So two professors from the University of California at Santa Cruz decided to write a book on physics. Sounds like the beginning of a joke, right? A book on the physics of surfing, maybe? No, actually the book is on quantum mechanics. But that is not the worst part – the book is based on physics classes they taught to California liberal arts students!
At this point, most of us would be thinking about moving on down the bookshelf to see what else is available – but that would be a mistake. The professors have written an excellent, useful, thought-provoking book, aimed at making a complex issue accessible to a broad non-specialist audience:
“Quantum Enigma: Physics Encounters Consciousness”, by B. Rosenblum & F. Kuttner, ISBN 978-0-19-975381-9 (2011).
The professors point out that the teaching of quantum mechanics to physics students focuses principally on how to apply the complex mathematical formulation of the theory; little attention gets paid to what it all means. When trying to explain quantum mechanics to liberal arts students, that gets reversed.
After some preliminaries, the authors take the reader on a quick tour through the history of the development of the scientific method and its triumph in the testable predictions of Isaac Newton’s classical mechanics. (Interestingly, the determinism of classical mechanics implies there can be no such thing as free will – but that is usually ignored in polite company). The commonsense intuition underlying classical mechanics is that physical reality exists “out there”, independent of the observer. However, classical mechanics could not explain certain observations about the behavior of matter at the atomic scale, as experiments on that became possible around the turn of the 20th Century. Attempts to explain those puzzling experimental observations led eventually to the development of quantum mechanics.
The authors argue that quantum mechanics has been stunningly successful; not a single prediction of the theory has ever been wrong. And it is a key foundation for about one third of the modern economy, through such technologies as lasers, transistors, Charge Coupled Devices in cameras, and Magnetic Resonance Imaging machines. Nevertheless, quantum mechanics has some very odd implications.
The authors discuss the well-known wave-particle duality which has repeatedly been demonstrated for photons, electrons, and even assemblages of atoms. If an experiment is set up to observe a particle, then the observer sees a particle; if instead the experiment is set up to observe a wave, then the observer sees a wave. The real physical state of the entity apparently depends upon the conscious expectation of the observer.
Given the intended audience, there is a good slice of material in this book on the “human interest” angle – the people who developed quantum theory like Max Planck, Albert Einstein, Niels Bohr, John von Neumann, Louis de Broglie, Arthur Compton, Erwin Schrodinger, Werner Heisenberg, Max Born, John Bell. The authors provide a fascinating well-told history. The end result of the years of struggle trying to explain various experimental observations is a quantum theory based on the mathematics of wavefunctions. Such wavefunctions describe all scales of matter, not just the atomic level. Quantum mechanics encompasses classical mechanics as a special case, being a good approximation for larger aggregations of matter.
The enigma about quantum mechanics is that it tells us the reality of the physical world somehow depends on our observation of it – an entirely non-intuitive conclusion. This quantum enigma comes from demonstrable experiments – NOT from quantum theory. And those experiments show us something even less plausible than entities which can sometimes behave as waves and sometimes behave as particles. To quote the authors:
“Quantum theory also tells us that an object can be in two places at the same time. Its existence at the particular place where it happens to be found becomes an actuality only upon its observation. Quantum theory thus denies the existence of a physically real world independent of its observation.”
Although observation is an essential part of quantum mechanics, what constitutes “observation” is not explained within quantum theory and remains controversial. Einstein had particular concerns about quantum theory’s need for an observer; hence his remark, “I like to think the moon is there even if I am not looking at it”.
For a long time, the conventional “Copenhagen Interpretation” of quantum mechanics swept that enigma under the carpet and did not brook questioning; nowadays, interest in the enigma is no longer a career-limiting move for a young physicist, but there are no accepted answers to the various controversies. It seems that quantum theory inevitably leads to questions about the nature of consciousness and about the existence of free will. The authors try to explain ten of the various approaches which have been proposed to resolve the puzzles.
For this reader, John Bell’s assessment seems the most reasonable: quantum mechanics is not wrong, simply incomplete – a view which is consistent with that advanced by Einstein, Podolsky & Rosen in their 1935 EPR paper. But your mileage may vary.
There have been very few books where my first inclination on reaching the end was to turn back to the beginning and start re-reading it. This fascinating volume is one of those rare books.