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Roger Penrose On Why Consciousness Does Not Compute

The emperor of physics defends his controversial theory of mind.

Once you start poking around in the muck of consciousness studies, you will soon encounter the specter of Sir Roger Penrose, the renowned…By Steve Paulson

Once you start poking around in the muck of consciousness studies, you will soon encounter the specter of Sir Roger Penrose, the renowned Oxford physicist with an audacious—and quite possibly crackpot—theory about the quantum origins of consciousness. He believes we must go beyond neuroscience and into the mysterious world of quantum mechanics to explain our rich mental life. No one quite knows what to make of this theory, developed with the American anesthesiologist Stuart Hameroff, but conventional wisdom goes something like this: Their theory is almost certainly wrong, but since Penrose is so brilliant (“One of the very few people I’ve met in my life who, without reservation, I call a genius,” physicist Lee Smolin has said), we’d be foolish to dismiss their theory out of hand.

Penrose, 85, is a mathematical physicist who made his name decades ago with groundbreaking work in general relativity and then, working with Stephen Hawking, helped conceptualize black holes and gravitational singularities, a point of infinite density out of which the universe may have formed. He also invented “twistor theory,” a new way to connect quantum mechanics with the structure of spacetime. His discovery of certain geometric forms known as “Penrose tiles”—an ingenious design of non-repeating patterns—led to new directions of study in mathematics and crystallography.

The breadth of Penrose’s interests is extraordinary, which is evident in his recent book Fashion, Faith and Fantasy in the New Physics of the Universe—a dense 500-page tome that challenges some of the trendiest but still unproven theories in physics, from the multiple dimensions of string theory to cosmic inflation in the first moment of the Big Bang. He considers these theories to be fanciful and implausible.

EMERGENT BEAUTY: Roger Penrose has always been in search of deep structures of the universe, reflected in the tiling he created, where basic shapes—in this case the rhombus—give rise to extraordinary patterns.

Penrose doesn’t seem to mind being branded a maverick, though he disputes the label in regard to his work in physics. But his theory of consciousness pushes the edges of what’s considered plausible science and has left critics wondering why he embraces a theory based on so little evidence.

Most scientists regard quantum mechanics as irrelevant to our understanding of how the brain works. Still, it’s not hard to see why Penrose’s theory has gained attention. Artificial intelligence experts have been predicting some sort of computer brain for decades, with little to show so far. And for all the recent advances in neurobiology, we seem no closer to solving the mind-brain problem than we were a century ago. Even if the human brain’s neurons, synapses and neurotransmitters could be completely mapped—which would be one of the great triumphs in the history of science—it’s not clear that we’d be any closer to explaining how this 3-pound mass of wet tissue generates the immaterial world of our thoughts and feelings. Something seems to be missing in current theories of consciousness. The philosopher David Chalmers has speculated that consciousness may be a fundamental property of nature existing outside the known laws of physics. Others—often branded “mysterians”—claim that subjective experience is simply beyond the capacity of science to explain.

Conventional wisdom goes something like this: The theory is almost certainly wrong, but Penrose is brilliant.

Penrose’s theory promises a deeper level of explanation. He starts with the premise that consciousness is not computational, and it’s beyond anything that neuroscience, biology, or physics can now explain. “We need a major revolution in our understanding of the physical world in order to accommodate consciousness,” Penrose told me in a recent interview. “The most likely place, if we’re not going to go outside physics altogether, is in this big unknown—namely, making sense of quantum mechanics.”

He draws on the basic properties of quantum computing, in which bits (qubits) of information can be in multiple states—for instance, in the “on” or “off” position—at the same time. These quantum states exist simultaneously—the “superposition”—before coalescing into a single, almost instantaneous, calculation. Quantum coherence occurs when a huge number of things—say, a whole system of electrons—act together in one quantum state.

It was Hameroff’s idea that quantum coherence happens in microtubules, protein structures inside the brain’s neurons. And what are microtubules, you ask? They are tubular structures inside eukaryotic cells (part of the cytoskeleton) that play a role in determining the cell’s shape, as well as its movements, which includes cell division—separation of chromosomes during mitosis. Hameroff suggests that microtubules are the quantum device that Penrose had been looking for in his theory. In neurons, microtubules help control the strength of synaptic connections, and their tube-like shape might protect them from the surrounding noise of the larger neuron. The microtubules’ symmetry and lattice structure are of particular interest to Penrose. He believes “this reeks of something quantum mechanical.”

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Still, you’d need more than just a continuous flood of random moments of quantum coherence to have any impact on consciousness. The process would need to be structured, or orchestrated, in some way so we can make conscious choices. In the Penrose-Hameroff theory of Orchestrated Objective Reduction, known as Orch-OR, these moments of conscious awareness are orchestrated by the microtubules in our brains, which—they believe—have the capacity to store and process information and memory.

“Objective Reduction” refers to Penrose’s ideas about quantum gravity—how superposition applies to different spacetime geometries—which he regards as a still-undiscovered theory in physics. All of this is an impossibly ambitious theory that draws on Penrose’s thinking about the deep structure of the universe, from quantum mechanics to relativity. As Smolin has said, “All Roger’s thoughts are connected ... twistor theory, his philosophical thinking, his ideas about quantum mechanics, his ideas about the brain and the mind.”

This is a heady brew, but unconvincing to critics. Most scientists believe the brain is too warm and wet for quantum states to have any influence on neuronal activity because quantum coherence only seems possible in highly protected and frigid environments. The most damning critique has come from Max Tegmark, a professor of physics at the Massachusetts Institute of Technology, who calculated that any quantum effects within microtubules would break down after 100 quadrillionths of a second. “For my thoughts to correspond to a quantum computation, they’d need to finish before decoherence kicked in, so I’d need to be able to think fast enough to have 10,000,000,000,000 thoughts each second,” Tegmark writes in his 2014 book Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. “Perhaps Roger Penrose can think that fast, but I sure can’t.” Even Penrose’s old collaborator Stephen Hawking is dubious. “I get uneasy when people, especially theoretical physicists, talk about consciousness,” he’s written. “His argument seemed to be that consciousness is a mystery and quantum gravity is another mystery so they must be related.” Penrose dismisses Hawking’s criticism, saying their disagreement is really about the nature of quantum mechanics.


Last year I saw Penrose in action at a one-day conference on consciousness in Lucerne, Switzerland. It was an intriguing assortment of speakers, including the neuroscientist Christof Koch, Buddhist monk Matthieu Ricard, The Tao of Physics author Fritjof Capra, and even an ayahuasca expert. Then there was Penrose, who played the part of the unworldly Oxford don—slightly rumpled in appearance, with an impish sense of humor. He had set up two overhead projectors on stage, and then darted back and forth between these machines, laying down a series of transparencies filled with his own handwritten notes and drawings of neurons and microtubules, the Leaning Tower of Pisa, a floating astronaut, and—as I recall—the Little Mermaid, all in an effort to explain the Orch-OR theory of consciousness. Modern science may be a high tech game, but this was a dazzling piece of performance art, and the overflowing audience loved it.

Hameroff was also at the conference, and it turned out their hotel rooms were just down the hall from mine. In my brief interactions with them, I got the sense that Hameroff plays the role of willing accomplice—not only touting the genius of Sir Roger, but also looking after Penrose when it came to travel arrangements and even getting to the conference site. Hameroff can also be the pugnacious bulldog defending their theory (which, in the panel discussion, he did by needling Koch about various details of brain activity).

Marvin Minsky once told me that the study of consciousness is “what people wasted their time on in the 20th century.”

This past March, when I called Penrose in Oxford, he explained that his interest in consciousness goes back to his discovery of Gödel’s incompleteness theorem while he was a graduate student at Cambridge. Gödel’s theorem, you may recall, shows that certain claims in mathematics are true but cannot be proven. “This, to me, was an absolutely stunning revelation,” he said. “It told me that whatever is going on in our understanding is not computational.”

He was also jolted by a series of lectures on quantum mechanics by the great physicist Paul Dirac. Like many others, Penrose struggled with the weirdness of quantum theory. “As Schrödinger clearly pointed out with his poor cat, which was dead and alive at the same time, he made this point deliberately to show why his own equation can’t be the whole truth. He was more or less saying, ‘That’s nonsense.’ ” To Penrose, the takeaway was that something didn’t add up in quantum theory: “Schrödinger was very upset by this, as were Dirac and Einstein. Some of the major figures in quantum mechanics were probably more upset than I was.”

But what, I asked, does any of this have to do with consciousness? “You see, my argument is very roundabout. I think this is why people don’t tend to follow me. They’ll pick up on it later, or they reject it later, but they don’t follow argument.” Penrose then launched into his critique of why computers, for all their brute calculating power, lack any understanding of what they’re doing. “What I’m saying—and this is my leap of imagination which people boggle at—I’m saying what’s going on in the brain must be taking advantage not just of quantum mechanics, but where it goes wrong,” he said. “It’s where quantum mechanics needs to be superseded.” So we need a new science that doesn’t yet exist? “That’s right. Exactly.”

Vanessa Penrose / Caroline Davis2010 / Flickr

After we’d talked for 20 minutes, I pointed out that he still hadn’t mentioned biology or the widely held belief that consciousness is an emergent property of the brain. “I know, I know,” he chuckled, and then told me why he felt compelled to write his first book on consciousness, The Emperor’s New Mind, published in 1989. It was after he heard a BBC interview with Marvin Minsky, a founding father of artificial intelligence, who had famously pronounced that the human brain is “just a computer made of meat.” Minsky’s claims compelled Penrose to write The Emperor’s New Mind, arguing that human thinking will never be emulated by a machine. The book had the feel of an extended thought experiment on the non-algorithmic nature of consciousness and why it can only be understood in relation to Gödel’s theorem and quantum physics.

Minsky, who died last year, represents a striking contrast to Penrose’s quest to uncover the roots of consciousness. “I can understand exactly how a computer works, although I’m very fuzzy on how the transistors work,” Minsky told me during an interview years ago. Minsky called consciousness a “suitcase word” that lacks the rigor of a scientific concept. “We have to replace it by ‘reflection’ and ‘decisions’ and about a dozen other things,” he said. “So instead of talking about the mystery of consciousness, let’s talk about the 20 or 30 really important mental processes that are involved. And when you’re all done, somebody says, ‘Well, what about consciousness?’ and you say, ‘Oh, that’s what people wasted their time on in the 20th century.’ ”

But the study of consciousness has not gone the way Minsky had hoped. It’s now a cottage industry in neuroscience labs and a staple of big-think conferences around the world. Hameroff is one of the driving forces behind this current enthusiasm. For years he and Chalmers have run the biennial “Toward a Science of Consciousness” conference that features dozens of speakers, ranging from hardcore scientists to New Age guru Deepak Chopra and lucid dream expert Stephen LaBerge. Hameroff’s connection to Penrose also goes back decades. He first contacted Penrose after reading The Emperor’s New Mind, suggesting he might have the missing biological component that would complement Penrose’s ideas about the physics of consciousness.

The science of consciousness feels stuck, and here’s a theory—however speculative—that suggests a possible way forward.

“I finished the book without really knowing what I was doing,” Penrose recalled. “Stuart wrote me a good old-fashioned letter in which he said, ‘It seems that you don’t know about microtubules.’ ” When they met in Oxford, Penrose realized that microtubules had the best chance of anything he’d seen that could mediate large-scale quantum coherence within the brain. And ever since, Penrose and Hameroff have been peddling their theory. Then in 2013, scientists in Japan announced that they had detected vibrations in microtubules, which, according to Penrose and Hameroff, seemed to show that the brain is not too warm and noisy for delicate quantum activity, and launched a new round of debate about the Orch-OR theory.

In some ways, Penrose and Hameroff are the odd couple of science. Hameroff is upfront about his spiritual views, talking openly about the possibility of the soul existing after death. Penrose is an atheist who calls himself “a very materialistic and physicalist kind of person,” and he’s bothered by New Agers who’ve latched onto quantum theories about non-locality and entanglement to prop up their paranormal beliefs.

I asked what he thought of Hameroff’s far-flung ideas about disembodied consciousness. “Well, I have to allow him his freedom,” he said. “It does worry me a bit. I mean, he goes a lot further than I would be prepared to.” Still, he acknowledges that consciousness is a huge mystery. “I’m not even sure what materialistic means, quite honestly. Quantum mechanics behaves in ways that one thinks are certainly at odds with the view we used to have.”

As we probed the deeper implications of Penrose’s theory about consciousness, it wasn’t always clear where to draw the line between the scientific and philosophical dimensions of his thinking. Consider, for example, superposition in quantum theory. How could Schrödinger’s cat be both dead and alive before we open the box? “An element of proto-consciousness takes place whenever a decision is made in the universe,” he said. “I’m not talking about the brain. I’m talking about an object which is put into a superposition of two places. Say it’s a speck of dust that you put into two locations at once. Now, in a small fraction of a second, it will become one or the other. Which does it become? Well, that’s a choice. Is it a choice made by the universe? Does the speck of dust make this choice? Maybe it’s a free choice. I have no idea.”

I wondered if Penrose’s theory has any bearing on the long-running philosophical argument between free will and determinism. Many neuroscientists believe decisions are caused by neural processes that aren’t ruled by conscious thought, rendering the whole idea of free will obsolete. But the indeterminacy that’s intrinsic to quantum theory would suggest that causal connections break down in the conscious brain. Is Penrose making the case for free will?

“Not quite, though at this stage, it looks like it,” he said. “It does look like these choices would be random. But free will, is that random?” Like much of his thinking, there’s a “yes, but” here. His claims are provocative, but they’re often provisional. And so it is with his ideas about free will. “I’ve certainly grown up thinking the universe is deterministic. Then I evolved into saying, ‘Well, maybe it’s deterministic but it’s not computable.’ But is it something more subtle than that? Is it several layers deeper? If it’s something we use for our conscious understanding, it’s going to be a lot deeper than even straightforward, non-computable deterministic physics. It’s a kind of delicate borderline between completely deterministic behavior and something which is completely free.”

It’s hard to know what to make of these pronouncements. Even if you’re skeptical of Penrose’s argument about consciousness, it’s tempting to root for him. The science of consciousness feels stuck, and here’s a theory—however speculative—that suggests a possible way forward. The fact that Penrose is asking so much of us—not just to accept quantum coherence in microtubules but also his contention that consciousness can only be explained by still-undiscovered laws of physics—may simply be too far-reaching to ground a new scientific theory. And there’s another problem as well. Suppose 20 or 200 years from now the broad outlines of Orch-OR are confirmed. Have we explained consciousness—or just pushed the mind-brain problem into a deeper mystery, the quantum mind-body problem? Can we ever bridge the gap between the physical and immaterial worlds?

As I wondered why Penrose keeps hammering away at his theory on consciousness after all these years, I asked him if he thinks there’s any inherent meaning in the universe. His answer surprised me. “Somehow, our consciousness is the reason the universe is here.” So does he think there’s intelligent life—or consciousness—somewhere else in the cosmos? “Yes, but it may be extremely rare.” But if consciousness is the point of this whole shebang, wouldn’t you expect to find some evidence of it beyond Earth? “Well, I’m not so sure our own universe is that favorably disposed toward consciousness,” he said. “You could imagine a universe with a lot more consciousness that’s peppered all over the place. Why aren’t we in one of those rather than this one where it seems to be a rather uncommon activity?

“So, yes, we want to see the purpose of it. I don’t know. Maybe it’s attributing the wrong word. Purpose—what does that mean?” He chuckled.


Steve Paulson is the executive producer of Wisconsin Public Radio’s nationally syndicated show To the Best of Our Knowledge. He’s the author of Atoms and Eden: Conversations on Religion and Science. You can subscribe to TTBOOK’s podcast here.

Lead photo collage: Vanessa Penrose / Caroline Davis2010 / Flickr

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