Re: Relativity without tears

J. J. Lodder wrote:
The Maxwell equations say nothing [about constancy of the speed of light].
They say so -only with the additional assumption-
that they hold in the same form for every (inertial) observer.

This is what nobody believed before 1905,
and what constituted Einstein's fundamental contribution.
(generalised to the relativity postulate)

IMHO you got it backwards here. The Principle of Relativity was well
established long before Einstein (it dates back to Galileo). Einstein's
departure was to consider Maxwell's EQUATIONS to be "laws of physics" in
their own right, INDEPENDENT of the aether theory Maxwell used to derive
them. Then he applied the PoR to the equations and followed where that
led (though his exposition in his 1905 paper is somewhat different).

Today this is almost unknown and rarely (if ever) taught in physics
courses -- we call them "Maxwell's equations", and not "Maxwell's aether
theory", but that's what it was originally. Of course now we also know
several derivations of the Maxwell's equations which do not involve an
aether, so this is really an aspect of history, not physics.

The fact that Einstein's method worked is on the surface quite
remarkable (accepting equations while rejecting their derivation via
physical arguments), but with today's understanding we know that it
happened because of deeper underlying symmetries. It seems that Einstein
"lucked out" here, but I think it was rather an aspect of his particular
insight and genius. After all, SR was the first major step in the modern
era of physics and its emphasis on underlying symmetries.

Before Einstein it was believed that the Maxwell eqns
would hold in their standard form for one priviledged obverser [...]

Yes. Because that is now Maxwell obtained them originally.

Tom Roberts

.

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