A quantum computer in the human brain?

20 years ago, mathematician Roger Penrose and anesthesiologist Stuart Hameroff laid the foundations for a theory of how the human brain and consciousness work. One of its elements implied the existence of quantum states that have decoherence resistance in the internal structure of neurons. Scientists claim that they have managed to find weighty arguments in favor of this hypothesis. However, although both of them are highly respected in scientific circles, their assumptions are still very skeptical.

Almost 20 years ago, the great mathematician and physicist Roger Penrose published a book that was the result of his reflections on the nature of the mind and consciousness. In addition, in this work called “Shadows of the Mind: A Search for the Missing Science of Consciousness” (Shadows of the Mind: A Search for the Missing Science of Consciousness), he talked about a number of ideas proposed in the 1980s by anesthesiologist Stuart Hameroff. In particular, it stated that Godel’s incompleteness theorem contradicted the conclusions of Alan Turing’s work on artificial intelligence: it means that calculations on a sufficiently complex machine can lead to the emergence of a conscious human mind.

According to Penrose, Godel’s results implied that the human mind and consciousness could not be reduced to calculations. Thus, he joined the camp of those who believe that the “difficult problem of consciousness,” in the words of the Australian philosopher David Chalmers, cannot be solved by reducing consciousness to the execution of certain algorithms. In other words, although we can relate a mathematical structure to the perception of sound or color, it cannot be reduced to this very structure and calculation, just as simulating a star, cyclone, or electromagnetic wave on a computer does not create these objects in real life. In addition, like other scientists before him (Einstein, Schrodinger and Bell), Penrose thereby expressed his dissatisfaction with the current state of quantum physics.

As you know, in quantum mechanics, the probability amplitude of a physical system (otherwise it is also called the wave function vector) varies in a well-defined way, since it is governed by only one law: the Schrodinger equation. Nevertheless, when we need to measure a certain physical quantity of the system, for example, the location of an electron or its spin, the second law also comes into play, as a result of which the wave function changes dramatically and indefinitely. All this is a bit like how an attempt to establish the presence of a certain note in a musical passage in the form of spherical sound waves radiating around the piano would lead to the disappearance of all other notes except one, which was chosen according to the law of probability.

It would take several books to address all the problems that have been raised by what physicists call “wave packet reduction”: It is closely related to the introduction of probability amplitudes and simply probability laws in quantum physics. In particular, it led to the Einstein—Podolsky—Rosen paradox and the Schrodinger cat paradox. As Penrose describes the situation in detail in the book, he recognizes the validity of the theory of decoherence regarding the Schrodinger’s cat paradox, he believes (and he is not alone in this) that the problem has not yet been completely solved.

In his opinion, we need some kind of new physics (as a consequence of the quantum theory of gravity, to which standard quantum mechanics should give only approximate values) if we really want to solve all the mysteries and overcome all the difficulties that certain aspects of quantum theory pose to us. In addition, this new physics should contain mathematical elements that cannot be reduced to algorithms, as follows from Penrose’s perception of Godel’s theorem. Finally, she would be able to shed light on the difficult problem of consciousness.

Based on the results of such reflections, which he presented in a slightly abridged version in the book “The New Mind of the King. About computers, thinking and the laws of physics” (The Emperor’s New Mind. Concerning Computers, Minds and The Laws of Physics), Penrose turned to Stuart Hameroff. He talked about these attempts as a biologist and anesthesiologist: in doing so, he was trying to understand the workings of the brain and the physical foundations of consciousness. Joining forces, scientists have proposed the following theory.

They took as a basis the statement that most of the work of our brain is perfectly explained using the laws of classical physics, in particular, at the connectome level, that is, neural connections. Nevertheless, something new is emerging at the level of synapse connections. These connections are strongly influenced by structures that are found in the cytoskeleton of neurons: we are talking about microtubules. They are something like fibers that consist of tubulin dimers (these proteins have a dipole moment). According to Penrose and Hameroff, these polarizing proteins transform microtubules into something like cellular automata that can accumulate qubits and perform calculations beyond those usually attributed to a neural network. If this is true, then the information processing capabilities of the human brain are much higher than is commonly believed today. In addition, this further postpones the prospect of creating a powerful enough computer that would be able to properly simulate its operation.

In addition, (this moment attracts the main criticism in the scientific community) Penrose and Hameroff stated that microtubules can represent efficient quantum computers, although the theory of decoherence claims that this is impossible. Brain cells and microtubules have too high a temperature and are too strongly exposed to ambient noise, which does not give enough time for long quantum calculations. In other words, even if we descend to the level of tibulins, the objects we have to deal with are still too hot and large to exhibit quantum properties.

Anyway, Penrose and Hameroff replied that we can’t be sure of anything here. We know that at the macroscopic level, objects can exhibit quantum behavior, which is manifested in properties such as superconductivity and superfluidity (so far, we are talking only about extremely low temperatures, but in the future, scientists hope to create superconductors that could work under normal conditions). In addition, we know that the Einstein—Podolsky—Rosen effect actually works, despite the distance of several meters between quantum systems. Signs of quantum coherence are also characteristic of biological systems and have been observed in them at low temperatures for several years. In particular, this applies to photosynthesis. It is possible that evolution has managed to circumvent the obstacle of quantum decoherence.

There is an even more controversial hypothesis in the theory of Penrose and Hameroff. If quantum calculations are indeed carried out in microtubules, they are under the influence of quantum gravity, which in turn involves processes that are inconsistent with Penrose’s calculations outside of traditional quantum mechanics. In particular, this occurs at the level of reduction of the wave packet when measuring data with the so-called objective reduction.

According to Penrose (as well as Einstein, and such renowned physicists as John Bell and GerardT. Hooft), the quantum physics at our disposal at the moment can only be a partial (albeit very effective in practice) solution to the problems of energy quantization and wave-particle dualism. Thus, at a deeper level of reality, there is a physics of consciousness that is still unknown to us (it includes classical quantum theory): At the moment, we see only its shadow in the connectome and microtubules. Just as the existence of space-time categories becomes truly tangible when we approach the speed of light and intense gravitational fields, so the physics of the mind reveals itself only when considering very complex objects.

As you might guess, here we are approaching the very heights of scientific speculation, where the risk of getting lost among metaphysical and unscientific considerations is especially high. In addition, as we all know, some well-known scientists like John Hagelin and Nobel Prize winner Brian Josephson are now using only pseudoscience when they try to approach the problem of the physical foundations of consciousness.

The hypotheses of Penrose and Hameroff are now viewed very critically in the scientific community, but it does not believe that these experts have crossed the forbidden red line. Rather, it seems that their proposals are on the same level as Schrodinger’s reflections in his famous book “What is Life? The physical aspect of a living cell” (What is Life? The Physical Aspect of the Living Cell) 1944: his theories helped the pioneers of molecular biology advance towards the discovery of DNA.

Penrose and Khmeroff published an article in Physics of Life Reviews about their theory of the origin of consciousness. The journal published several articles with comments and criticism of their theory, as well as their responses. Anyway, it is unfortunate to see among these articles the publication of the famous American doctor Deepak Chopra, who was noted for his more than confused theories. However, the most surprising thing is that Penrose and Hameroff are now talking about signs of quantum coherence in microtubules. In this regard, they are based on the work of Indian specialist Anirban Bandiopadhyay, who has been studying microtubules for several years together with colleagues from the National Institute of Materials Science in Tsukuba, Japan.

The articles by Penrose and Hameroff are truly puzzling, because only extensive knowledge of quantum physics, neuroscience, and solid-state physics could allow us to accurately indicate what can be believed in the theoretical constructions they put forward. It is difficult to say whether we are witnessing the first serious steps towards changes in the scientific paradigm (comparable in scale to the revolution in biology in the 1940s) or whether we are simply talking about a multitude of unsuccessful attempts by brilliant scientists to dispel the veil of mystery in the relationship between mind and matter. In any case, Penrose and Hameroff are definitely following in the footsteps of Schrodinger, Pauli, Wigner and Linde in physics and Alfred Whitehead and Karl Popper in philosophy. Hopefully, work in the field of quantum computers will help us expand our understanding of these issues in the coming decades.

Penrose and Hameroff’s reasoning provides food for thought, but we are still at the stage of working hypotheses that need to be developed and tested in practice (both scientists, by the way, are not at all trying to deny this fact). Now they resemble equilibrists who are trying not to fall into the pit of pseudoscientific quantum mysticism and not fall into the trap of fearful positivism, refusing to look for new and dangerous paths on terra incognita called the physics of the mind.

Source: RIA Novosti