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

"Juan R." <juanrgonzaleza@.com> escribió en el mensaje

> I already CITED to Poincaré saying that Lorentz 'local time' was a
> real time measured by a clock. Poincaré (1900):
>
> "I assume observers, situated at different points, to compare their
> clocks with the aid of light signals [...] The local time tau is the
> time READ from the CLOCKS thus controlled."

Which is immediately preceded by (p. 483):

"""
2º For the compensation to be done, phenomena had to be
referred not to the real time t, but to a certain local time
t' defined in the following way.
"""

But in fact this demonstrates nothing because we are
comparing words, not physical concepts. Why? Because
"local time" and "real time" are different things to
Poincare and Einstein. Poincaré considers the "real time"
is that of a clock _and_ its observer at rest w.r.t. the
ether, and the "local time" that of a moving clock _and_ its
observer w.r.t. the ether (i.e., the clock is at rest w.r.t.
the observer). With Eintein the distinction between "local"
and "true" times disappears and the "local time" (he does
not use these words but just "time") is simply the time in a
moving sistem -- clocks moving w.r.t. the observers are
synchonized with a c which is the same for _all_ observers
no matter how they are moving w.r.t. to the emitting body.
Even you have explained that!:

> [Einstein, 1907, italics mine]
>
> "Surprisingly, however, it turned out that a sufficiently
> sharpened conception of time was all that was needed to
> overcome the difficulty discussed. One had only to
> realize that an auxiliary quantity introduced by H. A.
> Lorentz, and named by him 'local time', couldbe defined as
> 'time' in general. If one adheres to this definition of
> time, the __basic equations__ of Lorentz's, theory
> correspond to the principle of relativity . . ."

That's one of the key points of SR and it's missing in the
Poincare's papers (note I reserve "SR" to Einstein's theory)
or at least I was unable to find it. In the 1900 paper, the
ether is implicit but in the 1908 paper (reproduced in part
in Science and Method) he extends his explanation about
clocks and the ether is made explicit, and as formulated
it's in clear contradiction with SR since he clearly
states that c is different for two observers _in the same
frame_ ("dans une translation commune", p. 564; they are
even fixed w.r.t the clocks) -- this is one of the reasons
I think Poincaré was answering the Einstein's ideas, but
this is just a personal opinion.

This also has consequences in the relativity of
simultaneity, which applies with Poincaré to observers at
different locations while applies with Einstein to observers
at different velocities.

To sum up, he had the right principle (and I've never
negated that), the right mathematical tools (particularly
the so called Poincaré's group -- I'm wondering why ;-)) and
a few basic formulas, but his translation to the physical
world was wrong. He explained very little of the physical
reality, while Einstein did (as demonstrated by the papers
published shortly after with new results --and corrections--
based on the SR).

Javier
-----------------------------
http://www.texytipografia.com

.

• Follow-Ups:
• References: