The Relativity of Simultaneity: A Fundamental Concept in Special Relativity

[harrylin]

Your logic looks good to me, mangaroosh, but I do not want to hijack this into another block universe discussion.

Ah yes, I forgot to mention that - ok then, I do that now!
Mangaroush you may be interested in this topic:
https://www.physicsforums.com/showthread.php?t=583606

Lorentzian relativity used the LT though, and doesn't incorporate RoS; no?

The LT certainly incorporates RoS, and Lorentz was perhaps the first to introduce the "local time" concept (note: it was probably Poincare who first understood what that means for clocks).

What Lorentzian relativity doesn't incorporate is the "block universe" interpretation, about which a still open discussion exists in the other thread.

 

[mangaroosh]

SR was derived from the observation of the independence of the speed of light from the speed of the source so as such it doesn't need any assumptions. Rather, the old aether model and SR's geometric model are two diametrically opposed philosophical interpretations of the same mathematical theory, the Lorentz Transforms. While it is useful to compare and contrast them, you can't mix them.

For example you say "my metre stick is contracted such that 'my meter' is shorter than 'your metre'" but that only applies in the aether interpretation. In SR, the metre stick is unchanged and the shortening is due to coordinate projection, a purely geometric effect. Mixing the models will usually create confusion simply because of their different interpretations and I butted in because I think that may be part of the cause of the difference of opinions.

The point being made though, is that all we ever have is a measurement of c; however, an ivariant measurement of c, by itself, doesn't imply RoS; only if RoS is assumed along with the measurement of c, can we conclude that RoS prevails - but this would be circular reasoning. That is, we have to assume RoS to arrive at the Eisteinian interpretation, but RoS is one of the conclusions of the Einsteinian interpretation, and so it appears to be circular reasoning.

Lorentz aether theory, or rather neo-Lorentzian relativity, has supposedly been divested of the concept of the aether

 

[Dale]

But RoS is a consequence of the actual speed of light remaining invariant. If the distinction between measured and actual values is made, then RoS doesn't arise.

Again, the distinction between actual and measured values is unimportant. Scientifically, all that matters is the measurements, so all of my statements here refer to measurements. If there is a hidden actuality that cannot be measured then it is irrelevant to physics.

It doesn't have RoS as a necessity though, does it? Again, RoS is not a part of Lorentzian relativity which uses the same transform, no?

No. The RoS falls directly from the Lorentz transform. It is a testable part of any theory which uses the Lorentz transform for experimental predictions. As you have been told multiple times by multiple people now.

 

[mangaroosh]

It was just a precision in my comment on you saying "physical effect"; however that is not the topic here, and that is why I did not elaborate on it.

ah OK, I'm still none the wiser though

No, here is at least one, but likely two errors in one sentence (not regarding a glitch on top of it):

- you mix up reality with a point of view: what I measure with my inertial frame cannot be claimed more "reality" than what you measure with your inertial frame. That is even the basis of SR.

But it isn't being claimed that one measurement is more real than another, it is simply being stated that the same figure of measurement, using different length instruments, means a different actual measurement.

- With my reference frame, the same light ray took - if for example your lab is moving in the same direction as the light ray - a little longer than a second to travel a distance greater than 300,000 km. That is because I measure the speed to be 300,000 km/s.

But if my clock is ticking slower, then it means that "my second" is longer than your second; and if "my metre" is contracted, it means that "my metre" is shorter than "your metre"; so, if I measure the speed of light to be 300,00 km/s and you measure it to be the same, but our measuring instruments are of different lengths, then the actual measurement represented by those units are different - unless the contractions don't acutally occur, and are only illusory.

If you like to suggest that to yourself, then it will look that way; what it suggests to me is what I replied to you earlier.

That isn't so much what I would like to suggest to myself, as opposed to what has been suggested to me by others. I'm not really clear how your formulation differs though.

The example that has been used to demonstrate this, is the lightning rod thought experiment, where the observers disagree about the simultaneity of the events; the observer on the train sees the lightning at the "forward" rod before the "rear" rod, while the observer on the platform sees them as simultaneous; where t=0 is the time when the lightning strikes the rods in the platform observers reference frame, and the time when the train observer is in-line with the platform observer.

The train observer calculates that the flash at B occurred at a time before t=0, while the platform observer calculates that they both occurred at t=0. In order for the platform observer to accept this, he must make an assumption about the existence of the lightning event before t=0, as well as the event after t=0. The train observer must make similar assumptions.

That kind of conclusions from the suggestion that you fell for suggest to me that it is likely a wrong one.

As Bobc2 mentiosn above, it appears to be necessary to accept the concept of "the block universe", or even RoS.

 

[mangaroosh]

Your logic looks good to me, mangaroosh, but I do not want to hijack this into another block universe discussion.



I don't think that is necessarily contrary to emprical evidence, but again, I don't want to get into this any further.

Thanks bob.

I'm not sure if it makes a difference, as the thread starter, to say that I don't think you'd be hijacking it; it seems to be a related concept.

 

[mangaroosh]

Again, the distinction between actual and measured values is unimportant. Scientifically, all that matters is the measurements, so all of my statements here refer to measurements. If there is a hidden actuality that cannot be measured then it is irrelevant to physics.

The point above demonstrates that it is an important distinction, because an invariant measurement of c doesn't necessarily imply RoS.

No. The RoS falls directly from the Lorentz transform. It is a testable part of any theory which uses the Lorentz transform for experimental predictions. As you have been told multiple times by multiple people now.

This conflicts with what has been said about Lorentzian relativity though, by multiple people, multiple times; that Lorentzian relativity doesn't include RoS, but yet it does use the Lorentz transform. If this is true, then it is a non-sequitir to suggest that RoS is necessarily a consequence of the LT.

As has also been stated by miltiple people, multiple times, RoS is a consequence of an invariant speed of light.

Again, as has been demonstrated, an invariant measurement of c does not imply an invariant actual speed of c.


That it may be a hidden actuality isn't relevant, it's that one interpretation appears to rely on circular reasoning, while the other doesn't.

 

[GeorgeDishman]

The point being made though, is that all we ever have is a measurement of c; however, an ivariant measurement of c, by itself, doesn't imply RoS; only if RoS is assumed along with the measurement of c, can we conclude that RoS prevails - but this would be circular reasoning. That is, we have to assume RoS to arrive at the Eisteinian interpretation, but RoS is one of the conclusions of the Einsteinian interpretation, and so it appears to be circular reasoning.

If you look at his paper though, you find he didn't assume RoS, his two postulates were only that light moved at a speed which was independent of the speed of the source and that the laws of electrodynamics and optics apply in any inertial frame. The RoS is then derived from those.

http://www.fourmilab.ch/etexts/einstein/specrel/www/

Lorentz aether theory, or rather neo-Lorentzian relativity, has supposedly been divested of the concept of the aether

Really? Lorentz's interpretation was that objects shrank by an amount determined by their speed relative to the aether in the direction of motion. How can that speed be defined without an aether? It not only must exist, it must also provide a reference against which motion can be measured (which is a much stricter requirement).

 

[harrylin]

[..]
But it isn't being claimed that one measurement is more real than another, it is simply being stated that the same figure of measurement, using different length instruments, means a different actual measurement.
[..]
so, if I measure the speed of light to be 300,00 km/s and you measure it to be the same, but our measuring instruments are of different lengths, then the actual measurement represented by those units are different [..]

Yes i can agree with that.
[..]

The example that has been used to demonstrate this, is the lightning rod thought experiment, where the observers disagree about the simultaneity of the events; the observer on the train sees the lightning at the "forward" rod before the "rear" rod, while the observer on the platform sees them as simultaneous; where t=0 is the time when the lightning strikes the rods in the platform observers reference frame, and the time when the train observer is in-line with the platform observer.

The train observer calculates that the flash at B occurred at a time before t=0, while the platform observer calculates that they both occurred at t=0. In order for the platform observer to accept this, he must make an assumption about the existence of the lightning event before t=0, as well as the event after t=0. The train observer must make similar assumptions.

As Bobc2 mentiosn above, it appears to be necessary to accept the concept of "the block universe", or even RoS.

Now assume that by chance (just for simplicity of discussion) that the train is at rest in the ether (Lorentz interpretation). Then everything will be measured as Einstein described. And then there is nothing mind-boggling going on at all.
Historically you can choose between the Lorentz interpretation (stationary ether) and the Minkowski interpretation (block universe), and in recent years a few more subtle variants have appeared (I think we had a recent topic on that). But all those interpretations of RoS should not be confounded with the RoS itself, which as Dalespam mentioned is a feature of the equations that we call Lorentz Transformations, and which apply to certain reference systems that are set up in a certain way.

 

[Dale]

an invariant measurement of c doesn't necessarily imply RoS.

I agree. That is why I said (\text{C} \cap \text{PoR})\rightarrow \text{RoS} and not \text{C}\rightarrow \text{RoS}

This conflicts with what has been said about Lorentzian relativity though, by multiple people, multiple times; that Lorentzian relativity doesn't include RoS, but yet it does use the Lorentz transform. If this is true, then it is a non-sequitir to suggest that RoS is necessarily a consequence of the LT.

As has also been stated by miltiple people, multiple times, RoS is a consequence of an invariant speed of light.

OK, point well made, we cannot appeal to numbers of sources for a correct analysis. That is why math derivations are so important. I can and have backed up all of my claims mathematically.

RoS is an unavoidable and testable consequence of any theory which uses the LT for its experimental predictions. Any assertion to that any Lorentz-transform based theory does not have RoS is either wrong or deliberately referring to something untestable and therefore scientifically irrelevant.

 

[mangaroosh]

If you look at his paper though, you find he didn't assume RoS, his two postulates were only that light moved at a speed which was independent of the speed of the source and that the laws of electrodynamics and optics apply in any inertial frame. The RoS is then derived from those.

http://www.fourmilab.ch/etexts/einstein/specrel/www/

The point being made, though, is that an invariant measurement of c is different to the actual speed of c remaining invariant; where only an invariant actual speed of c results in RoS, and a measurement of c doesn't necessarily.

Given that we only ever have a measurement of c, RoS would have to be assumed; although the points being raised by DaleSpam and Harrylin, below, might offer a different interpretation.

Really? Lorentz's interpretation was that objects shrank by an amount determined by their speed relative to the aether in the direction of motion. How can that speed be defined without an aether? It not only must exist, it must also provide a reference against which motion can be measured (which is a much stricter requirement).

I'm not so sure that the alternative that time and space are affected by the motion of an object is any less fantastical, particularly when the effects can only be measured using the objects that Lorentzian relativity claims would shrink. Also, I think neo-Lorentzian relativity does away with the concept of the aether, and instead uses the concept of an absolute rest frame.

Without the ether the speed could probably be defined by defining a "rest frame" for measurements, as opposed to an ether.

 

[mangaroosh]

Yes i can agree with that.
[..]

Now assume that by chance (just for simplicity of discussion) that the train is at rest in the ether (Lorentz interpretation). Then everything will be measured as Einstein described. And then there is nothing mind-boggling going on at all.
Historically you can choose between the Lorentz interpretation (stationary ether) and the Minkowski interpretation (block universe), and in recent years a few more subtle variants have appeared (I think we had a recent topic on that). But all those interpretations of RoS should not be confounded with the RoS itself, which as Dalespam mentioned is a feature of the equations that we call Lorentz Transformations, and which apply to certain reference systems that are set up in a certain way.

I think you've mentioned the difference between the two kinds of RoS before, but I'm not entirely clear on what is meant. The issue gets somewhat muddied for me when you mention the alternatives as being the block universe and a stationary ether, because I've read that the concept of the ether has been effectively removed from neo-Lorentzian relativity, with the concept of an "absolute rest" frame being retained.

When I think of RoS I think of it as contrasted with absolute simultaneity, or the idea that only the present moment exists.


--------------------------------------------------------------------------------
Have to run, will try and finish this at home

 

[Dale]

When I think of RoS I think of it as contrasted with absolute simultaneity, or the idea that only the present moment exists.

The idea that only the present moment exists is called presentism, and is contrasted with the idea that past present and future all exist on equal footing, which is called eternalism. They are both philosophical concepts that do not have any scientific meaning (i.e. they do not lead to testable predictions).

Simultaneity is the concept of whether or not two different events happened at the same time. Two things may be simultaneous regardless of if you accept eternalism or presentism.

The relativity of simultaneity means that two observers moving relative to one another will disagree about whether or not two events are simultaneous. Any theory which uses the Lorentz transform for its experimental predictions automatically incorporates the relativity of simultaneity into its measurements.

 

[GeorgeDishman]

The point being made, though, is that an invariant measurement of c is different to the actual speed of c remaining invariant;

You need to explain to me what you mean by "actual speed" if it isn't what is measured.

where only an invariant actual speed of c results in RoS, and a measurement of c doesn't necessarily.

RoS will always occur if the universe is Lorentz Invariant irrespective of interpretation as 'DaleSpam' has said.

Given that we only ever have a measurement of c, RoS would have to be assumed;

No, it follows as a consequence. You can define a method for synchronising clocks by sending a light signal from A to B and back to A for example. If you apply that method in two frames, you get different decisions as to whether two events are simultaneous. It turns out that all other physically possible methods are equivalent.

I'm not so sure that the alternative that time and space are affected by the motion of an object is any less fantastical

I would probably agree but that's not an interpretation I've ever heard of, the only ones I know are LET and SR.

Also, I think neo-Lorentzian relativity does away with the concept of the aether, and instead uses the concept of an absolute rest frame. Without the ether the speed could probably be defined by defining a "rest frame" for measurements, as opposed to an ether.

You will see that suggestion made by people who don't understand LET (or basic physics for that matter) but it has never been a theory. In LET, the mechanism that causes the various effects is an interaction with the aether hence the velocity that goes into the transforms is that of the object relative to the aether. Without some physical substance against which to measure velocity, there is no way to define the quantity. Note you can't even measure speed relative to something which is continuous, a uniform electric potential for example.

 

[GeorgeDishman]

They are both philosophical concepts that do not have any scientific meaning (i.e. they do not lead to testable predictions).

I'm not sure that is true, doesn't presentism require an aether-like approach to avoid temporal displacement in the twins scenario?

This is probably a topic better discussed in the philosophy forum though.

 

[harrylin]

I think you've mentioned the difference between the two kinds of RoS before, but I'm not entirely clear on what is meant. The issue gets somewhat muddied for me when you mention the alternatives as being the block universe and a stationary ether, because I've read that the concept of the ether has been effectively removed from neo-Lorentzian relativity, with the concept of an "absolute rest" frame being retained.

What is the difference, except for words?

When I think of RoS I think of it as contrasted with absolute simultaneity, or the idea that only the present moment exists. [..]

That sounds like the block universe interpretation to me.

A good start for such philosophical issues may be Newton's mechanics, which defines "absolute" and "relative" velocities. Newton's mechanics compares to classical mechanics as Lorentzian mechanics to special relativity.

Here's another one: in England people live in another time than in Germany. Do you think that such time definitions have anything to do with existence of a present moment or not?

Cheers,
Harald

 

[mangaroosh]

I agree. That is why I said (\text{C} \cap \text{PoR})\rightarrow \text{RoS} and not \text{C}\rightarrow \text{RoS}

That depends on the interpretation of the PoR. If the measurement of c remains invariant, then an observer cannot conduct an experiment to distinguish their reference frame from any other, but this still wouldn't necessarily imply RoS.

OK, point well made, we cannot appeal to numbers of sources for a correct analysis. That is why math derivations are so important. I can and have backed up all of my claims mathematically.

RoS is an unavoidable and testable consequence of any theory which uses the LT for its experimental predictions. Any assertion to that any Lorentz-transform based theory does not have RoS is either wrong or deliberately referring to something untestable and therefore scientifically irrelevant.

RoS isn't testable either though, is it?

Do you, by any chance, know what people might be referring to when they say that Lorentzian relativity incorporates absolute simultaneity, and not RoS?

 

[Dale]

That depends on the interpretation of the PoR. If the measurement of c remains invariant, then an observer cannot conduct an experiment to distinguish their reference frame from any other, but this still wouldn't necessarily imply RoS.

Yes, it does necessarily imply RoS. That was one of the points of sections 2 and 3 of Einstein's paper "On the Electrodynamics of Moving Bodies".

RoS isn't testable either though, is it?

Yes, it is. Synchronize two sets of clocks moving relative to each other, measure the time of two events, and see if they agree on the simultaneity.

 

[mangaroosh]

Yes, it does necessarily imply RoS. That was one of the points of sections 2 and 3 of Einstein's paper "On the Electrodynamics of Moving Bodies".

OK, but is there an issue with the logic, as outlined above, that it doesn't necessarily imply it, because you can have an invariant measurement of c without implying RoS; only an invariant actual measurement of c results in RoS; and we can't make such deductions from only an invariant measurement of c.

The consequence of the PoR would also remain intact.

Yes, it is. Synchronize two sets of clocks moving relative to each other, measure the time of two events, and see if they agree on the simultaneity.

There is an assumption in that which relates to a closed thread (which is under appeal) so I'm not sure how explicit I can be, without risking an infraction. The thread is in the general discussion section an pertains to the mechanics of a clock.


If, however, we take the example of two relatively moving atomic clocks, which use a laser and detector (or photon and detector) to "measure the time of two events"; the relatively moving clocks might tick at different rates because the photon in each clock has a different distance to travel to the detector. This wouldn't demonstrate RoS, rather slower ticking clocks.

 

[mangaroosh]

The idea that only the present moment exists is called presentism, and is contrasted with the idea that past present and future all exist on equal footing, which is called eternalism. They are both philosophical concepts that do not have any scientific meaning (i.e. they do not lead to testable predictions).

Simultaneity is the concept of whether or not two different events happened at the same time. Two things may be simultaneous regardless of if you accept eternalism or presentism.

The relativity of simultaneity means that two observers moving relative to one another will disagree about whether or not two events are simultaneous. Any theory which uses the Lorentz transform for its experimental predictions automatically incorporates the relativity of simultaneity into its measurements.

Is RoS compatible with presentism? My understanding is that it isn't.

My understanding is also that Lorentzian relativity includes presentism, and hence why I am of the understanding that it doesn't include RoS.

 

[mangaroosh]

You need to explain to me what you mean by "actual speed" if it isn't what is measured.

The point was that if two observers measure the speed of light to be 300,000km/s but the instruments of one of the observers are contracted, such that his metre stick is shorter than the metre stick of his counterpart, and his clock ticks slower than his counterparts clock, then the actual speeds represented by those two measurements are not the same.

RoS will always occur if the universe is Lorentz Invariant irrespective of interpretation as 'DaleSpam' has said.

OK, but people on here have mentioned that Lorentzian relativity includes absolute simultaneity (presentism) and not RoS.

No, it follows as a consequence. You can define a method for synchronising clocks by sending a light signal from A to B and back to A for example. If you apply that method in two frames, you get different decisions as to whether two events are simultaneous. It turns out that all other physically possible methods are equivalent.

This requires the assumption that it takes an equal amount of time for the light to travel in each direction, doesn't it?

I would probably agree but that's not an interpretation I've ever heard of, the only ones I know are LET and SR.

Does SR not suggest that time and space are affected by the motion of an observer, such that time slows down and space contracts?

You will see that suggestion made by people who don't understand LET (or basic physics for that matter) but it has never been a theory. In LET, the mechanism that causes the various effects is an interaction with the aether hence the velocity that goes into the transforms is that of the object relative to the aether. Without some physical substance against which to measure velocity, there is no way to define the quantity. Note you can't even measure speed relative to something which is continuous, a uniform electric potential for example.

I know that LET includes the aether, but what is termed neo-Lorentzian relativity supposedly has been divested of the concept of the aether

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

 

[mangaroosh]

What is the difference, except for words?

I'm not sure to be honest. My understanding is that neo-Lorentzian relativity includes, or is compatible with, presentism, but that presentism isn't compatible with RoS, which would lead to the conclusion that neo-Lorentzian relativity doesn't include RoS and so the Lorentz transform doesn't necessarily include RoS.

But, if RoS is included by necessity in the LT, then there must be two different interpretations of RoS - unless there is an issue with the reasoning above.

That sounds like the block universe interpretation to me.

Are there other interpretations of RoS?

A good start for such philosophical issues may be Newton's mechanics, which defines "absolute" and "relative" velocities. Newton's mechanics compares to classical mechanics as Lorentzian mechanics to special relativity.

Apologies, I don't fully understand the comparison.

Here's another one: in England people live in another time than in Germany. Do you think that such time definitions have anything to do with existence of a present moment or not?

Nothing whatsoever I would say. I would say that when it is 2pm in England, it is 3pm in Germany, but both exist, simultaneously, in the present moment.

 

[mangaroosh]

Yes, it does necessarily imply RoS. That was one of the points of sections 2 and 3 of Einstein's paper "On the Electrodynamics of Moving Bodies".

OK, but is there an issue with the reasoning, outlined above, that an invariant measurement of c doesn't imply RoS, that it is only an actual measurement of c that implies it?

Given that the oft stated consequence of the the PoR would remain intact i.e. no experiment could distinguish between reference frames.

Yes, it is. Synchronize two sets of clocks moving relative to each other, measure the time of two events, and see if they agree on the simultaneity.

Lorentzian relativity would suggest that the different time measurements of the clocks would be down to the mechanical effects on the clock, wouldn't it, and not due to time slowing down; this would preserve the concept of absolute simultaneity wouldn't it?

How would we determine that time, as opposed to the mechanics of the clock, has been affected?

 

[GeorgeDishman]

The point was that if two observers measure the speed of light to be 300,000km/s but the instruments of one of the observers are contracted, such that his metre stick is shorter than the metre stick of his counterpart, and his clock ticks slower than his counterparts clock, then the actual speeds represented by those two measurements are not the same.

"Speed" is a measurement. If the length of his ruler and times on his clock comply with the physical definition of the metre and second, then the actual speed he has measured is c.

OK, but people on here have mentioned that Lorentzian relativity includes absolute simultaneity (presentism) and not RoS.

Lorentz's aether assumed Galilean Relativity and proposed ad hoc physical changes in objects due to an unknown mechanical interation between matter and the substance of the aether to explain the invariance of the speed of light so it is compatible with both presentism and eternalism. However the Relativity of Simultaneity refers to events having different separation of their time coordinates in mutually moving frames so it still occurs in LET. LET offers an alternative philosophical explanation for the RoS but since it is an observed effect, it could not discard it without being falsified.

This requires the assumption that it takes an equal amount of time for the light to travel in each direction, doesn't it?

c can be derived from the permitivity and permeability in Maxwell's Equations. Both are scalar hence the speed must be scalar and therefore it must be isotropic.

Does SR not suggest that time and space are affected by the motion of an observer, such that time slows down and space contracts?

No, SR says that spacetime has fixed Reimann geometry. Draw two dots on a plain white sheet of paper. Place a grid drawn on a transparent sheet over the top and measure the X and Y coordinates of the dots. Now rotate the transparency a little. You get different coordinate separations but the white sheet of paper has neither shrunk nor stretched and the dots haven't moved. SR says changing your coordinate scheme will change the numbers that label an event but that's all. Spacetime intervals are invariant for the same reason that Pythagoras will give the same result for the separation of the dots regardless of how you orient the transparency with the gridlines.

 

[Dale]

OK, but is there an issue with the logic, as outlined above, that it doesn't necessarily imply it, because you can have an invariant measurement of c without implying RoS; only an invariant actual measurement of c results in RoS; and we can't make such deductions from only an invariant measurement of c.

Scientifically there is no issue since, as I have mentioned several times, any unmeasurable aspects are scientifically irrelevant. This site is for discussing science, not philosophy.

If, however, we take the example of two relatively moving atomic clocks, which use a laser and detector (or photon and detector) to "measure the time of two events"; the relatively moving clocks might tick at different rates because the photon in each clock has a different distance to travel to the detector. This wouldn't demonstrate RoS, rather slower ticking clocks.

Correct, as we have discussed previously TD and RoS are two entirely different concepts.

 

[Dale]

Lorentzian relativity would suggest that the different time measurements of the clocks would be down to the mechanical effects on the clock, wouldn't it, and not due to time slowing down; this would preserve the concept of absolute simultaneity wouldn't it?

No. In LET local time exhibits RoS.

How would we determine that time, as opposed to the mechanics of the clock, has been affected?

We cannot. That is why the distinction is scientifically meaningless.

 

[harrylin]

[..] My understanding is that neo-Lorentzian relativity includes, or is compatible with, presentism, but that presentism isn't compatible with RoS, which would lead to the conclusion that neo-Lorentzian relativity doesn't include RoS and so the Lorentz transform doesn't necessarily include RoS.

I don't know what you call "neo-Lorentzian relativity". Do you have a quality reference for that? And is it useful?

But, if RoS is included by necessity in the LT, then there must be two different interpretations of RoS - unless there is an issue with the reasoning above.

Yes, and several of us have mentioned and explained this several times to you...

Are there other interpretations of RoS?

Sure - as you know. Lorentz's "Local time" is RoS with an interpretation that differs from Minkowski's interpretation.

Apologies, I don't fully understand the comparison.

It's useful to first understand the basis of such discussions - thus, can you explain how there can be both absolute and relative velocity in Newton's mechanics? Or, in other words, is velocity absolute or relative in his theory?

I would say that when it is 2pm in England, it is 3pm in Germany, but both exist, simultaneously, in the present moment.

In SR (that is, the Lorentz transformation), when a certain clock of S indicates for example 2PM, another clock of S' that passes that clock at that time (thus at the same place and moment) will indicate for example 3PM. For some reason (a reason that escapes me), you think that this has big philosophical implications, while a similar case with time zones on Earth has none...

 

[mangaroosh]

"Speed" is a measurement. If the length of his ruler and times on his clock comply with the physical definition of the metre and second, then the actual speed he has measured is c.

Yes, but if the instruments used by one observer are contracted compared to anothers, then the same measurement of 300,000 km/s would represent different actual speeds.

Lorentz's aether assumed Galilean Relativity and proposed ad hoc physical changes in objects due to an unknown mechanical interation between matter and the substance of the aether to explain the invariance of the speed of light so it is compatible with both presentism and eternalism. However the Relativity of Simultaneity refers to events having different separation of their time coordinates in mutually moving frames so it still occurs in LET. LET offers an alternative philosophical explanation for the RoS but since it is an observed effect, it could not discard it without being falsified.

Apologies, I thought I had posted this already in this thread, but it must have been a different one:

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

This suggests, and has been echoed by others on here, that the concept of the aether has been removed from Lorentzian relativity, leaving just the concept of an "absolute reference frame".

The RoS in Lorentzian relativity is materially different to Einsteinian; indeed, absolute simultaneity is incorporated in Lorentzian relativity - as it must if presentism is to prevail - so I think referring to it as RoS is somewhat of a misnomer - but that might just be my interpretation of the concepts of absolute simultaneity and RoS.

Would you say that absolute simultaneity is compatible with RoS?

c can be derived from the permitivity and permeability in Maxwell's Equations. Both are scalar hence the speed must be scalar and therefore it must be isotropic.

apologies, I don't fully understand the point pertaining to the P & P in Maxwell's equations.

I'm not sure if it would help to give some context for the discussion, but this thread stems from a different discussion, where the contention was that the speed of c from Maxwell's equations tacitly assumes the Earth as the rest frame for measurements, so the conclusion would be that Maxwell's equations include the tacit assumption that the constancy of c is relative to the earth.

To avoid dragging this thread off on a tangent, here is a link to the constancy of c thread.

No, SR says that spacetime has fixed Reimann geometry. Draw two dots on a plain white sheet of paper. Place a grid drawn on a transparent sheet over the top and measure the X and Y coordinates of the dots. Now rotate the transparency a little. You get different coordinate separations but the white sheet of paper has neither shrunk nor stretched and the dots haven't moved. SR says changing your coordinate scheme will change the numbers that label an event but that's all. Spacetime intervals are invariant for the same reason that Pythagoras will give the same result for the separation of the dots regardless of how you orient the transparency with the gridlines.

Is spacetime a physical property/substance?

 

[mangaroosh]

Scientifically there is no issue since, as I have mentioned several times, any unmeasurable aspects are scientifically irrelevant. This site is for discussing science, not philosophy.

Is this site not also for discussing the philosophy of science, no? The conclusions drawn from experiments are largely a matter of philosophy, as this discussion on RoS is demonstrating.

We cannot determine that the actual speed of light remains constant, but some of the conclusions drawn assume it to be so; insofar as those conclusions are scientifically relevant, then so to are the unmeasurable aspects.

Correct, as we have discussed previously TD and RoS are two entirely different concepts.

No. In LET local time exhibits RoS.

OK, this is where we are at cross purposes I think.

It has been mentioned in a thread on Lorentzian relativity that it incorporates absolute simultaneity, in the form of presentism; to my mind - and this could be where the issue lies - RoS is not compatible with absolute simultaneity.

Again, to my understanding, form discussions on here and elsewhere, local time in LR isn't "real" time; the difference in time co-ordinates is due to the mechanics of the clock being affected by motion, as opposed to "time itself" being affected.

Again, how I understand it is, under an LR interpretation, absolute simultaneity, and a shared present moment, prevails, while under ER, the present moment is entirely relative and one observers past can be another's present, while one observers future can be another observers present; and other such combinations.


That is the distinction I would draw between RoS and absolute simultaneity; which I think is necessary because it refers to the simultaneity of physical events, as opposed to the ascription of mathematical time co-ordinates.

We cannot. That is why the distinction is scientifically meaningless.

I don't think it is scientifically meaningless when distinction materially affects the scientific models; where claims to the physicality of time are made, surely it is an important distinction.

 

[GeorgeDishman]

"Speed" is a measurement. If the length of his ruler and times on his clock comply with the physical definition of the metre and second, then the actual speed he has measured is c.

Yes, but if the instruments used by one observer are contracted compared to anothers, then the same measurement of 300,000 km/s would represent different actual speeds.

If the length of his ruler complies with the physical definition of the metre, his ruler is not contracted, though he might question that of the other observer. As I said "actual speed he has measured is c" unless you have some other meaning of "actual".

Apologies, I thought I had posted this already in this thread, but it must have been a different one:

No apology needed, you had it at the bottom of your previous message but I had already commented on it in the one before so I skipped repeating it:

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

You will see that suggestion made by people who don't understand LET (or basic physics for that matter) but it has never been a theory. In LET, the mechanism that causes the various effects is an interaction with the aether hence the velocity that goes into the transforms is that of the object relative to the aether. Without some physical substance against which to measure velocity, there is no way to define the quantity.

This suggests, and has been echoed by others on here, that the concept of the aether has been removed from Lorentzian relativity, leaving just the concept of an "absolute reference frame".

To be blunt, the idea that you can have an aether theory without an aether is brain-dead nonsense posted by idiots. You will see it said in many places but popularity is not a usable indicator.

The RoS in Lorentzian relativity is materially different to Einsteinian; indeed, absolute simultaneity is incorporated in Lorentzian relativity - as it must if presentism is to prevail

Aether theory was not based on presentism, it comes from assuming Galilean relativity and the "absolute time" defined by Newton in the Principia. See the third paragraph here:

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

Would you say that absolute simultaneity is compatible with RoS?

I think I said before though perhaps not clearly, RoS refers to the time coordinates given to events so it is occurs in LET as much as SR. LET only provides an alternative interpretation of why it is unavoidable so I would state it differently, I would say that presentism is not compatible with the non-existence of an aether. I also suspect that an aether-based model s not compatible with the observation of polarisation of light. Philosophically, that leads me to a perdurantist view, but that should really be left to the philosophy forum.

apologies, I don't fully understand the point pertaining to the P & P in Maxwell's equations.

1/√(ε*μ)

If ε and μ are just scalar numbers then they cannot have different values in different directions. That means the speed of light cannot have different values in different directions, but that is what is required in aether theory for any observer moving relative to the aether.

I'm not sure if it would help to give some context for the discussion, but this thread stems from a different discussion, where the contention was that the speed of c from Maxwell's equations tacitly assumes the Earth as the rest frame for measurements ...

That's another common error made by clueless cranks, if that were the case, the velocity of the observer relative to the Earth would appear in Maxwell's Equations. In fact they are independent of the choice of frame.

Is spacetime a physical property/substance?

That's a whole different question ;-)

http://plato.stanford.edu/entries/spacetime-holearg/

For SR, the question needn't arise as long as you can assume that a hypothetical right-triangle in empty space still obeys Pythagoras Theorem. SR says the vacuum is 4-dimensional and extends Pythagoras as:

s^2 = x^2 + y^2 + z^2 - (ct)^2

All we need say is that the vacuum of SR has the property that it exhibits Euclidean geometry in any spatial 3D slice and Riemann geometry with signature {+++-} in 4D.

 

[mangaroosh]

I don't know what you call "neo-Lorentzian relativity". Do you have a quality reference for that? And is it useful?

I've come across it in a few places.

the last vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The only difference was the metaphysical[C 7] postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory. As a result, the term "Lorentz ether theory" is sometimes used today to refer to a neo-Lorentzian interpretation of special relativity. The prefix "neo" is used in recognition of the fact that the interpretation must now be applied to physical entities and processes (such as the standard model of quantum field theory) that were unknown in Lorentz's day.

wiki


neo-Lorentzian relativity

I've come across it in a few other papers too, by Brown & Pooley, Gürel & Gürel, among others.

Yes, and several of us have mentioned and explained this several times to you...

Sure - as you know. Lorentz's "Local time" is RoS with an interpretation that differs from Minkowski's interpretation.

OK, I think I understand the distinction now. As I mentioned in the post to DS, to my understanding LR includes absolute simultaneity, in the form of presentism; for that reason I think it is a misnomer to refere to RoS with respect to LR, because it implies two different notions of simultaneity of events.

It's useful to first understand the basis of such discussions - thus, can you explain how there can be both absolute and relative velocity in Newton's mechanics? Or, in other words, is velocity absolute or relative in his theory?

Are both concepts not included? I'm not entirely sure how they might be, but I thought I had read that both were; just as both are in Galilean relativity (aren't they?)

In SR (that is, the Lorentz transformation), when a certain clock of S indicates for example 2PM, another clock of S' that passes that clock at that time (thus at the same place and moment) will indicate for example 3PM. For some reason (a reason that escapes me), you think that this has big philosophical implications, while a similar case with time zones on Earth has none...

I don't think the fact that the clocks in S and S' tick at different rates should have big philosophical implications at all; the philosophical implications arise with the interpretation that it is time that is ticking slower or faster, as opposed to the mechanics of the clock being affected.

We can - and do - arbitrarily wind the clocks in each time zone to afford us more daylight hours; some time zones do this, while others don't; but we don't conclude that time moves forward or backward when we do so.

 

[harrylin]

I've come across it in a few places.

wiki [..]

"[citation needed]" .. Perhaps the anonymous editor meant that one should not think of an ether made of matter... But it's not useful to guess what an anonymous editor may have meant.
However, if one means interpretations such as by Bell and Ives, who are also mentioned: these explicitly spoke of "ether" interpretations.

[rearrange:]

Are both concepts not included? I'm not entirely sure how they might be, but I thought I had read that both were; just as both are in Galilean relativity (aren't they?)

I never read anything about absolute velocities in my textbooks on classical mechanics. Looking at your other remark, which I now placed here below, do you think that it is a misnomer to talk of relative velocities in Newtonian mechanics, because it implies two different notions of velocities?

OK, I think I understand the distinction now. As I mentioned in the post to DS, to my understanding LR includes absolute simultaneity, in the form of presentism; for that reason I think it is a misnomer to refere to RoS with respect to LR, because it implies two different notions of simultaneity of events.

Following along the same lines, do you think that it is a misnomer to talk of local time zones on earth, because we have Universal Time?

I don't think the fact that the clocks in S and S' tick at different rates should have big philosophical implications at all;

I did not mention rates at all; instead I mentioned the disagreeing clock readings of RoS...

the philosophical implications arise with the interpretation that it is time that is ticking slower or faster, as opposed to the mechanics of the clock being affected.

In physics, mechanical clocks provide a measure of what we call "time", just as mercury thermometers provide a measure of what we call "temperature"; both are "affected" by what they measure.

We can - and do - arbitrarily wind the clocks in each time zone to afford us more daylight hours; some time zones do this, while others don't; but we don't conclude that time moves forward or backward when we do so.

Exactly - then why would we conclude strange things from different clock synchronizations in SR?

 

[Dale]

Is this site not also for discussing the philosophy of science, no?

No. The forum for philosophy is:
https://www.physicsforums.com/forumdisplay.php?f=112

We cannot determine that the actual speed of light remains constant, but some of the conclusions drawn assume it to be so; insofar as those conclusions are scientifically relevant, then so to are the unmeasurable aspects.

No, the unmeasurable aspects are NOT scientifically relevant, your personal fascination notwithstanding. The scientific method is a method for systematically checking the predictions of theories against the results of experiments, and experiments are measurements. If an aspect of a theory is unmeasurable then it is not experimentally testable and therefore it is scientifically irrelevant.

If you can't measure it then you can't experiment with it and if you can't experiment with it then it is not amenable to the scientific method.

Again, to my understanding, form discussions on here and elsewhere, local time in LR isn't "real" time; the difference in time co-ordinates is due to the mechanics of the clock being affected by motion, as opposed to "time itself" being affected.

The local time is the only time available for experimental testing in LET. So since LET uses local time for all experimental testing and since local time exhibits RoS therefore RoS is a testable aspect of LET, as I have claimed from the beginning.

All of my comments in this thread apply for measurements; I make no claims nor do I have any interest in any unmeasurable aspects of reality. Under that stipulation it is 100% clear that (\text{C} \cap \text{PoR}) \rightarrow (\text{LC} \cap \text{TD} \cap \text{RoS}) and that it is not circular. If you wish to discuss that further then I will contribute, if you wish to discuss non-scientific topics about the unmeasurable ghosts that haunt your thoughts then I am done responding. I will let you have the last word on the non-scientific unmeasurable-reality topic if that is your desire.

 

[mangaroosh]

"[citation needed]" .. Perhaps the anonymous editor meant that one should not think of an ether made of matter... But it's not useful to guess what an anonymous editor may have meant.
However, if one means interpretations such as by Bell and Ives, who are also mentioned: these explicitly spoke of "ether" interpretations.

I've PM'd George to see where he came across it; he mentions it here

[rearrange:]

I never read anything about absolute velocities in my textbooks on classical mechanics. Looking at your other remark, which I now placed here below, do you think that it is a misnomer to talk of relative velocities in Newtonian mechanics, because it implies two different notions of velocities?

I wouldn't be that familiar with classical mechanics, as is probably clear; I'm familiar with the concept of absolute rest and absolute motion, which I believed to be concepts in classical mechanics; I've come across the notion of absolute velocity before when it's been said that if absolute space could be detected, then absolute velocity could be defined.

From my understanding of the concepts of relative and absolute velocities, I wouldn't say that it is a misnomer as such, as the two concepts are not mutually exclusive, as I think RoS and absolute simultaneity are.

Following along the same lines, do you think that it is a misnomer to talk of local time zones on earth, because we have Universal Time?

It depends on the ontological status ascribed to both, but I would say no again, becaue they are not necessarily mutually exclusive.

The reason I see the term RoS as a misnomer with regard to the Lorentz transform is that the transform appears to lead to relativity of time co-ordinates; it is the ontological assumption about what those time co-ordinates represent which determines whether or not RoS or absolute simultaneity is deduced.

It might be the fact that Einsteinian interpretation has been the primary one for over a hundred years (or thereabouts) that this relativity of time co-ordinates is taken to mean RoS, but insofar as we are talking about the simultaneity of events in the physical world, the relativity of time co-orindates doesn't necessarily imply RoS of physical events; as the Lorentzian interpretation demonstrates.

In short, I see absolute simultaneity as being incompatible with RoS, because RoS implies that evetns are not absolutely simultaneous; if Lorentzian relativity (neo- or LET) incorporates absolute simultaneity, then I think it is a misnomer to refer to the relativity of time co-ordinates as RoS.

I did not mention rates at all; instead I mentioned the disagreeing clock readings of RoS...

Why would relatively moving clocks have different time readings?

In physics, mechanical clocks provide a measure of what we call "time", just as mercury thermometers provide a measure of what we call "temperature"; both are "affected" by what they measure.

This is a fairly contentious issue, and, unfortunately, one I don't think I can get into without fear of reprisal; but here is a link to a locked thread on the question of How does a clock measure time?.

I have appealed the decision to close the thread, so it may perhaps be re-opened; if you would be interested in continuing the discussion it might be worth PMing a relevant mentor.

Exactly - then why would we conclude strange things from different clock synchronizations in SR?

I don't think I'm the person to be asking; I wouldn't conclude such things, but it appears that it is a fairly common conclusion; I'm sure you're familiar with the concept of the block universe.

 

[mangaroosh]

If the length of his ruler complies with the physical definition of the metre, his ruler is not contracted, though he might question that of the other observer. As I said "actual speed he has measured is c" unless you have some other meaning of "actual".

If the length of his ruler complies with the physical definition of the metre, but his counterparts ruler is contracted, such that it is shorter, and his clock is ticking slower, then the actual speeds, represented by the measurements of 300,000km/s, must be different.

If both of their instruments conform to the definitions, but if any of them are contracted compared to the other, then it means that the definitions are variable and the actual speeds represented by both measurements are still different. Alternatively it means that neither is contracted.

No apology needed, you had it at the bottom of your previous message but I had already commented on it in the one before so I skipped repeating it:

To be blunt, the idea that you can have an aether theory without an aether is brain-dead nonsense posted by idiots. You will see it said in many places but popularity is not a usable indicator.

I think the whole point is that it is no longer an aether theory.

It was mentioned in this thread. I've PM'd the author to see if there are articles to support the contention.

Aether theory was not based on presentism, it comes from assuming Galilean relativity and the "absolute time" defined by Newton in the Principia. See the third paragraph here:

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

It's not necessarily based on presentism, but I think it is fair to say that presnetism is incorporated for the very reason you've mentioned. It is, at the very least, compatible with presentism, while RoS doesn't appear to be.

I think I said before though perhaps not clearly, RoS refers to the time coordinates given to events so it is occurs in LET as much as SR. LET only provides an alternative interpretation of why it is unavoidable so I would state it differently, I would say that presentism is not compatible with the non-existence of an aether. I also suspect that an aether-based model s not compatible with the observation of polarisation of light. Philosophically, that leads me to a perdurantist view, but that should really be left to the philosophy forum.

As I mentioned in response to Harry, the Lorentz transform appears to result in relativity of time co-ordinates, but not necessarily the RoS of physical events; the relativity of time co-ordinates requires a particular interpretation to conclude RoS of physical events. It could be the fact that this relativity of time co-ordinates has been given the Einsteinian interpretation for so long, that it is asssumed that the relativity of time co-ordinates, that the Lorentz transform produces, is actually RoS.

As I see it, absolute simultaneity is the case where two events are simultaneous for everybody in the universe; while this is not necessarily the case under RoS.

Lorentzian relativity incorporates absolute simultaneity and the Lorentz transform, so my reasoning would be that the Lorentz transform cannot necessarily result in RoS; it can result in relativity of time co-ordinates, however.

1/√(ε*μ)

If ε and μ are just scalar numbers then they cannot have different values in different directions. That means the speed of light cannot have different values in different directions, but that is what is required in aether theory for any observer moving relative to the aether.

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

That's another common error made by clueless cranks, if that were the case, the velocity of the observer relative to the Earth would appear in Maxwell's Equations. In fact they are independent of the choice of frame.

But if Maxwell's equations were derived from measurements made, using instruments, at rest relative to the earth, then that would be tacit assumption of the equation, not necessarily something expressed.

That's a whole different question ;-)

http://plato.stanford.edu/entries/spacetime-holearg/

For SR, the question needn't arise as long as you can assume that a hypothetical right-triangle in empty space still obeys Pythagoras Theorem. SR says the vacuum is 4-dimensional and extends Pythagoras as:

s^2 = x^2 + y^2 + z^2 - (ct)^2

All we need say is that the vacuum of SR has the property that it exhibits Euclidean geometry in any spatial 3D slice and Riemann geometry with signature {+++-} in 4D.

But are space and time i.e. spacetime, physical?

 

[mangaroosh]

No. The forum for philosophy is:
https://www.physicsforums.com/forumdisplay.php?f=112

But this forum is for peope who wish to discuss Einsteinian relativity though, and to develop their understanding of it.

No, the unmeasurable aspects are NOT scientifically relevant, your personal fascination notwithstanding. The scientific method is a method for systematically checking the predictions of theories against the results of experiments, and experiments are measurements. If an aspect of a theory is unmeasurable then it is not experimentally testable and therefore it is scientifically irrelevant.

If you can't measure it then you can't experiment with it and if you can't experiment with it then it is not amenable to the scientific method.

The local time is the only time available for experimental testing in LET. So since LET uses local time for all experimental testing and since local time exhibits RoS therefore RoS is a testable aspect of LET, as I have claimed from the beginning.

I think the confusion might be down to a matter of interpretation.

My understanding is that the Lorentz transform results in relativity of time co-ordinates, not necessarily RoS.

RoS as I see it is contrasted with absolute simultaneity, where absolute simultaneity means that two events that are simultaneous in one reference frame are simultaneous in every reference frame i.e. for all observers in the universe. RoS on the other hand means that events which are simultaneous in one referene frame may not necessarily be simultaneous in another. This means that the two are essentially mutually exlusive.

The relativity of time co-ordinates are a consequence of the Lorentz transform; but the Lorentzian interpretation incorporates absolute simultaneity, while the Einsteinian interpretation incorporates RoS.

This would mean that RoS is not necessarily a consequence of the Lorentz transform, rather that a specific interpretation, or assumption, is required to interpret the relativity time co-ordinates as meaning RoS.

Again, it might be the fact that the Einsteinian iterpretation has been so prevalent for so long, that the relativity of time co-ordinates has been conflated with RoS, but I think they are demonstrably different.

All of my comments in this thread apply for measurements; I make no claims nor do I have any interest in any unmeasurable aspects of reality. Under that stipulation it is 100% clear that (\text{C} \cap \text{PoR}) \rightarrow (\text{LC} \cap \text{TD} \cap \text{RoS}) and that it is not circular. If you wish to discuss that further then I will contribute, if you wish to discuss non-scientific topics about the unmeasurable ghosts that haunt your thoughts then I am done responding. I will let you have the last word on the non-scientific unmeasurable-reality topic if that is your desire.

It has been mentioned in another thread, and I think we can reason that it is true, that RoS is not actually measurable. What we have is relative time co-ordinates which require a specific interpretation, and assumption, to conclude that RoS results. The same can be said for absolute simultaneity, as it requires a specific interpretation of the relativity of time co-ordinates; however, it arguably requires fewer assumptions.

 

[lmoh]

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

I think that another way to put it is to say that those numbers are constant. As such, the value of the speed of light, being based upon two constants, is also constant.

 

[Dale]

My understanding is that the Lorentz transform results in relativity of time co-ordinates, not necessarily RoS.

Simultaneity means that two events have the same time coordinate. I.e. two events A and B with spacetime coordinates (t_A,x_A,y_A,z_A) and (t_B,x_B,y_B,z_B) respectively are called simultaneous if and only if t_A=t_B. Relativity of time coordinates is therefore necessarily the same as RoS by the definition of simultaneity.

It has been mentioned in another thread, and I think we can reason that it is true, that RoS is not actually measurable.

Yes it is. I even described an experiment for doing so.

The rest of your post seems to be focused on non-scientific unmeasurable interpretations.

 

[GeorgeDishman]

If the length of his ruler complies with the physical definition of the metre, but his counterparts ruler is contracted, such that it is shorter, and his clock is ticking slower, then the actual speeds, represented by the measurements of 300,000km/s, must be different.

OK, we are talking LET here. If he measures over a shorter distance than he thinks, the time taken should appear reduced. If his clocks run slow, again the time should be reduced. What you have forgotten is the RoS which results in his clocks being mis-synchronised by an amount that exactly compensates for the other errors hence he gets the same speed.

I think the whole point is that it is no longer an aether theory.

There are two points here. First is that there is only one theory which is the Lorentz Transforms. Remember that a scientific theory is an equation together with a definition of its variables as measurable quantities. The difference between SR and LET is only the philosophy.

The second point is that any mechanistic explanation for the cause of those equations (such as Lorentz's attempts) needs a physical substance with which matter can interact to produce the various ad-hoc phenomena. Anyone who tells you they have a theory that can model those interactions without an aether is lying to you.

I've PM'd the author to see if there are articles to support the contention.

OK, I'm not going to waste my time discussing something that doesn't exist, if he can cite an actual model, that's a different thing.

It is, at the very least, compatible with presentism, while RoS doesn't appear to be.

Yes and no, remember you need RoS to get the right results in LET as mentioned above.

As I mentioned in response to Harry, the Lorentz transform appears to result in relativity of time co-ordinates, but not necessarily the RoS of physical events;

It applies to the coordinates we apply to events. Nature doesn't provide us with coordinates as properties we can measure like quantum numbers.

As I see it, absolute simultaneity is the case where two events are simultaneous for everybody in the universe; while this is not necessarily the case under RoS.

Right, absolute simultaneity would mean that all observers would label events with the same time coordinates given agreement on a reference event for the origin of the scale.

Lorentzian relativity incorporates absolute simultaneity and the Lorentz transform, so my reasoning would be that the Lorentz transform cannot necessarily result in RoS; it can result in relativity of time co-ordinates, however.

What you need to realize is that the term "RoS" refers to coordinates, nothing else. You seem to be getting there though.

Again, apologies, I'm not well up enough on that sort of thing to fully comprehend the point.

Why could the speed of light not have different values because those numbers are scalar?

OK, you seem to have a problem with this. Take another example of a scalar value, say temperature. If I say the temperature at a particular point in my room is 22C, that should seem reasonable. If I said the temperature at that point was 23C east but 21C west, you should think I am confused. Temperature cannot have two values at the same location. The same is true of permeability and permitivity and their product must similarly be single-valued at any particular location, and hence so must the speed. If you don't get that, I think you need to lay relativity aside and sort out some basics first.

But if Maxwell's equations were derived from measurements made, using instruments, at rest relative to the earth, then that would be tacit assumption of the equation, not necessarily something expressed.

Maxwell's equations are just that, equations. You put numbers in and you get numbers out and the output numbers are valid in the same frame as the input numbers, end of story.

But are space and time i.e. spacetime, physical?

That's a complex philosophical question and the pertinent evidence is far beyond SR, no offence but you need to learn these basics before you try the more advanced stuff. It would also be inappropriate for this group, if you read the article on the Hole Argument and don't follow it, you might like to discuss it in the philosophy forum but first look back for previous discussions on it first.

 

[GeorgeDishman]

I think that another way to put it is to say that those numbers are constant. As such, the value of the speed of light, being based upon two constants, is also constant.

I try to avoid that term. In another post I give the example of temperature and we can use that as an analogy noting that the speed of sound depends on air temperature. Temperature can vary from place to place and as a function of time at anyone location so to call it a "constant" would be inappropriate. However, in still air at any temperature, the speed of sound is isotropic. Contrast that with wind speed. Since that is a vector and has associated direction, any non-zero value will produce anisotropy in the speed of sound. I think a better term might be "single-valued".

I dislike the term "Hubble Constant" for the same reason, it varies inversely with time in a matter or radiation-dominated universe and will only become asymptotically constant in the limit of the de Sitter solution. It would be clearer to call it the "Hubble Coefficient" IMHO.

 

[lmoh]

Sorry, but that is just how my Natural Science Prof. (also a physicist BTW) described the equation as a background to relativity and I thought the terminology would be easier for mangaroosh to understand. If I wasn't familiar with Maxwell before, I probably wouldn't be able to easily get your description either IMO (no offense), so I thought I should provide my own interpretation, but I hope the description isn't too inaccurate.

 

[GeorgeDishman]

Sorry, but that is just how my Natural Science Prof. (also a physicist BTW) described the equation as a background to relativity and I thought the terminology would be easier for mangaroosh to understand. If I wasn't familiar with Maxwell before, I probably wouldn't be able to easily get your description either IMO (no offense), so I thought I should provide my own interpretation, but I hope the description isn't too inaccurate.

Not at all, I'm essentially a layman myself. I got my degree in the 1970's but then got a job in communications and currently specialise in FPGA design. I've been studying relativity and cosmology just to keep my hand in for about 20 years. By all means show the posts to your prof. if you like, it's a bad idea to take anything on anyone's authority. That's why I gave the Hubble Constant as an example, I have seen many people surprised to find out it varies with time even though it is universally called a "constant".

 

[mangaroosh]

Simultaneity means that two events have the same time coordinate. I.e. two events A and B with spacetime coordinates (t_A,x_A,y_A,z_A) and (t_B,x_B,y_B,z_B) respectively are called simultaneous if and only if t_A=t_B. Relativity of time coordinates is therefore necessarily the same as RoS by the definition of simultaneity.

Time co-ordinates are given by clocks in experiments; Lorentzian relativity, apparently, says that two events can have different time co-ordinates but still be absolutely simultaneous, because the different time co-ordinates given by the clocks are a result of the mechanics of the clock. In order to deduce RoS a specific interpretation is required, based on certain assumptions about time and clocks.

Therefore, relativity of time co-ordinates is not necessarily the same as RoS; they are the same thing in Einsteinian relativity, but not in Lorentzian; if this is the case then RoS cannot be a consequence of the Lorentz transform.

It might be easier to answer the question; if two events are simultaneous in one reference frame, but not in another (RoS) can they be said to be simultaneous in all reference frames (AS)?

The answer is quite clearly no. If that is the case, then RoS cannot be a consequence of the Lorentz transform.

The issue appears to be in conflating relativity of time co-ordinates with RoS; undoubtedly bcos the Einsteinian interpretation has been the dominant interpretation for so long, that the association has never been questioned.

Yes it is. I even described an experiment for doing so.

I can't really remember the experiment, but presumably the Lorentzian interpretation would incorporate absolute simultaneity, such that RoS could only be demonstrated on the basis of certain assumptions.

The rest of your post seems to be focused on non-scientific unmeasurable interpretations.

It probably just boils down to the question of the relativity of time co-ordinates and RoS anyway.

Even if we allow that RoS is a consequence of the Lorentz transform, we are still discussing two different interpretations of it, such that the interpretation that doesn't involve absolute simultnaeity of events, would still be circular reasoning; because only by assuming the interpretation of RoS where the actual speed of light remains invariant, results in RoS of events.

 

[mangaroosh]

OK, we are talking LET here. If he measures over a shorter distance than he thinks, the time taken should appear reduced. If his clocks run slow, again the time should be reduced. What you have forgotten is the RoS which results in his clocks being mis-synchronised by an amount that exactly compensates for the other errors hence he gets the same speed.

But if we talk Einsteinian relativity; do contractions of the instruments actually occur or are they just optical illusions? If they do occur then the point holds.

The point about RoS is the subject of the discussion with DaleSpam; RoS is a consequence of the actual speed of light remainging invariable, while an invariable measurement of c doesn't result in RoS - as mentioned, because the actual speeds represented by the measurments are different. Saying that RoS has been neglected is circular reasoning.

This has lead to the point about RoS and relativity of time co-ordinates.

There are two points here. First is that there is only one theory which is the Lorentz Transforms. Remember that a scientific theory is an equation together with a definition of its variables as measurable quantities. The difference between SR and LET is only the philosophy.

Cheers; I've been learning about that on here alright.

The second point is that any mechanistic explanation for the cause of those equations (such as Lorentz's attempts) needs a physical substance with which matter can interact to produce the various ad-hoc phenomena. Anyone who tells you they have a theory that can model those interactions without an aether is lying to you.

What causes the contractions in Einsteinian relativity? I've been told that it isn't a matter of cause and effect, which seems a bit nonsensical, that physical effects don't have a cause. I've heard people mention that it is just geometry, but again, that suggests that physical phenomena are caused by mathematics, as opposed to the mathematics representing the physical phenomena. Does Einsteinian relativity require the same kind of physical substance?

Given that gravity is equivalent to acceleration, could acceleration and/or gravity cause the effects?

OK, I'm not going to waste my time discussing something that doesn't exist, if he can cite an actual model, that's a different thing.

cool. I'll wait to see if he mentions any articles.

Yes and no, remember you need RoS to get the right results in LET as mentioned above.
...
It applies to the coordinates we apply to events. Nature doesn't provide us with coordinates as properties we can measure like quantum numbers.

This is the point about the relativity of time co-ordinates (RoTC). I would agree that RoTC is included in LET, but not RoS.

I think RoS refers to the simultaneity of events - as per the name - such that two events that are simultaneous in one reference frame might not be simultaneous in another.

LET doesn't incorporate this concept at all; it is based on the idea that two events that are simultaneous in one reference frame are simultaneous in all reference frames.

What LET does incorporate, however, is RoTC. I think that RoTC has become conflated with RoS because the Einsteinian interpretation has dominated for so long, and under that interpretation RoTC does mean RoS.

Right, absolute simultaneity would mean that all observers would label events with the same time coordinates given agreement on a reference event for the origin of the scale.

Indeed, but in effect observers can disagree on time co-ordinates, because they don't have the reference event for the origin of the scale, but absolute simultaneity would still prevail.

What you need to realize is that the term "RoS" refers to coordinates, nothing else. You seem to be getting there though.

That's the point of contention. I think that RoS refers to the simultaneity of events not necessarily the co-ordinates; I think the co-ordinates require a certain interpretation, and certain assumptions about what the co-ordinates represent, in order to make conclusions about the simultaneity of events i.e. RoS or AS.

OK, you seem to have a problem with this. Take another example of a scalar value, say temperature. If I say the temperature at a particular point in my room is 22C, that should seem reasonable. If I said the temperature at that point was 23C east but 21C west, you should think I am confused. Temperature cannot have two values at the same location. The same is true of permeability and permitivity and their product must similarly be single-valued at any particular location, and hence so must the speed. If you don't get that, I think you need to lay relativity aside and sort out some basics first.

Ah yes, apologies, I'd come across scalar values before but had forgotten precisely what they meant; what do you call the ones with directions again?

EDIT: Vectors, that's it! I just read it in one of your replies.

Forgive the naiivey of this question but what are permeability and permitivity, and why do they dictate that an observer moving relative to the source of light cannot measure the speed to be lower than c.

Maxwell's equations are just that, equations. You put numbers in and you get numbers out and the output numbers are valid in the same frame as the input numbers, end of story.

Indeed, but if the measurements that go into the equation tacitly assume the Earth as the rest frame for experiments, then is it not possible that the laws deduced from them - such as the constancy of c regardless of the state of motion relative to the source - equally tacitly assume the Earth as the rest frame?

That's a complex philosophical question and the pertinent evidence is far beyond SR, no offence but you need to learn these basics before you try the more advanced stuff. It would also be inappropriate for this group, if you read the article on the Hole Argument and don't follow it, you might like to discuss it in the philosophy forum but first look back for previous discussions on it first.

I'm not familiar with the Hole Argument, but I'll check it out at some stage.

Cheers!

 

[harrylin]

[..] I wouldn't be that familiar with classical mechanics, as is probably clear; I'm familiar with the concept of absolute rest and absolute motion, which I believed to be concepts in classical mechanics; I've come across the notion of absolute velocity before when it's been said that if absolute space could be detected, then absolute velocity could be defined.

From my understanding of the concepts of relative and absolute velocities, I wouldn't say that it is a misnomer as such, as the two concepts are not mutually exclusive, as I think RoS and absolute simultaneity are.

I made the comparisons because absolute and relative simultaneity are not mutually exclusive, just as time zones and universal time aren't, and just as relative and absolute velocities aren't.

[..] The reason I see the term RoS as a misnomer with regard to the Lorentz transform is that the transform appears to lead to relativity of time co-ordinates; it is the ontological assumption about what those time co-ordinates represent which determines whether or not RoS or absolute simultaneity is deduced.

It might be the fact that Einsteinian interpretation has been the primary one for over a hundred years (or thereabouts) that this relativity of time co-ordinates is taken to mean RoS, but insofar as we are talking about the simultaneity of events in the physical world, the relativity of time co-orindates doesn't necessarily imply RoS of physical events; as the Lorentzian interpretation demonstrates.

Here I can't follow at all what you say... Lorentz called the relativity of time co-ordinates "local time" and later Einstein called it "RoS". And Einstein's descriptions were purely operational, without any implied metaphysics - he tried to eliminate metaphysics from physics.

When you say that based on your time reckoning two distant events both happened about 100 years ago, and someone else who uses a reference system that is moving relative to yours says that the one event happened about 99 years ago, and the other about 101 years ago, that is what is called "relativity of simultaneity". It is what Lorentz and Poincare called "local time", and it is about physical events.

In short, I see absolute simultaneity as being incompatible with RoS, because RoS implies that evetns are not absolutely simultaneous [..]

That is wrong, for (again) the same reason as why the following sentence is wrong:
"absolute velocity is incompatible with relative velocity, because relative velocity implies that velocities are not absolute."

Why would relatively moving clocks have different time readings? [..]

That is at the heart of Relativity of Simultaneity...
Here is again a famous illustration of independent reference systems:
http://www.bartleby.com/173/9.html
Now put clocks at the front and back of the train, as well as one in the middle of the train, next to you; and synchronize your clock with a clock that happens to be just next to it at the station at t=0 (so that at x=0 and t=0, also t'=0: the LT assumption). I hope that you understand that the distant clocks on the train cannot indicate the same times as clocks next to them at the station.

[..] I don't think I'm the person to be asking; I wouldn't conclude such things, but it appears that it is a fairly common conclusion; I'm sure you're familiar with the concept of the block universe.

In several recent threads this was discussed and explained that it's just one of several interpretations.

 

[Dale]

Therefore, relativity of time co-ordinates is not necessarily the same as RoS;

Yes, it is. Again, it is part of the definition of simultaneity:
http://en.wikipedia.org/wiki/Simultaneity
"Simultaneity is the property of two events happening at the same time in at least one frame of reference. "

http://www.thefreedictionary.com/simultaneity
"Happening, existing, or done at the same time."

If you wish to assert the contrary, please find a more credible source than Wikipedia and the Dictionary, which defines simultaneity as being something other than occurring at the same time.

I would also point out Einstein's comments on the importance of testability:
http://www.bartleby.com/173/8.html
" We encounter the same difficulty with all physical statements in which the conception “simultaneous” plays a part. The concept does not exist for the physicist until he has the possibility of discovering whether or not it is fulfilled in an actual case. We thus require a definition of simultaneity such that this definition supplies us with the method by means of which, in the present case, he can decide by experiment whether or not both the lightning strokes occurred simultaneously. As long as this requirement is not satisfied, I allow myself to be deceived as a physicist (and of course the same applies if I am not a physicist), when I imagine that I am able to attach a meaning to the statement of simultaneity. (I would ask the reader not to proceed farther until he is fully convinced on this point.)"

The scientific definition of simultaneity is clear. Any other definition is non-testable. RoS is the same as relativity of time coordinates.

 

[GeorgeDishman]

But if we talk Einsteinian relativity; do contractions of the instruments actually occur or are they just optical illusions?

Neither, they are not illusions, they are entirely real but in relativity they arise from geometry as you mention. The length of an object is the difference between the spatial coordinates of its endpoints and that difference will vary if you rotate the axes.

What causes the contractions in Einsteinian relativity? I've been told that it isn't a matter of cause and effect, which seems a bit nonsensical, that physical effects don't have a cause.

There is no physical effect, in its rest frame the object is unchanged so no cause is required. In relativity, "contraction" is the difference between the extent measured using two different coordinate schemes and the cause of that is the angle between the axes.

{p.s. You can say that it was the mistake of assuming 3D Euclidean space and time were separate rather than having a composite Reimann geometry that creates the illusion of effects described by LET.}

I've heard people mention that it is just geometry,

Correct.

but again, that suggests that physical phenomena are caused by mathematics, as opposed to the mathematics representing the physical phenomena.

That's the key point, unlike LET, there are no physical changes involved in the object's rest frame.

Does Einsteinian relativity require the same kind of physical substance?

SR does not. GR is much more complex because gravitational waves which are in part "ripples of time" can transport energy. You need to get a solid grasp of the geometrical nature of SR and a lot more before you will have any chance of following those arguments.

Given that gravity is equivalent to acceleration, could acceleration and/or gravity cause the effects?

There are no physical effects in the rest frame to be caused, just geometry.

I think RoS refers to the simultaneity of events - as per the name - such that two events that are simultaneous in one reference frame might not be simultaneous in another.

A) Two events are simultaneous if they "happen at the same time".
B) Two events are simultaneous if they "have the same value of time coordinate".

The two sentences above are synonomous and would are valid in both LET and SR, and Newton would have agreed with that definition too. I think your problem is that you have a vague notion of some other definition of what events being simultaneous might mean that is different from what everyone else understands by the term.

LET doesn't incorporate this concept at all ...

See above, LET includes precisely the same concept, you cannot get the correct answers without it.

What LET does incorporate, however, is RoTC. I think that RoTC has become conflated with RoS because the Einsteinian interpretation has dominated for so long, and under that interpretation RoTC does mean RoS.

The term was first invented for SR so that is its meaning. It can also be applied the same way to LET. If you want something different, you need to define your new concept and how to measure it.

Forgive the naiivety of this question but what are permeability and permitivity, and why do they dictate that an observer moving relative to the source of light cannot measure the speed to be lower than c.

You can look them up but in simple terms, if you put a charge onto two metal plates separated by a vacuum, the permittivity is the ratio of the amount of charge to the voltage (similar to a battery). Permeability similarly relates the current in a coil to the strength of the resulting magnetic field.

Since both numbers are scalar (single-valued), you can only get a single value of the speed of light from them hence if two flashes of light pass your nose in opposite directions, the speed at the point where they cross must be the same in both directions. SR follows from that.

Indeed, but if the measurements that go into the equation tacitly assume the Earth as the rest frame for experiments, ..

If an engineer used Maxwell's Equations to design an antenna for the Cassini Mission currently orbiting Saturn, the dimensions of the antenna are quite explicitly in the rest frame of the spacecraft , not the Earth! :-)

 

[harrylin]

But this forum is for peope who wish to discuss Einsteinian relativity though, and to develop their understanding of it. [..]

Einsteinian relativity is one option; however he was foremost of the "shut up and calculate" philosophy, which was followed by for example Feynman. As a result his "metaphysical" interpretation flip-flopped and drifted a bit along with popular opinions (from no ether and no block universe, to ether as well as block universe).

Main alternatives are Minkowskian relativity ("block universe") and Lorentzian relativity (which had been lurking in a corner but re-emerged thanks to Bell's Theorem).

Note: what you seem to deny is the fact that what you call "RoTC", is exactly what Einstein called "RoS".

 

[Dale]

Note: what you seem to deny is the fact that what you call "RoTC", is exactly what Einstein called "RoS".

And everyone else. Nobody besides mangaroosh has ever used the term Relativity of Time Coordinates AFAIK, and when everyone uses the term RoS they mean what he is calling Relativity of Time Coordinates. He is just making up things as he goes along.

Mangaroosh, please provide a mainstream scientific reference supporting your use of the term Relativity of Time Coordinates and your alternative definition of Relativity of Simultaneity.

 

[mangaroosh]

This is just a quick point with regard to "the relativity of time co-ordinates", because I'm using the term again in replies.

The term is being coigned for the sole purpose of clarity of discussion; the intention is to avoid equivocation and thus facilitate a more cogent discussion.

 

[Dale]

Find a mainstream reference that documents the term and explains the concept in detail then. Otherwise it brings confusion rather than clarity, and violates the rules.