PeterDonis said:
Because we *observe*, experimentally, that ##c## is constant in all IRF. We didn't just make up the postulate from thin air. Which we also observe, experimentally. If you don't like this postulate, take it up with Nature.
I am not contradicting that postulate; the two-way speed of light is supported by hard evidence. It is not
that postulate that is unnecessary. It's the others (isotropy of c and that clocks measure "real time" regardless of motion) that force us to an explanation in which time and space themselves are only relative things.
PeterDonis said:
No. First of all, we don't assume that all clocks measure time correctly; some clocks do it better than others. Second, we don't postulate that clocks measure time correctly; we postulate that "time" is what clocks measure. In other words, we have a theoretical model in which "time" appears, and we link this model to what we actually observe by linking the "time" in the model to the observations we make of clocks. This has to be done for any physical theory.
The postulate that moving clocks measure "actual time" is unnecessary to explain the Lorentz transformations, as is the postulate that the speed of light is the same in all directions.
You cannot prove the isotropy of c with experiments.
That moving clocks measure actual time is a definition of time in SR. That definition is unnecessary to explain the LTs.
Experiments are easily explained using wave physics in absolute space and time. In LET, moving clocks are demonstrated to tick slower than those at rest in the ether. The Lorentz transformation for time as measured by clocks is a direct consequence of a simple analysis of waves in a medium.
I can make a similar argument to yours. SR assumes some things that you cannot detect so why believe that it is the correct
interpretation of nature?
PeterDonis said:
Really? Why not? Can't we just observe light moving in different directions?
You can attempt to measure the one-way speed with a ruler and clocks, but you have to choose a
convention for clock synchronization to measure one-way velocity. There are many choices. Einstein's choice implicitly assumes that the speed of light is isotropic. That choice is not required to explain experimental results.
Because this "mechanism" is inherently unobservable.
I would agree that the absolute frame is undetectable in the context of the Lorentz transformations. Beyond that, who knows?
I think you will agree that isotropy of the speed of light is undetectable if you study some papers on the subject of clock synchronization.
Because there still is a need. Nobody actually observes this "absolute time" or "absolute space"; the "different idea about time and space" is about the time and space we actually *observe*.
You can define "space" as what is measured by similar rods in any frame and "time" as what is measured by a similar clocks in any frame regardless of motion, and assert that time and space are frame dependent i.e. relative. You can apply Minkowsky space and all the things that have already been done using the concept of relativity. That's perfectly correct in terms of results. You can do the same thing in LET.
What is lacking in SR is a physical theory of why "space' and "time" (as defined above) behave the way they do. This view that time and space are not absolute is forced by the "extra" postulates of SR.
On the other hand, it is easily demonstrated with a simple application of classical physics to waves in a medium that moving clocks tick slower and consequently that length is measured as contracted in a frame moving with respect to the medium. That the speed of light is an upper bound is obvious for waves in a isotropic medium from classical physics. In LET nothing can travel faster. Tachyons are
impossible.
Because we can't observe the medium, even in principle.
In SR you
cannot observe the one-way speed of light, even in principle. SR
assumes that c is isotropic.
There is nothing that you can observe "directly" in principle. All you ever get to do is measure quantities and
infer or
theorize what is actually there. These "things that you observe" have the same level of reality as ether.
In LET, waves in the ether is "all" that is observable. Light and matter are waves. Because we are waves we cannot directly perceive the ether but we can measure it's properties by seeing how the waves behave.
In summary, SR is forced to assume that actual time and space are relative by certain postulates that cannot be demonstrated.
SR deprives light waves and matter waves of a medium in which to propagate. All the other types of waves that we study in physics are the result of changes in a medium.
Many physicists have also pointed out that motion cannot be
entirely relative because we can detect absolute rotation using the Sagnac effect (laser gyros). Also, acceleration is absolute.