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| This theory was published in 1927 by Geroge Lemaitre, Albert Einstein, Edwin Hubble, Arno Penzias, and Robert Wilson. It states that the universe was created with a giant explosion. |
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| Dated as early as the 4th century BC, this theory was disproved by Aristotle. The theory states that the Earth is flat like a pizza. |
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| The ancient scientist Ptolemy theorized that the Earth was the center of the universe as it was God's creation. The term applied to this thought is geocentric. This theory was popular from the middle ages to the renaissance. |
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| In the 16th and 17th centuries, Copernicus went against the beliefs of the church and stated that the Earth was not the center of the universe, the sun was. The term used to describe this theory is heliocentric. |
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| Johannes Kepler stated in the 1600's that the planets were not in circular orbits, but eliptical orbits. |
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| Between 1920 and 1950, scientists Sir James Jeans, Hermann Bondi, Thomas Gold, and Sir Fred Hoyle proposed that the universe is always expanding, however new stars are created at the same rate that old ones are being destroyed. This means that there would always be a steady state of matter in the universe. |
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| In the 1920;s Alexander Friedmann added to the Big Bang theory and stated that eventually the universe will stop exlpanding and there will be a "Big Crunch." |
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| In 1973 Brandon Carter proposed that the only purpose for the universe to exist is to support human life and as long as there is human life, the universe will exist. |
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| Inflationary Universe Theory |
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| Sometime after the Big Bang theory, scientists Alan Guth, Andrei Linde, Paul Steinhardt, and others proposed that the there was a period right before the Big Bang in which the universe expanded exponentially faster than the rate at which it expands now. |
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| In 1983 James Hartle and Stephen Hawking stated that the universe was open and has no boundary much like the Earth, meaning that you can travel for as long as you want and never reach a point that you can travel no further. |
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| In the 20th century Richard Tolman added to Friedmann's theory. he said that there will be a series of "Big Bangs" and "Big Crunches". The universe will oscillate back and forth between the two states. |
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