
#55
Feb512, 07:15 PM

P: 359

It seems, although not expressly stated, that measurements expressed in those units tacitly assume the earth centred reference frame as the rest frame; as you mention atomic clocks are at rest on earth, and the "pure" definitions would have been relative to the earth centred rest frame too. 



#56
Feb512, 07:54 PM

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#57
Feb512, 07:59 PM

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#58
Feb512, 08:21 PM

P: 359





#59
Feb512, 09:11 PM

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Please read the wikipedia article to begin. It is clear that you have some misunderstanding of what proper time is, and it is one of the most important concepts of relativity. If you have any questions, I would be glad to clarify. They are three separate features of the Lorentz transform, and all three are required. You cannot simply use length contraction and time dilation and assume that relativity of simultaneity is somehow autmoatically included. 



#60
Feb612, 03:35 AM

P: 3,178

However, necessarily the velocity of a light ray relative to both frames as measured with an independent reference system is indeed different. As a matter of fact, that velocity (also called "closing velocity" in modern jargon) is equal to the vector subtraction (cv). Effectively Einstein assumed that when setting up a reference system we can make the oneway speed equal to the round trip speed which is postulated (as a law of physics) to be constant (everywhere and in all directions, independent of the motion of the source); and we postulate also that all laws of physics must be valid for all inertial reference systems. Combining those two postulates, we find that the round trip speed must be the same constant in all inertial reference systems, and we can make the oneway speed equal to the measured twoway speed by convenient clock synchronization. That is important to keep the laws of physics free from unnecessary complexity. 



#61
Feb612, 04:09 AM

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#62
Feb1412, 01:44 AM

P: 359

@George  just wondering if you had a chance to read this post by any chance; I had a few questions on the analogy you used.




#63
Feb1412, 03:51 PM

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#64
Feb1412, 06:52 PM

P: 359

Just referring back to the RC plane analogy, with the planes that don't experience wind resistance, if the RC planes making their journey across the "big" plane in flight were to arrive simultaneously at the detector, I don't think we would conclude that length contraction and/or time dilation occurred, would we? Also could we conclude that a person on the ground would measure the same speed of the planes as the RC operators? I think based on our previous discussions, that we couldn't; I'm just trying to figure out, what a reasonable conclusion would be from that scenario? Also, just wondering if you had any thoughts on the issue of the moving observer measuring the speed of light; we mentioned that he would measure the speed to be c if he used a light clock, but if he were to use a mechanical clock, for example, an infinitely precise pendulum clock, then he would measure a speed different to c. I'm wondering if there are any issues that mean we couldn't use such an idealised pendulum clock? Is the fact that it wouldn't work in an inertial reference frame in deep space sufficient reason to exclude it? Also, just on the point of being at absolute rest in the ether frame, this is something which also doesn't sit too well with me; I often hear that Lorentzian relativity contains the superfluous assumption of an undetectable, absolute rest frame, but Einsteinian relativity seems to include the assumption that reference frames are at rest in that rest frame, which doesn't seem to be any less of an assumption  to my mind it seems more objectionable. 



#65
Feb1512, 12:25 AM

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#66
Feb1512, 01:02 AM

P: 359

The objection to Lorentzian relativity, that usually seems to get cited as the reason for preferring Einsteinian relativity, is the fact that it doesn't have the undetectable, absolute rest frame; while Einsteinian relativity appears to treat each reference frames as though they are that absolute rest frame  that doesn't appear to be too different from my own reasoning. However, that I find it more objectionable is not necessarily a conscientious preference for one over the other, rather that from trying to develop an understanding of both theories, the process of assimiltation of information has lead, for some reason, to Einsteinian relativity not sitting well; that could be, in part, due to the reasons that are given for preferring Einsteinian relativity over Lorentzian. EDIT: also possibly because it seems like the superfluous assumption [of an absolute rest frame] that seems to make Lorentzian relativity less attractive, could probably be done away with, within the context of Lorentzian relativity. 



#67
Feb1512, 02:44 AM

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You said earlier, "I think I've got a half decent understanding of certain concepts, but obviously far from a full understanding". Could you please itemize those concepts that you feel you halfway understand? 



#68
Feb1512, 03:58 AM

P: 359

I try to picutre the MMX in such a scenario, but wonder if it would reveal that the light was traveling slower relative to the carriage, because the light would still be traveling at an actual speed of c. The obvious ones would be:  Time dilation  Length contraction  RoS (although that might be disputable  my level of understanding that is)  the constancy of the speed of light  twin paradox  reference frames  clock synchronisation  Principle of Relativity  Equivalence principle 



#69
Feb1512, 05:42 AM

P: 3,178

For example, Ives was a physicist who claimed to reject SR  until he apparently realised that what he rejected was not really the theory itself but a popular interpretation of the theory which he deemed inconsistent. In one of his later papers he even rederived SR, using other postulates (Maxwell + conservation laws). That could be instructive. 



#70
Feb1612, 02:56 AM

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There are no experiments that violate Einstein's second postulate because they cannot measure the oneway speed of light. The purpose of this forum is to learn relativity, not to try to find ways to disprove it. 



#71
Feb1612, 03:30 AM

P: 359

These coordinates can then be mathmatically transformed to give the coordinates of the same event from the perspective of a different reference frame. 



#72
Feb1612, 07:16 AM

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The best way to learn it is: 1) do homework problems so that you understand how it actually works (i.e. so that you don't mistakenly think that SR claims something it does not) 2) read the experimental evidence for and against it 


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