Does light escape the Universe when it is expanding or contracting? © Getty Images

Does light escape the Universe when it is expanding or contracting?

By definition the universe contains everything and not even photons are exempt from that.

Asked by: Barry Speight, Ireland

Advertisement

The universe contains everything by definition. Light can’t escape the universe, because in travelling outward it merely expands the boundary of the universe. It’s like asking if a sheep can escape from the herd: since the herd is defined as that collection of sheep, the radius of the herd can grow and shrink but all the sheep are always part of it. In our universe things are a little more complicated than that because space itself is also expanding so the edge of the universe is actually expanding faster than the speed of light.


Advertisement

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.