>> Actually, since to a very good approximation the systems are at rest
>> with respect to one another, it does.  [...distinguished inertial
>> frame, at rest with respect to the machnes...]

> Heh.  Minor nit to pick.  Since the earth is rotating, we aren't
> really in an intertial frame.

Oog.  Why do you have to go and be difficult on me? :-)

My back-of-the-envelope calculation says that the greatest speed two
machines are moving at with respect to one another because of the
rotation of the earth is about 158 metres per second.  Since I made
simplifying assumptions (eg, I assumed the earth is a sphere), this is
probably a bit out, but is likely the right order of magnitude.

I note that Larry Niven disagrees; in _The Theory And Practice Of
Teleportation_ is a line implying, if I recall it correctly, that the
correct figure is half a mile a second - and Niven usually has his
facts right.  Can someone check my work?  I started with the
circumference being 1/7 of a light-second, which checks roughly with
the original definition of a metre being one ten-millionth of the
equator-pole distance through Paris (42.857+e6 vs 40e6 metres
circumference).  This gives me 6.82+e6 metres radius.  At 86400
seconds/revolution, that means the surface is moving (at the equator)
at 6.82e6/86400 = about 78.9+ m/s.  Double since the opposite side is
going just as fast the other way.

Does this really affect attempts to achieve nanosecond synchronization?
I'm not physicist enough to be sure.  My guess is that it will matter,
if anyone is crazy enough to try to sync machines on opposite sides of
the globe; if I've got the right principles, a speed of 160 m/s one way
or the other at a distance of fourteen million metres introduces an
error of about 25 ns.  Of course, that's worst-case, opposite sides of
the globe at the equator.  And I'm also not a trained physicist; I
could very well have *not* got the right principles.

> But I agree we can get to a good approximation. :-)

I would certainly like to be able to try.  If nothing else, it would
make it a little easier for physics experimenters to have machines on
opposite sides of the lab synchronized to the point where the distance
between their ideas of time X is spacelike. :-)

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