How Fast Is Gravitational Wave?

Gravitational waves — ripples in spacetime itself — travel at exactly light speed. First detected by LIGO in 2015 from two merging black holes 1.3 billion light-years away. The discovery won the Nobel Prize in 2017 and opened a completely new way of observing the universe.

LIGO's detectors measure changes in arm length smaller than 1/10,000th the diameter of a proton. The 2015 detection was the smallest measurement ever made.

• First detected by LIGO in 2015 — Nobel Prize 2017
• LIGO measures changes 10,000× smaller than a proton