Universe is limited, but endless. 宇宙は有限だが、終わりがない。

宇宙は有限ですが、終わりはない・・・

Let's suppose we are people in the one dimensional world.

We live on a linear universe and move only back and forth. We don't have any idea of "side" or "height".

The line is so long, and we often wonder how it does look like the end of the line (the edge of the universe).

But, the fact is that the line forms a loop.

This linear universe does not have the end, although the length of the line is limited.

The shape of the universe is ..... circle.

Can we understand the shape of the universe?

No.

Circle is a two dimensional shape.

Because we are one dimension people, we are not capable of imagining any two dimensional shape.

There is no circle, square, triangle shape in the one dimensional universe.

No matter which direction you go, you end up being the same place.

No one could understand why.

If the circle becomes larger, it is felt that we are getting away from each other.

Interestingly, the universe appears expanding around any of "you". 

All of us feel "I am the center of the expansion".  And you are.

The farther the distance is, the faster the speed of getting away.

These phenomena are exactly the same observed in the three dimension universe as we live in real.

Our universe is also considered that it is endless, but limited. 

Can we understand the shape of our universe?

No.  The universe has a four dimensional structure.

Because we are three dimension people, we are not capable of imaging "the four dimensional shape."

When you look at the sky, it is you standing all over at the edge of universe, if you should be able to look at the farthest. 

Nothing interest will be seen.

No matter which direction you travel to, you end up being the same place.

Let's go back to the one dimension universe.

Any mass bends the line.

Because of this bending, two objects are attracted each other, if the distance is close.

This is considered the cause of attraction.

If the massive one shakes his body, it is postulated that a wave will propagate through the linear universe.

This is called "the gravitational wave."