How does gravity actually work?

What's actually happening

Start with the part nobody tells you: gravity is absurdly weak. A toy fridge magnet — something you can buy for a pound — beats the gravitational pull of the entire planet in a tug-of-war over a paperclip. Two people sitting a metre apart attract each other with roughly the weight of a grain of sand. The only reason gravity dominates your life is that the Earth has six trillion trillion kilograms to throw at the problem, and unlike magnetism, gravity never cancels out: every kilogram only ever adds.

Newton's law packs the whole behaviour into one line: the force grows with both masses multiplied, and shrinks with the square of the distance between them. That inverse square is the part the simulator makes visible — drag the masses to half the gap and the arrows quadruple. And the arrows always match: the Earth pulls you down with exactly the force you pull the Earth up. When you jump, the planet recoils — by about a trillionth of a trillionth of a metre, which is why the planet seems unbothered.

Two centuries later Einstein asked the awkward question Newton had dodged: how does the Earth "know" the Moon is there to pull on? His answer rebuilt the whole picture — mass doesn't reach out and grab things; it bends spacetime around itself, and things simply follow the straightest path available through the bent geometry. Falling, in this picture, isn't a force acting on you at all, which is why astronauts in free fall feel nothing. For everything on this page, though, Newton's simple law gets the right answer — NASA still flies missions on it.