The development of quantum physics through the 20th century is one of the great adventures of science, and here at last is a book aimed at the layperson which clearly explains its key concepts, while situating the scientific development in its broader setting. The result is a challenging and enthralling read.
Quantum is appropriately sub-titled, Einstein, Bohr and the Great Debate about the Nature of Reality. The long theoretical duel between these two giants of modern physics is a recurring theme of the book, but the story starts before them with the build-up to the discovery of Planck's constant at the turn of the century, and continues beyond their deaths (in 1955 and 1962 respectively) to take in Bell's Theorem and Everett's "many worlds" interpretation. Along the way we meet other great physicists such as Rutherford, Heisenberg, Pauli, Schrödinger, Dirac and Bohm.
One might suspect that a book of such scope would be in danger of being overcrowded with theories and theorists, yet Kumar rises to the challenge, displaying a novelist's sense of pacing allied with an impressive scientific clarity and succinctness. Clearly he has taken to heart the famous injunction attributed to Einstein to "make it as simple as possible, but no simpler!" He also strikes a judicious balance between scientific explanation and human context. This provided for me a welcome alternation between the physics and the lives of the physicists, with each stimulating an interest in the other.
What is so powerful and inspiring about this book is the way it conveys the passion for truth of those great pioneers. No doubt ego played its part as well, they would hardly have been human otherwise, but it is always secondary to the great quest to fathom the nature of sub-atomic reality. Characteristic of this passion is the anecdote of Bohr and Einstein on their first meeting in Copenhagen, straightaway so engrossed in debate that they repeatedly miss their bus-stop. Kumar evidently resonates to this passion, and conveys it vividly in his narrative. Here is an extract from his account of Bohr's first meeting with Schrödinger, one of Einstein's key allies in the great debate:
"After the exchange of pleasantries, battle began almost at once, and according to Heisenberg, `continued daily from early morning until late at night'... During one discussion Schrödinger called `the whole idea of quantum jumps a sheer fantasy'. `But it does not prove there are no quantum jumps,' Bohr countered. All it proved, he continued, was that `we cannot imagine them'. Emotions soon ran high... Schrödinger finally snapped. `If all this damned quantum jumping were really here to stay, I should be sorry I ever got involved with quantum theory.' `But the rest of us are extremely grateful that you did,' Bohr replied, `your wave mechanics has contributed so much to mathematical clarity and simplicity that it represents a gigantic advance over all previous forms of quantum mechanics.'
"After a few days of these relentless discussions, Schrödinger fell ill and took to his bed. Even as his wife did all she could to nurse their house-guest, Bohr sat on the edge of the bed and continued the argument. `But surely Schrödinger, you must see...' He did see, but only through the glasses he had long worn, and he was not about to change them for ones prescribed by Bohr."
This book is a brilliant and compelling account of the genesis of quantum physics, but it is more than that. In the midst of today's pervasive cynicism and disorientation, it is an inspiring reminder of what the human spirit is capable of when it devotes itself passionately to the highest aim, that of understanding the truth of our reality.