HAVE WE FOUND THE EDGE OF THE UNIVERSE?

Whether or not our cosmos comes to an end is a question astronomers are tackling with some surprising results

- Colin Stuart

Look out on a clear night and you can see pretty far into the universe. Some of the stars you’ll spot sit over 10,000 light years from Earth. Even further away is the famous Andromeda Galaxy, the nearest major star city to our own Milky Way and debatably the most distant object you can see with your eyes alone. It is a staggering 2.5 million light years from us. That means the light arriving on Earth today from Andromeda has been trekking across space for 2.5 million years to get here. All of human history has played out in the time it’s taken for light to reach us from just our nearest galaxy. With binoculars and telescopes you can continue to see objects further and further from home. But where does it all end? Does it even end?

“We just don’t know,” says Andrew Pontzen, a cosmologist at University College London. “There is no evidence for an edge to the universe, but there is an edge to what we can see.” We can only see objects in space if the light from those objects has had enough time to reach us. For Andromeda that time is 2.5 million years, but for increasingly more distant galaxies that travel time also increases. There are galaxies so far away that light hasn’t managed to make it here yet. This marks out the edge of our visible universe – the part of it we are able to see – but not the end of the universe itself. “It’s rather like how you can’t see over the horizon but the Earth doesn’t end there,” Pontzen says. In theory, each passing day should bring with it new light allowing us to push our cosmic horizon outwards. Yet it doesn’t quite work like that.