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Particles and interactions

Particles and interactions

The quantum century

25 Aug 2011

The Quantum Story: a History in 40 Moments
Jim Baggott
2011 Oxford University Press £16.99/$29.95 hb 496pp

Mechanics of the universe

Books that try to explain quantum physics to the general reader have become a well established non-fiction (well, mostly non-fiction) genre. In this recent addition to the field, The Quantum Story: a History in 40 Moments, Jim Baggott plucks from the 20th-century history of quantum physics a set of “moments”, each one being the brief story of a significant discovery, tied to a single individual or a small group. He proceeds, largely in chronological order, from the year 1900 to just beyond 2000. It is an ambitious undertaking, and makes for a literally weighty book. But although Baggott goes at his task with unrelenting enthusiasm, the results are ultimately disappointing.

Baggott’s choice of “moments” is not the problem. His selections are relatively well balanced. Of the 40, a dozen are devoted to the development of quantum physics, another 12 to particle physics, 11 to the “meaning” of quantum physics (too many, in my opinion), and five to quantum cosmology and quantum gravity. The only missing moment, as I see it, is Fermi’s 1934 theory of beta decay, which set the stage for understanding that annihilation and creation of particles is the bedrock of all interactions, not just those involving the electromagnetic force. Apart from this omission, and the overemphasis on complementarity and “reality”, I cannot fault the selection.

More problematic is Baggott’s philosophical bent, which he reveals in the book’s preface. Here, he states that recent experiments “strongly suggest that we can no longer assume that the particle properties we measure necessarily reflect or represent the properties of the particles as they really are”. Baggott chooses to emphasize these words by repeating them on page 356 (except for the qualifying “strongly suggest that”). Indeed, questions about the nature of reality run throughout the book, and Baggott cannot quite free himself from the supposition that if an electron is emitted at A and absorbed at B, it must have existed as a particle at points between A and B. In fact, we cannot even say that it was always the same electron, much less that it had a definable existence or definable locations between A and B. All of which shows that opinion about what is reasonable and what is not reasonable, what is real and what is not real, remains part of what we call physics.

Another problem – although this is more a matter of taste – is the book’s style. If you love breathless prose, this is the book for you. Baggott’s account has physics lurching from crisis to crisis on a collision course with philosophy, and his leading characters burn with emotion as they are consumed by anger, ambition or bitter disappointment. For example, on page 158, I I Rabi is said to have been “incensed” when he famously asked about the muon, “Who ordered that?” Actually, he was joking. Similarly, in its early days, the quark model was not just questioned, it was, says Baggott, “treated with derision”.

Baggott’s end notes run to 29 pages and his bibliography to nearly 150 titles. He has obviously worked long and hard on this project, and many of his discussions reflect a depth of understanding. For instance, in “Moment 11” he explains well that waves in classical physics exhibit a kind of uncertainty. Similarly, his treatment of Bell’s theorem (Moment 31), although not easy reading, is accurate. And his discussion, in an “interlude”, of the famous meeting between Heisenberg and Bohr that took place in German-occupied Copenhagen in 1941 is balanced.

Despite this careful preparation, the book still contains quite a few physics errors, which is perhaps not surprising in a work by a non-physicist. Some are minor, such as a wrong definition of a mole (p17) or an incorrect explanation of the way that polarizing sunglasses work (p321). Others are a bit more substantive, such as the statement on page 28 that in classical theory an electron spiralling down toward a nucleus will lose speed, or the assertion on page 29 that electron energies in the Bohr atom increase in direct proportion to the quantum number n. Neither these nor any of the other errors are significant enough to undermine interest in the book.

A more serious problem, perhaps, is that most of the book’s errors are irrelevant. Even when the physics is correct – which is most of the time – does it matter? The discussions of physics in the book, although earnest, vary from barely comprehensible to completely opaque. Who, even among physicist readers, will understand the discussion of spontaneously broken symmetry groups in the 25th “moment” or mixing angles in the 28th? It matters little whether the physics is wholly accurate or not. The book doesn’t teach any physics. At best, it gives some kind of flavour of what it is all about. For some readers, that may be enough.

Basically, Baggott’s book is about people – from Max Planck, Niels Bohr and Albert Einstein in quantum theory’s early years, to Ed Witten, Lee Smolin and Anton Zeilinger in more recent times. On people, he does a good job (even if, as noted above, the descriptions are a bit breathless in places). If you read this book, you will learn about Pauli’s temper, Gell-Mann’s erudition, Bohr’s paternalism, Heisenberg’s ambition, Schrödinger’s dalliances, Glashow’s zest, Feynman’s playfulness, Hawking’s triumphs, Einstein’s stubbornness, Aspect’s determination, Zeldovich’s White Horse scotch whisky bet and more. But with 410 pages of text, there is a lot of book to wade through for the pleasure of these engaging profiles.

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