June 29, 2023. Is quantum mechanics weird if no one is paying attention to it? Lots of people are paying attention to it now, including me. Two physicists often cited in debates about the theory’s meaning are John Wheeler and David Bohm, both of whom I interviewed in the early 1990s and feature in The End of Science. I thought my profiles of these physicists might contribute to current quantum debates. Below is my lightly edited profile of Wheeler, who died in 2008. You can find my profile of David Bohm here. --John Horgan

John Archibald Wheeler, the archetypal physics-for-poets physicist, is famed for his analogies and aphorisms, self-made and coopted. Here are one-liners he bestows on me when I meet him at Princeton on a warm spring day in 1991: “If I can't picture it, I can't understand it” (Einstein); “Unitarianism [Wheeler's nominal religion] is a feather bed to catch falling Christians” (Darwin); and “If you haven't found something strange during the day, it hasn't been much of a day” (Wheeler).

Wheeler is also renowned for his physical energy. When we leave his third-floor office to get some lunch, he spurns the elevator, declaring that “elevators are hazardous to your health,” and charges down the stairs. He hooked an arm inside the banister and pivots at each landing, letting centrifugal force whirl him around the hairpin and down the next flight. “We have contests to see who can take the stairs fastest,” he says over a shoulder. Outside, Wheeler marches rather than walks, swinging his fists smartly in rhythm with his stride. He pauses only when he reaches a door. Invariably he gets there first and yanks it open for me. After passing through the door, I pause in reflexive deference--Wheeler is almost 80—and then he’s past me, barreling toward the next doorway.

The metaphor is so obvious that I wonder whether Wheeler intends it. He has spent his career racing ahead of other scientists and throwing open doors for them. He has helped win acceptance--or at least attention--for some of science’s most outlandish ideas, from black holes to multiple-universe theories. Wheeler might have been dismissed as flakey if he did not have such unassailable credentials. In his early 20s, he traveled to Denmark to study under Niels Bohr (“because he sees further than any man alive,” Wheeler wrote in his fellowship application). In 1939 Bohr and Wheeler published the first paper to explain nuclear fission in quantum terms. Bohr also taught Wheeler to “be prepared for a surprise, and a very great surprise.”

After World War II, Wheeler became an authority on general relativity. He coined the term black hole in the late 1960s, and he helped convince astronomers that these bizarre, infinitely dense objects might actually exist. He also became increasingly intrigued by the philosophical implications of quantum physics. The most widely accepted explanation of the “meaning” of quantum mechanics was the so-called orthodox interpretation (although “orthodox” seems an odd descriptor for such a radical worldview). Also called the Copenhagen interpretation, because Bohr lectured on it in Copenhagen in the late 1920s, it holds that we cannot specify the nature of fundamental reality. Subatomic entities exist in a probabilistic limbo of many possible “superposed” states until they are brought into focus by the act of measurement.

Wheeler was one of the first prominent physicists to propose that reality might not be wholly physical; in some sense, our cosmos must be a “participatory” phenomenon requiring the act of observation--and thus consciousness itself. Wheeler also drew attention to intriguing links between physics and information theory, invented in 1948 by mathematician Claude Shannon. Just as physics builds on an elementary entity, the quantum, defined by the act of observation, so does information theory. Its “quantum” is the binary unit, or bit, which is a message representing one of two choices: heads or tails, yes or no, zero or one.

Wheeler became more convinced of the importance of information after conceiving a modified version of the famous two-slit experiment, which demonstrates the schizophrenic nature of quantum phenomena. When electrons are aimed at a barrier with two slits, the electrons act like waves; they go through both slits at once and form what is called an interference pattern, created by the overlapping of the waves, on a detector beyond the barrier. If the physicist closes off one slit at a time, however, the electrons pass through the open slit like simple particles and the interference pattern disappears.

In Wheeler’s version, called the delayed-choice experiment, the experimenter decides whether to leave both slits open or to block one after the electron has passed through the barrier--with the same results. The electrons seem to know in advance how the physicist will choose to observe it. The delayed-choice experiment has been carried out, confirming Wheeler’s prediction.

Wheeler accounts for this conundrum with yet another analogy. He likens the job of a physicist to that of someone playing the “surprise” version of 20 questions. In this variant of the old game, the guesser leaves the room while the rest of the group--or so the excluded person thinks--agrees on some person, place or thing. The guesser then re-enters the room and tries to guess what they have in mind with questions that can only be answered with a yes or no. Is it bigger than a toaster? Is it alive? Is it female?

Unknown to the guesser, the group has decided to play a trick on him. The first person to be queried will only think of an object and answer the question after the questioner asks his question. Each subsequent person will do the same, making sure her response is consistent both with the question directed at her and with all previous questions.

“The word wasn't in the room when I came in even though I thought it was,” Wheeler explains. In the same way, the electron, before the physicist chooses how to observe it, is neither a wave nor a particle; it is in some sense unreal, existing in an indeterminate limbo. “Not until you start asking a question, do you get something,” Wheeler says. “The situation cannot declare itself until you've asked your question. But the asking of one question prevents and excludes the asking of another.”

Wheeler has condensed these ideas into a phrase that resembles a Zen koan: “the it from bit.” In one of his free-form essays, Wheeler unpacks the phrase as follows: “...every it--every particle, every field of force, even the spacetime continuum itself--derives its function, its meaning, its very existence entirely--even if in some contexts indirectly--from the apparatus-elicited answers to yes-or-no questions, binary choices, bits.”

Inspired by Wheeler, physicists and other researchers began probing the links between information theory and physics in the late 1980s. String theorists have tried using strings to knit together quantum field theory, black holes and information theory. Wheeler acknowledges that these ideas are still raw, not yet ready for rigorous testing. He and his fellow explorers are still “trying to get the lay of the land" and "learning how to express things that we already know” in the language of information theory. The effort may lead to a dead end, Wheeler says, or to a powerful new vision of reality, “the whole show.”

Wheeler emphasizes that science has many mysteries left to explain. “We live still in the childhood of mankind,” he says. “All these horizons are beginning to light up in our day: molecular biology, DNA, cosmology. We're just children looking for answers.” He serves up another aphorism: “As the island of our knowledge grows, so does the shore of our ignorance.” Yet he is also convinced that we will someday find “the answer.”

Wheeler jumps up and pulls down a massive black book on gravity that he co-wrote in the late 1980s. Flipping to the book’s final page he reads: “Someday surely we will see the principle underlying existence as so simple, so beautiful, so compelling that we will all say to each other, 'How could we all have been so stupid for so long.” Wheeler looks up from the book, his expression beatific. “I don't know whether it will be one year or a decade, but I think we can and will understand. That's the central thing I would like to stand for. We can and will understand.”

Many modern scientists, Wheeler notes, have shared his faith that humans will one day find the key to the mysteries of existence. Kurt Gödel, once Wheeler’s neighbor in Princeton, believed that the key might have already been discovered. “He thought that maybe among the papers of Leibniz, which in his time had still not been fully smoked out, we would find the--what was the word--the philosopher's key, the magic way to find truth and solve any set of puzzlements.” Gödel felt this key “would give a person who understood it such power” that only “people of high moral character” should possess it.

Yet Wheeler’s mentor Bohr apparently doubted whether science or mathematics could achieve such a revelation. After Bohr died, his son told Wheeler that his father thought the search for the ultimate theory of physics might never reach a satisfying conclusion; as physicists delved more deeply into nature, they would face questions whose complexity would overwhelm them. “I guess I'm more optimistic than that,” Wheeler says, “but maybe I'm kidding myself.”

The irony is that Wheeler’s it from bit implies that a final theory will always be a mirage, and that truth is something created rather than objectively apprehended. His view comes dangerously close to postmodernism, or worse. In the early 1980s, organizers of the annual meeting of the American Association for the Advancement of Science placed Wheeler on the same program as three parapsychologists. Wheeler was furious. At the meeting, he made it clear that he did not share the belief of his co-speakers in psychic phenomena. He passed out a pamphlet that declared, in reference to parapsychology: “Where there’s smoke, there’s smoke.”

But Wheeler himself has suggested that there is nothing but smoke. “I do take 100 percent seriously the idea that the world is a figment of the imagination,” he told physicist/science writer Jeremy Bernstein in 1985. Wheeler must know that this view defies common sense: Where was mind when the universe was born? And what sustained the universe for the billions of years before we came to be? He nonetheless bravely offers us a lovely, chilling paradox: At the heart of everything is a question, not an answer. When you peer down into the deepest recesses of matter or at the farthest edge of the universe, you see, finally, your own puzzled face looking back at you.

Further Reading:

Wheeler’s ideas pop up throughout my free online book My Quantum Experiment.