If The Universe Is 13.8 Billion Years Old, How Can We See 46 Billion Light Years Away?
“There are a few fundamental facts about the Universe — its origin, its history, and what it is today — that are awfully hard to wrap your head around. One of them is the Big Bang, or the idea that the Universe began a certain time ago: 13.8 billion years ago to be precise. That’s the first moment we can describe the Universe as we know it to be today: full of matter and radiation, and the ingredients that would eventually grow into stars, galaxies, planets and human beings. So how far away can we see? You might think, in a Universe limited by the speed of light, that would be 13.8 billion light years: the age of the Universe multiplied by the speed of light. But 13.8 billion light years is far too small to be the right answer. In actuality, we can see for 46 billion light years in all directions, for a total diameter of 92 billion light years.”
Sure, the Universe is expanding, but how is it possible to see objects that are 46 billion light years away? After all, with an age of 13.8 billion years since the Big Bang, and a Universe where the cosmic speed limit is the speed of light, how can we see light that’s more than three times the expected distance away? It’s one of the most frequent questions that cosmologists get, and yet the root of the question is better framed as “how does the expanding Universe work?” While we normally think about things happening in space that doesn’t change much, or as individual objects moving relative to one another in a static space, we don’t, conventionally, have a solid intuition for how the fabric of space itself expands. But thankfully, the scientists who study it do!