ABSTRACT

In this chapter, we will consider Einstein’s general theory of relativity: the modern theory of gravity which forms the background to all cosmological considerations. While it is a staggeringly beautiful creation of a human mind, the theory is challenging to come to grips with on a technical level. We will only be able to brush its mathematical surface and try to build a picture of its physical interpretation from partial analogies. The detection of gravitational waves by the LIGO experiment increases our confidence in the theory, but we know that eventually a quantum theory of gravity must supplant general relativity in the extreme circumstances of the early universe and the centre of black holes.