Penrose’s Nobel Prize in Physics comes two decades late, a belated...

Annapurni SubramaniamOct 12, 2020 4:51:34 pm IST

This year’s Nobel Prize in Physics is awarded for research related to black holes. Half of the award went to British professor Sir Roger Penrose for his theoretical research, which confirmed that the black hole is a robust prediction of Einstein’s general theory of relativity. Penrose shared the prestigious award with Prof. Andrea Ghez and Prof. Reinhard Genzel for their experimental work and discovered the presence of a supermassive compact object in the heart of our Milky Way Galaxy.

Prof. Penrose received the award for research carried out 55 years ago. His research used Einstein’s general theory of relativity to prove that a singularity and the formulation for a black hole are mathematically possible. The Penrose-Hawking Singularity Theorems, as this series of results are called, also answer the question of when gravity creates singularities. These theorems used the Raychoudhuri equation – a key component in explaining space-time singularities and gravitational focusing properties in cosmology.

Also read: Hawking, Nobel Laureate in Black Hole Physics from Penrose, stands on the work of Indian physicist Amal Raychaudhuri

Although the above investigations are a collaboration between Sir Roger and Stephen Hawking, the latter came into the spotlight. Penrose, on the other hand, did not attract any media attention and was limited to academic activities. Penrose is a versatile intellectual and a talented mathematician with great interests. One has to wonder why it took the Nobel Committee so long to honor him with the award.

Meaning of Penrose Discovery

By observing the stars in our galaxy and others, we know that stars are forming and dying. Low mass stars like our sun live long and die as “white dwarfs”. Larger stars, more than eight times our solar mass, die in a spectacular explosion that we call a supernova. For stars that are much more massive – say, over 20 times the mass of the Sun – it is believed that the central collapsing core is much, much larger. The core becomes immensely dense and compact and forms a black hole.

This extraordinary event, in which a black hole forms and matter is squeezed beyond the nuclear scale to the limit, is theoretically complex to describe. It calls for a combination of gravity, quantum physics and mathematics. The best we can do without this theoretical work is a vague estimate of the density of a black hole from studying other compact objects in the universe.

Just recently, the first direct image of a black hole from a nearby galaxy (M87) was captured by astronomers around the world in a remarkable feat. However, there is still a huge gap in the modern understanding of black holes. We still need to understand the singularity that existed in the beginning, before the Big Bang, which supposedly gave birth to everything in the universe. We also don’t know what happens to an observer who falls into a singularity of the black hole.

Before the Penrose-Hawking singularity theorems hit the market in the 1970s, it was believed that singularities only formed in certain situations. For example, in a supernova explosion that creates a black hole from the collapse of a star’s core, it might be possible for a spinning star to partially counteract its own gravity. It was believed that no singularity would form under these circumstances – until the Penrose-Hawking Singularity Theorems refuted that belief. It turned out that in every case in which there is an event horizon, a singularity is formed – the fictional border around a black hole, behind which no light can escape.

Urgently needed recognition for the theoretical work

If there have been two ideas that have tarnished the imagination of many theoretical astrophysicists, it is black holes and Einstein’s general theory of relativity. One of the most fascinating questions in astrophysics remains: “What is a black hole?”. It’s a curiosity that piques the interest of school children and astrophysicists alike. In practice, many nations have invested enormous resources in building experimental detectors to detect the presence of a black hole. One of these experimental results, led by Ghaz and Genzel, was awarded half of the Nobel Prize in Physics in 2020. Still, the funding of international mega-projects like LIGO and VIRGO is not a recognition of real theoretical work that needs to be recognized.

Black hole detection experiments have been proposed, funded and are now fully operational research centers. The 2017 Nobel Prize in Physics was awarded to Rainer Weiss, Barry C. Barish and Kip S. Thorne for decisive contributions to the LIGO detector and the observation of gravitational waves. The signal captured by the LIGO observatory came from the fusion of two black holes. It was again surprising to find that the award was not given to those who made the actual predictions. Meanwhile, in 2018 the world lost one of the most brilliant minds in astrophysics, Professor Stephen Hawking. Nobel Prizes are not awarded posthumously. And so, despite all his contributions, Hawking will never receive the Nobel Prize.

Penrose’s Nobel Decades Overdue?

During a brief visit to the Indian Institute for Astrophysics from January 2 to 9, 1994, Sir Penrose lectured at an international conference on particle physics (excluding accelerators). We expected that he would receive a Nobel Prize in the next few years. I was a PhD student at the institute at the time and we were delighted to hear him speak and interact with him. During the conference, Prof. Penrose also wrote an article ‘On tThe role of gravity in quantum state reduction‚ for the Lectures of the International Conference on Non-Accelerator Particle Physics, published by the then director of the IIA, Prof. R Cowsik. Prof. Penrose was knighted in the same year for his “services to science”. It would be another 26 years before he received the Nobel Prize for his contributions to the theoretical understanding of black holes. It is encouraging to see that Sir Penrose was recognized by the Nobel Committee despite the delay.

Subramanyan Chandrasekhar, an astrophysicist of Indian descent, received the 1983 Nobel Prize in Physics for his work in the early 1930s. It took about 50 years for the Nobel Committee to recognize his work. So that we don’t forget that Albert Einstein never received the Nobel Prize for his timeless work on general relativity. Many great theoretical and discovered works are awarded late or not at all due to the examination of the Nobel Prize.

Perhaps this is because Alfred Nobel intended to award the prize to those inventions that will most benefit mankind?

The author is director of the Indian Institute for Astrophysics in Bangalore and works on the study of star clusters, star evolution and population in galaxies and magellanic clouds. She tweeted at @fiddlingstars