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Originally Posted by Ken G
The crucial problems with Ptolemy's model that Copernicus saves you from is that Ptolemy's includes incorrect notions about motion, inertia, gravity, and most importantly, the distance to the stars. Once you correct them, you find that there is nothing special about the motion of the Earth, which was really the core error in the Ptolemy model.
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Indeed, Ptolemy built upon Aristotle's views, where the Earth was the logical center of the universe. [Aquinas then added rebar to give it concreteness when he anchored it into theology, which was going adrift.]
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A more interesting comparision is between Copernicus and the model of Tycho Brahe, because Tycho made all the same errors the Greeks did about inertia, motion, gravity, and the distance to the stars, but he had better data than Ptolemy, so he knew Ptolemy's model didn't work. So he was led to the idea that all the other planets orbit the Sun, not the Earth, but he still had to have the Earth be stationary so he had to make the Sun orbit the Earth! This is not nearly the "paper tiger" that is Ptolemy's model, because it is actually much more like Copernicus' model, it just focuses attention on that most key of questions: is the motion of the Earth special in some way?
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Yes, it was the introduction of the Copernican model that caused him to rethink Ptolemy's. I suspect he was taken by the persuasiveness and elegance presented in
de Revolutionibus, again an Ockham's Razor view, no doubt.
It is interesting how Tycho combined the benefits of both models into his third model that brought the
tidal change for the Jesuit scholars, who quickly adopted it. It seems his math skills were not exceptional, however, since he had to rely on Kepler to put his data to real use. [Kepler knew this, too, and refused to be an underling to Tycho.]
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So it does require Newton's laws to give us the answer to this, nothing less will really suffice.
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Agreed, though I suppose we could argue that had Kepler's laws been understood by others, with the right dash or two of Ockham, then Copernicus would have been more respected. Yet, interestingly enough, GR is supportive of either the Tychonic or Copernican model, though I see this as a somewhat mathematical approach that is effective for launching rockets, for example.
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Newton's laws unify our understanding so completely that they leave no room for the sterile idea that the Earth's motion is special, and that's what selects Copernicus over Tycho. Note I do not say we know whether the Earth orbits the Sun or the Sun orbits the Earth, because general relativity tells us that this is a meaningless question-- it is how we choose to look at it.
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I see you had beat me to it.
However, I think we disagree here, just maybe. A causal foundation to any model has to be superior to one that offers little or no causal explanation if both models give the same predictions. This GR question is still quite foggy for me since both Newton and GR do offer a causal explanation for each: a gravitational field and spacetime warpage proportionate to mass, respectively. [Though my view of GR must be naive since we are still trying to snag some gravitons.]
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But what we can say is that there is nothing special about the motion of the Earth,...
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[I appreciate your view that it is the Earth's motion that is not special, as I doubt Copernicus would agree with the Copernican principle used to apply to Earth itself.]
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Reaching this destination required Galileo's notions about inertia, Newton's notions about the sources and nature of forces, and even to some extent Einstein's notions about the arbitrariness of reference frames. What will be the next chapter?
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I don't know, but it will probably add new dimensions on how we look at things. I'll probably try to
string along, in a flailing kind of way.
