Is spacetime independent of its universe?

[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.