Roger Penrose wins Nobel Prize

Difficulty level:   ★ ★ ★

Roger Penrose has been awarded (half) the 2020 Nobel Prize for Physics, for the discovery that black hole formation is a robust prediction of the general theory of relativity”. Penrose is a remarkable figure, known for his technical brilliance, communication of science to the general public, and having unique views. His main expertise is general relativity:

More than any other individual, it was Roger Penrose who originated the concepts, insights and techniques that have shaped Einstein’s general relativity as we understand and practise it today.

That is from a “biographical sketch” by Werner Israel (which appears as the last 2 pages of research paper ). It accompanies a republication of Penrose’ classic 1969 review on gravitational collapse. At that time, consensus had been building that black holes really are a thing, see for example §7.9 of   for history. I will write more on this another time.

Penrose is artistic. The review cited above contains a full-page drawing of people on rigid platforms, lowering ropes toward an event horizon. It makes a fun background slide during a talk! He also drew some optical illusion “impossible figures”, and corresponded with artist M. C. Escher. He worked on tiling problems, accessible to anyone, yet important mathematically and with physical applications too (quasicrystals). Penrose’ “conformal diagrams” depict spacetime in a way which clearly illustrates its overall structure. His graphical notation for tensors has spread into other fields including quantum computing.

Penrose is a mathematician, so it is natural to wonder how many other mathematicians have won the physics Nobel Prize. Max Born is one example apparently, though he was also a physicist. On the other hand, string theorist Ed Witten is said to be the only physicist to win a Fields Medal, the preeminent prize in mathematics. Penrose has broad interests, and seems to know a lot of physics, based on the topics in his 1100 page The Road to Reality (2007).

I do hear critique of Penrose from quantum physicists, specifically about his model with Lajos Diósi. Indeed one recent paper, coauthored by Diósi curiously enough, says the theory is largely ruled out experimentally. I will trust the consensus of specialists over the lone genius outside their main field. A different claim by Penrose and collaborators concerns circles in the cosmic microwave background, as evidence for his “conformal cyclic cosmology” model. But astrophysicists are skeptical (I heard John Barrow asked about this at one conference). I’ll lean towards Penrose when it comes to a theoretical general relativistic cosmology, but not for statistical analysis of observational data from our universe. Penrose is also criticised for his views on consciousness. Israel is euphemistic: “His views on gravitational interactions as a trigger for quantum state reduction, and on the non-algorithmic character of human intelligence have generated much discussion.”

Yet, with the above acknowledged, we should focus on Penrose’ strengths and main areas of expertise. Israel calls him a “wholly original non-conformist”, which I would not have picked from his demeanour, but helps explain the combination of his towering strengths along with more speculative ideas. One of the many things I have omitted is Penrose’ twistor theory. Personally, I am still trying to understand spinors, a prior concept, but the fact an individual can come up with their own quantum gravity theory which is admired by their peers is a huge achievement. I look forward to reading part of The Road to Reality sometime.