Hanson! -- read this, it is hilarious.

"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.
|
|
| Tom Roberts