Wednesday, December 21, 2011

Advent calendar #21: Bohr and the horseshoe

The web is full with anecdotes and quotations about physicists and mathematicians. It would not be difficult to fill a whole year with stories Google put at my fingertips, but then I could as well make them up myself. The time-intensive part of this advent calendar has not been to find the stories but to find out if they have a reliable source. Inevitably, some widely spread stories, if they had any source at all, turned out to have been altered several times, much like a digital game of Chinese whispers.

One such story is for example that of Niels Bohr and the horseshoe. The version on this website goes like this:
"An American scientist once visited the offices of the great Nobel prize winning physicist, Niels Bohr, in Copenhagen. He was amazed to find that over Bohr's desk was a horseshoe, securely nailed to the wall, with the open end up in the approved manner (so it would catch the good luck and not let it spill out). The American said with a nervous laugh,

"Surely you don't believe the horseshoe will bring you good luck, do you, Professor Bohr? After all, as a scientist --" Bohr chuckled.

"I believe no such thing, my good friend. Not at all. I am scarcely likely to believe in such foolish nonsense. However, I am told that a horseshoe will bring you good luck whether you believe in it or not."

In some other versions that you can find online it's a student who asks the question, in yet some other versions the horseshoe is not above the desk but above the door to Bohr's cottage. The above version is particularly interesting for the amount of irrelevant details that somebody or maybe several people have added. Wikipedia lists the quote as disputed.

To find the origin of that story it is useful if you speak German, since it goes back to Werner Heisenberg's book "Der Teil und das Ganze" (The part and the whole). Most of the book is a recollection of conversations Heisenberg had with Niels Bohr and Wolfgang Pauli, among others. Heisenberg wrote down these conversations long after they had taken place, so one should not expect the exchange to have been word by word exactly as he reported. Heisenberg finishes Chapter 8 on "Atomphysik und pragmatische Denkweise" (atomic physics and pragmatism) with an anecdote that Niels Bohr told:
Niels schloß das Gespräch ab mit einer jener Geschichten, die er bei solchen Gelegenheiten gern erzählte: "In der Nähe unseres Ferienhauses in Tisvilde wohnt ein Mann, der hat über der Eingangstür seines Hauses ein Hufeisen angebracht, das nach einem alten Volksglauben Glück bringen soll. Als ein Bekannter ihn fragte: "Aber bist du denn so abergläubisch? Glaubst du wirklich, dass das Hufeisen dir Glück bringt?", antwortete er: "Natürlich nicht; aber man sagt doch, daß es auch dann hilft, wenn man nicht daran glaubt.""

Niels finished with one of these stories he liked to tell on such occasions: "Near by our vacation house in Tisvilde lives a man who has a horseshoe above his door, after the old superstition that it brings luck. When a friend asked him "Are you superstitious? Do you really believe the horseshoe brings luck?" He replied "Of course not; but they say it also helps if you don't believe it."
~Werner Heisenberg, Der Teil und das Ganze, 1973, p. 112/13

So if you plan on winning a Nobel prize, be careful with the anecdotes you tell. Later generations might unashamedly turn the narrator into a subject and the details may be buried in translation.


  1. Hi Bee & Stefan,

    Very good research as to get to the heart of things. It gives me an ideas about how I could start another myth which would be what Abraham Pais’s reply to Einstein was when he annoyedly ask him, if he truly believed that the moon exists only when I look at it, to have responded the same, "Of course not; but they say it also helps if you don't believe it."



  2. And I suppose Dirac would have said "at least at one side" ;o)

  3. I first read this anecdote in Gamow's Thiry Years That Shook Physics, which was published in 1966, near the end of Gamow's life. The exact quote from Gamow's book is (from pages 57-58 of the 1985 Dover edition):

    "There is another amusing story illustrating Bohr’s whimsey [sic]. Above the front door of his country cottage in Tisvilde he nailed a horseshoe, which is proverbially instrumental in bringing luck. Seeing it, a visitor exclaimed: 'Being a great scientist as you are, do you really believe that a horseshoe above the entrance to a home brings luck?' 'No,' answered Bohr, 'I certainly do not believe in this superstition. But you know,' he added with a smile, 'they say that it does bring luck even if you don’t believe in it!'”

    Many of the delightful anecdotes in Gamow's book are clearly first-person, but the implication from Gamow's book is that this one is not ("There is another amusing story ..."). Pais references a 1979 work by P. Robertson, so it's seems clear that the quote in Pais's book is not first-person either.

    Heisenberg says that Bohr was fond of telling the anecdote, so it could be that Gamow heard it from Bohr and then wrote it up inaccurately many years later from memory. But it's one of my favourite anecdotes of any scientist, because it captures the spirit of paradox and complementarity that Bohr championed and that seems to be inherent in quantum mechanics.

  4. I was going to suggest the story where after Einstein had delivered a lecture, a young man stood up and said ' What Professor Einstein has said is not all nonsense. But...'
    However some sources identify this audacious young man to be Pauli (behaving typically) whereas some say it's Landau, speaking a broken German....

  5. Reminds me of this one:

    When Heidegger was asked at the end of his life by Max Mueller why he stopped at churches and chapels to take holy-water and kneel before the altar, he seems to have answered: Where there has been so much praying, the divine is near in a very special way.


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