In this video segment from NOVA, string theorist Brian Greene explains how, for more than 200 years, Isaac Newton's theory of gravity remained unchallenged despite the fact Newton himself had no idea how gravity actually worked. Albert Einstein eventually proved that Newton was mistaken about gravity, at least as it applied to the most massive stellar objects. To illustrate a key difference in their two theories, animations depict a cosmic catastrophe: the destruction of the Sun and the effects on the orbiting planets.
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