### Topic Page: Penrose, Sir Roger (1931 - )

**Penrose, Roger (1931- )**

*The Hutchinson Dictionary of Scientific Biography*

Place: United Kingdom, England

Subject: biography, maths and statistics, astronomy

English mathematician who, through his theoretical work, has made important contributions to the understanding of astrophysical phenomena. He has examined especially those anomalies in space-time, the singularities known as black holes, that occur when a sufficiently large mass is contained within a sufficiently small volume so that its gravitational pull prevents the escape of any radiation.

Penrose was born the son of an eminent English human geneticist, Lionel Sharples Penrose (1898-1972), in Colchester, Essex, on 8 August 1931. He grew up amid a family tradition of scholarship and creativity, and completed his education at University College, London. Even as he worked for his doctorate at Cambridge in 1957, Penrose and his father were devising geometrical figures of which the construction is three-dimensionally impossible. (Published the following year in the British Journal of Psychology, they became well known when incorporated by the Dutch artist M C Escher into a couple of his lithographs.) A series of lecturing and research posts followed, both in the UK (London and Cambridge) and the USA (Princeton, Syracuse, and Texas). In 1966 Penrose was made professor of applied mathematics at Birkbeck College, London. He was Rouse Ball Professor of Mathematics at Oxford University 1973-98 (emeritus thereafter). Since 1993 he has been Francis and Helen Pentz Distinguished Visiting Professor of Physics and Mathematics at Penn State University, USA. He was elected a fellow of the Royal Society of London in 1972 and a foreign associate of the US National Academy of Sciences in 1998. He was knighted in 1994. In 2008 the Royal Society awarded him its Copley Medal, for his outstanding contributions to geometry and mathematical physics.

Penrose's early work in mathematics included the formulation of some of the fundamental theorems that describe black holes. The explanation of the occurrence of black holes in terms of gravitational collapse is now usually given in a form that owes a great deal to Penrose's work in stressing the importance of space-time geometry. A model of the behaviour of stars that collapse upon themselves had first been proposed by Oppenheimer and Snyder in 1939 and their results have been proved valid to a remarkable degree by later work. Their model of spherical collapse, together with an interest in gravitational collapse stemming from study of black holes, led to vigorous research on the dynamics and the inevitability of collapse to a singularity. The most important result of such research was a set of theorems formulated by Penrose and Stephen Hawking in 1964, which extend the dynamics of simple spherical collapse to the much more complex situation of gravitational collapse. Singularities in any physical theory might naturally be taken to indicate the breakdown of the theory, but using techniques developed jointly with Hawking and Geroch, Penrose has established that once gravitational collapse has proceeded to a certain degree, assuming the truth of the general theory of relativity that gravitation is always attractive, singularities are inevitable. These techniques are now famous as the singularity theorems.

The existence of a trapped surface within an ‘event horizon’ (the interface between the black hole and space-time), from which little or no radiation or information can escape, implies that some events remain hidden to observers outside the black hole. But it remains unknown whether all singularities must be hidden in this way. Penrose has put forward the hypothesis of ‘cosmic censorship’ - that they are all so hidden - which is now widely accepted.

On moving to Oxford University, Penrose began developing an intuition that first occurred to him in Texas in 1964. This is a model of the universe whose basic building blocks are what he calls ‘twistors’. The model arises in response to a dichotomy in physics, in that calculations in the macroscopic world of ordinary objects (including Einstein's theory of gravity and the general theory of relativity) use real numbers, whereas the microscopic world of atoms and quantum theory often requires a system using complex numbers, containing imaginary components that are multiples of the square root of −1. Penrose holds that, as everything is made up of atoms, and as energy exists as discrete quanta bundles, all calculations about both the macroscopic and microscopic worlds should use complex numbers. Logically to maintain such a hypothesis would require reformulation of the major laws of physics and of space-time.

His publications include The Emperor's New Mind: Concerning Computers, Minds and the Laws of Physics (1989), which won the 1990 Science Book Prize; Shadows of the Mind: A Search for the Missing Science of Consciousness (1994); and The Nature of Space and Time (1996), written with Stephen Hawking. In 2004 Penrose published The Road to Reality: A Complete Guide to the Laws of the Universe.

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