If you were to go as far out into space as you can imagine, what would you encounter? Would there be a limit to how far you could go, or could you travel a limitless distance? Would you eventually return to your starting point, or would you continue to traverse space that you had never encountered before? In other words, does the Universe have an edge, and if so, where is it?
Believe it or not, there are actually three different ways to think about this question, and each one has a different answer. If you consider how far you could go if you:
- left today in an arbitrarily powerful rocket,
- considered everything that could ever contact us or be contacted by us from the start of the hot Big Bang,
- or used your imagination alone to access the entire Universe, including beyond what will ever be observable,
you can figure out how far it is to the edge. In each case, the answer is fascinating.
The key concept to keep in mind is that space isn’t how we normally conceive of it. Conventionally, we think about space as being like a coordinate system — a three-dimensional grid — where the shortest distance between two points is a straight line, and where distances don’t change over time.
But both of those assumptions, so thoroughly good in our everyday lives, fail spectacularly when we begin looking at the larger-scale Universe beyond our own planet. [Continue reading…]