By Yudhijit Bhattacharjee, ScienceNOW

Testing gravity is simple: walk out of a second-floor window and see what happens. It’s a lot tougher to test Albert Einstein’s theory of gravity — the general theory of relativity — which says that the gravity of an object warps space and time around it. Although researchers have proved general relativity on the scale of the solar system, validating it on cosmic scales has been more challenging. That’s exactly what a group of astrophysicists in Denmark have now done.

The researchers, led by Radek Wojtak of the Niels Bohr Institute at the University...