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Ptolemy's theory that all celestial objects (the planets, the Sun, the Moon, the stars, etc.) orbited the Earth, while Earth did not move at all.
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Newton discovers and publishes his three laws of motion, which lead to the knowledge that everything in the universe attracts each other through gravity.
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Olber argues that, if the universe were infinite, thus containing stars throughout it, then in any direction you looked, "your out-of-line sight" would fall on the surface of a star.
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Slipher discovers that the spectra of light from many of the previously discovered nebulous objects systematically shifted to longer wavelengths, or redshifted. Later, the aforementioned nebulous objects were revealed to be distant galaxies.
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Predicted that the space-time around Earth would be warped-as well as twisted- by Earth's rotation, and used it to determine that massive objects cause a distortion in space-time, which in turn is felt as gravity.
