Monday, October 13, 2008

Origin of the Milky Way


Perhaps the greatest watershed in human history is that between the eras of animism and naturalism. The former explains the world in terms of human agency, and invests every part of nature with humanlike spirits. The latter looks for explanations evoking impersonal laws of nature that explain not only Sun, Moon, stars, plants and animals, but ultimately humans too.

It is easy enough to account for animism. What is more natural than to see ourselves in nonhuman nature? Piaget and his successors have demonstrated that the default explanations of children are animistic.

Naturalism had its origin in astronomy -- the search for mathematical models of celestial motions that could be used for calendrical and astrological purposes -- and in technology.

We can trace the roots of naturalism back to the Greeks and perhaps beyond, with special reference to the astronomers and mathematicians of Alexandria. Although animism no longer plays a role in our explanations of the heavens or the Earth, it is still very much with us. Advocates of intelligent design are doing their best to reestablish an animistic foothold in science.

Where shall we draw the line between the two eras? The year 1600 might be as good a time as any.

I have reproduced above a painting by the Italian artist Tintoretto, completed between 1575 and 1580, called The Origin of the Milky Way, a late homage to animistic thinking (click to enlarge). Tintoretto gives expression to a classical myth. Jupiter has fathered a son, Hercules, by a mortal woman. Hoping to immortalize the infant, he places the boy on the divine Juno's breast. Jealously, she pushes Hercules away, and her milk spills into the sky.

Only a few decades later, in the winter of 1609-1610, Galileo turned his new telescope on the sky. In The Starry Messenger, he reports his discoveries, including: "I have observed the nature and the material of the Milky Way. With the aid of the telescope this has been scrutinized so directly and with such ocular certainty that all the disputes which have vexed philosophers through so many ages have been resolved, and we are at last freed from wordy debates about it. The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters. Upon whatever part of it the telescope is directed, a vast crowd of stars is immediately presented to view. Many of them are rather large and quite bright, while the number of smaller ones is beyond calculation."

I need not recount the successes of naturalism. The fact that most of us have lived beyond our 20s is just one confirmation of the effectiveness of naturalist thinking. Yet many people want to eat their naturalist cake and have their animism too. They still imagine their current version of Jupiter intruding his actions into the world.