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 0198539789 (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 nonalgorithmic, and thus is not capable of being modeled by a conventional Turing machinetype 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 nonalgorithmic, attempting a mathematical proof using Gödel's Incompleteness Theorem.
Contents 
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 counterexample, 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]}
Penrose and Stuart Hameroff have constructed the OrchOR 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 10^{10}. 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 PenroseHameroff proposal.
This article includes text originally by Philip Dorrell which is licensed under the GFDL
