A brief history of gravity by Dr Satish Kumar Saravanan

Today, VarahaMihira Science Forum had organised a talk at Tamil Virtual Academy, Chennai titled “A brief history of gravity”, delivered by Dr Satish Kumar Saravanan, Riemann Fellow of Riemann Center for Geometry and Physics.

Dr Satish started with the well-known (fiction?) story of a falling apple into the lap of Newton, who went on to discover the force of Gravity. Followed this was the fictitious(?) story of Galileo dropping two balls of varying mass and volume from the top of the leaning tower of Pisa. Then was a BBC video by Brian Cox on how in a vacuum if we drop a large iron ball and a bird feather will touch down at the same moment. Having pricked our interest, Dr Satish then started feeding us the Physics behind gravity, one drop at a time, without us knowing what we are drinking!

The four basic forces—gravitational, electromagnetic, strong, and weak

First, it was fundamental four forces—gravitational, electromagnetic, strong (holds together the atomic nucleus), and weak (forms of radioactivity). Following this was Michelson-Morley’s experiment leading to determining the speed of light is constant, then was Einstein’s thought experiment of a speeding train with two lightning bolts falling on the front and the back of the train, leading to the discovery of spacetime.

Einstein’s thought experiment

Dr Satish went on to define what are Gravitational Waves, which are ripples in space-time (the fabled “fabric” of the Universe) caused by massive objects moving with extreme accelerations (in outer space that means objects like neutron stars or black holes orbiting around each other at ever-increasing rates, or stars that blow themselves up). Gravitational waves travel throughout the universe, nothing can stop or slow them.

Gravitational Waves

What is a black hole? How a star becomes a black hole, for that we turn to the work of the famous Nobel Laureate Dr Chandrasekhar who discovered that a star with a minimum mass of 1.44 times of the sun (Chandrasekhar’s limit) will ultimately collapse (when it) into a neutron star or a black hole.  This was followed by, what happens when a small black hole approaches a big black hole – when this happens they emit so much power and gravitational waves, that we can measure them from Earth.

GW150914 – First observation of gravitational waves
Supermassive Black Holes

Dr Satish, lastly moved to his area of study, on the happenings around a black hole falling into a Supermassive black hole. Observational evidence indicates that all, or nearly all, massive galaxies contain a supermassive black hole, located at the galaxy’s centre. Dr Satish said that the answers to these mysteries of nature lie in mathematics and solving equations. The research work he was involved in with his fellows, led them to present a hypothesis that the path followed by the smaller black hole around the supermassive one will be a modified spiral and not a perfect spiral. Overall, an evening spent learning a lot of new things!

 (Above, the video recording of Dr Satish Kumar Saravan talking on the brief history of Gravity at the Tamil Virtual Academy - 23rd February 2019)

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