I've been away from the blog for two weeks, but I'm going to try to get caught up. So hopefully many posts in the next few days. I want to record some thoughts about each of my classes from these past two weeks.
The first was a discussion about different perspectives on the purpose of science. The discussion was motivated by the anonymous ad lectorum at the beginning of the De Revolutionibus. This preface was written by Andreas Osiander, a Lutheran theologian who was in charge of supervising the printing of Copernicus' great work. Osiander added the preface without Copernicus' authorization (at that seems to be the case), most likely in an attempt to protect Copernicus' ideas from hasty criticism. But what he basically says is that the notion of a moving Earth may be ridiculous, but that doesn't matter. Who cares if what Copernicus says is true? That's not the point of astronomy. The point of astronomy is to give us a way to calculate the apparent positions of the planets, and that is all. This is a view of science known as phenomenalism.
Copernicus himself was not a phenomenalist. He was a realist, who believed that astronomy could reveal the truth about the heavens. In the first book of De Revolutionibus he goes to great lengths to argue for the truth of his system (these are exactly the bits that would be censored by the Catholic Church much later). Copernicus thinks not only that the goal of science should be to reveal the truth, but he is convinced that he has achieved that goal.
Our class discussions focused on the different criteria that one might use to evaluate a scientific theory depending on whether one was a phenomenalist or a realist. Both, of course, want their theories to match the existing data (observations, measurements, whatever). Both value the successful prediction of future data (or past but previously unknown data). But for a phenomenalist that is really about all that matters. Phenomenalists might prefer simple theories to observationally equivalent but more complicated ones, but that is just for convenience. Otherwise it is all about fitting the data for a phenomenalist.
Realists, by contrasts, can bring in a host of other criteria to judge theories. For example, a realist may be concerned about whether or not a theory is compatible with other accepted theories. For a phenemenalist this is not an issue: each theory is designed to match certain types of data, and so what if it happens to be logically incompatible with a different theory that matches different data. So we have a theory for Venus that indicates the the distance from Earth to Venus changes dramatically. And theories of optics and planetary luminance that state that if the distance to a planet varies by a large amount then the planet should get much brighter and dimmer. But the brightness of Venus doesn't change so much. A realist would be bothered by this, but for a phenomenalist the theory of Venus' motion is just designed to predict where it will be in the sky. It isn't designed to predict Venus' brightness, so that issue is just irrelevant.
Likewise, realists (at least in the past) might be concerned about their theories being compatible with religious doctrine. In 16th century Europe you had to be cautious in promoting a scientific theory that might seem to contradict the Bible. Phenomenalists didn't have to worry about this issue, since they never claimed that their theories were true.
Finally, realists can bring to bear a host of aesthetic criteria. My students were pretty receptive to the idea that aesthetics are important in science, but maybe that's because I talk about it all the time. But it seems to me that a phenomenalist shouldn't worry about whether or not a theory is ugly or elegant. They might value ease of use, but not beauty. But for a realist, beauty is a sign of truth. Some explanations just seem more natural than others, and that sense of naturalness is a guide to truth for a realist.
What we discovered through this discussion is that, in the 16th century, it made a lot of sense to embrace the Copernican system as a phenomenalist tool. But if you were a realist then the cards were stacked against Copernicus. He scored major points on aesthetics, but his incompatibility with accepted theories (Aristotle's physics), with Scripture (interpreted in the most literal way), and with observational data (ie annual parallax) would lead most most realists to reject the Copernican system. And that's just what most of them did. Thankfully there were a few for whom the aesthetic properties trumped all else.
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