Roger Penrose:
SHADOWS OF THE MIND (Oxford Univ Press, 1994)

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(Copyright © 1999 Piero Scaruffi | Legal restrictions )

This book continues the story where THE EMPEROR'S NEW MIND (Oxford Univ Press, 1989) left it. The British physicist Roger Penrose resumes his attack on artificial intelligence, and recycles many of the points of the previous book (Goedel's theorem as proof that Artificial Intelligence is impossible, quantum mechanics as the foundation for a theory of consciousness). Furthermore, Penrose's conclusions imply that there is a separate mental world, grounded in the physical world, and there is also another separate world, that of abstract ideas.
The book is clearly divided in two parts, corresponding to the two central tenets of Penrose's philosophy. The first part is a proof that traditional Physics is not adequate to explain consciousness. The second part uses Quantum Theory to draft a theory of consciousness.
Penrose starts his argument by stating that classical Physics is inadequate to explain consciousness. Somehow this relates to Goedel's theorem, which puts a limit to what a Turing machine can do, a limit that does not apply to the human mind; ergo a Turing machine cannot be a mind, and, viceversa, a mind is not a Turing machine. Penrose is obsessed with that limit and is probably aware that all neurobiology is using brain models that are computationally equivalent to Turing machines (neurobiologists are happy to claim that they can simulate their models on a computer, but Penrose is happy to counter that this proves their model cannot be correct).
Consciousness must be a quantum phenomenon because neurons are too big to account for consciousness. Inside neurons there is a cytoskeleton, the structure that holds cells together, whose microtubules (hollow protein cylinders 25-nanometers in diameter) control the function of synapses. Penrose believes that consciousness is a manifestation of the quantum cytoskeletal state and its interplay between quantum and classical levels of activity. This is more or less consistent with the findings of the American biologist Hameroff, although Penrose's interpretation requires a major leap of faith.
Subjective reduction is what happens when an observer measures a quantity in a quantum system: the system is not in any specific state (the system is in a "superposition" of possible states) until it is observed, the observation causes the system to reduce (or "collapse") to a specific state. This is the only reduction known to traditional Quantum Theory.
Objective reduction is a Penrose discovery, part of his attempt at unifying Relativity Theory and Quantum Theory. Superpositioned states each have their own spacetime geometries. Under special circumstances, which microtubules are suitable for, the separation of spacetime geometry of the superpositioned states (i.e., the "warping" of these space-times) reaches a point (the quantum gravity threshold) where the system must choose one state. The system must then spontaneously and abruptly collapse to that one state.
This "self-collapse" results in particular "conformational states" that regulate neural processes. These conformational states can interact with neighboring states to represent, propagate and process information. Each self-collapse corresponds with a discrete conscious event. Sequences of events then gives rise to a "stream" of consciousness. The proteins somehow "tune" the objective reduction which is thus self-organized, or "orchestrated".
In general, the collapse of the wave function is what gives the laws of nature a non-algorithmic element. Otherwise we would simply be machines and we would have no consciousness.
Therefore, Penrose believes that "protoconscious" information is encoded in space-time geometry at the fundamental Planck scale and that a self-organizing Planck-scale process results in consciousness.
Penrose is led to believe in a Platonic scenario of conscious states that exist in a world of their own, and to which our minds have access. But his "world of ideas" is a Physics' world: quantum spin networks encode proto-conscious states. Different configurations of quantum spin geometry represent varieties of conscious experience. Access to these states (or consciousness as we know it) originates when a self-organizing process (the objective reduction) somehow coupled with neural activity collapses quantum wave functions at Planck-scale geometry.
Penrose is stronger in his own backyard, when he describes objective reduction and comments on what has been known as the "Von Neumann measurement problem" of Quantum Theory. On the other hand, his theory of consciousness is a wild speculation that will need a lot more data than Penrose offers.
By the same author:
Penrose, Roger: "The Road to Reality" (Oxford University Press, 2004)
Penrose, Roger: THE EMPEROR'S NEW MIND (Oxford Univ Press, 1989)

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