NASA’s Goddard Space Flight Center/CI Lab
The simultaneous detection of gravitational waves and light from a cosmic collision has left a few theories of dark matter and dark energy dead in its wake. These theories require gravitational waves – ripples in the fabric of space-time – to travel slower or even faster than the speed of light. But recent observations have proved otherwise.
On 17 August, the LIGO collaboration saw gravitational waves from two cosmic objects that were spiralling towards each other. About 1.7 seconds later, NASA’s Fermi satellite detected a gamma-ray burst (GRB). The instruments had seen the collision of two neutron stars, about 130 million light years from Earth.
Other telescopes too observed the smash, catching the electromagnetic waves that travelled alongside the gravitational waves – the first such observation.
“This allows us to measure the speed of gravitation relative to the speed of light,” says Miguel Zumalacárregui at the University of California, Berkeley. The signals from the smash-up, now named GW170817, show that gravitational waves do indeed travel at the speed of light, to an accuracy of about one in 1 million billion.
This seriously undermines some theories that modify Einstein’s general relativity to explain the mysterious dark energy thought to be driving the accelerated expansion of our universe, and the invisible dark matter that we detect only through its gravitational pull on ordinary matter.
The theories that died
The standard model of cosmology suggests that dark matter makes up about 27 per cent of the universe, and dark energy about 68 per cent. But this has some unanswered