Shadows of the Mind

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Shadows of the Mind: A Search for the Missing Science of Consciousness

Author	Roger Penrose
Cover artist	Joel Nakamura
Country	USA
Language	English
Subject(s)	Artificial Intelligence, mathematics, & quantum mechanics
Publisher	Oxford University Press, 1st edition
Publication date	1994 (1st ed.)
Media type	Hardback
Pages	457 pages
ISBN	ISBN 0-19-853978-9 (1st ed.)
Preceded by	The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics

Shadows of the Mind: A Search for the Missing Science of Consciousness is a 1994 book by mathematical physicist Roger Penrose, and serves as a followup to his 1989 book The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics.

In the book, Penrose expounds upon his previous assertions that human consciousness is non-algorithmic, and thus is not capable of being modeled by a conventional Turing machine-type of digital computer. Penrose hypothesizes that quantum mechanics plays an essential role in the understanding of human consciousness, specifically that microtubules within neurons provide the brain with the hardware necessary to perform quantum computation and therefore that the collapse of the quantum wavefunction plays an important role in brain function.

In Shadows of the Mind, Penrose takes a new approach in arguing that consciousness is non-algorithmic, attempting a mathematical proof using Gödel's Incompleteness Theorem.

1 Criticism
- 1.1 Microtubule hypothesis
2 See also
3 Notes and references

[edit] Criticism

Penrose's views on the human thought process are not widely accepted in scientific circles (Drew McDermott^[1], David Chalmers^[2] and others). According to Marvin Minsky, because people can construe false ideas to be factual, the process of thinking is not limited to formal logic. Further, AI programs can also conclude that false statements are true, so error is not unique to humans. Another dissenter, Charles Seife, has said, "Penrose, the Oxford mathematician famous for his work on tiling the plane with various shapes, is one of a handful of scientists who believe that the ephemeral nature of consciousness suggests a quantum process."

In May 1995 Stanford mathematician Solomon Feferman attacked Penrose's approach on multiple grounds, including the mathematical validity of his Gödelian argument and theoretical background.^[3] In 1996 Penrose offered a consolidated reply to many of the criticisms of 'Shadows'.^[4]

[edit] Microtubule hypothesis

Penrose and Stuart Hameroff have constructed a theory in which human consciousness is the result of quantum gravity effects in microtubules. But Max Tegmark, in a paper in Physical Review E, calculated that the time scale of neuron firing and excitations in microtubules is slower than the decoherence time by a factor of at least 10¹⁰. The reception of the paper is summed up by this statement in his support: "Physicists outside the fray, such as IBM's John Smolin, say the calculations confirm what they had suspected all along. 'We're not working with a brain that's near absolute zero. It's reasonably unlikely that the brain evolved quantum behavior', he says." The Tegmark paper has been widely cited by critics of the Penrose-Hameroff proposal. It has been claimed by Hameroff to be based on a number of incorrect assumptions, but Tegmark in turn has argued that the critique is invalid.