Aye, Carl Sagan's Cosmos is amazing
Anyway, since you're at work. It works like this.
Think of a 2 dimensional creature, doesn't know about the third dimension. He just walks around in his 2d world. So, what he doesn't realize is his worlds curved like a balloon. So if he starts walking, he'll be walking in what he thinks is an infinite flat surface, but he ends up arriving at where he started!
Now, add a third dimension, and this is what some scientists believe we live in. Additionally, since this balloon is expanding, it looks like all the universes are speeding away. This is because, if you take a balloon and tape some pictures of galaxies on there. Then blow it up, those two galaxies would see they're moving away from each other.
To a flatlander 2d person from one galaxy, it would appear as if the other galaxy is moving away. To a flatlander in the other galaxy, he'd see the same thing!
So one of them might think they're at the center of a universe that's accelerating away from them, but in reality, they aren't. (at the center)
Further more, Sagan goes on to say that the curve (if it does exist) is likely caused by gravitation, and if there's not enough matter, than it would be saddle shaped, with the universe above this saddle infinite.
He goes on to explain later (at the end of the video in some post-info after the credits), that science has discovered that the galaxies appear to be bubbling out of a center. Like if you were to blow bubbles in milk. They found this out because they mapped all known galaxies, and found that, when playing connect the dots, they almost look like they form bubbles out of some center.
Which is pretty fascinating if you consider that our universe may be saddle shaped.
It's not just for BYOND you know!