India, Oct. 8 -- "Spacetime tells matter how to move; matter tells spacetime how to curve." - John Archibald Wheeler

For centuries, space and time were considered separate. Space told us where something existed, and time told us when. Then came Albert Einstein and his theories of relativity; perceptions changed. Special relativity brought them together into spacetime, while general relativity showed how mass and energy shape its geometry. Wheeler later reduced this complicated idea to a single line.

Let me give you an example. In Einstein's description, the Sun does not need to be imagined as tugging the Earth with some unseen force to keep it in orbit. The Sun's mass bends spacetime around it, and the Earth follows that curvature. All ...