Question: if the universe is expanding, what is it expanding into?

James Lazenby answered on 6 Mar 2026:

I’m not a physicist, but did study physics so I’ll give it a go at explaining it. My physics professor once said the more you try and understand astro-physics the more you realise you don’t understand it.

The universe is defined as everything, so there is nothing for the universe to expand into. So the universe is expanding into itself. Picture an un-inflated balloon and you draw dots on it. As you blow the balloon up, the dots will get larger and further away from each other as they expand, but the matter that made up that balloon is still the same, the distances have just increased. That’s how we know the universe is expanding. Looking at galaxies light years away we see evidence of them getting further away because the spaces between us are getting larger, but nothing extra is being added.