All right, so we end up with two views of astronomy coming out of this. The Keplerian view we've inherited to develop a mathematical account of the motions that yields calculated longitudes and latitudes that at all times. Into the indefinite past and the future agree with observation to within the limits of precision of the observations.

Invoking considerations from physics we're hopeful. But with the hope that ultimately the details of the motions will shed light on the underlying physics. That's my attempt to describe the Keplerian dream. Now we have the Descartes. To develop an account of the physics of the celestial realm, cosmology as it were, fully anticipating that this physics will imply that the actual celestial motions are inordinately complicated in ways making any detailed regularities.

That happened to be discerned in these motions. Nothing more than transitory happenstance occurrences, apoco coincidences, and hence of limited significance. That's the Cartesian picture. And they could not be much more diametrically opposed from the view of ongoing research. Okay. Why try to predict the motion of the planets in the indefinite future and the indefinite past, when we know perfectly well that we can't?

By the way, do people know what the present situation is in that regard? Stick around to the last class, you'll find out next semester. Okay, so what is Descarte leave us with? Whatever else and Michael Snider's making this point in his dissertation. Descartes sort of set the stage for all future cosmology by posing a whole lot of questions that people really had not posed since Aristotle.

And when Aristotle posed them he had much, much less information than Descartes did. So I’m just going to single out the questions because they all become part of physics. His answers don't become part of physics, but the questions sure do. What is it, what is the physics of stars?

Why do they give off light? What gives rise to new stars? Second, what are sun spots, how do they form, propagate and evolve? Third, what are comets, where do they come from, where do they go? Fourth, what are planets? How do they form? Why do they persist in orbit?

Fifth, what is the general structure of the universe and how does our Sun and its system relate to other nearby stars and their systems? And sixth, what is light? How does it propagate from a source? What can it tell us about that source? Okay? Those have been questions absolutely central to cosmological things, cosmological thinking ever since.

They're also not easy questions to get at. So I don't, this is another example we're calling Descartes a philosopher, not a scientist. To a very great extent, the contributions he made to the science, if only in the form of questions for which he had answers. And then the question became, once we shifted to a Newtonian cosmology without the vortices, etc, the question then becomes okay, what are the answers to all these questions without going Descartes.

By the way if you're just wondering there's a wonderful moment in Huygens' notebooks. He's reading the Principia and he writes, no more vortices in French. He's decided we don't need them any more and it drove Leibniz crazy when he found out that was Huygens' view.