place (Westminster Abbey). Yet those whoopposed Newton must also be remem-bered: Charles Darwin refused to be buriedbeside Newton in Westminster Abbey;Einstein challenged Newton’s physics; and John Maynard Keynes and his economicscolleagues exclaimed, as Fara writes, that“Newton was not the first great scientist, butthe last great magician”.

Magic and science have never been easybedfellows, despite pronouncements abouttheir historical proximity in the early modernworld.The images of magicians and scientistsare different, and image-making withinnational settings is what this book is all about.Yet as time unfolds it becomes increasinglyless important to enquire about the degree towhich a particular scientist amounted to pure,disembodied genius, let alone to explore the quantum of his magic. We can assess Einstein’s achievements, for example, with-out resorting to such extremes. If he was agenius, he was also an impoverished GermanJewish immigrant who fled persecution toAmerica. Nor do we worry whether he wasunrivalled. The high-stakes, image-makingprocess has been transferred from scientiststo athletes,movie stars and politicians.

But there is one more turn of the screw.AsFara writes, “this duality as both an insanegenius and a dispassionate scientist is uniqueto Newton”. Unique it may be, but as timepasses the possibility of an integrated imageof Newton grows ever more remote, and in acentury’s time a unified view of Newton willappear even more elusive than it is now. Thismay not be so bad, or surprising: the lives ofeven the greatest scientists are no more ration-al or coherent than they are for the the rest of us.They never were and never will be. ■

George Rousseau, former regius professor of Englishat King’s College, Aberdeen, is research professor inthe School of Humanities, De Montfort University,Leicester LE1 9BH, UK.

Untangling quantummechanicsEntanglement: The GreatestMystery in Physicsby Amir AczelFour Walls Eight Windows/John Wiley: 2002.320 pp. $25/£16.99

Vlatko Vedral

Popularizing physics is no easy task. Thebasic laws of quantum mechanics in particu-lar contain many counterintuitive featuresthat lay readers might find difficult to under-stand. So, in order to convey the message,there is often a tendency to oversimplify facts to the point of making them incorrect.Regrettably, this makes quantum physicsmuch more mysterious than it really is.

Amir Aczel falls prey to this whendescribing entanglement, a key feature ofquantum mechanics, in his new book. Asmany other authors have done, he empha-sizes that when two quantum systems areentangled, and then we measure one of thesystems, we immediately know (or affect) the state of the other,no matter how far apartthe systems are.We are led to believe that this is somehow weird.

However, in the day-to-day world that is well described by classical newtonianphysics,we often encounter correlations.Forexample, imagine you are observing a bankrobbery. The robber is pointing a gun at theterrified bank clerk. By looking at the clerkyou can tell whether the gun has gone off ornot. If the clerk is alive and unharmed, youknow that the gun has not fired. If the clerk is lying dead, you know that the gun has fired. There is therefore a direct correlationbetween the state of the gun and the state ofthe clerk. ‘Gun fired’ means ‘clerk dead’, and‘gun not fired’ means ‘clerk alive’. Of course,we assume that the robber shoots to kill and never misses.

The key (and surprising) observation isthat quantum-mechanical systems may befurther correlated such that the gun is in thesuperposition ‘fired and not fired’, and theclerk is then in the state ‘dead and alive’ at the same time! Quantum mechanically, as aconsequence of this superposition, there issimply more correlation between atoms orphotons than we would expect classically.This kind of quantum ‘supercorrelation’,first quantified precisely by John Bell in 1964, is what we refer to as ‘entanglement’.

In the early days of quantum mechanicsthere were several attempts to use entangle-ment to uncover a paradox in the foun-dations of quantum physics. However, byquantifying these correlations, Bell took

them out of the philosophical realm ofEinstein and Niels Bohr, and demonstrated how entanglement and the completeness of quantum mechanics could coexist. Theseextra correlations are ‘real’, in that they havebeen confirmed by experiment and, moreimportantly, have been successfully appliedto quantum teleportation (which would otherwise be impossible) and to quantumcryptography.

The oversimplification of entanglementnotwithstanding, I find that Aczel has done a good job of describing its colourful history,as well as modern developments such as teleportation. But what he perhaps does best is enlighten us with some snippets about thekey physicists involved. For example, I foundmany interesting and humorous anecdotesabout Erwin Schrödinger’s love life, aboutJohn von Neumann being perceived as analien by the US public, and about the friend-ship between Heisenberg and Bohr. There is,however,a dangerous tendency in popularscience to idolize scientists beyond justifi-cation, making them appear more extra-ordinary than they really are. This bookwalks a fine line between historical accuracyand fictional infatuation.

I am altogether happy that there is nowfinally a book on entanglement, almost 70years after its discovery, and recommend it to people interested in the historical back-ground and practical implications of quan-tum mechanics. I am afraid, however, thatanyone interested in understanding quantummechanics, and the way in which scientiststhink about it, is much better off reading any of Richard Feynman’s popular accounts,such as QED: The Strange Theory of Light and Matter(Princeton University Press,1985). ■

Vlatko Vedral is at the Blackett Laboratory,Imperial College, Prince Consort Road,London SW7 2BZ, UK.

book reviews

NATURE | VOL 420 | 21 NOVEMBER 2002 | www.nature.com/nature 271

Dead or alive? The state of the cashier is correlated with whether Lee Marvin’s gun has been fired.

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