Some scientists seek to clarify reality, others to mystify it. David Bohm seemed driven by both impulses. He is renowned for promoting a sensible (according to Einstein and other experts) interpretation of quantum mechanics. But Bohm also asserted that science can never fully explain the world, and his 1980 book Wholeness and the Implicate Order delved into spirituality. Bohm’s interpretation of quantum mechanics has attracted increasing attention lately. He is a hero of Adam Becker’s new book What Is Real? The Unfinished Quest for the Meaning of Quantum Mechanics (reviewed by James Gleick, David Albert and Peter Woit). In The End of Science I tried to make sense of this paradoxical truth-seeker, who died in 1992 at the age of 74. Below is an edited version of that profile. See also my recent post on another quantum visionary, John Wheeler. –John Horgan
In August 1992 I visited David Bohm at his home in a London suburb. His skin was alarmingly pale, especially in contrast to his purplish lips and dark, wiry hair. His frame, sinking into a large armchair, seemed limp, languorous, and at the same time suffused with nervous energy. One hand cupped the top of his head, the other gripped an armrest. His fingers, long and blue-veined, with tapered, yellow nails, were splayed. He was recovering, he said, from a heart attack.
Bohm’s wife brought us tea and biscuits and vanished. Bohm spoke haltingly at first, but gradually the words came faster, in a low, urgent monotone. His mouth was apparently dry, because he kept smacking his lips. Occasionally, after making an observation that amused him, he pulled his lips back from his teeth in a semblance of a smile. He also had the disconcerting habit of pausing every few sentences and saying, “Is that clear?” or simply, “Hmmm?” I was often so hopelessly befuddled that I just smiled and nodded. But Bohm could be bracingly clear, too. Like an exotic subatomic particle, he oscillated in and out of focus.
Born and raised in the U.S., Bohm left in 1951, the height of anti-communist hysteria, after refusing to answer questions from a Congressional committee about whether he or anyone he knew was a communist. After stays in Brazil and Israel, he settled in England. Bohm was a scientific dissident too. He rebelled against the dominant interpretation of quantum mechanics, the so-called Copenhagen interpretation promulgated by Danish physicist Niels Bohr.
Bohm began questioning the Copenhagen interpretation in the late 1940s while writing a book on quantum mechanics. According to the Copenhagen interpretation, a quantum entity such as an electron has no definite existence apart from our observation of it. We cannot say with certainty whether it is either a wave or a particle. The interpretation also rejects the possibility that the seemingly probabilistic behavior of quantum systems stems from underlying, deterministic mechanisms.
Bohm found this view unacceptable. “The whole idea of science so far has been to say that underlying the phenomenon is some reality which explains things,” he explained. “It was not that Bohr denied reality, but he said quantum mechanics implied there was nothing more that could be said about it.” Such a view reduced quantum mechanics to “a system of formulas that we use to make predictions or to control things technologically. I said that's not enough. I don’t think I would be very interested in science if that were all there was.”
In 1952 Bohm proposed that particles are indeed particles--and at all times, not just when they are observed in a certain way. Their behavior is determined by a force that Bohm called the “pilot wave.” Any effort to observe a particle alters its behavior by disturbing the pilot wave. Bohm thus gave the uncertainty principle a purely physical rather than metaphysical meaning. Niels Bohr had interpreted the uncertainty principle as meaning “not that there is uncertainty, but that there is an inherent ambiguity” in a quantum system, Bohm explained.
Bohm’s interpretation gets rid of one quantum paradox, wave/particle duality, but it preserves and even highlights another, nonlocality, the capacity of one particle to influence another instantaneously across vast distances. Einstein had drawn attention to nonlocality in 1935 in an effort to show that quantum mechanics must be flawed. Together with Boris Podolsky and Nathan Rosen, Einstein proposed a thought experiment involving two particles that spring from a common source and fly in opposite directions.
According to the standard model of quantum mechanics, neither particle has fixed properties, such as momentum, before it is measured. But by measuring one particle’s momentum, the physicist instantaneously forces the other particle, no matter how distant, to assume a fixed momentum. Deriding this effect as “spooky action at a distance,” Einstein argued that quantum mechanics must be flawed or incomplete. But in 1980 French physicists demonstrated spooky action in a laboratory. Bohm never had any doubts about the experiment’s outcome. “It would have been a terrific surprise to find out otherwise,” he said.
But here is the paradox of Bohm: Although he tried to make the world more sensible with his pilot-wave model, he also argued that complete clarity is impossible. He reached this conclusion after seeing an experiment on television, in which a drop of ink was squeezed onto a cylinder of glycerine. When the cylinder was rotated, the ink diffused through the glycerine in an apparently irreversible fashion. Its order seemed to have disintegrated. But when the direction of rotation was reversed, the ink gathered into a drop again.
The experiment inspired Bohm to write Wholeness and the Implicate Order, published in 1980. He proposed that underlying physical appearances, the “explicate order,” there is a deeper, hidden “implicate order.” Applying this concept to the quantum realm, Bohm proposed that the implicate order is a field consisting of an infinite number of fluctuating pilot waves. The overlapping of these waves generates what appears to us as particles, which constitute the explicate order. Even space and time might be manifestations of a deeper, implicate order, according to Bohm.
To plumb the implicate order, Bohm said, physicists might need to jettison basic assumptions about nature. During the Enlightenment, thinkers such as Newton and Descartes replaced the ancients’ organic concept of order with a mechanistic view. Even after the advent of relativity and quantum mechanics, “the basic idea is still the same,” Bohm told me, "a mechanical order described by coordinates.”
Bohm hoped scientists would eventually move beyond mechanistic and even mathematical paradigms. “We have an assumption now that’s getting stronger and stronger that mathematics is the only way to deal with reality,” Bohm said. “Because it’s worked so well for a while, we’ve assumed that it has to be that way.”
Someday, science and art will merge, Bohm predicted. “This division of art and science is temporary,” he observed. “It didn't exist in the past, and there’s no reason why it should go on in the future.” Just as art consists not simply of works of art but of an “attitude, the artistic spirit,” so does science consist not in the accumulation of knowledge but in the creation of fresh modes of perception. “The ability to perceive or think differently is more important than the knowledge gained,” Bohm explained.
Bohm rejected the claim of physicists such as Hawking and Weinberg that physics can achieve a final “theory of everything” that explains the world. Science is an infinite, “inexhaustible process,” he said. “The form of knowledge is to have at any moment something essential, and the appearance can be explained. But then when we look deeper at these essential things they turn out to have some feature of appearances. We're not ever going to get a final essence which isn't also the appearance of something.”
Bohm feared that belief in a final theory might become self-fulfilling. “If you have fish in a tank and you put a glass barrier in there, the fish keep away from it,” he noted. “And then if you take away the glass barrier they never cross the barrier and they think the whole world is that.” He chuckled drily. “So your thought that this is the end could be the barrier to looking further.” Trying to convince me that final knowledge is unattainable, Bohm offered the following argument:
“Anything known has to be determined by its limits. And that’s not just quantitative but qualitative. The theory is this and not that. Now it’s consistent to propose that there is the unlimited. You have to notice that if you say there is the unlimited, it cannot be different, because then the unlimited will limit the limited, by saying that the limited is not the unlimited, right? The unlimited must include the limited. We have to say, from the unlimited the limited arises, in a creative process. That’s consistent. Therefore we say that no matter how far we go there is the unlimited. It seems that no matter how far you go, somebody will come up with another point you have to answer. And I don’t see how you could ever settle that.”
To my relief, Bohm’s wife entered the room and asked if we wanted more tea. As she refilled my cup, I pointed out a book on Buddhism on a shelf and asked Bohm if he was interested in spirituality. He nodded. He had been a friend of Krishnamurti, one of the first modern Indian sages to try to show Westerners how to achieve the state of spiritual serenity and grace called enlightenment. Was Krishnamurti enlightened? “In some ways, yes,” Bohm replied. “His basic thing was to go into thought, to get to the end of it, completely, and thought would become a different kind of consciousness.”
Of course, one could never truly plumb one’s own mind, Bohm said. Any attempt to examine one’s own thought changes it--just as the measurement of an electron alters its course. We cannot achieve final self-knowledge, Bohm seemed to imply, any more we can achieve a final theory of physics.
Was Krishnamurti a happy person? Bohm seemed puzzled by my question. “That's hard to say,” he replied. “He was unhappy at times, but I think he was pretty happy overall. The thing is not about happiness, really.” Bohm frowned, as if realizing the import of what he had just said.
I said goodbye to Bohm and his wife and departed. Outside, a light rain was falling. I walked up the path to the street and glanced back at Bohm's house, a modest whitewashed cottage on a street of modest whitewashed cottages. He died of a heart attack two months later.
In Wholeness and the Implicate Order Bohm insisted on the importance of “playfulness” in science, and in life, but Bohm, in his writings and in person, was anything but playful. For him, truth-seeking was not a game, it was a dreadful, impossible, necessary task. Bohm was desperate to know, to discover the secret of everything, but he knew it wasn’t attainable, not for any mortal being. No one gets out of the fish tank alive.
See also Q&As with physicists Scott Aaronson, David Deutsch, George Ellis, Marcelo Gleiser, Sabine Hossenfelder, Garrett Lisi, Priyamvada Natarajan, Martin Rees, Carlo Rovelli, Lee Smolin, Paul Steinhardt, Steven Weinberg, Edward Witten, Peter Woit and Stephen Wolfram.