Detection Methods

The technique behind the ground-based detectors: a laser beam is split down two perpendicular kilometre-scale arms and recombined, and a passing gravitational wave stretches one arm and squeezes the other by a fraction of a proton's width, shifting the interference pattern. LIGO, Virgo, and KAGRA all work this way.

Using an array of millisecond pulsars — nature's most precise clocks — as a galaxy-sized gravitational-wave detector. A passing nanohertz gravitational wave subtly shifts the arrival times of the pulsars' pulses in a correlated way; timing arrays have found evidence for a background of such waves from supermassive black-hole binaries.

Laser interferometry carried out between spacecraft millions of kilometres apart, free of the ground noise that limits Earth-based detectors. It opens the low-frequency gravitational-wave band — the mergers of massive black holes and the whir of compact binaries — that the ground detectors cannot reach. LISA is the leading example.