Have you ever thought about gravity? No, not the movie that came out in 2013 but the natural phenomenon that attracts a body towards any other body having mass. The force which, among many other things, keeps us rooted to the ground.
Well, Albert Einstein certainly did. He was well-versed with the Newtonian laws and the fact that it doesn’t explain where gravity comes from. He set about with Isaac Newton’s first law of motion according to which you will either sit still or keep moving at constant speed in a straight line if you feel no force acting on you.
He then began to question himself as to what would happen when he steps off the top of a building. He knew that he would feel weightless during freefall which in turn implied that he would experience no force despite accelerating towards the ground.
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Einstein effectively found himself confronted with a puzzling situation. An object should travel at constant speed when it feels no force. But here in this case, the object felt no force but was in fact accelerating because of gravity. Einstein realised that the origins of gravity lied in resolving this paradox.
And it was then that Einstein came up with the idea that gravity is in fact warped space and time. This implied that massive objects (think sun and earth) cause distortion in space-time and this curved space then dictates how these objects move.
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To better understand this, try and imagine space-time as a fabric - a trampoline or a large rubber sheet. If you place a heavy object, say a bowling ball, in the centre, what was a flat surface would now sag, pressing down the fabric. If you then place a marble along the edge of the sheet, it spirals inwards towards the bowling ball, not unlike how a planet’s gravity tugs at rocks in space.
Even though that path doesn’t look straight to us, freefalling objects experience no force when they follow the straightest possible path in space-time. It might be difficult to visualise but straight paths are curved in curved spaces. This will also help you appreciate the fact that the shortest distance when you are flying from A to B isn’t the straight line connecting A and B that you draw on a flat map of the earth, but is in fact a curved line!
Einstein spent years formulating this theory, explaining mathematically how the distribution of mass and energy warps space-time. Once developed, it was evident that the principles of special relativity, Einstein’s groundbreaking work from 1905, were in fact a special case of general relativity.
First experimental evidence
Einstein announced his work in November 1915 and on March 20, 1916 published an academic paper, the first consolidated view of the final version of general relativity, in Annalen der Physik. Bending of light rays observed during the solar eclipse of 1919 provided the first experimental evidence, catapulting Einstein to global stardom.
From Mercury’s anomalous orbit to gravitational redshift, general relativity’s predictions have been experimentally verified with immaculate accuracy over the course of the years. The gravitational waves predicted by this theory were detected at last in September last year, and was formally announced earlier in February. It has been over a century now, but general relativity remains among the most comprehensive theories ever formulated.