The following quip is often attributed to the physicist Richard Feynman:

If all of mathematics disappeared, physics would be set back by exactly one week.

See for example Quote Master, quotefancy, AZ Quotes, or Internet Pillar.

But did Feynman actually say this? None of the above websites gives a source. It sounds like something Feynman might have said. He did say other provocative things about mathematics, such as, "I bet there isn't a single theorem that you can tell me ­­what the assumptions are and what the theorem is in terms I can understand ­­where I can't tell you right away whether it's true or false." But I haven't been able to locate a source for the above quotation.

As an aside, my interpretation of the quip is that physicists are highly capable of reinventing whatever mathematics they need for the physics they are working on. So if they encounter some new situation in which unfamiliar mathematics is needed, then they have two options. They can either check the mathematics literature to see if the relevant mathematics has already been developed by mathematicians, or they can roll up their sleeves and reinvent the requisite mathematics themselves. The quip suggests that the latter approach will take at most one week longer than the former approach. I mention this interpretation because it might help search for the source of this quotation, or at least something similar to it.

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    One book (Music of Matter) said it came from QED, but I couldn't find anything there. (The book's other quote about shell games was, however.)
    – Laurel
    Commented Aug 12, 2023 at 13:31

1 Answer 1


The quote is reported in:

Cohen, Joel E. A Life of the Immeasurable Mind. Annals of Probability 14(4): 1139-1148 (October, 1986). DOI: https://dx.doi.org/10.1214/aop/1176992358

which is a review of mathematician Mark Kac's autobiography Enigmas of Chance. Cohen writes on page 1147:

One cannot find here one of the most famous Kac witticisms, which I verified with him the summer before he died.

Kac went to Pasadena to lecture at the California Institute of Technology. Richard Feynman was in the audience. After the lecture, Feynman got up and announced: "If all mathematics disappeared, it would set physics back precisely one week." Without a pause, Kac responded: "Precisely the week in which God created the world."

I guess this is still secondhand (Kac was there, and personally told Cohen, who published the account) but it seems to me about as good as we can expect for a purely verbal quote.

(It's too bad that all your sources reported Feynman's barb without Kac's retort, which I think makes it much funnier.)

Cohen repeats the anecdote in his book Absolute Zero Gravity with Betsy Devine, which is where I remembered having seen it, and cites his AoP review. This book is a collection of science jokes and humorous anecdotes, and is pretty well referenced, so it may be a helpful source for future questions like this. A full PDF of the book is currently available on Cohen's website.

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    I guess this might also explain why Feynman doesn't seem to have mentioned this in his own memoirs, seeing as he ended up on the receiving end of the sick burn. Commented Aug 13, 2023 at 4:11
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    I guess the other bit of context is that Feynman and Kac had been colleagues at Cornell and famously collaborated on the Feynman-Kac formula. So they knew each other. And so while Feynman's comment sounds on its face like a fairly harsh insult to a mathematician, in context it could have been more like friendly teasing. Commented Aug 13, 2023 at 12:58
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    Here is a chat for all further discussion of what Feynman and/or Kac meant by their comments, whether they are clever or funny, the relationship between mathematics and physics, etc. Comments can still be used for corrections or notes relevant to the question at hand, which is simply "did Feynman say it?". Commented Aug 14, 2023 at 15:00
  • Decimated comments not related to improving or clarifying the answer.
    – Oddthinking
    Commented Aug 16, 2023 at 14:42
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    @NotThatGuy: I would assume the quote was "famous" in the sense that it had circulated by word of mouth. There may well be earlier sources, but I suspect they would have been people who heard it from a friend of a friend, etc. Eyewitness accounts may be unreliable, but they're still better than accounts from people who weren't there at all. I'm really not sure what else we can hope for - it's not like there was a stenographer at the Caltech seminar. But by all means, if you find something better, post it. Commented Aug 17, 2023 at 21:34

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