Interferometers

Measuring with light

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• An interferometer splits a beam, sends it along two paths, and recombines it.
• Moving a mirror by $\lambda/2$ shifts the pattern by one fringe.
• LIGO measures length changes of about 1/400 of a proton’s width.

Steps

1. Michelson’s ruler
2. Counting fringes
3. A null result
4. Hearing spacetime ripple
5. Moving the mirror
6. A tenth of a millimetre