Michel Jullian wrote:
----- Original Message ----- From: "Stephen A. Lawrence"
<[EMAIL PROTECTED]> To: <vortex-l@eskimo.com> Sent: Thursday, February
15, 2007 10:33 PM Subject: Re: [Vo]: FW: Einstein's Twin Paradox ...
This is not a paradox, and the "paradoxical" nature of the problem
was in fact resolved something on the order of a century ago. The
traveling twin accelerates; the stay-at-home twin does not; thus,
the symmetry is broken.
...
To be more precise the traveling twin is the only one who accelerates
_wrt the initial common frame of reference_, that's what breaks the
symmetry (otherwise one could argue that they both accelerate wrt
each other)
No you could not. Acceleration is absolute, not relative.
This is where Mach's principle starts looking totally silly.
In a situation without gravity (which is what SR deals with) drop a
ball. Does it fall? If so, then you're accelerating. You can perform
this test without looking out a window or examining anything outside
your own laboratory. That is what I mean when I say it is "absolute" --
either you _are_ accelerating or you are _not_, and simple tests can
determine the difference (to a specified level of accuracy, of course).
When you transform to accelerated coordinates many things change,
including the metric. Neither Galilean relativity nor Einstein's
relativity ever tried to pretend that accelerating and inertial frames
were in all ways identical.
Inertial coordinates are special, and that's what puts the SPECIAL into
"special relativity" -- it's the limited form of the theory that applies
to inertial coordinates. As it happens it can be applied to
accelerating frames as well just by extending the math a bit, but to
take the jump to include gravitation you need to introduce curvature and
the field equations, and that's when special relativity is left behind.
Michel
