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As he detailed in his letters, Einstein over the years developed a complicated view of male-female relationships.

In a June 1953 letter, Albert Einstein tried to console a female friend who had discovered that her husband was having an affair, by advising her that she should resist taking it personally. Cheating, he explained, was the norm among humans.

“I am sure you know that most men (as well as quite a number of women) are not monogamously endowed by nature,” he wrote, according to a translation from the original German published decades later. “Nature will come through even stronger if convention and circumstances are putting resistances in the way of the individual.”

It was a subject that the great physicist knew something about from personal experience. Einstein himself had been unfaithful to his first wife, Mileva Maric, and eventually left her to marry his mistress, Elsa Einstein, who was also his cousin. After divorcing Mileva and marrying Elsa, he soon resumed having dalliances with numerous other women as well.

"You have to keep in mind that in Europe at the time, for a pursued, charismatic man, his behavior wasn't so unusual," Harvard physicist and science historian Gerald Holton told Discover magazine in 2006.
What was a bit more extraordinary, though, was Einstein’s frankness about his wandering attentions, and his deft construction of a nuanced moral code into which infidelity could fit comfortably. As he detailed in his letters, Einstein over the years had developed a complicated view of male-female relationships.

Einstein wasn’t that fond of matrimony to begin with. He and his first wife Mileva had lived together and conceived a child before their marriage. As Einstein biographer Walter Isaacson notes, after the couple separated, Einstein wasn’t in any rush to legally finalize their split so that he could marry Elsa, his lover, either. As he wrote in a 1915 letter: “The attempts to force me into marriage come from my cousin’s parents and is mainly attributable to vanity, though moral prejudice, which is still very much alive in the old generation, plays a part.”

Eventually, Einstein did relent, and obtained a divorce from Mileva so that he could say the vows with his cousin. According to Isaacson, Einstein told his soon-to-be ex-wife that he was concerned that the reputation of Elsa’s two grown daughters would be harmed by gossip about their mother’s relationship with Einstein.

Instead, Einstein seemed to prefer what we would call today free love.

After marrying Elsa, he started a passionate affair with his secretary, Betty Neumann, and in letters, even fantasized about having her live with him and Elsa in a big house. (When his lover dismissed the idea, he admitted that she had more appreciation “for the difficulties of triangular geometry than I.”)

In a letter that Einstein wrote to Elsa, who’d discovered that he’d had a fling with one of her friends, Berlin socialite Ethel Michanowski, Einstein explained that “one should do what one enjoys, and won’t harm anyone else.”

Einstein simply saw his flings as non-serious affairs that didn’t interfere with his feelings for his spouse. “Out of all the women, I am in fact attached only to Mrs. L. who is absolutely harmless and decent, and even with this there is no danger to the divine world order,” he wrote in a letter in the 1930s to his second wife Elsa’s daughter Margot, whom he relied upon to keep Elsa from becoming angry about it all. (According to biographer Isaacson, “Mrs. L” was an Austrian woman, Margarete Lebach, with whom Einstein had an extramarital affair.)

Moreover, Einstein told his friend whose husband was unfaithful that people had a natural desire to have affairs, and it didn’t do any good for them to resist the urge to do so. When a man forces himself to remain monogamous, he observed, “it is a bitter fruit for everyone involved.”
But that human proclivity came with a burden, Einstein wrote. It usually resulted in a man being caught between two women who would become hostile to one another because of him. “For a well-meaning person, there is no satisfactory solution to this problem,” he wrote.

It’s unclear whether Einstein’s “well-meaning” referred to the unfaithful husband or the wronged wife. But for both, as Einstein saw it, it wasn’t the infidelity itself that was a test of character, but how each of them behaved toward each other as a result. If a husband treated his spouse decently in other ways, she should tolerate his adultery. “You should be able to respond to his sins with a smile, and not make a case of war out of it,” he wrote.

In Einstein’s view, decency included discretion about one’s affairs—even though Einstein himself wasn’t particularly discreet about his liaisons. In his letter to Elsa about his affair with Ethel Michanowski, he lauded “Mrs. M” because she hadn’t hurt Elsa by telling her about the relationship. “She didn’t tell you a word,” Einstein wrote. “Isn’t that irreproachable?”

Einstein clearly enjoyed the company of women, but his casual attitude about relationships may have had something to do with his own discomfort with deep feelings. “When confronted with the emotional needs of others,” Isaacson wrote in his biography, “Einstein tended to retreat into the objectivity of his science.”

At the same time, the great scientist’s aversion to monogamy may have had exacted a cost. Upon the death of his best friend from college, Michele Besso, Einstein told Besso’s son, “What I admire in your father is that, for his whole life, he stayed with only one woman. That is a project in which I grossly failed, twice.”

By Patrick J. Kiger