Hawking-Presentation2012 - The New Cosmology: Our Expanding...

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Unformatted text preview: The New Cosmology: Our Expanding Universe From very early in human civilization, humans have tried to explain the universe. An early Babylonian idea was that Earth was a flat stationary plate, and the sky above was like a moving dome, or a roof enclosing earth as a half-circle. Later, the ancient Greeks figured out that Earth could not be flat. As travelers, the Greeks were navigating using the stars for orientation. One orientation point was the North Star. They noticed that starting out from Athens, the North star would hover just above the horizon, but the farther they traveled north, the further it would raise above the horizon. This could only be explained if the Earth was round and not flat. They also experimented with sticks of equal length placed on different locations on earth, for example, one in Athens and one in Alexandria. They would place them standing in right angles to the Earth, and measure the shadows they were throwing at one particular date and time. They now noticed that when one stick at one date and time threw no shadow in Alexandria, the stick in Athens at the same date and time would have a shadow. If the earth were flat, they should throw the same shadow; only if it was curved, the shadows would be different. From a Flat to a Spherical Earth Below: a man, living on the flat earth, under a dome of sun, moon, and stars, try to break out of the dome and take a look at the other side. If he goes any further he falls down. That the earth was flat was obvious from sense experience: earth is experienced as flat and we dont fall off. That the sky was moving was also obvious from experience, since all the objects in the sky seem to be moving around us in a half-circle from morning to dusk: the sun, the moon, the stars. The Ptolemaic conception of the universe. To different renditions, First, a Medieval: Earth is not only in the center of the universe, it is also huge compared to the sun and the other planets orbiting it. Second, a more formal model illustrating the centered earth and the eight spheres. The Greeks had the idea that the most perfect movement had to be circular. The circle was the most perfect geometrical form, so if sun, moon, and star revolved around earth, they would do so in perfect circles. Ptolemy elaborated on Aristotles ideas, and came up with a model of the universe, that would last for nearly two thousand years. In the middle we have Earth, and revolving around earth, we have eight different spheres, that each of them control the movement of different bodies in the sky. The sphere closest to earth would thus account for the movement of the moon; the fourth sphere would be the sphere of the sun; the eighth sphere, farthest away, would be the sphere of the fixed stars....
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This note was uploaded on 04/06/2012 for the course BUSINESS CS204, Eco taught by Professor Mr during the Spring '12 term at American University of Beirut.

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Hawking-Presentation2012 - The New Cosmology: Our Expanding...

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