Where we looked
It’s a great joke, and it sounds like the playful Feynman of the anecdote books. That’s exactly why it sticks to him. But we couldn’t find him telling it.
Wikiquote files it under “disputed”, and its editors note that the oldest book they found citing it is from 2000. We ran our own search through the full text of the Internet Archive’s books for “physics is like sex”. It found 59 matches. The earliest dated book that credits Feynman is the same one: science broadcaster Robyn Williams’ Scary Monsters and Bright Ideas (2000), which says “Richard Feynman added, ‘Physics is like sex: sure, it may give some practical…’”.
Feynman died in 1988. A quote that first shows up under his name twelve years later, with no source, is a quote to be careful with.
The physicist who said it first
The same search turned up an older relative of the joke, with a different name attached. In The Universe and the Teacup (1998), the science writer K. C. Cole opens her first chapter with this:
“Understanding is a lot like sex. It’s got a practical purpose, but that’s not why people do it normally.” (Frank Oppenheimer)
Frank Oppenheimer was a particle physicist, the younger brother of J. Robert Oppenheimer, and the founder of San Francisco’s Exploratorium science museum, which he ran until his death in 1985 (Wikipedia). Education researchers picked up his line from Cole: a 2002 paper by Mark Girod and Cheryl Rau quotes it with the citation to her book (ERIC ED474444).
In 2009 Cole wrote a whole biography of Oppenheimer, and one of its sections is called “Understanding Is a Lot like Sex”. There she notes: “I have seen a version of this quote attributed to Richard Feynman”, and gives the popular wording.
What we can and can’t say
We can’t prove Feynman never made the joke. Physicists trade one-liners, and the two men knew each other: Cole’s biography tells of Feynman driving with Frank Oppenheimer to introduce him to a potential funder. But every trace we found points the same way: the line has a documented owner, printed before anyone put Feynman’s name on it, and the Feynman version has no source at all.
Our take
Misattributed. If you want the joke, credit Frank Oppenheimer, and use his words: “Understanding is a lot like sex. It’s got a practical purpose, but that’s not why people do it normally.” It’s arguably the better line, since it’s about understanding anything, not just physics. If someone has a recording or a document with Feynman saying it, we’ll gladly update this page.
