Gravity

What you're looking at

This is a gravitational N-body simulation. Each glowing point is a star with mass, position, and velocity. On every frame the simulation works out the gravitational pull between each star and every other star using Newton's inverse-square law, adds it all up, and nudges each star along. Run it long enough and a flat disk winds itself into spiral arms, two galaxies tear each other into tidal streams, and a cold cloud collapses into knots — all from nothing but gravity.

How does this run in a browser tab?

The honest answer is that it doesn't run on your CPU. Computing the pull between every pair of stars is an all-pairs problem: with sixteen thousand stars that's around a quarter of a billion force calculations, and it has to happen sixty times a second. JavaScript on a single core would manage a slideshow. Instead this uses WebGPU, the new browser API for talking to your graphics card directly. The force loop is written as a compute shader and run across thousands of GPU threads at once, with each block of stars streamed through fast on-chip workgroup memory so the GPU isn't constantly waiting on slow reads. It's the same tiling trick that real GPU physics engines use. Your graphics card was built for exactly this, and the whole thing stays on your machine — there's no server in the loop.

Things to try

Hit Galaxy collision and watch the two cores swing past each other and fling out long tidal tails. Drop the Speed to zero, then nudge it up to step through the dynamics slowly. Press and drag anywhere on the canvas to drop a moving gravity well and stir the stars by hand. Crank Stars up to 65,536 if you've got a real GPU, or pull it down if your fans start spinning. Everything is live — change gravity mid-collision and watch the whole system respond.