Space and time are a single, flexible fabric, not a fixed backdrop

Greene explains Einstein's general relativity as revealing that space and time aren't a neutral stage on which events happen, but an active, malleable fabric — spacetime — that bends and stretches in response to mass and energy. What we experience as gravity is really the effect of massive objects curving this fabric, so that other objects moving through the curved space simply follow the straightest available path, which appears to us as being 'pulled' toward the mass.

This overturns Newton's older picture of gravity as an invisible force acting instantly across empty space, replacing it with a geometric picture where mass literally reshapes the arena within which everything moves. Greene uses accessible imagery — a heavy ball resting on a stretched rubber sheet, distorting the paths of smaller balls rolling nearby — while being careful to note the limits of that analogy.

This reframing was later confirmed by observations, including the bending of starlight around the sun.

*Takeaway: gravity isn't a force reaching across empty space — it's the shape of space itself, bent by mass.