Browser Demo Slows Light to a Walking Pace So You Can See Relativity

A new interactive WebGL demo by Dmitry Brant reimagines a virtual park where the speed of light is just 5 km/h — roughly a brisk walk. Because light is capped at that crawl, the full menu of special-relativistic effects becomes visible at ordinary movement speeds. As you accelerate with the arrow or WASD keys, you watch length contraction squeeze the scene ahead, time dilation split your wristwatch from a separate world clock, and Terrell rotation warp nearby objects.

The simulation also renders the relativistic Doppler shift: objects in front turn blueshifted, objects behind turn redshifted, and moving objects show transverse Doppler effects. On-screen readouts track velocity, the β ratio (v/c), the Lorentz factor γ, and a length-contraction multiplier, while toggles let you switch individual effects — including a Galilean view with aberration disabled — on and off for comparison. As in reality, c itself stays unreachable and can only be approached asymptotically.

The value here is pedagogical rather than technical: relativity is normally invisible because everyday speeds are a vanishing fraction of light speed. By dialing c down to human scale, the demo turns abstract textbook math into something you can navigate first-hand, making it a sharp teaching tool for an effect most people never get to experience directly.