Spacetime

Spacetime is the four-dimensional fabric, three of space and one of time, that Einstein's general relativity treats as a single entity. Mass and energy curve spacetime, and that curvature is what we experience as gravity. Objects follow the straightest available paths through the curved geometry, which is why planets orbit and light bends near massive bodies. Ripples in spacetime are gravitational waves, and its extreme distortion defines black holes.

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