The Invariant Interval

What everyone agrees on

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• The interval $s^2 = (c\Delta t)^2 - \Delta x^2$ is the same for all observers.
• For a clock moving between two events, s/c is its proper time.
• Light rays have zero interval.

Steps

1. A new kind of distance
2. Proper time
3. The invariant hyperbola
4. Boosting the whole diagram
5. Proper distance
6. Compute an interval
7. Light’s interval