to resolve the paradox purely by using special theory of relativity. kzread.info/dash/bejne/fIR3pq2tkZWyhqg.html

@russellstephan6844

Жыл бұрын

Acceleration is still necessary... Acceleration alters the angle of the "now" timeslice. On a typical space time diagram where time is the X-axis and all three dimensions of space are combined into the y-axis, acceleration causes the "now" time slice line to slope negatively. The alteration of that slope is what causes the local clock discrepancy. Brian Greene has a marvelous "now" timeslice visual: kzread.info/dash/bejne/m5in2Ztyg7bde8Y.html

You are only talking about Special Relativity. Relative acceleration does play a role in General Relativity, where a single non-inertial reference frame is allowed for the spaceship’s entire journey. The person in the spaceship can believe that he is standing still by believing that there is a gravitational field present throughout all of space, and that gravitational time dilation is what causes him to be older than his twin.

@fakherhalim

6 жыл бұрын

I agree. Pure Inertial frames are too simplistic subsets of reality!

@vacuumdiagrams652

6 жыл бұрын

Well, if the acceleration is only about 1 g, the time dilation due to acceleration will be tiny---it would be comparable to the time dilation we experience by sitting on the Earth, which is not much! So GR adds some (very small) correction, but doesn't change the main picture.

@jmckaskle

6 жыл бұрын

The issue with using general relativity is that spacetime does not curve due to acceleration, and so gravitational time dilation is not a factor in the paradox.

@airplayrule

6 жыл бұрын

stecordas uh....isn't it impossible for an occupant to determine the difference between acceleration and gravity? who says BOTH don't cause curving of spacetime?

@eriknicholas7294

5 жыл бұрын

AirPlayRule For the same reason centrifugal force is not a real force; apparent force is an illusion of your finite senses. The universe doesn't care what your brain is falsely interpreting, it cares what your bundle of atoms are actually doing in -dimensional spacetime.

Thank you, and very well diagrammed and explained as usual. I guess the hardest part would be physically setting up the experiment.

Watching 5 years later. Thank you Dr. Lincoln

"I'll pause for a moment so you can look at them..." LOLOLOLOL!!!

Ron needs to fly 8 lightyears and it will take him 4 months. Does he need 8 years worth of fuel on the spaceship or 4 months?

@SerenityReceiver

6 жыл бұрын

Time is the same for him as for his fuel (so: 4 months). But: To get to his speed he needs a lot of energy to accelerate. Once his velocity near c is reached, I assume his fuel-cost-efficiency is pretty neat, if he never wants to stop again.

@pavelmalena1154

5 жыл бұрын

no fuel needed, Ron does not accelerate in this experiment! Instead, Ron got schizophrenic, he's now Ron b and Ron c, new approach to interstellar travels, you become two (sorry I'm being sarcastic at the faulty setup of the experiment)

@mr.h4267

4 жыл бұрын

Good question. He'll need enough fuel to accelerate to .99c, then to decelerate to go around alpha centauri, then to accelerate back up to .99c again, and then finally to decelerate to 0 back at earth. He wouldn't use any fuel during the parts of the trip at constant speed. So, no idea...

@allahspreadshate6486

4 жыл бұрын

I'm not sure if you meant to, but you've stumbled across a VERY interesting 'philosophical' question. :D

@caccioman

4 жыл бұрын

Lets give it a twist: does he need oxygen and food supply for 4 months or 8 years? I think its for 8 years, but I might be wrong

I literally understanding your each concept you are explaining even when i explain what u had explained in your video in schl teachers also not believe that how i know this as this is far high concept according to my age sir.........you are best.🌼🌼🌼🌼

To Dr. Don Lincoln and Fermilab: I like that you have experimented with a changed scenario to try to finally end the twin paradox of the special theory of relativity. But I got completely lost at the end of the video. I think that such an important theory experiment should be well worth the added time to end the video with a detailed explanation. My theory, matter theory, explains the same observables as the special theory of relativity, but differently, and without any paradoxes. If you are interested, you can view my video, “You’ve Learned Relativity Theory”, which challenges anyone’s understanding of relativity theory. I am curious to learn what you think of this video. You can find my videos using the search keywords: matter theory marostica.

I have a notepad full of scribbles which give a very impressive look to my total failure to perform the transformation. I'm not even sure how the additional reference frame solves the paradox. Still, there's nothing better than having something you firmly believed shown to be completely wrong and I'm not beaten yet. Back to my scribbling I go...

@davidmurphy563

6 жыл бұрын

So A's perspective is good old Galileo: Ai. x=0, t=0 Aii. x=L, t=L/v Aiii. x=0, t=2L/v Let's focus on the spacial transformation and employ x2=y(x1 + vt1) Bi. x= It's very obvious B is where the event is happening so x=0 from his perspective. So the maths should be easy and we can confirm we get the right number. We need the x transformation: x2=y(0 + v*0) Great, we get x=0. Quick check for t: t2 = y(t1 + v/c^2 * x1) so y(0 + v/v^2 * 0) = 0. Ok good, zero again. Bi. x=0, t=0 For Bii, the right answer is also obvious but let's do it. First question, it's t1 (so A's then and t=L/v) but whose v?? Is it from A's perspective (so positive) or B's (negative)? It must be A's because the whole point is to calculate B's from A's. Second question, is x1 A's perspective on its own distance to the event or A's perspective on B's distance? I'll try the former: x2 = y(L + v*L/v) so yL. That is not zero. The latter then: x means A's opinion on the distance between B and the event. Jesus... ok. y(0 + v * 1/v) so y(0 + 0). Mmm. I'm getting zero but I'm not convinced. Let's skip ahead to the end to x on the third event for C which isn't zero: Ciii. x=y(2 + v*2/v)=y(2L) - is that the same as your answer 2yL?? I have no idea... I wish I had a working example with velocities and times to check my answers... I have no idea if I'm doing it completely wrong or if these are valid answers... Given this, I think the latter isn't the likeliest option! If anyone wishes to point out my abject stupidity then I'd be grateful!! :-)

@avaescaner

6 жыл бұрын

I got lost at the same place, this guy does not explain or defines half of the things he writes, it is very hard to follow him and understand what he tries to say. I assume constant V (capital) is the speed to the right and -V the speed to the left for the guys in the example. In the Lorenz transformations, there is a lowercase v, which is a variable. For case II, you have as seen from A (x,t) = (L, L/V). So when you replace in the Lorenz transform for the position, you get: x' = gamma (L + v * L/V). Then what is v in this formula? I guess it is the speed of A seen from B, because that is what matches his result: x' = gamma (L + -V*L/V) = gamma (L-L) = gamma * 0 = 0. An then for the Lorenz transformation for time: t' = gamma ( L/V + -V*L/c^2) = L * gamma * (1/V - V/c^2) = > (multiplying by V on both sides) => t'*V = L * gamma * (1/V - V/c^2) * V = L * gamma * (V/V - V^2/c^2) = L * gamma (1 - v^2/c^2) = (hmmm that looks familiar!) = L * gamma / gamma^2 = L/gamma => t' = L/(V * gamma). Oh crap, I just got this one trying to show where I got stuck, I promise! :)

@Reddles37

6 жыл бұрын

For some reason he actually has the inverse Lorentz boost written in the video, which means you need the velocity from B's perspective (negative for B, positive for C). Normally the Lorentz boost is written from A's perspective and the equations have negative signs. There also appears to be a typo in the results, for Cii it should be x = 2 * γ * L I hope that helps.

Help from a physicist please: Don says that there is no acceleration in the case of the twin paradox - but isn't the transition from one reference frame to another what acceleration is? Where am I going wrong here?

@theophilus749

6 жыл бұрын

Don's example still confuses me (though it is new to me, I must confess). In the twins case, the two twins A & B part company then rejoin.

@thstroyur

6 жыл бұрын

+Theo Philus Yer not wrong: describing the motion via 'clock swapping' still requires gluing together different inertial frames comoving with actual observers - i.e., acceleration

@socalfan3268

6 жыл бұрын

"His example shows that the acceleration isn't relevant" But, by definition, the twin paradox REQUIRES that Observer B travel to Alpha Centauri AND return. The ONLY way Observer B can return is by transitioning to Observer C's reference frame at Alpha Centauri. And the ONLY way Observer B can do this is by accelerating from v to -v at Alpha Centauri. Without this acceleration, Observer B continues to travel away from Observer A so (1) there is no twin paradox, and (2) the thought experiment is only 2 separate examples of time dilation added together. The twin paradox requires that the twins MEET in the future to compare ages side by side. Bottom line: 2 twins start and end in the same place. Which twin is younger? The twin who traveled and who experienced the acceleration.

@vampyricon7026

6 жыл бұрын

ScienceNinjaDude But can't we set the rocket person as the stationary frame and say Earth is the frame that's moving out and back? That's using the same treatment with two different frames for the Earth "frame". I guess what I'm trying to say is, why is the rocket the one with 2 frames? Why isn't Earth the one with two frames?

@ChenfengBao

6 жыл бұрын

I agree. Whether it's "acceleration" or "frame jumping" is just a semantic difference. I don't find any deep meaningful difference between the two explanations. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any people with any relevant credential claiming this. Credential: PhD student in physics.

Big thanks to dr. Lincoln for another great video, especially about relativity which I'm trying to understand myself, twin paradox in particular. I understood everything in this video, except for why A was in one referance frame, and B and C in two frames? What were the 2 frames? I understand there are 3 referance frames from the perspective of A, B and C

@ciprianstanescu

6 жыл бұрын

Of course all 3 frames are distinct. What do you mean by changing reference frame?

@fakherhalim

6 жыл бұрын

Dr. Lincoln thinks that from B and C's perspective A is not moving, and hence he is not growing younger!

@RoboBoddicker

6 жыл бұрын

B&C both agree that A is in the same frame (ie A is traveling at velocity v with respect to both B & C). Whereas, B has velocity v with respect to A and velocity 2v with respect to C. And the same deal for C.

@Trident_Euclid

6 жыл бұрын

Ciprian Stanescu I understand frames as a portion or a point in space-time.

Help me out here. What are the two reference frames he is referring to at the end? A stationary one and a moving one?

sir, suppose both Ron and Don are not familiar with STR & time dilation. Now Ron knows it will take him atleast 4yrs to reach the star since his ship travels at 0.99C. But due to time dilation he realizes he has reached in merely 22 mnts. So he decides to crosscheck his speed and finds out he must be travelling at 2.2C to cover 4 light years in 22 mnts. How is this possible,please explain?

@rikkathemejo

6 жыл бұрын

length contraction?

@alexanderreusens7633

6 жыл бұрын

For Ron, the distance to reach the star was a bit more then 22 lightmonths, or 1.83 ly. Travelling at high speed shortens distances too. Accelerating warps the space around you. I advice you to check this game: Velocity Raptor. It shows you what would happen if the light speed was ridiculously low. (featured on Vsauce's channel DONG) testtubegames.com/velocityraptor.html

@mrjava66

6 жыл бұрын

Aashish Hegde the distance is dilated as well.

@RoboBoddicker

6 жыл бұрын

Distances are relative. A lightyear isnt any more absolute than a mile or a foot. Remember light is moving at c in both reference frames. So a lightyear measured by Ron is much longer than a lightyear measured by Don.

@onehitpick9758

6 жыл бұрын

Ron forgot about length contraction.

I'm quite disappointed with this "real" explanation. Isn't "frame jumping" just acceleration? I find the difference only semantic. Although it is wrong to say time dilation happens _only_ because of or _only_ during acceleration, I'm not aware of any person with any relevant credentials claiming this.

@chriskennedy2846

6 жыл бұрын

No, they are not the same - acceleration is real and frame jumping is a shell game. Einstein used acceleration in his paradox resolution in 1918. This doesn't.

@onehitpick9758

6 жыл бұрын

+Chenfeng It's wrong to say that time dilation happens only during acceleration, but it's not wrong to say that it happens because of acceleration. Go back to the real twin paradox (not one without twins that is shown here). If there is no differential acceleration, there is no differential time, period. This is, by accepted definitions of the term, a causal relation between differential acceleration and differential time dilation.

@alexvolkov223

6 жыл бұрын

What if there is a theoretical person A travelling at a constant velocity to infinity, and a variable twin B that just exists in V = 0 - wouldn't that person A age slower, without any change in velocity? If person A was born into the shape-ship already in motion. Of course this is no possible in the Twin example (no one would return to earth here), but just a theoretical example doesn't till still hold true? Especially if you had theoretical person C at the opposite end of the distance from person A, also in motion travelling to the direction of A.

@frede1905

5 жыл бұрын

Chenfeng Bao But that is pretty much the same thing that happens when you go to a point a distance L appart from a stationary observer, and then back again. You change the direction of your velocity when you turn and go back. The only difference between observer B and observer C is that their velocity has opposite directions. So "jumping" from frame B to frame C is equivalent to just "suddenly" turn and go in the opposite direction without accelerating. Of course, this is physically impossible, because you have to accelerate to do so, but this shows that if it was possible, or if you can do something similar to it, then special relativity would still work.

@parityviolation968

5 жыл бұрын

Felis Super You could assume a constant speed, but smooth change in direction (curve) until B's velocity vector is pointing right back at A, if you truly want to make the example "realistic"... But since it is just a thought experiment, there's no need for that! The point is, that a change in direction (no matter how realistic) will always break the (relativity-) symmetry between A and B. When linear motions are involved, all frames of reference are equally valid. But as soon as one of the two observers changes direction (or speed), it will know! (forces etc.). If we truly cared about a realistic change in speed that much, we should also include the traveling twin's acceleration from earth into space to begin with, which is not possible to be instantaneous either....If the creator of this video actually tried to get rid of "change in direction" by introducing new observers, complicating the thought experiment, he should also have introduced a new observer D in order to get rid of the take off discontinuity in velocity, although I guess making B just fly by earth (observer A) while exchanging time information would've sufficed.

This is very interesting. Could you recommend a text book for new learner like me in order to explore more? Thank you sir.

Nice! I had assumed that both twins would still be the same age, that one moving and the other not moving would have cancelled each other out. (my simple mind) Awesome video!

So to solve the Twin Paradox you actually need a triplet?

@chriskennedy2846

6 жыл бұрын

Right - why do physicists propose to tell you that there is really no "twin paradox" at all but then when they try to prove it, their example has a traveling twin who never returns to earth? In the tradition of 7 fictitious dimensions I can sell you and a host of super symmetric particles that will be detected any minute now (just you wait!) you will have to believe your twin brother is younger than you even though you will never see him again because they sent him away for life. Watch my rebuttal video to Brian Greene's explanation.

Dr. Don Lincoln... my guy! :D

First error is : x'=g(x+vt). The correct one is x'=g(x-vt), so is for t'=g(t-vx/c^2)

simply excellent!!! especially the acceleration comment ...keep going for more videos!!!

I gather from this video that acceleration myth has been busted. Youthfulness is proportional solely to the number of reference frames, whatever the method of counting those frames is. Now, why did physics design such an awkward thought experiment 100 years ago, full of unnecessary circumstances? No wonder it lead to the myth. Studying this newest explanation (by the way, it's somewhat hard to grasp when sitting here looking at the explanation from the fourth reference frame, looking at paradox that cancels out with another paradox sort of stuff) I can't help looking for simpler explanation. Perhaps some explanation along the lines on how one gets minimum youthfulness in absolute zero temperature environment and every moving beyond that then increases youthfulness, up to a photon in vacuum that doesn't age at all. Something simpler that is. The slippery relativistics make my head spin.

@good4usoul

6 жыл бұрын

See what you think of this: kzread.info/dash/bejne/pKaOpZJ7nJm0dLw.html Rather than describe the math, I've put everything into mathematica, and actually make IT do all the calculations to perform the Lorentz Transformation on the spacetime diagram over the course of the traveling twin's journey.

@KasiusKlej

6 жыл бұрын

Your animation is a brilliant head spinner, Jonathan. I like it, it has all the necessary details I think. Of course, I'm just a layman looking for a word that would best describe what makes one twin younger and not the other. All the videos I find have always somehow preestablished that the traveler will come out younger, but what if for example the Earth was really massive, so that the twin on Earth would spend his time in a considerable gravitational free fall, while the traveler would have an easy ride. Could there then be a situation when the earthling comes out younger?

@LuisAldamiz

6 жыл бұрын

Are you saying that the explanation is that the traveler goes through more reference frames (space "slices") than the non-traveler and that's why he ages less (experiences more space but less time)? That sounds much more clear to me than Dr. Lincolns' explanation. Thank you very much.

@buzzbee5840

6 жыл бұрын

Acceleration is NOT a myth. No myth busted here. An instantaneous acceleration of the Twin Paradox rocket occurs at the point of turnaround but is completely ignored by the flawed proposed "two frames of reference" assertion in this video. See my posted comment for more.

Acceleration isn‘t the cause! That cannot be stressed enough, as it is such a widespread misconception! So thanks a lot for that superb video on this topic, Dr. Lincoln!

@thstroyur

6 жыл бұрын

It _is_ ; check out my comment on why. The contrived 'two frames' conclusion here, though seemingly getting rid of acceleration, doesn't do so because it requires swapping a _global_ chart for an _atlas_ of _local_ ones to describe the motion. This is a technicality of diff geo, that relates to things like the stereographic projection, but it's at the heart of the equivalence principle: local inertial motion = acceleration = gravity

@onehitpick9758

6 жыл бұрын

No relative acceleration, no clock difference. This passes many tests of causality. Define cause?

@Arkalius80

6 жыл бұрын

I feel like it's important to say acceleration isn't the proximal cause. It is, however, important in the scenario. The proximal cause is the fact that the traveling twin exists in more than one inertial frame of reference on his trip. The reason he does this (in the classical twin paradox) is because he must accelerate to turn around. So it would be wrong to say the answer has nothing to do with acceleration. However, it would also be inaccurate to focus on the acceleration itself rather than its result.

@yoghurt3643

6 жыл бұрын

Arkalius80 There is also the case of the identically accelerated twins. Here both twins undergo identical acceleration, yet one ends up older. See for example www.researchgate.net/publication/241349452_The_case_of_the_identically_accelerated_twins

@yoghurt3643

6 жыл бұрын

onehit pick That’s wrong. See the case of the identically accelerated twins.

Your explanations are extremely helpful

The acceleration explanation is IMHO the best one. The heart of paradox is that both twins can claim to be stationary and hence after the journey both can claim to be the older (or younger) one since according to relativity you can't decide who was moving and who wasn't. However this is not true. The acceleration breaks the symmetry of the problem. So the argument is not that the acceleration causes you to age more slowly but that it prevents one of them to claim to be stationary.

Great explanation. Thank you

Although I agree with the point raised in the comments (that the conclusion is terse) I was pleased to have Dr Lincoln, with his broad understanding of the subject, provide a signpost to solving the apparent paradox. There is now plenty of work I need to do, to understand the physics of the twin's mission, but I believe I can safely discard the argument that it is the changes in acceleration that create the paradox and focus on the argument that it is the transition from one frame to another that causes it.

@buzzbee5840

6 жыл бұрын

It IS acceleration that breaks the symmetry. Not the false causality of frame-jumping. In the correct model of the Twin Paradox in Special Relativity the traveling observer jumps frames 'because' of acceleration, 'because' of the course reversal. By reversing course (decelerating/accelerating) symmetry is broken. A new inertial frame of reference must be used for the return flight. But the frame jump is not the cause for the break in symmetry. The frame jump only represents the acceleration, the course reversal. Dr. Lincoln is sooo very wrong on this topic and many heads are going to be messed up by this dogmatic attempt to dismiss acceleration. Acceleration is does not account for 'all' the time dilation. Velocity accounts for most of it. But in the case of the Twin Paradox acceleration (course reversal) is THE symmetry breaker and is critical for establishing which twin is the moving twin and for solving the paradox. Frames of reference are not even needed to solve the Twin Paradox for Special Relativity. Good fortune in all your studies! ;) ...Read my posts here for more.

I've never seen this thought experiment. That's a really clever way of looking at the problem.

Great video, thanks. Still hard to get, but enlightening.

A point of possible confusion with this is at 8:07 where the statement is made that you can work out how you can get from 1 to 2 and back to 1 again without any acceleration. This is true for non-massive quantities, and it actually would take an infinite, impossible acceleration at position 2 to accomplish this with anything that has mass. You have shown that you can get information from 1 to 2 and back again this way, but not an observer or clock. If you compare the clocks of observers B and C and the "end" of the experiment, there is no difference. This example should be re-presented in a physically realistic point of view from observers starting from a common space-time point. Mixing observers that are in different frames from the start might create confusion and is not the essence of twin "paradox" since the starting point has two opposing frames that are not twins.

keep up the good work love your channel

@Fermilab THANK YOU DON AND TEAM! I am an undergrad physics student at UCSB and this just helped me for my up coming FINAL!

The 3 reference frame illustration is great. I think there should be a clear statement in the video that there is no paradox - the person 3rd frame reached the starting point and has different age but he started at different place. When twin moving away returns to same ref frame (as opposed to staying in ref frame moving back) , his age would be same as 1st twin. All we have shown is that time passes differently for different ref frame - but that is setup we started with when deciding to use Lorentz transformation. I would prefer a general relativity example which can happen in real world rather than a thought experiment

I learnt special relativity from "WORLD SCIENCE U - Brian Greene Lectures"... Thank you for making me More clear in basic concepts..

I so wish you had said what I was thinking, that "Ron would truly only be four months older than when he left, while his twin brother - born at the exact same time back here on earth - would be nearly a decade older."

I don't understand. The only reason why we know we need to describe the space ship with two reference frames is because we know it is moving. If we observed this situation from the space ship's point of view and considered the stationary person as moving away and towards the space ship again, we would also need to use 2 reference frames to describe the stationary person from the space ship's point of view. I think my question is "how do we know what is moving and what isn't". Is it because the ship is expending fuel that we know that it is moving? But it isn't, because it isn't accelerating. If the ship stayed at the star, would there still be an age difference? Because at that point, even if we considered the space ship to be moving, we would only need one reference frame to describe its movement relative to the stationary person. I have a lot of questions and I cant find the answers to them. If anyone has any insights, please help. Edit: I think the question I am most baffled about is "Why do we know the movement of the space ship (and definitely not the movement of stationary observer when observed from the space ship) requires two reference frames?"

@trsomas

4 жыл бұрын

The spaceship experiences some real force. So it does not remain in the same frame of reference. Note that real force does not depend on frame of reference. kzread.info/dash/bejne/fIR3pq2tkZWyhqg.html

At 5:32, the equations are ambiguous, without clear specification of the (x2,t2) and (x1,t1) coordinates. The Lorentz transform equations are often written with a - sign inside the bracket where (x2,t2) is the coordinate of an event occurring in an initially co-aligned system moving at constant velocity, relative to another "fixed" observer who logs (x1,t1) for the same event. It's OK to downplay the math for such a wide audience but not OK to the point of spawning confusion. Physics is not pure algebra - the symbols all have physical meaning! Having criticized this omission, I still do appreciate the intuitive explanation of the twin non-paradox using A, B, and C observers.

Hi Dr. Ron, this was a very helpful video to understand time dilation. Could you explain how you calculated return time: tsubIIIc - tsubII,c = (1/gamma) * (L/v)?

@michelcolman314

Жыл бұрын

Just subtract the two formulas, put them over a common denominator, and you'll see a c^2-v^2 in the numerator with a c^2 in the denomiator. That's a one over gamma squared which cancels and turns around the gamma that was already in front. It's not as trivial as he makes it seem, indeed.

Dear Dr. Don Lincoln. It is a real pleasure to watch your precise and well explained presentations but let me to comment on the current one. The calculations here use the Lorentz Transforms which are derived by using a moving "light watch" (a beam of light reflected between 2 mirrors). One can claim that both Don and Ron may be defined according to relativity as either moving or stationary, but it contradicts the basic assumption of the Lorentz Transform. The "relative" movement of Don relatively to Ron does not allow the use of the Lorentz Transform which are based on actual (not relative) movement of a "light watch".

Okay, I think the proper take on this, this lack of symmetry, is that the distance from A to the "goal" (space station or star) is different for the A, B, and C observers. Since A and the goal are traveling at the same speed (more or less) there is no Lorentz contraction involved. A sees the "proper" length. But since B and C are moving with respect to A *and* the goal they see the distance between A and the goal as shortened. A, B, and C all agree on the speed that B and C are moving with respect to A and the goal. This *must* mean that B and C will take less time to travel the shorter distance than A experiences back on Earth. It's that simple.

@robertbrandywine

3 жыл бұрын

@Anshari Hasanbasri It seems to me that the triggering of time dilation isn't the solution because A looking at B and C's clocks will see the same time dilation that B and C will see on A's clock.That's symmetric. What isn't symmetric is that the distant star is in the same inertial frame as is A but it is *not* in the same inertial frame(s) as B and C. This means that A will see the distance to the distant star as different than B and C see it.

Hi Dr. Lincoln! I'm the guy who met you at O'Hare yesterday. Thanks for giving me 5 minutes of your time and sorry I had to run, I had a certain space and time to be at.