Quantum versus Classical

This post is a review of The Infamous Boundary: Seven Decades of Controversy in Quantum Physics by David Wick. The book is intended to be a relatively popular exposition; for those who are experts/practitioners there is a mathematical appendix by William Farris. The booked is dated (published in 1995) but since quantum mechanics is still controversial, worth looking into.

The boundary refers to that between classical and quantum physics. I was attracted to the book because it is a relatively slim volume (244 pages) and on flipping through, seemed well arranged. On reading, it largely did not disappoint. Though I can hardly say the topic is lucidly clear to me (if anything the total opposite), I did gain some interesting insights, historical knowledge and anecdotal material from the text.

Wick, who is a mathematician by trade (sometimes I feel this gives the book, which is on physics, a refreshing slant) writes with clarity (except where it is simply not possible) and humor. The book is divided into crisp short chapters (each about 8 pages long).

Content

The book picks the story up with Mach who claimed there is no reality except for our sensations; Mach did not believe in atoms. The developments of Rutherford's experiments and Bohr's model follow, along with the work of Heisenberg and Schrodinger.

The conceptual struggles of these pioneers are described succinctly and with authority, including Einstein's disapproval of the probabilistic nature of quantum mechanics, culminating in the titanic Bohr-Einstein debates. These, as is well known, were won by Bohr.

Nonetheless, Einstein was not happy with the idea that quantum mechanics did not refer to an underlying reality - hidden variables - which was not statistical. Von Neumann's incorrect theorem 'proving' that there could be no hidden variables is described in the book; followed by the famous EPR paper, and the work of David Bohm.

Then the book comes to the work of John Bell, who devised a quantitative test for hidden variables; and Clauser and Aspect who implemented it experimentally. The observation of single atoms (rebutting Mach) and quantum jumps (rebutting Schrodinger who had refused to believe in them) is dramatically described.

So far the historical facts and scientific advances have kept the philosophical discussion in check. From this point on the book became increasingly opaque to me. There are discussions on linguistics, philosophy, psychology, mysticism and their links (or not) to quantum mechanics. A bunch is said about the double-slit experiment, which Feynman epitomized as the central mystery of quantum mechanics.

Summary

I felt this book was a useful resource. I might go back to it later just to figure out what the issues in the debate were. It has a wealth of painstakingly gathered information, including visits to labs and interviews with the relevant physicists (those that were still around).

The short chapters keep the author honest and away from too much philosophizing (except for those chapters entirely devoted to it). There is the best explanation I have seen, of why spooky-action-at-a-distance does not transmit any signals that violate special relativity (apparently originally due to Mermin).

The book maybe too much for a single read, but is definitely worth sampling repeatedly over time.