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Who really said it

It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature

Attributed to Niels Bohr 1885–1962 · Danish physicist
Attributed In copyright

Hearsay, not Bohr’s own text. The words come from his assistant Aage Petersen, who recalled in “The Philosophy of Niels Bohr” (Bulletin of the Atomic Scientists, September 1963) that this is how Bohr “would answer” one question. Bohr never published the wording himself.

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

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Unconfirmed quote & credit

“It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature” attributed to Niels Bohr, as recalled by his assistant Aage Petersen, “The Philosophy of Niels Bohr,” Bulletin of the Atomic Scientists, September 1963 · Verbatim: “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.”

Can you use it?

Still under copyright (rights held by Bulletin of the Atomic Scientists (Educational Foundation for Nuclear Science) and the estate of Aage Petersen). A short, credited quote is generally fine for talks, teaching, and internal decks; for commercial, published, or large-scale reuse, get permission.

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In context

Evoking the world of Niels Bohr — Danish theoretical physicist, Nobel Prize in Physics 1922. Theme: "It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature". Atmospheric and restrained, cinematic directional light, a muted period-appropriate palette, fine grain and texture. Compose with generous empty space for the quote and a small credit line. No lettering in the image itself.

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Provenance

Where the words actually appear

Work
“The Philosophy of Niels Bohr”
Author
Aage Petersen, Bohr’s assistant, recalling Bohr’s habitual reply
Published
Bulletin of the Atomic Scientists Vol. 19, No. 7 (September 1963), after Bohr’s death
Bohr’s own writings
Not found. Per Mermin, Bohr “never published such an assertion”

When asked whether the algorithm of quantum mechanics could be considered as somehow mirroring an underlying quantum world, Bohr would answer, “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” Petersen’s framing + the reported reply

These are Petersen’s words, as quoted in N. David Mermin’s Physics Today column (February 2004). Wikiquote’s transcription of the same passage reads “algorism” instead of “algorithm” and italicizes is and say. The popular two-sentence version leaves out the opening “There is no quantum world.”

N. David Mermin, “What’s Wrong With This Quantum World?” Physics Today (Feb 2004)

How we verified this

  • September 1963: Aage Petersen’s essay “The Philosophy of Niels Bohr” appears in the Bulletin of the Atomic Scientists, September 1963 ↗. It presents the lines as what Bohr “would answer” when asked whether quantum mechanics mirrors an underlying quantum world.
  • Wikiquote lists the full passage under “Quotes about Bohr” on its Niels Bohr page ↗, credits it to Petersen’s 1963 essay, and adds Mermin’s account of Victor Weisskopf objecting to it.
  • February 2004: N. David Mermin’s Physics Today column ↗ reports that more than 90% of the pages he found credit the words to Bohr. He shows the source is Petersen’s essay and calls it “at best an attempt by a close associate to characterize Bohr’s general response.”
  • Scholarship: Jeffrey Bub’s “There is No Quantum World” (arXiv) ↗ describes Petersen as Bohr’s assistant from 1952 to 1962. It notes that no similar statement appears in Bohr’s published writing, but sees no reason to doubt Petersen’s recollection.
In copyright

The wording first appeared in Aage Petersen’s essay in the September 1963 Bulletin of the Atomic Scientists, a work published after 1931. We treat it as in copyright, held by the publisher and/or Petersen’s estate. Quoting a short passage here is fair use.

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

How Petersen’s memory became “Bohr’s dictum”

The line circulates as something Bohr wrote or proclaimed. It is a secondhand recollection, published after Bohr died, and the people who knew him disagreed about whether it sounded like him.

Niels Bohr, as his own written words Hearsay

Mermin found that more than 90% of the pages he searched credit the passage to Bohr, some saying “Niels Bohr wrote.” He reports that Bohr “never published such an assertion in any of his writings” and that the statement comes from Petersen’s essay (Physics Today, 2004 ↗).

Victor Weisskopf vs. Rudolf Peierls Disputed recollection

Mermin describes reading the Petersen passage at a 1982 MIT colloquium, where Weisskopf objected that Bohr could not have said anything like it. Peierls later told him it was exactly the kind of thing Bohr loved to say. Mermin warns that his own wording of both reactions is reconstructed from memory (Mermin ↗).

The two-sentence version Excerpt

Petersen’s passage opens with “There is no quantum world. There is only an abstract quantum physical description.” The popular form drops those sentences and Petersen’s framing, so his report of Bohr’s typical reply reads like a direct quotation (Wikiquote ↗).

These are Aage Petersen’s words for what Bohr used to say, published in September 1963. The closest passage Mermin found in Bohr’s own writing is “physics is to be regarded not so much as the study of something a priori given, but as the development of methods for ordering and surveying human experience” (Essays 1958–1962 on Atomic Physics and Human Knowledge, p. 10, as cited in Mermin’s column ↗).

Context

Why the source matters

The passage is often used as a one-line summary of the Copenhagen interpretation, the view that physics describes what we can say about our experiments, not an underlying reality. Because it reached print only after Bohr died, he never had a chance to endorse or correct it.

Mermin’s point was not that Petersen invented the idea. He argued that Bohr’s own published sentences come close to it, and he asked readers to keep “Petersen’s Bohr” separate from “Bohr’s Bohr.”

“There is no quantum world. There is only an abstract quantum physical description.” (Petersen’s account of Bohr)

Explore

Filed under

More provenance-checked quotes on the same theme, each with its reuse status.

Knowledge Truth Humility

Go further

Dig deeper

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

What’s Wrong With This Quantum World? (N. David Mermin)physicstoday.aip.org

Physics Today column (Feb 2004) tracing the line to Aage Petersen’s 1963 essay, not to anything Bohr published
Niels Bohr — Wikiquoteen.wikiquote.org

Full Petersen passage under “Quotes about Bohr,” with its 1963 Bulletin citation and Mermin’s Weisskopf anecdote
Bulletin of the Atomic Scientists, September 1963books.google.com

The issue of the magazine that carried Petersen’s essay
There is No Quantum World (Jeffrey Bub)arxiv.org

Philosophy paper on the Petersen quotation, Petersen’s years as Bohr’s assistant, and its absence from Bohr’s published work
Niels Bohr — Wikipediaen.wikipedia.org

Biography: life dates, Nobel Prize, and the Copenhagen school

The author

About Niels Bohr

Niels Bohr

7 Oct 1885 – 18 Nov 1962 · Danish theoretical physicist, Nobel Prize in Physics 1922

Niels Bohr was a Danish theoretical physicist who won the 1922 Nobel Prize in Physics. He was the central figure of the Copenhagen school of quantum mechanics and the author of the principle of complementarity. He wrote slowly and carefully about the philosophy of quantum theory, and the line most often quoted as his view of physics is not in those writings. It comes from his assistant, Aage Petersen.

For writers & researchers

Cite this

Earliest documented source

Aage Petersen, “The Philosophy of Niels Bohr,” Bulletin of the Atomic Scientists 19, no. 7 (September 1963): 8. This is Petersen’s recollection of Bohr’s typical reply, not a text by Bohr. See N. David Mermin, “What’s Wrong With This Quantum World?” Physics Today 57, no. 2 (February 2004): 10.

This verification page

Quotle.info. “Who really said ‘It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature’?” Last verified 3 Nov 2026. https://quotle.info/who-said/it-is-wrong-to-think-that-the-task-of-physics-is-to-find/

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