Some physicists have proposed that maybe the universe has one or more extra dimensions that show up on very large scales, making the universe accelerate. In these theories, light and matter are confined to the four dimensions we know, but gravity “leaks” into the other dimensions. As a result, gravity gets a little weaker the farther out in space we look, but light shouldn’t be affected by the extra dimensions.
The problem is that it’s hard to test gravity on very large scales. However, gravity makes gravitational waves: ripples in spacetime that travel at the speed of light. LIGO and Virgo detected gravitational waves from two colliding neutron stars about 130 million light-years away, which by itself is very exciting. But other observatories also saw light from that collision, which means astronomers have two very different ways to study the same event.
“For the first time ever, we’re seeing gravitational waves and light emitted from the same source,” said Maya Fishbach of the University of Chicago, who is part of the LIGO collaboration, said.