: : Lau: Consider a bucket of water, and you start spinning the bucket. The water will start to climb up the side of the bucket and the surface of the water will become concave. Now the question is how does the water know it's spinning? Relatively if we think of it as the bucket is stationery and the surrounding is moving, should the surface stay flat or concave??

: Relatively this becomes a Moch's principle question. The answer from this perspective is that the matter of the universe circling around the bucket induces a component to a gravitational field much like magnetism is induced by moving charges. Relativisticaly all the "fictitious" forces are actually real. Sometimes this phenomenon is called a gravomagnetic or sometimes gravitomagnetic field. I believe it was in the nineteen tens that Thirring first proved this gravomagnetic field could be found in the framework of general relativity finding the solution for the case of a rotating spherical mass.

Lau: So with the induced component to the gravitational field, what are the resulting effect?

• Re: how does it know?? - Zephram_Cochrane/">Zephram Cochrane - January 4, 2000 - 09:56 UTC