Sir **Roger Penrose** OM (born August 8 1931) is an English mathematical physicist. He is highly regarded for his work in mathematical physics, in particular his contributions to cosmology. He is also a recreational mathematician and controversial philosopher.

In 1967, Penrose invented twistor theory which maps geometric objects in Minkowski space into the 4-dimensional complex space with the metric signature (2,2). In 1969 he conjectured the cosmic censorship hypothesis. This proposes (rather informally) that the universe protects us from the inherent unpredictability of singularities (such as black holes) by hiding them from our view.

Roger Penrose is well-known for his 1974 discovery of Penrose tilings, which are formed from two tiles that can only tile the plane aperiodically. In 1984, similar patterns were found in the arrangement of atoms in quasicrystals. His most important contribution may be his 1971 invention of spin networks, which later came to form the geometry of spacetime in loop quantum gravity. He was influential in popularizing what are commonly known as Penrose diagrams (causal diagrams).

He has written controversial books such as *The Emperor's New Mind* where he argues that known laws of physics do not constitute a complete system and that human conciousness cannot be explained until a new physical theory (what he terms correct quantum gravity, CQG) has been devised. He argues against the strong AI viewpoint that the processes of the human mind are algorithmic and can thus be duplicated by a sufficiently complex computer. This is based on claims that human conciousness transcends formal logic systems because things such as the insolvability of the halting problem and Gödel's incompleteness theorem restrict an algorithmically based logic from traits such as mathematical insight. These claims were originally made by the philosopher John Lucas of Merton College, Oxford.

Later on, Penrose followed up *The Emperor's New Mind* with *Shadows of the Mind* and *The Large, the Small and the Human Mind* , further updating and explaining his theories.

The views expressed in Penrose's books on topics such as human reasoning are not widely accepted in scientific culture. According to Marvin Minsky, human beings can understand things to be true facts which are false, and therefore the process of understanding is not limited by mathematical systems of formal logic. Further, AI programs can also conclude that false statements are true, so this is not unique to humans.

Penrose and Stuart Hameroff have constructed a theory in which human consciousness is the result of quantum gravity effects in microtubules. 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 10,000,000,000; this paper has been widely cited by critics of the Penrose-Hameroff proposal. However, this paper has since been claimed by Hameroff to be based on a number of incorrect assumptions. See the refutation linked below from Hameroff, Hagan and Tuczynksi . The general gist of the linked page is summed up by this statement in support of Tegmark : *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.* And another quote, this one from Charles Seife : *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 2004 Penrose released *The Road to Reality: A Complete Guide to the Laws of the Universe*, a 1,099-page book aimed at giving a comprehensive guide to the laws of physics. In the same year he was awarded the De Morgan Medal for his wide and original contributions to mathematical physics, to quote the citation from the LMS

*His deep work on General Relativity has been a major factor in our understanding of black holes. His development of Twistor Theory has produced a beautiful and productive approach to the classical equations of mathematical physics. His tilings of the plane underlie the newly discovered quasi-crystals.*

Roger Penrose is the son of scientist Lionel S. Penrose, and the brother of mathematician Oliver Penrose and chess grandmaster Jonathan Penrose.

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Last updated: 06-01-2005 22:38:36