Two Things Are Infinite The Universe

The attribution of this quip to Einstein is unproven. The psychiatrist Frederick Perls first published a version in his 1942 book Ego, Hunger and Aggression, attributing it to an unnamed "great astronomer" rather than Einstein. It was only in his 1969 memoir In and Out the Garbage Pail — written 27 years later — that Perls claimed Einstein had said it to him personally. Alice Calaprice, who spent decades working on Einstein's collected papers at Princeton, lists the quote as "Probably not by Einstein," noting the saying resembles a remark by Flaubert in an 1880 letter.