How big is the universe anyway? Well, according to a book: “Beyond Earth” by David Devorkin, the universe expands; space itself is expanding. As it expands, it carries galaxies along with it. The Big Bang was an explosion of space. This means that galaxies gradually move away from each other; this of course includes the Milky Way, our home galaxy. Edwin Hubble was the one who found out this fact about galaxies.

People have wondered if this means that we’re aren’t at the center of the universe after all, but actually it means that there’s no preferred center. The universe is centerless.  The Big Bang has no preferred direction because we’re inside it! Everything in the universe is part of the big bang.

But why are the galaxies moving away from us? The Hubble law for the universe’s expansion says that galaxies move away from us at speeds proportional to their distances. If a galaxy is a certain distance “D” away from us, and it’s moving away at a velocity “V”, then a galaxy twice the distance away “2D” will be moving away twice as fast “2V”. This is true for whichever direction we look for galaxies.

Now imagine if aliens were to observe our galaxy from theirs. To them, we would appear to be moving away from them in the opposite direction. When they look at the galaxy that is twice away from them as us, they see that galaxy moving away twice as fast as we are, in the same direction! To any observers, it appears that they are at the center.

Since the universe expands, it also means that the universe is bigger today than it was yesterday! In a way, the universe itself tells us what time it is. 

Derek C. Jr. the Blue Monkey-Man & Brain make a point about counting the number of things in the universe, let alone measuring its size.