Historical Physicist Smackdown Explained: Electric Theory

So, who are the people in yesterday's poll about theoretical physicists, and why should you know them?

Three of the four shared a Nobel Prize for developing quantum electrodynamics. In reverse order of voting:

Julian Schwinger was an American physicist who came up with a very formal, mathematically rigorous way of describing the behavior of electrons interacting with light. This turns out to be a hard problem, because any attempt to calculate an electron's energy by simple, straightforward means ends up giving an infinite answer. Schwinger helped "renormalize" the theory, getting rid of the infinity with some elegant mathematics.

Shin-Ichirio Tomonaga was a Japanese physicist who independently developed the same renormalization theory. I broke the tie between him and Schwinger in his favor, because he did his work in postwar Tokyo, which had been essentially flattened by American bombing. His achievement is all the more impressive for being done with fewer resources and in relative isolation.

Richard Feynman was an American physicist and noted colorful character, who also came up with a quantum theory to describe the interaction of electrons with light. His method was less rigorous but more intuitive than Schwinger's, which initially earned it a cool reception. His method of representing the necessary calculations graphically with Feynman diagrams turned out to be a much more convenient way of handling complex calculations than Schwinger's theory provided, so Feynman's approach to QED has become the best-known of the three.

(Feynman and Schwinger had dramatically different approaches to theory, and neither really cared for the other's methods. There's an apocryphal story of some physicist staying the night at Schwinger's house, and spending a bunch of time in his library, trying in vain to find a single Feynman diagram in Schwinger's papers...)

The three theories of Feynman, Schwinger, and Tomonaga were shown to be identical by Freeman Dyson, who turned up in comments as a write-in vote.

The fourth physicist in the poll, and the subject of my current bedtime reading, is Paul Adrien Maurice Dirac, a British physicist who developed the first quantum description of an electron that was consistent with relativity. The Dirac equation is notable for both including the electron's spin as an essential property of the particle and also for predicting the existence of a positively-charged particle with the same mass as the electron. This was later identified as the positron, the anti-matter equivalent of the electron, and its discovery was a great triumph for his theory.

Dirac was also legendarily taciturn, and tactless. A frequently related story about him is about a talk at Wisconsin, where he finished his prepared remarks, and then offered to answer questions. Someone in the audience raised a hand and said "Professor, I didn't understand the equation in the upper right part of the board."

Dirac remained silent for long enough the the seminar organizer finally said "Aren't you going to answer the question?" Dirac replied "That wasn't a question. It was a comment."

So, those are the four great theorists of the electron. Dirac soundly beat Feynman in the poll, and Feynman had almost six times as many votes as Tomonaga or Schwinger. This wasn't an entierly fair poll, though, as both Dirac and Feynman are noted as characters, beyond their achievements in physics. Tomonaga and Schwinger had much less notoriety.

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A great interview with Dirac. (Whose taciturnity also inspired the unit "the dirac": one word per year.)

By Ambitwistor (not verified) on 26 Sep 2009 #permalink

I forgot who said this, so I'll paraphrase it: 'Feynman was another Dirac, only human.'

I like how the Nobel prize sometimes acknowledges otherwise little known (general public wise) fundamental contributions. We do love our "star characters", but almost all science is an ensemble cast sort of enterprise.

Before you can equate Feynman with Dirac, you'd have to list several other Nobel-worthy papers he came up with on his own. Some would argue that the Dirac equation isn't even Dirac's most important contribution to quantum mechanics. Consider, for example, his proof the connection between classical and quantum mechanics via the Poisson bracket - commutator, or something as fundamental as Fermi-Dirac statistics. Or his magnetic monopole theorem? Vacuum polarization?

By CCPhysicist (not verified) on 28 Sep 2009 #permalink