The Relativity of Simultaneity: A Fundamental Concept in Special Relativity

[ghwellsjr]

My understanding of this would be that "local clocks", therefore, cannot be used to determine the simultaneity of events. Only the absolute frame can determine if events are simultaneous or not. If events are simultaneous in the absolute rest frame, then they are simultaneous in all reference frames even if the observers disagree because of the time co-ordinates provided by their inaccurate clocks.

You are conflating Galilean transformation and Lorentz transformation. Prior to Maxwell, the dominate view was the principle of relativity based on the Galilean transform in which time and space were separate and time did not enter into the transformation so that all frames had the same absolute time. But it wouldn't make sense to speak of an "absolute frame" or an "absolute rest frame". There was no preferred frame. The transformation operated only on one spatial dimension along the direction of motion.

OK, but the current state of affairs is that LR uses the LT, no?

Yes, but remember, it was developed after SR and is nothing more than SR with a preferred frame which is what you get when you substitute Einstein's second postulate with the postulate that light propagates at c only in a single elusive absolute rest frame.

If "local clocks" cannot determine "true time", and if their different times are the result of mechanics, then they presumably cannot be used to determine the simultaneity of events, in any meaningful way.

True.

If events are simultaneous in the absolute rest frame, then presumably they must be simultaneous in all reference frames, even if the observers cannot determine this to be so, due to their inaccurate clocks.

Again, this is conflating concepts from LET and the Galilean PoR where all reference frames agree on the absolute time and where there is no need for an absolute rest frame and where there are no inaccurate clocks.

They might disagree on whether events are simultaneous or not, but presumably they can't really say; and instead of the Einsteinian notion that both reference frames are equal, it would be possible that, according to LET, that one observer actually is correct, because they might actually be in the absolute rest frame, just unable to determine it.

Everybody and everything is in every reference frame. But if you mean that if an observer is at rest in the absolute rest frame, his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame tick, then that would be correct. But it would also be correct to say that in another frame moving at v in the x direction, if there were an observer moving at v in the -x direction, then his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame. When we're talking about simultaneity, we are not concerned about an observer's clock and its motions or rest state in a frame. We are talking about the infinite number of coordinate clocks that define time in a particular frame and whether or not two events at different locations occurred at the same time.

It might be worth mentioning that, if time did not exist, a notion mentioned in this, mainstream source, then it would arguably be pretty much identical to the notion of absolute time, insofar as presentism would be prevalent. In that instance, the "relative time" of local clocks could not be used to determine RoS.

I don't think that is how LET is formulated presently though is it? Although I think the notion would be more compatible with LET than Einsteinian relativity.

No, that's not worth mentioning.

As I have said before, present day LET is usually exactly the same as SR but with a presumed preferred frame in which light propagates at c and in no others.

 

[mangaroosh]

I've rearranged the order of your response, but I don't think it misrepresents you - please let me know if you believe it does. I've taken your response to one point and made it the main focus of this post, because it cuts straight to the heart of the question; I've replied to the rest below, but this I think might offer the quickest route to reolution. This is followed by a point which is directly relevant to that.

Does Lorentzian relativity incorporate AS?

Yes, but perhaps not explicitly: he referred to it as "true time".

OK, this is the critical issue, as I see it.

It might be helpful to re-state the definitions again, for clarity:

Absolute simultaneity means that events which are simultaneous in one reference frame, are simultaneous in all reference frames.

RoS is where events that are simultaneous in one reference frame are not, necessarily simultaneous across all reference frames; that is, it allows for the joint possibility of simultaneity and non-simultaneity across reference frames.

AS doesn't allow for the joint possibility of simultaneity and non-simultaneity across reference frames; therefore, AS and RoS are incompatible.


If LR incorporates AS, then it can't incorporate RoS; if LR utilises the Lorentz transform, then RoS cannot be a necessary consequence of the LT.


Under Lorentzian relativity, if events are simultaneous in the absolute rest frame, and that frame only, then they are simultaneous across all reference frames - irrespective of differing time co-ordinates from "local clocks".

"Absolute simultaneity" commonly refers to the same unique reference frame as "absolute velocity". See aslo:
http://en.wikipedia.org/wiki/Absolute_time_and_space
I hope that you see that that resolves all confusion on this matter.

I understand that AS is linked to the same unique reference frame as absolute velocity, but I don't think alluding to it sufficiently explains the "absolute velocity" and "velocity is absolute" point being made.

As above, under Lorentzian relativity, if events are simultaneous in the absolute rest frame, and that frame only, then they are simultaneous across all reference frames - irrespective of differing time co-ordinates from "local clocks".

As Lorentz's concise statement showed, it is mistake to think of "in contrast".
Instead, simply put: SR + ether = LR.
Similarly: SR + block universe = MR.

We don't necessarily need to think of it in contrast, we can think of it in conjunction with, but there are differences in the models which automatically lend themselves to contrast, or comparison.


If absolute simultaneity means, events that are simultaneous in one reference frame i.e. the absolute reference frame, are simultaneous in all reference frames, then it means that simultaneity (of those events) is absolute.

I'm quite sure that I let you read the explanation from the original paper in a discussion here not long ago... Now I have no time to search it back again but in a nutshell, it was already applied before time dilation was added to the transformations of Lorentz.

OK, I can't specifically remember it in this, or any similar context, but I may just not have made the connection. It isn't really an essential point I don't think, so I won't labour it.

Yes - exactly! Didn't you read it? If you had searched for it with "simultaneous" you would have found it in a minute... and the first pages of that article are much shorter than the total of pages that you had us write here in discussions with you...
As a matter of fact, if you don't paste that passage in your next reply to me, I will not reply to you for at least one month.

I had already read it before you posted it; I was more trying to re-iterate that the concept of RoS had been understood.

That, along with the subsequent questions, were intended to show the path of logic that I was following, to see if there was an issue there. The answer to each individual question would have helped determine where I am going wrong. I was confident that it wasn't on the point of RoS, but just stated it more as a "road marker".

Is this the relevant passage

Definition of Simultaneity​

We have to take into account that all our judgments in which time plays a part are always judgments of simultaneous events. If, for instance, I say, “That train arrives here at 7 o'clock,” I mean something like this: “The pointing of the small hand of my watch to 7 and the arrival of the train are simultaneous events.”3
...
It is essential to have time defined by means of stationary clocks in the stationary system, and the time now defined being appropriate to the stationary system we call it “the time of the stationary system.”

No difference after 1905 (before 1905 Lorentz did not have a clear idea about it, but Poincare already applied it to the time measured by clocks).

There is no difference in the readings, or behaviour of the clocks, but there is a difference in the underlying assumptions of what the readings, and behaviour represent, isn't there?

Definitely not: observers can only use "local time", since they cannot know true time.

But this would just mean that they can't know the true time co-ordinates for events, as opposed to implying that the events are not simultaneous. They would disagree about simultaneity, but unlike the Einsteinian interpretation, there is the possibility that one, or both of them is wrong; because one or both of their clocks doesn't tell the "true time".

Presumably it is the "true time" co-ordinates of events that determines whether or not they are simultaneous, as opposed to the inaccurate, or "not-the-true-time", co-ordinates.

1. That has nothing to do with Einstein's train illustration which you claimed to understand and which you claimed to comment on - thus your claim was totally wrong. So, please explain Einstein's train example, as a test.

We may be arguing over semantics here.

I'll speak in terms of Albert and Henry moving relative to each other, as per the video posted in this, or another thread; from Albert's perspective, Henry's clock runs slower because the photon in his clock has to travel a longer distance between mirrors i.e. the path represented by the hypotenuse of a right angled triangle.

If, however, the speed of light is c for all observers, it means that lengths must contract and time must slow down for Henry (according to Albert). This means that, according to Albert, Henry's clock ticks slower.

The phrase I would use here is to say that Henry's clock ticks at a slower rate.

2. Your logic appears very incomplete to me - but that's irrelevant at this point.

That is the primary motivation for posting here, to find where the error in the logic is and to, hopefully, correct it.

Here's again the key section that you can't have missed (but of which you did read the context so that you surely won't misunderstand it) - and funny enough, it appears that the first section wasn't authored by Lorentz:

(1)"it was necessary incidentally to throw over the one universal time, and substitute local times attached to moving bodies and varying according to their motion. The equations on which the theory of relativity is based are due to Lorentz, but Einstein connected them with his general principle, namely, that there must be nothing, in observable phenomena, which could be attributed to absolute motion of the observer. [..] In orthodox Newtonian dynamics the principle of relativity had a simpler form, which did not require the substitution of local time for general time. " [..]
(2)"It is not necessary to give up entirely even the ether. [..] In my opinion it is not timpossible that in the future this road, indeed abandoned at present, will once more be followed with good results, if only because it can lead to the thinking out of new experimental tests. Einstein's theory need not keep us from so doing; only the ideas about the ether must accord with it."

Now, the "time" of a system in rest with the ether is often called "absolute" or "true" time, consistent with Newton's defnitions. I hope that it is now clear to you that such a "true time" is not at all incompatible with RoS, just as also our "universal time" is not incompatible with RoS - even if astronauts use it. As a matter of fact, astronauts could use both local and universal time, and thus use "dual time" - that would be a neat example of RoS.

I'm not 100% sure of the intention of the initial part of the post; the concept of RoS under Einsteinian relativity isn't the issue as such. The question pertains to the notion of RoS under Lorentzian relativity, so that we can deduce what the necessary consequences of the Lorentz transform are.

While Einsteinian relativity abandoned the idea of one universal time, Lorentzian relativity retained it; and while both theories utilise the concept of "local clocks", the underlying assumptions as to what they represent are materially different; to the extent that the Einsteinian interpretation leads to the notion that time is relative, while Lorentzian relativity retains the notion of universal, or "true time". This means there are fundamentally different assumptions about time and clocks, and therefore the time co-ordinates of events.


It seems like you are suggesting that because ER uses "local clocks" that AS and RoS are compatible; but as mentioned, there are fundamental, underlying assumptions, about what the time co-ordinates of those clocks represent, which pertains directly to the simultaneity of events.

If I might be so bold as to ask you to spell out how the notion of absolute time is not inconsistent with RoS, because you seem to stop just short of it every time; it could simply be that I am not making the connection, but I can't seem to. I have the tendency to assume that the points I make are going to be understood also, but I often find that spelling it out clearly allows for any issues to be clearly identified.


As mentioned, my understanding would be that the simultaneity of events is determined by the "true time" co-ordinates of events, as opposed to the "untrue" time co-orindates.

Good!

Should get time this evening; I was busy replying to posts when I got the chance during the day.

Yes indeed! And as I mentioned before, a lot of expressions had acquired multiple compatible meanings before SR, which became incompatible afterwards. Consequently, one often has to consider the context to understand what a writer means when using certain words.

OK, but is there a conceptualisation of AS other than the one I have been referring to?

 

[mangaroosh]

All this is accurate and good as long as you understand it is all predicated on an unproved and possibly perpetually unprovable assumption of the existence of an absolute rest frame. You are also apparently using the term simultaneous in a sense of meaning actually/absolutely simultaneous as opposed to the normal definition of equal clock readings ,,,,I hope you are now aware of the difference.

I do understand that it is predicated on said assumption, but that is, in itself, a separate matter. The point of contention is whether or not RoS is a necessary consequence of the Lorentz transform. If my understanding is accurate, as you say, then the conclusion that can be drawn is that RoS is not a necessary consequence of the Lorentz transform; insofar as RoS is the joint possibility of events being simultaneous and non-simultaneous, across reference frames.

The point about equal clock readings is mentioned in the part that you said was accurate. It suggests that equal clock readings, across "local clocks", is part of the definition of simultaneity under the Einsteinian interpretation, but not necessarily the Lorentzian. Under the Lorentzian interpretation, it seems as though "local clocks" can disagree on the times of events, but the events would still be simultaneous, if they have the same time co-ordinates in the absolute rest frame only.

That is, if the "true time" co-ordinates of events are the same, then they are said to be simultaneous, under Lorentzian relativity; if, however, the time co-ordinates of local clocks, in different reference frames, are the same, then events are not necessarily simultaneous - or perhaps definitely not simultaneous - because those co-ordinates don't represent the "true time" co-ordinates of the events.

It is true "local clocks" cannot determine "true time", but unfortunately we have NO clocks whatsoever that can tell true time . It is also true that clocks cannot determine simultaneity in the sense you seem to mean here . Even so they provide a "conventional simultaneity" which is quite meaningful in that it accurately correlates physical measurements with the mathematical structure we use to order and understand the world. And does it in all possible inertial frames.
Even if there is a preferred frame and all the clocks in other frames could be magically synched from them so there were all "actually" simultaneous , they would no longer work in all those other frames. Physical measurements would no longer be consistent but would vary from frame to frame and even with direction within any frame. To function we would still need conventionally synched clocks and RoS

We can't necessarily say that we have no clocks that can tell the "true time", because we cannot determine the motion or rest of any reference frame. That, however, is again a separate matter to the question of whether or not RoS is a necessary consequence of the Lorentz transform.

The point you raise, however, is pertinent to a thread that was locked in the General Discussion forum, so unfortunately I don't think we can go into it here.

Once again this all might possibly be accurate but is beyond determination

There is an alternative conventionw which could help determine it, but again, it is the subject of a locked thread.

Again, however, it is a separate point to the question of whether or not RoS is a consequence of the Lorentz transform.

If you are correct, and the point above is accurate, then the logical deduction would be that it isn't necessarily a consequence of the Lorentz transform, but an interpretation of it.

 

[Dale]

I tend to find that I develop a better understanding of something when I subject it to critical reasoning; the distinction between actual and measured values came about on the basis of that reasoning. It also seems to be an important distinction, again for the reasoning that was outlined. Again, based on logical reasoning, it would seem that RoS is a consequence of the actual speed of light remaining invariant, but the actual speed of light would be unmeasurable, given the distinction between actual and measured speeds.

As much as I would like to eschew reason in my attempts to understand relativity, it isn't something that comes naturally.

Nonsense. Belief in and obsession over undetectable entities is the purview of ghost stories and superstition, not reason. You do not need to "eschew reason" in order to understand SR.

Btw, the language of reason is math, so if you really want to use reason then you need to learn the math. So far, I have seen no indication of that from you. In fact, I think that you do not want nor embrace reason, but rather intuition. I think your trouble with SR is that it is not intuitive; you are having trouble eschewing intuition and embracing reason.

This is where the point of contention lies. According to LR, only the absolute rest frame has the "true time", so presumably only this frame can be used to determine the simultaneity of events.

This is a different concept from the AS concept presented above, and it is much more in line with the language of LET. Let's look at these two concepts.

AS, as you defined it above, requires a set of at least two equivalent reference frames and a transformation between them. If the transformation between the frames is such that any pair of events which have the same time coordinate in one frame have the same time coordinate in all of the equivalent frames then there is AS. If not, there is RoS. This concept of AS is opposite to RoS, and can be determined simply by looking at the transformation between the equivalent frames.

LET's concept of "true time" identifies a single reference frame, the aether frame, as being unique and not equivalent to any other frame. Time in the undetectable aether frame is called "true time", and so events which are simultaneous in the aether frame would be truly simultaneous. There is no reference to nor comparison of time in different frames, so this is not AS as defined by you above. I don't know if Lorentz ever used the term, but based on the terminology that he did use he would probably call it "true simultaneity".

Note that true simultaneity (refers to simultaneity in a single frame) is not the opposite of relativity of simultaneity (compares simultaneity in multiple frames). LET has RoS, it also has this concept of true simultaneity which is distinct from your and my concept of AS.

If events are simultaneous in the absolute rest frame, then they are presumably simultaneous across all reference frames

This is incorrect. Simply apply the definition of simultaneity to determine if two events are simultaneous or not. That events are simultaneous in the aether frame does not imply that they are simultaneous in all frames. In fact, the LT from the aether frame to the local frames guarantees that is not the case.

Surely where two theories are experimentally equivalent to one another theory, both theories must be someway understood before one can be rejected in favour of the other? How else could it be determined that they are experimentally equivalent?

This is true, but not relevant to your stated goal of learning SR. You do not need to reject LET in favor of SR in order to learn SR. Nor do you need to determine that they are experimentally equivalent in order to learn SR.

If the time co-ordinates differ then, according to LR, it is because the "local clocks" are, effectively, wrong.

Hence the schizophrenic nature of LET: It purports to be a scientific theory, science uses experimental measurements to test theories, but measurements are wrong according to the theory.

 

[mangaroosh]

You are conflating Galilean transformation and Lorentz transformation. Prior to Maxwell, the dominate view was the principle of relativity based on the Galilean transform in which time and space were separate and time did not enter into the transformation so that all frames had the same absolute time. But it wouldn't make sense to speak of an "absolute frame" or an "absolute rest frame". There was no preferred frame. The transformation operated only on one spatial dimension along the direction of motion.

I don't think I am conflating the two, am I?

The concept of reference frames is relevant to Galielan relativity as well isn't it? Galileo's observer on the ship is a particular example, no?

The Galilean Principle of Invariance, or the consequence of it, suggests that an observer cannot determine if they, and by extension their reference frame, are in motion or at rest. This referred to absolute motion and absolute rest, with the implication that they were in one or the other state. If they were indeed at absolute rest, then presumably the concept of an absolute rest frame would make sense.

Is Lorentzian relativity not based on the notion of absolute space, or does it not incorporate it? My understanding was that the Lorentz transform determines the physical contractions of objects as they moved through the ether, or relative to the absolute rest frame.

Yes, but remember, it was developed after SR and is nothing more than SR with a preferred frame which is what you get when you substitute Einstein's second postulate with the postulate that light propagates at c only in a single elusive absolute rest frame.

Would it be accurate to say that it is SR with absolute time and space, as opposed to relativised spacetime; where the contractions of objects are physical, as opposed to geometrical (is that correct??), and are due to the motion relative to the absolute space; and the Lorentz transform allows observers to determine to what extent the physical instruments of a relatively moving reference frame are contracted, relative to their own reference frame?

True.

Does that not then mean, that even if events have the same time co-ordinates, after the transform, that it cannot necessarily be said that they are simultaneous, because at least one of those time co-ordinates is not the true time co-orindates of the events?

Equally, if events don't have the same time co-ordinates, after the transform, it cannot necessarily be said that they are not simultaneous, because, again, at least one of the time co-ordinates is not the true time co-ordinates of events?

Again, this is conflating concepts from LET and the Galilean PoR where all reference frames agree on the absolute time and where there is no need for an absolute rest frame and where there are no inaccurate clocks.

Would it be fair to say that LR is effectively just Gailean relativity with physical contractions?

Everybody and everything is in every reference frame. But if you mean that if an observer is at rest in the absolute rest frame, his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame tick, then that would be correct. But it would also be correct to say that in another frame moving at v in the x direction, if there were an observer moving at v in the -x direction, then his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame. When we're talking about simultaneity, we are not concerned about an observer's clock and its motions or rest state in a frame. We are talking about the infinite number of coordinate clocks that define time in a particular frame and whether or not two events at different locations occurred at the same time.

Apologies, the emboldened was indeed what I meant.

The reason the [traveling v in the -X direction] observer's clocks would tick at the same rate as the absolue rest frame clocks, is because he would be in the absolute rest frame.

When talking about simultaneity, it has repeatedly been mentioned that events are simultaneous if they have the same time co-orindates; if time co-ordinates are provided by clocks, and the state of relative motion affects the time co-ordinates given by a clock, it is difficult to see how that isn't a factor.

The definition of simultaneity - whether or not two events at different locations occurred at the same time - is agreed upon. My reasoning would lead me to deduce that the underlying assumptions about the nature of time play a fairly pivotal role in determining the simultaneity of events, insofar as those assumptions affect the interpretation of what time co-ordinates represent.

Einsteinian relativity seems to suggest that events with the same time co-ordinates, provided by local clocks, are simultaneous; while events with different time co-ordinates are not simultaneous; because those time co-ordinates represent "proper time". Under ER it is possible that events are simultaneous across some reference frames, while the same events are not simultaneous across others.

It would seem that, under Lorentzian relativity, the time co-ordinates provided by local clocks (excluding the absolute rest frame clocks) cannot be used to determine the simultaneity of events because they do not represent the "true" time co-ordinates of events. It, also, doesn't seem to allow for the possibility that events are simultaneous across some reference frames, but not simultaneous across others; that is, if they are simultaneous in the absolute reference frame, then they are simultaneous in every reference frame because time is absolute, not relative.

No, that's not worth mentioning.

As I have said before, present day LET is usually exactly the same as SR but with a presumed preferred frame in which light propagates at c and in no others.

In the context of the question of whether or not RoS is a consequence of the Lorentz transform, you may be right, it probably isn't worth mentioning.

In a broader discussion on the concept of simultaneity, however, I think it is pretty relevant.

LET does incorporate absolute space and time though, doesn't it?


Just as an aside, would you now of any good resources on LET, or neo-Lorentzian relativity? Not necessarily for understanding SR better, but just for the purpose of developing an all round understanding of scientific theories.

 

[harrylin]

[...stuff that we discuss in all recent posts.]
I don't see the similarities in this case, but if you could elaborate and draw a more direct comparison, then I might be able to see it. My reasoning would lead me to question how only relative velocities can exist, without absolute motion; not necessarily absolute velocity, which might be a contradiction in terms. This is probably a point better suited to the "at rest" thread though.

You claimed that you understood that essential point of Newtonian mechanics; but I already guessed that it was wrong, else you would have understood the comparison. In short, relative velocities are explained as manifestations of absolute velocities. It's all explained/defined here:

http://gravitee.tripod.com/definitions.htm

(just press cancel and scroll on to Scholium! )

You mention about words that had compatible meanings before relativity but not after, and indicate the term "absolute"; how did "absolute" acquire incompatible meanings after relativity, and what does it mean now?

In fact I may have simplified to much, as it seems to have happened already before SR. "Absolute" used to refer to what Newton defined here above; however, it also acquired the meaning as something about which everyone agreed. So, it was common to say for example that velocity is relative, but acceleration and time were "absolute" - meaning that everyone agreed on the measured quantities. Thus Langevin could say that "uniform translation has no absolute sense", without contradicting Newton who claimed that absolute uniform motion exists.
http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

Also, is there an issue in my understanding of "absolute simultaneity" as outlined above?

Yes, and I (as well as others) have been explaining that in the last too-many posts. It's useless to repeat them.

 

[harrylin]

[..]
OK, this is the critical issue, as I see it.

It might be helpful to re-state the definitions again, for clarity:

Absolute simultaneity means that events which are simultaneous in one reference frame, are simultaneous in all reference frames. [..]

That is wrong, as you now know. However, just to repeat for the zillionths time: if measured simultaneity were "absolute" (second meaning of the word), then events which are simultaneous in one reference frame, are simultaneous in all reference frames.

Under Lorentzian relativity, if events are simultaneous in the absolute rest frame, and that frame only, then they are simultaneous across all reference frames - irrespective of differing time co-ordinates from "local clocks".

No. It doesn't make sense to say that events are simultaneous in the absolute rest frame, and that frame only. Instead, that frame gives the label "absolute simultaneity" to clocks that are at rest relative to it and Einstein-synchronised in that condition.
Consequently, any Einstein synchronised clocks at rest in frames that are moving relative to it cannot be truly synchronised, for that would be a contradiction.

I understand that AS is linked to the same unique reference frame as absolute velocity, but I don't think alluding to it sufficiently explains the "absolute velocity" and "velocity is absolute" point being made.

I hope that after reading Newton's definitions, it is finally clear.

[..] If absolute simultaneity means, events that are simultaneous in one reference frame i.e. the absolute reference frame, are simultaneous in all reference frames, then it means that simultaneity (of those events) is absolute.

Indeed; and it doesn't mean that. Instead, it simply means events that are simultaneous in the absolute reference frame - that's where it gets its name from.

Note: I'm not very good in un-brainwashing (or in fact, it's called "de-programming")...

OK, I can't specifically remember it in this, or any similar context, but I may just not have made the connection. It isn't really an essential point I don't think, so I won't labour it.

I think that it's an important point for the topic (and it was already discussed with you!), but it's not the one that bugs you now.

[..] Is this the relevant passage

No, not exactly. In my estimation, you searched about 10 seconds too little! Here is the lacking passage that together with the ones you cited corresponds to your question:

"So we see that we cannot attach any absolute signification to the concept of simultaneity, but that two events which, viewed from a system of co-ordinates, are simultaneous, can no longer be looked upon as simultaneous events when envisaged from a system which is in motion relatively to that system."

There is no difference in the readings, or behaviour of the clocks, but there is a difference in the underlying assumptions of what the readings, and behaviour represent, isn't there?

Sure - it's the difference between taking things at face value and having a model about underlying invisible reality. At the time, Einstein just took things at face value (positivist), only later did he consider such "metaphysics". I guess that is the case for most of us!

But this would just mean that they can't know the true time co-ordinates for events, as opposed to implying that the events are not simultaneous. They would disagree about simultaneity, but unlike the Einsteinian interpretation, there is the possibility that one, or both of them is wrong; because one or both of their clocks doesn't tell the "true time". [..]

SR (and physics, as a matter of fact!) only makes use of operational definitions for measurements. According to the "Definition of Simultaneity", which you pasted here: what is "simultaneous in one frame", is" not simultaneous in other frames"". There is little place for "true" things that cannot be detected in modern physics.

We may be arguing over semantics here.

I'll speak in terms of Albert and Henry moving relative to each other, as per the video posted in this, or another thread; from Albert's perspective, Henry's clock runs slower because the photon in his clock has to travel a longer distance between mirrors i.e. the path represented by the hypotenuse of a right angled triangle.

If, however, the speed of light is c for all observers, it means that lengths must contract and time must slow down for Henry (according to Albert). This means that, according to Albert, Henry's clock ticks slower.

The phrase I would use here is to say that Henry's clock ticks at a slower rate.

Again: Nothing of what you write has anything to do with Einstein's train example. Thus this certainly isn't about semantics but about 100% non-understanding on your part. Again: he discusses relativity of simultaneity and not at all time dilation! Moreover (ans logically), nothing of what you write can found in that passage, here once more:
http://www.bartleby.com/173/9.html

[...] I'm not 100% sure of the intention of the initial part of the post; the concept of RoS under Einsteinian relativity isn't the issue as such. The question pertains to the notion of RoS under Lorentzian relativity, so that we can deduce what the necessary consequences of the Lorentz transform are.

The essential line is "In orthodox Newtonian dynamics the principle of relativity had a simpler form, which did not require the substitution of local time for general time."

Perhaps you don't understand those words? "general time" is what Lorentz earlier noted as "t", and is the same as "absolute" or "true" time.

While Einsteinian relativity abandoned the idea of one universal time, Lorentzian relativity retained it; and while both theories utilise the concept of "local clocks", the underlying assumptions as to what they represent are materially different; to the extent that the Einsteinian interpretation leads to the notion that time is relative, while Lorentzian relativity retains the notion of universal, or "true time".

Again, I wonder if you don't understand the definitions of SR, and even physics in general: the "time" that we use in physics is clock time. We can only work with the tools we have! So, the "time" that you use, on your watch, is the only kind of time that we have access to for physical measurements. And the equations of physics are destined for physical measurements. "Einsteinian interpretation" (of that period) is a kind of non-interpretation: it's simply stating what we will observe, and nothing more.

This means there are fundamentally different assumptions about time and clocks, and therefore the time co-ordinates of events.

Not really: the time co-ordinates of events are man-made. And there is no disagreement about them. That makes the (rather long-winding I fear) article by Langevin so interesting, as he combines the two approaches in a single expose without any problem.

It seems like you are suggesting that because ER uses "local clocks" that AS and RoS are compatible; but as mentioned, there are fundamental, underlying assumptions, about what the time co-ordinates of those clocks represent, which pertains directly to the simultaneity of events.

For a last time (as we have been here several times, we're like a broken record): the assumptions about what the time co-ordinates of those clocks represent, is simply what those clocks indicate - they are merely tools for describing events and processes.
However, Lorentz had until 1905 also problems to understand the simple fact that in practice we never measure metaphysical time, and I vaguely remember that I also had problems with the concept "time" - Not sure, my memory is too poor.

If I might be so bold as to ask you to spell out how the notion of absolute time is not inconsistent with RoS, because you seem to stop just short of it every time; it could simply be that I am not making the connection, but I can't seem to. I have the tendency to assume that the points I make are going to be understood also, but I often find that spelling it out clearly allows for any issues to be clearly identified. [..]

I think that I did, and others too, but here once more: Absolute time is simply the time of the absolute frame, just as absolute velocity is the velocity in the absolute frame. And I think to have presented for you in a very long post how the assumption of such a frame works out perfectly the same as Einstein's 1905 paper, which I had modified accordingly for you for the exact same result.

And we also had this same discussion in February, where I also spelled it out, here:
https://www.physicsforums.com/showthread.php?t=574624

PS I referred here especially to my posts #6 and #54 in that thread.

 

[Dale]

"Absolute" used to refer to what Newton defined here above; however, it also acquired the meaning as something about which everyone agreed. So, it was common to say for example that velocity is relative, but acceleration and time were "absolute" - meaning that everyone agreed on the measured quantities.

I almost exclusively use this more modern meaning of "absolute" rather than Newton's. I.e. "absolute" is short-hand for "frame invariant".

 

[ghwellsjr]

I don't think I am conflating the two, am I?

The concept of reference frames is relevant to Galielan relativity as well isn't it? Galileo's observer on the ship is a particular example, no?

The Galilean Principle of Invariance, or the consequence of it, suggests that an observer cannot determine if they, and by extension their reference frame, are in motion or at rest. This referred to absolute motion and absolute rest, with the implication that they were in one or the other state. If they were indeed at absolute rest, then presumably the concept of an absolute rest frame would make sense.

Is Lorentzian relativity not based on the notion of absolute space, or does it not incorporate it? My understanding was that the Lorentz transform determines the physical contractions of objects as they moved through the ether, or relative to the absolute rest frame.

Galileo did not say, "I believe in an absolute rest frame but I don't believe we can tell if we are at rest or moving in it so I will establish the Principle of Invariance which states that no one can determine if they are at rest or moving in the absolute rest frame". He said, "I don't believe anyone can determine an absolute state of motion so I will establish my Principle of Invariance 'which states that the fundamental laws of physics are the same in all inertial frames'--[Wikipedia article on Galilean invariance]".

Your twisting of such a simple and obvious concept is like someone claiming that unicorns must exist otherwise no one would know what we mean by "I don't believe in unicorns".

Would it be accurate to say that it is SR with absolute time and space, as opposed to relativised spacetime; where the contractions of objects are physical, as opposed to geometrical (is that correct??), and are due to the motion relative to the absolute space; and the Lorentz transform allows observers to determine to what extent the physical instruments of a relatively moving reference frame are contracted, relative to their own reference frame?

Modern day LR, like SR, is not concerned with the mechanics of length contraction or time dilation. It is enough to show that the mathematical laws of physics can go through the Lorentz Transformation process and come out the same as they went into settle the matter. That's all that matters. After Einstein established SR, previous laws of physics that did not come out of the Lorentz Transform the same way they went in were modified until they did. In fact it was the neglect of doing this for all the laws of physics that doomed all the actual Lorentz Ether Theories prior to Einstein and it was his insistence that this be done and could be done in a consistent and meaningful way that made SR superior to all previous attempts. After Einstein showed the way, LET adherents simply adopted all the same predictions and conclusions of SR except insisting that light propagated at c only in one reference frame. Sure sounds like plagiarism to me.

Does that not then mean, that even if events have the same time co-ordinates, after the transform, that it cannot necessarily be said that they are simultaneous, because at least one of those time co-ordinates is not the true time co-orindates of the events?

Equally, if events don't have the same time co-ordinates, after the transform, it cannot necessarily be said that they are not simultaneous, because, again, at least one of the time co-ordinates is not the true time co-ordinates of events?

It is abundantly obvious that you don't have the slightest concept for what an event is and what a transformation does, let alone what a Frame of Reference is. Do you think that is the reason you aren't grasping what everyone is trying to tell you?

Would it be fair to say that LR is effectively just Gailean relativity with physical contractions?

Not even close. Galilean relativity does not incorporate time in the transform. LR does. How do you expect adding length contraction can produce time dilation?

The more you talk, the more obvious it is you haven't even attempted to learn the basics of any kind of relativity. Is that the reason we aren't making any progress?

Everybody and everything is in every reference frame. But if you mean that if an observer is at rest in the absolute rest frame, his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame tick, then that would be correct. But it would also be correct to say that in another frame moving at v in the x direction, if there were an observer moving at v in the -x direction, then his clock would be ticking at the same rate as the coordinate clocks in the absolute rest frame. When we're talking about simultaneity, we are not concerned about an observer's clock and its motions or rest state in a frame. We are talking about the infinite number of coordinate clocks that define time in a particular frame and whether or not two events at different locations occurred at the same time.

Apologies, the emboldened was indeed what I meant.

Why do you apologize and then completely ignore what I just said--as if you never read it?

The reason the [traveling v in the -X direction] observer's clocks would tick at the same rate as the absolue rest frame clocks, is because he would be in the absolute rest frame.

Please say that he is at rest in the absolute rest frame. I just said everyone is in every frame so merely saying that he is in the absolute rest frame doesn't mean anything.

When talking about simultaneity, it has repeatedly been mentioned that events are simultaneous if they have the same time co-orindates; if time co-ordinates are provided by clocks, and the state of relative motion affects the time co-ordinates given by a clock, it is difficult to see how that isn't a factor.

This is more evidence that you have no idea what a frame of reference is.

The definition of simultaneity - whether or not two events at different locations occurred at the same time - is agreed upon. My reasoning would lead me to deduce that the underlying assumptions about the nature of time play a fairly pivotal role in determining the simultaneity of events, insofar as those assumptions affect the interpretation of what time co-ordinates represent.

Einstein's method of building a Frame of Reference defines what time is. Do you remember how many times he used the word "define" and variations of it in just one section of his 1905 paper?

Einsteinian relativity seems to suggest that events with the same time co-ordinates, provided by local clocks, are simultaneous; while events with different time co-ordinates are not simultaneous; because those time co-ordinates represent "proper time". Under ER it is possible that events are simultaneous across some reference frames, while the same events are not simultaneous across others.

I hope there will come a day after you have decided to learn ER that you will come back and read this paragraph of yours and understand how utterly mixed up it is.

It would seem that, under Lorentzian relativity, the time co-ordinates provided by local clocks (excluding the absolute rest frame clocks) cannot be used to determine the simultaneity of events because they do not represent the "true" time co-ordinates of events. It, also, doesn't seem to allow for the possibility that events are simultaneous across some reference frames, but not simultaneous across others; that is, if they are simultaneous in the absolute reference frame, then they are simultaneous in every reference frame because time is absolute, not relative.

In the context of the question of whether or not RoS is a consequence of the Lorentz transform, you may be right, it probably isn't worth mentioning.

In a broader discussion on the concept of simultaneity, however, I think it is pretty relevant.

LET does incorporate absolute space and time though, doesn't it?

Yes, somewhere over the rainbow.

Seriously, mangaroosh, you have so much to learn and you're not learning by doing so much writing. You should stop posting and just read. Read this thread. Read your other threads. Read threads started by other people. Read the first part of Einstein's 1920 book. Read it over and over again. Forget about LET. You'll understand it after you understand SR. SR is really very simple but not if you keep refusing to grasp its basics.

Just as an aside, would you now of any good resources on LET, or neo-Lorentzian relativity? Not necessarily for understanding SR better, but just for the purpose of developing an all round understanding of scientific theories.

It depends on whether you are asking about resources that debunk SR and promote LR or resources that show the practical equivalence of SR and LR. Which do you prefer?

 

[GeorgeDishman]

I think we're in agreement on here, but just to clarify. The term "simultaneity" in both concepts refers to the same thing i.e. happening at the same time.

But both are different concepts, in and of themselves.

Yes, there is a clear difference between whether simultaneity in one frame transfers to others but both phrases use the same meaning of simultaneity.

There is no disagreement over the concept of "simultaneity". I think we agree that it means "happen at the same time"

What I am not clear on is whether the equality of numerical values is a necessary requirement for determining simultaneity in Lorentzian relativity. As I see it, it boils down to a question of what the time co-ordinates represent.

In Lorentzian relativity "local clocks" don't tell the "true time", ...

This where you are making your mistake, the idea of a different type of time is purely philosophical. In order to compare values, we only have available the times read from clocks so simultaneity must be judged on his "local time". That makes it the same as Newton's time and Einstein's. Note the slight difference in meaning where Newton talked of "absolute time" as being the perfectly uniform flow of physical time to distinguish it from the practical time measured by astronomers. He was acutely aware of the inadequacies of clocks and needed to distinguish measured time from that which appears in his equations of motion.

so I can't see how inferences can be made concerning the simultaneity of events, from inaccurate clocks. Those clocks can be used for the purpose of transforming co-ordinates from one reference frame to another, but I don't see how inferences about simultaneity can be made.

Simply because simultaneity in LET refers to "local time", anything else is unmeasurable and hence unscientific, and Lorentz was a scientist.

The inference of simultaneity of events appears to be only possible in the absolute rest frame ..

There is no such thing as an "absolute rest frame" in any of the theories. In Newtonian theory, Galilean Relativity applied. In the philosophy associated with LET, the rest frame of the material aether is significant but it is not "absolute" in any sense, it is just a physical reference material like any other with the exception of being unmeasurable.

, such that if they are simultaneous in that reference frame then they are simultaneous in all reference frames, regardless of the disagreement between observers.

There is no disagreement, they all agree such events are simultaneous as you said.

That we cannot determine the absolute rest frame, is not necessarily important in determining whether LR incorporates AS, or not.

Again, there is no such frame in any of the three theories.

We agree on the idea that simultaneous means "happen at the same time"; where the issue is, as I see it, is in whether or not "at the same time" means having the same time co-ordinate values. The understanding I have is that under Einsteinian relativity it does mean this, but that it doesn't necessarily mean this under Lorentzian relativity.

The reasoning that has lead me to this conclusion is that the time co-ordinates provided by "local clocks", under the Lorentzian interpretation, are not the "true time" co-ordinates of an event.

Exactly, you have put your finger on the error. Relativity of Simultaneity applies to measured time regardless of any putative unmeasurable alternative. Once you understand that, you should see that it operates in the same way in LET and SR.

The "true time" co-ordinates can only be provided by a clock at rest in the absolute rest frame, ..

There is no "absolute rest frame", you have to use the aether-referenced frame because effects like clock slowing depended on the speed of the clock relative to the aether. Bear in mind that the aether was a substance hence some parts might be moving relative to others, life gets more complex in what are known as "dragged aether" theories.

This might be more helpful in clarifying the distinction, because I can't see how RoS is compatible with presentism i.e. the idea that there is only one, single present moment for all observers; the present moment isn't relative, it is the same for all observers.

Things are seldom certain in philosophy, but you are right, presentism is very much on the back foot these days, it is very difficult to reconcile it with relativity.

No, generally we just talk of clocks and time, it is the method that matters and that's always the same. A time is what you read from a clock.

But the underlying assumptions about time are fundamentally different, such that what those clock readings represent are fundamentally different.

Philosophically but that is of no concern to scientists. "Relativity of simultaneity" is purely a scientific term, jargon if you like, and as such it refers specifically to what is measured by clocks.

I'm not certain about the claim that Lorentz's model didn't exhibit absolute simultaneity;

Well it has been explained to you many times but several people so it should be clear by now. I don't think I could make it much clearer, RoS refers to Lorentz's "local times", not unmeasurable aether-relative times.

"Absolute" in this sense means "agreed by all" so "absolute simultaneity" means that, if one observer using local clocks which he considers are synchronised assigns the same time coordinate to two events, then the physics will ensure that any other observer moving relative to the first will also assign equal coordinates using clocks local to the events which he considers synchronised. That would happen if the transforms of Gallilean Relativity applied, it doesn't happen under the Lorentz Transforms. Newton's world model did exhibit absolute simultaneity, those of Lorentz and Einstein do not.

my understanding of RoS is that events which are simultaneous in one reference frame are not necessarily simultaneous in another, such that events can be simultaneous in one reference frame and not simultaneous in another.

My understandin of AS is that events that are simultaneous in one reference frame are simultaneous in all reference frames?

I might be misunderstanding the point you are making here, but I wouldn't say the statements are equivalent at all, I would say that the two statements are incompatible.

I said "absolute simultaneity" means that if one observer assigns equal times to two events, so will others. You said "events that are simultaneous in one reference frame are simultaneous in all reference frames". They are the same, just phrased slightly differently, we both said that AS means agreed by all.

The concept of simultaneity is the same in both, but RoS refers to the joint possibility of simultaneity and non-simultaneity of events, while AS only allows for one or the other; such that RoS is not compatible with AS because AS doesn't allow for the conditions which would constitute RoS.

Correct.

This is something you agreed to above, so I must be misinterpreting what you mean by equivalent.

I do agree, I don't see why you think we differ.

Ultimately I want to understand the physical world better; this requires an understanding of SR, but is not limited to it. In the context of this discussion, however, a large part of the question can be boiled down to what the necessary consequences of the Lorentz transform are; in that context, understanding LET is important, as it also utilises the transform; if there are differences in the theories, then we can make certain deductions about what are and what aren't the necessary consequences of the transform.

Sadly from about 15 years experience of explaining this stuff to many people, I know it doesn't work that way. The only way to make the intellectual switch in your understanding is to lay LET aside for a while, learn SR, and then go back to LET separately. You can see that already in the posts where I have said some things in SR are down to geometry and you struggle to understand how that is possible because your thinking is locked into the philosophy of LET. The transforms are only a tiny part of the subject and you need to clear your mind of contradictory concepts in order to get the SR picture. SR and LET share the maths but the visualisations you need to develop to understand them are diametrically opposed on almost every aspect. When you feel you've done enough on LET to satisfy your curiousity, we can park it and start on SR. You can always go back to it after you master SR of course.

 

[GeorgeDishman]

That sounds great. Take your time in doing it, and certainly don't rush on my account.

I had people round for a private lesson on an entirely different subject tonight, I'm at a class tomorrow and teaching Thursday night and running an event on Sunday so it's getting difficult!

It might be worth clarifying that I (think I) have a decent enough understanding of the notion of relative time; the issue is when I subject it to critical reasoning I come to conclusions which are at odds with Einsteinian relativity; so there must be some issue in my reasoning or in my understanding of certain, key, concepts.

There is. It seems very clear that you don't have a picture of relativistic time in mind at all though I could be wrong, but this is indicative:

In relativity, mass is invariant. It is one of those odd quirks of history that the effect known as "relativistic mass" as a physical change only happens in aether theory!

How does mass increase with speed though?

Invariant means it is the same in all frames i.e. changing speed doesn't change mass! In LET, mass changes in a very strange way (IIRC it is a rank 2 tensor) but like all LET phenomena, there was never an explanation for the effect, it is just pressumed to happen due to an unknown interaction with the aether.

In relativity mass doesn't change with speed, it is the magnitude of the energy-momentum 4-vector and hence is an invariant scalar.

Do you see what I meant in the previous post about the mental pictures you need to learn being diametrically opposed?

Would it be fair to say that the block universe appears to be the logical conclusion of relativity?

I think it would be fair to say it is one of a family of models which are preferred. Relativity favours four-dimensionalism certainly and probably eternalism, and I think perdurantism over endurantism but I'm not sure about exdurantism (which I know little about) and of course there is the question of worm versus stage theory too. It's really too big and inappropriate a subject for this forum.

 

[mangaroosh]

Nonsense. Belief in and obsession over undetectable entities is the purview of ghost stories and superstition, not reason. You do not need to "eschew reason" in order to understand SR.

Btw, the language of reason is math, so if you really want to use reason then you need to learn the math. So far, I have seen no indication of that from you. In fact, I think that you do not want nor embrace reason, but rather intuition. I think your trouble with SR is that it is not intuitive; you are having trouble eschewing intuition and embracing reason.

I don't think I've presented anything other than a reasoned outline of my understanding; I've tried to outline the logic that has lead to the conclusions drawn, and am looking to address any discrepancies logically. According to the logic presented, it is the actual speed of light which would be undetectable, and with it RoS.

Also, math is a subset of reason; would Gödel's incompleteness theorems apply? Either way, insofar as mathematics represents the physical world, what the mathematics represents can be translated into language. There are certain things which maths cannot be used to discuss, such as, why "time" only appears to go in one direction.

This is a different concept from the AS concept presented above, and it is much more in line with the language of LET. Let's look at these two concepts.

AS, as you defined it above, requires a set of at least two equivalent reference frames and a transformation between them. If the transformation between the frames is such that any pair of events which have the same time coordinate in one frame have the same time coordinate in all of the equivalent frames then there is AS. If not, there is RoS. This concept of AS is opposite to RoS, and can be determined simply by looking at the transformation between the equivalent frames.

LET's concept of "true time" identifies a single reference frame, the aether frame, as being unique and not equivalent to any other frame. Time in the undetectable aether frame is called "true time", and so events which are simultaneous in the aether frame would be truly simultaneous. There is no reference to nor comparison of time in different frames, so this is not AS as defined by you above. I don't know if Lorentz ever used the term, but based on the terminology that he did use he would probably call it "true simultaneity".

Note that true simultaneity (refers to simultaneity in a single frame) is not the opposite of relativity of simultaneity (compares simultaneity in multiple frames). LET has RoS, it also has this concept of true simultaneity which is distinct from your and my concept of AS.

The definition of AS, presented, doesn't necessarily require two equivalent reference frames and a transformation between them; I think it requires either the notion of absolute time and space, or timelessness; and LET has the former.


I think it comes back, again, to the distinction between the actual speed of light and the measured speed of light. RoS is a consequence of the constancy of c, but LET postulates that the speed of light is only c in the absolute rest frame; the contractions that occur mean that observers will always measure the speed of light to be c. It is only if the actual speed of light remains constant that RoS occurs, though.

This is incorrect. Simply apply the definition of simultaneity to determine if two events are simultaneous or not. That events are simultaneous in the aether frame does not imply that they are simultaneous in all frames. In fact, the LT from the aether frame to the local frames guarantees that is not the case.

The LT from the aether frame to the local frames will result in different time co-ordinates for the events; but these time co-ordinates are not the "true" time co-ordinates of the events, according to LET; they are false time co-ordinates. If observers could detect the absolute rest frame, they could presumably use that information to calculate that the events were actually simultaneous. That the absolute rest frame cannot be detected just means that they cannot determine if the events were simultaneous; but it can still be reasoned that, if they are simultaneous in the absolute rest frame, then they would be simultaneous in all frames.

Given the experimental equivalence of the two theories, it suggests that simultaneity cannot be determined experimentally, because the two theories cannot be distinguished.

This is true, but not relevant to your stated goal of learning SR. You do not need to reject LET in favor of SR in order to learn SR. Nor do you need to determine that they are experimentally equivalent in order to learn SR.

The stated learning goal was to better understand SR, or expand my understanding of it; here the distinction between simply learning SR and understanding SR can be drawn.

My ultimate learning goal, as I'm sure is the same for everyone here, is to better understand the world; part of this learning goal is to expand my understanding of SR; this includes understanding any and all of the tacit assumptions upon which the theory is based.

LET fortunately provides an alternative interpretation of relativity, which allows for contrast and comparison, which better enables the identification of those tacit assumptions.

Hence the schizophrenic nature of LET: It purports to be a scientific theory, science uses experimental measurements to test theories, but measurements are wrong according to the theory.

Assuming that the measurements are right, is in no way, any more scientific.

 

[GeorgeDishman]

Again, there is no such frame in any of the three theories.
...
There is no "absolute rest frame", you have to use the aether-referenced frame because effects like clock slowing depended on the speed of the clock relative to the aether. Bear in mind that the aether was a substance hence some parts might be moving relative to others, life gets more complex in what are known as "dragged aether" theories.

Actuall, I'm wrong on that, if you look at Newton's Scholium, he did talk of absolute rest and absolute places in his philosophy but they never appear in his science:

"And so, instead of absolute places and motions, we use relative ones; and that without any inconvenience in common affairs; but in philosophical disquisitions, we ought to abstract from our senses, and consider things themselves, distinct from what are only sensible measures of them."​

http://plato.stanford.edu/entries/Newton-stm/scholium.html

 

[mangaroosh]

You claimed that you understood that essential point of Newtonian mechanics; but I already guessed that it was wrong, else you would have understood the comparison. In short, relative velocities are explained as manifestations of absolute velocities. It's all explained/defined here:

http://gravitee.tripod.com/definitions.htm

(just press cancel and scroll on to Scholium! )

Again, apologies, I'm not fully clear on the point you are making; which essential point of Newtonian mechanics are you referring to?

It might be better if I try to outline my understanding of your point, and you can highlight where I am going wrong.

The initial point you were making was that AS is compatible with RoS, because absolute velocity is compatible with relative velocity; I was hoping you would explain why, but you seem to keep referring back to definitions of absolute space and velocity, as well as relative velocity, and saying that the connection should be obvious. Personally I don't see how the example you have provided is the same, hence I was hoping you could outline the logic a little more clearly.

I can see how absolute velocity and relative velocity are compatible, because bodies that are in absolute motion will, by necessity, be in motion relative to other bodies (assuming differing velocities).

Motion, however, is a fundamentally different concept to simultaneity, such that, just because the noun velocity can be preceded by the adjectives "absolute" and "relative" without becoming incompatible; the same cannot be said for simultaneity.

AS refers to where events happen at the same time, for everyone and it doesn't allow for the conditions that constitute RoS i.e. events can happen at the same time for some, but not for others.

In fact I may have simplified to much, as it seems to have happened already before SR. "Absolute" used to refer to what Newton defined here above; however, it also acquired the meaning as something about which everyone agreed. So, it was common to say for example that velocity is relative, but acceleration and time were "absolute" - meaning that everyone agreed on the measured quantities. Thus Langevin could say that "uniform translation has no absolute sense", without contradicting Newton who claimed that absolute uniform motion exists.
http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time
I think it is more prudent, and perhaps more accurate, to take the stricter interpretation of Absolute, which is devoid of the opinion of individuals. It is understandable how it might have acquired such a meaning, when certain assumptions about time and space were prevalent; but removing those assumptions, I think, returns us to the stricter definition.

Yes, and I (as well as others) have been explaining that in the last too-many posts. It's useless to repeat them.

Indeed, and we have been discussing them logically thus far, and there appear to remain some unresolved issues.

 

[harrylin]

[..]
Given the experimental equivalence of the two theories, it suggests that simultaneity cannot be determined experimentally, because the two theories cannot be distinguished.
[..]

It's funny to see you come to a conclusion, after months of discussion, which is the starting point of the 1905 and 1907 papers to which we referred you in the beginning.

Note that Einstein and Lorentz promoted a single theory of physics (purely based on experimental facts, without philosophy) according to which no absolute simultaneity can be established.

 

[harrylin]

Again, apologies, I'm not fully clear on the point you are making; which essential point of Newtonian mechanics are you referring to?

It might be better if I try to outline my understanding of your point, and you can highlight where I am going wrong.

The initial point you were making was that AS is compatible with RoS, because absolute velocity is compatible with relative velocity; I was hoping you would explain why, but you seem to keep referring back to definitions of absolute space and velocity, as well as relative velocity, and saying that the connection should be obvious. Personally I don't see how the example you have provided is the same, hence I was hoping you could outline the logic a little more clearly.

I can see how absolute velocity and relative velocity are compatible, because bodies that are in absolute motion will, by necessity, be in motion relative to other bodies (assuming differing velocities).
[..]
AS refers to where events happen at the same time, for everyone and it doesn't allow for the conditions that constitute RoS i.e. events can happen at the same time for some, but not for others.

[..] "Absolute" used to refer to what Newton defined here above; however, it also acquired the meaning as something about which everyone agreed. [..]

I think it is more prudent, and perhaps more accurate, to take the stricter interpretation of Absolute, which is devoid of the opinion of individuals. It is understandable how it might have acquired such a meaning, when certain assumptions about time and space were prevalent; but removing those assumptions, I think, returns us to the stricter definition. [..]

Fine. Thus you now use Newton's definitions from which follows that "absolute simultaneity" means the same as "true simultaneity", or as some would say, the simultaneity according to "absolute frame" measurements - that is, measurements with a reference system that is at rest in "absolute space". According to SR, we cannot distinguish such a reference system which we may give the label "absolute" from any other inertial frame.

RoS implies that reference systems that are in motion relative to such a reference system (even if we label it "absolute", with corresponding "absolute simultaneity") and which are synchronized in the standard way, will have a different measure of simultaneity.

Why do you think that that is self contradictory?

My comparison was that relativity of velocities implies that reference systems that are in motion relative to such a reference system (even if we label it "absolute", with corresponding "absolute velocities") and which are synchronized in the standard way, will have a different measure of velocities.

And why do you think that that is not self contradictory?

 

[Austin0]

Clock rates have nothing to do with it.
The relevant factor is synchronization. Not that the time readings in one frame don't agree with the readings of another frame but that the clocks in the other frame don't appear to agree with the other clocks in that same frame [appear asynchronous].

Not quite so: clock rates do not directly have to do with Einstein synchronization. However, in the case of clock transport, clock rates have indirectly to do with it.

Of course you are quite right. But My first sentence here is directed , not to the process of synchronization, but to RoS as the OP seemed to think that time dilation and differing clock rates was responsible for the disagreement between frames regarding simultaneity

As to why , one answer seems to be in the Einstein method of synchronization.
This system, based on the speed of light and the calculated length of the light path between clocks automatically produces asynchronous clock systems if the system is in motion. In this case the receiving clock will have moved while the light is in transit so the path from the front to the back of the systems will be shorter than the path from the back to the front

{...yet I believe there is compelling reason to consider this [asynchronicity] actual and relevant, and that is the invariance of measured light speed.)

For example a system at rest with a clock system set up to time light speed in all directions is accelerated to a new velocity will still measure the same speed as previously.

The first two sentences are correct, but your last sentence seems to contradict it... If you accelerate a system, afterwards the clocks are not synchronous anymore according to the synchronization definition; the clocks need to be re-synchronized. Perhaps you just forgot to mention that essential fact?

Yes I forgot. As I had just described how the Convention would produce asynchronous clocks when applied in a moving system and suggested how this particular asynchronicity could explain the measured invariance of c I assumed it was implicit that the Convention was going to be applied at new velocities.Otherwise there was no point whatsoever to the last sentence. Forgive my lack of clarity
Actually my intention in mentioning invariance at all was as logical support for the assumption that the Convention caused asynchronous clocks.
I.e.:Conventionally synched clocks measure a constant c in all frames. Asynchronous clocks offer the only logical explanation for that invariance. Therefore it is logical to assume that the Convention produces an actual, if unquantifiable , degree of asynchronicity.

And no matter how much we accelerate to new velocities the measurement of c will remain the same.
SO it seems to me that unless you consider these changes of velocity somehow illusory and not effecting any change of velocity relative to the light measured it is relevant to seek a rational mechanism to explain why we can't measure this change.

Again, that is wrong, so I now think that you did not just forget to mention it: the change of velocity can directly be measured inside the train on the not-yet re-synchronized clocks - you could use the system as an optical accelerometer.

I see I also forgot to explicitly state that the "new velocity" was inertial and not an instantaneous velocity while accelerating. Oops
Actually acceleration itself desynchronizes clocks but not in a way likely to produce an invariant c.

I have heard various attempts to do this through time dilation and length contraction, but found that not only do these not logically explain the facts, but in fact may be completely irrelevant to the question.


Not that I am suggesting there is anything arbitrary or artificial about the the convention itself. Not only is it totally rational but as far as I can see may be the only rational system possible.
If anyone has an alternative explanation for the measured invariance I would like to hear it.

I missed your explanation (sorry). The explanations that I know are:

1. stationary ether + conservation laws
2. block universe + relativity principle
3. any combination of the above

I find this very interesting but cannot fathom how any of the above could either explain the invariant measurement of c or suggest an alternate rational method of synchronization. I would like to hear the explanation but it is off topic in this thread so I may post a new thread and maybe you might respond there. Thanks for your input.

 

[GeorgeDishman]

No, what it says is that all non-degenerate inertial coordinate systems are equally valid. Remember relativity is geometric so think of it in those terms: on a spacetime diagram the velocity of one object is the angle between their worldlines when they cross. What the PoR is saying is that it is meaningless to ask what the "angle between" is if you only have one line. In fact the same was true in the Newtonian world because it included Galilean Relativity but you can't use the geometric view.

That is essentially what the POR says, but the stated consequence of that is that observers cannot determine if they are in motion or at rest.

In motion or at rest relative to what? In Newton's view, there was 'absolute space' but as he said it only occurs in "philosophical disquisitions", all the science was based on relative motion as he said. In LET, it is your velocity relative to the aether which you cannot determine, there is no absolute frame and in SR all velocities are angles between worldlines so can only ever be relative.

I'm not sure how beneficial it is to think of relativity as solely geometric ..

You haven't learned SR yet, I have. SR deals with the geometry of the physical world and all the effects are purely geometric.

In that case, the stated consequence of the PoR is that if you try to conduct an experiment, wherever you are, to determine if you are moving or at rest, you will not be able to do so.

We aren't talking about Newton's world this time, there is no such concept in SR as being moving or at rest other than relative to some other object, the origin of the coordinate frame you are using. This is a good example of how trying to learn the different models at the same time will make your life more difficult, you will almost certainly continue to make these errors until you concentrate on just one at a time.

 

[harrylin]

Of course you are quite right. But My first sentence here is directed , not to the process of synchronization, but to RoS as the OP seemed to think that time dilation and differing clock rates was responsible for the disagreement between frames regarding simultaneity

OK - and as I found out, you discerned the OP's misunderstanding correctly.

Yes I forgot. As I had just described how the Convention would produce asynchronous clocks when applied in a moving system and suggested how this particular asynchronicity could explain the measured invariance of c I assumed it was implicit that the Convention was going to be applied at new velocities.Otherwise there was no point whatsoever to the last sentence. Forgive my lack of clarity [..] Conventionally synched clocks measure a constant c in all frames. Asynchronous clocks offer the only logical explanation for that invariance. Therefore it is logical to assume that the Convention produces an actual, if unquantifiable , degree of asynchronicity. [..] I see I also forgot to explicitly state that the "new velocity" was inertial and not an instantaneous velocity while accelerating. Oops [..]

Thanks for the clarifications!

And I also made a little glitch: in fact such a set-up with the resulting asynchronicity could be used in principle as an optical speedometer, not just as an accelerometer. I correctly understood that you meant steady velocity.

I find this very interesting but cannot fathom how any of the above could either explain the invariant measurement of c or suggest an alternate rational method of synchronization. I would like to hear the explanation but it is off topic in this thread so I may post a new thread and maybe you might respond there. Thanks for your input.

Looking forward! (and if by chance I happen to miss it, don't hesitate to message me).

 

[harrylin]

[..] You haven't learned SR yet, I have. SR deals with the geometry of the physical world and all the effects are purely geometric. [..]

Sorry, although a discussion of that would be off-topic I think that I should comment: the above is a confusion between a theory and its interpretation - or perhaps you mean a different theory than the one defined by Einstein in 1905-1907, which he gave the name "SR" around 1916.
See also this description of Einstein's general theory: http://en.wikisource.org/wiki/The_Einstein_Theory_of_Relativity

 

[GeorgeDishman]

SR deals with the geometry of the physical world and all the effects are purely geometric.

Sorry, although a discussion of that would be off-topic I think that I should comment: the above is a confusion between a theory and its interpretation - or perhaps you mean a different theory than the one defined by Einstein in 1905-1907, which he gave the name "SR" around 1916.
See also this description of Einstein's general theory: http://en.wikisource.org/wiki/The_Einstein_Theory_of_Relativity

I'm an interested layman and always open to correction but I think my statement is not as inaccurate as you suggest. From about half way down your reference:

"At this point Einstein intervened with a hypothesis which, apart altogether from subsequent verification, deserves to rank as one of the great monuments of human genius. After correcting Newton, it remained to correct Euclid, and it was in terms of non-Euclidean geometry that he stated his new theory. ...

Einstein supposes that space is Euclidean where it is sufficiently remote from matter, but that the presence of matter causes it to become slightly non-Euclidean — the more matter there is in the neighborhood, the more space will depart from Euclid. By the help of this hypothesis, together with his previous theory of relativity, he deduces gravitation — very approximately, but not exactly, according to the Newtonian law of the inverse square."​

In a sense you are right though, I am taking perhaps a more modern viewpoint as GR is now often taught as differential geometry and SR can then be seen as a limiting case of that later theory rather than as it was in the 1905 paper.

I don't claim any originality in this of course, I am only following the example of Taylor and Wheeler with their "Parable of the Surveyors" in Spacetime Physics as I think it provides an intuitive introduction to the subject that emphasises the need to disconnect one's views from the aether-based models.

 

[yuiop]

You haven't learned SR yet, I have. SR deals with the geometry of the physical world and all the effects are purely geometric.

SR is about space and time. Geometry is about space only. Therefore it is inaccurate to claim that all the effects are purely geometrical. Same goes for GR. Geometry does not explain time dilation in SR or GR. However, most physics can be expressed in mathematical terms and most mathematical terms can be expressed in geometrical terms but this does not mean all physics is just geometry any more than it can be claimed that all physics is just mathematics.

 

[DrGreg]

SR is about space and time. Geometry is about space only. Therefore it is inaccurate to claim that all the effects are purely geometrical. Same goes for GR. Geometry does not explain time dilation in SR or GR.

That is a very restrictive view of the term "geometry". In the context of 4-dimensional space time, relativity is all about 4-dimensional geometry. And 4-dimensional geometry explains time dilation very well, it's just an orthogonal projection of one line onto another.

 

[Dale]

My understanding of Absolute Simultaneity (AS) is that if events are simultaneous in one reference frame, then they are simultaneous across all reference frames.

The definition of AS, presented, doesn't necessarily require two equivalent reference frames and a transformation between them

Sure it does. Without more than one reference frame what is the meaning of the phrase "across all reference frames" and without a transformation between the frames how can you determine the time coordinates of the events in the different frames in order to apply the definition of simultaneity in each frame?

Assuming that the measurements are right, is in no way, any more scientific.

This is the single most eggregiously wrong statement you have made during this entire conversation.

In the scientific method the results of experiments (measurements) ALWAYS trump theory. If a theory is shown to be inconsistent with measurements then the theory is FALSIFIED, not the other way around. That is the core of science. Honestly, the whole rest of your issue with LET and SR is completely irrelevant until you get a basic understanding of the scientific method.

http://en.wikipedia.org/wiki/Scientific_method
"To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence"

Not only is assuming that the measurements are right "more scientific", it is the single key characteristic of science which distinguishes it from other forms of learning. Please do not proceed with the rest of your investigation of SR and LET until you have understood the scientific method.

 

[harrylin]

In order not to hijack this thread I will only comment once more on this:

I'm an interested layman and always open to correction but I think my statement is not as inaccurate as you suggest. From about half way down your reference:

"At this point Einstein intervened with a hypothesis which, apart altogether from subsequent verification, deserves to rank as one of the great monuments of human genius. After correcting Newton, it remained to correct Euclid, and it was in terms of non-Euclidean geometry that he stated his new theory. ... [..]

That was not about SR but about GR.
BTW, deviating even further from the topic, what that means is also explained here:
http://www.bartleby.com/173/24.html
http://www.bartleby.com/173/27.html

In a sense you are right though, I am taking perhaps a more modern viewpoint as GR is now often taught as differential geometry and SR can then be seen as a limiting case of that later theory rather than as it was in the 1905 paper.

Exactly.

I don't claim any originality in this of course, I am only following the example of Taylor and Wheeler with their "Parable of the Surveyors" in Spacetime Physics as I think it provides an intuitive introduction to the subject that emphasises the need to disconnect one's views from the aether-based models.

I don't know that parable - you could perhaps start a thread on that.

Cheers,
Harald

 

[GeorgeDishman]

I don't claim any originality in this of course, I am only following the example of Taylor and Wheeler with their "Parable of the Surveyors" in Spacetime Physics as I think it provides an intuitive introduction to the subject that emphasises the need to disconnect one's views from the aether-based models.

I don't know that parable - you could perhaps start a thread on that.

I don't intend to continue the point either but as it is relevant to this thread, here are some references:

http://www.upscale.utoronto.ca/GeneralInterest/Harrison/SpecRel/SpecRel.html#Surveyors

http://spiff.rit.edu/classes/phys200/lectures/intro/parable.html

See slide 7 onwards (this is closest to Taylor and Wheeler):
http://courses.washington.edu/bbbteach/311/2007/Lecture1.pdf

The original:
http://www.amazon.com/dp/0716723271/?tag=pfamazon01-20

 

[mangaroosh]

Hey guys, I will take the time to respond to the other posts, but I think it might be possible to distill the question, of RoS being a consequence of the Lorentz transform, down to a couple of fundamental questions.

Firstly, is RoS compatible with Presentism i.e. the idea that there is one, universal present?
My understanding is that it isn't.

Secondly, is prensentism incorporated in LET?
My understanding is that it is.




The question of laying aside LET to learn SR is not relevant in this particular instance, because we are discussing the LT, and it's necessary consequences, which is used in both theories; therefore, it is necessary, and helpful, to juxtapose both theories to better determine what the necessary consequences of the transform are.

I think the two questions above should help to determine that.

 

[harrylin]

[..]
Firstly, is RoS compatible with Presentism i.e. the idea that there is one, universal present?
My understanding is that it isn't. [..]
Secondly, is prensentism incorporated in LET?
My understanding is that it is. [..]

OK - one last try, on top of all the above! I guess that you will agree that RoS corresponds with differing definitions of distant simultaneity, and evidently you hold that that the stationary ether model implies Presentism.

1."We have seen that simultaneity, as well as the spatial distance of two simultaneous events, have an absolute sense in the usual conceptions of time and space. [..]
Einstein first showed how [..] to determine the characteristics of space and time required by the new conception of the world. [..] observers associated with the two rulers in motion relative to each other don't define simultaneity the same way."

2. "it should not be concluded, as has sometimes happened prematurely, that the concept of aether must be abandoned, that the aether is non-existent and inaccessible to experiment. Only a uniform velocity relative to it cannot be detected, but any change of velocity, or any acceleration has an absolute sense."

- http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

 

[GeorgeDishman]

Hey guys, I will take the time to respond to the other posts, but I think it might be possible to distill the question, of RoS being a consequence of the Lorentz transform, down to a couple of fundamental questions.

Firstly, is RoS compatible with Presentism i.e. the idea that there is one, universal present?
My understanding is that it isn't.

If you consider the twins scenario in the context of presentism, you get something like a Moving Spotlight philosophy. That requires that the ticks of a clock whose worldline is not perpendicular to the hypersurface called "the present" occur at a rate lower than that of a clock that is. That effect implies a physical interaction to cause the slowing thus it implies an aether and with a bit more effort LET falls out.

Secondly, is prensentism incorporated in LET?
My understanding is that it is.

Effectively, LET is a consequence of assuming presentism. Lorentz was assuming Galilean Relativity which is equivalent.

The question of laying aside LET to learn SR is not relevant in this particular instance, because we are discussing the LT, and it's necessary consequences, which is used in both theories; therefore, it is necessary, and helpful, to juxtapose both theories to better determine what the necessary consequences of the transform are.

Your two questions relate only to LET. The current in an R/C circuit and the growth of bacteria both use the exponential function. It is neither necessary nor helpful to juxtapose electrical theory with biology to understand the mathematics of an exponential function. You also have no way to compare the two theories until you have learned them both and since many facets are strongly opposed, my advice remains that you will make it unnecessarily difficult by trying to learn them simultaneously.

 

[GeorgeDishman]

2. "it should not be concluded, as has sometimes happened prematurely, that the concept of aether must be abandoned, that the aether is non-existent and inaccessible to experiment. Only a uniform velocity relative to it cannot be detected, but any change of velocity, or any acceleration has an absolute sense."

- http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

To continue the quote:

We therefore have hold on the ether through accelerations, and acceleration has an absolute sense as determining the production of waves from matter that has undergone a change in velocity, and the aether manifests its reality as the vehicle, as the carrier of energy transported by these waves.​

The document was written in 1911, some time before Einstein's work on the photoelectric effect showed that light is a particulate and before GR removed the absolute sense of acceleration.

IMHO, the nearest modern philosophical equivalent to an aether is Metric Substantivalism, but that's really quite different.