The discovery of gravitational waves has shaken the world – literally, when the wave was detected, on September 14, 2015 and figuratively, when it was announced in February. One of the people at the heart of this discovery is a 77-year-old Bangaluru-based Professor Vishweshwara who is not only among the first in India to study black holes, but who has also made a very important calculation that was used in this discovery.
To recap briefly, about 1.3 billion years back, two black holes, of masses 36 and 29 times that of the sun, merged to form a unit. This cataclysmic event shook the fabric of space-time and emanated a characteristic disturbance, which our scientists have detected using the advanced LIGO (Laser Interferometer Gravitational Wave Observatory) detectors. The black holes first came close to each other, then locked in circular orbits and then abruptly merged. The corresponding signal would also have three parts, the inspiral, merger and ringdown. The beauty is that this waveform was recorded and the last part is akin to a bell, ringing and fading away.
It is for this portion of the calculation that we have to thank Professor Vishveshwara. The “ringdown” signal, arising out of a black hole merger, originally called the “quasinormal modes” was first predicted by him in a paper that he published in Nature in 1970. Not just that, earlier he had worked out two important papers on the theory of black holes, with famous general theory of relativity specialist, Charles Misner, as his thesis adviser. At the time, the term “black holes” had not been coined and the event horizon went by the name “Schwarzchild surface”.
“It was a natural question then to ask: how does one see a black hole? So, using a computer, I scattered packets of gravitational waves from a black hole and the quasinormal modes emerged carrying the signatures of the black hole… this was theoretical. I had never dreamed that this would take on an aspect of reality some day,” says Prof. Vishveshwara, who is now the Emeritus Director of Jawaharlal Nehru Planetarium which he founded.
As described earlier, the initial signal, the “chirp”, the steadily increasing frequency and amplitude of the gravitational waves indicates the inspiralling of two black holes and the ring down ( or the quasi-normal mode, QNM) indicates the newly created black hole after the merger.
“When I saw at IUCAA [Inter University Centre for Astronomy and Astrophysics] the QNM recorded by LIGO, I felt the same kind of euphoria that I had experienced 45 years earlier when they emerged out of a computer — it was like time travel back into the past,” he says.
Prof. Vishveshwara is far from being a bookish nerd. Among other things, he is interested in cartooning too. He says: “I dreamt of becoming an artist… while working on the QNM in New York, I studied painting at the Art Students’ League, which was reputed to be a favourite haunt of many artists including Salvador Dali… Only after returning to India did I start cartooning for conference proceedings, my own books etc.” He laughingly adds that in 2005, Spektrum der Wissenschaft, a German science magazine had published his Einstein cartoons — and paid for it too!
Scientists are many times given to whimsy and there is one cartoon of his which combines the philosophical “law of parsimony”, the Occam’s Razor with black hole physics. Occam’s Razor prescribes simplicity and the shearing of all redundant complexity, made popular in The Name of The Rose, by Umberto Eco; it states that among competing theses, the one with the fewest assumptions must be selected.
When the discussion of whether there were “hairy” fields coming out of a black hole (which resulted in the famous no-hair theorem) came up, Prof. Vishveshwara presented an appropriate Occam cartoon (shown here).
With his father, Padmashri C.K. Venkata Ramayya, being a celebrated man of letters, Prof. Vishveshwara’s childhood, filled with music, literature and banter, has endowed him with a ready wit. His books “Einstein’s Enigma or Black Holes in My Bubble Bath,” and “Universe Unveiled or the Cosmos in my Bubble Bath,” are hugely popular.
“The most unexpected finding I have seen is that the universe is accelerating. We now have dark matter, dark energy, all mysterious…is this the dark age of cosmology?” he quips. Winding up with a few words about the latest LIGO discovery, he says,
“Gravitational waves had been predicted by Einstein a hundred years ago and LIGO’s finding is a major event expected for nearly thirty years. The wait is over and the future is bright.”