• Question: How big is the universe?

    Asked by anon-252493 to Sheila on 4 May 2020.
    • Photo: Sheila Kanani

      Sheila Kanani answered on 4 May 2020:

      We think the universe it about 14 billion years old, and about 93 billions light years in diameter. This means it is so big that it would take light 93 billion years to cross the universe! And the universe is still expanding!!

Comments

  • Photo: Greg

    Greg commented on :

    You’ve got to be careful with what you mean by universe here. As far as we know the universe could be infinite because we can’t see it all. light sets the universal speed limit, and so we can only see as far as light has had time to reach us. We think the universe is 14 billion years old so we can see a sphere of radius 14 billion light years. However, the universe has been expanding so something that was 14 billion light years away when the universe was formed is now much further away. Precisely how far away depends on how rapidly you think the universe has expanded throught history as there’s no good reason why the rate of expansion should be constant (as far as i know, I’m not actually an astrophysicist). I think the 90 odd billion light year radius comes from our best theory for how the universe has expanded since the big bang