Relativity of Simultaneity

James_Harford

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


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).

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.

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

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.

mangaroosh

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.


According to George and wikipedia
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.


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?


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

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

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

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

[QUOTE=Naty1;3762411] [..]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

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

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

James_Harford

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.


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

mangaroosh

I referenced post #31 in #48.

mangaroosh

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


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

James_Harford

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

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

Of course it is. And from that follows,

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

Simultaneity requires no clock!
Again, see post 42.

harrylin

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.

mangaroosh

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.