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Name: Planck
Status: N/a
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993

According the theory of relativity, nothing can surpass the speed of light, even the flow of information. But what of events that necessarily take place instantaneously? Ex: An object moves, and the gravitational force instantly changes proportionately a light-year away. I believe that Einstein resolved this difficulty in terms of gravity's warping space - time, but I still do not understand his explanation. And on a more basic level, if I were to shake a move a one light- year long pole, would not the tip move instantaneously, beating light by roughly 12 months? Or would some sort of spring action occur just to thwart my attempt of disproving relativity?

Actually, it turns out that all forces, including gravity, the electromagnetic and other forces, are what is called "retarded". That means that although they look like they act at a distance, they do not act instantaneously at a distance. In your example, the gravitational field one light-year away would not start changing until exactly one year later. Time- dependent forces are tricky. Concerning a pole that was extremely long - how do you suppose forces move from one end to the other? They actually cannot move any (or at least not much) faster than the speed of sound in the pole. Very rigid poles have very high speeds of sound but far less than the speed of light.

A. Smith

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