starnut wrote:Cosmologists are of the opinion that there is no center and no edge to the universe and that the term "Big Bang" is misleading and confusing to lay people. It gives people an impression that the universe came into existence in an explosion, hence there should be a center of the explosion. I am having a hard time trying to visualize how the universe could come into existence without a center. The best I can come up with is a sheet of infinite size that suddenly popped into existence and expanded outward, but this would still give the universe two edges.
Oh, my aching head...anyone got a better idea?
Cosmologists don't say that the Universe has no center. What they say is that the Universe has no three-dimensional center. I find that the famous balloon analogy is a big help. It considers the view of 3D universe as seen by 2D creatures. From our viewpoint, the balloon is a 3D object with a center. Its surface expands outward from that center. But for 2D creatures living on the balloon, there is no center. "Up" and "down" are not directions they can perceive. To them, they are living on an infinite surface. If they travel far enough in one direction, they come back to where they started. They can even do clever experiments, such as measuring the summed angles of triangles, and figure out that their universe is spherical in 3D. But they can still never see its center.
To see the center of our 4D universe, you'd need to be a 4D creature living outside of it. As 3D creatures embedded in our 4D universe, we only see the surface- a 3D section. The "center" lies in a direction that we can't perceive, but which we can understand mathematically. We can do the same sort of triangle measuring experiments to figure out the 4D shape- in fact, such experiments are planned (they need to be done in space, over vast distances).
The shape of the Universe shouldn't be confused with the shape of the observable Universe. The latter is spherical in 3D, and has a center- the observer. We are each the center of our own observable Universe.