|
How far does the universe stretch out? What is outside the universe? Or, is
there a center of the universe? These are some questions you may wonder about
when you become interested in the universe. If we say "we will explain
the structure of the universe," you might expect to find the answer to
questions above. Well, the answer is that "the utmost end and the center
of universe does not exist." There is no edge or center of this universe.
When we say edge and center, we mean the edge and the center of universe as
a whole. There is no such special place or direction in our whole universe.
This idea is called "cosmological principle." A distance (size) which
we can observe does exist and is called "the horizon of the universe."
Imagine a sphere. Let's say you are walking on that sphere. Because we live in a 3 dimensional world that consists of 3 axes-- length, width, and depth--you will realize that from the center of the sphere, you can only walk to the surface of the sphere which is the distance of the length of radius. So you can imagine that there is an end of the sphere.
But what if you look at this sphere from a 2 dimensional view? In a 2 dimensional world, there are only 2 axes--length and width. If you were standing on the sphere, you would think that the surface (in this case, the ground) stretches out forever, no matter how far you walk, because you are on a sphere. You will not reach the end; you can go on forever. Therefore, the area you can pioneer is limited (if you keep on walking, eventually you will cover the whole surface), but that area where you can walk is infinite and continuous. Therefore, because the end is not known, it is impossible to define its center.
Just think that the universe is like this too. Rather than saying that there
is no end or a center of the universe, we simply can't think about those things.
We can not define "what exists outside the universe" if there is no
outside.
|
![]](../images/end.gif){kind=small}
Utmost End and Center
Introduction
The Universe Expansion
