Is spacetime independent of its universe?

[Fredrik]

If you can not detect ether it is scientifically irrelevant,

Everyone agrees with this part.

SR is 4D block spacetime.

"The block universe" (not to be confused with Minkowski spacetime) is just an interpretation too. A special relativistic theory is defined by the mathematical definitions of things like Minkowski spacetime and proper time, and some correspondence rules that tell us how to interpret the mathematics as predictions about results of experiments. Special relativity is the framework in which special relativistic theories is defined.

An interpretation of a theory is an attempt to state explicitly what the theory is suggesting about what reality is really like. LET may have started as a "theory" (something that can be used to make predictions), but the proper way to view it today is as an interpretation of SR. This is what DaleSpam is doing.

The block universe interpretation is (roughly) the idea that reality is like a 4-dimensional "painting" that's already finished. An object's entire existence is just a bunch of lines in that painting, and the idea of a "now" (objective or subjective) is an illusion.

People usually associate this idea with SR, but pre-relativistic classical theories can be interpreted this way as well.

You cannot cut that part. What else would be SR? Just mathematics and everything else is philosophical interpretation? Again, then science = philosophy. That's when I quit.

No one is saying that "science=philosophy".

 

[DrGreg]

SR shows ether is not necessary. If you can not give any observation/measurement of any specific aspect of ether or enything else, then it is not an option.

Just because something isn't necessary doesn't prove it doesn't exist.

Perhaps you missed the part where I said I reject LET. But the reason I reject it isn't mathematical logic or experiment, as there is no evidence from either of those. Lack of evidence isn't evidence of a lack. Ultimately I reject it because I don't like it and I like Einstein's interpretation much better.

 

[ghwellsjr]

So you have a theory that considers anything that can not be measured/detected as a valid interpretation? Hilarious.

Special Relativity is a theory that has something that cannot be measured/detected--the propagation of light being c in any Inertial Reference Frame (IRF), just like LET which only claims that light propagates at c only in one IRF. If SR is consistent with anything that can be measured/detected then it affirms LET, doesn't it?

Or did you think that there was a way to measure/detect the propagation of light apart from postulating/defining/assuming/stipulating that it is c in any IRF?

 

[ash64449]

Ultimately I reject it because I don't like it and I like Einstein's interpretation much better.

you cannot reject because you do not like it. If LET makes prediction different from that of SR,we need to conduct experiment and need to look whose prediction nature follows. And then only we can reject a theory.

 

[DrGreg]

you cannot reject because you do not like it.

But LET is only an interpretation of a theory. I'm not rejecting any theory. I don't like the interpretation and prefer Einstein's interpretation of the same theory. It doesn't matter whether I reject it or not because both interpretations are fully compatible with experiment. And it's not a permanent rejection. If anybody found any evidence that the LET interpretation was superior to Einstein's, I'd change my mind.

In fact "reject" is too strong a word. I really mean "dismiss as irrelevant for me".

If LET makes prediction different from that of SR...

It doesn't, at least not for anything you can measure experimentally.

 

[Dale]

Again, I'm afraid we are really talking past each other at a very basic level... ;-)

I agree. However, others such as Fredrik and DrGreg clearly understand my posts, so I don't think that the communication breakdown is on my end.

I cannot follow your reasoning. Correct me if I am wrong, but you are the one considering ether (LET) a valid SR alternative

As Frederik mentione LET is not an alternative to SR, it is an interpretation of SR, just like the block universe is another interpretation of SR. Do you understand the difference between an "alternative theory" and an "interpretation of a theory"?

hence you first have to give me an experiment/observation/measurement of (any specific aspect of) the ether.

According to LET things moving through the aether length contract and time dilate such that the transformation between inertial frames is given by the Lorentz transform. Therefore all of these experiments can be taken as experimental confirmation of LET: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

Furthermore, my only claim is that no experiment is possible which favors the block universe interpretation of SR over the LET interpretation of SR. This claim can be proven mathematically by the simple fact that both interpretations use the Lorentz transforms to make all of their experimental predictions, therefore since they use the same equations they make the same predictions. If you dispute that claim then on what grounds do you dispute it?

 

[Dale]

SR is 4D block spacetime. You cannot cut that part. What else would be SR? Just mathematics and everything else is philosophical interpretation?

SR (the theory, not any interpretations of the theory) consists of the Lorentz transforms and a set of rules about how the terms in the equations correspond to experimental results. For example, there is a rule (called the Einstein synchronization convention) about how to take a set of standard clocks and rods and use light signals to synchronize them such that the values on the clocks and the rods correspond to the variables in the Lorentz transform. That is SR.

Whenever you take that and go beyond it to claim "reality is a 4D block universe" or "reality is a 3D universe with a Lorentzian aether" then you are doing philosophy. Note the use of the philosophical term "reality", which is a strong indication that the following statements are philosophical, not scientific.

 

[Dale]

you cannot reject because you do not like it.

You cannot reject a theory because you do not like it. But LET is not a theory, it is an interpretation of a theory. You can reject or accept interpretations for any reason or no reason at all, and you can change which interpretation you use at will.

My personal recommendation is to learn all of the interpretations of any theory you use, and use whichever interpretation is most practical for the scenario at hand. With SR, I tend to use LET for relativistic Doppler problems, and block universe for everything else.

Do you understand the difference between a theory and an interpretation of a theory?

 

[bobc2]

Therefore all of these experiments can be taken as experimental confirmation of LET: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

These experiments confirm special relativity. I challenge the assertion that LET is an interpretation of special relativity. LET theory does not apply the Lorentz transformations symmetrically. The object moving with respect to ether is always the contracted object in LET theory. This contradicts special relativity. So far as I am aware, no one has ever cited a paper that derives a mechanism for relativistic contraction that is applied symmetrically.

That may be why Rindler wrote in his special relativity textbook that LET has faded into oblivion and why DrGreg and others dismiss LET.

 

[TheBC]

These experiments confirm special relativity. I challenge the assertion that LET is an interpretation of special relativity. LET theory does not apply the Lorentz transformations symmetrically. The object moving with respect to ether is always the contracted object in LET theory. This contradicts special relativity. So far as I am aware, no one has ever cited a paper that derives a mechanism for relativistic contraction that is applied symmetrically.

That may be why Rindler wrote in his special relativity textbook that LET has faded into oblivion and why DrGreg and others dismiss LET.

This is what I referred to in my post #34,last paragraph:

If LET is a melting pot of 4D spacetime and 3D aether space, then LET is simply an awful attempt to mix dynamical ether effects in one frame and pure 4D spatio-temporal 4D effects in another. It would mean that in one frame one has to accept that the origin of contraction and dilation is dynamical, and in the other frame the cause is not dynamical but pure spatio-temporal. Two different causes in one theory that has the intention to show how all laws are physical equal in all frames.

Can this be considered a valid interpretation for SR?

 

[Dale]

These experiments confirm special relativity.

Yes, the experiments confirm SR and LET is an interpretation of SR. An experiment which confirms a theory can be taken as evidence for any or all of its interpretations.

I challenge the assertion that LET is an interpretation of special relativity. LET theory does not apply the Lorentz transformations symmetrically. The object moving with respect to ether is always the contracted object in LET theory. This contradicts special relativity.

Contradicts? In what way? Not experimentally, which is what makes it an interpretation.

 

[Dale]

This is what I referred to in my post #34,last paragraph:

Can this be considered a valid interpretation for SR?

Yes.

 

[bobc2]

Yes, the experiments confirm SR and LET is an interpretation of SR. An experiment which confirms a theory can be taken as evidence for any or all of its interpretations.

Contradicts? In what way? Not experimentally, which is what makes it an interpretation.

Yes. Contradicts. Notice in the Minkowski Space-Time sketch below that Einstein's special relativity applies the Lorentz transformation between blue and red symmetrically. The LET theory applies the theory in one direction for an object at rest with respect to ether and another object in motion relative to ether. So, the space-time diagram would not look the same.

Even though you never know if an object is at rest with respect to the ether, the transformation would still not be applied symmetrically. The object moving faster relative to the ether is still more contracted than the slower moving object.

Now, if you assert that I'm just resurrecting the old LET, then my response is that your new LET is nothing more than special relativity with a postulate that there is an ether. However, in that case, you cannot maintain that LET is an interpretation of special relativity, because special relativity in no way implies an ether.

However, special relativity certainly implies a 4-dimensional space-time universe.

 

[ash64449]

You cannot reject a theory because you do not like it. But LET is not a theory, it is an interpretation of a theory. You can reject or accept interpretations for any reason or no reason at all, and you can change which interpretation you use at will.

But only one interpretation can be correct or only accepted by nature. I know we can explain data in many ways.but nature follows only one of those interpretations. So we need to look for more predictions made by those two different interpretation and look whether they make different predictions. If we find it,then check which one nature follows. So You cannot reject interpretation at your will. Only by more and more expreiment we can reject it.

My personal recommendation is to learn all of the interpretations of any theory you use, and use whichever interpretation is most practical for the scenario at hand. With SR, I tend to use LET for relativistic Doppler problems, and block universe for everything else.

And wherever we go,try to find different predictions made by those interpretation,and if we failed to do find,it is more likely that both interpretations are one and the same.

Do you understand the difference between a theory and an interpretation of a theory?

Of course,I know.

 

[DrGreg]

So we need to look for more predictions made by those two different interpretation and look whether they make different predictions.

But we have looked and there are none.

I don't mean there might be some but we haven't found any yet. I mean that we have proved mathematically that both interpretations always make exactly the same predictions about any raw measurements that you could make in an experiment.

The two interpretations do differ over things that you calculate from the raw measurements but can never measure directly, such as "time dilation".* But those are internal details of the interpretation that are never visible on the outside.

But only one interpretation can be correct or only accepted by nature. I know we can explain data in many ways.but nature follows only one of those interpretations.

That's just your belief. It's not a fact. Nature doesn't understand any interpretations, it just does what it does.

_____

*In case anyone finds this confusing, I don't mean the sort of cumulative clock difference that occurs in the twins paradox, which is experimentally measurable without any theory. I mean an instantaneous comparison of clock rates, which depends on coordinates and synchronisation conventions, which can only be calculated within the context of a particular theory or interpretation.

 

[Dale]

Yes. Contradicts. Notice in the Minkowski Space-Time sketch below that Einstein's special relativity applies the Lorentz transformation between blue and red symmetrically. The LET theory applies the theory in one direction for an object at rest with respect to ether and another object in motion relative to ether. So, the space-time diagram would not look the same.

OK, the spacetime diagram would not look the same. I assume that you mean that in LET the only "real" spacetime diagram is the one in the aether frame. If so then I agree. But the spacetime diagram is a calculation tool, not an experimental outcome. In the aether frame the spacetime diagram is the same for the block universe and LET and all experimental outcomes can be calculated in that one frame and all experimental outcomes will agree between the two interpretations. So the contradiction is not experimental.

you cannot maintain that LET is an interpretation of special relativity, because special relativity in no way implies an ether.

Of course SR in no way implies an ether. Theories never imply their interpretations. If they were implied then they would be consequences of the theory, not interpretations.

However, special relativity certainly implies a 4-dimensional space-time universe.

It certainly does not. The existence of a second interpretation proves that. If the block universe were implied then there could be no other interpretation.

 

[Dale]

So we need to look for more predictions made by those two different interpretation and look whether they make different predictions.

If they make different predictions then they are different theories, not different interpretations. By definition two interpretations make ALL of the same predictions.

So You cannot reject interpretation at your will. Only by more and more expreiment we can reject it.

There is never any possible experiment which distinguishes two interpretations, by definition. So you cannot use "more and more experiment" as a criterion for rejecting. Since both interpretations are equally valid experimentally the choice between them is entirely a matter of personal preference.

 

[ghwellsjr]

I have redrawn your Loedel diagram as a conventional Inertial Reference Frame (IRF) to show how the red observer comes to the conclusions that you describe in your Loedel diagram. In my diagram, both observers are moving at 0.5c in opposite directions which gives them a relative speed of 0.8c and a gamma factor of 1.667 and an inverse gamma factor of 0.6. I am using one foot per nanosecond as the speed of light:

The thin red lines represent three radar measurements that the red observer makes which he calculates to have been applied all at the same time. Recall that a radar measurement is assumed to have been applied at the midpoint in time between when the radar signal was sent and when it was received and the distance measured is one half the difference in those two times multiplied by the speed of light. So the three distance measurements are 8, 5.5 and 4 feet in the order that the signals are sent (and the opposite order that their reflections are received). I have drawn in a green line that connects red's time at which red calculates that all these measurements were made with the distant events at which those measurements were calculated to have "happened".

Red calculates that the length of blue's rod is 8-5.5=2.5 feet.
Red calculates that the length of his own rod is 4 feet (his last measurement).
Red calculates that Blue's clock was at 6 nanoseconds when his own clock was at 10 nanoseconds (this is what the green line shows).

All of these calculations are based on red's assumption that the time that it takes for each radar signal to hit its target is the same as the time it takes for the reflection to return--identical to Einstein's synchronization convention. Note that red cannot tell the coordinate times that are assigned by this IRF. In fact, we could transform this IRF into the IRF in which red is at rest and then his assumption would match his rest IRF and his calculations would match the coordinate times and distances.

I could also show similar radar measurements for blue and they would be mirror images of red's with identical calculations.

I take issue with the comments in your drawing that the each observer can see the other ones time dilation and length contraction.

For example, you state:

When the red guy is at his worldline event with his clock reading t₂ [10 nSec], he (red) sees blue's clock reading t₁ [6 nSec].

This is false. The red guy doesn't see blue's clock reading 6 nSec until his own clock reads 18 nSec and only then is he able to make the calculation that I described earlier that allows him to conclude that blue's clock was at 6 nSec when his was at 10 nSec based on his assumption regarding the speed of light.

 

[TheBC]

As Frederik mentione LET is not an alternative to SR, it is an interpretation of SR, just like the block universe is another interpretation of SR. Do you understand the difference between an "alternative theory" and an "interpretation of a theory"?

LET = Lorentz Ether Theory

 

[TheBC]

Yes.

In LET in one frame the origin of contraction and dilation is dynamical, and in the other frame the cause is not dynamical but pure spatio-temporal. Two different causes in one theory/interpretation that has the intention to show how all laws are physical equal in all frames.

In LET there is a built-in asymmetry that's not present in SR at all. How can LET then be a valid 'interpretation'?
Block universe does not have any asymmetry...

 

[TheBC]

Maybe Gwellsjr has to take this further. In an old post of him I read:

Yes, Einstein traces that development in Lorentz's ether theory but he never stops calling it a theory different than his own or pointing out that it is his second postulate which make the difference as a starting point and the lack of an ether as an ending point. I count at least seven times in the first column of page 513 where Einstein refers specifically to Lorentz's 1904 theory and two of those times are in contrast to his own theory of relativity. He never claims that they are merely two interpretations of the same theory. In this and other papers, he always shows a contrast to Lorentz's ether theory as a result of his second postulate. https://www.physicsforums.com/showpost.php?p=3750271&postcount=26

 

[TheBC]

I have redrawn your Loedel diagram as a conventional Inertial Reference Frame (IRF) to show how the red observer comes to the conclusions that you describe in your Loedel diagram. In my diagram, both observers are moving at 0.5c in opposite directions which gives them a relative speed of 0.8c and a gamma factor of 1.667 and an inverse gamma factor of 0.6. I am using one foot per nanosecond as the speed of light:

The thin red lines represent three radar measurements that the red observer makes which he calculates to have been applied all at the same time. Recall that a radar measurement is assumed to have been applied at the midpoint in time between when the radar signal was sent and when it was received and the distance measured is one half the difference in those two times multiplied by the speed of light. So the three distance measurements are 8, 5.5 and 4 feet in the order that the signals are sent (and the opposite order that their reflections are received). I have drawn in a green light that connects red's time at which red calculates that all these measurements were made with the distant events at which those measurements were calculated to have "happened".

Red calculates that the length of blue's rod is 8-5.5=3.5 feet.
Red calculates that the length of his own rod is 4 feet (his last measurement).
Red calculates that Blue's clock was at 6 nanoseconds when his own clock was at 10 nanoseconds (this is what the green line shows).

All of these calculations are based on red's assumption that the time that it takes for each radar signal to hit its target is the same as the time it takes for the reflection to return--identical to Einstein's synchronization convention. Note that red cannot tell the coordinate times that are assigned by this IRF. In fact, we could transform this IRF into the IRF in which red is at rest and then his assumption would match his rest IRF and his calculations would match the coordinate times and distances.

I could also show similar radar measurements for blue and they would be mirror images of red's with identical calculations.

I take issue with the comments in your drawing that the each observer can see the other ones time dilation and length contraction.

For example, you state:


This is false. The red guy doesn't see blue's clock reading 6 nSec until his own clock reads 18 nSec and only then is he able to make the calculation that I described earlier that allows him to conclude that blue's clock was at 6 nSec when his was at 10 nSec based on his assumption regarding the speed of light.

Ghwellsjr,
good job there,
Bobc2 will correct me if I'm wrong, but I'm sure it was just a slip of the tongue stating that the observer *sees* it at that moment. He just meant that at that moment the rod *is* shorter and the clock time indication *is* dilated. I am sure Bobc2 can add to his awesome diagram the lightbeams from the events to the observer's eyes, if you feel that's necessary.

 

[Fredrik]

LET = Lorentz Ether Theory

Right. It's named that way because it started out as a theory. But this theory makes the same predictions of SR and it suggests away to interpret SR. So it can also be thought of as an interpretation of SR. Considering the simplicity of SR, this seems like the proper way to think of it in this century.

 

[Dale]

In LET there is a built-in asymmetry that's not present in SR at all. How can LET then be a valid 'interpretation'?

Because the "built-in asymmetry" is not measurable, and all of the measurable phenomena exhibit the full symmetry of SR.

I note that neither myself, nor you, nor bobc2, nor Fredrik, nor Dr Greg, nor vandam, nor any other person who has ever discussed this topic on this forum has been able to produce an experiment where LET and the block universe differ in their predicted experimental outcomes. This is strong evidence that they are different interpretations of the same theory, not different theories.

Should you come up with an experiment to distinguish them then send me a PM and I will be glad to re-open this thread. Otherwise, the OP is long gone and this thread has run its course.