The Relativity of Simultaneity: A Fundamental Concept in Special Relativity

[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.

 

[Austin0]

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.

Hi ,I don't know the historical evolution of RoS but I will give you my take on it.

It is a consequence of the second postulate , the measured invariance of c ,and Einsteins perception that our normal understanding and determination of simultaneity did not apply in a relativistic context. These conditions led to their implementation through the Synchronization Convention and the Lorentz math which charted the resulting relationships (asynchronicity) between clocks at different locations in different inertial frames.

is RoS compatible with Presentism?
Einstein demonstrated that our idea of simultaneity was indeterminable.
That it was meaningless to say (or think) any two spatially separated events were simultaneous in any absolute sense. But this is just as true if this is a presentistic (?) universe.

SO yes, RoS, is as compatible with presentism as it is with block time, as both are essentially philosophical or metaphysical concepts and questions.

Interesting in their own right but unverifiable and superfluous to the understanding and application of SR

IMO the very word simultaneous, with all it's deeply ingrained baggage, should be replaced with a term that had no implication of actual temporal significance. Clockronous maybe?

 

[Austin0]

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.

Hi I can't remember specific source but am sure that Einstein in addressing peers and writing at a much later time expressing these and similar thoughts regarding a medium as a necessary requirement of the propagation of waves. I seem to remember something like "to contemplate that propagation without it was unthinkable."
You are talking about removing the absolute sense of acceleration wrt gravity not with regard to accelerated motion , correct?

 

[Dale]

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.

I think this is a bad approach in principle. How can you hope to gain a better understanding of a well-defined theory like SR by discussing poorly defined concepts like presentism.

What are the experimental consequences of presentism, or is it merely a philosophical viewpoint?

If there are experimental consequences then it should be possible to mathematically derive whether or not the RoS is compatible with it, and if so then it is incorporated in both LET and SR.

If it is merely a philosophical viewpoint with no experimental consequences then the first question is clearly "yes" since it would be compatible with any experimental feature of any theory.

 

[GeorgeDishman]

My previous reply sort of missed the point of this question.

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

IMHO, the term "relativity of simultaneity" in LET refers to measured times. It is therefore unrelated to and independent of any choice of philosophical interpretation such as Presentism.

BTW, if you want to discuss the philosophical side, this is the wrong forum.

 

[harrylin]

[..] Einstein's work on the photoelectric effect showed that light is a particulate and before GR removed the absolute sense of acceleration. [..]

Hmm, not really. If you post that in the QM group you will certainly find that some experts disagree with you about light being a particulate that is incompatible with wave theory; and while GR was meant to remove the absolute sense of acceleration, this is not widely accepted nowadays (you could start a topic on that; meanwhile see for example the physics FAQ: http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html).

PS. as Austin0 mentioned, even Einstein seems to have dropped (or at least weakened) that GR claim a few years later.

 

[mangaroosh]

My apologies, I genuinely believed that the questions I posed were simple, yes or no, questions.

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.

I'm not fully clear on what you mean by "differing definitions of distant simultaneity". Do you mean that RoS corresponds to RoS and Absolute, or true, Simultaneity?

The definition of RoS that I have been working off, as I think we've clarified at this stage, is that events which are simultaneous in one reference frame can be non-simultaneous in another.

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

[/quote]
I'm not sure I can relate the two points above to the questions posed. Is the first point addressing the question of, "is RoS compatible with presentism?"

Is it a simple yes or no question; is RoS compatible with presentism?

Presentism is generally the notion that there is a single, universal present, shared by all observers; while RoS would seem to suggest that the present is relative to each observer and that there isn't actually, or necessarily, a single universal present.

For that reason I would say that the two are not compatible.


Is the second point addressing the question of presentism and LET? The impression that I have gotten from discussing LET on here is that it does incorporate presentism.

 

[mangaroosh]

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.

Does the concept of the block unvierse not require something like a moving spotlight philosophy to explain how static world lines can give rise to the perception of relative motion?

I don't think such a philosophy would be required in a presentist theory.

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

OK, so LET does incorporate presentism.

The question which then remains is, is RoS compatible with presentism?

Where presentism is the notion that there is a single universal present moment, common to all observers, and RoS is the idea that the present moment is relative to each observer and that no single, common present moment actually, or necessarily, exists, then I would say that both are incompatible - is that a fair deduction, or have I erred somewhere?

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.

The discussion is centred on the necessary consequences of the Lorentz transform; as both LET and Einsteinian relativity use the LT, it both necessary and helpful to juxtapose them to help discern what the necessary consequences of the LT are.

If there is an aspect of one theory which is incompatible with the other, then it can't be a necessary consequence of the LT, seeing as how both theories use it.


In order to deduce this, only knowledge of the concepts of presntism and RoS are required, and which theory incorporates which concepts. It isn't necessary to have a working knowledge of the LT, as we are only interested in the outputs of it.

 

[mangaroosh]

Hi ,I don't know the historical evolution of RoS but I will give you my take on it.

It is a consequence of the second postulate , the measured invariance of c ,and Einsteins perception that our normal understanding and determination of simultaneity did not apply in a relativistic context. These conditions led to their implementation through the Synchronization Convention and the Lorentz math which charted the resulting relationships (asynchronicity) between clocks at different locations in different inertial frames.

is RoS compatible with Presentism?
Einstein demonstrated that our idea of simultaneity was indeterminable.
That it was meaningless to say (or think) any two spatially separated events were simultaneous in any absolute sense. But this is just as true if this is a presentistic (?) universe.

SO yes, RoS, is as compatible with presentism as it is with block time, as both are essentially philosophical or metaphysical concepts and questions.

That appears to be a non-sequitir.

That our idea of simultaneity is indeterminable does not necessarily mean that RoS is compatible with presentism.

You mention the possibility that this could be a presentistic universe, suggesting that RoS is itself indeterminable, and therefore a philosophical, or metaphysical, concept. Again, that both are metaphysical concepts does not imply that they are compatible, because they appear to be contradictory philosophical concepts.

Presentism is the idea that there is a single universal present moment, common to all observers; RoS is the idea that the present moment is relative to each observer and that no single, universal present actually, or necessarily, exists.

Interesting in their own right but unverifiable and superfluous to the understanding and application of SR

IMO the very word simultaneous, with all it's deeply ingrained baggage, should be replaced with a term that had no implication of actual temporal significance. Clockronous maybe?

Am I right in saying that you are suggesting that RoS is unverifiable also?

I think the use of the term clockronous could be useful in discussions alright, because it opens the discussion up somewhat. It could be used to try and clarify any potential differences in meaning.

 

[GeorgeDishman]

My apologies, I genuinely believed that the questions I posed were simple, yes or no, questions. ... Is it a simple yes or no question; is RoS compatible with presentism?

Presentism is generally the notion that there is a single, universal present, shared by all observers; while RoS would seem to suggest that the present is relative to each observer and that there isn't actually, or necessarily, a single universal present.

For that reason I would say that the two are not compatible.

Let's see if I can put my answer in more practical terms. Consider an observer, Alice, who has a long rigid pole with a clock at each end, A and B. She uses some practical physical technique to synchronise the clocks, for example by sending a light pulse from A to B where it is immediately reflected back to A. If the time of the pulse being reflected at B is midway between the send and receive times at A, the clocks are defined as being synchronised. A second observer, Bob, traveling past this setup who uses the same technique determines that the clocks are not synchronised. The determination is therefore related to the motion of the observer. That is called the relativity of simultaneity.

1) Can you see that the Lorentz Transforms can be used to calculate by how much Bob will consider the clocks to differ from being synchronised?

2) Can you see that the above scientific definition of synchronisation is independent of any philosophical musing on the nature of time?

 

[GeorgeDishman]

Our posts crossed, sorry for the slight duplication.

Does the concept of the block unvierse not require something like a moving spotlight philosophy to explain how static world lines can give rise to the perception of relative motion?

No, AIUI the Block Universe is considered a version of eternalism while the Moving Spotlight is a version of presentism. The perception of the flow of time is a more complex question perhaps related to the arrow of time and certainly connected with the fact that we only remember in one direction, pastwards.

I don't think such a philosophy would be required in a presentist theory.

It is not necessarily required, there are other versions of presentism.

The question which then remains is, is RoS compatible with presentism?

Where presentism is the notion that there is a single universal present moment, common to all observers, ...

Correct so far.

.. and RoS is the idea that the present moment is relative to each observer and that no single, common present moment actually, or necessarily, exists, then I would say that both are incompatible - is that a fair deduction, or have I erred somewhere?

The error you are making is in grasping what "relativity of simultaneity" means. As I explained in my previous post, it refers to the practical synchronisation of clocks which is governed by the Lorentz Transform.

In order to deduce this, only knowledge of the concepts of presntism and RoS are required, and which theory incorporates which concepts. It isn't necessary to have a working knowledge of the LT, as we are only interested in the outputs of it.

OK, in my previous reply I have tried to isolate the LTs from both the philosophical aspects and the choice of interpretation. You still need the understanding of the transforms but it can be reduced to a "shut-up-and-calculate" (SUAC) philosophy, just put in the numbers, turn the handle and see what you get.

 

[mangaroosh]

Again, I genuinely believed that the questions posed were simple, yes or no, questions.

I think this is a bad approach in principle. How can you hope to gain a better understanding of a well-defined theory like SR by discussing poorly defined concepts like presentism.

What are the experimental consequences of presentism, or is it merely a philosophical viewpoint?

If there are experimental consequences then it should be possible to mathematically derive whether or not the RoS is compatible with it, and if so then it is incorporated in both LET and SR.

If it is merely a philosophical viewpoint with no experimental consequences then the first question is clearly "yes" since it would be compatible with any experimental feature of any theory.

The intention is to better understand what the necessary consequences of the Lorentz transform are; where there are two theories that use the same transform it is necessary to contrast them to help determine what the necessary consequences of that transform are. If there are certain, specific aspects of one theory that are not present in the other, then we can logically deduce that they are not necessary consequences of the transform.


I'm fairly sure that you are relatively familiar with the concept of presentism; the idea that there is a single universal present moment, common to all observers. You may also be aware of the A- and B-theories of time; presentism conforms to the A theory. This article might help to illucidate it more. We also don't necessarily need to mathematically derive if it is compatible with RoS; by examining the concepts we can determine if they are compatible or not.

I know that I've read in another thread, on here, where you have clearly stated that the difference between LET and Einsteinian relativity is philosophical, and that it is essentially a matter of choice which one chooses; given the experimental equivalence of both.

So, although the experimental features of LET are entirely compatible with Einsteinian relativity, they are philosophically quite different. In order to determine what the necessary consequences of the Lorentz transform are, we need to examine some of those concepts.


Are you familiar with the concept of presentism, at all; and is it incorporated into LET, do you know?

 

[GeorgeDishman]

Hmm, not really. If you post that in the QM group you will certainly find that some experts disagree with you about light being a particulate that is incompatible with wave theory;

Oh certainly, I wasn't referring to modern QM but to the idea of light as being waves in the luminiferous aether.

and while GR was meant to remove the absolute sense of acceleration, this is not widely accepted nowadays

I think the Equivalence Principle is still fundamental to an understanding of GR. Anyway my specific source would be d'Inverno:

https://www.amazon.com/dp/0198596863/?tag=pfamazon01-20

There's a table showing what is absolute and what is relative in the various theories. Sorry I don't have a page reference available at the moment.

(you could start a topic on that; meanwhile see for example the physics FAQ: http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html).

From that page:

Although most scenarios in Special Relativity are most easily described using inertial frames, there is no reason why these frames absolutely must be used. The Equivalence Principle analysis of the twin paradox simply views the scenario from the frame in which Stella is at rest the whole time. This is not an inertial frame; it's accelerated, so the mathematics is harder. But it can certainly be done. When the mathematics is described fully, what results is that we can treat a uniformly accelerated frame as if it were an inertial frame with the addition of a "uniform pseudo gravitational field". By a "pseudo gravitational field", we mean an apparent field (not a real gravitational field) that acts on all objects proportionately to their mass; by "uniform" we mean that the force felt by each object is independent of its position. This is the basic content of the Equivalence Principle.​

 

[harrylin]

[..] I'm not fully clear on what you mean by "differing definitions of distant simultaneity". [..] The definition of RoS that I have been working off, as I think we've clarified at this stage, is that events which are simultaneous in one reference frame can be non-simultaneous in another.

That's the same thing: a differing (=disagreeing) definition of distant simultaneity has as consequence that distant events that "are" simultaneous in the one reference frame, "are" non-simultaneous in the other (note again that in SR no philosophical "is" or "are" exist).

I'm not sure I can relate the two points above to the questions posed. Is the first point addressing the question of, "is RoS compatible with presentism?" [..]

Instead, it simply tells you that this presentation introduces the RoS of relativity as fact.

Is the second point addressing the question of presentism and LET? [..]

Together with the first point, it answers the question if the RoS of relativity is compatible with a Lorentz ether. And as you know, the Lorentz ether supports such philosophical ideas as a metaphysical "absolute time" (although not measurable).

 

[Dale]

Again, I genuinely believed that the questions posed were simple, yes or no, questions.

Even simple yes or no questions may be unclear. As in "Are flubnubbits always red?" Simple yes or no questions may also be themselves logically unsound, such as "Have you stopped beating your wife yet?". Your yes or no question is of the former type, unclear. Which is why I asked for clarification:

What are the experimental consequences of presentism, or is it merely a philosophical viewpoint? (the link you posted seems to indicate that it is merely a philosophical viewpoint)

Please clarify your meaning of the word "presentism".

Are you familiar with the concept of presentism, at all; and is it incorporated into LET, do you know?

I have heard the word, but I have never used nor studied the concept, which is why I asked for clarification and also why I think that it is not necessary to a proper understanding of SR.

 

[mangaroosh]

That's the same thing: a differing (=disagreeing) definition of distant simultaneity has as consequence that distant events that "are" simultaneous in the one reference frame, "are" non-simultaneous in the other.

Ah, OK, I didn't get that.

Instead, it simply tells you that this presentation introduces the RoS of relativity as fact.

Forgive me if I leave that for the time being

Together with the first point, it answers the question if the RoS of relativity is compatible with a Lorentz ether. And as you know, the Lorentz ether supports such philosophical ideas as a metaphysical "absolute time" (although not measurable).

Apologies, I couldn't discern that.

But just in relation to the question, is presentism, specifically, incorporated into LET?

Apologies for assuming you are familiar with the concept of presentism, if you are not.

 

[harrylin]

Here we deviate too far from the topic (again, please start a topic of this if you want), so my last comments on these topics here:

Oh certainly, I wasn't referring to modern QM but to the idea of light as being waves in the luminiferous aether.

I fear that possible disproof would be identical; it's quite similar as with Mangaroosh's questions.

I think the Equivalence Principle is still fundamental to an understanding of GR. [..]

There is no issue with the EP, except if you insist that what nowadays are called "pseudo fields", are in fact "real" fields - as discussed in the link that I provided.

 

[harrylin]

[...] But just in relation to the question, is presentism, specifically, incorporated into LET? Apologies for assuming you are familiar with the concept of presentism, if you are not.

Sorry, I'm not familiar with the concept of presentism and disagree with the "LET" concept.

 

[mangaroosh]

Hey George, thanks for the replies; hopefully you can bare with me because I think I'm getting closer to being able to explain my perspective; it is a bit frustrating for me, because I am having dificulty putting my understanding into precise language that might cut through any misunderstanding. I find it is a bit like learning a new language, I can understand more than I can articulate, but through practice I develop the latter ability.

My previous reply sort of missed the point of this question.

IMHO, the term "relativity of simultaneity" in LET refers to measured times. It is therefore unrelated to and independent of any choice of philosophical interpretation such as Presentism.

The term "relativity of simultaneity" as I understand it, and as has been discussed in this thread, refers to the idea that events can be simultaneous for one observer and not simultaneous for another. This leads to the idea that there is no single, universal present moment, commone to all observers.

If presentism is incorporated in LET, then the above description of RoS is not compatible with LET.

That would mean that RoS has two distinct meanings, which are not necessarily compatible with each other.

BTW, if you want to discuss the philosophical side, this is the wrong forum.

This forum is for people who wish to expand their understanding of relativity, and doesn't preclude the philosophical aspects of the theory, I don't think.

Let's see if I can put my answer in more practical terms. Consider an observer, Alice, who has a long rigid pole with a clock at each end, A and B. She uses some practical physical technique to synchronise the clocks, for example by sending a light pulse from A to B where it is immediately reflected back to A. If the time of the pulse being reflected at B is midway between the send and receive times at A, the clocks are defined as being synchronised. A second observer, Bob, traveling past this setup who uses the same technique determines that the clocks are not synchronised. The determination is therefore related to the motion of the observer. That is called the relativity of simultaneity.

1) Can you see that the Lorentz Transforms can be used to calculate by how much Bob will consider the clocks to differ from being synchronised?

2) Can you see that the above scientific definition of synchronisation is independent of any philosophical musing on the nature of time?

I can see how the LT allows Bob to do the calculations. But my understanding of RoS is that it refers more to the simultaneity of events i.e. events could be simultaneous according to Bob, but Alice would disagree.

If we take the asynchronicity of clocks, but assume presentism, then the events would either be simultaneous, or not, regardless of the asynchronicity of the clocks.

If the asynchronicity of the clocks is used to determine RoS, then it requires certain philosophical assumptions about the nature of time.

Our posts crossed, sorry for the slight duplication.

No, AIUI the Block Universe is considered a version of eternalism while the Moving Spotlight is a version of presentism. The perception of the flow of time is a more complex question perhaps related to the arrow of time and certainly connected with the fact that we only remember in one direction, pastwards.

My apologies, I have a different notion of "time" in my head with regard to presentism, so I misread the moving spotlight point.

I think the perception of the flow of time is indeed connected to the fact that we only remember the past, and project the future, but I think the issue of perception of relative motion for static worldlines, in a block universe is much more complex than that.

It is not necessarily required, there are other versions of presentism.

again, apologies, that was my misinterpretation of what you said. I was referring more to the block universe and an explanation for how static world lines perceive motion and change.

Correct so far.

The error you are making is in grasping what "relativity of simultaneity" means. As I explained in my previous post, it refers to the practical synchronisation of clocks which is governed by the Lorentz Transform.

The concept of RoS we have been working off, in this thread, incorporates the synchronisation of clocks, but refers to where events can be simultaneous for one observer and not simultaneous for another; this leads to the conclusion that there is no single, universal present moment commone to all observers. That would mean that RoS is not compatible with presentism.

If presentism is incorporated into LET, then RoS cannot be a necessary consequence of the lorentz transform - as far as I can deduce anyway; but there may be an issue with my logic.

OK, in my previous reply I have tried to isolate the LTs from both the philosophical aspects and the choice of interpretation. You still need the understanding of the transforms but it can be reduced to a "shut-up-and-calculate" (SUAC) philosophy, just put in the numbers, turn the handle and see what you get.

The issue is that the LT is used in two theories with two quite different philosophical interpretations, so when determining if certain philosophical concepts are necessary consequences of the LT, it isn't practical to isolate the LT from the philosophy.

 

[mangaroosh]

Even simple yes or no questions may be unclear. As in "Are flubnubbits always red?" Simple yes or no questions may also be themselves logically unsound, such as "Have you stopped beating your wife yet?". Your yes or no question is of the former type, unclear. Which is why I asked for clarification:

What are the experimental consequences of presentism, or is it merely a philosophical viewpoint? (the link you posted seems to indicate that it is merely a philosophical viewpoint)

Please clarify your meaning of the word "presentism".

Presentism refers to the idea that there is a single, universal present moment, common to all observers.

This would be contrasted with the idea that there is no single, universal present moment, common to all observers; which is a consequence of RoS.

Assuming that the above is an accurate representation of the concept of presentism, would you agree that those two concepts are incompatible?

I have heard the word, but I have never used nor studied the concept, which is why I asked for clarification

It might be worth asking GeorgeDishman for further clarification, as he appears to be familiar with the concept, and may be better able to clarify it that I can, or he might just be able to put it in terms that are more meaningful to you.

and also why I think that it is not necessary to a proper understanding of SR.

This seems to be a recurring point, which I thought I had addressed, but maybe not. Hopefully I can clarify it though.

The topic in question relates to the necessary consequences of the Lorentz transform, which is an integral part of Einsteinian relativity. Considering a second, experimentally equivalent, theory, which also uses the Lorentz transform, can help us to deduce what the necessary consequences of the LT are, thereby expanding our understanding of the LT, with it, Einsteinian relativity.

I refer to the collective "us", not necessarily you and I.

 

[harrylin]

[..]
Apologies for assuming you are familiar with the concept of presentism, if you are not.

PS: I already referred you to Einstein's 1905 paper, and how with only a few small changes of formulation one obtains a version that would have been to Lorentz's taste.

So here are two simple questions to you:
- Do you agree that Einstein's 1905 paper refers to RoS?
- Do you agree that Lorentz believed in "true time"?

Your answer on those questions will surely also answer your own questions.

Harald

 

[mangaroosh]

Sorry, I'm not familiar with the concept of presentism and disagree with the "LET" concept.

The concept of presentism refers to the idea that there is a single, universal present moment, common to all observers.

Assuming this is an accurate representation of "presentism", would you agree that it is incompatible with RoS, which leads to the conclusion that there is no single, universal present moment, common to all observers?


With regard to your disagreement with the LET concept (I presume you refer to the theory as opposed to the concept of presentism), I've read on this site that it is a matter of philosophical preference which you choose to accept, so I don't think there is any issue with regard to your acceptance of it. The question relates to the incorporation, or otherwise, of the concept of presentism in LET.

The impression I have gotten from discussing LET, on this site, is that it does incorporate the concept of presentism.

 

[mangaroosh]

PS: I already referred you to Einstein's 1905 paper, and how with only a few small changes of formulation one obtains a version that would have been to Lorentz's taste.

So here are two simple questions to you:
- Do you agree that Einstein's 1905 paper refers to RoS?
- Do you agree that Lorentz believed in "true time"?

Your answer on those questions will surely also answer your own questions.

Harald

I agree on both counts, but again, I can only ask you to supply a direct answer, because I cannot deduce the answer from what you allude to.

The issue might perhaps lie in the unfamiliarity with the concept of presentism, however.

 

[mangaroosh]

@Harry and Dale

just wondering if you guys are familiar with Newtonian physics; am I right in saying that Newton's theory incorporated absolute space and time, as well as the idea of a single, universal present moment?

I ask bcos I presume there may perhaps be a greater level of familiarity with that theory, than LET, perhaps.

 

[harrylin]

I agree on both counts, but again, I can only ask you to supply a direct answer, because I cannot deduce the answer from what you allude to.

The issue might perhaps lie in the unfamiliarity with the concept of presentism, however.

Perhaps; I can only assume that "presentism" corresponds to "true time". If so, then the fact that Einstein's relativity paper (certainly the part on RoS) is compatible with Lorentz's views makes you already know that the RoS of Einstein's paper is compatible with presentism.

[..] just wondering if you guys are familiar with Newtonian physics; am I right in saying that Newton's theory incorporated absolute space and time, as well as the idea of a single, universal present moment?

Yes and yes (I even referred you to that); and Lorentz's metaphysics was based on such concepts, despite the fact that he introduced "local time" - which includes RoS.

 

[mangaroosh]

Perhaps; I can only assume that "presentism" corresponds to "true time". If so, then the fact that Einstein's relativity paper (certainly the part on RoS) is compatible with Lorentz's views makes you already know that the RoS of Einstein's paper is compatible with presentism.


Yes and yes (I even referred you to that); and Lorentz's metaphysics was based on such concepts, despite the fact that he introduced "local time" - which includes RoS.

Is the idea of a single, universal present moment compatible with the idea that there is no single, universal present moment?

 

[yuiop]

Is the idea of a single, universal present moment compatible with the idea that there is no single, universal present moment?

If I rephrase your question like this:

"Is the idea of a single, (unmeasurable) universal present moment compatible with the idea that there is no single, (measurable) universal present moment?",

then the answer is yes.

 

[mangaroosh]

Hey yuiop.

i don't think your re-statement addresses the issue-it a appears to just make it tautological.

We can simply re-order the adjectives to get,is the idea of an unmeasurable, single, present moment compatible with the idea that there is no measurable, single present moment?

Measurable or not, presentism-as described- would not be compatible with RoS (measurable or not).

 

[GeorgeDishman]

Perhaps; I can only assume that "presentism" corresponds to "true time".

No, crudely, presentism is the philosophy that things that exist are 3-dimensional and that time is an emergent property resulting from the perception of change. It contrasts with eternalism which considers that the past, present and future existence of entities are equally real. See here for a more rigorous introduction:

http://plato.stanford.edu/entries/temporal-parts/

However, I would suggest that you move the discussion to the philosophy forum

https://www.physicsforums.com/forumdisplay.php?f=112

and in particular the "Time: A-series or B-series?" thread.

 

[GeorgeDishman]

Hey George, thanks for the replies; hopefully you can bare with me because I think I'm getting closer to being able to explain my perspective; it is a bit frustrating for me, because I am having dificulty putting my understanding into precise language that might cut through any misunderstanding. I find it is a bit like learning a new language, I can understand more than I can articulate, but through practice I develop the latter ability.

Practice will help but in learning a new language, you also have to listen to people who already speak it when they tell you what the jargon terms mean where they are specific to that language.

The term "relativity of simultaneity" as I understand it, and as has been discussed in this thread, refers to the idea that events can be simultaneous for one observer and not simultaneous for another. This leads to the idea that there is no single, universal present moment, commone to all observers.

The term "relativity of simultaneity" is one of those jargon terms which has a very specific meaning and is not something you can reinvent for yourself if you want to communicate with people who already know the conventional definition. That is why I took the trouble to explain it to you carefully in the previous post.

If presentism is incorporated in LET, then the above description of RoS is not compatible with LET.

Presentism is not "incorporated in LET" as I again tried to explain before. Presentism is a philosophical view while LET is a scientific theory so the two are independent. Let's leave that topic for the philosophy forum.

That would mean that RoS has two distinct meanings, which are not necessarily compatible with each other.

No, it is a jargon term so has only one specific meaning which several people including myself have been patiently explaining to you for several weeks. You seem determined to avoid understanding it.

This forum is for people who wish to expand their understanding of relativity,

Indeed, but you have discussed nothing but LET's version of RoS and philosophy, there isn't a single comment related to relativity in anything you have posted.

and doesn't preclude the philosophical aspects of the theory, I don't think.

You have moved the presentism to the other forum so let's leave that there.

Let's see if I can put my answer in more practical terms. Consider an observer, Alice, who has a long rigid pole with a clock at each end, A and B. She uses some practical physical technique to synchronise the clocks, for example by sending a light pulse from A to B where it is immediately reflected back to A. If the time of the pulse being reflected at B is midway between the send and receive times at A, the clocks are defined as being synchronised. A second observer, Bob, traveling past this setup who uses the same technique determines that the clocks are not synchronised. The determination is therefore related to the motion of the observer. That is called the relativity of simultaneity.

1) Can you see that the Lorentz Transforms can be used to calculate by how much Bob will consider the clocks to differ from being synchronised?

2) Can you see that the above scientific definition of synchronisation is independent of any philosophical musing on the nature of time?

I can see how the LT allows Bob to do the calculations.

Bob doesn't exist, he's hypothetical. The LTs allow you to do the calculations.

But my understanding of RoS is that it refers more to the simultaneity of events i.e. events could be simultaneous according to Bob, but Alice would disagree.

Think about the words. Two clocks are sychronised if their ticks are simultaneous. The time when an event occurs is defined by the reading on a clock local to the event. That means that two events are simultaneous if their times are the same as measured by synchronised clocks or, to put it another way, if their time coordinates are the same. Work through those definitions carefully, we went over this some time ago but you still seem to be having trouble with it. I've repeated the description above because it is key to the context.

If we take the asynchronicity of clocks, but assume presentism, then the events would either be simultaneous, or not, regardless of the asynchronicity of the clocks.

No, that is where you are making you fundamental mistake, you are confusing your philosophy with the science. The phrase "relativity of simultaneity" refers to clock synchronisation, nothing else.

If the asynchronicity of the clocks is used to determine RoS, then it requires certain philosophical assumptions about the nature of time.

No, it refers to the nature of synchronisation of clocks which is an observable fact regardless of any philosophical interpretation.

My apologies, I have a different notion of "time" in my head with regard to presentism, so I misread the moving spotlight point.

So it seems, the references in the other forum should help you on that.

The concept of RoS we have been working off, in this thread, ...

You don't get to choose. The term has been defined for decades. Try learning what it means instead.

If presentism is incorporated into LET ...

It isn't. What I said was that if you assume presentism, you probably get LET but it doesn't follow the other way round. Anyway, let's leave presentism for the philosophy forum.

 

[Austin0]

Hi ,I don't know the historical evolution of RoS but I will give you my take on it.

It is a consequence of the second postulate , the measured invariance of c ,and Einsteins perception that our normal understanding and determination of simultaneity did not apply in a relativistic context. These conditions led to their implementation through the Synchronization Convention and the Lorentz math which charted the resulting relationships (asynchronicity) between clocks at different locations in different inertial frames.

is RoS compatible with Presentism?
Einstein demonstrated that our idea of simultaneity was indeterminable.
That it was meaningless to say (or think) any two spatially separated events were simultaneous in any absolute sense. But this is just as true if this is a presentistic (?) universe.

SO yes, RoS, is as compatible with presentism as it is with block time, as both are essentially philosophical or metaphysical concepts and questions.

Interesting in their own right but unverifiable and superfluous to the understanding and application of SR

IMO the very word simultaneous, with all it's deeply ingrained baggage, should be replaced with a term that had no implication of actual temporal significance. Clockronous maybe?

That appears to be a non-sequitir.

That our idea of simultaneity is indeterminable does not necessarily mean that RoS is compatible with presentism.

That is a non-sequitur as I clearly never said that. I stated that the condition of indeterminacy would be just as much a fact even if the universe was "actually" presentistic.

You mention the possibility that this could be a presentistic universe, suggesting that RoS is itself indeterminable, and therefore a philosophical, or metaphysical, concept. Again, that both are metaphysical concepts does not imply that they are compatible, because they appear to be contradictory philosophical concepts.

yes I cannot rule out the possibility that the universe is presentistic but that in no way suggests that RoS is indeterminable as it simply deals with what IS determinable i.e. Empirical measurements and observations; CLOCKS
At the risk of being redundant; the source of much of your confusion and difficulty in understanding what everybody has been telling you is that you are continually mixing apples and oranges.

Presentism and Block Time are philosophies.
These concepts ARE NOT compatible

SR and LET are scientific theories.
AS theories that that make the same empirical predictions they ARE compatible.

Some LETists are Presentists and some Relativitists are Block Timers but this is completely irrelevant to the Theories themselves.
Philosophically Newton was an Absolutist but as a scientist he was as much of a Relativitist as Einstein. The theories had no element of absolutism.

Presentism is the idea that there is a single universal present moment, common to all observers;

Right.

RoS is the idea that the present moment is relative to each observer and that no single, universal present actually, or necessarily, exists.

WRONG. RoS says absolutely nothing about a present moment or whether or not a universal present moment actually exists. It simply correlates proper time readings in differing
inertial frames.
Once again you are confusing two different interpretations of simultaneous.
RoS is the idea that the proper time reading is relative for each observer.
You are free to interpret this however you choose. Eg; There is a universal now and the clocks are all incorrectly desynchronized according to the universal instant.
RoS is not incompatible with that interpretation , it is merely irrelevant.

Am I right in saying that you are suggesting that RoS is unverifiable also?

No; block time and presentism are unverifiable

But block time is neither a necessary condition for , nor an inevitable logical derivation from RoS
They are mutually independent. But you seem to keep trying find a necessary correspondence and insisting there is one.