Putting Ourselves Back in the Equation, page 12
But when Zeilinger and his team played the quantum equivalent of this game, they saw a single coin about 90 percent of the time. That’s astronomically unlikely if the outcomes were determined in advance. Ergo, they were not determined in advance, but on the fly. Superpositions persist until the moment a measurement is made.
In keeping with the lesson about never being too sure of ourselves, I should acknowledge that not everyone accepts this conclusion—there are ways to think of superpositions as illusory. But they involve their own weirdnesses and are definitely not an easy out. The leading such approach, developed by David Bohm, involves instantaneous action at a distance.17 It may well be the way to go. My point is simply that you can’t say superposition is “just” our ignorance of the true state of affairs.
DECOHERENCE
A third response to the measurement problem is that the second quantum law implies the first: that the evolution of waves can naturally produce a collapse of sorts. This ersatz collapse goes under the rubric of what physicists call decoherence. The basic idea is that a quantum wave is never isolated from its surroundings. As it propagates, it encounters other matter and becomes so jumbled that it is no longer perceptible as organized wave motion. Thus a particle appears to lose its wavelike qualities, including superposition, as if it had collapsed.
Through decoherence, a localized infection of ambiguity snowballs into a pandemic. The particle’s superposition spreads not only to the measuring apparatus and your brain, but also to your entire body, to the air in the room, to the building, and ultimately to the entire universe. This unstoppable spread of quantum superposition can look, to someone caught up in it, like collapse. For instance, it is all but irreversible. By the time the infection reaches global proportions, there’s no undoing it.
Decoherence also addresses an important and often unappreciated aspect of quantum measurement, which you might call the menu problem. When they collapse, particles do not choose their final state from among limitless options; their options are highly structured. Yet quantum mechanics itself provides no menu. In the example of the half-silvered mirror, I’ve been assuming the two options are to reflect off the mirror or to pass through the glass; by the end of the experiment, the photon is on one side or the other. But that’s not a given. The theory works equally well with less intuitive options such as “a little bit reflected plus a little bit transmitted” and “a little bit reflected minus a little bit transmitted,” in which the photon winds up straddling multiple locations. Because quantum theory doesn’t specify the menu of options, that task must fall to some other physical process, and decoherence performs this function. Because decoherence typically involves particles making direct contact, it defines a menu of distinct spatial positions, which matches our classical intuitions.
But decoherence doesn’t touch the central puzzle, and its originators never claimed it did.18 The outcome of a measurement is still a multiplicity rather than one particular answer, leaving physicists at a loss to explain why we see a single result. Furthermore, decoherence requires that you differentiate “object,” “observer,” and “surroundings,” which reinserts the observer into the picture.19 “Decoherence is dependent on the perspective of the self onto the world,” said Heinrich Päs, a theoretical physicist at the Technical University of Dortmund.
However much physicists might wish to eliminate the mind from their basic theories, it’s not clear that they can. “The core issue is that we really don’t understand conscious experience,” said Mile Gu, a theoretical physicist at Nanyang Technological University in Singapore. “We don’t really understand what it means to experience something. And when we don’t understand that, it’s very hard to make any concrete statement about a physical theory that involves conscious measurement.” Whether or not observers play some direct physical role, interpreting quantum theory at the very least requires thinking about how our minds perceive the world and reason about it. “Consciousness is fairly deeply ingrained in a lot of these interpretations,” said Gu.
DOES THE MIND CAUSE COLLAPSE?
Though widely considered to be a fringe notion, the most straightforward conclusion is that the mind really does cause collapse. Even Wigner, who spoke up for the idea in the ’60s, later backed away from it.20 But it hasn’t always been deemed nutty. In 1939 the theoretical physicists Fritz London and Edmond Bauer, who worked at nearby institutes in Paris, outlined a role for consciousness.21 They didn’t feel they were going out on a limb; they thought they were just filling in the orthodox interpretation of the theory.22 London had made his name creating the first quantum theory of superconductors, proving that quantum effects show up at large scales, so it stood to reason that humans were fully part of the quantum world and thus of any experiment. The outbreak of war disrupted the two men’s work: Not long after finishing up their paper, London paid a bribe to get on a ship bound for New York. Bauer stayed on in France, and his four children fought in the Resistance.23
As with many other ideas in physics that fall out of favor, the problem wasn’t plausibility so much as vagueness. If you don’t know what consciousness is, how can you build a theory of physics on it? That’s where emerging theories of consciousness can now help. They make concrete predictions about when a lump of matter is conscious.
In 2013 David Chalmers and fellow philosopher Kelvin McQueen, both then at the Australian National University, began to use integrated information theory (IIT from chapter 3) to clarify the collapse rule. They trailed the idea for years in talks both to physicists and to neuroscientists, which is how I heard of it, and finally published a paper in 2022.24 Several other physicists and philosophers also took up the idea in the meantime and offered their own analyses.25
Their proposition is that a conscious system stands outside quantum physics. If you try to put it into a superposition, it will fight back. “It will resist this superposition,” explained McQueen, who is now a professor at Chapman University in Orange, California. In the taxonomy of solutions to the measurement problem, this conjecture falls into the category of supposing that quantum theory fails at some level. The idea is that highly interconnected systems such as our brains violate it.
Chalmers and McQueen and the others formulated their theories by repurposing the equations that physicists over the years had proposed for setting a size threshold for quantum mechanics. They replaced that threshold with the IIT general measure of consciousness, Φ, as well as its criteria for specific conscious experiences. They calibrated the equations so that a simple neural network, with zero or low Φ, obeys quantum mechanics to the letter, whereas an intricate network deviates. “Systems with sufficient integrated information do not respond to entanglement by superposing, but by collapsing the entangling system,” McQueen said.
The way it works is that, during a measurement, the experimental apparatus connects a particle or other object to the brain. We normally think of measuring as transferring information from a particle to our brain, but in these theories the traffic is two-way. Through the connection that the measurement system establishes, the mind reaches out, grabs particles that are poised between possibilities, and tells them, Choose!
One reason it took Chalmers and McQueen so long to publish their paper is that they had to work out the menu of options that particles choose among when they collapse. Because they are postulating a real collapse rather than an ersatz one, they can’t assume that the process of decoherence sets the menu. Instead, the menu must be determined by the conscious experiences that our brains are capable of. The particle will settle into a state that is consistent with a specific pattern of neural connectivity. McQueen and Chalmers don’t explain why that would translate into seeing the photon either here or there—why, in other words, our experience is of localized objects. Presumably this has some practical rationale. Our conscious experience is shaped by evolution and by education to represent the world in a way that helps us to survive, which entails seeing the world as laid out spatially. The cosmologist Max Tegmark has also suggested that IIT itself could provide an answer to the menu problem—the world may appear to be made of separate but interacting parts because our own minds, according to IIT, are made that way.26
This raises the mind-blowing possibility that other sentient beings might think in vastly different categories. Päs calls them “quantum aliens.”27 Depending on how their minds are structured, they might perceive the fundamental unit of space to be a line rather than a point, so to them, there would be nothing weird about existing at multiple locations at once. Instead, they might find it mystifying that anything could ever confine itself to just one spot. The science-fiction writer Ted Chiang, in “Story of Your Life,” imagined extraterrestrial visitors who see all of time laid out before them. Per the IIT-based theories, these aliens would have a different effect on the particles they observe than we do.
Another fascinating issue that McQueen and Chalmers comment on is that collapse takes time, so there is a brief window during which the brain is in a superposition of two conscious experiences. What would that even mean? They explore several options. Perhaps it would be a kind of split-brain syndrome in which two independent minds occupy the same brain—an option that physicists have considered in the past and that I will return to in chapter 5. But they lean toward thinking of it as a bizarre new category of experience, like synesthesia or an LSD trip, that merges qualities of more familiar ones.
To test the IIT-based theories, McQueen and others have proposed adapting existing quantum threshold experiments so that experimenters can compare objects with different degrees of integration. Even a tiny quantum computer might do—small though it is, it might still have a high enough value of Φ to quickly collapse any particle it came into contact with. “What’s nice about that is that the theory can be tested without needing to test on large quantum systems,” McQueen said. Physicists who do threshold experiments are receptive: “We plan to go along this direction of study as well,” the quantum researcher Cătălina Curceanu at the Istituto Nazionale di Fisica Nucleare in Rome told me in 2021.
At the end of the day, you might still wonder how and why the mind would exert a collapse effect. McQueen said he sees his and Chalmers’s theory as merely a stepping-stone—first, clarify the circumstances of collapse; later, worry about the underlying mechanism. Perhaps the collapse is triggered not by consciousness or information integration per se, but by deeper physics that integrated systems are somehow more sensitive to. “The immediate goal is self-consistent description,” McQueen said. “But the process of reaching such a goal can often lead unexpectedly to new kinds of explanation.”
IMMUNE TO SUPERPOSITION
Penrose comes at the problem of quantum measurement from the opposite direction. Instead of supposing that consciousness causes collapse, he argues that collapse causes consciousness. He starts by identifying an entirely objective mechanism for collapse—“It takes place in the physics, and it’s not because somebody comes and looks at it,” he told me—and then he mulls what such a mechanism might mean for our mental experience.
The mechanism he proposes is gravitational. In our current understanding, gravity is produced by a field akin to the electric or magnetic field. This field is a structure that pervades all of space (and indeed is an aspect of space). When we say that Earth exerts a force on an apple, what we mean is that the planet affects the field, which in turn acts on the apple. Most physicists think that the gravitational field is as quantum as anything else in nature—this has been their starting assumption in seeking a unified theory of physics. Penrose thinks the unification project has stalled because it presupposes that quantum physics is the more fundamental concept and that gravity must somehow fit into its framework, whereas he thinks that gravity might alter the quantum framework.28
Building on work in the ’60s by the physicists Richard Feynman and Frigyes Károlyházy, Penrose suggested in the ’80s that the gravitational field stands outside quantum physics, unable to remain in a superposition for very long, or at all.29 Whereas an ordinary particle will remain in superposition forever if it is kept isolated, the gravitational field will quickly collapse. That in turn affects planets, apples, and anything else the field touches.
Penrose’s theory adds a new element to the textbook account of measurement. During a measurement, the particle’s superposition spreads to the measuring equipment, eyes, and brain. If the equipment has a dial, the dial might point to multiple positions at once. Within the eyes and brain, ions and proteins might move to both the left and the right sides of a cell. Thus the widening superposition will affect the arrangement of mass in the laboratory. Because the force of gravity is a function of mass, this superposition threatens to put the gravitational field into superposition, too. On Penrose’s account, that’s where superposition must stop. Being immune to superposition, the gravitational field settles into one state or the other, and once it does, it resolves the ambiguity of everything else. The brain, eye, equipment, and particle settle down, too. “Gravity does not like superposition,” Curceanu explained. “Gravity is classical! So it reacts back on the wave function.”
So far, this approach is actually quite similar to Chalmers and McQueen’s. Both speculate that the process of observation causes a particle to collapse, not because of some mystical power that the mind has, but because connecting the particle to a larger system exposes it to some new kind of physics, be it information integration or gravitational effects. Where the approaches diverge is in the neuroscience. While Chalmers and McQueen adopt IIT, Penrose developed an entirely new theory of consciousness. Having proposed new gravitational physics to explain quantum collapse, he speculated that this new physics might have something to do with the mind. His reasoning was straightforward: if the known laws of physics can’t explain our minds, you apparently need new laws—and hey, here is a new law. As a physicist, however, Penrose didn’t have much to add about the neuroscientific details. That’s where Stuart Hameroff entered the story.
While a medical student in the early ’70s, Hameroff spent a summer in a lab doing research on cancer biology. One thing that can go awry in the cells of cancer patients is mitosis, the process of cell division. During mitosis, a cell makes copies of its chromosomes, pulls the copies apart, and splits in two. Hameroff became fascinated by what does the pulling. This was his introduction to microtubules.
These miniature filaments had been discovered in the ’50s.30 Composed of a protein called, appropriately, tubulin, they are the bones of a cell’s miniature skeleton. Watching them choreograph cell division, Hameroff thought that they seemed awfully smart for bones. Indeed, biologists at the time were finding that microtubules perform a range of surprisingly sophisticated functions. Cilia and flagella, the little tentacles of a cell, are made of microtubules. Microtubules give the cell a primitive sense of touch and smell, let it differentiate among stimuli, and fuse information from multiple sources.31 Tubulin molecules can change in shape, and electric charges moving back and forth within them can store information.
Hameroff contributed to the study of microtubules in the ’80s by working out how these structures have all the makings of tiny computers.32 Most neuroscientists, he concluded, had been looking at the wrong level of the brain to understand how we think and feel.33 “Neuroscience tells us that neurons are dumb—nodes in a network—and you get consciousness from networks,” Hameroff said. He came to think that the basic unit is not the neuron, but the microtubule, that the arrangement of microtubules within neurons may be as or more important than the connections among neurons. This was a controversial claim—arguably even more so than Penrose’s ideas about quantum effects. In recent years, neuroscientists have come to agree that neurons are complex computers in their own right, containing what amounts to a miniature neural network.34 Whether microtubules are involved, though, remains contentious.
For microtubules to serve a computing function, they’d need, as all digital computers do, a clock to synchronize their signals. Hameroff turned to a mechanism proposed by the physicist Herbert Fröhlich in the ’60s. Fröhlich argued (and experimenters later proved) that, using microwaves or mechanical vibrations, you can cause protein molecules to oscillate in a coordinated way, overcoming the chaotic motions that ordinarily prevail inside a cell.35 Hameroff thought such oscillations could serve as a computer clock—a bit like a quartz clock, in fact. He suggested that general anesthetics knock you out by stopping the clock. That would mean the oscillations help to make us conscious.36 Fröhlich’s comparison of the oscillations to a quantum process known as Bose-Einstein condensation gave Hameroff his first inkling that quantum effects might be important to consciousness.37
When he read Penrose’s book in 1992, Hameroff decided he was holding the missing puzzle piece. Quantum effects, including the ones Penrose was proposing, tend to be most prominent at small scales. Microtubules just so happen to be the right size. Hameroff reached out to Penrose, and the two hit it off. They were part of a minitrend. Around the same time, other scientists—most prominently John Eccles, who had won the Nobel Prize for studying the transmission of neural signals across synapses—were also suggesting that quantum effects might create our conscious experience.38
QUANTUM PANPSYCHISM
What Penrose and Hameroff proposed is that each of our conscious experiences is a quantum collapse. Our minds don’t cause collapse, but are constituted by it. When we see red or hear a minor chord, quantum wave functions are collapsing to give these experiences a quality beyond their bare information content. Why that should be the case, Penrose and Hameroff do not claim to be able to explain. Rather, they take it as a primitive feature of the universe. “Consciousness in some way has been there all along,” Hameroff said. They are proposing, in short, a form of panpsychism, the old doctrine that mentality is ubiquitous in the natural world.39
