Gravitational Waves
Ripples in the curvature of spacetime that propagate outward as transverse waves at the speed of light, generated by accelerating asymmetric mass distributions.
Governing formula
h_ij = (2 G / (c⁴ r)) (d²I_ij / dt²), Strain h = ΔL / L ~ 10⁻²¹
SI unit
Dimensionless Strain h (10⁻²¹)
In depth
Predicted by Albert Einstein in 1916. Gravitational waves compress spacetime along one transverse axis while expanding it along the orthogonal axis. Directly detected by LIGO in 2015 from colliding binary black holes.
Examples in the real world
LIGO laser interferometers detecting spacetime strain h ~ 10⁻²¹ from GW150914 black hole merger.