Word: spaced
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Dates: during 1990-1999
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...German University in Prague in 1911. He realized that there is a close relationship between acceleration and a gravitational field. Someone in a closed box cannot tell whether he is sitting at rest in the earth's gravitational field or being accelerated by a rocket in free space. (This being before the age of Star Trek, Einstein thought of people in elevators rather than spaceships. But you cannot accelerate or fall freely very far in an elevator before disaster strikes...
...return to Zurich in 1912 Einstein had a brainstorm. He realized that the equivalence of gravity and acceleration could work if there was some give-and-take in the geometry of reality. What if space-time--an entity Einstein invented to incorporate the three familiar dimensions of space with a fourth dimension, time--was curved, and not flat, as had been assumed? His idea was that mass and energy would warp space-time in some manner yet to be determined. Objects like apples or planets would try to move in straight lines through space-time, but their paths would appear...
With the help of his friend Marcel Grossmann, Einstein studied the theory of curved spaces and surfaces that had been developed by Bernhard Riemann as a piece of abstract mathematics, without any thought that it would be relevant to the real world. In 1913, Einstein and Grossmann wrote a paper in which they put forward the idea that what we think of as gravitational forces are just an expression of the fact that space-time is curved. However, because of a mistake by Einstein (who was quite human and fallible), they weren't able to find the equations that related...
...during a visit to the University of Gottingen in the summer of 1915, and Hilbert independently found the same equations a few days before Einstein. Nevertheless, as Hilbert admitted, the credit for the new theory belonged to Einstein. It was his idea to relate gravity to the warping of space-time. It is a tribute to the civilized state of Germany in this period that such scientific discussions and exchanges could go on undisturbed even in wartime. What a contrast to 20 years later...
...theory of curved space-time was called general relativity to distinguish it from the original theory without gravity, which was now known as special relativity. It was confirmed in spectacular fashion in 1919, when a British expedition to West Africa observed a slight shift in the position of stars near the sun during an eclipse. Their light, as Einstein had predicted, was bent as it passed the sun. Here was direct evidence that space and time are warped, the greatest change in our perception of the arena in which we live since Euclid wrote his Elements about...