After a century of speculation, scientists have announced the first ever detection of gravitational waves. The discovery of oscillations that distort the fabric of spacetime confirms the last prediction of Einstein’s general theory of relativity.
1.3 billion years ago, in a galaxy 1.2×1023 kilometers away, two black holes collided. After circling each other at up to half the speed of light, this system of binary black holes merged to form a new supermassive black hole. And in its last 20 milliseconds, the collision released more energy than the rest of the universe combined, as a mass 3 times that of the sun was converted into energy. In the form of gravitational waves, stretching and compressing space as they travelled, a tiny fraction of the energy released reached earth on September 14, 2015.
The Laser Interferometer Gravitational-Wave Observatory, or LIGO, in Washington, has been being designed and refined for fifty years. September marked its first-ever confirmed detection, days after a seven-year upgrade to improve sensitivity, when an unexpected squiggle on a screen matched exactly the black hole-merger wave signal predicted using Einstein’s general theory of relativity. Einstein himself believed his theorised gravitational waves were too weak to ever be detected, but black holes, high-density systems with massive effect on spacetime, gave more recent physicists hope.
The experiment consists of a laser beam projected through a vacuum along each of two 4-km long tubes. Analysis of the light reflected off mirrors at each end allows a 1000-strong team of scientists worldwide to detect distortions of spacetime no wider than a human hair. The instruments involved are so sensitive that to confirm the reliability of a signal, a similar experiment in Louisiana should detect the same signal as its instruments are hit 10 milliseconds later by the same wave, travelling at the speed of light.
This detection marks the dawn of a new era that will “revolutionise astronomy”, according to Professor Stephen Hawking. Gravitational waves provide a means of looking back in time as far as the Big Bang. Even electromagnetic waves, science’s current method of reconstructing the interactions of the universe, can be distorted by spacetime’s effects. Nothing can stop a wave of gravity.
After more development, LIGO should soon be able to detect not only black hole mergers but mergers of neutron stars, incredibly dense collapsed stars a few kilometres across. Both events are incredibly rare, occurring less than a dozen times per year in a cube 3 billion light years across. This detection might even lead to ways of modelling the dark matter that makes up 90% of the universe, and thereby help us learn more about the Universe’s greatest mysteries.