" Time, he realized, must be warped by the masses of heavy bodies such as the Earth or a black hole, and that warping is responsible for gravity. He embodied this insight in what I like to call “Einstein’s law of time warps,” a precise mathematical formula that I describe qualitatively this way: Everything likes to live where it will age the most slowly, and gravity pulls it there. "

― Kip S. Thorne , The Science of Interstellar