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A very popular quote attributed to Albert Einstein but did he really say it? If so, what is the original document containing the original explanation of it?

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    I thought it was Richard Feynman, but maybe not: en.wikiquote.org/wiki/Talk:Richard_Feynman#Teaching_quote
    – Andrew Grimm
    Apr 3, 2012 at 6:14
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    @AndrewGrimm He apparently says the contrary as this quote seems to be atributed to him: "If I could explain it to the average person, I wouldn't have been worth the Nobel Prize." imdb.com/name/nm0275509/bio
    – Renan
    Apr 3, 2012 at 20:04
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    @Renan: He said both, in different contexts. He was asked for a brief quote of what he won the Nobel for, and he said if it could be summarized in a sentence, it wouldn't be worth the prize. But when asked to explain the spin-statistics theorem in an undergraduate lecture in the 1960s-1970s (don't know when) he said he couldn't reduce it to the undergraduate level, so we don't understand it well enough. This seems to have motivated his 1986 Dirac lecture on the spin-statistics theorem.
    – Ron Maimon
    Apr 6, 2012 at 2:47
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    It would be quite amazing if Einstein said anything at all in the 60's being that he died in the 50's! You seem to be refering to Feynman, however I do believe it is an Einstein quote.
    – user9112
    Nov 4, 2012 at 6:04
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    I swear I remember Feynman saying something like "If you can't teach something to a 6-year-old, that means you don't really understand it" in 'Surely You're Joking, Mr. Feynman'
    – BlueRaja - Danny Pflughoeft
    Dec 20, 2013 at 17:18

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The quote "An alleged scientific discovery has no merit unless it can be explained to a barmaid." is popularly attributed to Lord Rutherford of Nelson in as stated in Einstein, the Man and His Achievement By G. J. Whitrow, Dover Press 1973. Einstein is unlikely to have said it since his theory of relativity was very abstract and based on sophisticated mathematics.

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    Unrelated, but reminds me of the joke about the mathematicians who were trying to play a joke on their colleague in a bar and coached the "barmaid" to reply "one third x cubed" when they offhand asked her what the integral of x^2 was. when the colleague comes back and they try to play the prank she responds as they prompted her, and then non-chalantly adds, "plus a constant".
    – Michael
    Jan 2, 2016 at 0:25
  • I wouldn't say unlikely, unlike quantum mechanics. Einsteins theories are not that hard to fathom. Hell, even his e = mc2 is extremely simplistic.
    – dan-klasson
    Nov 1, 2020 at 20:37
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The short answer is: probably no he didn't say this quote. There is no citation supporting this claim.

Other unsourced variants:

You do not really understand something unless you can explain it to your grandmother.

If you can't explain something to a six-year-old, you really don't understand it yourself.

But if you open page 418 of Einstein: His Life and Times (1972) by Ronald W. Clark, it says that Louis de Broglie did attribute a similar statement to Einstein:

To de Broglie, Einstein revealed an instinctive reason for his inability to accept the purely statistical interpretation of wave mechanics. It was a reason which linked him with Rutherford, who used to state that "it should be possible to explain the laws of physics to a barmaid." Einstein, having a final discussion with de Broglie on the platform of the Gare du Nord in Paris, whence they had traveled from Brussels to attend the Fresnel centenary celebrations, said "that all physical theories, their mathematical expressions apart ought to lend themselves to so simple a description 'that even a child could understand them.' "

See all misattributed Einstein quotes here: http://en.wikiquote.org/wiki/Albert_Einstein#Misattributed.

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    So... isn't the answer "Yes" then?
    – Pacerier
    Jun 10, 2015 at 9:43
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    @Pacerier: But those two barmaid and child quotes merely assert that we should or ought to be able to "explain the laws of physics" or "all physical theories" simply. (Why we ought to do so is not clear from the quoted passage. One possible interpretation is that Einstein believes all true laws of physics are, for whatever mystical reason, "simple".) Absent from these quotes are the additional and arguably more interesting assertion that an inability to do so indicates that we human beings don't understand these laws or theories well enough.
    – user17967
    Mar 10, 2017 at 3:55
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    Yes. Even if he didn't say the exact literal words, "if you can't explain it simply then you don't understand it well enough" is a good paraphrase.
    – Fomalhaut
    Apr 15, 2019 at 5:26
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Just to add two quotes that come close.

Peter Singer (2016):

There is a view in some philosophical circles that anything that can be understood by people who have not studied philosophy is not profound enough to be worth saying. To the contrary, I suspect that whatever cannot be said clearly is probably not being thought clearly either.

Attributed to Richard Feynman, by two of his colleagues at Caltech in 1989 (after his death):

Feynman was once asked by a Caltech faculty member to explain why spin 1/2 particles obey Fermi-Dirac statistics. He gauged his audience perfectly and said, "I’ll prepare a freshman lecture on it." But a few days later he returned and said, "You know, I couldn’t do it. I couldn’t reduce it to the freshman level. That means we really don’t understand it."

Daniel Dennett (2013):

if I can’t explain something I’m doing to a group of bright undergraduates, I don’t really understand it myself.

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