Pentcho Valev
2010-12-26 08:37:36 UTC
http://www.bourbaphy.fr/damourtemps.pdf
Thibault Damour: "The paradigm of the special relativistic upheaval of
the usual concept of time is the twin paradox. Let us emphasize that
this striking example of time dilation proves that time travel
(towards the future) is possible. As a gedanken experiment (if we
neglect practicalities such as the technology needed for reaching
velocities comparable to the velocity of light, the cost of the fuel
and the capacity of the traveller to sustain high accelerations), it
shows that a sentient being can jump, "within a minute" (of his
experienced time) arbitrarily far in the future, say sixty million
years ahead, and see, and be part of, what (will) happen then on
Earth. This is a clear way of realizing that the future "already
exists" (as we can experience it "in a minute"). No wonder that many
people, attached to the usual idea of an external flow of time,
refused to believe that the travelling twin will come back younger
than his sedentary brother."
Paradigms of the special relativistic upheaval of the usual concept of
length: (if Einstein's 1905 constant-speed-of-light postulate is
true, then) an 80m long pole can be trapped inside a 40m long barn
(generally, an infinitely long object can be trapped inside an
infinitely short container) and a bug can be both dead and alive:
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
"These are the props. You own a barn, 40m long, with automatic doors
at either end, that can be opened and closed simultaneously by a
switch. You also have a pole, 80m long, which of course won't fit in
the barn. Now someone takes the pole and tries to run (at nearly the
speed of light) through the barn with the pole horizontal. Special
Relativity (SR) says that a moving object is contracted in the
direction of motion: this is called the Lorentz Contraction. So, if
the pole is set in motion lengthwise, then it will contract in the
reference frame of a stationary observer.....So, as the pole passes
through the barn, there is an instant when it is completely within the
barn. At that instant, you close both doors simultaneously, with your
switch. Of course, you open them again pretty quickly, but at least
momentarily you had the contracted pole shut up in your barn. The
runner emerges from the far door unscathed.....If the doors are kept
shut the rod will obviously smash into the barn door at one end. If
the door withstands this the leading end of the rod will come to rest
in the frame of reference of the stationary observer. There can be no
such thing as a rigid rod in relativity so the trailing end will not
stop immediately and the rod will be compressed beyond the amount it
was Lorentz contracted. If it does not explode under the strain and it
is sufficiently elastic it will come to rest and start to spring back
to its natural shape but since it is too big for the barn the other
end is now going to crash into the back door and the rod will be
trapped IN A COMPRESSED STATE inside the barn."
http://www.quebecscience.qc.ca/Revolutions
"Cependant, si une fusée de 100 m passait devant nous à une vitesse
proche de celle de la lumière, elle pourrait sembler ne mesurer que 50
m, ou même moins. Bien sûr, la question qui vient tout de suite à
l'esprit est: «Cette contraction n'est-elle qu'une illusion?» Il
semble tout à fait incroyable que le simple mouvement puisse comprimer
un objet aussi rigide qu'une fusée. Et pourtant, la contraction est
réelle... mais SANS COMPRESSION physique de l'objet! Ainsi, une fusée
de 100 m passant à toute vitesse dans un tunnel de 60 m pourrait être
entièrement contenue dans ce tunnel pendant une fraction de seconde,
durant laquelle il serait possible de fermer des portes aux deux
bouts! La fusée est donc réellement plus courte. Pourtant, il n'y a
PAS DE COMPRESSION matérielle ou physique de l'engin. Comment est-ce
possible?"
http://alcor.concordia.ca/~scol/seminars/conference/abstracts/Durand.html
"La contraction une longueur est un phénomène à la fois réel mais sans
déformation structurelle. C'est un phénomène réel (et non pas une
illusion) car, par exemple, une perche dont la longueur au repos est
plus grande que la longueur au repos d'une grange peut réellement être
contenue dans cette dernière si elle se déplace assez rapidement. Par
contre, il ne peut y avoir de contraction structurelle de la perche,
i.e de déformation matérielle de l'objet, car la contraction de sa
longueur aurait aussi lieu si c'était plutôt l'observateur qui se
mettait en mouvement sans changer l'état de mouvement de la perche.
Autrement dit, sans changer l'état de la perche, en se mettant soi-
même en mouvement, on change sa longueur: ce n'est donc clairement pas
une contraction matérielle (l'état de la perche est le même dans les
deux cas)."
http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html
"The bug-rivet paradox is a variation on the twin paradox and is
similar to the pole-barn paradox.....The end of the rivet hits the
bottom of the hole before the head of the rivet hits the wall. So it
looks like the bug is squashed.....All this is nonsense from the bug's
point of view. The rivet head hits the wall when the rivet end is just
0.35 cm down in the hole! The rivet doesn't get close to the
bug....The paradox is not resolved."
The following scenario will show that, in accordance with Einstein's
special relativity, the travelling twin will find himself OLDER than
his brother who remained behind. A long rocket passes the twin at
rest, and the rocket is so long that the twin at rest will see it
passing by all along. According to Einstein's special relativity,
observers in the rocket see their clocks running faster than the twin
at rest's clock, that is, observers in the rocket age faster than the
twin at rest. At some initial moment the travelling twin, standing so
far next to his brother, jumps into the rocket, joins the observers
there and starts, just like them, aging faster than the twin at rest.
Later the rocket stops and immediately starts moving in the opposite
direction. Again, according to Einstein's special relativity,
observers in the rocket, including the travelling twin, age faster
than the twin at rest.
Finally the travelling twin jumps out of the rocket and rejoins his
brother at rest. Who is older? REDUCTIO AD ABSURDUM par excellence.
Pentcho Valev
***@yahoo.com
Thibault Damour: "The paradigm of the special relativistic upheaval of
the usual concept of time is the twin paradox. Let us emphasize that
this striking example of time dilation proves that time travel
(towards the future) is possible. As a gedanken experiment (if we
neglect practicalities such as the technology needed for reaching
velocities comparable to the velocity of light, the cost of the fuel
and the capacity of the traveller to sustain high accelerations), it
shows that a sentient being can jump, "within a minute" (of his
experienced time) arbitrarily far in the future, say sixty million
years ahead, and see, and be part of, what (will) happen then on
Earth. This is a clear way of realizing that the future "already
exists" (as we can experience it "in a minute"). No wonder that many
people, attached to the usual idea of an external flow of time,
refused to believe that the travelling twin will come back younger
than his sedentary brother."
Paradigms of the special relativistic upheaval of the usual concept of
length: (if Einstein's 1905 constant-speed-of-light postulate is
true, then) an 80m long pole can be trapped inside a 40m long barn
(generally, an infinitely long object can be trapped inside an
infinitely short container) and a bug can be both dead and alive:
http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html
"These are the props. You own a barn, 40m long, with automatic doors
at either end, that can be opened and closed simultaneously by a
switch. You also have a pole, 80m long, which of course won't fit in
the barn. Now someone takes the pole and tries to run (at nearly the
speed of light) through the barn with the pole horizontal. Special
Relativity (SR) says that a moving object is contracted in the
direction of motion: this is called the Lorentz Contraction. So, if
the pole is set in motion lengthwise, then it will contract in the
reference frame of a stationary observer.....So, as the pole passes
through the barn, there is an instant when it is completely within the
barn. At that instant, you close both doors simultaneously, with your
switch. Of course, you open them again pretty quickly, but at least
momentarily you had the contracted pole shut up in your barn. The
runner emerges from the far door unscathed.....If the doors are kept
shut the rod will obviously smash into the barn door at one end. If
the door withstands this the leading end of the rod will come to rest
in the frame of reference of the stationary observer. There can be no
such thing as a rigid rod in relativity so the trailing end will not
stop immediately and the rod will be compressed beyond the amount it
was Lorentz contracted. If it does not explode under the strain and it
is sufficiently elastic it will come to rest and start to spring back
to its natural shape but since it is too big for the barn the other
end is now going to crash into the back door and the rod will be
trapped IN A COMPRESSED STATE inside the barn."
http://www.quebecscience.qc.ca/Revolutions
"Cependant, si une fusée de 100 m passait devant nous à une vitesse
proche de celle de la lumière, elle pourrait sembler ne mesurer que 50
m, ou même moins. Bien sûr, la question qui vient tout de suite à
l'esprit est: «Cette contraction n'est-elle qu'une illusion?» Il
semble tout à fait incroyable que le simple mouvement puisse comprimer
un objet aussi rigide qu'une fusée. Et pourtant, la contraction est
réelle... mais SANS COMPRESSION physique de l'objet! Ainsi, une fusée
de 100 m passant à toute vitesse dans un tunnel de 60 m pourrait être
entièrement contenue dans ce tunnel pendant une fraction de seconde,
durant laquelle il serait possible de fermer des portes aux deux
bouts! La fusée est donc réellement plus courte. Pourtant, il n'y a
PAS DE COMPRESSION matérielle ou physique de l'engin. Comment est-ce
possible?"
http://alcor.concordia.ca/~scol/seminars/conference/abstracts/Durand.html
"La contraction une longueur est un phénomène à la fois réel mais sans
déformation structurelle. C'est un phénomène réel (et non pas une
illusion) car, par exemple, une perche dont la longueur au repos est
plus grande que la longueur au repos d'une grange peut réellement être
contenue dans cette dernière si elle se déplace assez rapidement. Par
contre, il ne peut y avoir de contraction structurelle de la perche,
i.e de déformation matérielle de l'objet, car la contraction de sa
longueur aurait aussi lieu si c'était plutôt l'observateur qui se
mettait en mouvement sans changer l'état de mouvement de la perche.
Autrement dit, sans changer l'état de la perche, en se mettant soi-
même en mouvement, on change sa longueur: ce n'est donc clairement pas
une contraction matérielle (l'état de la perche est le même dans les
deux cas)."
http://hyperphysics.phy-astr.gsu.edu/Hbase/Relativ/bugrivet.html
"The bug-rivet paradox is a variation on the twin paradox and is
similar to the pole-barn paradox.....The end of the rivet hits the
bottom of the hole before the head of the rivet hits the wall. So it
looks like the bug is squashed.....All this is nonsense from the bug's
point of view. The rivet head hits the wall when the rivet end is just
0.35 cm down in the hole! The rivet doesn't get close to the
bug....The paradox is not resolved."
The following scenario will show that, in accordance with Einstein's
special relativity, the travelling twin will find himself OLDER than
his brother who remained behind. A long rocket passes the twin at
rest, and the rocket is so long that the twin at rest will see it
passing by all along. According to Einstein's special relativity,
observers in the rocket see their clocks running faster than the twin
at rest's clock, that is, observers in the rocket age faster than the
twin at rest. At some initial moment the travelling twin, standing so
far next to his brother, jumps into the rocket, joins the observers
there and starts, just like them, aging faster than the twin at rest.
Later the rocket stops and immediately starts moving in the opposite
direction. Again, according to Einstein's special relativity,
observers in the rocket, including the travelling twin, age faster
than the twin at rest.
Finally the travelling twin jumps out of the rocket and rejoins his
brother at rest. Who is older? REDUCTIO AD ABSURDUM par excellence.
Pentcho Valev
***@yahoo.com