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Ptolemy's understanding was as simple as this. He believed that the earth was actually the center of the universe. He believed that the irregular paths of the sun and moon were because we were viewing their several different perfectly circular paths from a stationary earth.
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Somayaji Nilakantha a scientist from India made the observation/claim that the planets other than the earth orbited the sun, and the sun then orbited the earth.
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For over a thousand years people believed that Ptolemy was correct that the earth was the center of the universe, and everything revolved around us. It wasn't until the 16th century that it was debunked, by Copernicus. He found out that the sun is actually at the center of our galaxy, and we, and the planets around us revolve around it. But that the moon does in fact revolve around the earth. This is now what we know to be true today.
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Issac Newton one of the most famous and celebrated scientists, claimed that the universe is infinite. Matter on the large scale is uniformly distributed, and the universe is gravitationally balanced but essentially unstable.
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Before Einstein, Issac Newton's theory of the universe was widely accepted all of the world, for hundreds of years. Einstein found that space and time were interwoven into a single continuum known as space-time. It basically means that, items with bigger mass can actually bend space-time. Einstein defined a set of field equations, which represented the way that gravity behaved in response to matter in space-time. These field equations could be used to represent the geometry of space-time.
