How It Works
A view of the visible universe.

How big is the universe?

A view of the visible universe.

A view of the visible universe.

No one knows for sure, but we can make estimates based on the expected age of the universe and the motions of galaxies throughout the universe. The universe itself is expanding, but not in the way a balloon expands. The expansion is taking place throughout the universe, where space-time itself is being stretched outwards. Whereas a balloon pushes its edges out as it expands, the universe is also pushing its insides outwards as well, but there is no centre of the universe, so everything is moving away from everything else. It’s a bit like baking a ball of dough; the entire dough expands and grows, not just its edges.

However, based on our knowledge of how old the universe is, roughly 14 billion years, we can observe a theoretical ‘edge’ of the visible universe about 14 billion light years away from us. This is the furthest distance we can see, as light that might be further away has not had time to reach us yet. Thus, we can say that the visible universe has a diameter of 28 billion light years, 14 billion light years in either direction from Earth. However, what’s beyond this distance is unknown. The 28 billion diameter visible universe we can observe could be just a tiny fraction of a much larger universe, or perhaps just one in a system of many universes.




  • According to Lecture 12 of Professor David Meyer’s lecture course Experiencing Hubble (go to the website http://www.greatcourses.co.uk) you cannot look back in time any further than 380,000 years after the Big Bang. Why? Because the cosmos as it it exists did not become ‘transparent’ until after this time. In other words although you can estimate the age of the cosmos no one will ever be able to see right back to the moment of the Big Bang itself. If you want to know what ‘transparent’ means then buy yourself a copy of this marvellous course. It does not cost the earth.