Re: accruate "sundials"

Chris L Peterson wrote:
> I've often wondered about the accuracy of this statement. In an
> accelerating room, the force of acceleration is uniform everywhere in
> that room. But how do you create a uniform gravitational field? In
> reality, there will always be a tidal force. The statement that the
> force in an accelerating frame are identical to the force in a frame
> subject to a gravitational field seems only to be true in a limiting
> case (the field produced by a mass at infinity) that isn't physically
> realizable. Or maybe you can create a locally uniform gravitational
> field through some clever superposition of masses?

I think you can, but the elevator gedankenexperiment just ignores the
tidal forces. Ultimately, general relativity concerns itself (just
as Newtonian gravity does) with point particles.

Incidentally, I suspect compression of the elevator (due to its finite
rigidity) and air pressure differences would overwhelm any slight tidal
force present in a stationary elevator on the Earth's surface.

Brian Tung <brian@xxxxxxx>
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