Speed of spacetime ripples rules out some alternatives to dark energy
Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.
On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17). Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection. That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.