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feynmann
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Does the curvature of spacetime describe gravity or tidal force?
jtbell said:To make an analogy, consider two airplanes at the equator, one at the prime meridian (0° longitude) and the other at 10° longitude. They each fly northwards along their respective longitude lines. As far as each plane is concerned, it is flying in a "straight line," with a constant heading. Each plane's pilot does not have to steer the plane except perhaps to compensate for weather conditions.
At the equator, they start out flying parallel to each other, but as they proceed northward, their paths gradually converge until they collide at the North Pole. If the pilots didn't know the Earth is actually a sphere, but assume it's flat instead, they might be tempted to postulate a fundamental "convergence force" that causes initially-parallel straight paths to converge.