The two major revolutions of 20th Century physics are Einstein’s General Relativity which is a theory of the gravitational force and Quantum Mechanics which deals with sub-atomic phenomenon. Both are successful theories in their domains of application. With the direct observation of gravitational waves by LIGO, it becomes more imminent than before to reconcile these theories. However, applying the rules of quantum mechanics to Einstein’s theory does not yield a consistent theory which would be needed to describe the early universe and its future.
What is to be done?
A way out is a new framework of Physics in the making called `String Theory’, in which gravity is inevitable! We will take a guided tour of String theory and indicate some landmarks on the way. Black holes will be our beacons on this journey. One inevitable conclusion is that Einstein’s continuous space-time is only an approximate description of an underlying microscopic theory very much like fluids have an underlying atomic structure.