The
Twin Paradox

How it works

1. Enter the starting age and use the slider to set the traveling twin's speed as a fraction of the speed of light, c.

2. Click the "Simulate" button, and the simulator will determine how much each twin ages during a 10-year Earth round-trip.

3. A visual timeline displays the aging difference with color-coded bars—blue for the Earth twin and red for the traveling twin.

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About

The Twin Paradox is a famous thought experiment in special relativity that demonstrates how time slows down for a person moving at speeds close to the speed of light. According to Einstein’s theory of relativity, "a clock moving at high speed relative to an observer will tick more slowly than a clock at rest" This means that a twin traveling in a spaceship at near-light speeds would age more slowly compared to their sibling who remains on Earth.

This simulation allows you to explore the Twin Paradox by adjusting the traveling twin's speed and seeing how time dilation affects their aging.