A Guess at the Riddle: Essays on the Physical Underpinnings of Quantum Mechanics

By David Z Albert

From the celebrated author of Quantum Mechanics and Experience comes an original and exhilarating attempt at making sense of the strange laws of quantum mechanics.

A century ago, a brilliant circle of physicists around Niels Bohr argued that the search for an objective, realistic, and mechanical picture of the inner workings of the atom—the kind of picture that had previously been an ideal of classical physics—was doomed to fail. Today, there is widespread agreement among philosophers and physicists that those arguments were wrong. However, the question of what that picture might look like, and how it might fit into a comprehensive picture of physical reality, remains unsettled.

In A Guess at the Riddle, philosopher David Z Albert argues that the distinctively strange features of quantum mechanics begin to make sense once we conceive of the wave function, vibrating and evolving in high-dimensional space, as the concrete, fundamental physical “stuff” of the universe. Starting with simple mechanical models, Albert methodically constructs the defining features of quantum mechanics from scratch. He shows how the entire history of our familiar, three-dimensional universe can be discerned in the wave function’s intricate pattern of ripples and whorls. A major new work in the foundations of physics, A Guess at the Riddle is poised to transform our understanding of the basic architecture of the universe.

• Language: English
• Publisher: Harvard University Press
• Release date: Sep 19, 2023
• ISBN: 9780674294820

Book preview

Introduction

Quantum mechanics, when it was first written down, was famously obscure about the circumstances in which one or another of the possible outcomes of a measurement actually makes its appearance in the world. All it said was that the outcome emerges when the measurement is performed, and it offered no precise idea of what the phrase inside the quotation marks was supposed to mean.

You might have expected people to see that obscurity as a defect or an incompleteness in the quantum-mechanical formalism—you might have expected them to see it (that is) as something that needed to be fixed. But (as it actually happened) there was an enormously influential circle of physicists around Niels Bohr, at his institute in Copenhagen, who saw it very differently. It struck them as something revolutionary and profound. It seemed to them to point to a tension, the likes of which had never been encountered before, at the very heart of the scientific project itself.

The tension was supposed to run something like this: On the one hand, the language of classical physics was supposed to be indispensable to the business of observing and recording and communicating and reasoning about the outcomes of experiments—the language of classical physics was supposed to be indispensable (that is) to the general business of doing empirical science. And on the other hand, some of those experiments—the experiments (in particular) by means of which physicists had lately begun to explore the interior of the atom—were supposed to have shown that the language of classical physics was radically unfit for the business of actually describing the world.

And Bohr and his circle insisted that as soon as one had appreciated this predicament, as soon as one had taken the full measure of this predicament, it became clear that the obscurity I alluded to above was not susceptible of being fixed, and that the mechanism of the transition from the possible outcomes of a measurement to the actual outcome of that measurement was not going to admit of any detailed scientific account, and that the only way of making sense of the scientific project, and that the only way of going on with the scientific project, was to look at it through the lens of an especially militant version of instrumentalism. Science (on this way of thinking) is in no other or more expansive or more ambitious business than the business of predicting the outcomes of measurements. And the proper employment of words like measurement and outcome themselves, at least insofar as the discourse of empirical science is concerned, is as something like primitive terms. And so the business of analyzing how the elementary examples of measurement work, the business of clarifying how it is that the outcomes of elementary measurements ever actually make their appearance in the world, if there is any such intelligible business at all, can certainly not be the business of empirical science. And so the goal of somehow fixing or eliminating the obscurity I alluded to above is simply confused, and the traditional aspiration of physics—the aspiration (that is) to offer us a true and objective and exhaustive and literal and realistic and mechanical account of what the world is like—will need to be abandoned.

And all of this quickly hardened into a rigid and powerful orthodoxy. As early as 1927 (for example) Werner Heisenberg and Max Born were prepared to declare that the standard quantum-mechanical formalism, with all of its accompanying obscurity, amounted to a closed theory, whose fundamental physical and mathematical assumptions are no longer susceptible of any modification. And from then on, all sorts of questions about what things do, and how they work, were more or less universally declared to be nonsense, and the business of inquiring any further into these matters was actively and relentlessly and often brutally discouraged. Clear and simple and devastating critiques of the ideas of Bohr and his circle—from figures like Erwin Schrödinger and David Bohm and Hugh Everett and John Bell, and especially and particularly from Albert Einstein himself—were met with silence, or with derision, or with inexplicable misunderstanding, or answered with outright gibberish. Lives and careers were destroyed. And all of this persisted, in any number of different forms, and by any number of different means, and with undiminished zeal and intensity, for most of the previous century.

Bohr and his circle saw themselves as the vanguard of a brave and visionary and world-historical intellectual upheaval—and they saw figures like Einstein and Schrödinger and Everett and Bohm and Bell as somehow too timid, or too mired in what they called classical ways of thinking, to keep up. But a case can be made that exactly the opposite was true. A case can be made (that is) that what had always been genuinely revolutionary in the scientific imagination was the original and unbounded and omnivorous and terrifying aspiration to reduce the entirety of the world to a vast concatenation of simple mechanical pushings and pullings. And what Bohr and his circle were up to (on this way of looking at things) was a profoundly conservative attempt to somehow set a limit to aspirations like that.

And there is something poignant and remarkable about all of this having happened at just the historical moment that it did. It was precisely in the 1920s, and precisely with the advent of quantum mechanics, that the possibility of a unified and comprehensive and thoroughly physical account of our everyday empirical experience of the world first began to take palpable shape. Such things had, of course, been dreamed of before. Boscovich and Laplace (for example) had been thinking, as far back as the eighteenth century, about what things might be like if the world as a whole were governed by the laws of something like Newtonian mechanics. But nobody had any idea, prior to the work of Faraday and Maxwell and Einstein, how phenomena like electricity and magnetism and light were going to fit into the picture. And nobody had any idea, prior to the discovery of quantum mechanics, how atoms worked, or could work, or what chemistry might be about. And it must have been impossible even to imagine, prior to the work of figures like Darwin and Wallace and Boltzmann, what a believable mechanical account of the origins and designs of living organisms was going to look like. And it was only sometime in the 1920s that one could begin to see, dimly (to be sure) but well enough, how relatively ordinary sorts of scientific ingenuity might someday actually clear all these impediments away. And it was then that the logical positivists began to think about assembling their International Encyclopedia of Unified Science. And it was then that H. P. Lovecraft remarked, The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the light into the peace and safety of a new dark age. And you might say that it turns out to have been just that flight, and just that blindness, and just that dark age, that Bohr and his circle, at the last possible moment, at what apparently presented itself to many people as the very precipice of madness, bequeathed to us.¹

Anyway, as everybody knows, everything that Bohr and his circle had to say about these matters turns out to have been wrong. And we are now aware of a number of very promising strategies for modifying or completing or precisifying the standard quantum-mechanical framework in such a way as to simply eliminate the obscurity about the process of measurement that I alluded to above. And with that obscurity out of the way, physics can again aspire to offer us an objective and literal and realistic and comprehensive and mechanical picture of what the world is actually like. And there has lately been a great deal of interest in the business of asking what quantum mechanics itself may have to contribute to a picture like that.

And that latter business is the business of this book.

Here are two ways one might go about looking into the question of what it is that quantum mechanics has to tell us about the fundamental structure of the