The 2001 edition of the annual String Theory conference, a major event for scientists working in the field, was happening at the Tata Institute of Fundamental Research in Mumbai. Several hundred delegates from all over the world were participating. Among them were many celebrity scientists, including Nobel laureates and Field medallists. One does expect a lot of media attention as well on such occasions.
I was scheduled to give a talk at the Home Bhabha auditorium. As I entered the stage of the conference hall, I was surprised at the massive turn-out. There were people sitting on the ground, on the aisles and everywhere else. There was a very large presence of media persons as well. Before I had time to feel perplexed by my overnight rise in popularity, I was reminded by one of the conference organisers that the speaker after me happened to be Stephen Hawking. That explained everything.
Hawking had a celebrity status which few others in the scientific world have enjoyed. That day at TIFR, he was not even giving a public talk. It was a rather technical lecture on some subtle aspects of quantum theory, not something one would expect laypersons to fully follow or grasp. But here they were, young and old, all mesmerised just to see and hear Hawking talk.
What gave him such a celebrity status? It certainly had a lot to do with Stephen Hawking, the man. He was a man with indomitable spirit, who, despite his ever-worsening motor neurone disease, lived his life more zestfully than many others of his age who were completely healthy. He participated in a zero gravity — free fall — experiment at the age of 65, appeared on TV shows, worked ceaselessly as a science communicator (his book The Brief History of Time, by no means an easy bedtime read, is a best-seller) and visited institutions all over the world.
I met him for the first time in the annual String theory conference in 1996 at the Kavli Institute of Theoretical Physics, Santa Barbara, California and was awed by his incisive intelligence, and a very British sense of humour, with lightning repartee — all through his talking machine.
On another occasion, again in a Santa Barbara meeting, somebody pulled a prank, circulating a fake email with Hawking as the apparent sender in which he admitted a mistake in some famous work of his. Hawking was not one to let this go. As he came to give his talk, and we were in nervous anticipation about what he might say, he started his talk with a fake title page that said, “Why I have always been wrong”, causing an uproar of laughter in the audience.
Hawking was no less a star in the world of science. The scientist Hawking was a cosmologist par excellence and, along with the mathematician Sir Roger Penrose, mathematically proved the inevitability of a singular beginning of the universe — the Big Bang. I should add that in this body of work, he used and acknowledged the profound insight into Einstein’s equations of general relativity provided by the work of Amal Kumar Raychaudhuri, the Indian cosmologist and my professor at Presidency College.
The pinnacle of Hawking’s scientific work, to most theoretical physicists, is the celebrated paradox he discovered in 1974 — the information paradox, or simply, the Hawking paradox. He arrived at the surprising conclusion that the two pillars of modern physics — quantum mechanics and Einstein’s general theory of relativity — appear to be irreconcilable. If the paradox is true, it would require some radical revision of physics as we know it.
Simply stated, Hawking applied the framework of quantum mechanics to black holes and arrived at the conclusion that black holes must radiate thermal radiation, and eventually evaporate completely. Since thermal radiation carries virtually no information other than the temperatureof the radiation, this leads to a loss of all the information that was contained in the black hole, which is a violation of principles of quantum mechanics.
Attempts at resolving this paradox have been made ever since its discovery, and the problem inspired many physicists. It has been possible to throw some light on this paradox using String theory, such as by showing the consistency of Hawking radiation with quantum mechanics, and people in TIFR, including Avinash Dhar, Spenta Wadia and myself, and Sumit Das and Samir Mathur, have contributed to this effort. However, it is fair to say that the paradox remains unresolved till date and will continue to throw a challenge to the ingenuity of scientists for years to come.
I hope that the resolution comes through some radical insight into the workings of quantum mechanics and the theory of gravity or perhaps lead to a completely new theoretical framework altogether, as some other paradoxes had done nearly a century ago. That would be a fitting conclusion to the work of a great mind such as Stephen Hawking’s, even though he will not be there among us to applaud the new era.