On February 17, 1600, in the Campo de' Fiori in Rome, a former Dominican friar was stripped naked, gagged with a metal spike through his tongue so he could not speak, and burned at the stake. His name was Giordano Bruno. His crime was thinking thoughts the Catholic Church had not authorized. He had proposed that the universe was infinite. He had proposed that the stars were suns with their own planets. He had proposed that life might exist on those planets. He had proposed that the Earth moved. He had refused to stop proposing these things despite eight years of imprisonment and repeated opportunities to recant.

He Went Further Than Copernicus Dared

Copernicus had placed the sun at the center of the solar system. This was radical enough. But Copernicus still assumed the universe was finite, bounded by a sphere of fixed stars. Bruno looked at the Copernican model and asked the obvious question: if the Earth is not the center, why should the sun be? Why should there be a center at all? Historians of science at the University of Naples have documented that Bruno's cosmology was not merely heliocentric but genuinely infinite. He proposed that space extends without limit in all directions. He proposed that every star is a sun. He proposed that the universe has no edge, no boundary, no privileged position. This was four hundred years before Edwin Hubble confirmed the existence of galaxies beyond the Milky Way. Bruno was not working from telescopic observation. The telescope would not be invented for another decade. He was working from philosophical reasoning and from the atomic theory of Lucretius, the Roman poet who had described an infinite universe in De Rerum Natura fifteen centuries earlier. Bruno took Lucretius seriously when nobody else would.

The Inquisition Gave Him Eight Years to Change His Mind

Bruno was arrested in Venice in 1592 and transferred to Rome, where the Inquisition held him for eight years. The charges were comprehensive: denying the Trinity, denying the divinity of Christ, denying the virginity of Mary, believing in the transmigration of souls, and asserting the infinity of the universe and the plurality of worlds. Scholars of Inquisition records at the Vatican's Congregation for the Doctrine of the Faith have studied Bruno's trial documents and noted that the cosmological charges were entangled with the theological ones. The Church could not separate his ideas about the universe from his ideas about God. An infinite universe with no center implied no special place for humanity, no privileged Earth, no stage designed by God for the drama of salvation. The cosmology was heresy because of what it meant for theology. Bruno was offered repeated chances to recant. He refused. According to one account, when the sentence was read, he told his judges that they pronounced the sentence with greater fear than he received it. The statue that now stands in the Campo de' Fiori where he burned was erected in 1889 over the objections of the Vatican. It shows him hooded and defiant, looking toward St. Peter's Basilica. He said the universe was infinite. They killed him for saying it. The universe turned out to be infinite. The killing turned out to be the only finite thing about the whole affair.