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Review - Quantum - Manjit Kumar 

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The first thing that strikes you about this book it's big. It's a chunky tome. It looks suspiciously like the sort of book that assumes you've written a 'big' book if you have written a long one, and sadly the contents don't do anything to counter this opinion. It goes on too long, it's often dull and I couldn't really find any new ground being covered here - it has all been done before, better and more readably.

For example, the early chapters on Planck and Einstein feel very samey with all the other material I've read on them (though it's particularly plodding here). The trouble is, you feel you have to put all this stuff in, but there's no doubt that it's going over old ground with a will. Things do live up a little when we get onto Bohr, who has relatively little biographical information written about him. However, even here things aren't all sweetness and light. The problem with this section is the author's poor structuring. We keep diving back and forth in time. Part way through Bohr we jump back to JJ Thomson's mini biography, before we can really get any progress we then jump out again for Rutherford's biography, part way through which (nest jumps!) we pop out for Roentgen's biography and so on.

Later on, when we get onto the massed brigade of young quantum turks, there are just too many being thrown at us, the biographies get very dull and samey. It's not so much unputdownable at this point as unpickupable.

All the way through it's a touch too technical for the general reader. There are unnecessary formulae and units are rarely explained. The science is often it bit too close to what I remember from first year physics lectures at university.

All in all, this would make a good textbook to give some context to those studying quantum physics, but it's a poor attempt at a popular science book on the topic. Take a look at Marcus Chown's Quantum Theory Cannot Hurt You for a much better effort.

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Reviewed by Brian Clegg

Community Review by Max Wallis (originally published in Viewpoint Newsletter 90 of British Society for History of Science, October 2009)

Kumar’s book reached the Royal Society’s long-list for the 2009 Prize for Science Books.  On 30th  June, BBC2 showed a short film of it.   How does it rank among the numerous histories of the great debate?  Combining racy science and human drama, Kumar ranges in history from Isaac Newton to John Bell, employing vivid portraits of physicists as science detectives, to explore concepts of  physical reality involved in the Einstein-Bohr debate.

But his framing of the debate is over-narrow.  There’s nothing on Faraday initiating the search for a unified field theory, pursued for decades by Einstein.  Gravitation is represented as warping of space, but not the alternative of a field supporting gravitational waves, analogous to the electromagnetic field supporting light waves.  The speed of light (or any influence) being finite is fundamental to relativity - quantum mechanics is not relativistic - yet this issue critical to causality is missing.

Kumar runs through early 20th century discovery of atomic and nuclear structure, replete with unexplained concepts like electron ‘spin’ and exclusion rule.  Schrödinger’s wave equation, to model standing waves in the atom, was a big step, but relating the wave function to real probabilities was formulaic. Kumar quotes Murray Gell-Mann on the “mysterious, confusing discipline which none of us really understands”, yet quantum theory (QT) became mainstream intellectual intercourse in the first half of the twentieth century and has spun off popular concepts and mythology lasting to the present day. 

Nevertheless, QT is not a ‘complete’ theory, while its rules and equations do not amount to explanations.   Kumar describes the epic series of thought-experiments in the battle between Einstein and Bohr, culminating in 1935’s famous EPR paper (Einstein-Podolsky-Rosen).  Einstein challenged QT as an “incomplete description of reality”, but its giving the observer a privileged position and not explaining the measurement process (collapse of the wave function) were easy targets. 

Einstein’s basic, underlying objections were to ‘spooky action at a distance’ (faster-than-light influence) and denial that an underlying reality exists (in ‘hidden variables’).  He won over Erwin Schrödinger to declare ‘measurement of separated systems cannot directly influence each other – that would be magic’ (‘separability’ and ‘locality’ principles) and devise his famous Cat, which ridiculed the quantum notion of superposition of (live and dead) states.                                                                                                              

John Bell in the 1960s, post-Einstein, disproved a famous mid-30s disproof of hidden variable theories and proposed tests of ‘locality’ via ‘Bell’ inequalities.  The experimental testing used EPR’s paired particles - however photon pair experiments of the next decade were inconclusive.  Kumar suggests a 1983 experiment (Alain Aspect) was near conclusive and ‘loopholes’ were closed off, but does not see the extra assumptions of ‘fair sampling’ and ‘no enhancement’ by the photo-detectors (crisisinphysics.co.uk*).  

Kumar scarcely mentions the subsequent 25 years.   New experiments in non-linear optics found that laser light photons passing through optical crystals appear to divide into two lower frequency photons (parametric down-conversion). Experiments with such ‘entangled’ photons led to ‘bizarre’ quantum interpretations – behaviour depends on whether an observer could look, not on whether s/he actually detects which path a photon takes.  Field theory (Faraday-Maxwell) appears more natural, describing ‘entanglement’ simply as correlated phases of two light waves and the dividing process as coupling of two wave oscillations in crystals with complex refractive properties. 

Media critics in welcoming Kumar’s book appear unaware of the restricted, paradigmatic physics relating to the closed teaching of modern UK courses, despite notable sceptics like Roger Penrose and recent popularised challenges to physics orthodoxy from within (eg. Lee Smolin).  Kumar draws no lessons from philosophical analysis, nor gives pointers to physics emerging from its 20th century impasse.  To rehabilitate Einstein’s pioneering insistence on physical reality needs an author with greater courage and deeper appreciation of fundamentals.


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