SR, LET, FTL & Causality Violation

[kmarinas86]

Yes, the LET uses the Lorentz transform to make its experimental predictions. Therefore "variations of contraction" that are not derived from the Lorentz transform are inconsistent with LET.

I'm not so sure how you come with that conclusion. How exactly are "variations of contraction" inconsistent with LET? That's like saying that the existence of a black swan is inconsistent with an argument that depends on the existence of white swans.

 

[Dale]

The black swan analogy doesn't make sense to me.

Please answer this clearly: Do you agree or disagree that LET uses the Lorentz transform to make its experimental predictions?

 

[kmarinas86]

The black swan analogy doesn't make sense to me.

Please answer this clearly: Do you agree or disagree that LET uses the Lorentz transform to make its experimental predictions?

I agree. But I disagree with the implications. The way I see it, this simply means that "LET uses the Lorentz transform to make its experimental predictions". It doesn't entail exclusion of other transforms to make its experimental predictions. Likewise, one can state that "Science uses the Lorentz transform to make its experimental predictions". Again, such a statement does not exclude other transforms be used to make experimental predictions in science.

 

[zonde]

I agree. But I disagree with the implications. The way I see it, this simply means that "LET uses the Lorentz transform to make its experimental predictions". It doesn't entail exclusion of other transforms to make its experimental predictions. Likewise, one can state that "Science uses the Lorentz transform to make its experimental predictions". Again, such a statement does not exclude other transforms be used to make experimental predictions in science.

I would like to say that I agree with DaleSpam. If you speak about different transformation than Lorentz transform then don't say that this is LET you are speaking about. Then this is you own speculation that uses LET as a starting point.

You can arrive at LET if you assume that structure of matter is maintained by means of electromagnetic interactions that all propagate at speed of light.
If you want to modify LET you have to introduce some additional factors that will complicate picture. So this modification can not be viewed on equal level as original simple version.

 

[PeterDonis]

Newtonian structure says there is absolute space and time.

And that information can propagate with infinite velocity, so that Galilean invariance holds. If that isn't part of your definition of "absolute space and time", then you are not talking about "Newtonian structure", you're talking about something else.

Hence by this mechanism one can change "Galilean invariance to Lorentz invariance just by "overlaying" additional structure on top of Newtonian physics.

Doing this is *not* overlaying additional structure on Newtonian physics; it is *changing* the causal structure of Newtonian physics, i.e., it is *destroying* the old causal structure and replacing it with a new one. SR doesn't just introduce length contraction and time dilation; it introduces a finite speed of light (i.e., finite speed of information propagation). That changes the causal structure of spacetime; events that would have been causally connected under Galilean invariance are no longer causally connected under Lorentz invariance. You can't do that with just an "overlay".

 

[Dale]

I agree. But I disagree with the implications. The way I see it, this simply means that "LET uses the Lorentz transform to make its experimental predictions". It doesn't entail exclusion of other transforms to make its experimental predictions.

Such a theory (one that changes its method of making predictions on a whim) is non-falsifiable and therefore non-scientific. If you want to have a scientific theory then you have to make a specific prediction that is subject to experimental falsification. You should read up on falsifiability.

With regards specifically to LET, can you provide any authoritative source claiming that the LET uses any other mathematical framework besides the Lorentz transform?

 

[kmarinas86]

Newtonian structure says there is absolute space and time.

And that information can propagate with infinite velocity, so that Galilean invariance holds. If that isn't part of your definition of "absolute space and time", then you are not talking about "Newtonian structure", you're talking about something else.

[Overlaying additional structure on top of it means that when an object moves, it physical contracts and slow downs which has same effect as length contraction and time dilation... which falls under Lorentz Transformation. Therefore by merely adding physical length contraction and time slowing down in moving objects over Newtonian structure. This LET like mechanism produce the same prediction as SR.] Hence by this mechanism one can change "Galilean invariance to Lorentz invariance just by "overlaying" additional structure on top of Newtonian physics.

Doing this is *not* overlaying additional structure on Newtonian physics; it is *changing* the causal structure of Newtonian physics, i.e., it is *destroying* the old causal structure and replacing it with a new one. SR doesn't just introduce length contraction and time dilation; it introduces a finite speed of light (i.e., finite speed of information propagation). That changes the causal structure of spacetime; events that would have been causally connected under Galilean invariance are no longer causally connected under Lorentz invariance. You can't do that with just an "overlay".

Lorentz invariance is a property of spacetime. LET does not have spacetime. Time and space are not linked in LET. There is no such thing as a spacetime interval in LET. In LET, causal structure is only "real" in the preferred inertial frame of LET. So LET cannot have Lorentz invariance. In the strict sense of the way the term "Lorentz transformation" is now used, LET cannot even have a Lorentz transformation, because this term now refers to the transformation of space and time as described by SR.

LET cannot be accurately described as a theory of "Lorentz transformations". The Lorentz-FitzGerald contraction hypothesis applied to an "immobile aether" is what LET ultimately relies upon to make predictions also made by SR. That contraction was originally conceived in three dimensional Euclidean space, no spacetime.

 

[kmarinas86]

The black swan analogy doesn't make sense to me.

Please answer this clearly: Do you agree or disagree that LET uses the Lorentz transform to make its experimental predictions?

In light of my recent post just above that the Lorentz transform involves spacetime, while LET has no spacetime, I retract my agreement. Now my corrected response is: I disagree.

 

[Dale]

LET cannot be accurately described as a theory of "Lorentz transformations".

In light of my recent post just above that the Lorentz transform involves spacetime, while LET has no spacetime, I retract my agreement. Now my corrected response is: I disagree.

OK, thanks for the clarification. That at least crystallizes the real issue: this is simply a misunderstanding of LET. I would be glad to provide references if you wish, but LET does in fact use the Lorentz transform to make its experimental predictions.

 

[kmarinas86]

The black swan analogy doesn't make sense to me.

Please answer this clearly: Do you agree or disagree that LET uses the Lorentz transform to make its experimental predictions?

In light of my recent post just above that the Lorentz transform involves spacetime, while LET has no spacetime, I retract my agreement. Now my corrected response is: I disagree.

OK, thanks for the clarification. That at least crystallizes the real issue: this is simply a misunderstanding of LET. I would be glad to provide references if you wish, but LET does in fact use the Lorentz transform to make its experimental predictions.

I would like to see one reference that LET involves spacetime. Thanks.

 

[PeterDonis]

In LET, causal structure is only "real" in the preferred inertial frame of LET.

Which inertial frame is that? Nobody knows, nor does LET give any way of finding out. So this statement may sound good, but doesn't actually say anything useful.

Also, unless LET claims that whether two events are causally connected is observer-dependent (which would contradict SR), LET and SR must agree on which pairs of events are and are not causally connected. So the above statement is also irrelevant, since SR doesn't care whether the causal structure is "real" in every inertial frame; it only cares that the causal connection, or lack thereof, between any given pair of events is invariant.

LET cannot be accurately described as a theory of "Lorentz transformations". The Lorentz-FitzGerald contraction hypothesis applied to an "immobile aether" is what LET ultimately relies upon to make predictions also made by SR.

How do you make these predictions if you don't know which inertial frame is the "immobile aether" frame?

That contraction was originally conceived in three dimensional Euclidean space, no spacetime.

What about time dilation?

 

[Dale]

I would like to see one reference that LET involves spacetime. Thanks.

You don't need spacetime to have a transform. E.g. the Galilean transform. I never claimed that the LET uses spacetime, only that it uses the Lorentz transform.

Whether you take Minkowski's approach and combine space and time into spacetime or you take Lorentz's approach and keep them separate, the experimental predictions are determined by the Lorentz transform. Spacetime is simply an elegant way of expressing the Lorentz transform, not a necessary part of it.

 

[kmarinas86]

Also, unless LET claims that whether two events are causally connected is observer-dependent (which would contradict SR), LET and SR must agree on which pairs of events are and are not causally connected.

As it was long ago conceived at the prior turn of the century, LET and SR have to agree on the predicted observational measurements.

However, whether those observational measurements actually reflect "causality" or just "order of appearance" is where LET begins to stray from SR (or vice versa). SR invokes relativity of simultaneity. LET rejects relativity of simultaneity.

What about time dilation?

In LET, time dilation was conceived without the spacetime metric.

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

A substantially extended work (the so called „Palermo paper“)<ref group=A name=dynam>Poincaré (1906)</ref> was submitted by Poincaré on 23 July 1905, but was published on January 1906, because the journal only appeared two times in a year. He spoke literally of "the postulate of relativity", he showed that the transformations are a consequence of the [[principle of least action]]; he demonstrated in more detail the group characteristics of the transformation, which he called [[Lorentz group]], and he showed that the combination <math>x^2+ y^2+ z^2- c^2t^2</math> is invariant. While elaborating his gravitational theory he noticed that the Lorentz transformation is merely a rotation in four-dimensional space about the origin by introducing <math>ct\sqrt{-1}</math> as a fourth imaginary coordinate, and he used an early form of [[four-vector]]s. However, Poincaré later said the translation of physics into the language of four-dimensional metry would entail too much effort for limited profit, and therefore he refused to work out the consequences of this notion. This was later done by Minkowski, see "The shift to relativity".<ref group=B>Walter (2007), Kap. 1</ref>

 

[PeterDonis]

As it was long ago conceived at the prior turn of the century, LET and SR have to agree on the predicted observational measurements.

However, whether those observational measurements actually reflect "causality" or just "order of appearance" is where LET begins to stray from SR (or vice versa). SR invokes relativity of simultaneity. LET rejects relativity of simultaneity.

What does this mean? Does it mean that the "order of appearance" of two spacelike-separated events is not different for different observers in LET? How does that work?

Or does it just mean that LET admits that the "order of appearance" of spacelike separated events can be different for different observers, but still claims those events can be causally connected? This would mean that LET denies that invariant time ordering is a necessary condition for causal connection. This would not necessarily contradict SR, since strictly speaking, SR's definition of "causality" only requires that spacelike-separated experiments must commute (i.e., the results must be independent of which experiment occurs "first"); it does not require that we absolutely rule out causal connection between spacelike-separated events. (For example, the quantum experiments that violate the Bell inequalities are consistent with SR.)

If you don't mean one of the above, but you are saying that LET's definition of "causal connection" is different from SR's, then I don't understand LET's definition of "causal connection".

In LET, time dilation was conceived without the spacetime metric.

Yes, so was standard SR. That's not what I was asking. You said LET conceives length contraction in 3-dimensional space, which obviously can't hold for time dilation. So how does LET conceive time dilation?

 

[D H]

Yes, so was standard SR.

Exactly. The concept of spacetime was developed after the fact -- and by Poincare, not Einstein. The two key Lie groups that pertain to special relativity are the Lorentz group and the Poincare group. Lorentz and Poincare: These just happen to be the two key people behind Lorentz Ether Theory. The concept of spacetime as an algebraic structure was developed first for LET, and then carried over to simplify/solidify the description of special relativity. That wasn't that hard to do because mathematically, LET and special relativity are one and the same. The two theories differ only in their postulates. Physically, they are not one and the same because we physicists have this nifty little tool called Occam's razor.

 

[ghwellsjr]

The difference between LET and SR is in the second postulate. Einstein claims that light propagates at c in any rest state whereas LET postulates that light propagates at c only in one rest state. Since we cannot know what that rest state is, LET interprets virtually all rest states as being in inertial motion with respect to that one preferred rest state and therefore experiencing time dilation and length contraction (but of some unknowable amount). SR interchanges these two rest states, any rest state is exactly like the LET preferred absolute rest state of the ether where the speed of light is c and so experiences no time dilation or length contraction--all other frames in relative inertial motion are the ones that experience the time dilation and length contraction.

Aside from that one ever-so-minor point of view, there is no difference between LET and SR.

 

[Dale]

As it was long ago conceived at the prior turn of the century, LET and SR have to agree on the predicted observational measurements.

Exactly. And this is a direct result of the fact that both use the Lorentz transform to predict all experimental measurements.

Are you back in agreement now?

 

[D H]

but of some unknowable amount

Einstein's postulate that the speed of light is the to all observers is simply stated. Seemingly paradoxical, but simple. Compare that to the ad hoc LET postulates of length contraction and time dilation.

But that wasn't what ultimately did LET in. What did it in was that the rest frame of the luminiferous aether, while central to the theory, was inherently unknowable and untestable.

 

[atyy]

Einstein's postulate that the speed of light is the to all observers is simply stated. Seemingly paradoxical, but simple. Compare that to the ad hoc LET postulates of length contraction and time dilation.

But that wasn't what ultimately did LET in. What did it in was that the rest frame of the luminiferous aether, while central to the theory, was inherently unknowable and untestable.

OTOH, couldn't one say LET "did itself in" (the part about there being only one preferred frame) by being successfully predicting:) the existence of the whole class of Lorentz inertial frames?

 

[D H]

OTOH, couldn't one say LET "did itself in" (the part about there being only one preferred frame) by being successfully predicting:) the existence of the whole class of Lorentz inertial frames?

I suppose.

OTOH, telling physicists that the central thesis of LET was inherently unobservable and untestable was probably a bit too much in and of itself.

 

[atyy]

IOTOH, telling physicists that the central thesis of LET was inherently unobservable and untestable was probably a bit too much in and of itself.

Yet many prefer GR formulated as a spin-2 field on unobservable flat spacetime (ok, I'm guilty:)

 

[stglyde]

And that information can propagate with infinite velocity, so that Galilean invariance holds. If that isn't part of your definition of "absolute space and time", then you are not talking about "Newtonian structure", you're talking about something else.



Doing this is *not* overlaying additional structure on Newtonian physics; it is *changing* the causal structure of Newtonian physics, i.e., it is *destroying* the old causal structure and replacing it with a new one. SR doesn't just introduce length contraction and time dilation; it introduces a finite speed of light (i.e., finite speed of information propagation). That changes the causal structure of spacetime; events that would have been causally connected under Galilean invariance are no longer causally connected under Lorentz invariance. You can't do that with just an "overlay".

I see. So you mean even if the Lorentz preferred frame can be distinguished. The lorentz preferred frame on Earth doesn't have the same time as the lorentz preferred frame at alpha centuari 4 light years away (because of the finite velocity of light). But then quantum entanglement is instantaneous across the universe. How do you discount the possibility quantum entanglement uses our old friend Galilean invariance (nothing what you said in the first sentence above "And that information can propagate with infinite velocity, so that Galilean invariance holds").

 

[Dale]

Quantum entanglement cannot be used to transmit information. Many things which do not transmit information go faster than light, but they cannot produce a causality violation.

 

[stglyde]

Quantum entanglement cannot be used to transmit information. Many things which do not transmit information go faster than light, but they cannot produce a causality violation.

I know. But the randomness simultaneous correlations share a "preferred frame" across the universe. So it's like you have something going back and forth in time in different frames.
(In this argument, let's ignore MWI and Copenhagen which explains the correlations in other ways like how locality doesn't exist.. hence nothing to be non-local about. For the purpose of this thread, let's just deal with old fashioned General Relativity (or gLET) spacetime... ).

 

[Dale]

But the randomness simultaneous correlations share a "preferred frame" across the universe.

No, they don't. In every frame the collapse happens instantaneously. There is nothing in that to prefer one frame over another.

 

[stglyde]

No, they don't. In every frame the collapse happens instantaneously. There is nothing in that to prefer one frame over another.

But since each frame has different time... this is because each frame as compared to another is limited in speed by the speed of light. Then the collapse occurs in different time. This is because if you say collapse happens instantaneously in all frames across the universe. Then you are talking about Galilean or Newtonian spacetime. Remember that my time now can't be compared to the time "now" at Alpha Centauri.. which is the essence of Spacetime. Hence you can't say my time now is instantaneous to the time "now" at alpha centari.

 

[Dale]

But since each frame has different time... this is because each frame as compared to another is limited in speed by the speed of light. Then the collapse occurs in different time. This is because if you say collapse happens instantaneously in all frames across the universe. Then you are talking about Galilean or Newtonian spacetime.

I think that you misunderstand what it means for there to be a preferred frame. A preferred frame means that there is some frame where the laws of physics are different than in other frames. If you have a law of physics that says that something happens instantaneously and if that law of physics is the same in each frame then it does not imply a preferred frame.

Remember that my time now can't be compared to the time "now" at Alpha Centauri.. which is the essence of Spacetime. Hence you can't say my time now is instantaneous to the time "now" at alpha centari.

Sure you can. As long as you specify the reference frame you certainly can make such comparisons and statements. They are not invalid statements, just frame-variant.

 

[stglyde]

I think that you misunderstand what it means for there to be a preferred frame. A preferred frame means that there is some frame where the laws of physics are different than in other frames. If you have a law of physics that says that something happens instantaneously and if that law of physics is the same in each frame then it does not imply a preferred frame.

Sure you can. As long as you specify the reference frame you certainly can make such comparisons and statements. They are not invalid statements, just frame-variant.

Wiki says:

"http://en.wikipedia.org/wiki/Preferred_frame

In general relativity, some cosmological models have a preferred frame that allows motion to be defined."

The context means a preferred frame is large across the universe. So if there is something in the preferred frame... then it is instantaneous within that frame. You mentioned that "A preferred frame means that there is some frame where the laws of physics are different than in other frames.". That's right. Laws of physics are different in that frame because it supports superluminal influence for example. Refute it.

 

[Fredrik]

Wiki says:

"http://en.wikipedia.org/wiki/Preferred_frame

In general relativity, some cosmological models have a preferred frame that allows motion to be defined."

The context means a preferred frame is large across the universe. So if there is something in the preferred frame... then it is instantaneous within that frame. You mentioned that "A preferred frame means that there is some frame where the laws of physics are different than in other frames.". That's right. Laws of physics are different in that frame because it supports superluminal influence for example. Refute it.

The "preferred frames" in GR are just coordinate systems in which it's particularly easy to describe the distribution and other properties of matter in the universe. In a FLRW solution for example, the "preferred" coordinate system is the one in which the distribution of matter in space (defined as a 3-manifold of constant time coordinate) is homogeneous and isotropic everywhere. There are no superluminal influences.

 

[stglyde]

Sure you can. As long as you specify the reference frame you certainly can make such comparisons and statements. They are not invalid statements, just frame-variant.

I thought relativity taught that it is meaningless to compare the now here and the "now" in alpha centauri because of SR. But you said it is possible. So how do you specify the reference frame that can compare the now here and in the alpha centauri?