Dirac Number 2

Dirac Number 2

Paul Dirac was one of the early quantum mechanics who, among his many significant contributions, predicted the existence of antimatter in 1928, as a consequence of finding the correct relativistically invariant wave-equation for the electron. He also formulated the original many-body description of how light interacts with matter, viz., Quantum Electrodynamics.
Although Dirac has not received the same degree of public awarenes as say Einstein and Feynman have, there are now a couple of biographies available [1,2]. My review of The Strangest Man has been published by the New York Journal of Books.

1  The Number

My Master's degree thesis adviser was Prof. Christie Eliezer, himself one of Dirac's few research students. He worked under Dirac in the early 1940's. Since Eliezer worked with Dirac, he gets a Dirac number of 1 (analogous to 1 hop between nodes on the Internet). I get number 2 since I worked with someone who worked with Dirac. I was 2 hops away from working with Dirac (not that Dirac was supervising students at that time, but you get the idea).
Dirac (left) and Eliezer (center). The person on the right is unidentified (It's not me).
Update of Feb 2010:
Originally, I thought I had taken this photograph, thus making me the "genius" behind the camera and forever losing the opportunity to say "This is me with Dirac!" I now recall that, as a poor student, I didn't even own a camera at that time. Someone else took this photo. I also remember that I was with a group of people immediately in front of Dirac and, based on the angle, it looks like the photographer was in our group. The good news is, I'm not as dumb as I thought.
Update of Mar 2011:
Apparently, the unidentified person in the photo above is Prof. John Carver, who was then deputy chair of the Dept. of Physics at Adelaide University [3].
The reason Dirac had so few students was, in part, due to his taciturn nature. Actually, taciturn does not really capture the dimensions of the effect. You really had to experience it to fully comprehend its impact (See Section 2.2). There is a famous story about Leopold Infeld who dreamed of working with Dirac. When he finally got the chance to meet Dirac as part of an interview for a research position, he came away in tears because nothing was said and Infeld knew immediately he could never cope with that total lack of personal interaction.

2  Dirac in Australia 1975

Dirac visited Australia in 1975. I don't recall why. Eliezer and I flew from Melbourne to Adelaide to visit with him while he was a guest of the Physics Dept. at the University of Adelaide under the auspices of Prof. Angus Hurst. On the weekend we went for a hike. It was rather cold, so people had their jackets and coats on. Naturally, only Cambridge types would be caught dead in a suit in the Australian outback.

2.1  Up a Gum Tree

Dirac had a thing about trees. I had read somewhere that someone went to visit Dirac at his home in Cambridge and his wife (Wigner's sister) answered the door. When the visitor enquired if Dirac was home, she said that he was home, but he was up a tree.
During our walk (see photo above), I had some confirmation of this story. I was walking in front of Dirac with some other people when I suddenly heard something like an animal moving quickly off to one side of the track. I turned around to discover to my astonishment that it was Dirac. He had taken off like a rocket up the slope (in Sunday suit and shoes, mind you) toward a gum tree. Apparently, he was fascinated by a particular tree and wanted to get a closer look at it. I was impressed at how he actually sprinted up the hill, given that he was in his mid seventies!
Here is another explanation of Dirac's penchant for trees:
English physicist and Cambridge University professor Paul Dirac was an avid mountain climber and occasionally ascended such well-known peaks as Mount Elbruz in the Caucasus. In preparation for such excursions, Dirac would often climb trees in the hills just outside Cambridge—wearing the same black suit in which he was invariably seen around the university campus.
This story can be found repeated on the web, and it is supported by the fact that the Russian physicist, Igor Tamm, taught Dirac the basics of mountain climbing using trees to practice on. In return, Dirac taught Tamm how to drive a car [2, p. 190].
So, it may have been pure coincidence that Dirac displayed such energetic interest in the gum tree.

2.2  Dinner with Dirac

A dinner party was thrown for Dirac while he was in Adelaide. It was buffet style. While Dirac's wife was holding court in the dining room (some of us thought she was a real Brunhilde), Dirac snuck off into an adjacent, darkened room to eat his dinner. Since I was the only one who seemed to notice his stealthy departure, I decided that this was my big moment to talk privately with the icon of quantum theory.
I followed him and sat down beside him. No words words or glances were exchanged but, as a twenty-something, I was quite optimistic that a good physics question would be the way to impress the old boy and strike up a conversation in the privacy of the darkened room. Instead, I was about to step into the psychological abyss that is the Dirac silent treatment.
After some qucik thinking, I decided to ask him about black holes and singularities. No answer. No acknowledgement of any kind. Just dead silence, as if I hadn't spoken at all. It was impossible to decide whether Dirac hadn't heard my question, didn't have an answer or just didn't want to speak while eating. None of these were the issue.
Small talk is a very important social lubricant, so it quickly becomes distressing when no response is evoked. The only analogy I can think of is, it's like you opened your mouth and Dirac just died. Now, you're asking yourself: what the hell just happened? Did I cause his death with my words? Will I go to prison? And so on. The point is, it causes you to start interrogating yourself as though it's your fault. Even though I had been told about Dirac's taciturn nature, I had completely forgotten about that, now that I was in the middle of this mental maelstrom. All I was focused on was trying to recover the situation and having no idea where to begin. And I was too paralyzed with fear to even run away.
Suddenly, after what seemed like an eternity, I heard some kind of vocalization. It was Dirac starting up with what turned out to be a very considered reply. He began with some dismissive remark about singularities, but continued at length; or what seemed long, given his long silence. It sounded like this. By that time, however, I had a new problem. I had become so confused and distressed by his total lack of response, I'd forgotten what my question was! But one thing was for sure. I wasn't about to repeat the process. I think I know how Infeld felt.

2.3  Dirac's Monopole

Dirac gave three lectures while he was in Adelaide, all of which were quite boring because he talked about things he had done some 40 or 50 years earlier without providing any personal insight into how he developed his ideas.
The more exciting thing, it turned out, was news that Blas Cabrera at Stanford was claiming to have seen Dirac's magnetic monopole. If such a thing really existed, it would account for the size of the electric charge. I remember that Dirac got on the phone and talked with the experimental physicist Luis Alvarez at Berkeley. Dirac finally told us that he didn't believe Cabrera's results. He was right, but there was a hint of irony in that the inventor of the monopole didn't really believe in them.

References

[1]
Helge Kragh, Dirac: A Scientific Biography, Cambridge University Press, 2005
[2]
Graham Farmelo The Strangest Man: The Hidden Life of Paul Dirac, Basic Books, 2009
[3]
Peter Lyster, private communication, March 5, 2011.


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On 6 Mar 2011, 11:24.