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But “assuming this,” let us grant their doctrine of the earth’s motion. If the earth moves, it is a planet and shines for those on the moon and for the other planetary inhabitants, just as the moon and they shine for us on earth. And shine it does, as Galileo, Kepler, and others prove.
Then, consequently, the rest of the planets are inhabited, as well as the moon. Kepler grants in his discussion with Galileo’s Starry Messenger “that there are inhabitants of Jupiter and Saturn,” and so on; and those several planets have their several moons around them, as the earth has hers, as Galileo has already demonstrated with his telescopes.
Four around Jupiter, two around Saturn—though Sitius the Florentine, Fortunio Liceti, and Giulio Cesare La Galla find fault with it. Yet Kepler, the emperor’s mathematician, confirms from his own experience that he saw as much with the same aid, and more around Mars and Venus. They hope to discover the rest, perhaps even among the fixed stars, as Bruno and Brutius have already asserted.
Then, I say, the earth and they are alike planets, alike inhabited, and alike moved around the sun, the common centre of the world. Perhaps those two green children who, according to William of Newburgh, fell from heaven in his time came from there; and so did that famous stone which fell from heaven in Aristotle’s time, in the third year of the eighty-fourth Olympiad, beside the streams of Capua, as recorded by Laertius and others; or the ancile, the shield in Numa’s time recorded by Festus.
We may likewise infer with Campanella and Bruno what Pythagoras, Aristarchus of Samos, Heraclitus, Epicurus, Melissus, Democritus, and Leucippus maintained in their respective ages: there are infinite worlds, infinite earths or systems “in infinite aether.” Eusebius gathers this from their doctrines, because there are infinite stars and planets like this one of ours. Some still do not hesitate to maintain and publicly defend it: “Full of hope, I look forward to wandering through innumerable worlds in eternity,” and so on. Nicholas Hill of London, Epicurean Philosophy.
For if the firmament is of such incomparable size as these Copernican giants would have it, “infinite, or approaching infinity,” so vast and full of innumerable stars, infinite in extent, one above another, some higher, some lower, some nearer, some farther off, so widely separated, and themselves so enormous—
So much so that, if the whole sphere of Saturn and everything contained within it, “the entire aggregate,” as Fromondus of Louvain argues in his treatise On the Immobility of the Earth, “were carried up among the stars, we could not see it except as a point, so immense is the distance between the earth and the fixed stars,” and so on. If our world is small by comparison, why may we not suppose a plurality of worlds? Why may those infinite stars visible in the firmament not be so many suns, each with its own fixed centre and its subordinate planets, just as the sun has his, always dancing around him?
Cardinal Cusanus, Walkarinus, Bruno, and some others have held this, and some still maintain it: “Minds nourished on Aristotelianism and accustomed to minute speculations may perhaps think otherwise,” and so on. Though they seem close to us, they are infinitely distant, and consequently there are infinite habitable worlds. What prevents it? Why should an infinite cause, such as God, not produce infinite effects, as Nicholas Hill argues in his Democritean Philosophy?
Kepler, I confess, will by no means admit Bruno’s infinite worlds, or that the fixed stars are so many suns with planets circling them. Yet that same Kepler, half in jest and half in earnest in his works on optics, his Lunar Geography, his Dream, and his Discussion with the Starry Messenger, seems partly to agree with this and partly to contradict it. He grants that the planets are inhabited; he is doubtful about the stars.
Tycho too, in his Astronomical Letters, is led by reflection on their vastness and magnitude to break into similar remarks. He will never believe that those enormous bodies were made for no other use than the one we perceive: to illuminate the earth, an imperceptible point in comparison with the whole.
But who is to dwell in these vast bodies, earths, worlds, “if they are inhabited? Rational creatures?” as Kepler asks. “Or have they souls to be saved? Or do they inhabit a better part of the world than we do? Are we or they lords of the world? And how are all things made for man?” “It is difficult to untie this knot, because we have not yet explored everything that bears on it”: it is hard to determine. This alone he proves: that we are “in the foremost recess of the world,” in the best place, the best world, nearest the heart of the sun.
Tommaso Campanella, a Calabrian monk, agrees with this view of Kepler’s in book 2, chapter 4 of On the Sense of Things. He certainly supposes that they are inhabited, though he cannot say by what kind of creatures, and labours to prove it by every means; also that there are infinite worlds. He has written a Defence of Galileo and dedicates this doctrine of his to Cardinal Caetani.