To the Fifth Dimension and Beyond  

If the universe has extra dimensions for gravity to leak into, the gravitational wave signal from the colliding neutron stars would be weakened. That in turn would make the source look like it was farther away, just like a faint light could be a dim flashlight or a brighter light farther off. The brightness of the light signal and the strength of the gravitational wave signal are independent ways to measure how far away the colliding neutron stars were.