Michelson Interferometer

Move one mirror by nanometres and watch the circular fringes shift. The 1887 experiment that disproved the luminiferous aether.

ΔL = 0 nm
Δφ = 0 waves
Pattern: —
Path difference ΔL = 2(d₁ − d₂)
Bright fringes: ΔL = mλ
Dark fringes: ΔL = (m+½)λ

In the circular fringe pattern, rings contract/expand as ΔL changes by λ/2.