Re: Does motion affect the operation of clocks or not ?

Thus spake Andrew Harland <leohar@xxxxxxxxxx>
Hi everybody

In his paper - "The Confrontation between General Relativity and
Experiment: A 1998 Update" - http://xxx.lanl.gov/abs/gr-qc/9811036
Clifford M. Will wrote on page 12 that
the Global Positioning System (GPS) provides absolute
accuracies of around 15 m (even better in its military mode)
anywhere on Earth, which corresponds to 50 nanoseconds in
time accuracy at all times. Yet the difference in rate between
satellite and ground clocks as a result of special and general
relativistic effects is a whopping 40 microseconds per day
(60micros. from the gravitational redshift, and -20micros. from
time dilation). If these effects were not accurately accounted
for, GPS would fail to function at its stated accuracy.

This seems to indicate that the GPS clocks are really affected by
motion. However, in their book "Spacetime Physics - Introduction to
Special Relativity" (W. H. Freeman and Company - 1992) Edwin F.
Taylor and John Archibald Wheeler write on page 77:
We conclude that free-float motion does not affect the
structure or operation of clocks.

I'm not sure what to believe now. Does motion affect the operation of
clocks or not? Can anybody enlighten me on this?

The fundamental postulate is the general principle of relativity.
According to this the local laws of physics are the same for all
observers. So one clock, as seen by an observer moving with it, must
behave in exactly the same way as a second, identical, clock as seen by
an observer moving with the second clock.

However, when these observers look at each others clocks, they find time
dilation effects, both the special relativistic effect from motion and
the gravitational effect. It is not right to say that motion has
effected the clocks, because motion of matter only makes sense relative
to other matter. It would be better to say that motion affects the way
in which a clock is seen by a moving observer, and that position affects
the way in which it is seen by a distant observer.

Regards

--
Charles Francis
moderator sci.physics.foundations.
substitute charles for NotI to email

.

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