Direct detection of gravitational waves
Do ripples in spacetime predicted by Einstein's general relativity — gravitational waves produced by cataclysmic events like merging black holes — actually exist and can they be directly measured on Earth?
History and references
Settled in 2016 by LIGO Scientific Collaboration and Virgo Collaboration.
Einstein predicted gravitational waves in 1916 as a consequence of general relativity, but their effects were expected to be so minuscule that many, including Einstein himself at times, doubted they could ever be measured. On September 14, 2015, the Advanced LIGO detectors recorded a signal (GW150914) matching the merger of two black holes roughly 1.3 billion light-years away, publicly announced in February 2016 — a century after the prediction. This opened the field of gravitational-wave astronomy, with dozens of further detections since, including the neutron-star merger GW170817 in 2017, and earned Rainer Weiss, Barry Barish, and Kip Thorne the 2017 Nobel Prize in Physics.
A century-old prediction that space itself can ripple like a pond was confirmed by detecting a distortion smaller than one ten-thousandth the width of a proton in mirrors four kilometers apart.
Explanations that circulated
- That indirect evidence from the Hulse-Taylor binary pulsar (1974, Nobel Prize 1993) was already a 'direct' detection — that was strong indirect confirmation via orbital decay, not a direct measurement of a passing gravitational wave
References
- Observation of Gravitational Waves from a Binary Black Hole Merger, B. P. Abbott et al. (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters, 2016
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