Newly Discovered Letter Catches Galileo in a 400-Year-Old Lie

Fearing repercussions of his groundbreaking scientific claims, which flew in the face of church doctrine, the famed astronomer fibbed

Portrait of Galileo Galilei (1636) by Justus Sustermans Public Domain

After attracting the ire of the Catholic Church for stating the Earth orbited the Sun, Italian astronomer Galileo Galilei was put on trial at the Inquisition headquarters in Rome. To avoid being burned at the stake, the 69-year-old was forced to renounce his belief in a heliocentric model of the universe. Nevertheless, the famed polymath still was sentenced to live out his last years under house arrest. As Alison Abbott reports in a Nature News exclusive, a long-lost letter reveals that before Galileo was convicted on “vehement suspicion of heresy,” he already lived in fear of persecution—and was willing to create a fake paper trail in an attempt to fool the Inquisition.

Galileo wrote the 1613 missive to his friend, the mathematician Benedetto Castelli. The original letter, recently uncovered in a misdated library catalogue at the Royal Society in London, is believed to be the first documented account of his inflammatory arguments for the secular pursuit of science, and it includes his support of Polish astronomer Nicolaus Copernicus’ 1543 theory of a Sun-centered universe.

Perplexingly, two versions of the letter are around today: One contains far more passive language about Galileo’s findings; the other, a more inflammatory copy, is what ultimately ended up in the hands of the Inquisition. Researchers have long wondered: Which letter was the original? Was the more cautious one written by Galileo himself, in an attempt to soften his revolutionary beliefs? Or was the more radical one doctored by members of the Inquisition, charging Galileo’s language to build their case against him?

The truth of the matter wasn’t resolved until early August, when Salvatore Ricciardo, a science historian at the University of Bergamo in Italy, stumbled upon that original letter in the Royal Society library archives filed under an incorrect date. The original wording of the letter matched the copy seized by the Inquisition—not the one attached to Galileo’s plea. Four centuries after the fact, Galileo has been caught in a lie.

“I thought, ‘I can’t believe that I have discovered the letter that virtually all Galileo scholars thought to be hopelessly lost,’” Ricciardo explains to Abbott. Ricciardo’s findings will be published in an article in the Royal Society journal Notes and Records.

The revelation demonstrates Galileo’s craftiness. Within two years of Galileo sending the fateful letter, the correspondence found its way to the Inquisition. Acutely aware of the fates that had befallen his predecessors (at the turn of the century, after Dominican friar and mathematician Giordano Bruno made public his own enthusiastic support of the Copernican theory, for instance, he was promptly burnt at the stake), Galileo sent a strategic letter to a friend that suggested the Inquisition’s copy had been doctored to paint him as a heretic. To set the record straight, he then enclosed a copy of what he claimed was the “original.”

The amendments to the document weren’t severe; they mostly euphemized Galileo’s beef with the Church and watered down the vehemence of his claims. For instance, Galileo originally called out certain Biblical passages as “false if one goes by the literal meaning of the words”—but, in his later amendments, he crossed out the word “false” and scrawled in, “look different from the truth.”

Even in its original form, the letter was by no means Galileo’s only offense to the Catholic Church. In 1632, after the Church had pulled Copernicus’ writings out of circulation and outlawed publications supporting the heliocentric theory, Galileo published a book laying out scientific support for the Copernican model.

That proved to be the final nail in Galileo’s coffin.

Once again, Galileo attempted to manage the story. As the Inquisition descended upon him, he claimed he was writing “hypothetically,” reports Sarah Pruitt for But the Church didn’t buy it this time either, and in 1633 he was put on trial.

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