Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality Illustrated Edition

The history of the development of quantum physics has been told many times, sometimes for the benefit of future physicists and sometimes more for the general public (as in John Gribben’s books). This book covers the same ground with two differences. One is that Manjit Kumar opts for a middle road in describing in more detail the history of the quantum. As in other histories, the same characters from Max Planck to John Bell are here with biographical sketches of each one in the text. But Kumar also presents more (not a lot) of the basic equations and more of the technical aspects of their work. Kumar does a fine job of digging into the details of the quantum revolution and the non-physicist can always gloss over the material he or she is not interested in. But, while the book is being sold as written for the general public and centered on the Bohr-Einstein debate about reality, it has more details than some readers may expect.The second difference from other histories of the quantum is Kumar’s emphasis (as the title indicates) on the difference between Einstein and Bohr on how to interpret the quantum results. Einstein never denied the reality of the strange results but claimed the theory was “incomplete.” Do cause and effect function at all levels of the universe independent of our observation? Einstein never wavered in the belief that a complete theory of reality could be understood causally (the famous “God does not play dice” quote) and that the weirdness of quantum results would be explained by (or be a subdivision of) that larger more complete picture. Bohr’s claim was that the “quantum world” (he did not like that term) did not function in the same way as our everyday world. Trying to find a theory that encompassed both was pointless because causality as we understand it could not be imposed on the subatomic world. If, as some have claimed, we have to think causally to make sense of our world, then we are in principle incapable of “understanding” the quantum dimensions. What we are left with is the math and the usefulness (and strangeness) of the results of quantum mechanics, from transistors to computers. There is no point trying to subsume electrons or quarks into our classical way of understanding.This is a fascinating debate and Kumar does an excellent job spelling it out when he gets there but he does not actually get there until two-thirds of the way through the book. When the Great Debate finally arrives, it is profoundly interesting. But the book’s title is somewhat misleading since the actual Bohr-Einstein debate is not sharply defined until Part 3, “Titans Clash Over Reality,” on page 251. Kumar covers a great deal of ground and his research is extensive. So, if the reader is looking for a book not just about the main debate itself but also a book with detailed background leading up to the Bohr-Einstein core disagreement, this book is ideal. I would then recommend it.

I have been reading books on the historical development of 20th century physics and especially quantum mechanics for about 40 years. The first I ever read was Banesh Hoffman's, The Strange Story of the Quantum" which woke me up to the debates in physics. Manjit Kumar's book is among the finest I have read during these 40 years. My own particular interest lies in the development and understanding of the periodic table and here Kumar's book has been extremely illuminating.I have previously presented a somewhat opinionated picture of Bohr's explanation of the periodic table as being somewhat ad hoc, to the extent that Bohr did not derive the configurations of atoms but rather cobbled them together after consulting chemical and spectral information. I am not alone in expressing this view and many historical sources stress how physicists like Pauli were also somewhat underwhelmed at the time by Bohr's explanation. However, on seeing Kumar's carefully reconstructed account of the events I realized more than ever that Bohr's work was still a tremendous triumph. For example Kumar notes how even Einstein was impressed by Bohr's theory. This is something that I will need to include in the eventual second edition of my book on the periodic table.Similarly, Kumar's book has given me a clear and simple way to present the discovery of the second and third quantum numbers. But these are all technical matters and may not be of much value to the general educated reader. I mention them just to emphasize that Kumar's book is a popular exposition but not a vulgarization.Kumar's book is a popularization in the best possible sense of the word, much like the work of Brunowski and Sagan. It presents a very much needed antidote to the, frankly shameful, popularizations by the boy-wonder of British science TV who among other things espouses a completely misleading account of the Pauli Exclusion Principle, apparently believing that heating a diamond causes an effect in every other electron across the universe.Returning to Manjit Kumar, I highly recommend his book to all scientifically literate readers. Complete beginners might feel a little lost but I am referring to those who enjoy the kinds of articles in New Scientist and Scientific American. What I especially liked was the combination of factual accuracy, an excellent historical narrative which helps to bring the major characters to life, and the philosophical insight expressed in a fairly non-demanding fashion. In addition I believe that experts in physics, chemistry, history of science and even the philosophical foundations of physics will derive great benefit from seeing the history of the developments laid out from such a clear and penetrating vantage point as this book achieves.

Based on the title I expected a detailed report focused on the great debate between Einstein and Bohr. However, when the narrative started with Max Planck I realized the contents was much broader. Kumar presents a very compelling account of the entire quntum revolution including all of the key players and the background drama that unfolded (and continues to unfold).At first I was dissapointed with the broader scope, however, as I continued I was impressed with Kumar's ability to draw me into the background of the people and the events. There wasn't a lot that was new to me, but the quality of his story telling made it a very enjoyable read. And, his account of the debate itself is excellent, including his description of the famous photo of Einstein and Bohr walking (and debating) together in Brussels during the 1930 Solvay conference.This is highly recommended for anyone, like me, who obsesses on the nature of reality.