Galileo's condemnation: The real and complex story

Next, Kepler quotes from Ecclesiastes 1:4. "A generation passes away and a generation comes, but the earth stands forever." He asks: "Does it seem here as if Solomon wanted to argue with the astronomers?" Kepler answers by calling attention to the subsequent verses: "No; rather, he wanted to warn men of their own mutability, while the earth, home of the human race, remains always the same, the motion of the sun perpetually returns to the same place, the wind blows in a circle and returns to its starting point, rivers flow from their sources into the sea, and from the sea return to the sources, and finally, as these men perish, others are born. Life's tale is ever the same; there is nothing new under the sun." Kepler argues that there is no physical dogma here; the message is a moral one. Solomon, Kepler concludes, "by mentioning what is evident to all, warns of that which almost everyone wrongly neglects. (16)." So this passage is like the others. While there is an allusion to physical reality, the thrust of these passages is about something else other than any physical reality. Galileo made little or no reference to these arguments. This was the same situation we already saw with Kepler's scientific discoveries.

Heretics

Why did Galileo ignore Kepler's and Brahe's scientific work? They had the most accurate and numerous observations of anyone at that time. One could claim that Galileo's telescopic discoveries superseded Brahe's data, but then why would Galileo champion Copernicus, whose observations were fewer and more dated?

In the dedication of his Dialogues on the Two World Systems (1632), Galileo called Ptolemy and Copernicus the greatest minds ever to have philosophized about the structure of the universe. This immediately raises the question about why he left out Brahe and especially Kepler. In a 1624 letter, Galileo referred to Brahe and Kepler as heretics (17). This could be the reason Galileo slighted them and advocated the veracity of Copernican epicycles over Kepler's elliptical orbits or Brahe's system (18). Another reason might be that Galileo could not break away from the perfection of the circle that had influenced the thinking of all the ancient philosophers (19).

Some authors have alluded to Kepler's "mystical" thinking and speculated that this may have been the reason why Galileo was wary of Kepler (20). However, this is an unwarranted twentieth-century criticism. In reality, Galileo had taught students how to cast horoscopes, and on several occasions he cast them himself. In January 1609, he reviewed the horoscope for the ailing Grand Duke Ferdinando. He predicted many more happy years, but the Grand Duke died of his illness just three weeks later (21). This experience no doubt made Galileo more skeptical of astrology, but my point is that mysticism was no stranger to Galileo or his times, and therefore is not a valid explanation for why Galileo rejected Kepler.

Galileo's Anti-Aristotelianism

Flushed with the success of his telescopic findings (1610), Galileo busily began promoting the Copernican system and attacking those aspects of Aristotelian science he had shown wrong. One error concerned Aristotle's theory of light, which did not explain the newly discovered property of barium sulphide. Alchemists called this mineral a "solar sponge" because it absorbed light and then glowed in the dark. This property suggested to Galileo that light was not a quality as Aristotle thought, but rather, it consisted of invisible corpuscles. Here is the source of Galileo's atomism. Besides his advocacy of Copernicus over Aristotle, Galileo's study of falling bodies caused him to begin questioning Aristotle's theory of motion.