The Philosopher of Quantum Reality

by David Kordahl

This column is ultimately a review of A Guess at the Riddle: Essays on the Physical Underpinnings of Quantum Mechanics, the short new book by David Z Albert, a philosopher at Columbia University and (as I found out last week) the graduate advisor of the founding editor of 3QuarksDaily, S. Abbas Raza. Unlike Raza, I have never met Albert, but my parasocial relationship with his work is midway through its second decade, which I am now acknowledging upfront.

I first became aware of David Z Albert when I was an undergraduate at a small Lutheran college in rural Iowa. On its top floor, the Wartburg College library had a large painting of Martin Luther, our hero, overseeing a bonfire of Catholic theology. But in the basement, where the unburnt books were held, I found a copy of Albert’s 1992 debut, Quantum Mechanics and Experience. The book’s style seemed wholly unusual to me. As a physics student, I wasn’t accustomed to books that were at once about science but somehow separate from it. I was impressed how Albert had retained only enough detail for a conceptual critique. I didn’t know, then, that its peculiar patois was just that of the analytic philosophers, with Albert merely adopting an eccentric dialect of that communal tongue.

In my last column for 3QD, I wrote about how quantum models work. A physical system is associated with a quantum state. As time passes, the quantum state changes according to a deterministic rule, the Schrodinger equation, branching smoothly into distinct outcomes. At the end, you compare how much of the wave-function—what percentage of its total squared amplitude—is parked in each possible branch, and this gives you the probability of observing each outcome.

Quantum Mechanics and Experience is a book about the measurement problem in quantum mechanics, which (roughly) is the question of how nature decides which one of the predicted possibilities within the final quantum state we actually end up observing. Albert’s book wasn’t my first exposure these issues—I had read Nick Herbert’s 1987 book, Quantum Reality, a few years earlier—but it represented the first time I got the sense that these issues were still debated, and still up for grabs.

The summer before I first entered physics grad school, I read Albert’s follow-up book, Time and Chance (published in 2000, read by me in 2008), which did for thermodynamics what his previous book had done for the measurement problem. That is, it made thermodynamics seem dangerous, strange, deep.

But I soon found out that physicists are not, in general, very sympathetic to the philosophical approach. When I told my physics advisers that I enjoyed reading philosophy of physics, even professors who explored such issues themselves warned me off. “David,” one told me, “you have to understand that these people”—philosophers—“are two hundred years behind us! They’re not used to being challenged. When they talk to actual physicists, they leave shell-shocked!

Three years later, I left grad school, myself a bit shell-shocked, quitting without finishing a dissertation. I stopped thinking of myself as a physicist—at least, to the extent that that was possible while still earning a living teaching physics—but kept track of my old heroes. For instance, I was delighted by Albert’s public tiff with the physicist Lawrence Krauss, where Albert wrote an extremely negative New York Times review of Krauss’s book, A Universe From Nothing, and Krauss, as a physicist, didn’t enjoy being challenged.

I clearly had things to learn from Albert, who, love him or hate him, could make his preoccupations intelligible. A few years later, in 2015, I saw that Albert’s third book, After Physics, had been published, and I jumped at the chance to review it. My review was, unsurprisingly, a rave. I was fully on board with Albert’s project, which I understood as helping us to imagine what our scientific accounts really imply.

The godfather of such realist attempts at making sense of quantum theory was John Stewart Bell, whose papers on the subject were collected as Speakable and Unspeakable in Quantum Mechanics a few years before his death in 1990. (Last year, 3QD contributor Jochen Szangolies discussed Bell’s famous theorem in a lucid column.) Much of what Albert has written on quantum theory, so far as I can tell, involves making explicit what was quietly implicit in Bell’s work.

Consider the idea I found most startling in After Physics. Albert first expressed this startling idea in his 1995 paper, “Elementary Quantum Metaphysics,” where he described it as deriving from “a few casual remarks scattered here and there in various papers and private communications of John Bell.” Either with extreme modesty or extreme hubris, Albert found the idea to be “so straightforward and so ineluctable to me since then as not to merit any further discussion.” Here it is: if we take quantum theory seriously, the three-dimensional space of our everyday experience is an illusion, a shadow on Plato’s cave. The real space to consider is the 3N-dimensional configuration space of the wave-function, where N is the number of particles in your universe—a number estimated, in our universe, to be on the order of 1080, not even counting contributions from neutrinos or light.

This all sounds a little nuts, and it finally brings us to the new book.

A Guess at the Riddle is, as mentioned, a short book, 130 small pages including the index. It’s compact because Albert doesn’t repeat anything from his other books. Since he explained them in Quantum Mechanics and Experience, Albert expects readers to understand Bohmian, GRW, and Everettian approaches to quantum measurement. The “past hypothesis,” a term coined in Time and Chance, is used without explanation, as is the “Mentaculus,” a joke he introduced in After Physics. Take this as a warning. I could follow his arguments, but I’m a superfan.

In the new book, Albert returns to the subject of quantum mechanics to ask, can we imagine a quantum world? Albert insists that we shouldn’t let the old historical baggage get in our way. The first step in this is to flatly admit that

the attempts of Bohr and his circle to come to grips with this riddle somehow got off on the wrong foot, and all of a sudden Hegel and Kierkegaard and Buddhism and modernist crises of representation and principles of complementarity and verificationist theories of meaning and alternative systems of logic and interactive dualism and the cold war and the House Un-American Activities committee and God knows what else got dragged into the conversation, and the result was a gigantic and protracted intellectual disaster.

Good. (Albert is fond of single-word, single-paragraph declamations of this sort.) So what can we do, instead, that might allow us to bypass all that guff?

There are just three essays here. The first two present new arguments in favor of the sort of wave-function realism that Albert has been defending since the mid-90s, and the third piece…well, I’m not entirely sure, but I’ll take a stab at it.

“A Guess at the Riddle,” the first long essay, is a revised version of a paper that used to be titled “How to Teach Quantum Mechanics” (no doubt an homage to J.S. Bell’s “How to teach special relativity”). This piece labors to make the reader aware that the dynamical “space” that emerges in quantum mechanics is conceptually distinct from the physical space that we mark off with meter sticks. To make this clear, Albert works through simple examples with one particle described in one dimension, one particle described in two dimensions, and so on.

But the moral, here, is essentially the same as that of “Elementary Quantum Metaphysics,” or of the essay “Primitive Ontology” in After Physics. The world may not be as it seems, but that doesn’t mean it isn’t some particular way:

The trick (in a nutshell) is to learn to think of what we see in our experiments as the to-ings and fro-ings of shadows on a wall. The idea is that all those to-ings and fro-ings can actually be understood, the idea is that all of those to-ings and fro-ings can actually be explained, notwithstanding their almost unspeakable original weirdness, in terms of a simple and visualizable and mechanical account of something that’s going on (as it were) behind our backs, in a part of the cave at which we are forbidden to directly look.

The second essay, “Physical Laws and Physical Things,” argues for the fundamental status of wave-functions in a different way. Albert notices that it’s logically possible to get rid of elements of a theory by moving their status from that of a physical thing to that of a physical law. Logically possible, but incredibly weird—the physicist’s version of a reductio ad absurdum. Albert applies the argument to a version of quantum theory, and notes how it would be strange not to go with what the theory seems to be telling us—i.e., that the wave-function is a physical thing, not something up at the level of a physical law.

But in the third essay, some doubts surface. This last essay, “The Still More Basic Question,” addresses those who harbor skepticism that the wriggling of stuff in some stupendously high-dimensional space (i.e., that of the quantum wave-function) can credibly be reduced to the tables, chairs, rocks, and trees of common experience. To put this sharply, Albert invents a fanciful protagonist:

Image that somebody—call her Darleen—says, “I have a new proposal for a fundamental physical theory of the world: The world consists entirely of fundamental objects called schmoozles, whose physical states evolve in time in accord with such-and-such equations of motion. Tell me what you think!” And we tell Darleen that we have no idea what to think, because she has told us nothing whatever about how to apply her theory to the business of making predictions about the behaviors of the various macroscopic paraphernalia of our everyday experience of the world, and so we have no way to make a judgment of its empirical adequacy. And Darleen responds—apologetically—that she somehow neglected to mention, and that she certainly ought to have mentioned, that whenever the schmoozles are behaving this way then we have a table, and that whenever the schmoozles are behaving that way then we have a chair, and so on. And now we understand each other. Now we have been presented with a theory. And now we are in a position to consider the question of how well or how poorly this theory succeeds as an account of our empirical experience of the world.

Physics, unfortunately, only offers us schmoozles. Is that enough?

I should come clean about something. Since reviewing David Z Albert’s last book, I have once again joined the physicists. The year after I reviewed After Physics, I returned to physics grad school, joined a research group, and wrote a dissertation. Along the way, some of the physicists’ attitude of pragmatic dismissal rubbed off on me. And I’ll admit that I felt exasperated by the end of A Guess. I wish that Albert’s discussions connected with ongoing scientific investigations, as the strongest arguments against wave-function realism (cf. David Wallace’s “Against Wavefunction Realism”) stress that its scientific content is about one century behind, stuck with the puzzles of the 1920s, rather than practices of today.

Still, many physicists stop thinking when they moo about philosophy, and Albert has proven himself time and again to be a visionary who faces these old puzzles without flinching. I hope, in another half-decade, to read his next book.