When things look bleak in this world, it is perhaps natural to turn one's mind to conditions on other worlds. This is what the Dutch astronomer Christiaan Huygens did in the late 1680s. He had been ejected from his influential post as a government scientist of Louis XIV in Paris and found himself isolated back home in the provincial town of The Hague, frequently ill with depression and fevers, and missing the companionship of his brother Constantijn, who was away serving as secretary to the Dutch King William III in England.
It was then that Huygens began to write Cosmotheoros, a book-length speculation on the possibility of life on other planets, and the first such work to be based on recent scientific knowledge rather than philosophical conjecture or religious argument. Fearful of censure by “those whose Ignorance or Zeal is too great”,1 Huygens instructed his brother to publish the work only after his death, which he did in 1698. Originally written in Latin, Cosmotheoros was quickly translated into Dutch and other languages. A lively English translation appeared that same year under the audacious title, The Celestial Worlds Discover’d.
Philosophers had of course always thought about the existence of life beyond the Earth. Aristotle ruled it out, believing that the Earth was unique and that other celestial bodies were pure geometrical entities. But the atomists, among them Democritus and Epicurus, accepted the notion of a plurality of worlds, somewhat on the analogy of particulate matter of various kinds existing with space in between. Medieval thinkers picked up on this debate, but could only add to it their own concerns about the implications of one view or another for church doctrine, which did nothing to advance it.
