Book Review: What Is Real?
For a non-trivial portion of my life, I’ve held an understanding of quantum theory that puts me somewhere on the knowledge ladder between a five year old who has read Quantum Physics for Babies and Niels Bohr. The fundamentals of atomic structure that govern everything from chemical reactions to the generation of radiation were etched deep into my brain by my high school chemistry and physics teacher (shout out to Mrs. Jacobsen!), but both high school and first-year university physics focused, as they should, on classical mechanics—after all, you need to know what a wave is and what a particle is before (should that be if?) you can grasp wave-particle duality. In the decades since my formal physics education ended, I’ve read dozens of books either exclusively devoted to quantum theory (e.g., Manjit Kumar’s Quantum: Einstein, Bohr, and the Great Debate about the Nature of Reality, thanks to which I—finally!—understood blackbody radiation and its role in the formulation of Planck’s law) or that integrate it as a core topic for conversations on, say, relativity or cosmology or particle physics (e.g., Stephen Hawking’s A Brief History of Time, Sean Carroll’s The Big Picture, David Bohm’s Wholeness and the Implicate Order, and a ton more that I can’t recall because my books have been sitting upstairs in unpacked boxes for three years). I would like to tell you that, after all the years and brain cells devoted to consuming volumes of information, I have a firm grasp on the subject (at least as firm a grasp as someone who can’t do the math but can read words and more or less derive meaning from them can manage), but a more accurate depiction of the state of my hold on the matter involves a cat other than Schrödinger’s: conjure, if you will, the time-worn meme of a kitten clinging to a branch with a single paw that is, clearly, about to slip.
Turns out, physicists don’t fully understand quantum physics either, or so contends Adam Becker in his book What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics. The pro cats are more securely ensconced among the branches of the quantum tree than this little meowmer, but as to understanding why any of us are up this particular tree in the first place, well . . . a hundred-plus years of quantum physics and it’s still not clear. This mystery of the meaning is what drives Becker’s work, and he has the bona fides to probe it: he has a doctorate in computational cosmology and is currently the Science Communicator in Residence at the Simons Institute for the Theory of Computing at UC Berkeley.
If you are the sort of reader who wants the mystery resolved by the time you reach the end of the book, skip What Is Real? and curl up instead with a cozy mystery from Richard Osman or Rita Mae Brown or a classic from Christie or Conan Doyle. This lack of resolution, however, is not due to an inability to knot the narrative bow by Becker but is, instead, simply the reality of contemporary physics. We have found in quantum physics a remarkable tool that:
tells us how long it will take to heat up your frying pan to cook your eggs and how large a dying white dwarf star can be without collapsing. It reveals the exact shape of the double helix at the core of life, it tells us the age of the immortal cattle on the rock walls at Lascaux, it speaks of atoms split beneath the stone heart of Africa eons before Oppenheimer and the blinding light of Trinity. It predicts with uncanny accuracy the precise darkness of the blackest night. It shows us the history of the universe in a handful of dust. (275)
Now that’s pretty fucking useful. But the ability to use something does not imply that the user knows how that something works. I have a smart phone, and while I understand some of the fundamentals—e.g., the rf that carries the voice and data in my plan; the capacitance that allows my finger to touch a screen and pull up a picture or open an app; the millions of transistors etched into a tiny silicon chip that play stop and go with the flow of 1s and 0s and bring everything on that phone to life—I have no bloody idea what all else is happening in that lovely little metal and glass box, much less how all of it comes together to create a device—a tool—that works, and works beautifully. There are, of course, people who do understand how this tool works because it was built by people. But dumb ole me, who isn’t one of these brilliant folks, can still use the tool they engineered.
Quantum physics was built by people, but the universe in which we use it was not. Despite the myriad uses to which we have successfully applied this tool over the last century, there is a problem at the heart of quantum physics that has not been resolved: the measurement problem. If you adhere to the Copenhagen interpretation, you are likely muttering something to the effect of what measurement problem; there is no measurement problem followed by a stream of imprecations both wide and deep aimed at my empty head. But I, like Becker—and Bohm, Bell, Einstein and others before him—believe the measurement problem is a problem and by no means a trivial one. The very existence of objective reality hinges upon its answer, and on a more human scale, the matter of how we define science and its purpose is reflected in our willingness to ignore or address it.
So what the hell is the measurement problem? Pretty much the entirety of What Is Real? is devoted to explicating not only the problem and its history but also why it is a problem and what the potential resolutions to it might be, so condensing all that into a few words that provide both a thorough and accurate description is not something I’m going to do well. But here’s the gist. If you roll a billiard ball across a pool table, you can measure several things about it at once. You can, courtesy of classical physics, measure its velocity, its position on the table (though that position changes as it rolls; cue differential calculus), the direction in which it’s moving, etc. But when scientists started looking at atoms and subatomic particles like electrons and photons, they noticed something peculiar. If they measured how fast the particle was moving, they could not measure its position with any precision. If they measured its position, they could not precisely determine its velocity.
Why is this the case? Atoms and subatomic particles are tiny compared to billiard balls and other objects we see and interact with in our daily lives. For example, a billiard ball is ~ 6 centimeters (6 hundredths of a meter, .06 m or 6 x 10-2m) wide, while the largest atom is 343 picometers (343 trillionths of a meter, .000000000343 m or 343 x 10-12) wide, making the billiard ball roughly 174,927,114 times bigger than the biggest atom. That’s a pretty ginormous difference in scale, so perhaps classical physics doesn’t apply in the atomic—much less the sub-atomic—realm. And as time wore on and more physicists performed more experiments, it became clearer and clearer that whatever was happening here was not classical mechanics writ small. Here was a brave new world in which particles were waves, each of which had its own wave function that determined its behavior according to the Schrödinger (he of cat fame) equation. The wave function is essentially a probability—the probability that, given the universe, you will find a particle in a particular spot therein.
Here's where the weirdness train really picks up speed. The instant you perform some measurement on a particle—say, an electron—its wave function collapses—that is, “it [the wave function] instantly becomes zero everywhere except in the place where you found the electron” (17). Why is this weird? It seems obvious that once you know where a electron is, it can’t be anywhere else. But why does your measurement of the particle cause its wave function to collapse? As Becker continues: “somehow, the laws of physics seem to behave differently when you make a measurement: the Schrödinger equation holds all the time, except when you make a measurement, at which point the Schrödinger equation is temporarily suspended and the wave function collapses everywhere except a random point. This is so weird that it gets a special name: the measurement problem” (17-18). And even if you accept that, for whatever reason, measurements change the world on a quantum scale, how do you define a measurement?
Does a measurement require a measurer? Does the quantum world depend on whether it has an audience? Can anyone at all collapse a wave function? Do you need to be awake and conscious for it, or can a comatose person do it? What about a newborn baby? Is it limited to humans, or can chimps do it too? “When a mouse observes, does that change the [quantum] state of the universe?” Einstein once asked. (18-19)
This is the quantum physics equivalent of “if a tree falls and there’s no one to hear it, does it make a sound?” I took a few sips from the deconstructionist Kool-Aid back in grad school, but I found the taste foul and spit it out with haste. My experience of reality is surely subjective, but that there is an objective reality outside of me that existed long before I made my earthly debut and will exist long after I depart the stage and is, save for the brief span of spacetime during which I will inhabit it, utterly indifferent to my existence is not a question but a fact. My knowledge of objective reality is limited by my experience, my intelligence and the perceptual apparatus (both biological and technological) with which I apprehend and process it; thus, my version of that reality is inherently partial and subjective. But it is that reality beyond in which my own little subjective self dwells and tries heartily to understand. If I take my little subjective bubble to be the measure of the universe and declare that nothing exists beyond its bounds, I am a solipsistic narcissist with nihilistic tendencies who believes in nothing but myself—but I’m damned confident in that belief. Imagine what would happen in a world full of such folks when their bubbles collide and burst—and none of them believe in a shared objective reality that could provide common ground for the creation of a collective (if still subjective) reality. No need to imagine it; welcome to the 21st century. But like it or not, brothers and sisters of this terrifying time, the fucking tree makes a fucking noise every fucking time it falls. Get over your damn selves.
As for physics, the measurement problem is definitely a bit of a pickle, leading to everything from cats who are both alive and dead until we observe them to entangled particles (i.e., particles that share the same wave function) that “change” simultaneously the instant one of them is measured even if they are separated by phenomenal distances, the message regarding the measurement “transmitted” from the measured to the non-measured particle faster than the speed of light (which justifiably freaked out Einstein, whose special relativity recognized the speed of light as the universal speed limit, so much so that he labeled this “spooky action at a distance”). If someone walked up to you on the street and started telling you all of this stuff, you’d likely think he was batshit crazy, but when a group of highly trained and well-respected scientists conclude, based on both experiment and theory, that, yeah, it’s weird, but, well, measurement changing the thing that is being measured is just the way the quantum world works and the measurement “problem” is no problem at all, we call it the Copenhagen interpretation and dole out the Nobel Prizes.
Which are deserved because, by golly, the world does seem to work this way. Recall the laundry list of things noted above that quantum mechanics has enabled us to learn, create and do and add to it everything from the aforementioned smartphone I tote around in my pocket to the incredible images provided by the James Webb Space Telescope to the determination, via radiometric dating, that our home planet is 4.54 billion years old. Even with all of the complications around the measurement problem (and those complications are more complicated than I’ve covered here; Becker’s book provides the deep dive that does them justice), the math behind the Copenhagen interpretation just bloody works.
However, please note the use of the word interpretation in the previous sentence. The online version of the Cambridge Dictionary defines an interpretation as “an explanation or opinion of what something means” (https://dictionary.cambridge.org/us/dictionary/english/interpretation). And that is exactly what the Copenhagen interpretation is: an explanation—or more precisely, a set of explanations since the Copenhagen interpretation includes explanations proffered by a range of physicists that, despite minor variances, are similar enough to be grouped together under the “Copenhagen” banner—of quantum phenomena. And while they might have small differences in interpretation, the scientists who contributed to the founding of what we call the Copenhagen interpretation “all agreed that it was pointless to talk about what was ‘really’ happening in the quantum world” (49). Becker continues:
It was enough to merely describe measurable features of the world accurately, without talking about what was actually happening. Quantum physics, in short, shouldn’t be taken seriously as a theory of the way the world actually is. Instead, quantum physics is a mere tool, an instrument for predicting the outcomes of measurements. (49)
This is not merely Becker’s interpretation of the Copenhagen interpretation’s founders’ interpretation. Here’s what Neils Bohr himself, Copenhagen’s grandaddy, said about physics generally: “’It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature’” (49).
Really? If the task of physics is just to say things about nature, we’re all physicists. We all can make observations: the sky is blue, the ocean is filled with waves, thunderstorms occur. And we all can come up with explanations: the sky is blue because blue is god’s favorite color, waves are the result of Poseidon waving his trident, thunder means the gods are bowling. But observing phenomena and hypothesizing about them are not sufficient for science. Measuring these phenomena in some way brings us closer to science, but measurement itself is not science. Using a thermometer to tell me it is currently 72 degrees outside does nothing to tell me why it is 72 degrees. To understand the why behind my current meteorological conditions, I need to understand how a lot of things work. Current conditions are a direct result of previous conditions, so I need to understand how time works and that the past affects the present. It rained earlier today, so understanding how the evaporation cycle works and how it acts as a sort of atmospheric heat release valve helps me understand why my rainy today is cooler than my sunny yesterday. There’s a good breeze blowing from the west, so understanding how wind is generated as a result of an atmospheric pressure differential that may be related as well to a temperature differential can also help me understand that 72 degree reading.
Observation plus explanation, or even observation plus explanation plus measurement, provides some understanding of the world, and that understanding may of course, be very useful. Knowing that burning coal produces heat powered the Industrial Revolution, an historical inflection point if there ever was one. But having the ability to run a steam engine does nothing to explain why the coal in the boiler can heat the water and produce the steam that drives the engine. Bohr and company might be satisfied with calculating how much coal is necessary to produce sufficient steam to drive a train 20 miles down the track, but fortunately for them, their forebearers were not. Maxwell, Roentgen, Rutherford, Lord Kelvin, Planck and many, many others puzzled over electromagnetism and radiation, stopping not at the observation of these phenomena but reaching always toward an understanding of how they occurred and what that said about nature, and it was their work that laid the groundwork for Heisenberg, Schrödinger, de Broglie, Born, Bohr and others to observe, theorize and develop the mathematics sufficient to turn quantum mechanics into the marvelous tool that it is. And with that, quantum physics, its task fulfilled, was done.
But not all physicists share Bohr’s view of physics—or the completeness of quantum physics. Becker discusses many of these physicists—David Bohm, John Bell, Hugh Everett III, etc.—and explicates the theories they have advanced, looking into the field of quantum foundations in some detail. But long before quantum foundations was a recognized area of inquiry, another physicist with a Nobel of his own adhered to a very different view of physics from the view held by Bohr and others, a view that led him to doubt the Copenhagen interpretation.
In an essay replying to Bohr and other critics in 1949, [Albert] Einstein wrote that what he found unsatisfactory about quantum physics was that it denied the possibility of “the programmatic aim of all physics: the complete description of any (individual) real situation (as it supposedly exists irrespective of any act of observation or substantiation). (173)
In other words, it is the job of physics to describe why the fucking tree makes a fucking noise every fucking time it falls. Einstein again: “’What we call science . . . has the sole purpose of determining what is’” (173). He did not doubt that the behaviors reported by quantum mechanics did, in fact, occur, nor did he deny the efficacy of the calculations couched within quantum physics. What he doubted was that the theory the Copenhagen group advanced was complete. His doubts were expressed in a paper he published with Boris Podolsky and Nathan Rosen in 1935 aptly entitled “Can Quantum Mechanical Description of Physical Reality Be Considered Complete?” but more famously known as the EPR paper based on the initials of the last names of its authors. Einstein was not particularly happy with the paper; he told Schrödinger shortly after it was published that it “’was written by Poldolsky after much discussion. Still, it did not come out as well as I had originally wanted; rather the essential thing was, so to speak, smothered by the [mathematics].’” (55)
Rather than smother you with mathematics and delve deeply into EPR’s argument, I will content us both by noting that its primary concern is locality, i.e., “the principle that something that happens in one location can’t instantly influence an event that happens somewhere else” (51). Einstein rejected the violation of locality quantum phenomena suggest not by denying that the violation of locality did seem to occur (the “spooky action at a distance” referenced earlier) but by asserting that, in fact, locality is not violated and that quantum theory itself was incomplete because it could not explain what was actually happening. After the paper was published, he wrote the following to Max Born:
When I consider the physical phenomena known to me, and especially those which are being so successfully encompassed by quantum mechanics, I still cannot find any fact anywhere which would make it appear likely that [locality] will have to be abandoned. I am therefore inclined to believe that the description of quantum mechanics in the sense of [the Copenhagen interpretation] has to be regarded as an incomplete and indirect description of reality, to be replaced at some later date by a more complete and direct one. (56)
This assertion did not sit well with the Copenhagen crew, and Bohr made a response to Einstein that reassured his followers—so much so that most physicists to this day adhere more or less to Copenhagen and have generally considered anyone who strays from the flock as not doing real science.
Becker devotes the last chapter of the book to theorizing about why this is the case. He cites the astounding success of what physicist N. David Mermin has termed the “’Shut up and calculate!’” (227) methodology of Copenhagen, and the fact that the Copenhagen interpretation was the first formulation of quantum physics. He also notes that “[t]he deep problems at the boundaries of physics—quantum gravity chief among them—have not yielded solutions for decades” (285), a potential consequence of the scholarly consensus that quantum physics as we know it is complete and has been since Bohr and company formulated it nearly a hundred years ago. That adherence has consequences: “[s]imply dismissing the quantum world as a convenient mathematical fiction means we aren’t taking or best theories of the world seriously enough, and we are hobbling ourselves in the search for a new theory” (287). Seriously considering other potential interpretations of quantum behavior—the pilot wave interpretation, the many worlds interpretation, the spontaneous collapse interpretation—could bring us to that more complete and direct description of reality Einstein foretold. As Becker notes: “Quantum physics is at least approximately correct. There is something real, out in the world, that somehow resembles the quantum. We just don’t know that that means yet. And it’s the job of physics to find out.” (287) I truly hope it does.
Learn more about Adam Becker and his work.