• Question: If the universe is expanding, what is it expanding into?

    Asked by Izzywizzy to Daniel, Hannah, Maggie, Ry, Scott on 10 Nov 2017.
    • Photo: Maggie Lieu

      Maggie Lieu answered on 10 Nov 2017:

      The Universe isn’t expanding into anything. Think of it as a balloon as its getting blown up. Every part of the surface of the balloon is moving away from each other, but if you were to live on the surface of the balloon, you wouldn’t be able to see it expand into anything

    • Photo: Ry Cutter

      Ry Cutter answered on 10 Nov 2017:

      That is a dizzying question! We say expanding because we don’t really have a word that describes ‘what’ the universe is doing. Some people use the word stretching.
      Maggie’s example of a balloon is perfect for this discussion. If you put two dots on a balloon then blow the balloon up, the two dots will separate (end up further apart). But the dots haven’t moved.. this is the same for galaxies and space! Space stretches out which makes the galaxies separate, and to us it makes it look like the galaxies are moving when they aren’t!
      Here’s the tricky part, when we blow up a balloon it occupies more space. So we’d say that the balloon is expanding into the air.
      The whole of space can’t occupy more space, there is none!? The best answer I’ve seen to this is like adding a number to infinity. Infinity is the biggest and most uncountable number:
      Infinity + 1 = Infinity.
      If we say the size of the universe is infinity, as it stretches out we can say:
      size of the universe + size of expansion = new size of the universe
      which is:
      infinity + (a number) = infinity!
      So even though the universe has gotten bigger it hasn’t changed in size! Which is completely mind bending!
      I hope this helps :p
      Ryan

    • Photo: Hannah Middleton

      Hannah Middleton answered on 10 Nov 2017:

      Maggies answer sounds great – in the universe everything is getting further away from each other, but it’s not really expanding into anything. It’s pretty strange to try and think about!

    • Photo: Scott Melville

      Scott Melville answered on 13 Nov 2017:

      There are two things going on here: the first is what Maggie and Ryan are explaining, where we’re kind of living on some kind of balloon which is slowly inflating, but the second thing is that light travels at a finite speed. These two things are unrelated, but the light thing is maybe easier to think about (which is why I’m going to talk about that one 😉 ). The Universe is almost 14 billion years old. In one year, light travels exactly one light-year (duh). So the ‘size’ of the observable Universe is about 14 billion light-years (give or take) 🙂
      It’s a little more complicated because of the balloon expansion business, but one of the reasons that we can see further and further each year is just because the Universe is getting older, so light can have traveled further.
      If you shone a torch at the sky, you would have to wait several years before that light reached the nearest star – similarly, when you look at the sky, you ‘see’ the light which the stars emitted many years ago. (it’s kinda cool – the image of the Sun in the sky is actually what it looked like about 8 second ago – that’s how long it takes sunlight to reach the Earth. If the Sun suddenly disappeared, it would take 8 seconds for the Earth to go dark!)

Comments