Speaking Volumes: The Principles of Quantum Mechanics

June 2, 1995

Graham Farmelo on Paul Dirac's The Principles of Quantum Mechanics .

I shall always be indebted to Jeremy Thorpe's Liberal Party. As a teenager, it enabled me to earn my spending money and the job led to my introduction to the work of one of the century's most illustrious scientists, Paul Dirac, the author of what is for me the greatest scientific work since Newton's Principia.

The Orpington branch of the Party organised a weekly prize draw and I was responsible for collecting 10p from 100 households. In an attempt to attract a new member, I called one Friday evening on a gentleman who astonished me first by instantly calculating the desperately long odds of winning, and then by joining.

My new client turned out to be an agreeably eccentric Ministry of Defence mathematician fond of playing Chopin and the stock market and an almost obsessive admirer of Paul Dirac. It was no coincidence that one of his daughters had been named Paula.

Towards the end of December on calling to collect his 10p, I found him surrounded by discarded sections of the Sunday Times, his head barely protruding above the pages of Dirac's The Principles of Quantum Mechanics, an account of the subject the author did much to invent, particularly in Cambridge and Gottingen between 1925-19. I had interrupted a one man pagan festival, the "Christmas Dirac", which comprised an annual reading of the master's magnum opus.

Within hours of first leafing through this handsome though austere volume, I knew I wanted to be a theoretical physicist. Although I did not understand much of it, I could see that this was the work of a genius who was demonstrating how to construct a completely new theoretical framework from scratch. I later saw that this was a masterpiece of Cartesian science, in which problems were tackled top-down, by working on the great principles with the details left to look after themselves.

High school physics enabled me to come to grips only with the first chapter, a cool and measured case for having to abandon, in the atomic domain, concepts that had served classical physicists for centuries. Dirac constructed the logical structure of the theory in fresh, opaline prose whose every word had plainly been carefully weighed. Yet it was no easy read: its 82 sections contained 785 equations but neither a single diagram nor the slightest trace of humour. Yet somehow, this austerity was essential to its beauty.

At university, I measured my growth as a physicist by how many pages of the book I could understand (average rate of progress: about ten lines a day). This was not the kind of student-friendly textbook that lecturers like to recommend - only Cambridge undergraduates appeared to be using it. One of them told me that he had written to Dirac in the United States, asking for clarification of four particularly recondite lines. The author wrote back to say that he had thought carefully about the passage and could find no clearer way of expressing it. Such are the sentiments of a poet.

What a shock it was later to find the low esteem in which research colleagues held the book (and sometimes, its author). From their dull utilitarian point of view, it was useless as a teaching aid and hopelessly unsound on anything done much after 1940 (Dirac was notoriously dismissive of attempts to build on his theory of radiation, attempts that he insisted merely "swept infinities under the carpet").

My response to the critics is to quote the wise words of Julian Barnes in Flaubert's Parrot when he writes of literary critics who "act as if Flaubert, or Milton, or Wordsworth, were some tedious old aunt in a rocking chair, who smelt of stale powder, was only interested in the past and hadn't said anything new in years. Of course, it's her house, and everybody's been living in it rent free for years . . ."

Graham Farmelo is head of programmes at the Science Museum, London.

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