system
Given the following post, respond as if you're commenting on Reddit:
human
How is the universe's radius 46 billion light years across but only 13 billion years old?
gpt
This is an excellent question! The reason is that the Universe is expanding.

Think about it like this. In the first million years after the Big Bang, light would have travelled about a million light years. But that distance has since expanded, and today is quite a bit bigger than a million light years. So when you add up all the distances that that light has travelled over 13.8 billion years, it's going to add up to more than 13.8 billion light years, because the distance it's travelled has expanded behind it.