Copernicus did not demote humanity

Stephen Jay Gould was fond of observing that of the two revolutions identified by Freud as having dethroned humanity – Copernicus, and Darwin’s – that Darwin’s was the more revolutionary, because (as he put it) Copernicus and Galileo merely changed our real estate, while Darwin changed our essence. But it is common to say something like this:

… the Catholic Church fought tooth and nail to suppress Galileo’s finding that the earth was not the center of the universe, because they believed that’s where humanity ought to be.

This is a deep misunderstanding. Copernicus did not demote humanity by making the earth not the centre of the universe; he promoted us.

In the Ptolemaic system, a physics had been partially inherited, although it was at its heart inconsistent with it.

According to the “two-sphere” universe of Aristotle, the outer sphere was the stars’ firmament, and the only motion that was possible in the universe was circular motion, for that was the only eternal motion, and the heavens, being as close to perfect as it was possible to be, were eternal, neither corrupting nor generating.

The place in the universe where things generated and corrupted, grew and decayed, was within the lunar sphere that surrounded the earth. All partial or temporary motion occurred there, for a simple reason: in the heavens there was only a fifth element, later called the quintessence, and it would neither rise nor fall, since it was where it was supposed to be. In the sublunary sphere, our part of the world, things were composed of one of four essences: earth, air, fire and water. Air and fire were light elements and sought their place by rising or staying where they were; water and earth were heavy elements and would tend towards the centre of the universe.

Since the sublunary sphere was where temporary motion could occur, it was in effect the least perfect part of the cosmos. In other words, the earth was the cosmic rubbish dump. Generation and corruption were marks of things that were least eternal and therefore least important.

By making the earth go around the sun, Copernicus challenged two thousand years of physics (although many others, especially the later scholastics, had done this too). Ptolemy’s cosmography had heavenly things going in circles, but they were increasingly not the centre of the universe, what with equants and epicycles and deferents. Copernicus retained the idea of circular motion (not until Kepler were elliptical orbits accepted), but fundamentally he had undercut the whole rational for Aristotelian physics, as Galileo argued a couple of centuriesy or so later.

Copernicus implied that the universe and we were of the same stuff. Galileo made this explicit. This was not, contrary to the Freudian myth, a demotion. It was in fact a radical promotion to star stuff, as Sagan later put it so eloquently.