IT’S an intergalactic race in which the firing pistol is a supernova and the finishing line is Earth. The result could finally decide which of two rival theories explains how galaxies are held together. Is dark matter responsible, or does gravity behave differently on galactic scales from the way we expect (see “Dark matter vs modified gravity: new battle lines are drawn”)?
Cosmologist Emre Kahya, a graduate student at the University of Florida, Gainesville, claims he has a definitive test that could settle the debate. His idea is to compare the arrival times on Earth of different waves and particles…
