Dark matter makes up 80 per cent of the universe’s matter but scarcely interacts with ordinary matter. A novel particle is the most popular candidate, but Andrei Derevianko and Maxim Pospelov at the Perimeter Institute in Waterloo, propose that kinks or cracks in the quantum fields that permeate the universe could be the culprit.
If they are right, fundamental properties such as the mass of an electron or the strength of electromagnetic fields would change at the kinks. "The effect is essentially locally modifying fundamental constants," Derevianko says. Clocks would be affected too, measuring time slightly differently as a result.
That’s where GPS comes in. The network of satellites is about 50,000 kilometres in diameter, and is travelling through space, along with the entire solar system, at about 300 kilometres a second. So any time shift when the solar system passes through a cosmic kink will take a maximum of 170 seconds to move across network.
Other things could perturb GPS timekeeping, but only a signal from dark matter would have that signature, say Derevianko and Pospelov. Derevianko is already mining 15 years’ worth of GPS timing data for dark matter’s fingerprints. If he doesn’t find anything, he plans to continue the search using the Network for European Accurate Time and Frequency Transfer (NEAT-FT), a network of ground-based atomic clocks that is under construction in Europe. Each of these clocks is far more sensitive than a satellite clock.
If the cosmic kink idea is right, we could also search for dark matter using pulsars, the rapidly spinning corpses of stars that exploded as supernovae. Pulsars emit beams of electromagnetic radiation that hit Earth with periods that can be more precise than our best clocks. "There’s a tantalising hint from pulsar data," says Derevianko. "These are like atomic clocks, highly regular."