Re: What is the history of relativity theory? (continuation of Poincare thread)

Javier Bezos wrote:
> cmaj10@xxxxxxxxx wrote:
>
> > "The laws of physical phenomena must be the same for a `fixed' observ=
er
> > as for an observer who has a uniform motion of translation relative t=
o
> > him: so that we have not, and cannot possibly have, any means of
> > discerning whether we are, or are not, carried along in such a motion=
.."
> > (Poincare, 1904) as cited by Juan R. Gonz=E1lez-=C1lvarez
>
> I knew this statement, which was published in an article
> whose title is "L'avenir de la Physique math=E9matique" and
> not "The principle of Relativity" as Gonz=E1lez-=C1lvarez says
> on his site. A translation into English could be "The
> future of Mathematical Physics" (which is very revelatory
> about Poincar=E9's intentions).

So it's clear to me that he knew that the speed of light (true or
apparent) was the same in all frames, if emitted from a source at rest.

>
> > "From all these results there must arise an entirely new kind of
> > dynamics, which will be characterised above all by the rule, that no
> > velocity can exceed the velocity of light."
>
> The original reads:
>
> Peut-=EAtre devrons-nous construire toute une m=E9canique
> nouvelle //que nous ne faisons qu'entrevoir//, o=F9,
> l'inertie croissant avec la vitesse, la vitesse de
> la lumi=E8re deviendrait une limite infranchissable.
>
> Italics are mine, and that important part is missing in
> the cite as given by Gonz=E1lez-=C1lvarez. It means, more or
> ess, "which we only can guess". The part "characterized
> above all by the rule" is not in the original. This is
> quite a general statement by Poincar=E9, which is important
> and he has to credited for it, but provides no hints about
> the fact c is independent from the **emitting body**,
> which is the currently accepted PoR formulated in very
> specific physical terms.

I have to agree that the two versions are quite different. In the
second version, it looks like matter is limited to speed c, but it
doesn't explicitly say anything about the speed of signals. Whereas the
first version looks more general and encompasses signals too. Maybe
Gonz=E1lez-=C1lvarez has some explanation.

So in summary, he knew that the speed of light is c in every frame, but
it's not clear whether or not he knew that the speed of light was
independent from the velocity of its source.

I bet he knew that too, since he must have viewed light as a wave; and
the velocity of waves is independent of the source. And he probably
viewed that fact as fairly obvious. Of course, I'm speculating here,
but that's a very plausible educated guess. Gonz=E1lez-=C1lvarez's quote
would confirm this guess, but you claim it's wrongly cited.

Chris

.

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