Ptolemaic Theory vs Copernican Theory

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During the Age of Galileo, people believed in the existence of only one truth. This guiding principle would prove to be a problem when the Copernican theory rose to challenge the Ptolemaic theory as the true model of the universe. The two rival theories were contradictory; either the earth was at the center of the universe or it wasn’t. The task at hand was to decide which theory was the true one, and this is when the scientific stalemate between the two theories began.

The scientific stalemate that Cardinal Bellarmine referred to when he wrote his letter to Foscarini in 1615 was due to the inability of anyone to prove the superiority of either the Copernican or Ptolemaic/Aristotelian theory to the other. Both theories of the universe, although “saving the appearances” made by astronomers over the years, offered a different explanation of celestial mechanics. The Aristotelian theory held that the earth is motionless at the center of the universe, and that the sun, planets, and stars revolve daily around it. It was the most easily understood model, agreeing with simple observations such as the sun, moon, planets, and stars apparently racing across the sky daily. The Copernican theory argued that the sun lay at the center of the universe, and the earth and planets revolve around the sun. Both theories made predictions agreeing, with great accuracy, to observation. However, only one theory could be the correct one.

Two important points of disagreement that existed between the Ptolemaic and Copernican astronomers before Galileo were the poor structure of the Copernican model compared to the Ptolemaic, and the lack of any experimental evidence that could both support the Copernican model and argue against the Ptolemaic. These t...

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...ed to find another contestable theory that will also explain the new observation in addition to the previous ones. This means that if the Ptolemaic theory is falsified, then people will have to move to the Copernican theory and test its claims for falsifiability. However, although falsificationists will have helped people to become interested in the Copernican theory, they still would not have satisfied Bellarmine’s demand for a conclusive demonstration of the truth of Copernican theory. The only way that Bellarmine would support the Copernican theory was if someone could give “a true demonstration that the sun was in the center of the universe and the earth in the third sphere, and the sun did not travel around the earth, but the earth circled around the sun.” Although this demonstration would not occur within Bellarmine’s lifetime, it still would eventually occur.

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