Paul Adrien Maurice Dirac was a physicist of genius but with certain personality eccentricities. Niels Bohr called him the strangest man and that became the title of a biography for him. Bohr also said that Dirac was an Englishman and the Danes had come to expect almost anything from Englishmen. Physicists circulated stories of his strangeness. For example, when someone asked Dirac if he played a musical instrument, he replied, "I do not know; I have never tried." Dirac turned down a British knighthood because he did not want to be called Sir Paul. He signed his name as P.A.M. Dirac and this was the name used for the authorship of his books.

Some of his colleagues defined a unit of conversation as a dirac. It was one word per hour. This was a joke but the reality was not much different. His sparingly use of language stemmed from his childhood. Dirac's father was a French-speaking Swiss who migrated to England. To force Dirac to become fluent in French his father refused to speak to him unless he spoke in French. Dirac's reaction was to say very little and only it was absolutely necessary.

One physicist said that when he needed some assistance from Dirac he would pose his questions in the simplest possible terms. That physicist said Dirac, upon hearing the question, would stare at the ceiling for five minutes, then stare out the window for five minutes and finally answer yes or no. That physicist also said the Dirac was always right.

Although the physicists of his acquaintance joked about his peculiarities they also recognized his extraordinary talents. Werner Heisenberg referred to an Englishman that was so smart that it was hopeless to compete with him in theoretical research. Heisenberg was undoubtedly referring to Dirac. Albert Einstein said that in reading Dirac's articles it was hard to tread the narrow path between genius and madness. Wolfgang Pauli characterized Dirac's form of theorizing as acrobatic.

I myself had an adverse reaction to Dirac's work when I first saw it . In seeing the equations he conjured up my first thought was, "How in the world does he expect there to be any meaningful solutions to such equations?" It was like someone who built strange cages for a zoo and then tried to find creatures to fill them rather than having a collection of creatures and building the cages of a zoo to hold them.

Against all intuition Dirac's approach was the right one. There was no assurance that the explanation of some physical phenomenon would be in terms of the variables that a theorist had in mind, such as ordinary real numbers. Instead there was some assurances about the form of the equations which would be required. Dirac conjectured about the equations. If a proposed equation implied something contradicted by experiment he discarded it and went on to another equation. An essential part of the analysis was finding out what types of variables would satifiy the equation and this was not easy, but ultimately Dirac found the equations and the types of variables required to satisfy them.

In contrast Wolfgang Pauli took the opposite approach. He started with the notion that a theory should be expressed in terms real or complex variables. Unfortunately for Pauli there was no such theory and consequently Pauli, even though possessing stellar abilities accomplished relatively little in physics. Dirac's acrobatic theorizing got him to the unexpectedly complex nature of reality.

Here are links to webpages on Dirac's works on the complex nature of reality.

• The Theory of the Electron
• The Bra and Ket Notation of Paul Dirac
• The Spin of Electrons
• Transformation Theory

(To be continued.)