Monday, August 24, 2009

Kepler's Astronomia Nova

by the Sandwichman

I was under the impression that Copernicus definitively established the idea of the heliocentric universe. However:
In Kepler's day three models existed to explain the observed motions of the "wandering stars." However, no clear criteria of physical "truthfulness" existed to discern which of these models corresponded to the actual, physical universe. Each model could be used to predict the future longitude and latitude of planets in the sky for a few years out. All of them became less accurate as time progressed.
Copernicus's model was no more accurate than Ptolemy's because he built his system on Ptolemy's 1,500-year old data!

It was Kepler who painstakingly, over the course of 10 years, worked out the orbits and orbital planes of Mars and Earth and thus established a system for accurate measurement of the movements of the planets solar system.

What was the key to Kepler's intellectual rigor? The "difference between the straight and the curved" or the importance of "incommensurable magnitudes." Now, if we assume, "for simplicities sake" that a line is as good as a curve, we might be able to make short-term predictions, but we're going to miss something essential.


Jack said...

OK, I'll bite. And this is significant because......??

Sandwichman said...

I'm afraid you'll have to read the book for that, Jack.

Sandwichman said...

(Hint: if astronomers were economists, we'd still be predicting the position of the planets with epicycles and equants.)

Jack said...

If you meant to try to get across the point that modern day economists need to look to a new set of tools and ideas I'd suggest that you be a bit more direct. Your story occurs on an economics oriented blog and might, therefore, be expected to be read as an allegory. However, economists being experts in an assumptive process can be expected to make no such assumptions that do not support their own held beliefs.

Sandwichman said...

Oh, c'mon, Jack. Since when haven't I been "a bit more direct"?

Anonymous said...

First, Kepler had access to Tycho Brahe's rigorous observations. Second, he worked under the Copernican paradigm, by noting the observations of Mars one Earth-year apart. This makes no sense unless he was trying to control for the orbit of the Earth around the Sun. Third, he worked for a long time under the Platonic paradigm, trying to fit orbits into perfect solids (because the heavenly realm is perfect). Fourth, as regards modern prediction, because of the complexity of the n-body problem, modern ephimerides are computed by numerical methods, not by theory. ;)

-- Min

gordon said...

I'm not quite sure which book Sandwichman is recommending to Jack, but I would recommend Arthur Koestler's "The Sleepwalkers", in which Koestler painstakingly tried to get inside the heads of both Copernicus and Kepler and to understand the social in intellectual influences on both men. He incidentally performed a Kuhnian analysis before Kuhn and wrote a fascinating and highly perspicuous account.

I loved the little animated graphics in Sandwichman's link. Why don't all modern books have a disc or a weblink to that sort of thing? Publishing is still in the 16th century in some ways.

Jack said...

I'm not saying that you're never direct in your commentary about the obtuse thinking problems of many economists. All the more reason not to digress from that tact. You don't want the thick skulled set to get the impression that your simply talking aboout man's role in the universe

Sandwichman said...

gordon, the mysterious book is one that I'm writing (title withheld to build suspense).

Jack, But I AM talking about man's role in the universe! Sorry if I appear to be a bit 'elliptical' at times. ;-0