http://www.rehseis.cnrs.fr/Philosophie_Physique/Jumeaux_Saint-Ours.pdf
Alexis de Saint-Ours: "Par ailleurs, comment se fait-il que
l'accélération soit responsable de l'asymétrie et qu'en même temps
elle n'apparaisse pas dans la différence d'âge entre les deux
protagonistes ? Si l'accélération est la cause, comment se fait-il que
l'effet ne soit proportionnel qu'à T ? (...) Conclusion: Il existe des
versions du paradoxe sans accélérations (...) Il faut qu'il y ait une
asymétrie si l'on veut avoir une ligne d'univers plus longue qu'une
autre mais cette asymétrie peut résulter d'autre chose que de
l'accélération."
Quelle "autre chose"? Selon Einstein (1918), l'accélération du jumeau
voyageur est la seule cause de sa jeunesse (pourquoi n'en discutez-
vous pas?):
http://en.wikisource.org/wiki/Dialog_about_objections_against_the_theory_of_relativity
Dialog about Objections against the Theory of Relativity (1918), by
Albert Einstein
"...according to the special theory of relativity the coordinate
systems K and K' are by no means equivalent systems. Indeed this
theory asserts only the equivalence of all Galilean (unaccelerated)
coordinate systems, that is, coordinate systems relative to which
sufficiently isolated, material points move in straight lines and
uniformly. K is such a coordinate system, but not the system K', that
is accelerated from time to time. Therefore, from the result that
after the motion to and fro the clock U2 is running behind U1, no
contradiction can be constructed against the principles of the theory.
(...) During the partial processes 2 and 4 the clock U1, going at a
velocity v, runs indeed at a slower pace than the resting clock U2.
However, this is more than compensated by a faster pace of U1 during
partial process 3. According to the general theory of relativity, a
clock will go faster the higher the gravitational potential of the
location where it is located, and during partial process 3 U2 happens
to be located at a higher gravitational potential than U1. The
calculation shows that this speeding ahead constitutes exactly twice
as much as the lagging behind during the partial processes 2 and 4.
This consideration completely clears up the paradox that you brought
up."
John Norton confirme la conclusion d'Einstein de 1918 (donc il n'est
pas si facile de résoudre le problème en oubliant l'accélération):
http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/spacetime_tachyon/index.html
John Norton: "Then, at the end of the outward leg, the traveler
abruptly changes motion, accelerating sharply to adopt a new inertial
motion directed back to earth. What comes now is the key part of the
analysis. The effect of the change of motion is to alter completely
the traveler's judgment of simultaneity. The traveler's hypersurfaces
of simultaneity now flip up dramatically. Moments after the turn-
around, when the travelers clock reads just after 2 days, the traveler
will judge the stay-at-home twin's clock to read just after 7 days.
That is, the traveler will judge the stay-at-home twin's clock to have
jumped suddenly from reading 1 day to reading 7 days. This huge jump
puts the stay-at-home twin's clock so far ahead of the traveler's that
it is now possible for the stay-at-home twin's clock to be ahead of
the travelers when they reunite."
Alexis de Saint-Ours, je vous ai référé à l'article de Peter Hayes
mais évidemment vous n'avez rien compris:
http://www.informaworld.com/smpp/content~content=a909857880
Peter Hayes "The Ideology of Relativity: The Case of the Clock
Paradox" : Social Epistemology, Volume 23, Issue 1 January 2009, pages
57-78
"The argument that the prediction of time difference between a moving
and a stationary clock violates the principle of relativity is well
known. Certainly, it must have become known to Einstein, for in 1918
he created a dialogue in which "Kritikus" voiced exactly this
objection (Einstein 1918). In response to this criticism, Einstein
underwent a volte-face, reversing his reasoning in 1905 and 1911. The
sudden change in direction of the moving clock, far from having
unknown effects that needed to be minimised, was now said to provide
the entire explanation for the change. Instead of imagining a moving
clock travelling in a huge polygon or circle to make sudden changes in
direction as insignificant as possible or the journey as smooth as
possible, Einstein imagined an out and back journey. He then explained
that the slow-down in the moving clock occurred during the sudden jolt
when it went into reverse. (...) Given Einsteins argument in 1918, it
seems inescapable that his 1905 prediction of time dilation was not,
in fact, a "peculiar consequence" of his forgoing account of special
relativity (Einstein 1923, 49). When it is also remembered that in
1904 Lorentz deduced the existence of "local time", it is reasonable
to conclude that the prediction that the clocks would end up showing
different times can be reached without entering into Einstein's
reasoning on the special theory at all. The supporters of Einstein,
however, generally maintain that one needs to move beyond the special
theory to the general theory to understand why the times shown by the
clocks would be different. However, as Einstein's prediction preceded
the general theory, this argument is problematic (Lovejoy 1931, 159;
Essen 1971, 14). It has been seen that: (a) in 1911 Einstein
explicitly rules out the ability of the special theory of relativity
to say what happened if the moving clock suddenly changed direction,
and (b) in 1918 Einstein tacitly admitted that his explanation of the
clock paradox in 1905 was incorrect by transforming the polygonal or
circular journey of the moving clock into an out and back journey. If
the general theory is necessary to explain the clock paradox, then
Einstein must have (a) predicted the effects of acceleration in 1905
even though he did not incorporate them into his theory for another
decade, and (b) hidden his intuition by describing a journey that
discounted their significance. (...) There is, nonetheless, some
divergence about how to resolve the clock paradox amongst mainstream
scientists and philosophers who address the issue. The majority
suggest that (a) the general theory is required to resolve the paradox
because like "Kritikus" they have deduced - quite correctly - that it
cannot be explained by the special theory. However, a minority believe
that (b) the paradox can be explained by the special theory because
they have deduced - again quite correctly - that it is incredible to
suppose that only the general theory can explain a prediction
ostensibly arising from the prior special theory. Each deduction,
considered in isolation, is allowable within the mainstream; what is
not permitted is to bring the two of them together to conclude that
( c) neither the special nor the general theory explains time
dilation."
Pentcho Valev
pva...@yahoo.com