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Comment by happyscrappy | Hacker News Reader

Does Feynman's "if you can't explain it to a laymen in a few paragraphs then you don't truly understand it" no longer hold?

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I'd really like the source for that quote, because it's dumb for obvious reasons, and I don't know Feynman to be dumb.

In fact he said pretty much the opposite to the interviewer asking about magnets in this well known video: https://www.youtube.com/watch?v=MO0r930Sn_8

Hmm. The closest I can find is this:

"Once I asked him to explain to me, so that I can understand it, why spin-1/2 particles obey Fermi-Dirac statistics. Gauging his audience perfectly, he said, "I'll prepare a freshman lecture on it." But a few days later he came to me 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." David L. Goodstein, "Richard P. Feynman, Teacher," Physics Today, volume 42, number 2, February 1989, p. 70-75, at p. 75

I think Feynman is drawing a distinction between being able to calculate an accurate prediction, and "understanding" things intuitively enough to describe with plain English.

That particular version of a quote is listed on Wikiquotes as unsourced, and therefore unreliable. [1] However, he did say, "I couldn't do it. I couldn't reduce it to the freshman level. That means we don't really understand it." [2]

[1] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Unsourced

[2] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Teaching_q...

I have never heard the quote with the middle section you included "to a laymen in a few paragraphs"

I have frequently heard the quote without that section, that section seems flawed in that a layman would need to have all the underlying concepts explained to them also, indicating that application of the quote would not scale, as more underlying concepts were necessary to include.

I also generally subscribe to the idea that, if you can't adequately explain something to someone unfamiliar with the idea, then you don't properly understand it yourself. But my inability to explain something to someone says nothing about whether the phenomenon "is understood" in the more general sense.

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