Extraterrestrial Life Debate, Antiquity to 1915: A Source Book

4. GALILEO, KEPLER, DESCARTES, AND PASCAL

GALILEO, KEPLER, DESCARTES, AND PASCAL GALILEO GALILEI (1564 –1642) When around 1608 Galileo Galilei turned the newly invented telescope to the heavens , he made a number of sensational discoveries, which he published in 1610 in his Sidereus nuncius (Starry Messenger). Among the discoveries reported in that book are: (1) that the Moon has mountains and seas, (2) that Jupiter is orbited by four moons, and (3) that the number of stars far exceeds what had previously been seen. Striking as these results were, their impact becomes all the more evident when they are interpreted, as eventually some authors did, in terms of the idea of a plurality of worlds: (1) that the Moon has a number of earthlike features, (2) that at least Jupiter also has definite similarities to the Earth, and (3) that if the stars are suns and if suns are orbited by inhabited planets, then our universe must be extremely richly stocked with life. It is interesting to ask how Galileo himself interpreted these and other observations in regard to the question of extraterrestrial life. Did he see them, for example, as a vindication of or support for the pluralist universe championed by Giordano Bruno? The first fact to be noted is that never in his published writings or letters F F O O U U R R 51 a n t i q u i t y t o n e w t o n 52 did Galileo ever mention Bruno.1 Another indication comes from 1613, when Galileo published his Letter on Sunspots, directed to the Jesuit astronomer Christopher Scheiner. Galileo states: I agree with Apelles [Scheiner] in regarding as false and damnable the view of those who would put inhabitants on Jupiter, Venus, Saturn, and the moon, meaning by “inhabitants” animals like ours, and men in particular. Moreover, I think I can prove this. If we could believe with any probability that there were living beings and vegetables on the moon or any planet, different not only from terrestrial ones but remote from our wildest imaginings, I should for my part neither affirm it nor deny it, but should leave the decision to wiser men than I.2 That Galileo’s reservations about, possibly even opposition to, claims for extraterrestrials had not diminished by 1616 is indicated in a letter he wrote on 28 February of that year to Giacomo Muti: A few days ago, when paying my respects to the illustrious Cardinal Muti, a discussion arose on the inequalities of the moon’s surface. Signor Alessandro Capoano, in order to disprove the fact, argued that if the lunar superfecies be unequal and mountainous, one may say as a consequence that, since Nature has made our earth mountainous for the benefit of plants and animals beneficial to man, so on the moon there must be other plants and other animals beneficial to other intellectual creatures. Such a consequence, he said, being most false, therefore the fact from which it is drawn must also be false, therefore lunar mountains do not exist! To this I replied: As to the inequalities of the moon’s surface we have only to look through a telescope to be convinced of their existence ; as to the ‘consequences,’ I said, they are not only not necessary but absolutely false and impossible, for I was in a position to prove that neither men nor animals, nor plants as on this earth, nor anything else at all like them can exist on the moon. I said then, and I say now, that I do not believe that the body of the moon is composed of earth and water, and wanting these two elements we must necessarily conclude that it wants all the other things which without these other things cannot exist or subsist. I add further: even allowing that the 1. Alexandre Koyré, From the Closed World to the Infinite Universe (New York: Harper and Brothers, 1957), 99. 2. Galileo Galilei, “Letter on Sunspots,” in Discoveries and Opinions of Galileo, trans. Stillman Drake (Garden City, New York: Doubleday Anchor, 1957), 137. matter of the moon may be like that of the earth (a most improbable supposition), still not one of those things which the earth produces can exist on the moon, since to their production other things besides earth and water are necessary—— namely, the sun——the greatest agent in nature——and the resulting...