Physics
Special relativity
Speed a light clock up to 0.999c and compare how fast a clock at rest and a moving clock tick.
Launch simulationHow it works
A light clock measures time by bouncing light between two mirrors. In a frame where the clock moves, the light travels a longer diagonal path between the mirrors. The speed of light c is the same for every observer, so one tick takes longer. The Lorentz factor γ says how much longer: at 0.8c, γ = 1.667, so a tick that lasts 1 s at rest lasts 1.667 s.
γ = 1 / √(1 − v²/c²)Δt = γ · Δτ
Try it yourself
- Start with “At rest · v = 0”. Both clocks tick at the same rate and γ = 1.
- Choose “Fast fly-by · v = 0.8c” and press “One tick”. One tick of the moving clock takes 1.667 s: the light follows a longer diagonal path, still at speed c.
- Choose “Almost light · v = 0.999c”. The factor γ grows to about 22.4, so one tick of the moving clock takes more than 22 seconds.
- Switch the reference frame to “From the rocket”. Now Earth moves and the Earth clocks tick more slowly. Time dilation is mutual.
Model limitations
The model covers only uniform motion without acceleration or gravity, so it does not resolve the twin paradox with a turning rocket. Times of distant clocks are coordinate values, not what a telescope would show. Objects are not drawn to scale and the length contraction of the rocket is not shown.