Philip Ball’s Beyond Weird is the best popular survey I’ve seen of the contemporary state of discussions about the “interpretation” of quantum mechanics. It appeared earlier this year in a British edition (which I just read a copy of), with the US edition scheduled to come out next month. Since it’s already out in Britain, there are several reviews you can take a look at, an insightful one is Natalie Wolchover’s at Nature.
The topic of the “weirdness” of quantum mechanics is one receiving a lot of attention these days, with two other books also appearing this year: Adam Becker’s What is Real? (which I wrote about here), and Anil Ananthaswamy’s Through Two Doors at Once. Lack of time as well as not having much of interest to say about the book has kept me from writing about Through Two Doors at Once. It’s much more focused than the other two, giving close attention to the two-slit experiment and surprising variants of it that have actually been performed in recent years.
Some of what I very much liked about Beyond Weird is the way Ball avoids getting into the usual ruts that books on this topic often end up in (with the Becker book one example). He avoids the temptation to follow a historical treatment, something that is almost irresistible given the great story of the history of quantum mechanics. The problem is that the early history of quantum mechanics and the struggles of Bohr, Einstein and Heisenberg to understand what it was saying is a fascinating story, perhaps the most compelling in the history of physics, but it is one that has been well-told many times in many places. Books that cover the later history have found it hard to resist the temptation of revisionism, caricaturing Bohr, Heisenberg and the dominant “Copenhagen interpretation” while making heroes instead of David Bohm, John Bell and Hugh Everett.
Ball has little to say about the personalities involved, but instead seriously engages with the central troublesome issues of the quantum mechanical picture of the world. The Copenhagen interpretation is given a fair treatment, as a warning about the limits one runs up against trying to reconcile the quantum mechanical and classical pictures of reality.
Instead of spending a lot of time in the rut of Bohmian mechanics, Ball dismisses it quickly as
But it is hard to see where the gain lies… Even Einstein, who was certainly keen to win back objective reality from quantum theory’s apparent denial of it, found Bohm’s idea ‘too cheap.”
Dynamical collapse models like GRW also get short shrift:
It’s a bodge, really: the researchers just figured out what kind of mathematical function was needed to do this job, and grafted it on… What’s more of a problem is that there is absolutely no evidence that such an effect exists.
As for the “Many-Worlds Interpretation”, which in recent years has been promoted in many popular books, Ball devotes a full chapter to it, not because he thinks it solves any problem, but because he thinks it’s a misleading and empty idea:
My own view is that the problems with the MWI are overwhelming – not because they show it must be wrong, but because they render it incoherent. It simply cannot be articulated meaningfully… The MWI is an exuberant attempt to rescue the ‘yes/no’, albeit at the cost of admitting both of them at once. This results in an inchoate view of macroscopic reality suggests we really can’t make our macroscopic instincts the arbiter of the situation…
Where Copenhagen seems to keep insisting ‘no,no and no’, the MWI says ‘yes, yes and yes’. And in the end, if you say everything is true, you have said nothing.
There’s a lot of material about serious efforts to go beyond Copenhagen, by understanding the role that decoherence and the environment play in the emergence of classical phenomena out of the underlying quantum world. This discussion includes a good explanation of the work of Zurek and collaborators on this topic, including the concept of “Quantum Darwinism”.
The last part of the book is up to date on what seem to be some currently popular ideas about the foundations of quantum mechanics. One aspect of this goes under the name “Quantum Reconstruction”, the attempt to derive the supposedly hodge-podge axioms of quantum theory from some more compelling fundamental ideas, hopefully the kind your grandmother can understand. These ideas are conjectured to somehow have to do with “information” and limits on it. I’m not sympathetic to these, since the axioms seem to me not “hodge-podge”, but connected to the deepest unifying ideas of modern mathematics. At the same time, I remain confused about what “information” is supposed to be and how these new foundations are supposed to work. And, as far as I’ve ever been able to tell, these are not things your grandmother is likely to understand, unless your grandmother is Scott Aaronson…