Heisenberg and Dirac

Beatrice’s story about Heisenberg possibly inspiring the "Schunkelwalzer" dancing tradition at Lindau reminds me of an ancedote about Heisenberg and Paul Dirac. Both were two of the most accomplished scientists of the twentieth century who made foundational contributions to quantum mechanics. But while Heisenberg loved song, dance and wine, Dirac was a very quiet man and a singularly unusual character who generously extended his abstract thinking to interpreting the world literally. This inevitably led him to being an anecdote generator throughout his life and many stories about him abound. Here are a few, concluding with the story about him and Heisenberg.

Dirac’s taciturn nature hid a razor sharp mind that could analyze the logical essence of any conversation, technical or human. While his comments would strike people as odd at first, they would quickly realize that his comments made perfect logical sense. It’s just that the human world with its deliberately constructed frailties and ambiguities of language was not rigorous enough for this genius. What some might see as literary flourishes and subtleties of language, Dirac would only see as obstacles to clear thinking.

Dirac had genuine trouble understanding metaphor. He and Robert Oppenheimer were friends and spent some time together in Göttingen in the 20s. Oppenheimer was a polymath who was interested in everything including poetry. Once Dirac said to him, "Oppenheimer, they tell me you are writing poetry. I do not see how a man can work on the frontiers of physics and write poetry at the same time. In science you want to say something that nobody knew before, in words which everyone can understand. In poetry it seems to be the opposite". Dirac also had no problem criticizing someone as famous as Niels Bohr, who was known for being long-winded and mumbling. Bohr was once writing a scientific paper – hesitating and with several drafts as was his habit. Frustrated, he stopped and quipped: "I do not know how to finish this sentence." Dirac replied: "I was taught at school that you should never start a sentence without knowing the end of it." And then of course there is the anecdote about Dirac being told by a student in class that he could not understand an equation. Dirac simply nodded his head and continued unabated. When asked again he expressed puzzlement because he thought the student had simply uttered a fact, not asked a question.

Which leads us to the ancedote about Heisenberg and Dirac. The two were on a trip to Japan for a conference. The social Heisenberg used to dance with the young girls on the ship before dinners while Dirac used to sit watching. Once Dirac asked him, "Heisenberg, why do you dance?" Heisenberg replied that when there were nice girls he felt like dancing with them. Dirac fell into deep thought and after about fifteen minutes, asked Heisenberg again, "Heisenberg, how do you know beforehand that the girls are nice?".

One almost gets the feeling that the brains of people like Dirac and Einstein were wired fundamentally differently. It was astonishing for me to see Dirac being so lively and chatting with fellow scientists and students at Lindau. But it shouldn’t be surprising. Dirac’s taciturn nature and seemingly cold and logical exterior hid a warm, sensitive and gentle human being whose emotions had been marred by a rather harsh childhood. It was only later that he seemed to open up and talk about personal matters to a select few friends.

Dirac once explained why he spoke so little by invoking yet another great truism: "There are always more people willing to speak than there are to listen"….

One can read all about this remarkable man in the marvelous biography of him published a few months ago- The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom by Graham Farmelo.