The Relativity of Simultaneity: A Fundamental Concept in Special Relativity

[Dale]

my reply was deleted because I used an invalid reference

Try the reply without the invalid reference. Btw, I saw the reference, and if that is the kind of material that you are trying to learn relativity by reading then it is no wonder that you are confused.

 

[mangaroosh]

http://en.wikipedia.org/wiki/Relativity_of_simultaneity

From wikipedia:



Is this helpful? According to SR the speed of light on Earth is not c in relation to the gravitational field of the Earth but relative to "any inertial frame". Thus the observer on the platform sees the front- and the backside of the wagon lit up at different times but the guy on the train will think that the front and the backside of the train are lit up simultanesously, because the light coming back from the rear and the front end of the wagon walls will hit him simultaneously.

I think this type of thought experiments are always what is meant when someone talks about "relativity of simultaneity", but I might be wrong...

Thanks Agerhall, I am familiat with the thought experiment alright, and it is essentially the same one that James posted, I think.

What phenomena occur that means the speed of light is c "in any inertial frame"? We would, ordinarily, expect the moving observer to measure a different speed of light - why is this not the case?

 

[harrylin]

I didn't miss it, my reply was deleted because I used an invalid reference; although I didn't intend for it to be a reference per se, rather as a means of explaining a point that was made more eloquently than I could have done. [...]

Then, evidently, you did not understand it. As Dalespam suggests, you can simply re-post the reformulation of your question without including a link to a crank(?) site.

 

[Agerhell]

Thanks Agerhall, I am familiat with the thought experiment alright, and it is essentially the same one that James posted, I think.

What phenomena occur that means the speed of light is c "in any inertial frame"? We would, ordinarily, expect the moving observer to measure a different speed of light - why is this not the case?

If you first assume that the speed of light is c in relation to the guy standing on the platform. The guy on the platform would classically expect that it takes longer time for the light from the guy on the train to reach the back and front wall and bounce back towards the guy on the train than if the train had not been moving. You can do the math, it is simple.

However, in Special Relativity the Time Dilation formula kicks in and it so happens that if the guy on the platform would expect it to take a factor k longer for the light to reach the back and front wall and get back to the guy on the train again, then the time for the guy on the train slows down with the same factor k so he thinks the two way speed of light has the same value, c, no matter what the velocity of the train relative to the ground is...

In this way the "two-way speed of light is the same in all inertial frames".

I believe this is how it is always explained...

 

[harrylin]

If you first assume that the speed of light is c in relation to the guy standing on the platform. The guy on the platform would classically expect that it takes longer time for the light from the guy on the train to reach the back and front wall and bounce back towards the guy on the train than if the train had not been moving. You can do the math, it is simple.

However, in Special Relativity the Time Dilation formula kicks in and it so happens that if the guy on the platform would expect it to take a factor k longer for the light to reach the back and front wall and get back to the guy on the train again, then the time for the guy on the train slows down with the same factor k so he thinks the two way speed of light has the same value, c, no matter what the velocity of the train relative to the ground is...

In this way the "two-way speed of light is the same in all inertial frames".

I believe this is how it is always explained...

The way you describe it, you probably mean the ceiling and the floor. Else you should add length contraction to the mix...
And to top it off (in view of the topic!), one usually makes the one-way speed equal to the two-way speed by means of the Poincare-Einstein synchronization procedure.

 

[James_Harford]

Your OP question:

this might seem like yet another basic question, but I was wondering about RoS. The impression that I got from reading about relativity was that relativity of simultaneity was a consequence of Lorentz contractions, primarily time dilation.

And your latest question about LET:

... the trouble I have is understanding how one interpretation [SR] includes RoS while the other [LET] includes absolute simultaneity. George suggested that it is down to the different assumptions about the propagation of light, but I don't see how that would lead to RoS without some intermediary step(s).

are answered in my earlier post. I guess I missed that you have a third question:

I don't think we're too concerned with Lorentzian relativity in this particular instance, what we're looking for, or rather, what I'm trying to understand, is what phenomena must occur in order for the speed of light to remain constant for all observers, regardless of their motion realtive to the source of the light...

May I suggest that we work on them one at a time? Bouncing back and forth between all of them and adding time dilation and lorentz contractions and LET makes all of this a rather poisonous mix of unrelated factors. Please go back to my earlier post and note that it fully answers your first two questions, as stated. The only valid questions about that post are
1. Is it a correct analysis?
2. Do you understand it?

If you do not, then, I would not go on to the third question until you do.
If you do, then you have just the third question.

That question, unlike the others, is about the ratio of a time and a space measurement, and this unavoidably requires some level of understanding of the Lorentz transforms themselves, which is bad news for you. Give up the notion that time dilations and Lorentz space contractions are sufficient. You will fail. You need a complete coordinate transformation, because only that gives exactly the differences in how the various observers make these measurements.

I would recommend that you start playing around with pencil and paper with various XT coordinate systems, and see if you can find (by trial and error) two coordinate systems in which the path of a photon (a slanted line) has the same speed. Whether you succeed or not, the exercise will get you past a psychological obstacle and improve your chances of grasping what your friends here are telling you.

One thing he might disagree on is that Lorentzian relativity necessarily includes the superfluous concept of an aether.

I doubt it.

- Regards

 

[Naty1]

I hope I'm using the right phraseology here when I say that, under Galilean transformations we would expect the moving observer to measure a different speed of light to the pulse operator, but under Lorentz transformations this isn't the case; is that accurate?

yes. Galileo would have EXPECTED to measure a different speed, but if he had the proper apparatus, would have been dumbfounded when he actually observed the fixed speed of light! And probably so would have Newton.

Dalespam:

I don't think that anything productive will come from a discussion of Lorentzian relativity. It is a defunct interpretation which asserts the reality of undetectable entities. All of the confusion with LET comes from the simple fact that the aether is undetectable, so in LET you continually have to make careful distinctions between measurements and what is happening in (undetectable) reality. It is a rabbit hole not worth going down.

YES! YES! ...I was just about to post similar when I realized there is this last page.

Harford:

May I suggest that we work on them one at a time? Bouncing back and forth between all of them and adding time dilation and lorentz contractions and LET makes all of this a rather poisonous mix of unrelated factors.

again, YES! Let's get the proper theory explained, then it
will become clear why older theories were inadequate.


The HISTORY section here explains why such confusion reigned before Einstein...nobody had Einstein's physical insights...

http://en.wikipedia.org/wiki/Minkowski_space

 

[mangaroosh]

If you first assume that the speed of light is c in relation to the guy standing on the platform. The guy on the platform would classically expect that it takes longer time for the light from the guy on the train to reach the back and front wall and bounce back towards the guy on the train than if the train had not been moving. You can do the math, it is simple.

However, in Special Relativity the Time Dilation formula kicks in and it so happens that if the guy on the platform would expect it to take a factor k longer for the light to reach the back and front wall and get back to the guy on the train again, then the time for the guy on the train slows down with the same factor k so he thinks the two way speed of light has the same value, c, no matter what the velocity of the train relative to the ground is...

In this way the "two-way speed of light is the same in all inertial frames".

I believe this is how it is always explained...

The way you describe it, you probably mean the ceiling and the floor. Else you should add length contraction to the mix...
And to top it off (in view of the topic!), one usually makes the one-way speed equal to the two-way speed by means of the Poincare-Einstein synchronization procedure.

Does this not just verify the point of the OP that RoS is just a consequence of Lorentz contractions, and isn't necessarily a separate, third aspect of Einsteinian relativity?

 

[mangaroosh]

That is fine. If you don't understand then ask new questions that will help me get at your root concern. But if you merely repeat the same incorrect claim that I answered already then all I can do is as I did above and refer back to my previous answers.

You are correct, I was traveling for about two weeks with reduced time and access. However, I did find it frustrating to come back and find you repeating the same mistake that I already addressed weeks ago.

Apologies DS, I tend to treat each conversation individually and try not to take it for granted that every poster reads every post, so I tend to restate certain points for the purpose of the conversation. A number of the times I have restated the point, however, has either been in somewhat different context or for the purpose of reformulating for clarity.

I would argue, though, that the times I have restated it it hasn't necessarily been superfluous to the two-way conversation. I can understand how it might be frustrating to read the same point repeated, particularly when you are under the impression that you have already answered it, but, as mentioned, I had subsequent questions which were taken up by someone else; this lead me to repeat and/or reformulate the point for the purpose of that discussion.

I don't think that anything productive will come from a discussion of Lorentzian relativity. It is a defunct interpretation which asserts the reality of undetectable entities. All of the confusion with LET comes from the simple fact that the aether is undetectable, so in LET you continually have to make careful distinctions between measurements and what is happening in (undetectable) reality. It is a rabbit hole not worth going down.

The purpose of this thread isn't necessarily to discuss Lorentzian relativity, I think it is sufficient to discuss it in the competing theories thread; the purpose of bringing up Lorentzian relativity here, was solely to juxtapose it with Einsteinian relativity for the purpose of clarification; namely that it appears that the same transformations can result in both absolute simultaneity and RoS. The question that is begged from that is, what is the difference between the two; why RoS under one interpretation, but absolute relativity in the other?

Please forgive the repetition there, I'm using it solely to emphasise that the question hasn't been addressed just yet.


I'm not sure the specific example of the transform you gave fully addresses the question, because the question is more general. It might be the case that length contraction and time dilation do not lead every single event to be relatively simultaneous, but if time dilation and/or length contraction never occurred at all, anywhere, would RoS still prevail?

Try the reply without the invalid reference. Btw, I saw the reference, and if that is the kind of material that you are trying to learn relativity by reading then it is no wonder that you are confused.

It's not so much that I'm confused, rather I haven't made the logical connection yet as to how RoS is separate, stand-alone aspect of Einsteinian relativity and not just a consequence of Lorentzian contractions.

It's probably also worth pointing out that I don't try to learn relativity from sources such as the one posted; I learn relativity largely from discussions with people on sites like this, from the references they post and from my own searches; however, I tend not to simply accept as gospel what I am told, and try to subject such things to critical inquiry, which usually serves the purpose of developing a better understaning; on that basis I will consider alternative viewpoints as long as they stand up to reason, and of course experiment.

The "reference" posted seems to make quite a reasonable point about the propagation of light, which I haven't seen considered elsewhere. Unfortunately I'm not in a position to subject it to the level of critical reasoning required so I can only present it as it is and see if there are arguments against it. However, as it strikes me as being quite reasonable, and conforms to [more reliable] information I have encountered previously, I would lean more towards accepting it (without accepting it fully).

Incidentally, I posted the reply without the reference in the other thread.

 

[mangaroosh]

Your OP question:



And your latest question about LET:



are answered in my earlier post. I guess I missed that you have a third question:



May I suggest that we work on them one at a time? Bouncing back and forth between all of them and adding time dilation and lorentz contractions and LET makes all of this a rather poisonous mix of unrelated factors. Please go back to my earlier post and note that it fully answers your first two questions, as stated. The only valid questions about that post are
1. Is it a correct analysis?
2. Do you understand it?

If you do not, then, I would not go on to the third question until you do.
If you do, then you have just the third question.

That question, unlike the others, is about the ratio of a time and a space measurement, and this unavoidably requires some level of understanding of the Lorentz transforms themselves, which is bad news for you. Give up the notion that time dilations and Lorentz space contractions are sufficient. You will fail. You need a complete coordinate transformation, because only that gives exactly the differences in how the various observers make these measurements.

I would recommend that you start playing around with pencil and paper with various XT coordinate systems, and see if you can find (by trial and error) two coordinate systems in which the path of a photon (a slanted line) has the same speed. Whether you succeed or not, the exercise will get you past a psychological obstacle and improve your chances of grasping what your friends here are telling you.


I doubt it.

- Regards

Hi James, if possible I'd like to change the first question; I didn't formulate it in reply to yourself, but did in reply to Agerhall.

Your explanation was based on the second postulate, the constancy of c in every reference frame, regardless of the motion relative to the source. The question that arises from that is, what phenomena have to occur to allow for this possibility? Ordinarily, with the addition of velocities we would expect the moving observer to measure a different speed of light; what phenomena occur that leads to him measuring the speed of light to be the same as the other observer?

 

[mangaroosh]

I don't think that anything productive will come from a discussion of Lorentzian relativity. It is a defunct interpretation which asserts the reality of undetectable entities. All of the confusion with LET comes from the simple fact that the aether is undetectable, so in LET you continually have to make careful distinctions between measurements and what is happening in (undetectable) reality. It is a rabbit hole not worth going down.

DS, just wondering if you would agree with what George said was accurate, that Lorentzian relativity had been divested of all the trappings except for the absolute rest frame?

 

[mangaroosh]

It would probably be fair and correct to say that the mathematics going into and coming out of the Lorentz Transformation and their usage is very different comparing Einstein-Minkowski and Lorentz-Poincare relativity. While the Lorentz Transformation itself is obviously common. For the most part, Lorentz worked with vectors, differential equations and their initial and boundary conditions. Einstein and Minkowski built a platform where those things were abstracted away in which tensors and 4-vectors are preferred.

Thanks Phil.

The points being raised appear to pertain to the Lorentz transformation; does it make sense then to ask why the transformation under one interpretation has RoS while under the other interpretation has absolute simultaneity?

 

[mangaroosh]

Then, evidently, you did not understand it. As Dalespam suggests, you can simply re-post the reformulation of your question without including a link to a crank(?) site.

I could be completely wrong Harry, but based on your posts and the fact that you mentioned you prefer to base your understanding on Einstein's original German paper I would guess that either English or German is your native language - of course you could be form a bilungual family. But if one of them isn't your native language, then you presumably have experience in learning a foreign language. If so, I'm sure you will have noticed that there is usually a disconnect between how much a person can understand and how much they can express themselves, such that it is possible to understand something without necessarily being able to express it [adequately] in your own words. The inability to express it in your own words wouldn't necessarily mean that you haven't understood something that has been said.

The post has been re-posted without the link. As to whether or not the site is a "crank" site, I prefer to examine the content and judge it on that basis.

 

[Dale]

I'm not sure the specific example of the transform you gave fully addresses the question, because the question is more general. It might be the case that length contraction and time dilation do not lead every single event to be relatively simultaneous, but if time dilation and/or length contraction never occurred at all, anywhere, would RoS still prevail?

I specifically addressed that in the math above. In one transform I showed there can be no length contraction nor time dilation at all, anywhere, and there is still RoS.

The opposite claim is that the RoS is a consequence of length contraction and time dilation, and I disproved that claim also by providing a transform that had length contraction and time dilation, but no RoS.

Both claims have been disproven by counter-example. I don't know why you persist in them.

 

[Dale]

DS, just wondering if you would agree with what George said was accurate, that Lorentzian relativity had been divested of all the trappings except for the absolute rest frame?

He and I disagree about LET, but it is such a useless topic that I do not intend to dispute it, neither with him nor with you.

 

[mangaroosh]

I specifically addressed that in the math above. In one transform I showed there can be no length contraction nor time dilation at all, anywhere, and there is still RoS.

The opposite claim is that the RoS is a consequence of length contraction and time dilation, and I disproved that claim also by providing a transform that had length contraction and time dilation, but no RoS.

Both claims have been disproven by counter-example. I don't know why you persist in them.

I have a few questions relating to that, so if it is possible to proceed from here I might be able to get my head around it.

Were the transformations you gave for just one event EDIT: between two reference frames?

Would the same transformations be used in Lorentzian relativity and not include RoS in any of them?

In the example of the transform where there was no RoS, would we conclude that absolute simultaneity prevails, right across the universe, under the Einsteinian interpretation?

 

[Dale]

Were the transformations you gave for just one event?

They were for all events.

Would the same transformations be used in Lorentzian relativity and not include RoS in any of them?

Those transforms are not the Lorentz transform, so it is not used in LET.

In the example of the transform where there was no RoS, would we conclude that absolute simultaneity prevails, right across the universe, under the Einsteinian interpretation?

Again, those transforms are not the Lorentz transform, so it is not used by SR.

 

[mangaroosh]

They were for all events.

Those transforms are not the Lorentz transform, so it is not used in LET.

Again, those transforms are not the Lorentz transform, so it is not used by SR.

sorry, you've thrown me with the last 2 comments; I thought we were talking about Lorentz transformations under Einsteinian relativity.

EDIT: that might be where the confusion is arising from.

 

[James_Harford]

Apologies DS, ... I can understand how it might be frustrating to read the same point repeated, particularly when you are under the impression that you have already answered it, but, as mentioned, I had subsequent questions which were taken up by someone else; this lead me to repeat and/or reformulate the point for the purpose of that discussion.

Repeating a question that has already been answered to your satisfaction "for the purpose of that discussion" is puzzling, to put it mildly.

...the purpose of bringing up Lorentzian relativity here, was solely to juxtapose it with Einsteinian relativity for the purpose of clarification; namely that it appears that the same transformations can result in both absolute simultaneity and RoS. The question that is begged from that is, what is the difference between the two; why RoS under one interpretation, but absolute relativity in the other?.

In terms of predictive capability, there is no difference between the two. The only difference is of interpretation. Lorentz assumed, in accordance with the conventional belief of that time in the aether, that a preferred frame of reference existed. Einstein' noted that since no such frame was detactable, it is a superfluous assumption. That, in a capsule, is all you need to know about Lorentz Ether Theory (LET).

... but if time dilation and/or length contraction never occurred at all, anywhere, would RoS still prevail?

Yes. A simple example of your hypothetical question is a Euclidean space spacetime. It also has RoS, but unlike Minkowski spacetime of SR, moving objects undergo the opposite effects, i.e. time contraction and space dilation. So if you want to insist that such effects "explain" RoS, you must include these as well. Learning Euclidean spacetime is, relatively speaking (!), a snap, so you might want try out your questions on this spacetime first, perhaps with pencil and paper. Hint : the axis of every coordinate system in a Euclidean spacetime are at right angles. You will see exactly how RoS interacts with space dilation and time contraction, and having done this, you will have some idea of how to adapt what you have learned to actual relativistic, or Minkowski, spacetime.

It's not so much that I'm confused, rather I haven't made the logical connection yet as to how RoS is separate, stand-alone aspect of Einsteinian relativity and not just a consequence of Lorentzian contractions.

You don't know that it is a consequence, so why assume that it is? That no one can explain your belief should tell you that maybe this duck can't fly. Indeed, it cannot.

- Regards

 

[James_Harford]

Hi James, if possible I'd like to change the first question; I didn't formulate it in reply to yourself, but did in reply to Agerhall.

Then you should have done so.

Your explanation was based on the second postulate, the constancy of c in every reference frame, regardless of the motion relative to the source. The question that arises from that is, what phenomena have to occur to allow for this possibility? Ordinarily, with the addition of velocities we would expect the moving observer to measure a different speed of light; what phenomena occur that leads to him measuring the speed of light to be the same as the other observer?

The general phenomena that you are looking for is that every object defines a proper reference frame in which all of the laws of physics, including the speed of light, are the same as that of a stationary observer. These frames are related by the Lorentz transformations derived from Einstein's postulates. All relativistic effects can be obtained from these transformations. Therefore learn about these transformations and their derivation.

 

[mangaroosh]

Repeating a question that has already been answered to your satisfaction "for the purpose of that discussion" is puzzling, to put it mildly.

The issue is that it hadn't been answered to my satisfaction, in the sense that I didn't fully understand it; hence I repeated the question and/or reformulated it in discussion with someone else, to see if they could highlight where my misunderstanding lay.

Addressing subsequent questions by referring back to the original answer which lead to those subsequent questions doesn't address those subsequent questions - yes that sounds complicated, but that is precisely what appears to me to be happening.

In terms of predictive capability, there is no difference between the two. The only difference is of interpretation. Lorentz assumed, in accordance with the conventional belief of that time in the aether, that a preferred frame of reference existed. Einstein' noted that since no such frame was detactable, it is a superfluous assumption. That, in a capsule, is all you need to know about Lorentz Either Theory (LET).

According to George and wikipedia

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory

current status

It is probably even possible to get rid of the notion of an absolute rest frame also, which appears to be an oft cited reason why Einsteinian relativity is preferred.

Yes. A simple example of your hypothetical question is a Euclidean space spacetime. It also has RoS, but unlike Minkowski spacetime of SR, moving objects undergo the opposite effects, i.e. time contraction and space dilation. So if you want to insist that such effects "explain" RoS, you must include these as well. Learning Euclidean spacetime is, relatively speaking (!), a snap, so you might want try out your questions on this spacetime first, perhaps with pencil and paper. Hint : the axis of every coordinate system in a Euclidean spacetime are at right angles. You will see exactly how RoS interacts with space dilation and time contraction, and having done this, you will have some idea of how to adapt what you have learned to actual relativistic, or Minkowski, spacetime.

I'm not sure I understand the point re: Euclidean spacetime; it appears to suggest that RoS prevails because effects very similar to time dilation and length contraction occur. I have difficulty seeing how that demonstrates that RoS under Einsteinian relativity is not a consequence of Lorentz contractions.


Quite a few explanations have been provided thus far as to how RoS prevails without length contraction and time dilation, but I'm not sure of the relevance to the question being asked. I thought I was discussing Lorentzian transformations according to Einsteinian relativity, but the answers being provided appear to relate to anything but that. Unfortunately I don't immediately see the relevance of such answers to the question in hand, so that may be part of the reason for the general frustration and annoyance in this thread; people are answering a question in a manner they believe addresses the question, but I am having trouble seeing how it does.


If we stick with Einsteinian relativity, however, would RoS still prevail if time dilation and length contraction didn't manifest anywhere?

You don't know that it is a consequence, so why assume that it is? That no one can explain your belief should tell you that maybe this duck can't fly. Indeed, it cannot.

The impression I got was that it was a consequence and thus far I haven't encountered an explanation which clarifies why that impression is inaccurate.


For example, if we take your explanation involving the pulse operator and the moving observer, your explanation was based on the constancy of c, but, to my understanding, in order for the speed of light to be c in all reference frames regardless of the motion relative to the source, then length contraction and/or time dilation have to occur; which again would suggest that RoS, under Einsteinian relativity is a consequence of contractions.

 

[mangaroosh]

Then you should have done so.

The general phenomena that you are looking for is that every object defines a proper reference frame in which all of the laws of physics, including the speed of light, are the same as that of a stationary observer. These frames are related by the Lorentz transformations derived from Einstein's postulates. All relativistic effects can be obtained from these transformations. Therefore learn about these transformations and their derivation.

I'll try a more direct question: if length contraction and/or time dilation did not occur, would an observer moving relative to another observer, and a light source, measure the same speed of light as the other observer?

 

[mangaroosh]

They were for all events.

Those transforms are not the Lorentz transform, so it is not used in LET.

Again, those transforms are not the Lorentz transform, so it is not used by SR.

hey DS, I'm just wondering if you could explain how this pertains to the question about RoS under Einsteinian relativity, because I can't make the connection.

 

[James_Harford]

I'll try a more direct question: if length contraction and/or time dilation did not occur, would an observer moving relative to another observer, and a light source, measure the same speed of light as the other observer?

Length contraction, time dilation, and RoS are all consequences of the Lorentz transformations, which in turn are derived from Einstein's postulates, which includes the constancy of the speed of light. Therefore, if any of these effects did not occur, Einstein's postulates would be violated.

Time dilation and Lorentz contraction lack the completeness of Einstein's postulates. They cannot be used as postulates to derive the RoS, constant speed of light, etc.

-Regards

 

[harrylin]

[..]

again, YES! Let's get the proper theory explained, then it
will become clear why older theories were inadequate. [..]

The older theory that you seem to refer to is Lorentz theory of electrons; and this is rather well explained in Einstein's 1907 paper which is discussed in a parallel thread. And there is already a parallel thread about other theories. So yes, please let's not mix those topics!

 

[mangaroosh]

Length contraction, time dilation, and RoS are all consequences of the Lorentz transformations, which in turn are derived from Einstein's postulates, which includes the constancy of the speed of light. Therefore, if any of these effects did not occur, Einstein's postulates would be violated.

Time dilation and Lorentz contraction lack the completeness of Einstein's postulates. They cannot be used as postulates to derive the RoS, constant speed of light, etc.

-Regards

Thanks James, this is somewhat clearer. There are still a few questions arising for me though, one which I have repeated but haven't really had a discernable answer to yet.


You say that Length contraction, time dilation and RoS are all consequences of the Lorentz transformations; but Lorentzian relativity uses the same transformations doesn't it? If so, then RoS is not necessarily a consequence of the Lorentz transformations, because RoS is not a part of Lorentzian relativity, which includes length contraction and clock retardation, due to mechanical effects; clock retardation appears to be almost the exact same thing as time dilation except for a different metaphysical explanation.


The differences appear to be:
- time dilation in Einseinian relativity; but mechanical retardation of a clock in Lorentzian
- RoS in Einsteinian relativity; absolute relativity in Lorentzian.


There appears to be some correlation between time dilation and RoS, is that a fair assessment?

 

[harrylin]

Does this not just verify the point of the OP that RoS is just a consequence of Lorentz contractions, and isn't necessarily a separate, third aspect of Einsteinian relativity?

No - and that answer is already contained in my posts #31 and #34.

 

[James_Harford]

The impression I got was that it was a consequence and thus far I haven't encountered an explanation which clarifies why that impression is inaccurate.

Consequence means "derivable from". RoS is not derivable from the "lorentz contraction" and/or "time dilation", without also assuming the constancy of the speed of light.

For example, if we take your explanation involving the pulse operator and the moving observer, your explanation was based on the constancy of c, but, to my understanding, in order for the speed of light to be c in all reference frames regardless of the motion relative to the source, then length contraction and/or time dilation have to occur; which again would suggest that RoS, under Einsteinian relativity is a consequence of contractions.

Correlation means little. By this one can equally argue that contractions are a consequence of RoS.

 

[mangaroosh]

No - and that answer is already contained in my posts #31 and #34.

I referenced post #31 in #48.

 

[mangaroosh]

Consequence means "derivable from". RoS is not derivable from the "lorentz contraction" and/or "time dilation", without also assuming the constancy of the speed of light.

Is it possible to assume the constancy of the speed of light without assuming "lorentz contraction" and/or "time dilation"?

Correlation means little. By this one can equally argue that contractions are a consequence of RoS.

I would say not, if the simultaneity of an event is contingent on the time co-ordinate provided by a clock.

 

[James_Harford]

You say that Length contraction, time dilation and RoS are all consequences of the Lorentz transformations; but Lorentzian relativity uses the same transformations doesn't it? If so, then RoS is not necessarily a consequence of the Lorentz transformations, because RoS is not a part of Lorentzian relativity, ...

Stop right there! RoS is most assuredly an effect of Lorentzian relativity. The predictions of the two theories are exactly the same. In either theory two observers can disagree on the order of two distant events. LET claims that one observer is wrong and the other right, but doesn't know which. LET claims that one definition of now is the "right one" but doesn't know which. In other words, the differences between the two theories are non-physical, or metaphysical. LET is SR with metaphysical baggage.

- Regards

 

[harrylin]

Hi James, if possible I'd like to change the first question; I didn't formulate it in reply to yourself, but did in reply to Agerhall.

Your explanation was based on the second postulate, the constancy of c in every reference frame, regardless of the motion relative to the source. The question that arises from that is, what phenomena have to occur to allow for this possibility? Ordinarily, with the addition of velocities we would expect the moving observer to measure a different speed of light; what phenomena occur that leads to him measuring the speed of light to be the same as the other observer?

The combination with the first postulate leads to the conclusion that the operationally defined speed of light must be the same constant in every inertial reference system (did you carefully read Einstein's description?). And most textbooks as well as some already given replies here provide the answer to your question. I'm afraid that you think that a theory can be learned from merely having discussions on a discussion forum; however, that's just a waste of time of the people here. It's even not an efficient use of your own time.

 

[James_Harford]

Is it possible to assume the constancy of the speed of light without assuming "lorentz contraction" and/or "time dilation"?

Of course it is. And from that follows,

1. the lorentz contraction
2. time dilation
3. and RoS (as shown in post 42) .

I would say not, if the simultaneity of an event is contingent on the time co-ordinate provided by a clock.

Simultaneity requires no clock!
Again, see post 42.

 

[harrylin]

Hi Harry, the conversation with DaleSpam is in reference to mathematical transformations, while your reply in post #28 was with respect to clocks; unfortunately I don't have the nous to make the connection between the two, [...]

I find that an astonishing comment; for it means that you did not understand (if you indeed read) the introduction in Einstein's 1905 paper to which I referred earlier.

I had a quick glance at the reference in post #31, but statement immediately following the link was something you had mentioned before, with respect to detecting absolute simultaneity (or the time on a distant clock) and which I had addressed in #18;
[..]
so that affected my judgement of the necessity to go through it in detail. Is there a specific part that I can jump to that would address the issue?

It addresses how and why "local" simultaneity first emerged, independent of the concept of time dilation (of which the possibility also is suggested); and I already pointed to it. I would have to look up another paper to direct you to how this next lead to the concept of "relative" simultaneity. However only reading one part is not the correct way to surely understand a discourse - and jumping around between text fragments and parts of explanations of people here isn't a good way to learn a topic. The proper way would be to first study a textbook, do some exercises, and check out the explanations in some of the original papers.

Post #20:

The issue being raised appears to be the idea of detecting absolute simultaneity; but that isn't necessarily an issue that needs to be addressed. We don't need to figure out how to synchronise clocks to say that if all clocks remained synchronised then there would be absolute simultaneity; it's somewhat of a tautology. [...]

Only if with you mean "absolute simultaneity" in an operational sense without the implication of "true" simultaneity. I would call that "universal simultaneity", and it's what one effectively does in descriptions of the universe as a whole.
ADDENDUM: Perhaps you meant with " remained", the method of slow clock transport. Then my last remark doesn't apply. Instead, the clarifications of PAllen apply: slow clock transport is a way to naturally approximate the same outcome as is achieved with the Poincare-Einstein synchronization. And it illustrates in which way time dilation and relativity of simultaneity are not fully independent in SR. However, this will hardly be possible to understand without first learning SR; and we can't do that for you.

 

[mangaroosh]

Einstein's 1905 paper

I find that an astonishing comment; for it means that you did not understand (if you indeed read) the introduction in Einstein's 1905 paper to which I referred earlier.

It addresses how and why "local" simultaneity first emerged, independent of the concept of time dilation (of which the possibility also is suggested); and I already pointed to it. I would have to look up another paper to direct you to how this next lead to the concept of "relative" simultaneity. However only reading one part is not the correct way to surely understand a discourse - and jumping around between text fragments and parts of explanations of people here isn't a good way to learn a topic. The proper way would be to first study a textbook, do some exercises, and check out the explanations in some of the original papers.

Only if with you mean "absolute simultaneity" in an operational sense without the implication of "true" simultaneity. I would call that "universal simultaneity", and it's what one effectively does in descriptions of the universe as a whole.
ADDENDUM: Perhaps you meant with " remained", the method of slow clock transport. Then my last remark doesn't apply. Instead, the clarifications of PAllen apply: slow clock transport is a way to naturally approximate the same outcome as is achieved with the Poincare-Einstein synchronization. And it illustrates in which way time dilation and relativity of simultaneity are not fully independent in SR. However, this will hardly be possible to understand without first learning SR; and we can't do that for you.

I am acutely aware that I might be exhausting peoples' patience here, but I am genuinely trying to understand this. I appreciate your advice that consulting a textbook would be a good place to start, and if you could recommend a worhtwhile one, I would eagerly consult it. I do however believe that people on here, and indeed elsewhere, give a relatively relaible representation of the concepts and phenomena contained in many textbooks, because from discussions I've had with people, the information they've presented has been almost entirely representative of the textbook-like resources that I have encountered - through their references. The added benefit of discussing it in a forum is that it offers the chance to question what is meant by certain terminology, something that isn't possible with a textbook.

I appreciate people taking the time to post detailed replies, but because of my lack of a scientific or mathematic background, I am not always able to make the logical connections between points that some people might think is obvious - for example, DaleSpams non-Lorentzian transformation example, which didn't pertain to Einsteinian relativity, when I was working on the assumption that it was Lorentzian transformations, under Einsteinian relativity, that we were talking about. Unfortunately, in such instances, unless it is spelled out for me, I can't see the logical connection between the two.


the 1905 Paper
I did indeed read, and understand, the introduction to the paper you posted; but I'm still unsure as to how DaleSpams example relates to it; it is more the maths used by Dalespam that I don't understand than the introduction to the paper, I would say.

If it would be possible to proceed slowly on the basis of Einstein's definition of simultaneity in that paper, I can give my understanding and if everyone hasn't put me on ignore by then, maybe, just maybe, someone can point out where it is I'm going wrong.

 

[mangaroosh]

Of course it is. And from that follows,

1. the lorentz contraction
2. time dilation
3. and RoS (as shown in post 42) .

Of course, that should have been obvious. I can see how 1 & 2 follow, but I can't yet see how 3 is separate from 1 & 2.

Simultaneity requires no clock!
Again, see post 42.

Is it not required for assigning the time co-ordinate of an event?

 

[mangaroosh]

Stop right there! RoS is most assuredly an effect of Lorentzian relativity. The predictions of the two theories are exactly the same. In either theory two observers can disagree on the order of two distant events. LET claims that one observer is wrong and the other right, but doesn't know which. LET claims that one definition of now is the "right one" but doesn't know which. In other words, the differences between the two theories are non-physical, or metaphysical. LET is SR with metaphysical baggage.

- Regards

Neo-Lorentzian theory appears to have been divested of a lot of that metaphysical baggage, as George mentioned and as the person who posted the widipedia enty also maintains (assuming they're not one and the same person):

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory. As a result, the term "Lorentz ether theory" is sometimes used today to refer to a neo-Lorentzian interpretation of special relativity

The remaining metaphysical baggage appears to be the "postulate of a unique absolute rest frame", which could probably be done away with, without the assumption that reference frames are at rest in the ether, as George has suggested Einsteinian relativity has.

 

[Dale]

sorry, you've thrown me with the last 2 comments; I thought we were talking about Lorentz transformations under Einsteinian relativity.

EDIT: that might be where the confusion is arising from.

hey DS, I'm just wondering if you could explain how this pertains to the question about RoS under Einsteinian relativity, because I can't make the connection.

You have repeatedly made the mistaken assertion that RoS is not a separate feature of the Lorentz transform, but rather is somehow automatically implied by LC and TD. You have even made incorrect conclusions based on that assumption by considering LC and TD and assuming that RoS was included and your conclusions were identical to what the Lorentz transforms would predict.

IF your assertion were correct, then all transforms which included LC and TD would automatically also include RoS and would therefore be equivalent to the Lorentz transform. I have provided counter examples which demonstrate that there are transforms (which are not the Lorentz transform) which have TD and LC but not RoS and vice versa.

The connection is that, by considering LC and TD but neglecting RoS, you are unwittingly using one of these alternate transforms, instead of the Lorentz transforms. Thus you are reaching incorrect conclusions.

Is that clear?

 

[harrylin]

[..] the 1905 Paper
I did indeed read, and understand, the introduction to the paper you posted; but I'm still unsure as to how DaleSpams example relates to it; it is more the maths used by Dalespam that I don't understand than the introduction to the paper, I would say.

If it would be possible to proceed slowly on the basis of Einstein's definition of simultaneity in that paper, I can give my understanding and if everyone hasn't put me on ignore by then, maybe, just maybe, someone can point out where it is I'm going wrong.

Yes it may be better if you restart on that basis!

 

[Agerhell]

Thanks James, this is somewhat clearer. There are still a few questions arising for me though, one which I have repeated but haven't really had a discernable answer to yet.


You say that Length contraction, time dilation and RoS are all consequences of the Lorentz transformations; but Lorentzian relativity uses the same transformations doesn't it? If so, then RoS is not necessarily a consequence of the Lorentz transformations, because RoS is not a part of Lorentzian relativity, which includes length contraction and clock retardation, due to mechanical effects; clock retardation appears to be almost the exact same thing as time dilation except for a different metaphysical explanation.


The differences appear to be:
- time dilation in Einseinian relativity; but mechanical retardation of a clock in Lorentzian
- RoS in Einsteinian relativity; absolute relativity in Lorentzian.


There appears to be some correlation between time dilation and RoS, is that a fair assessment?

Special Relativity basically says:

1. There is no way to measure the one-way speed of light, one can only measure the two way speed of light.
2. The two way speed of light is the same for all inertial observers.

Length contraction and time dilation is then used to explain how the two way speed of light is the same for all observers.

That is all there is to it.

Yes in LET you assume a universal preferred frame and there is no "relativity of simultaneity".
"Relavity of simultaneity" occurs when you decide that all inertial observers should get the same result when they measure the speed of light.

It has nothing to do with time dilation per se.

Yes LET uses the same formulas for time dilation and length contraction but it does not state that the speed of light is the same in all inertial systems and thus has no need for relativity of simultaneity.

 

[harrylin]

Special Relativity basically says:

1. There is no way to measure the one-way speed of light, one can only measure the two way speed of light.
2. The two way speed of light is the same for all inertial observers.

Length contraction and time dilation is then used to explain how the two way speed of light is the same for all observers.

That is all there is to it.[...]

That's almost all there is to it. However some people here find it important to state "the obvious" and it does relate to the topic of this thread: the one-way speeds in an inertial reference system can be made equal to the two-way speeds by means of appropriate clock synchronization (and next one can "measure" that they are indeed equal. ). That can be easily understood as a mathematical theorem about averages.

 

[James_Harford]

The connection is that, by considering LC and TD but neglecting RoS, you are unwittingly using one of these alternate transforms, instead of the Lorentz transforms. Thus you are reaching incorrect conclusions.

Is that clear?

Well stated.

 

[mangaroosh]

You have repeatedly made the mistaken assertion that RoS is not a separate feature of the Lorentz transform, but rather is somehow automatically implied by LC and TD. You have even made incorrect conclusions based on that assumption by considering LC and TD and assuming that RoS was included and your conclusions were identical to what the Lorentz transforms would predict.

IF your assertion were correct, then all transforms which included LC and TD would automatically also include RoS and would therefore be equivalent to the Lorentz transform. I have provided counter examples which demonstrate that there are transforms (which are not the Lorentz transform) which have TD and LC but not RoS and vice versa.

The connection is that, by considering LC and TD but neglecting RoS, you are unwittingly using one of these alternate transforms, instead of the Lorentz transforms. Thus you are reaching incorrect conclusions.

Is that clear?

Ah, sorry, I understand your rationale now, but I still don't understand the maths.

the part I don't understand is the initial equations; I read t'=t-vx as meaning t' equals t minus the velocity along the X-axis, but I don't understand why the velocity comes into it.

and x'=x-vt I read as x' equals x minus the velocity multiplied by the time - which makes a bit more sense to me [without understanding how it demonstrates length contraction]

While I don't doubt that your examples demonstrate transformations which include LC and TD but not RoS, and RoS but not LC and TD I can't discern how they do so. I also have difficulty relating them to the physical phenomena which they represent. That is why I find it easier to discuss the physical phenomena affecting clocks than the maths.

You mentioned that the example of the transform you gave wasn't a useful one in physics, but was useful for demonstrating that RoS wasn't a consequence of LC and TD; I'm just wondering if the examples you gave correspond to physical phenomena, that might help with understanding them?

Just on the point "by considering LC and TD but neglecting RoS, you are unwittingly using one of these alternate transforms, instead of the Lorentz transforms". Are the transforms you used based on the assumption of the constancy of c, as with Einsteinian relativity?

 

[mangaroosh]

Special Relativity basically says:

1. There is no way to measure the one-way speed of light, one can only measure the two way speed of light.
2. The two way speed of light is the same for all inertial observers.

Length contraction and time dilation is then used to explain how the two way speed of light is the same for all observers.

That is all there is to it.

Yes in LET you assume a universal preferred frame and there is no "relativity of simultaneity".
"Relavity of simultaneity" occurs when you decide that all inertial observers should get the same result when they measure the speed of light.

It has nothing to do with time dilation per se.

Yes LET uses the same formulas for time dilation and length contraction but it does not state that the speed of light is the same in all inertial systems and thus has no need for relativity of simultaneity.

Thanks Ager.

My understanding of that explanation would be:

RoS is a consequence of the assumption that the speed of light is the same for all inertial observers.

The assumption about the constancy of c requires Length contraction and/or time dilation to explain it, therefore RoS is a consequence of length contraction and/or time dilation.

If Length contraction or time dilation didn't occur, then the speed of light would not be c for all observers and there would be no RoS.

i must stress, that's just according to that explanation.

EDIT: to summarise, it appears as though length contraction and time dilation are a necessary intermediate step before we can arrive at the conclusion the RoS is a consequence of the constancy of c.

 

[mangaroosh]

That's almost all there is to it. However some people here find it important to state "the obvious" and it does relate to the topic of this thread: the one-way speeds in an inertial reference system can be made equal to the two-way speeds by means of appropriate clock synchronization (and next one can "measure" that they are indeed equal. ). That can be easily understood as a mathematical theorem about averages.

Does the clock synchronisation rely on the constancy of the one way speed of light?

 

[kmarinas86]

What on Earth is a two-way speed of light?

Speed is the magnitude of velocity. Speed is the velocity SANS the directional component.

Edit: HMMM. WEIRD:

http://en.wikipedia.org/wiki/One-way_speed_of_light

One-way vs. two-way speed of light
[edit] The two-way speed

The two-way speed of light is the average speed of light from one point, such as a source, to a mirror and back again. Because the light starts and finishes in the same place only one clock is needed to measure the total time, thus this speed can be experimentally determined independently of any clock synchronization scheme. Any measurement in which the light follows a closed path is considered a two-way speed measurement.

Experiments have shown within tight limits that in an inertial frame the two-way speed of light is independent of the closed path considered.

Since 1983 the meter has been defined as the distance traveled by light in vacuum in 1⁄299,792,458 second.[11] This means that the speed of light can no longer be experimentally measured in SI units, but the length of a meter can be compared experimentally against some other standard of length.
[edit] The one-way speed

Although the average speed over a two-way path can be measured, the one-way speed in one direction or the other is undefined (and not simply unknown), unless one can define what is "the same time" in two different locations. To measure the time that the light has taken to travel from one place to another it is necessary to know the start and finish times as measured on the same time scale. This requires either two synchronized clocks, one at the start and one at the finish, or some means of sending a signal instantaneously from the start to the finish. No instantaneous means of transmitting information is known. Thus the measured value of the average one-way speed is dependent on the method used to synchronize the start and finish clocks. This is a matter of convention.

The Lorentz transformation is defined such that the one-way speed of light will be measured to be independent of the inertial frame chosen.[12]

wow... -They- really don't want to show this stuff very often, do -they-?

 

[mangaroosh]

What on Earth is a two-way speed of light?

Speed is the magnitude of velocity. Speed is the velocity SANS the directional component.

I think it refers to the round-trip speed of light.

 

[Dale]

I also have difficulty relating them to the physical phenomena which they represent. That is why I find it easier to discuss the physical phenomena affecting clocks than the maths.

You mentioned that the example of the transform you gave wasn't a useful one in physics, but was useful for demonstrating that RoS wasn't a consequence of LC and TD; I'm just wondering if the examples you gave correspond to physical phenomena, that might help with understanding them?

They do not correspond to physical phenomena, that is precisely why they are not useful and why your unwittingly using them is such a problem.

 

[kmarinas86]

Does the clock synchronisation rely on the constancy of the one way speed of light?

No. The following is why:

http://en.wikipedia.org/wiki/One-way_speed_of_light

The "one-way" speed of light from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector. What can however be experimentally measured is the round-trip speed (or "two-way" speed of light) from the source to the detector and back again. Albert Einstein chose a synchronization convention (see Einstein synchronization) that made the one-way speed equal to the two-way speed. The constancy of the one-way speed in any given inertial frame, is the basis of his special theory of relativity although all experimentally verifiable predictions of this theory do not depend on that convention.[1][2][3][4][5][6][7][8]

Experiments that attempted to probe the one-way speed of light have been proposed, but none has succeeded in doing so.[9] It was later shown that these experiments are in fact measuring the two-way speed.[1][10]

The 'speed of light' in this article refers to the speed of all electromagnetic radiation in vacuum.

Other clock synchronization conventions need not hold this assumption.

References [1] through [8]:

^ a b Yuan-Zhong Zhang (1997). Special Relativity and Its Experimental Foundations. World Scientific. ISBN 9789810227494.
^ Anderson, R.; Vetharaniam, I.; Stedman, G. E. (1998), "Conventionality of synchronisation, gauge dependence and test theories of relativity", Physics Reports 295 (3-4): 93–180, Bibcode 1998PhR...295...93A, doi:10.1016/S0370-1573(97)00051-3
^ Conventionality of Simultaneity entry by Allen Janis in the Stanford Encyclopedia of Philosophy, 2010
^ Mathpages: Conventional Wisdom and Round Trips and One-Way Speeds
^ a b Edwards, W. F. (1963). "Special Relativity in Anisotropic Space". American Journal of Physics 31 (7): 482–489. Bibcode 1963AmJPh..31..482E. doi:10.1119/1.1969607.
^ Winnie, J. A. A. (1970). "Special Relativity without One Way Velocity Assumptions". Philosophy of Science 37: 81–99, 223–38. JSTOR 186029.
^ Rizzi, Guido; Ruggiero, Matteo Luca; Serafini, Alessio (2004). "Synchronization Gauges and the Principles of Special Relativity". Foundations of Physics 34 (12): 1835–1887. arXiv:gr-qc/0409105. Bibcode 2004FoPh...34.1835R. doi:10.1007/s10701-004-1624-3.
^ Sonego, Sebastiano; Pin, Massimo (2008). "Foundations of anisotropic relativistic mechanics". Journal of Mathematical Physics 50 (4): 042902-042902-28. arXiv:0812.1294. Bibcode 2009JMP...50d2902S. doi:10.1063/1.3104065.

 

[mangaroosh]

They do not correspond to physical phenomena, that is precisely why they are not useful and why your unwittingly using them is such a problem.

I'm not sure that I am unwittingly using them; maybe my reply to Agerhell can clarify what I was trying to get at

EDIT: the point being made by a number of people is that RoS is a consequence of the constancy of c; but the constancy of the speed of light does not cause length contraction and time dilation, length contraction and time dilation must occur in order for all observers to measure the speed of light to be c - hence RoS is a consequence of them - in terms of real world phenomena, as opposed to hypothetical mathematics that doesn't correspond to physical phenomena.