It might have escaped lay people at the time, but for some observers the ascension of Leo XIV as head of the Catholic Church this year was a reminder that the last time a Pope Leo sat in St. Peter’s Chair in the Vatican, from 1878 to 1903, the modern view of infinity was born. Georg Cantor’s completely original “naïve” set theory caused both revolution and revolt in mathematical circles, with some embracing his ideas and others rejecting them.
Cantor was deeply disappointed with the negative reactions, of course, but never with his own ideas. Why? Because he held firm to the belief that he had a main line to the absolute—that his ideas came direct from l’intellect divino (the divine intellect). And, like the Blues Brothers Jake and Elwood, that he was on a mission from God. So when he soured on the mathematical community in 1883, he sought new audiences in Pope Leo XIII’s Catholic Church.
This was during Cantor’s later years, a time during which his mind became fouled. He developed what I call an Isaac Newton complex: a loathsome and pathological hatred for publishing that is informed by the paranoid certainty that your contemporaries are out to sabotage you. Either they are a bunch of backstabbing haters ignorant of your work, or, far worse, they are jealous of your genius and selfishly despise you because of it. (Newton himself swore off publishing for years because of criticism of his early work.)
“My own inclinations do not urge me to publish,” Cantor wrote in 1887, echoing Newton from two centuries before. “And I gladly leave this activity to others.”
For the next several years, Cantor is increasingly focused on new audiences and tries to make inroads with Catholic authorities. The 1880s are a time when the Catholic Church is becoming more interested in scientific discovery than ever before. Leo XIII, who became pope in 1878, takes a special interest in science, especially cosmology. Science is a way forward, he claims, and he maintains an astronomical observatory at the Vatican—one whose construction he personally oversees. He fills it with the best modern equipment and keeps professional astronomers on staff.
Cantor thinks the church has a lot to offer and that set theory has a lot to offer in return. He wants the Catholic church to become aware of his views because set theory is a way to understand the infinite nature of the divine—perhaps even the mind of God, reflected in math. Isn’t that worth considering?
It’s a hard sell.
Cantor shares his work with Cardinal Johannes Franzelin of the Vatican Council, one of the leading Jesuit theologians of his day. Franzelin writes Cantor a letter on Christmas Day 1885, saying he’s gratified to receive Cantor’s work. “What greatly pleases me,” he says, is that it “appears to take not a hostile, but indeed a favorable position with regard to Christianity and Catholic principles.” Having said that, Franzelin adds, Cantor’s ideas probably could not be defended and “in a certain sense, although the author does not appear to intend it, would contain the error of pantheism.”

