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Question:
According to Newton's theory, a planet moves around the sun because of the gravitational force put out by the sun. According to Einstein's theory of general relativity, the planet chooses the shortest possible path throughout the four-dimensional world. If Einstein is right, and no gravity y is involved, why have not the planets collided into the sun instead of circling the sun forever, which they seem to be doing. My first guess s would be centripetal force, but this force all involves the gravitational pull. Can you explain this?



Replies:
Einstein did not claim that gravity did not exist: Einstein's theory is actually exactly equivalent to Newton's theory for very weak gravitational forces of normal slow-moving bodies. What happens is that in Einstein's theory the sun (or other heavy body) distorts space time around it, in a way that mimics Newton's gravity.

Arthur Smith



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