swansont Posted January 30, 2015 Share Posted January 30, 2015 So the non-simultaneity does not follow from the Cm being equidistant from Cf and Cr and would be true whether or not equidistance holds. It is a direct consequence of the motion of the train, relative to the track. Equidistance is the only way you can have simultaneity in the train's frame. So while it's true that "non-simultaneity" will hold in general* other frames, if it's not simultaneous in the train's frame the whole scenario is pointless. * other than a particular frame where it could be Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 But that's not what's happening, so this doesn't apply to the discussion. In the thought experiment set up post #1 the clocks are moved along the train. In your hands you hold two more stop-clocks. You synchronize them. You hand them to two assistants. They casually walk, at the same time and at the same rate, to each end of the train and place each stop-clock there, then leave the train. Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 swansont Equidistance is the only way you can have simultaneity in the train's frame. So while it's true that "non-simultaneity" will hold in general* other frames, if it's not simultaneous in the train's frame the whole scenario is pointless. I didn't say it wasn't, and indeed the OP took pains to specify this condition. robbitybob In your hands you hold two more stop-clocks. You synchronize them. You hand them to two assistants. They casually walk, at the same time and at the same rate, to each end of the train and place each stop-clock there, then leave the train. robbitybob, the whole point is that yes the history of the forward and rear clocks is not quite the same subsequent to synchronisation, but the OP has taken pains to make this effect negligable. It could have been reduced even further by placing the train on a turntable and rotating 180 half way through the slow walk back with the clocks. Equally the issue of front v rear acceleration is a non starter. For instance the train could have beeb pushed from the rear or driven by two locos from each end. But hey, these are ideal though experiments so we can have ideal equipment, just as the centre clock can be a true ideal simultaneity detector. Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 I didn't say it wasn't, and indeed the OP took pains to specify this condition. robbitybob, the whole point is that yes the history of the forward and rear clocks is not quite the same subsequent to synchronisation, but the OP has taken pains to make this effect negligable. It could have been reduced even further by placing the train on a turntable and rotating 180 half way through the slow walk back with the clocks. Equally the issue of front v rear acceleration is a non starter. For instance the train could have beeb pushed from the rear or driven by two locos from each end. But hey, these are ideal though experiments so we can have ideal equipment, just as the centre clock can be a true ideal simultaneity detector. IMO even if the clocks stay synchronised and they are equidistant from CM, if the train is moving the stopwatch will not be stopped. OK that view goes against the postulates but if you do the experiment tell me if I'm right or wrong. Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 robittybob but if you do the experiment tell me if I'm right or wrong. Sure I'll do the experiment, where do I get the ideal equiment? This reminds me of a book I had as a kid called the "Book of Experiments" Each experiment started with a list of equiment and I remember one that started You will need 1 Thunderstorm ....... ....... Far better to discuss this rationally from the comfort of an armchair with whisky in hand. Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2015 Share Posted January 30, 2015 I see this problem as more akin to the extended lifetime of the muon than an Einstinian simultaneity issue. Even though the OP asks about simultaneity and the setup is identical to Einstein's explanantion of relativity of simultaneity? OK. Link to comment Share on other sites More sharing options...
swansont Posted January 30, 2015 Share Posted January 30, 2015 In the thought experiment set up post #1 the clocks are moved along the train. The train isn't moving, and the movement of the clocks doesn't disrupt the synchronization (it's the Eddington slow clock transport protocol A.S. Eddington, The Mathematical Theory of Relativity, 2nd ed., Cambridge University Press (1924) ) IOW, the clocks are synchronized in the train frame, and remain in the same frame for the rest of the experiment. IMO even if the clocks stay synchronised and they are equidistant from CM, if the train is moving the stopwatch will not be stopped. OK that view goes against the postulates but if you do the experiment tell me if I'm right or wrong. Your opinion vs established physics? That's an easy choice. Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 (edited) Sure I'll do the experiment, where do I get the ideal equiment? This reminds me of a book I had as a kid called the "Book of Experiments" Each experiment started with a list of equiment and I remember one that started You will need 1 Thunderstorm ....... ....... Far better to discuss this rationally from the comfort of an armchair with whisky in hand. Don't drink it too fast! The train isn't moving, and the movement of the clocks doesn't disrupt the synchronization (it's the Eddington slow clock transport protocol A.S. Eddington, The Mathematical Theory of Relativity, 2nd ed., Cambridge University Press (1924) ) IOW, the clocks are synchronized in the train frame, and remain in the same frame for the rest of the experiment. Your opinion vs established physics? That's an easy choice. OK the train wasn't moving when they synchronized the clocks but it got moving soon after Now the train gets moving. It reaches a velocity close to the speed of light. Were the postulates tested at these speeds? They were formulated in slow moving situations weren't they? Edited January 30, 2015 by Robittybob1 Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 Were the postulates tested at these speeds? They were formulated in slow moving situations weren't they? That kinda depends on what you mean by slow. The postulates in particle physics in natural and artificial accelerators has been tested at greater than 0.9C I expect swansont or sensie has better inofrmation here. Link to comment Share on other sites More sharing options...
md65536 Posted January 30, 2015 Share Posted January 30, 2015 (edited) It was: no one has said the clock doesn't stop. For the obvious reason that it does (under any reasonable interpretation of the very slightly ambiguous description). In all frames of reference. I say the clocks don't stop. The clocks were synchronized in the track frame before the train started moving. They won't be sync'd in the moving train frame unless the parts of the train are started in a peculiar way to achieve this result, with either parts of the train having different velocity profiles or the train being deformed in its own frame when moving. Incorrect. In the FRAME that the clocks are synchronized, they STAY synchronized. In all OTHER frames (in motion wrt the frame above), the clocks are NOT synchronized. This is because synchronization is a relative phenomenon, i.e. it is FRAME-DEPENDENT. The clocks were synchronized in the track frame. They'll stay synchronized only if they accelerate at the same time in that frame. However if that is the case, the moving train will not be length-contracted shortened in the track frame (it will be stretched in its own frame as the front started moving too long before the back did, but stretched plus length-contracted to maintain its rest length in the track frame, as in Bell paradox). If this is the case, the problem can be solved without even considering relativity, just delay of light will tell you that in the track frame the simultaneously emitted signals won't reach the moving middle of the train simultaneously. In the track frame, the middle of the frame closes the distance to where the front signal was emitted, to intercept it before the rear's signal. In the train's frame, the front clock is ahead and the signal is emitted before the rear signal. Edited January 30, 2015 by md65536 Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 That kinda depends on what you mean by slow. The postulates in particle physics in natural and artificial accelerators has been tested at greater than 0.9C I expect swansont or sensie has better inofrmation here. The postulate I'm thinking of is the one about all physics done in a moving frame will be identical to a stationary frame. Was that what you were referring to? Link to comment Share on other sites More sharing options...
swansont Posted January 30, 2015 Share Posted January 30, 2015 The postulate I'm thinking of is the one about all physics done in a moving frame will be identical to a stationary frame. Was that what you were referring to? Lots of experiments confirm it, because relativity works. Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 I have already mentioned the muons. http://web.mit.edu/lululiu/Public/pixx/not-pixx/muons.pdf Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 That kinda depends on what you mean by slow. The postulates in particle physics in natural and artificial accelerators has been tested at greater than 0.9C I expect swansont or sensie has better inofrmation here. Wikipedia:Postulates of special relativity http://en.wikipedia.org/wiki/Postulates_of_special_relativity 1. First postulate (principle of relativity)The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of coordinates in uniform translatory motion. OR: The laws of physics are the same in all inertial frames of reference. 2. Second postulate (invariance of c) As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body. OR: The speed of light in free space has the same value c in all inertial frames of reference. I agree with #2 but have my doubts about #1 especially when the motion become relativistic. Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2015 Share Posted January 30, 2015 I say the clocks don't stop. The clocks were synchronized in the track frame before the train started moving. They won't be sync'd in the moving train frame unless the parts of the train are started in a peculiar way to achieve this result, with either parts of the train having different velocity profiles or the train being deformed in its own frame when moving. They will stay synchronised in the train frame. But actually that is irrelevant. Even if the flashes occur with a time difference of t in the train frame, the time difference would not be t in track frame. So, however much you try and complicate it, it doesn't change the underlying facts. So you might as well stick with the simple example, instead of adding all sorts of irrelevant bells and whistles. Were the postulates tested at these speeds? They were formulated in slow moving situations weren't they? The postulates are independent of speed. By definition. If the postulate is that the laws of physics (specifically, the speed of light) is the same in all inertial frames, then that means ALL inertial frames. Speed doesn't come into it. Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 (edited) They will stay synchronised in the train frame. But actually that is irrelevant. Even if the flashes occur with a time difference of t in the train frame, the time difference would not be t in track frame. So, however much you try and complicate it, it doesn't change the underlying facts. So you might as well stick with the simple example, instead of adding all sorts of irrelevant bells and whistles. The postulates are independent of speed. By definition. If the postulate is that the laws of physics (specifically, the speed of light) is the same in all inertial frames, then that means ALL inertial frames. Speed doesn't come into it. Was that you conflating them together? I said I agree the speed of light is invariant (is the same in all inertial frames) but postulate 1 was formulated at relatively slow speeds. By "speed of light" I mean based on the measurement of the time light takes to travel a distance, there and back, i.e. the two way speed of light. Edited January 30, 2015 by Robittybob1 Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 robittybob The laws of physics are the same in all inertial frames of reference. You have to be careful with this one. There are many 'laws of physics'. Some are the same some are not and some need to be (can be) adjusted to be the same in all inertial frames. Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 You have to be careful with this one. There are many 'laws of physics'. Some are the same some are not and some need to be (can be) adjusted to be the same in all inertial frames. Name one that differs then? Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 (edited) Newton's First, Second and Third Laws. A good background book on this stuff is the University of Sussex student booklet Relativity Physics by R E Turner Edited January 30, 2015 by studiot Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2015 Share Posted January 30, 2015 Was that you conflating them together? I said I agree the speed of light is invariant (is the same in all inertial frames) but postulate 1 was formulated at relatively slow speeds. By "speed of light" I mean based on the measurement of the time light takes to travel a distance, there and back, i.e. the two way speed of light. "The laws of physics are the same in all inertial frames of reference." Where does that mention "low speed"? Newton's First, Second and Third Laws. If that were true, then it would be possible to determine your speed without reference to something else. I say the clocks don't stop. The clocks were synchronized in the track frame before the train started moving. They won't be sync'd in the moving train frame unless the parts of the train are started in a peculiar way to achieve this result, with either parts of the train having different velocity profiles or the train being deformed in its own frame when moving. OK. I think you are right about this and I was wrong. Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 (edited) Strange If that were true, then it would be possible to determine your speed without reference to something else. Since you were again so hasty in replying perhaps you would like to show how the following system of two particles (mass m1 & m2) and one force (F) is inertially invariant when transformed to a new system whose origin is at (x0 , x0) compared to (in) the original. The Newtonian equations of motion in the original are [math]{m_1}\frac{{{d^2}{x_1}}}{{d{t^2}}} = F({x_1},{x_2})[/math] [math]{m_2}\frac{{{d^2}{x_2}}}{{d{t^2}}} = - F({x_1},{x_2})[/math] Edited January 30, 2015 by studiot Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 30, 2015 Share Posted January 30, 2015 (edited) "The laws of physics are the same in all inertial frames of reference." Where does that mention "low speed"?... I'm not saying it is wrong, just my doubt about aspects of it when applied to frames moving at relativistic speeds, and especially in the way it is being applied in this paradox. Edited January 30, 2015 by Robittybob1 Link to comment Share on other sites More sharing options...
Strange Posted January 30, 2015 Share Posted January 30, 2015 Since you were again so hasty in replying perhaps you would like to show how the following system of two particles (mass m1 & m2) and one force (F) is inertially invariant when transformed to a new system whose origin is at (x0 , x0) compared to (in) the original. As you are claiming that relativity is wrong, it is up to you show that is not. Perhaps a new thread in Speculations? (But as your equations don't even mention the origin, it isn't clear how changing it could make any difference.) I'm not saying it is wrong, just my doubt about aspects of it when applied to frames moving at relativistic speeds, and especially in the way it is being applied in this paradox. Do you have any basis for that opinion? Link to comment Share on other sites More sharing options...
studiot Posted January 30, 2015 Share Posted January 30, 2015 Strange As you are claiming that relativity is wrong Trying reading again whatever you misread before, I made no such claim. Link to comment Share on other sites More sharing options...
Robittybob1 Posted January 31, 2015 Share Posted January 31, 2015 (edited) As you are claiming that relativity is wrong, it is up to you show that is not. Perhaps a new thread in Speculations? (But as your equations don't even mention the origin, it isn't clear how changing it could make any difference.) Do you have any basis for that opinion? Instead of dealing with photons deal with balls and no wind resistance. If a ball was from thrown the ends of the train would the balls reach the center at the same time? "yes" if thrown from within the moving train but "no" if they were thrown at the same time from the right position on platform into the moving train. But if the train was stationary at the platform they would. So the situation is different if the train is moving. Photons fired from two flashlight devices equidistant from the center of the platform (flash occurs when the train is dead center), so light would travel the length of the train at the same rate whether inside the train or outside of it. So when the middle of the train aligns with the center of the platform and the lights flash so that light can both move inside the train (shines through front and back windows as well as along the platform, the observer will see the lights flash at the same time but the person in the train I believe will see the light from the front of the train first. Because light is only traveling at c it didn't matter if the flashlights were on the train or the platform. Edited January 31, 2015 by Robittybob1 Link to comment Share on other sites More sharing options...
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