"Androcles" wrote in message
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"Tom Roberts" wrote in message
...
| Martin Hogbin wrote:
| "Igor" wrote in message
...
| Many modern relativists think the two postulates are redundant.
| Why is that?
|
| Using just the Principle of Relativity [#] one can derive the Lorentz
| transform with an unknown parameter "c" (infinite yields the Galilean
| transform, imaginary yields an unphysical Euclidean-like transform [@]).
| The value of c is then an experimental issue, and it is found to be
| equal to the speed of light (in vacuum) to high accuracy.
|
| [#] One also needs standard definitions of terms like "inertial
| frame", and basic assumptions like "clocks and rulers have no
| memory". Group theory is needed, but is inherent for the
| transformations to be self-consistent.
|
| [@] Among the reasons it is unphysical is the fact that the
| composition of two velocities to the right can result in a
| velocity to the left. Another reason is that "time" acts
| just like "space". Neither of these are true in the world
| we inhabit.

That you think that is somehow funny just shows further your ignorance.

All Tom is saying is the PoR has effectively two solutions for how frames
are related .. one with velocities being unbounded (that gives Galilean
transforms) and one where there is a finite bound (the gives Lorentz
transforms).

Both are equally mathematically valid and derivable from the PoR. But only
one corresponds to our reality.

To see which one is 'correct', one needs more information (eg experimental
results). Those confirm that the Lorentz Transforms are the better model.