Roger Penrose

Research and career

Penrose spent the academic year 1956–57 as an assistant lecturer at Bedford College (now Royal Holloway, University of London) and was a research fellow at St John's College, Cambridge. Before the fellowship ended Penrose won a NATO Research Fellowship for 1959–61, first at Princeton University and then at Syracuse University. Returning to the University of London, Penrose spent 1961–1963 as a researcher at King's College, London, before returning to the United States to spend 1963–64 as a visiting associate professor at the University of Texas at Austin. He later held visiting positions at Yeshiva University, Princeton and Cornell University during 1966–67 and 1969.

Dennis Sciama drew his attention from mathematics to physics. In 1964, while a reader at Birkbeck College, Penrose, per Kip Thorne, "revolutionised the mathematical tools that we use to analyse the properties of spacetime". Until then, work on the curved geometry of general relativity had been confined to configurations with sufficiently high symmetry for Einstein's equations to be solvable explicitly, and there was doubt about whether such cases were typical. One approach to this issue was by the use of perturbation theory, as developed under the leadership of John Archibald Wheeler at Princeton. The other, and more radically innovative, approach initiated by Penrose was to overlook the detailed geometrical structure of spacetime and instead concentrate attention just on the topology of the space, or at most its conformal structure, since it is the latter – as determined by the lay of the lightcones – that determines the trajectories of lightlike geodesics, and hence their causal relationships. The importance of Penrose's paper "Gravitational Collapse and Space-Time Singularities" (summarised roughly as that if an object such as a dying star implodes beyond a certain point, then nothing can prevent the gravitational field getting so strong as to form a singularity) was not its only result. It also showed a way to obtain similarly general conclusions in other contexts, notably that of the cosmological Big Bang, which he dealt with in collaboration with Sciama's student Stephen Hawking.

In 1969, he proposed his cosmic censorship conjecture, that any ensuing singularities would be confined within a well-behaved event horizon surrounding a black hole, leaving a visible exterior region with strong but finite curvature. The paper also suggested that gravitational energy may be extractable by what is now known as the Penrose process; he followed up that suggestion with more details in 1971. In 1979, he formulated the "strong censorship hypothesis".

Together with the Belinski–Khalatnikov–Lifshitz conjecture and issues of nonlinear stability, settling the censorship conjectures is one of the most important outstanding problems in general relativity. That year, Penrose formulated his influential Weyl curvature hypothesis on the initial conditions of the observable universe and the origin of the second law of thermodynamics. Penrose and James Terrell independently realised that objects travelling near the speed of light will appear to undergo a peculiar skewing or rotation. This effect has come to be called the Terrell rotation or Penrose–Terrell rotation.

In 1967, Penrose developed twistor theory, which maps geometric objects in Minkowski space into the 4-dimensional complex space with the metric signature (2,2).

In 1971, he discovered spin networks, which later came to form the geometry of spacetime in loop quantum gravity. In 1974, Penrose discovered Penrose tilings, which are formed from two tiles that can only tile the plane nonperiodically, and are the first tilings to exhibit fivefold rotational symmetry. In 1984 such patterns were observed in the arrangement of atoms in quasicrystals. He was influential in popularising what are commonly known as Penrose diagrams (causal diagrams).

In 1983, Penrose was invited to teach at Rice University in Houston, by the then provost Bill Gordon. He worked there until 1987. His doctoral students have included Andrew Hodges, Lane Hughston, Richard Jozsa, Claude LeBrun, John McNamara, Tristan Needham, Tim Poston, Asghar Qadir and Richard S. Ward.

Penrose published The Road to Reality: A Complete Guide to the Laws of the Universe (2004), a guide to the Laws of Physics from Euclid's axioms to Penrose's own theories. The Penrose Interpretation predicts the relationship between quantum mechanics and general relativity, and proposes that a quantum state remains in superposition until the difference of space-time curvature attains a significant level.

Penrose is the Francis and Helen Pentz Distinguished Visiting professor of Physics and Mathematics at Pennsylvania State University.

Conformal cyclic cosmology

In 2010 Penrose reported possible evidence, based on concentric circles found in Wilkinson Microwave Anisotropy Probe data of the cosmic microwave background sky, of an earlier universe existing before the Big Bang of the present universe. He mentions this evidence in the epilogue of Cycles of Time (2010), a book in which he presents his reasons, to do with Einstein's field equations, the Weyl curvature C,and the Weyl curvature hypothesis (WCH), that the transition at the Big Bang could have been smooth enough for a previous universe to survive it. He made several conjectures about C and the WCH, some of which were subsequently proved by others, and he also popularized conformal cyclic cosmology (CCC). Penrose postulates that at the end of the universe all matter is eventually contained within black holes, which subsequently evaporate via Hawking radiation. At this point, everything contained within the universe consists of photons, which "experience" neither time nor space. There is essentially no difference between an infinitely large universe consisting only of photons and an infinitely small universe consisting only of photons. Therefore, a singularity for a Big Bang and an infinitely expanded universe are equivalent.

Penrose believes that the singularity in Einstein's field equation at the Big Bang is only an apparent singularity, similar to the well-known apparent singularity at the event horizon of a black hole. The latter singularity can be removed by a change of coordinate system, and Penrose proposes a different change of coordinate system that will remove the singularity at the big bang. One implication of this is that the major events at the Big Bang can be understood without unifying general relativity and quantum mechanics, and therefore we are not necessarily constrained by the Wheeler–DeWitt equation, which disrupts time. Alternatively, one can use the Einstein–Maxwell–Dirac equations.

Consciousness

Penrose has written on the connection between physics and consciousness. In The Emperor's New Mind (1989), he argues that known laws of physics are inadequate to explain consciousness. Penrose proposes the characteristics this new physics may have and specifies the requirements for a bridge between classical and quantum mechanics (what he calls correct quantum gravity). Penrose uses a variant of Turing's halting theorem to demonstrate that a system can be deterministic without being algorithmic. (For example, imagine a system with only two states, ON and OFF. If the system's state is ON when a given Turing machine halts and OFF when the Turing machine does not halt, then the system's state is completely determined by the machine; nevertheless, there is no algorithmic way to determine whether the Turing machine stops.)

Penrose believes that such deterministic yet non-algorithmic processes may come into play in the quantum mechanical wave function reduction, and may be harnessed by the brain. He argues that computers today are unable to have intelligence because they are algorithmically deterministic systems. He argues against the viewpoint that the rational processes of the mind are completely algorithmic and can thus be duplicated by a sufficiently complex computer. This contrasts with supporters of strong artificial intelligence, who contend that thought can be simulated algorithmically. He bases this on claims that consciousness transcends formal logic because factors such as the insolubility of the halting problem and Gödel's incompleteness theorem prevent an algorithmically based system of logic from reproducing such traits of human intelligence as mathematical insight. These claims were originally espoused by the philosopher John Lucas of Merton College, Oxford.

The Penrose–Lucas argument about the implications of Gödel's incompleteness theorem for computational theories of human intelligence has been criticised by mathematicians, computer scientists and philosophers. Many experts in these fields assert that Penrose's argument fails, though different authors choose different aspects of the argument to attack. Marvin Minsky, a leading proponent of artificial intelligence, was particularly critical, writing that Penrose "tries to show, in chapter after chapter, that human thought cannot be based on any known scientific principle." Minsky's position is exactly the opposite – he believed that humans are, in fact, machines, whose functioning, although complex, is fully explainable by current physics. Minsky maintained that "one can carry that quest [for scientific explanation] too far by only seeking new basic principles instead of attacking the real detail. This is what I see in Penrose's quest for a new basic principle of physics that will account for consciousness."

Penrose responded to criticism of The Emperor's New Mind with Shadows of the Mind (1994) and The Large, the Small and the Human Mind (1997). In those works, he also combined his observations with those of anesthesiologist Stuart Hameroff.

Penrose and Hameroff have argued that consciousness is the result of quantum gravity effects in microtubules, which they dubbed Orch-OR (orchestrated objective reduction). 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 billion. The paper's reception is summed up by this statement in Tegmark's support: "Physicists outside the fray, such as IBM's John A. 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'". Tegmark's paper has been widely cited by critics of the Penrose–Hameroff position.

Phillip Tetlow, although himself supportive of Penrose's views, acknowledges that Penrose's ideas about the human thought process are a minority view in scientific circles, citing Minsky's criticisms and quoting Charles Seife's description of Penrose as "one of a handful of scientists" who believe that the nature of consciousness suggests a quantum process.

In January 2014 Hameroff and Penrose ventured that a discovery of quantum vibrations in microtubules by Anirban Bandyopadhyay of the National Institute for Materials Science in Japan supports the hypothesis of Orch-OR theory. A reviewed and updated version of the theory was published along with critical commentary and debate in the March 2014 issue of Physics of Life Reviews.

He and Ted Honderich discussied consciousness on In Our Time.

Personal life

Penrose married Joan Isabel Penrose (née Wedge) in 1959. They had three sons. Penrose is now married to Vanessa Thomas, director of Academic Development at Cokethorpe School in Witney, Oxfordshire, and former head of mathematics at Abingdon School. They have one son. Penrose is a devotee of Johann Sebastian Bach. On Desert Island Discs, he said he was tempted to choose an all Bach playlist. His first choice was the Mass in B minor.

Religious views

Penrose stated, "I don't believe in established religions of any kind." He regards himself as an agnostic. In Errol Morris's A Brief History of Time (1991) he said, "I think I would say that the universe has a purpose, it's not somehow just there by chance ... some people, I think, take the view that the universe is just there and it runs along—it's a bit like it just sort of computes, and we happen somehow by accident to find ourselves in this thing. But I don't think that's a very fruitful or helpful way of looking at the universe, I think that there is something much deeper about it."

Regarding consciousness, he says "There is something going on which might resonate with a religious perspective. ... The presence of consciousness is not an accident. It certainly has connections with a view that people often have, that you have these constants of Nature, and nobody knows where they come from, and if they didn't have the particular values that they have, we wouldn't have interesting chemistry, we wouldn't have life."

Penrose is a patron of Humanists UK.