From: utzoo!utcsrgv!donald
Newsgroups: net.misc
Title: Ants on spinning wheels
Article-I.D.: utcsrgv.489
Posted: Mon Aug  2 13:37:34 1982
Received: Mon Aug  2 14:28:57 1982


The ant on the rotation wheel problem is a variation on Newton's bucket
and brings up the ugly question of Mach's principle.  The argument is that
if you have a spinning bucket full of water, inertial effects cause
the surface of the water to become concave, thus showing that it is the
bucket, not the rest of the universe that is "really" moving.

If I recall Gardner's "Relativity for the Million" correctly, General
Relativity comes to the rescue with the following explanation:
the rest of the universe is rotating about the bucket, which generates
a gravitational field (indistinguishable from accelaration according to
the General theory), thus causing the surface of the water to go concave.
Note that this does not violate Special Relativity by requiring the rest
of the universe to spin faster than light:  the requirement that no
signal be propagated faster than C is satisfied.

Contrary to Doug Lerner's statements, the inertial effects caused by
the spinning bucket (or wheel) are not a property of movement "relative
to space time" (whatever that means).  Consider this though:  what if
the bucket were the only object in the universe and it was started spinning
(relative to what, you might ask!), would the surface go concave?

					Don Chan