91AggieLawyer said:
Quote:
The radius of the universe is about 46 billion light years.
How in the world can we even estimate this? I know math can take over from observation at some point but isn't this very assumption driven?
We know the universe is expanding, so we can work backwards to when it wasn't. This means we can get an estimated age. Based on that and the speed limitations imposed by relativity, we can get a maximum diameter for the known universe. Basically, the maximum possible diameter is universal age*c.
Beyond that, we can sort of estimate the speed and acceleration of the expansion of the universe, though these aren't universally agreed upon (pun intended). With calculus, we can take those numbers to get a better estimate than above that takes into account changes in velocity (The universe isn't expanding at a speed of c, or the speed of light).
The most basic assumption is that there is not some kind of universe next to ours. Say our universe started from a big bang. Well, the assumption is that it was the only one in the infinite void of space, by there could have been, or might even be right now, one that is 100 billion light years away that we don't and couldn't know about. This is what that while estimate should be prefaced with "known."