By IVAN SEMENIUK
Saturday, June 15, 2019
There was an air of melancholy about the theoretical physicist David Bohm when he came to speak at the University of Toronto in the mid-1980s - or so it seemed to me at the time, a student with only a passing understanding of Bohm's place in history. Born and educated in the United States, Bohm had, by then, spent half his life as a political and scientific exile. The politics was bad timing. In 1949, during the peak of McCarthy-era paranoia, Bohm's prior membership in the Communist Party while a graduate student had landed him in front of the U.S. House Un-American Activities Committee. He was later arrested after refusing to testify against colleagues. The episode crippled his career. Stigmatized and unable to find work at home, Bohm left for a teaching position in Brazil. By the time I saw him speak he was in his 60s and based in London.
What fascinated me then, and what filled the Toronto lecture hall, was not Bohm's political history, but his status as a scientific heretic. He was an unapologetic opponent of quantum mechanics - the strange but powerful theory that physicists use to explain the behaviour of matter and light. That did not mean he questioned the theory's results. On that score, few would argue - then or now - that quantum mechanics is one of the most successful theories in history, with practical applications that encompass lasers, computer chips and other indispensable components of the modern world. But Bohm was certain that what the theory's founders thought quantum mechanics had to say about the nature of reality was dead wrong.
Fast-forward 35 years and we find Lee Smolin, another physicist in his 60s, reviving Bohm's objections. Like Bohm, Smolin comes from the United States, but, since 2001, has lived in Canada as a founding faculty member of the Perimeter Institute for Theoretical Physics in Waterloo, Ont.
As a scientist, Smolin is best known for working on ideas that try to reconcile quantum mechanics with general relativity - Einstein's pre-eminent theory of gravity. Relativity has proved to be a remarkably reliable description of nature with some useful side benefits. For example, GPS satellites can't pinpoint your location on Earth without taking Einstein's equations into account.
Yet, relativity and quantum mechanics do not play well together because they do not treat reality in the same way.
The weirdness of quantum mechanics comes down to our apparent inability to know everything about a physical system. A particle has both a position and a momentum and in the classical mechanics of Isaac Newton, knowledge of those properties makes it possible to predict, with complete certainty, the particle's location at some point in the future. But, in the mathematical language of quantum mechanics, a fundamental level of uncertainty creeps in with the act of measurement.
The more one tries to pin down a particle's position, for example, the less certain one is about its momentum, and vice versa. The particle's future status can only be expressed as a probability. It is literally everywhere at once with varying degrees of presence, until we choose to check.
The logical consequences of this have been well explored in popular science writing. They include the idea that particles sometimes behave as waves and that cats can be both alive and dead at the same time. More broadly, it seems that the universe exists as a cloud of possible outcomes that we call into being by observing them. For the better part of a century, physicists have been willing to put up with this to get on with the business of doing physics. Their approach, as Cornell University professor David Mermin wryly summed up, was "shut up and calculate."
This is what Bohm objected to and what he tried to counter with his own "pilot wave" theory, in which particles are guided in their motion in ways that we can't see. I still recall the metaphor Bohm used to describe this: For him, reality is a ballet in which some of the dancers are hidden behind the curtain.
Smolin is not sold on the details of Bohm's approach, but in his previous books, including The Trouble with Physics and Time Reborn, he has explored why physicists have been stalled in their efforts to come up with one overarching theory that includes both relativity and quantum mechanics and reveals the hidden architecture behind the particles and forces that govern our existence.
With his new book, Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum, he makes his strongest case yet that the blame lies squarely with those who developed quantum mechanics in the 1920s, and their insistence that reality is effectively what we choose to measure. For Smolin, a staunch realist, their position is not just unsatisfying - it amounts to a betrayal of the scientific enterprise.
"I don't want a theory of myself intervening with nature," Smolin says. "I do science because I want to understand how nature is in our absence. What is really going on?" Philosophically, Smolin aligns himself with Einstein, who played a central role in launching the quantum revolution starting in 1905, but who became increasingly disturbed by its outcome. Rather than Einstein, it was the Danish physicist Niels Bohr and his younger colleague Werner Heisenberg who led the development of the new physics by building the mathematical framework of quantum theory and, by 1927, introducing the "Copenhagen interpretation" - the dominant view of what that theory means.
That view, as Smolin writes, essentially holds that "physics does not give a description of what exists ... but is only a way to keep track of what is observable." In retrospect, it's easy to imagine why such an idea would have appealed to a generation of young theorists steeped in the modernism of Picasso and Joyce and distrustful of the rationalism that had led Europe into the horrors of the First World War. But in the current context, when public acceptance of basic scientific facts about climate change, vaccination and other policy-relevant matters is undermined by the toxic churn of social media, a theory that appears to challenge objective reality poses real risks. Smolin argues that it's time for realism to reassert itself at the core of physics, the pedestal upon which the entire scientific enterprise rests.
The rub - which Smolin readily admits - is that there is no evidence that quantum mechanics is wrong. On the contrary, experiments designed to expose a flaw in the theory have instead demonstrated that the universe is a lot weirder than we thought. Weirdest of all is the effect called "entanglement," which links the state of particles that have become widely separated. This phenomenon has been verified in the laboratory many times over and is the basis for efforts to develop commercially useful quantum computers.
Ironically, the practical question of how quantum computer systems work has created a new wave of writing and thinking about what quantum mechanics really means - a discipline known as "quantum foundations" that physicists of Smolin's generation were once taught to avoid if they valued career success. Readers looking to sample the academic conversation can dip into Emergent Quantum Mechanics, a new, open-access collection of papers drawn from a 2017 symposium marking David Bohm's centenary.
Those looking for a more plainlanguage and even-handed take should consult Beyond Weird, by Philip Ball, a master explainer whose forward-looking perspective captures the growth of quantum information theory and its role in advancing the foundations of quantum theory.
A more narrative exploration can be found in What Is Real?, Adam Becker's superbly written history of the Copenhagen interpretation and its challengers.
Here, the embattled Bohm comes to life as he struggles to advance his "pilot wave" alternative to the Copenhagen juggernaut. So, too, does Hugh Everett, a hard-drinking and philandering genius who made his fortune optimizing how the U.S. military allocated its resources during the Cold War.
While still a PhD student, Everett developed the "many worlds" interpretation of quantum mechanics, still an area of active research, which requires the universe to branch into separate but equally real versions of itself every time a particle is faced with doing one thing or another. Other forgotten characters also receive their due, including Grete Hermann, a German mathematician who demonstrated in 1935 that an influential "proof" that the Copenhagen interpretation had to be correct was simply wrong. Her contribution when unnoticed, Becker writes, adding, "It's hard to imagine that her gender had nothing to do with the reception of her work."
Becker also exposes another form of intellectual chauvinism when he examines the philosophical backdrop against which quantum mechanics emerged, and suggests that one reason the Copenhagen interpretation has persisted this long is that scientists have now stopped paying attention to, and benefiting from, the work of philosophers.
As the latest entry into the conversation, Smolin's book feels the most immediate and personal.
Here is no detached narrator, but an active participant in the fray who perceives the debate over the nature of reality in personal terms. While discussing Everett's many-worlds theory, for example, he recounts how he narrowly missed being a passenger on Swissair Flight 111, which crashed into the ocean off Nova Scotia 21 years ago. If Everett is correct, then Smolin's life in a parallel universe ended with a deadly plunge into the Atlantic. The implication, he notes, presents a challenge to the concept of morality. What is the point of a good act when that act automatically generates another universe in which we choose not to do good?
Unlike Bohm or Everett, Smolin does not have his own alternative theory to roll out. But he firmly rejects the Copenhagen interpretation and insists, instead, on a reality that exists independently from us and obeys the bedrock principle of cause and effect. For Smolin, entanglement is not proof that the Copenhagen crowd got it right in 1927, but rather an important clue that resolving the quantum impasse will require a radically new understanding of the nature of space and time.
"Realism, in any version, has a price," he writes. "The question is what price we have to pay to get a new theory that makes complete sense and describes nature correctly and completely."
Certainly, Bohm, who died in 1992, paid a price for his resistance in the form of professional isolation. After he spoke, I remember raising my hand and asking, with skepticism, why anyone should believe in his metaphorical dancers behind the curtain instead of in the cleaner, simpler idea that the universe is at it appears - in a state of perpetual contingency.
The look on his face betrayed the burden of one used to being discounted by lesser minds.
While the way forward remains elusive, Smolin and others who seek to illuminate how physics got to where it is today are at least making the quest for answers a bit less costly.
Physicist Lee Smolin, below, has lived in Canada since 2001 as a founding faculty member of the Perimeter Institute for Theoretical Physics in Waterloo, Ont. For Smolin, a firm realist, the theories of quantum mechanics developed in the 1920s are not just unsatisfying - their insistence that reality is simply what we choose to measure amounts to a betrayal of science itself.
PHOTOS BY PERIMETER INSTITUTE