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A comment on Academics sharing paywalled papers with a codeword on Twitter. Parent comment

Re:Academics sharing paywalled papers with a codeword on Twi... by kragen on Thursday October 22, 2015 @02:47PM (#10434098)
"Because it's stuff" is considerably better than "because it's Quintessence", and "stuff is attracted to other stuff with a force F⃗ = GD̂m₁m₂/D², which accelerates it by a vector m/F⃗, whose integral is its velocity vector, whose integral ∫∫(GD̂(t)m₂/D²(t))dt² is its displacement, and the Sun has a whole hell of a lot of stuff in it, from which we can derive Kepler's Three Laws as follows…" is really a dramatically better explanation than "the natural motion of Quintessence is eternally circular".

But that was Newton, not Galileo. (And the notation of course is more or less modern, except to the extent I've screwed it up.)

The main problem with Copernicus's new theory in Galileo's time, as I understand it, was not that it didn't make numeric predictions well; the problem was that it predicted qualitative phenomena that were "known" to be false, like stellar parallax.

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Re:Academics sharing paywalled papers with a codeword on Twi... by thaumasiotes on Thursday October 22, 2015 @06:20PM (#10435525)
Not so, though. If you read the page about the Tychonic system, you saw that the objection to Copernicus was not "that theory requires stellar parallax, but there is no stellar parallax". It was "If that theory is true, then the fact that there is no stellar parallax implies that the stars are very far away". The Copernicans rightly responded "so what?" But the Tychonians trusted their guts, which told them that that was a priori impossible.

And everything you've said about Newton refers to answering the question of how much stuff is attracted to other stuff, not why it is. He was able to show that the natural motion of everything is circular (unless it's in perfect stasis), and to describe with great precision the form of the circles involved (and how they deform into ellipses), but there's no why anywhere. Newton can't justify the force of gravity varying with the square of distance except by observing that it happens to work in practice. He certainly can't explain why it's not zero -- it could have been zero. (Sure, it's very fair to say he told us why Kepler's laws obtained. But that wasn't the question, the question was "why is stuff attracted to other stuff?")

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