Quantum: A guide for the perplexed by Jim al-Khalili, Weidenfeld & Nicolson, 拢18.99, ISBN 0297843052 Reviewed by Marcus Chown
鈥淭HERE is something fascinating about science,鈥� Mark Twain famously wrote. 鈥淥ne gets such wholesale returns of conjecture out of such a trifling investment of fact.鈥�
Twain鈥檚 words sprang to mind as I was leafing through Jim Al-Khalili鈥檚 Quantum: A guide for the perplexed. For, never in the history of science can so trifling an investment of fact have spawned so fabulous a wealth of extraordinary consequences as in the case of quantum theory.
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The central fact is remarkably easy to state: in the microscopic world of atoms and their constituents, particles can behave like waves and waves like particles. There are a few quantitative details, of course. The waves in question are peculiar, abstract things. They have an amplitude represented by a complex number, propagate in space and time according to the Schr枚dinger equation and the square of the amplitude at any place is the probability of finding a particle there if anyone decides to look.
Among the consequences of this mere handful of facts is that atoms can be in many places at once, penetrate 鈥渋mpenetrable鈥� barriers, 鈥渒now鈥� about each other instantly even when on different sides of the universe, and do things with total disregard for cause and effect 鈥� arguably the most shocking and unsettling of all the consequences of their 鈥渨ave-particle鈥� nature.
Throw a few more facts into the pot, such as the existence of spin and the utter impossibility of telling apart two electrons, two photons and so on, and you get lasers, superconductors, liquids that can flow uphill and an explanation for why we live in a complex world built from 92 wildly different kinds of atom, rather than simply one.
Al-Khalili, a lecturer at the University of Surrey in Guildford, surveys a large range of these quantum phenomena. He ends up explaining everything from black body radiation and the double-slit experiment to quantum teleportation, quantum computers and Bose-Einstein condensates.
I hope that this excellent and lavishly illustrated book will leave you less perplexed. But whether it does or not, it will certainly leave you with a powerful impression of the beauty and magic of quantum theory.