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 Wheeler, often described as the quintessential “physics-for-poets” physicist, was renowned for his captivating analogies, insightful aphorisms, and his profound contributions to our understanding of the universe. Meeting him at Princeton on a bright spring day in 1991, I was immediately struck by his intellectual agility and vibrant personality. He peppered our conversation with memorable quotes, attributing to Einstein the notion, “If I can’t picture it, I can’t understand it,” and to Darwin, a witty observation about his own Unitarianism as “a feather bed to catch falling Christians.” And then, a classic John Wheeler original: “If you haven’t found something strange during the day, it hasn’t been much of a day.” These pronouncements offered a glimpse into the mind of a man who thrived on curiosity and the pursuit of the extraordinary.
Beyond his quotable wisdom, John Wheeler was equally famed for his remarkable physical energy, a trait that mirrored his relentless intellectual drive. As we prepared to leave his third-floor office for lunch, he dismissed the elevator with a playful declaration that “elevators are hazardous to your health,” and bounded towards the stairs. His descent was a spectacle of controlled momentum, hooking an arm on the banister, pivoting at each hairpin turn, centrifugal force propelling him down to the next level. “We have contests to see who can take the stairs fastest,” he shared with a grin, his energy infectious. Outside, Wheeler didn’t walk, he marched, fists pumping rhythmically, pausing only to reach a door, which he invariably yanked open, always a step ahead. This constant motion seemed a perfect metaphor for his career – perpetually pushing boundaries, leading the charge into new scientific frontiers.
A Career Forging New Paths in Physics: From Bohr to Black Holes
John Archibald Wheeler‘s career was indeed marked by racing ahead and opening doors for others in the scientific community. He played a pivotal role in gaining acceptance, or at least serious consideration, for some of the most mind-bending concepts in physics, from the enigmatic black holes to the perplexing multiple-universe theories. Had it not been for his impeccable credentials, Wheeler‘s audacious ideas might have been easily dismissed. His foundation was built upon solid ground. In his early twenties, he sought out Niels Bohr in Denmark, driven by the conviction that Bohr “sees further than any man alive,” as he wrote in his fellowship application. This mentorship proved transformative. In 1939, Bohr and Wheeler co-authored a groundbreaking paper that provided the first quantum explanation of nuclear fission, a discovery that would reshape the world. Bohr also instilled in Wheeler a crucial scientific mindset: to “be prepared for a surprise, and a very great surprise.”
Following World War II, John Wheeler solidified his position as a leading authority in general relativity. He is credited with coining the term “black hole” in the late 1960s, a name that perfectly captured the bizarre nature of these cosmic entities. More importantly, Wheeler was instrumental in convincing the astronomical community that black holes, these objects of infinite density and gravitational pull so strong that nothing, not even light, can escape, might actually exist in the universe. His work on black holes alone would have secured his legacy, but Wheeler‘s intellectual curiosity extended far beyond, drawing him into the philosophical depths of quantum physics.
Delving into the Quantum Realm: Observation and the Nature of Reality
John Wheeler became increasingly fascinated by the philosophical implications of quantum mechanics. The prevailing interpretation of quantum mechanics at the time was the Copenhagen interpretation, an ironic label for such a revolutionary perspective. This interpretation, stemming from Niels Bohr’s lectures in Copenhagen in the 1920s, essentially posited that we cannot definitively define the fundamental nature of reality at the quantum level. Subatomic particles exist in a state of probabilistic uncertainty, a “superposition” of multiple possibilities, until the act of measurement forces them into a definite state. This idea challenged classical physics and raised profound questions about the role of observation in shaping reality.
Wheeler was among the first prominent physicists to suggest that reality might not be solely physical. He proposed a “participatory universe,” arguing that our cosmos is, in some fundamental sense, a phenomenon that requires observation—and therefore, consciousness itself—to bring it into being. This radical idea positioned the observer not as a passive bystander, but as an active participant in the unfolding of reality. Further expanding his conceptual framework, John Wheeler recognized intriguing parallels between physics and information theory, a field pioneered by Claude Shannon in 1948. Just as quantum physics is built upon the quantum, the fundamental unit defined by observation, information theory rests on the bit, the binary unit representing a choice between two possibilities: yes or no, 0 or 1. This connection between the observer-dependent quantum and the binary bit sparked Wheeler‘s most famous and enigmatic concept: “it from bit.”
The “Delayed Choice” Experiment and the “It from Bit” Universe
John Wheeler’s conviction about the central role of information in the fabric of reality deepened after he conceived a variation of the famous two-slit experiment, a cornerstone demonstration of quantum weirdness. In the classic two-slit experiment, when electrons are directed at a barrier with two slits, they behave like waves, passing through both slits simultaneously and creating an interference pattern on a detector screen. This pattern is characteristic of wave behavior, arising from the overlapping crests and troughs of waves. However, if one slit is closed, the electrons behave like particles, passing through the open slit and eliminating the interference pattern. This wave-particle duality is a central mystery of quantum mechanics.
Wheeler’s ingenious twist was the “delayed-choice experiment.” In this version, the experimenter decides whether to keep both slits open or close one after the electron has already passed through the barrier. Remarkably, the outcome remains the same. If the decision is made to observe wave-like behavior (both slits open), the electron behaves as a wave, even retroactively. If the choice is to observe particle-like behavior (one slit closed), the electron acts as a particle, again, seemingly in retrospect. The electron appears to “know” in advance how it will be observed, defying classical notions of time and causality. The delayed-choice experiment has been experimentally verified, confirming Wheeler‘s counterintuitive prediction and further solidifying the strange nature of quantum reality.
To illuminate this profound puzzle, John Wheeler employed another insightful analogy: the “surprise” version of twenty questions. In this game, the guesser leaves the room while the others decide on a person, place, or thing. However, unbeknownst to the guesser, there’s a twist. The group hasn’t pre-selected an object. Instead, each person will only decide on an answer to the guesser’s question after the question is asked, ensuring their answer is consistent with all previous responses.
“The word wasn’t in the room when I came in even though I thought it was,” Wheeler explained, drawing a parallel to the quantum realm. Similarly, before the physicist chooses how to observe it, the electron is neither definitively a wave nor a particle; it exists in an indeterminate, unreal state. “Not until you start asking a question, do you get something,” Wheeler stated. “The situation cannot declare itself until you’ve asked your question. But the asking of one question prevents and excludes the asking of another.”
These ideas coalesced into John Wheeler‘s famous, Zen-like phrase: “the it from bit.” In his essay expounding on this concept, Wheeler elaborated: “…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.” The universe, in Wheeler‘s view, is fundamentally built upon information, and our observations are crucial in bringing that information, and thus reality itself, into being.
The Ongoing Quest for Understanding: Mysteries and Horizons
Inspired by John Wheeler‘s “it from bit” concept, physicists and other researchers began exploring the deep connections between information theory and physics in the late 1980s. String theorists, for example, have attempted to weave together quantum field theory, black holes, and information theory using the concept of strings as fundamental building blocks. Wheeler acknowledged that these were still nascent ideas, not yet ready for rigorous empirical testing. He and his fellow scientific explorers were 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. He recognized that this path might lead to a dead end, but also held the exciting possibility of a revolutionary new understanding of reality, “the whole show.”
John Wheeler always emphasized the vastness of the unknown and the abundance of mysteries still confronting science. “We live still in the childhood of mankind,” he asserted. “All these horizons are beginning to light up in our day: molecular biology, DNA, cosmology. We’re just children looking for answers.” He offered another of his characteristic aphorisms: “As the island of our knowledge grows, so does the shore of our ignorance.” Yet, despite the immensity of the unknown, Wheeler maintained a deep conviction that humanity would eventually find “the answer,” the underlying principle governing existence.
With characteristic enthusiasm, Wheeler leaped up and retrieved a massive black book on gravity, a magnum opus he co-authored in the late 1980s. Flipping to the final page, he read aloud: “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.” Looking up from the book with a beatific expression, Wheeler declared, “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.”
John Wheeler noted that many scientists throughout history have shared this faith in humanity’s capacity to unravel the universe’s deepest secrets. Kurt Gödel, a fellow intellectual giant and one-time neighbor of Wheeler in Princeton, believed that this key to understanding might have already been discovered. Gödel thought that “maybe among the papers of Leibniz…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 even believed this key “would give a person who understood it such power” that it should only be entrusted to “people of high moral character.”
However, Wheeler’s mentor, Niels Bohr, seemed to harbor doubts about whether science or mathematics could ever achieve such a complete and final revelation. After Bohr’s death, his son confided to Wheeler that his father suspected the quest for the ultimate theory of physics might never reach a fully satisfying conclusion. Bohr believed that as physicists probed deeper into the nature of reality, they would encounter questions of overwhelming complexity. “I guess I’m more optimistic than that,” Wheeler conceded, “but maybe I’m kidding myself.”
The Paradox of “It from Bit” and the Puzzled Face
The irony, as the original article points out, is that John Wheeler‘s “it from bit” concept itself suggests that a final, definitive theory might always remain elusive, a mirage. His perspective implies that truth is not something objectively discovered, but rather something created through our interactions with the universe. This view treads dangerously close to postmodernism, a philosophical stance that Wheeler himself seemed to resist, as evidenced by his strong reaction to being placed on a program with parapsychologists at a science conference.
Despite his skepticism towards parapsychology, John Wheeler himself ventured into similarly unconventional territory by suggesting that “the world is a figment of the imagination,” as he told science writer Jeremy Bernstein in 1985. This statement raises profound questions. Where was mind when the universe was born? What sustained the cosmos for billions of years before consciousness emerged? Wheeler, undeterred by these paradoxes, bravely presented us with a captivating, and perhaps unsettling, conclusion: “At the heart of everything is a question, not an answer.” When we delve into the deepest mysteries of matter or gaze at the farthest reaches of the universe, we ultimately confront our own “puzzled face looking back at you.” John Wheeler‘s legacy is not in providing definitive answers, but in posing profound questions that continue to drive our exploration of the universe and our place within it.
Further Reading:
Wheeler’s ideas pop up throughout my free online book My Quantum Experiment.
