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Shadows of the Mind: A Search for the Missing Science of Consciousness  
Shadows of the Mind.jpg
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.)
OCLC Number 30593111
Dewey Decimal 006.3 20
LC Classification Q335 .P416 1994
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.



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. But, this is exactly Penrose's point -- that human thinking and consciousness is not formal logic, not a Turing machine, as are today's computers. 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]

John Searle criticizes Penrose's appeal to Gödel as resting on the fallacy that all computational algorithms must be capable of mathematical description. As a counter-example, Searle cites the assignment of license plate numbers to specific vehicle identification numbers, in order to register a vehicle. According to Searle, no mathematical function can be used to connect a known VIN with its LPN, but the process of assignment is quite simple—namely, "first come, first served"—and can be performed entirely by a computer.[5]


Microtubule hypothesis

Penrose and Stuart Hameroff have constructed the Orch-OR theory in which human consciousness is the result of quantum gravity effects in microtubules. But Max Tegmark, in a paper in Physical Review E,[6] 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.

See also

Notes and references

  1. ^ Penrose is Wrong Drew McDermott, PSYCHE, 2(17), October, 1995
  2. ^ Minds, Machines, And Mathematics - A Review of Shadows of the Mind by Roger Penrose David J. Chalmers, PSYCHE 2(9) June 1995
  3. ^ Penrose's Gödelian argument (PDF) Feferman, PSYCHE 2(7) May 1995
  4. ^ Beyond the Doubting of a Shadow - A Reply to Commentaries on Shadows of the Mind Roger Penrose, PSYCHE, 2(23), January 1996
  5. ^ Searle, John R. The Mystery of Consciousness. 1997. ISBN 0940322064. pp 85-86.
  6. ^ Tegmark, M. (2000), "Importance of quantum decoherence in brain processes", Phys. Rev. E 61: 4194–4206, doi:10.1103/PhysRevE.61.4194,  

This article includes text originally by Philip Dorrell which is licensed under the GFDL


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