The last 50 years have produced some of the most fascinating ideas from physics which have ever been known to us mere mortals. Whether it is the idea of string theory where the world is made of tiny strings smaller than whatever lengths we can possibly encounter or whether it is the astonishing revelations that we possibly do not understand 96% of what constitutes the Universe, all of these brilliant ideas have caught the attention of both professional physicists and the normal population alike. This has also shot loads of world class physicists to limelight, with the likes of Roger Penrose, Edward Witten, Juan Maldacena, Abhay Ashtekar and Erik Verlinde amongst a huge number of physicists who have achieved great public acclaim for their work on Gravitational theories while the likes of Alan Guth, Andrei Linde, Paul Steinhardt, Jim Peebles amongst others have become famous names for their groundbreaking work in Cosmology. But perhaps the best-known figure of theoretical physics in the last half century has been someone who, despite all kinds of odds stacked against him, has contributed deeply to both Gravitational Physics and Cosmology, and his name is Stephen Hawking!
The depth and the length of Hawking’s scientific discoveries can not possibly be described to their full glory in one single article and that speaks volumes of the kind of incredible physics he pursued throughout his life. But intriguingly enough, physics was not what a young Stephen was supposedly going to do in his life. Stephen was born into a family which placed a high value towards a good education, as his father, Frank, was a medical researcher while his mother, Isobel, (having read Philosophy at Oxford, where she met Hawking’s father) was a secretary at a medical institute. While Hawking was named “Einstein” in his school days, his father actually wanted him to also study medicine like him. However, the young Stephen was actually fond of mathematics and since Oxford - where he pursued his undergraduation - didn’t offer a Mathematics degree at the time, he decided to major in Physics instead. Slowly, he gained an incredible amount of interest towards Physics although he was a conventionally “lazy” student throughout his undergraduation. He would not study seriously as he found most of work really easy and interestingly enough, it was the boat club in his university which slowly propelled him towards putting efforts as a student.
When Hawking started his PhD in Cambridge, he was quite disappointed to have not been made a student of legendary astronomer Fred Hoyle, instead he was made a student of Dennis Sciama. This proved fortuitous however, as Sciama was incredibly knowledgeable about almost everything in Cosmology and eventually became a central figure in British Cosmology. It was through him that Hawking got to meet his life-long collaborator and recently awarded Nobel Prize Winner, Sir Roger Penrose. The meeting with Penrose, who was then working on some bewildering properties of the Black Hole, proved to be a pivotal moment of Hawking’s career. Penrose had shown in a general way the existence of space-time singularities, which is a point inside the black hole where the known laws of Physics, like General Relativity, collapse. Hawking used Penrose’s theorem to show that if one completely rewinds the entire history of the universe, then one would reach exactly to the kind of point which Penrose had described for a black hole; a Space-Time or in this case the Big-Bang Singularity.
This idea shows that the universe began from an infinitesimally small point of seemingly infinite density, and hence, Einstein’s seminal theory of General Relativity also fails to explain the properties of the Universe at the time of its creation. This work of Hawking came to be of an astounding magnitude, and this has propelled work on loads of theories both of the early universe and even towards considerations of modifying General Relativity itself! This excellent work got Stephen his doctorate degree at Cambridge, a fact made even more stupendously inspirational considering that he was diagnosed with the Motor Neuron Disease by this time which made him completely paralyzed. He was in a state of depression after being diagnosed with this disease with doctors claiming that he had not much time left to live. It was then through the support of his family and his girlfriend (who soon became his wife) that got him through a very dark realization and motivated him to again pursue physics to the best of his abilities.
After his great work on the Big Bang, Hawking shifted his attention quite literally towards Black Holes. He produced a number of incredible theorems regarding them with Sir Penrose, which are now known as “Penrose—Hawking singularity theorems”. He was also collaborating vigorously with James Bardeen and Brandon Carter at this time, and together they produced some excellent work which showed how Black Holes could lose energy. Around the same time Jacob Bekenstein (who was then a PhD Student at Princeton University) showed that there had to be the existence of some quantum mechanical effects which would lead to the Black Hole having a so-called “entropy” (which is the classical measure of the disorder of a physical system). On the basis of his work with Carter and Bardeen with considerations to Bekenstein’s ideas, Hawking then showed that Black Holes lose energy by radiating it away through a particular mechanism. Considering Einstein’s seminal idea of Mass-Energy equivalence through E=MC2, this incredible work of Hawking meant that Black Holes actually lose Mass by radiating it away in a process now fittingly known as “Hawking Radiation''. Hawking Radiation has become a central idea in studies of Black Holes, Quantum Gravity and the very early universe, and was the key idea which propelled the concept of “Primordial Black Holes”, which refers to the Black Holes which were created in the very early universe. Recently there has been a lot of work which points towards the realization that these primordial black holes may constitute a huge part, if not all, of the dark matter in the universe (which is a mysterious form of matter which forms approximately 23% of the universe). If it is indeed the case, then Hawking’s work will inadvertently be the propeller towards the understanding of dark matter.
Throughout the time in which Hawking did all the above-mentioned work, his research was up there with the finest (if not the finest itself!) on gravitational physics and cosmology in the world. In his later years, Hawking became fascinated with even more exotic ideas which ranged from understanding quantum gravity (the theory of gravity at the smallest scales) and the Multiverse (the idea of an infinite number of universes) to the prospect of Extraterrestrial life and Time Travel. He produced some really insightful work on Quantum Gravity, and his work on Hawking Radiation has fueled loads of work in quantum gravitational theories like String theory and Loop Quantum Gravity. He even hosted a party for time travelers and discussed in length about Aliens & the effects of AI on humans in his later life.
But let’s end this very brief note of his life with this anecdote. Somak Raychoudhary, the current director of IUCAA in India, reminisces how he once met Sir Penrose’s office during his PhD days in Oxford about the allowance to attend one of his classes. Penrose was discussing some work with another PhD student at that time and was startled when he heard Somak’s surname. He said “ Are you related to the Raychoudhary?”. Somak was startled by hearing this and asked who it was that Penrose referred to. Penrose then exclaimed that he was referring to Amal Kumar Raychaudhuri, the Indian astrophysicist who discovered a seminal equation known by his name as the “Raychaudhri Equation”. When Somak told that he had indeed taken classes from Professor Amal, Penrose was very happy and immediately granted him permission to attend his classes. At this, the quiet PhD Student sitting with Penrose said to Somak “ We (him and Penrose) are incredibly inspired by his work and wish to meet him once in person “. That PhD Student was none other than Stephen Hawking and goes to show, the incredibly high regard Raychaudhri’s work is held in, while the general Indian don’t know much about him.