For a while now, astronomers have been confronting a conundrum. Studies of the early universe, looking at the era just after the Big Bang, tell us that the cosmos should be expanding at one speed. But when astronomers actually measure today’s universe, they find a faster rate of expansion.

Scientists have known that the universe is expanding for around a century. Astronomers like Edwin Hubble first noticed that every distant galaxy they could measure seemed to be moving away from Earth –