Microtubule Symmetry and the Timing of Conscious Acts

Roger Penrose opens his 2024 talk at The Science of Consciousness meeting by apologizing for a slide. The image on screen is a microtubule he drew years ago, a hollow tube built from a lattice of protein subunits, and he warns the audience that the idea attached to it has since fallen out of fashion. What follows, in a recording later posted to YouTube by Julia Mossbridge, is one of the more unusual arguments a Nobel-winning physicist has made in public about the mind: that the collapse of the quantum wave function may be non-computable, that the geometry of microtubules might be physically meaningful rather than accidental, and that the timing of conscious acts could be tangled up with retrocausal physics. The talk is short on conclusions and long on open questions, which is exactly what makes it worth slowing down for.

Why would a physicist think consciousness needs non-computable physics?

The starting point is not biology. It is logic. Penrose says that decades ago he was struck by Gödel's theorem and by the sense that understanding, the thing a mathematician does when a proof suddenly makes sense, seemed impossible to capture fully in algorithms. If that is true, and if brains are physical objects, then something in the physics of the brain must lie outside what a computer can do.

He then ran through the candidates. Electromagnetism, general relativity and most of physics, as he put it, can all be placed on a computer, at least in principle, although continuous variables mean every calculation is an approximation. Quantum mechanics seemed like a better bet, because the wave function itself can be simulated. But one piece stood out:

"I had the view that it was the collapse of the wave function which somehow had to be outside what you could compute." (Penrose, 2024 Science of Consciousness talk, 2:21)

That single sentence is the spine of the whole talk. Penrose is not claiming that consciousness is quantum in some vague, decorative sense. He is claiming that a specific, mathematically undefined step in quantum theory, the moment a superposition resolves into one outcome, is the only place he can imagine a non-algorithmic process hiding. He also admits this is not a finished position; he calls the idea a loophole he never fully closed.

How did microtubules end up in a theory of mind?

Penrose's early work on this problem appeared in his book The Emperor's New Mind. In it, he argued that if collapse were to play any role in the brain, the brain would need quantum systems large enough to keep their coherence for a meaningful stretch of time. He looked at the physiology of nerve signaling, the Hodgkin-Huxley account of how neurons fire, and concluded there was no hope. The signals moving through neurons, he reasoned, would jostle the surrounding material in ways too random to preserve coherence.

So the book ended on an admitted gap. The missing piece came from Stuart Hameroff, who read the book and pointed Penrose toward microtubules, the cytoskeletal structures inside cells. Penrose says this changed the picture. In his telling, the second book was where he realized there might be something to explore in microtubule behavior, even though he had no clear idea what that something was. The talk is his attempt to say one specific thing about the microtubule that he had not put into print before.

What is the symmetry puzzle inside a microtubule?

This is the part of the talk that will reward a reader who has never seen a crystal lattice. Penrose describes the microtubule's underlying structure as something like a hexagonal lattice, a flat sheet that repeats itself in three different directions. When you roll that sheet into a cylinder, those three directions behave differently. One direction corkscrews around the tube one way, another corkscrews the other way, and the third runs straight along the tube's length.

The microtubules found in cells, he says, have a particular arrangement: 13 columns of subunits around the circumference. That number matters. Change it to 12 or 14 and you can still build a tube, but it loses what Penrose calls translational symmetry along the tube's length. It becomes all twist and no straight repeat. Here is the line that gives the puzzle its edge:

"It always struck me as rather strange that the microtubules you found here have this particular symmetry which goes along the microtubule itself." (Penrose, 2024 Science of Consciousness talk, around the 6-minute mark)

In other words, the number 13 is a fact of biology, and Penrose is asking whether it is also a fact of physics. If the straight-line symmetry is the only arrangement that serves some physical role, then nature may have selected it for reasons that go beyond chemistry. He does not claim to know whether that is so. He says the question simply seems worth exploring.

Why bring carbon nanotubes into the argument?

Penrose's analogy is to carbon nanotubes, rolled-up sheets of carbon atoms that physicists study intensively. He recalls reading that nanotubes with translational symmetry along their length can exhibit superconductivity. He admits he cannot remember which paper he had in mind and asks the audience to help him find it. He is also careful about room temperature: he says he is not sure such superconductivity has been achieved with these structures, and he does not extend the claim to microtubules.

The logic is suggestive rather than proven. If a symmetry that depends on how a tube is shaped can influence electron behavior in one material, then a similar symmetry in a biological tube might be associated with effects that are more global than the local quantum events biologists usually discuss. Penrose's own summary is modest: there is something here that should be explored, and he would not say much more because he had not thought about it in depth.

Where does the Schrödinger equation stop and collapse begin?

To understand why the collapse of the wave function matters so much to Penrose, the talk walks through the basic machinery of quantum mechanics. There are, he says, two procedures. One is the Schrödinger equation, which describes how a quantum state evolves smoothly over time. The other is the collapse, which takes the amplitudes of the superposition and turns them into the probabilities of an actual outcome.

He is blunt that the second step is not really explained by conventional quantum mechanics. Textbooks often blur the two together, talking about the Schrödinger equation as though it accounts for what we observe. Penrose argues that it does not. The equation is smooth and computable. The collapse is the part where the theory simply states that the transition happens, without a mechanism for how it happens. That gap is where his argument pushes.

What does retrocausality have to do with a clock?

The talk's most ambitious section moves from the wave function into spacetime. Penrose uses spacetime diagrams to explain how a superposition might involve two different geometries, and he works through the timing implications of those diagrams. The argument is dense, and the captions of the recording are imperfect at points, so a faithful summary has to stay close to what he states outright.

What he does state outright is important. In the description of the video, the talk is framed around the idea that retrocausality must somehow be part of whatever version of quantum mechanics eventually emerges. Penrose's proposed direction, as summarized there, is a gravitization of quantum mechanics rather than a quantum gravity model, a distinction that matters a great deal to specialists. He also refers to the ways a clock's hands can seem to tell a story about the present when the underlying physics runs in more than one direction.

Is Libet's readiness potential a precognitive signal?

Penrose connects these threads to the work of Benjamin Libet, whose experiments suggested that the brain's preparation for a voluntary movement begins before the person becomes consciously aware of deciding to move. In the talk's closing stretch, Penrose returns to the idea that some processes in the brain must be unconscious, and he discusses causal loops, the way a sequence of events can seem to run backward when the physics allows it.

Mossbridge's own note in the video's description takes that connection further. She writes that her work suggests Libet's readiness potential is likely precognitive in origin, a retrocausal reflection of the future event, rather than an unconscious capture of free will. That is her interpretation, and it is not the position Penrose lays out in the portions of the talk that are available in the recording. Penrose's contribution is the physics scaffold: the claim that collapse is non-computable, that retrocausality may be unavoidable, and that the brain's timing could reflect physics we do not yet understand. Whether that scaffold supports precognition is a question the talk raises and leaves open.

What is still unresolved?

The honest answer is a great deal. Penrose does not claim that microtubules are superconductive, that consciousness is a quantum computation, or that the brain uses retrocausal signals. He presents a chain of reasoning in which each link is a question. Is the collapse of the wave function a real, non-computable process? Is the 13-column symmetry a clue or an accident? Do the physics of superconducting nanotubes say anything about living tubes? Each question carries the weight of a research program, and the talk ends before any of them is settled.

That is why the talk remains useful. It shows how a working scientist moves from a puzzle in logic, to a dissatisfaction with a textbook, to a specific geometric observation, and then to a willingness to follow the implications even when they point somewhere uncomfortable. Penrose's apology at the start was about an old slide. The more interesting thing he offers is the habit of noticing when a structure seems too neat to be accidental.

Where to go from here

Start with the talk itself and listen for the three moves: the Gödel argument about understanding, the microtubule symmetry question, and the discussion of collapse versus smooth evolution. Then read The Emperor's New Mind, where the collapse argument first appears in full, and compare it with the more cautious framing in this 2024 talk. If you want the other side of the debate, look for critics of the microtubule hypothesis and for experimental work on Libet-style timing. Mossbridge's linked papers on readiness potentials offer one interpretation to test against the physics. Keep the distinction clear as you go: what Penrose proposes, what he explicitly leaves open, and what others have built on top of his ideas.