An animated visual demonstration showing a beam of light crossing an accelerating elevator. Because the elevator moves upward while the light travels across, the light appears to curve downward to an observer inside. By equivalence, light must also curve in a gravitational field.
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Foundations of General Relativity
Bending of Light
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If acceleration mimics gravity, what happens to light? Picture a laser beam shooting horizontally across an accelerating elevator. To an outside observer, the light travels in a straight line. But because the elevator floor is rushing up to meet it, the light hits the opposite wall lower than where it started. To the observer inside, the light path looks curved. Since acceleration equals gravity, light must also bend when passing near a massive object.
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