Philosophy 167: Class 3 - Part 2 - Kepler: a Brief Biography, and the Appreciation of Physical Theory.
Smith, George E. (George Edwin), 1938-
2014-09-16
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So a little about Kepler. Kepler was born in 1571, he died in 1630, so he didn't quite make 60 years old. From a single parent Lutheran family, not well-to-do. There are two prominent figures in this semester. Two prominent figures in science who are not financially well enough off that they could basically just live off their wealth.
Kepler is one and Robert Hook is the other. Hook had the good fortune of people taking care of him, giving him a position. Kepler his whole life was struggling for money. People would, the people who were sponsoring him, would promise him money, not deliver it, and who would nastily go beg for it and not always get it.
And I want to, the other thing I emphasize, he was from a Lutheran family. He went Tubingen, the school Tufts has an exchange program with, got his master's degree in 1595 in theology, philosophy and astronomy, studying under Maestlin. When he graduated from there, he wanted a job in theology, could not get one.
Finally got a job in Roman Catholic Austria as a professor of math and that led just a few years later to his either being called up. Every non-catholic in the city was called before the city magistrates and given a choice. Convert to Catholicism or get the hell out.
At least they didn't chop the heads off. That's something that you could say. But it forced him out. And time and again his refusal to convert to Catholicism while he was almost always being sponsored by somebody who was Roman Catholic, time and again that created a problem, but it also was one of the reasons he had trouble collecting money, because they knew they had him.
He really didn't have much choice most of the time. What always amazes about him, again, John Banville has a novel about him but I haven't been able to go through it because, unlike the one for Copernicus, I have a preconception of Kepler. Kepler had, by my standards, an incredibly miserable life.
I'll give you some examples. His first wife died, 8 of their 12 children died before they were 15 years old. His second wife, the marriage was reasonable, but not anything like the first wife. His marriage to Barbara was a very loving marriage. As I say, all his life, he was persecuted to some extent, for being Lutheran in a Roman Catholic world.
His mother ultimately got tried as a witch and he had to take a year or two off and defend her. Probably the hardest thing of all, is he had a very good idea of what he had achieved. And he struggled throughout his life to get recognition from other people and he got none.
Virtually zero recognition until a year after he died. You'll see that in week after next when all of a sudden people realize for the first time he's basically right, what he's been doing all along was extremely sound. And the remarkable part of this as you read him, you read anything he's written, we'll do another week on it, next week.
And he just plugs away. He doesn't seem to get bitter. He doesn't seem to get despondent. He just keeps working away doing six digit calculations after six digit calculation for a period, essentially from 1600 to 1630. When he died, and he was still very active at the time.
And I don't really understand how somebody can have a life like that and not give up somewhere along the way. That's a comment about me, not about him. I just don't see myself surviving something like that. He did a book in 1596 where he had a bright idea, we'll talk about it more next week.
He thought he could explain exactly why there are six planets, snd I'll just summarize the idea. There are five regular solids, as proved by Theaetetus, the same Theaetetus who's a figure in the Plato dialogue. Five regular solids, and they can be nested inside of one another. And the ratios of those distances, he thought, corresponded to the ratios of the distances in the Copernican system to the planets from the sun.
So in effect God designed the system so that the five regular solids were nested one in side of one another. The first trouble was he couldn't figure out how to get the precise non-uniform distances in Copernicus so he turned to Maestlin for help. And that's Corey was asking before about the Maestlin appendix to Mysterium Cosmigraphicum, which I will put up on reserve tomorrow, or put up on supplementary material.
So after that, after he figured out how to do the distances, they're weren't perfect. And that bothered him. And, he knew of course that he was in fact working from the pretended tables and very few observations. He knew a Tycho, so he asked to come to Tico to work with him.
Initially, Tycho, by the way, Tycho was very guarded about his observations. He would not show them to Kepler. Very selectively. But, what happened is, the people who were working under Tycho ended up the most important ones. Langio Montana decided to go back to Denmark, cuz he could then make a name for himself independently of Tycho.
And all of a sudden, Tycho didn't have a decent mathematician working underneath him. So, he took on Kepler, but he took on Kepler, and just within weeks after that. Tycho died apparently from uremia from excess drinking October of 1601. I don't trust the story. Any story about how people died, etc., I never trust because they get so embellished over time.
So I'm not even telling you some of the more shocking details that are supposed to have happened, but he died. He died fairly young and there was Kepler and Kepler was just fell into his position. The emperor hired him to replace Tycho and do that promise. One of the preconditions for Kepler to join Tycho is that Ursus had cited a letter from Kepler.
The letter from Kepler was an attempt to, and he sent a complimentary copy of Mysterium Cosmographicum and his scheme, asking what every astronomer thought. He sent it to Galileo, he sent it to Maestlin, and he sent it to everybody he could, trying to attract attention. And Ursus quotes it in an attack on Tycho as if Kepler's on my side here.
Tycho is a plagiarist, he stole this system from Copernicus. So one of the preconditions was a defense of Tycho against Ursus, and that's what the Apologia is that I gave you. It ended up not being published until the 20th century when Kepler's late 19th century when Kepler's complete works were put out.
So, it's not part of science. That is, I always describe science as a public matter of stuff in the public. If anything is private it's not part of science, but it is somewhat instructive what Kepler's attitude was toward this problem at the time. That's why I had you read it.
It's also your first occasion to be reading any primary source. So the issue he poses is the diversity of hypotheses and he grants Ursus that here's a diversity of hypotheses. First remark is none of them work. That is none of them are actually accurate. And therefore, what we really should be doing is taking them, looking at the discrepancies, and seeing how to refine them into new trajectories, new orbits.
Then he makes the remark and I'm quoting here. The quotes from page 141. Even if the conclusions of two hypothesis coincide in the geometrical realm, each hypothesis will have it's own peculiar corollary in the physical realm. And that became the picture Kepler had, and it's gonna get very dramatic tonight.
Even after all of his reforms, the reforms he's famous for that got accuracy down to within five minutes of arc in one fell swoop. Even after that, exactly the same moves can be transferred to any of the three systems to yield exactly the same geocentric longitudes and latitudes.
And he knew that and he tells you that in the introduction to Astronomia Nova. They can definitely be transferred. That means from his point of view no geocentric longitudes and latitudes observe longitudes and latitudes can possibly settle the question between these three. On the other hand, his idea was, once we reform and get accurate orbits, accurate motions, I mean, until we have accurate motions, we shouldn't take ourselves that seriously.
Once you get an accurate representation of the motions on all three schemes, then it is legitimate to ask, what physical mechanism could be producing this motion? And his thought was that physical mechanism will clearly show Copernicus is right and the other two are wrong. Okay? So that's the theme of Astronomia Nova.
First figure out what the actual trajectories and motions are, and then, ask yourself what physics can produce this? Now the physics he expressly describes, you're gonna read the introduction to Astronomia Nova next week. I wanted you to read it after you know what was in the rest of the book.
He expressly says, of course the physics is conjectural. And he adds right away, it has to be conjectural. Physics has to be a matter just of conjecture. And of course, from my point of view, I read that and say okay, that's the question. Did Newton do better than make it merely conjectural?
Well that's the question of the course, and it's quite legitimate, cuz Newton ends up doing much of what, much of what Kepler wanted to do. Namely settle the Copernican question on the basis of the physics of the actual trajectories. His physics was based on a book in 1600.
I'll pass this around. This of course is an English translation of William Gilbert De Magnete. It's a fairly remarkable book published in 1600 and this edition 360 pages long. I'll just pass it around, I don't need to look at it. It is not what we would call modern science, it's naturalistic science.
It's like going out and describing plants and animals. Except it's describing magnetism and it's part of a tradition that's come to be known as Renaissance naturalism to actually contrast it to modern science. It's a forerunner to modern science, but the view was what we should be doing is describing nature in great detail rather than theorizing about it all over the place.
It's a remarkable book. It really does describe virtually everything we still know qualitatively about magnetism. Including the magnetic field of the Earth and thankfully of course he didn't call it field, the magnetism of the Earth. All sorts of things are just, it's a remarkable book. We'll encounter it again when we get to Descartes cause Descartes feels obligated to show how magnetism works.
And he simply takes all the features I think it's 17, don't hold me to that, 16 or 17 features identified by Gilbert and he simply has to show that he has a theory of magnetism that reproduces them all. I think he's the only one who took the trouble to try to do that.
But the magnetism for him, for Kepler, becomes one that Gilbert doesn't describe. Kepler's picture is that, first of all, he's the one who introduced inertia into technical language but it is not our inertia as you will discover later. That word as we use it is, yeah, coined by Newton.
Kepler's inertia, it says that every object in motion left to itself will slow down and stop. So something has to keep it going. And so what's needed is a push on the planets to overcome their inertia. And that push is provided by a rotating sun. He's stipulating a rotating sun throwing off a magnetic flux that drives the planets.
Now, Gilbert does not describe a rotation of a magnet that throws off a flux and drives anything. Because, unfortunately, that doesn't happen. What Kepler's looking at is the magnetism of Gilbert, the one physics we had, knowing that the Earth has magnetism as a celestial from Kepler's point of view, a celestial body, and now saying the others have to, too.
We will come back to that. But the central point is he's gonna take the best physics he has, and try to combine that with reasoning about what the trajectories really are. Which is what we're going to focus on mostly tonight, to get at Copernicus system
