What Is Real: The Unfinished Quest for the Meaning of Quantum Physics (2018)
Adam Becker (1984)
370 pages
Based on the title, physicist Adam Becker’s
What is Real: The Unfinished Quest for the Meaning of Quantum Physics promises a relatively sober, if potentially fascinating, exploration of how to understand what could be considered the fundamental scientific advancement of the 20th century. His book certainly delivers on the
fascinating part, providing an accessible discussion of efforts over the past century to achieve a consensus about the physical meaning behind the mathematics of quantum physics.
But whoo, boy, the path toward consensus has turned out to have been anything but sober and dispassionate, despite broad agreement that the theory is “wildly successful” (287) in explaining experimental results. Becker describes what has been a bitter, century-long internecine battle among physicists over how to interpret quantum physics, a struggle that has included broadside attacks against, and repeated backstabbing of, colleagues and students, and has even involved connections between some physicists’ interpretations of the theory and their political stance in the cold war disputes between Marxism and the West. And all of this has involved many of the most famous physicists of the twentieth century, as we discover in this entertaining tour of the history.
Who knew what darkness lurked behind the staid, popular image of objective scientists simply dedicated to pursuing understanding?
Early on, Becker introduces the central dilemma that has driven these disputes:
Quantum physics – the physics of atoms and other ultra-tiny objects, like molecules and subatomic particles – is the most successful theory in all science. … But … [it] doesn’t seem to apply to anything at human scale. … Why not? Maybe quantum physics really is only the physics of tiny things, and it doesn’t apply to large objects … [but then] where is the boundary, and how does it work? (1-2)
Even just the possibility of coming to a concrete interpretation of what the mathematics of quantum physics tells us about reality has divided physicists. Early in the 20th century, Niels Bohr, along with his colleagues and students at the Institute for Theoretical Physics in Copenhagen, “developed and championed” (13) what came to be known as the
Copenhagen interpretation of how to think about the quantum world. Summarizing it, Becker writes:
What does [the mathematics] of quantum physics tell us about the world? According to the Copenhagen interpretation, this question has a very simple answer: quantum physics tells us nothing whatsoever about the world. … According to Bohr, there isn’t a story about the quantum world because “there is no quantum world. There is only an abstract quantum physical description.” (14)
Effectively this constitutes, as one disparaging physicist later observed, a “shut up and calculate” (6) view of quantum physics – use the theory as a development tool that describes the quantum world, and don’t worry about trying to develop a detailed understanding of the reality of it.
The Copenhagen interpretation came to be, already in the first half of the 20th century, the leading way of thinking about quantum physics for most physicists. Some, however, had serious misgivings about its cavalier attitude toward knowing actual reality; Albert Einstein, for example, wrote that “the theory reminds me a little of the system of delusions of an exceedingly intelligent paranoiac.” (14)
Such criticism of the Copenhagen interpretation has been driven in large part by what is referred to as the
measurement problem. Schrödinger’s wave function, which lies at the heart of quantum physics, describes a particle’s behavior by “tell[ing] you the
probability that the electron is in [a particular] place.” (17) The measurement problem arises from the fact that
once you do find [an] electron, a funny thing happens to its wave function. Rather than following the Schrödinger equation like a good wave function, it collapses – it instantly becomes zero everywhere except in the place where you find the electron. 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 at a random point. (17-18)
And this inexplicable behavior, Becker points out, relates then to the
boundary problem of quantum mechanics: large objects do not seem to follow quantum behavior, and so there seems to be a boundary between the size of tiny objects that do, and larger objects that do not. But that boundary, or threshold, beyond which quantum mechanics apparently no longer applies, doesn’t appear to be definable.
Acolytes of Bohr’s Copenhagen interpretation, according to Becker, have effectively side-stepped these issues by viewing measurements as obeying classical physics – that is, they distinguish between the quantum world and the world of larger objects, but without ever defining where that boundary exists. They argue, in particular, that it can’t be known, and so isn’t worth pursuing.
Despite these criticisms, the predominance of the Copenhagen interpretation expanded in the wake of World War II according to Becker, as funding for physics – and the number of freshly minted physicists – increased dramatically to support the technology demands of the growing military-industrial complex. In that post-war environment, physicists had a rich field of well-funded practical applications to work on, and since the mathematics of quantum physics worked so well, they simply accepted the Copenhagen interpretation as taught. It seemed a waste of effort (and funding) for anyone to explore the more fundamental questions of what Becker refers to as
quantum foundations, the pursuit of the understanding of
what is real at the quantum level.
And yet some physicists have continued to balk at this decision to remain ignorant of an understanding of what’s physically happening in the quantum world. Even as the Copenhagen interpretation has cemented its place among the majority of their colleagues, these physicists have continued to seek out alternative interpretations that resolve the measurement issue, while still maintaining the fundamental mathematics that has proven through testing to work so well. In the process they have faced at best indifference from many of their colleagues, though more often outright disdain and active resistance.
Becker explores several of the alternative interpretations that have been developed, and in so doing demonstrates the push-back faced by the physicists who proposed them. This has included rejection of their work from colleagues, journal editors, and even their own doctoral advisors, often apparently behind their backs. And, it’s important to recall, such rejection is not associated with the proposed interpretations being
proven wrong, through theoretical counter-arguments or experimental results, but rather out of principle, out of a hardened belief that their interpretation simply couldn’t be correct.
One such example was the work of physicist David Bohm in the 1950’s. Through his studies, Bohm had learned about and come to accept the Copenhagen interpretation without serious concern. But a meeting with Einstein led him to take a closer look, and what he found unsettled him enough that he decided to pursue an interpretation that addressed the measurement issue. His solution was
mathematically equivalent [to the Schrödinger equation] … but the picture of the world suggested by the math, the story it told, was radically different. … Objects have definite positions at all times, whether or not anyone is looking at them. Particles have a wave nature [but] particles are just particles, and their motions are guided by pilot waves. (97-98)
His theory provided a concrete description of what was happening at the quantum level, resolving the measurement issue, and also showing that quantum physics applies to all objects – eliminating the boundary question.
In the mix with Bohm was that he was watching developments in Europe in the 1940’s and had become a Marxist, even briefly joining a communist party chapter at Berkley, until finding the meetings interminable. This got him into trouble in the US of the 1950’s, and he ended up in Brazil.
At this point the story gets wild, as scientists’ political beliefs and interpretation of the science collide.
Becker explains that the development of the Copenhagen interpretation was heavily influenced by a school of thought known as
logical positivism, according to which “any statement that made reference to something unobservable was not only bad science, it was literally meaningless. Thus, talking about what happens in quantum systems when nobody’s looking is nonsensical.” (48) The promoters of the Copenhagen interpretation used logical positivism to support their rejection of any pursuit of an interpretation of quantum physics that attempted to make concrete statements about what happens at the quantum level, including Bohm’s, since they considered it “unobservable."
However, Becker notes that in the Soviet Union, from the time of Lenin through to Stalin’ death, there was a strong ideological “emphasis on “materialism” and rejection of positivism [in] Marxist thought.” (108) And Bohm’s theory aligned well with his own Marxist philosophy supporting materialism – in that it provided a specific description of what happened at the quantum level. Thus,
Bohm [had] hoped for support from Soviet physicists and other communists [in that] his interpretation made quantum physics explicitly about stuff existing in the world, rather than an abstract statement of what physicists can say about experimental outcomes. (108)
That is, like the Copenhagen interpretation.
It turned out, however, that the disdain in the Soviet Union for positivism “died with Stalin in 1953,” (109) right around the time Bohm’s work was published. The resulting political changes freed Soviet physicists who had studied with Bohr to be more vocal in their support of the Copenhagen interpretation, and so also to reject Bohm’s work, one of them in fact referring to its way of thinking as an “illness.” (109) Likewise,
Léon Rosenfeld, Bohr’s right-hand man in Copenhagen … successfully prevented Bohm from publishing a paper in Nature … [and later] wrote a scathing review, claiming Bohm had hopelessly misunderstood quantum physics. (109-110)
In the end, political shifts inflected even Bohm’s thinking about his own theories. He gradually abandoned them in the mid-1950’s for a number of reasons, but, notes Becker, this change of heart came
at roughly the same time as another, related, major intellectual shift for Bohm: in the wake of the brutal suppression of the Hungarian Uprising in 1956, Bohm abandoned his Marxism. This change in philosophy altered Bohm’s thinking about the nature of the quantum world, which further motivated him to abandon his old ideas. (115)
Certainly there has been a long history of political and social ideologies influencing the interpretation of scientists’ work and conclusions – one must look no farther than to current day topics such as climate change. Becker points out, however, that different than for climate change, “in the debate over quantum foundations, everyone agrees that science works … [the debate] has been a dispute among physicists about the meaning of a theory they all agreed was correct.” (281)
Aside from the political wrangling over Bohm’s theory, a challenging aspect of it is its strange and unintuitive feature of
nonlocality.
Locality, Becker writes, is “the principle that something that happens in one location can’t instantly influence an event that happens somewhere else” (51) – effectively, non-locality requires faster-than-light information transfer between particles. He notes that the Copenhagen interpretation also assumes non-locality, though considers it not something worth questioning, and that Einstein was no more comfortable with Bohm’s theory than with the Copenhagen interpretation, “reject[ing] any violation of locality, calling it “spooky action at a distance” … [
and
that] the facts at hand could easily be explained by the incompleteness of quantum theory.” (56)
Tackling the connection between non-locality and quantum physics head-on, according to Becker, was a theorem developed by physicist John Bell. (Bohr, Bohm, Bell: perhaps there’s an opportunity for a Ph.D. thesis in psychology on
Becker’s attraction to physicists whose names start with B….) Bell's theorem establishes two possibilities: “either the predictions of quantum physics are wrong and nature can be local, or quantum physics is right and “spooky action at a distance” is real." (151)
In clear and engaging prose, Becker describes a series of experiments in the late 20th century set up to test Bell’s theorem, and so explore the non-locality implications of quantum physics. A central feature of these experiments was to send two photons in opposite directions, and, while they are
en route, randomly change the polarization of devices they then pass through at their destinations. To-date these experiments have consistently demonstrated the apparent non-locality characteristic of quantum mechanics: the results do not demonstrate the random behavior that might be intuitively expected, instead leading to the conclusion that the photons communicate with each other
en route. In the terms of Bell’s theorem, the results match the expectations from quantum physics in that the photons’ behavior is correlated to a greater degree than if it was random and independent.
Thus, Bohm’s theory of particles on pilot waves provides an explanation of what happens at the quantum level, but fundamental to it is non-locality – “spooky action at a distance."
Becker describes an alternate explanation, proposed by physicist Hugh Everett in the mid-1950’s, that
doesn’t require non-locality, but leads to a perhaps even stranger and more non-intuitive explanation. Everett showed that quantum mathematics can be interpreted as describing that
a single universal wave function is all there is, a massive mathematical object describing the quantum states of all objects in the entire universe … [one that] obeyed the Schrödinger equation at all times, never collapsing, but splitting instead. Each experiment, each quantum event, spun off new branches of the universal wave function, creating a multitude of universes in which that one event had every possible outcome. Everett’s shocking idea came to be known as the “many-worlds” interpretation of quantum physics. (124)
Although Everett’s paper was ignored for many years, Becker notes that nowadays, as the field of cosmology has blossomed, the many-worlds interpretation has become a part of a set of theories together labeled the
multiverse, an infinity of universes that exist in parallel to ours. Becker summarizes these ideas in his book, but a deeper and quite fascinating exploration of them can be found in physicist Max Tegmark’s
Our Mathematical Universe, in which he details the various theories that have been proposed about the multiverse, from the fairly mainstream to the still controversial. (A link to my review of Tegmark’s book at right.)
As an introduction to Everett’s theories, Tegmark describes his own sudden awakening regarding concerns with the Copenhagen interpretation:
No, this just doesn’t make sense! There’s got to be a mistake somewhere! I’m alone in my girlfriend’s dorm room in Stockholm, studying for my first college quantum-mechanics exam. The textbook says that small things such as atoms can be in several places at once, whereas big things such as people can’t. No way! I tell myself. We people are made of atoms, so if they can be in several places at once, surely we can, too! It also says that every time a person observes where an atom is, it randomly jumps to just one of the places where it previously was. But I can’t find any equation defining what exactly is supposed to count as an observation. Would a robot count as an observer? How about a single atom? And the book just said that every quantum system changes deterministically according to the so-called Schrödinger equation. Isn’t that logically inconsistent with this random-jumping business?
Flustered, I muster up the courage to knock on the door of our great expert, a physics professor on the Nobel Committee. Twenty minutes later, I emerge from his office feeling stupid, convinced that I’ve somehow misunderstood the whole thing. This marks the beginning of a long personal journey of mine that still continues, and leads to quantum parallel universes. It’s not until a couple of years later, when I move to Berkeley to do my Ph.D. that I realize that it wasn’t I who had misunderstood. I eventually learn that many famous physicists had been vexed by these problems with quantum mechanics. (157, Our Mathematical Universe)
Interestingly, Everett’s theory has even made it into a fictional setting, playing a central role in the short story
Anxiety is the Dizziness of Freedom in Ted Chiang’s collection
Exhalation. Chang describes a device central to the plot, one that operates based on the many-worlds interpretation:
Every prism – the name was a near acronym of the original designation, “Plaga interworld signaling mechanism” – had two LEDs, one red and one blue. When a prism was activated, a quantum measurement was performed inside the device, with two possible outcomes of equal probability: one outcome was indicated by the red LED lighting up, while the other was indicated by the blue one. From that moment forward, the prism allowed information transfer between two branches of the universal wave function. In colloquial terms, the prism created two newly divergent timelines, one in which the red LED lit up and one in which the blue one did, and it allowed communication between the two. (273-4, Exhalation)
In describing the interpretations of Bohm, Everett and others, Becker’s point is not that one or the other is necessarily correct. Rather, he wants to encourage the pursuit of understanding the quantum world, and to not simply, as those who follow the Copenhagen interpretation do, “shut up and calculate.” And in that pursuit he notes, considering now also Everett’s interpretation,
Bell’s theorem really leaves only three unequivocal possibilities: either nature is nonlocal in some way, or we live in branching multiple worlds despite appearances to the contrary, or quantum physics gives incorrect predictions about certain experimental setups. (160)
Thus, one must accept nonlocality or multiple worlds, or resign oneself to the possibility of, as Einstein wrote “the incompleteness of quantum theory.” (56)
Unfortunately, from Becker’s point of view, despite the fact that the study of quantum foundations – the pursuit of an understanding of what the world is like at the quantum level – is no longer as disparaged by the scientific community as it once was, the vast majority of physicists still subscribe to the Copenhagen interpretation, even if only passively. He ascribes this in large part as due to the increased specialization that occurred after WWII, which he concludes has led current-day physicists, unlike their forbearers, to be not only ignorant of, but openly dismissive of the study of philosophy:
Even Einstein complained about this, and how it helped keep the Copenhagen interpretation entrenched. “This state of affairs will last for many years,” he wrote in 1951, “mainly because physicists have no understanding of logical and philosophical arguments." (273)
The result, according to Becker, is that physics students learn the Copenhagen interpretation during their studies, and then, motivated by funding and the pursuit of tenure, put their heads down and focus on concrete problems. Without the scholastic training and tools that the study of philosophy could give them, they remain unwilling to engage in the logical evaluation of the validity of the underpinnings of particular interpretations, and so unmotivated to pursue a more complete understanding of the quantum world.
In
What is Real, Becker tells the fascinating history of the search for meaning in quantum physics, a theory that physicists universally agree works, but which has seen “deep and bitter conflict” (281) over its interpretation. He describes the coalescence of physicists around the Copenhagen interpretation, with its rejection of the need to, or even the possibility of understanding the details of the world at the quantum level. And he examines the lives and work of those who have dissented from this consensus, scientists from Einstein through to the present day who have refused to be cowed by the willful desire among followers of the Copenhagen interpretation to remain ignorant of the physical reality behind quantum physics, and who have as a consequence risked the disapproval and opprobrium of their colleagues to pursue a deeper understanding of the quantum world.
Becker clearly encourages this spirit of exploration – not at the expense of the work done by the “shut-up and calculate” crowd, but as an acceptable and important addition to that work.
We have a wildly successful theory, an embarrassment of interpretations, and a major challenge in moving past our theory to the next one. Pluralism about interpretations might be the right answer, pragmatically, while we face that challenge. Or if not pluralism, at least humility. 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 what that means yet. And it’s the job of physics to find out. (287)
Other notes and information:
As it is something that I find to be too often neglected and poor in many works of non-fiction, I want to take note of the fact that the book’s Index is excellently executed: complete, thorough and very helpful for tracking down connections as you read the book. Bravo!
Have you read this book, others by this author, or even similar ones by other authors? I’d enjoy hearing your thoughts.
Other of my book reviews: FICTION Bookshelf and NON-FICTION Bookshelf
