The Sleepwalkers: A History of Man's Changing Vision of the Universe

by Arthur Koestler

Bellarmine had placed the burden of proof for the Copernican system back where it belonged: on the advocates of the system. There were only two possibilities left to Galileo: either to supply the required proof, or to agree that the Copernican system should be treated, for the time being, as a working hypothesis. Bellarmine had, in a tactful way, reopened the door to this compromise in the opening sentence of his letter, where he pretended that Galileo had ‘contented himself with speaking hypothetically and not absolutely’, had praised his prudence, and acted as if the Letters to Castelli and the Grand Duchess, which were before the Inquisition, did not exist. But Galileo was by now beyond listening to reason. For, by accepting the compromise, he would disclose to the world that he had no proof, and would be ‘laughed out of court’. Therefore he must reject it. It was not enough to be allowed, and even encouraged, to teach the superiority of the Copernican over the Ptolemaic hypothesis. He must insist that the Church endorse it, or reject it, absolutely – even at the risk of the latter alternative, which Bellarmine’s letter, Dini’s and Ciàmpoli’s warnings must have made clear to him. But how can he motivate his rejection of compromise? How can he refuse to produce proof and at the same time demand that the matter should be treated as if proven? The solution of the dilemma was to pretend that he had the proof, but to refuse to produce it, on the grounds that his opponents we...