The genius who was 17,000,000,000 atoms high

This collection of six lectures by the flamboyant physicist Richard Feynman, is a sort of sequel to an earlier collection entitled Six Easy Pieces . Both are taken from a series of undergraduate physics lectures that Feynman gave at Caltech in Pasadena in the early 1960s. What is so special about these 30-year-old lectures that entices hard-nosed publishers to package selections of them as semi-popular offerings?

The answer is Richard Feynman. In his introduction to this collection, Roger Penrose emphasises the need to appreciate Feynman's stature as one of the outstanding figures of 20th-century physics in order to understand why Feynman was such a great teacher. Some idea of his achievements may be gauged from the fact that Feynman developed a totally new way of looking at quantum mechanics based on summing over all possible quantum paths, including those apparently travelling backwards in time. His "path integral" approach to quantum theory led him directly to quantum electro-dynamics, or QED, for which he shared the Nobel prize with Julian Schwinger and San-Itiro Tomonaga in 1965.

Feynman's great contribution was to make it possible for normal mortals to make calculations in QED by using his "space-time" diagrams and following a set of simple calculational rules. This demonstrates perfectly Feynman's ability to get to the heart of a physics problem and not be intimidated or deflected by unnecessarily fancy mathematical formalism.

Feynman brought his unique, no-nonsense approach in research to his teaching. Caltech was having a problem in motivating their bright young students who wanted to learn exciting things like quantum mechanics and relativity instead of spending their first two years struggling with such things as balls rolling down inclined planes. So for the first and only time that he gave a formal course purely for undergraduates, Feynman devoted himself to the creation of these celebrated lectures. In them he covered most of physics in a tour de force unequalled in its scope and originality of approach. Physicists still marvel at Feynman's explanation of the second law of thermodynamics using a ratchet and pawl.

In this selection, Feynman tackles such difficult topics as vector analysis, symmetries of physical laws and Einstein's special and general theories of relativity. Physicist David Pines came up with a title - Six Not-So-Easy Pieces - which does not violate the Trade Descriptions Act. At this level some familiarity with mathematics is necessary to follow the plot completely but Feynman displays all his tricks for keeping his audience interested. His down-to-earth use of ordinary language to describe physical concepts is much in evidence. In his discussion of symmetry Feynman says: "the substance of [Weyl's definition] is that a thing is symmetrical if there is something we can do to it so that after we have done it, it looks the same as it did before."

Feynman also brings physics to life by inventing imaginary conversations. In communicating our height to a Martian on another planet he says "we are 17,000,000,000 hydrogen atoms high!" Another feature of a Feynman lecture is the introduction of new ideas arising directly from his research. His discussion of symmetry includes time reversal, reflection and matter-antimatter symmetries and references to experiments actually performed at Caltech.

Laughter also plays an important role in enabling Feynman to keep his audience engaged. Having talked about reflection symmetry, and about how matter and antimatter can annihilate each other to produce energy, he imagines a meeting with a Martian made of antimatter. The two rush forward to shake hands. Feynman brings the house down with the beautifully timed punch-line "Well, if he puts out his left hand, watch out!" To fully appreciate the appeal of Feynman to physicists, it is really necessary to have heard Feynman at least once on tape or CD. One can then appreciate his rough-hewn lecture style and wonderful "Noo Yawk" accent, pick up asides edited out of the written text and join in the audience reaction.

Unusually for a world-famous physicist, Feynman was a consummate showman who loved being centre stage. Physicist Freeman Dyson once said of him "Feynman is the young American professor, half genius and half buffoon, who keeps all physicists and their children amused with his effervescent vitality". For me, Abraham Pais was closer to the mark when he wrote that Feynman was "a man who clowns while talking but who is in fact deeply serious".

Tony Hey is professor in electronics and computer science, University of Southampton.