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Lecture 3: Copernicus

Astronomy and Biology

Why is it that most of the historical conflicts occurred in astronomy and biology? Because these were two "observational" sciences that were accessible to everyone. Aristotle wrote extensively on these, and therefore they also had lengthy commentaries in the medieval period. Since Astronomy might be considered the most advanced of ancient sciences (you should see the math these guys could do!), it isn't too surprising that this was one of the cutting edge debates between religion and science.

Copernicus 1473-1543

Mathematics, up to this point in history, had always been a tool for understanding the world. One didn't make a big deal out of "mathematical truth" because arithmetic was just so obvious as to not need any justification. The real issue, was not the math symbols, but the objects one was counting. "Two" was an adjective, never a proper noun. (Have you ever thought how much simpler life would be if adjectives never became nouns?) Perhaps this is clarified by analogy with language. Did Plato or Aristotle ever worry about the meaning of language, whether it was possible for words to have a meanings independent of the sentence they lived in? Probably not, but that has become almost the entire obsession of the 20th century philosophy. This sophistication, if you want to call it that, began a few centuries earlier in mathematics. It was this revolution about reality that was the truly controversial point with Copernicus, a revolution that we perhaps can't even see because we (like Copernicus' contemporaries) take it for granted.

To understand this revolution, let's review some history of science. Plato had this thing for "regular solids" and geometry, as did most of the Greeks. So if one were going to describe the motion of, say, planets, geometry would be naturally employed, probably with compass and regular polyhedrons. Now Aristotle, in trying to understand friction, had proposed that everything on Earth eventually comes to rest (friction), whereas the stars and planets have been moving for millenia. He then argues that friction must not exist for objects away from the earth, and this must be an inherent property we'll call "perfection". But Plato had already described geometric perfection, so it was a natural fit to say, planets and stars move on perfect circles, in a perfect realm, that eternally rotated above the earth.

This theory of the heavens had a lot to commend it, and for almost 2000 years was developed and tweaked and worked just great. There were a few minor inconsistencies, as you can find in every theory, particularly with Mars and the outer planets. After all, the main reason they are called planets (wanderers) is that they wander among the stars. Mars for example, rises and sets with the stars, but night to night it appears to move against the stars, occasionally even going backwards or making loops. The Greeks had a solution that kept circular motion alive, Mars was on its own "circle" or epicycle, that meant two circles rotating together. Ptolemy, around 200AD, made some major tweaks when he tried to reconcile the epicycles with data, ending up with something like 4 or 5 epicycles per planet to account for its motion. It worked, but now you needed a PhD in geometry to get predictions out. (Does this sound like modern astrophysics to you?)

So Copernicus has this bright idea (which actually wasn't even his, since Nicholas of Oresme had discussed it in the century before) that orbits could be calculated much faster if we assumed that the Sun was the center, and all the planets moved on circles around the Sun. It didn't give as good a prediction as Ptolemy, (and was criticized for that), but then it didn't require a PhD to make calculations either. What do we make of this innovation? Is it just a "stupid math trick" that could be used as a less-accurate shortcut? Did it mean that Ptolemy's epicycles were wrong? Did it suggest that the Earth was *really* moving? Did have anything to say about Catholic theology at all?

Copernicus evidently thought that it reorganized the heavens, as did a number of Protestants who had an axe to grind with the Catholic church and used this "fact" to argue that nearly all of Catholic theology was obsolete. Osiander, in his introduction to Copernicus' book recognized that his words might be used by this debate, carefully said it was just a stupid math trick that "saved the appearances" but said nothing about reality. The church, which had spent the last 1500 years finding good agreement between Scripture and Greek science, wasn't very encouraging (as indeed, they should be, at least, until the bugs were worked out of Copernicus' theory), especially with inflammatory Protestants claiming some sort of victory. The scholars, who used to get paid for these calculations, no doubt felt threatened with the thought that every village priest could be doing astonomical predictions with ease. As Brook discusses, scientific theories don't just get expressed in a vacuum, but they always come mixed with turf battles and politics and people.

My own view, is that until a theory is actually superior (with respect to the data) to its competitors, one has every reason to be suspicious. And the Copernican theory was NOT superior (only simpler) than Ptolemy's until Johannes Kepler made his famous contribution almost 100 years later. Modern science writers make a big deal that Copernicus had removed the Earth from its privileged position at the center of the universe, and this was what the Catholic church objected to. This is far too simplistic for many reasons. First, Hell was actually the center of the Earth, so why should occupying the center of the universe be such a favorable position? Second, many of the powerful positions in the Catholic church were occupied by educated scholars, who were not theological dogmatists in the slightest, but well informed scientists. Third, it was not the location of the Earth that made Catholic theology regard humans as occupying a special place, it was the fact that the Bible says "God made man in his own image". Science was accommodated to theology, not the other way around. Fourth, the Catholic church was well aware of the deficiencies of Copernican astronomy, and with their conservative, even reactionary tendencies in everything, were unwilling to adopt new-fangled theories until all the evidence was in. And finally, of course, was the whole theological / sociological movement we call today the Protestant Reformation, that was just getting into high gear. So keep this in mind as we look at the Galilean affair.

Last modified, January 11, 2002, RbS