Or did he make it up? (Part – 4)

By : Niranjan Kambi, Department of Psychology, University of Wisconsin-Madison, USA

In early 20th century, Einstein took the latter path. He questioned the existence of gravitational force, and revolutionised physics by postulating a universe where such a force is rendered superfluous. In place of Newton’s theory, Einstein came up with an even more bizarre formulation, the General Theory of Relativity. It posits that gravity is not a force but a result of the fabric of space – comprising the three spatial dimensions of length, breadth and height, and the fourth dimension of time – being bent by the presence of massive objects like the sun or a planet.

Let’s go back to our observation that an apple always falls to the ground. The Einsteinian explanation for this would be that space-time between the apple and the earth is “squeezed out” due to the earth’s large mass and this appears to us as if the apple is falling towards the earth. What about the earth then? Why doesn’t it fall into the sun, which is almost 13,00,000 times heavier? Einstein would say the speed with which the earth revolves around the sun (1,10,000 km per hour) keeps it from falling into the sun. The earth is just traversing a “straight line” in a space-time geometry warped by the presence of the sun in the centre.

Notwithstanding the counterintuitive nature of this explanation, Einstein’s theory and its mathematical formulation was not only able to explain more observations than Newton’s did, it also removed the certainty and absoluteness Time and Space enjoyed in our minds. Einstein’s theory even predicted many hitherto unknown phenomena such as gravitational waves (or ripples in the space-time continuum which were indeed recently detected), black holes and the expansion of the universe.

To be continued… Next Week