What is the theory of general relativity? Understanding Einstein's space-time revolution

Graphic illustration of Einstein's theory of general relativity showing two spheres in close proximity and a series of ripples emanating from them.

General relativity is physicist Albert Einstein's understanding of how gravity affects the fabric of space-time.

The theory, which Einstein published in 1915, expanded the theory of special relativity that he had published 10 years earlier. Special relativity argued that space and time are inextricably connected, but that theory didn't acknowledge the existence of gravity.