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The Author's Explanation of the Science Just Doesn't Work
on 5 August 2009
I was an undergraduate at St John's, Cambridge in Dirac's time. I wanted to relish this book. But I can't. It has been greatly overrated.
The biographer of a great scientist has a massive problem: the science. Say nothing about the science and you omit the very thing that made the scientist notable; get deep into the science, and you greatly reduce the potential readership of the book; summarise the science for the general reader - ah, that's not at all easy.
Farmelo does attempt to explain Dirac's science in a way that won't put anybody off. There is rarely more than one page of science before attention shifts back to something easier, such as the rise of Hitler or Dirac's relations with his mother. There are no equations and no long chains of reasoning; most of the technical terms seem vaguely familiar: electron, proton etc. All these are sensible precautions, but does the author actually succeed in explaining the science in a way that the general reader can understand? I don't think he does, but to help you judge for yourselves I've picked a representative extract.
On page 336 Farmelo introduces the technique of `renormalisation':
`According to (Dyson's) theory, the observed energy of an electron is the sum of its self-energy - resulting from the interaction between the electron and its field - and the bare energy, defined to be the energy the electron is supposed to have when completely separate from its electromagnetic field. But the bare energy is a meaningless concept because it is actually impossible to switch off the interaction between the electron and its field; only the observed energy can be measured.'
`The virtue of renormalisation is that it enables every mention of bare energies in the theory to be removed and replaced with quantities that depend only on observed energies. Using this technique, theorists could use quantum electrodynamics to calculate - to any degree of accuracy - the value of any quantity the experimenters cared to measure. Despite the success of the technique, Dirac abominated it, partly because . . . `
Farmelo goes on to say what it was that Dirac didn't like about `renormalisation', but that explanation won't mean anything to you unless you have already understood from the words just quoted what `renormalisation' actually is. Well, have you understood that? I haven't, but then I only read Modern Languages.
This `renormalisation' thing seems to have been pretty important in Dirac's life. On page 356 Dirac comes up with `a new approach .. that dispensed with one of the foundations of renormalisation theory that Dirac most disliked .. ` On page 398 `Renormalisation was now widely accepted as a rigorous branch of mathematical physics, with no sleights of hand; Dirac vehemently disagreed.' On page 405 `Dirac mounted one of his last attacks on renormalisation in front of an audience of some two hundred students and Nobel laureates.' On page 412 Dirac `wanted his final published words to execrate renormalisation.. ..' On page 425 Farmelo, assessing Dirac in retrospect, opines that `He was always uneasy with algebraic approaches to physics and with any mathematical process he could not picture - one of the reasons why he was so uncomfortable with renormalisation.' We readers who don't come close to grasping even what kind of a concept `renormalisation' might be tend to feel a bit left out of things.
The extract I've given is a pretty fair sample, so you can make up your own mind. I think that many other readers will, like me, find most of Farmelo's explanation of Dirac's science quite useless. It might as well not be there. Of course, you can easily skip over the science stuff - but that is the very part of the book which ought to show you what Dirac actually did which made him more eminent than a thousand other eccentric professors. No, this does not come close to being a five-star book!