Why would a successful investigative journalist spend three years writing a book about quantum mechanics?
Well, the answer is that he knew he'd found a story. Like most people, I had uncritically accepted the standard platitudes. If you think you understand quantum mechanics, that just shows you don't understand quantum mechanics. Or, as Feynman says in a memorable passage from The Character of Physical Law
, don't ask yourself how it can be like that. If you do, you will go down the drain into a blind alley that nobody has escaped from. No one knows how it can be like that.
But isn't this really very odd? There are plenty of difficult subjects in science, and people don't go around saying that it's impossible to understand them in intuitive terms. If you want to know about DNA, or relativistic cosmology, or chaotic systems, no one claims that they're incomprehensible. They just require intelligence and an appropriate investment of effort. Granted, you may not be smart enough to get it; but that goes for everything. Why should quantum mechanics be the great exception?
The central claim of this book is that there is, in fact, a way to understand quantum mechanics which makes perfectly good sense. It's been around for more than 50 years. There are two reasons why it hasn't caught on. The first is that it requires you to accept a major change in your view of the world: that there is not just one universe, but an infinite number of parallel universes, all equally "real", with new ones continually branching off. This is, needless to say, somewhat counterintuitive, but the same can be said of many novel ideas in science. Proponents of the Many-Worlds Interpretation (MWI) like to compare themselves with Copernicus. If you are just willing to accept that the Earth is not stationary in the middle of the universe but is a planet like the other planets, a large number of perplexing facts suddenly fall into place and make sense. The Many-Earths Interpretation of the Solar System also appears counterintuitive at first. Once you've got over the initial shock, however, you see that it's very clever; after a while, it almost starts to feel natural. The MWI is not dissimilar. Well, that was the first reason. The second, which is why this book ended up being written by a journalist rather than a scientist, is that it appears there was a determined effort by influential members of the scientific community to marginalize and ridicule the Many-Worlds Interpretation. The people concerned are some of the most revered names in 20th century physics, and the disrespectful way in which Byrne writes about them made me wince more than a few times. But it's hard to deny that he has a case.
As the title suggests, the central figure in the story is Hugh Everett III, a smart young grad student who was doing a PhD under the legendary John Archibald Wheeler in the early 50s. Wheeler mentored several generations of top physicists - his star pupil was Feynman - and he was one of the key people in the field for a long time. Many of his students just took Wheeler's ideas and elaborated them. But Everett was a natural rebel, and wanted to do his own thing. He started looking at the core conceptual issues in quantum mechanics and became convinced that the way people were thinking about them was completely wrong. Above all, he was sure that the whole idea of the "collapse of the wavefunction" was misguided. This was basically the thing that made quantum mechanics incomprehensible. When you looked at classic experiments like the "double slit", you saw that an electron gave every appearance of being in many places at once, as you could tell from the fact that it was apparently able to interact with other copies of itself; but as soon as you performed a measurement, the electron was suddenly just in one place. According to the standard Copenhagen Interpretation, the measurement caused all the other possibilities to disappear. But how could this make sense? Some people (Wheeler was one) guessed that the experimenter's consciousness had some mystical effect on quantum systems. Others preferred not to interpret the equations at all. The math worked: why did we need to worry about what it "meant"?
Everett argued that there was a straightforward explanation. There was no "collapse", and the other possibilities didn't miraculously disappear. They were simply not able to influence each other any more, a conclusion which seemed perfectly consistent with what was known about quantum mechanics. The natural way to conceptualize this was that every quantum interaction made the universe split into multiple copies which quickly separated apart. Critics of the MWI often complain that it violates Occam's Razor; they object to having all these other invisible universes. People who like the theory turn the argument around 180 degrees. They say that you can see the other universes quite clearly for a short time, and there is no reason to believe that all but one of them cease to exist when they stop interacting. It is, rather, the unnecessary "collapse of the wavefunction" which violates Occam's Razor.
Wheeler was intrigued by Everett's idea, and he agreed that the math made sense. But he was an enormous admirer of Niels Bohr, who was the chief architect of the Copenhagen Interpretation, and he felt unable to sign off on Everett's thesis without receiving Bohr's blessing. He made a determined effort to sell MWI to the Great Dane, but Bohr, who was now about 70, found the suggestion bizarre and incomprehensible. Wheeler, who had worshipped Bohr throughout his whole career, was unable to discount his opinion. He forced Everett to emasculate his dissertation and rewrite it to minimize the areas of conflict. Everett, disgusted with the way he felt he had been treated, left academia and went to work for the Pentagon. As we would say today, he went over to the dark side. He rapidly made a name for himself doing strategic planning for nuclear war scenarios; among other things, he worked closely with the diabolical Herman Kahn, widely reputed to be the real-life prototype for Kubrick's Dr. Strangelove. He became increasingly addicted to nicotine, alcohol and sex (he chain-smoked and patronized prostitutes), and died of heart failure at the age of 51. But his work lived on, and the MWI's profile has become steadily higher. It's an idea that just won't go away.
Peter Byrne, the author of this book, has done a great deal of work tracking down the various tangled strands of the story. He read through all of Everett's papers, which had been sitting in a California basement for 25 years, and he interviewed most of the surviving people who knew Everett. He has also spent a lot of time talking to physicists who like the Many-Worlds Interpretation. Some reviewers complain that there are mistakes in the science. That may be true (I am for example uncertain whether Byrne properly understands how Hilbert spaces are used in quantum mechanics, or if he knows what a Lebesgue measure is). But as far as I'm concerned, what's much more interesting is how much he seems to be getting right. My impression is that there are quite a few scientists who are reluctant to come out and say openly what they think about Everett, who is still rather controversial; they prefer to have their opinions ascribed to Byrne. And, whatever people may say in public, there is no doubt that Everett is being taken seriously. A quick look at Google Scholar shows over 2200 citations of his thesis: this is not the kind of attention that a fringe theory is going to attract.
The Many-Worlds Interpretation is one of the most interesting and thought-provoking ideas in modern science. If you want to know about the mathematical and philosophical details, I warmly recommend David Wallace's The Emergent Multiverse
. But if you want an unputdownable human account written in layman's language, then get Byrne. This is investigative journalism at its very finest.
Much as I liked the book, it is fair to warn the prospective buyer that the copy-editing is quite extraordinarily careless. There are slips and errors everywhere: the same name can be spelled differently in two chapters, "its" is sometimes confused with "it's", "xenophobic" is once spelled with a Z (my personal favorite), and a couple of sentences are just mangled completely, looking as though they were interrupted halfway through an edit. I honestly don't understand it. What happened?