A book review by Bobulous.

The tagline on the front cover reads Einstein, Bohr and the great debate about the nature of reality

, which is fitting because this book focuses on the physicists as much as their discoveries. And the subject which gets the greatest amount of coverage is the long, passionate, and at times heated disagreement about how to interpret the observations and theorems that solidified into what became known as quantum mechanics.

Beginning with a prologue that sets the scene, stating that physicists of the late nineteenth century felt confident they'd pretty much found all the pieces and behaviours that made up the universe, the next chapter introduces the cause of future unrest. Max Planck, while studying the blackbody problem, was forced to model heat transfers as being split up into chunks that he named quanta, each quantum only permitted to have an amount of energy that was the product of its frequency and a constant that took Planck's name. This nicely explained the blackbody behaviour, but at the time neither Planck nor his peers actually believed that energy was anything but a continuous stream, and they saw this quantum model as purely a short-term fix that someone would iron out later.

Albert Einstein played a major role in the early development of the quantum, modelling electromagnetic energy itself (such as visible light) as being comprised of quanta (called photons). Using this quantum model he made predictions about phonomena such as the photoelectric effect, and his model proved its worth when the predictions later turned out to be correct. Much to the consternation of those who had always believed that electromagnetic energy existed as waves rather than particles.

A few years after Einstein's breakthroughs, a Danish physicist called Niels Bohr was busy trying to resolve problems in Rutherford's atomic model. His solution was to model the atom such that electrons could only hold certain orbits, again tied to Planck's constant, and that it was electrons instantaneously jumping between these permitted orbits which explained why different elements emitted specific energies and frequencies. His model was initially greeted with horror, but was quickly adopted as experimental data matched his predictions.

Other talented physicists helped to form a model known as quantum mechanics. The mathematics of the quantum model clearly fit with experimental data, but how should the theory be interpreted? What did it say about the universe itself? Bohr believed that the theory showed that particles don't have properties until an observation measures those properties. Einstein loathed this idea, and believed that particles have an inherent reality of their own, whether or not observations are made. Einstein and Bohr came to stand on either side of a split that divided the theoretical physics community for years.

The author does a good job of describing the fundamental concepts of quantum theory, focusing on the tales of the physicists and eschewing mathematical exposition. The tales of the players are clearly laid out, looking at their paths into science, the discoveries and theories they made, the troubles caused them by the first and second world wars, and the pressures they felt to solve the mysteries thrown up by this new and strange area of physics.

I had been hoping for a chapter about the modern applications of quantum theory, and where current research is going, but these are barely mentioned in the final chapter. That is fitting, really, as this book is a history of the people who founded quantum physics, rather than a clinical exhibit of the theories and applications. And as a history of the strangest realm of physics, Quantum by Manjit Kumar does an excellent job.

[Note: Looking back on my review of Quantum Enigma, I have to say that I'm even less convinced now having read Quantum. For a start, Quantum briefly mentions a viable alternative to the Copenhagen interpretation: the many worlds interpretation, which does not require consciousness. And according to Quantum, Bell's inequality led to the conclusion that at least one of either underlying reality or locality have to be abandoned, which is not the same as Any objects that have ever interacted continue to instantaneously influence each other

.]