[ELI5] If the beginning of the universe was 13B+ years ago, how is the boundry of the universe 46.5B ly away?
In: 7
It’s important to know what we mean by “the boundary of the universe”. There’s a few boundaries, this one is the farthest parts of the universe we can see. This comes from a combination of light moving 13 billion light years, and the fact that space itself is expanding. So the things that were already very far away when they emitted that light have moved even further in the time since.
The most useful analogy for space expanding is to imagine two dots on the surface of a balloon. If you inflate the balloon more, the dots get farther apart, even though they haven’t moved on the balloon itself. This effect is particularly noticeable for far objects because the farther apart two things are, the more space there is in between to expand.
So to clarify: the things we are seeing are 45 B light years away *now* but we’re much closer when they gave off their light 13 B years ago.
Latest Answers