A quote I love from Seven Brief Lessons on Physics, regarding Einstein’s General Theory of Relativity:
“It’s a moment of enlightenment. A momentous simplification of the world: space is no longer something distinct from matter–it is one of the ‘material’ components of the world.
An entity that undulates, flexes, curves, twists.
We are not contained within an invisible, rigid infrastructure: we are immersed in a gigantic, flexible snail shell.
The sun bends space around itself, and Earth does not turn around it because of a mysterious force but because it is racing directly in a space that inclines, like a marble that rolls in a funnel.
There are not mysterious forces generated at the center of the funnel; it is the curved nature of the walls that causes the marble to roll.
Planets circle around the sun, and things fall, because space curves.”