Relativity: The Special And The General Theory,... Instant

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Einstein breaks down the conventional idea of "absolute time". He introduces the Principle of Relativity , which states that the laws of physics are the same for all observers moving at constant speeds, and the fact that the speed of light is constant regardless of motion. This leads to the famous conclusion that time and space are relative and linked as "spacetime". Relativity: The Special and the General Theory,...

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This section expands relativity to include gravity. Einstein describes gravity not as a force between objects, but as a curvature of spacetime caused by mass and energy. He uses the "Principle of Equivalence" to show that being in a gravitational field is indistinguishable from accelerating. Read the full text at the Project Gutenberg