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Who really said it

Anyone who is not shocked by quantum theory has not understood it

Not Niels Bohr’s words — a later paraphrase Niels Bohr 1885–1962 · Danish physicist
Disputed Rights unconfirmed

Bohr never wrote this sentence. The idea comes from colleagues’ memories of what he said. Werner Heisenberg recalled Bohr saying that “those who are not shocked when they first come across quantum theory cannot possibly have understood it” (Physics and Beyond, 1971). Otto Frisch remembered a “giddy” version. The short “Anyone who is not shocked…” form is a later paraphrase, in print by 1981. Wikiquote ↗ lists it under “Disputed.”

Last verified 3 Nov 2026 · how we verify · spot an error?

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Disputed — copy with the correction

“Anyone who is not shocked by quantum theory has not understood it” attributed to Niels Bohr, but not his words: a later paraphrase of a remark Werner Heisenberg recalled in Physics and Beyond (1971). The short wording is in print by 1981. (Quotle.info)

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Provenance

The closest documented remark

Closest recorded form
Physics and Beyond: Encounters and Conversations
Recorded by
Werner Heisenberg, recalling a conversation with Bohr and Pauli (Harper & Row, 1971), p. 206, as cited by Wikiquote
Popular wording
A later paraphrase, in print by 1981 (Kit Pedler, Mind over Matter)
In Bohr’s own writings
Not found

Those who are not shocked when they first come across quantum theory cannot possibly have understood it. As Heisenberg recalled it

This is Heisenberg’s memory of something Bohr said in conversation, not a sentence Bohr wrote. The page number is the one Wikiquote cites. The familiar “Anyone who is not shocked by quantum theory has not understood it” is a shorter rewording of it.

Wikiquote: Niels Bohr (Quotes and Disputed sections)

How the line took shape

  • 1967: A colleague’s memory appears in Stefan Rozental’s collection Niels Bohr: His Life and Work as Seen by His Friends and Colleagues (p. 139). In it, Bohr replies to someone who said the questions made him giddy: “that only shows he has not understood the first thing about them.” Otto Frisch tells the same story in What Little I Remember (1979), p. 95 (ADS-L, Garson O’Toole and Ben Zimmer ↗).
  • 1971: Heisenberg’s Physics and Beyond (p. 206) has Bohr saying that those “not shocked when they first come across quantum theory cannot possibly have understood it.” Wikiquote also cites the German Der Teil und das Ganze (1969), p. 280 (Wikiquote ↗).
  • 1981–1984: The short wording appears in print. Kit Pedler’s Mind over Matter (1981) introduces it with “Niels Bohr wrote,” and John Gribbin’s In Search of Schrödinger’s Cat (1984) uses it as an epigraph (ADS-L, Bill Mullins ↗).
  • Today: Wikiquote lists the exact wording under “Disputed.” It reproduces David Mermin’s report that he searched the three volumes of Bohr’s philosophical writings for remarks like this and found none (Wikiquote ↗).

No single work is the source of the popular wording. It is an anonymous paraphrase, in print by 1981, so we make no public-domain claim. The remembered versions it grew from all come from 1931-or-later books: Rozental (1967), Heisenberg (1969 German; 1971 English) and Frisch (1979). Those are under copyright in their own right.

Rights status is our research, not legal advice — and copyright varies by country and edition. For commercial or published use, confirm with the rightsholder. See terms.

Fact-check

Where the attribution goes wrong

Bohr probably did say something like this. Two colleagues remembered versions of it. But the crisp sentence going around today is not his, and the claim that he wrote it has no support.

“Niels Bohr wrote…” Unsupported

Kit Pedler’s Mind over Matter (1981) introduces the line with “Niels Bohr wrote” (ADS-L ↗). But David Mermin searched the three volumes of Bohr’s philosophical writings for remarks like this and “failed to turn up anything comparable” (Wikiquote ↗).

The Philosophical Writings of Niels Bohr No page given

Karen Barad’s Meeting the Universe Halfway (2007) cites this collection for the line, but, as Wikiquote notes, gives no volume or page number. Ben Zimmer found no searchable copy of the collection to check it against (ADS-L ↗).

“Anyone who is not shocked by quantum theory has not understood it” Paraphrase

Heisenberg’s version is longer: “Those who are not shocked when they first come across quantum theory cannot possibly have understood it” (Wikiquote ↗). The short form is in print in 1981 and 1984. The Oxford Dictionary of Quotations gives a third version (“Anybody who is not shocked by this subject has failed to understand it”), citing Nature, 23 August 1990 (ADS-L ↗).

“…without feeling dizzy / getting giddy…” Separate memory

Otto Frisch remembered Bohr telling a visitor that anyone who could think about quantum theory “without getting giddy” had not “understood the first thing about it” (What Little I Remember, 1979, p. 95). The quote is also usually given in Danish with “dizzy” (svimmel), not “shocked” (ADS-L ↗).

The thought is Bohr’s as his colleagues remembered it. The wording is not. Credit the familiar line as “attributed to Niels Bohr, paraphrasing Heisenberg’s account in Physics and Beyond (1971)” (Wikiquote ↗), not as something he wrote.

Context

Why the line sticks to Bohr

Bohr was the central figure of the “Copenhagen” reading of quantum mechanics, and generations of physicists passed on stories about him. The “shocked” remark matches his insistence that quantum theory forces us to change how we describe nature. That fit made it an easy line to put in his mouth.

His own prose was nothing like it. When physicist David Mermin went looking for quotable lines in Bohr’s collected essays, he found careful, abstract sentences, not slogans. The memorable versions come from Heisenberg’s and Frisch’s memories, and the polished one-liner from later popular-science books.

Others attributed spectacular remarks to him, but he seemed to take pains to avoid any hint of the dramatic in his own writings. — David Mermin, as reproduced on Wikiquote

The remembered versions, side by side

Rozental (1967), p. 139: “But if anybody says he can think about quantum problems without getting giddy, that only shows he has not understood the first thing about them.” Ben Zimmer’s snippet-view search suggests the passage is part of Otto Robert Frisch’s remembrance (ADS-L ↗).

Heisenberg, Physics and Beyond (1971), p. 206: “Those who are not shocked when they first come across quantum theory cannot possibly have understood it.” Wikiquote places it in a 1952 conversation with Heisenberg and Pauli in Copenhagen (Wikiquote ↗).

Frisch, What Little I Remember (1979), p. 95: “if anybody says he can think about quantum theory without getting giddy it merely shows that he hasn’t understood the first thing about it!” Garson O’Toole checked this against the printed book (ADS-L ↗).

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Trusted places to keep pulling the thread — primary archives, fact-checks, and scholarship. We show how we used each one before you leave.

Niels Bohr: Quotes and Disputed sectionsen.wikiquote.org

Gives Heisenberg's 1971 version with its page, lists the short wording under Disputed, and reproduces Mermin's report that Bohr's writings contain nothing comparable.
ADS-L thread: Niels Bohr Quote (Pedler 1981, Gribbin 1984)listserv.linguistlist.org

Fred Shapiro's 2017 query, citing the Oxford Dictionary of Quotations and Nature (1990), and Bill Mullins's reply with the 1981 and 1984 printings of the exact wording.
ADS-L thread: the Frisch "giddy" anecdotelistserv.linguistlist.org

Garson O'Toole's transcription of Frisch's 1979 memoir, checked on paper, with Ben Zimmer's Rozental (1967) finding.
Physics and Beyond (Heisenberg, 1971)archive.org

Internet Archive record of Heisenberg's Harper & Row memoir, where his version of Bohr's remark appears (borrowable scan).
What Little I Remember (Frisch, 1979)archive.org

Internet Archive record of Otto Frisch's Cambridge University Press memoir with the "giddy" anecdote (borrowable scan).
Niels Bohren.wikipedia.org

Biography: life dates, 1922 Nobel Prize, the Copenhagen institute and complementarity.

The person the idea traces to

About Niels Bohr

Niels Bohr

1885–1962 · Danish physicist, Nobel Prize in Physics 1922

Niels Bohr (born in Copenhagen, 7 October 1885; died there 18 November 1962) won the 1922 Nobel Prize in Physics for his work on the structure of atoms. He led the Copenhagen institute now named after him, and he gave quantum theory the principle of complementarity. His published essays are famously careful and undramatic. Most of the striking one-liners credited to him come from colleagues’ memories, not from his own pen.

For writers & researchers

Cite this

Cite this

Closest recorded remark: Werner Heisenberg, Physics and Beyond: Encounters and Conversations (New York: Harper & Row, 1971), 206 (as cited by Wikiquote). Exact popular wording in print by 1981: Kit Pedler, Mind over Matter: A Scientist’s View of the Paranormal (London: Thames Methuen, 1981).

This verification page

Quotle.info. “Who really said ‘Anyone who is not shocked by quantum theory has not understood it’?” Last verified 3 Nov 2026. https://quotle.info/who-said/anyone-who-is-not-shocked-by-quantum-theory-has-not/

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