From: louisnews Newstrom (louisnews@comcast.net)
Date: Fri Aug 23 2002 - 12:12:21 MDT
From: scerir <scerir@libero.it>
> 1. The postulate of relativity says that if 2 clocks separate,
> and then meet again, there is no physical phenomenon
> which can show you, in absolute terms, that one clock
> moved and the other did not, or viceversa.
This is NOT what relativity says.
This argument comes up a lot on the sci.* groups in the "Twin Paradox"
which is supposed to prove relativity is wrong.
First, relativity says that if two clocks are moving with respect to
each other, each will perceive the other as running slower.
Although this is always mentioned in the set-up of the "paradox" it has
no effect. When the two clocks synchronize their velocities, as they
do when they meet again, they perceive each other as running normally,
once more. This effect makes no prediction as to which clock should
have "lost time".
Second, relativity says that an accellerating clock (whether changing
to a faster speed, or changing to a slower speed) will "lose time".
Although position is relative, and velocity is relative, accelleration
is not. All observers will point to the same clock and proclaim that
it is changing its velocity. So there is no paradox. All observers
agree on which clock changed velocity, and which clock should
have "lost time".
> 2. Anyway if, after the 2 clocks meet again, you find that
> one clock is late, this means that the same clock moved
> away, and the other did not.
Exactly.
> 3. But, from both the statements above, we can say that
> both clocks are equally late
Wrong. Only the clock that accellerated is late. The stationary clock
is not late.
--- Louis Newstrom louisnews@comcast.net
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