The doughnut's surface looks curvature, but it's mathematically flat.

In other words, the surface of a doughnut is like a flat surface, mathematically without curvature.

But if you go straight along the surface of the doughnut, you'll be back in place.

The doughnut's surface is flat and finite, but if you go straight, like a sphere, you can get back in place.

This is called a two-dimensional torus in mathematical terms.

The Earth is like that.

The Earth is flat and finite, but if we go straight, we can get back to where we are.

So far, we've believed that this is because the Earth is round like a ball.

We didn't think about a two-dimensional torus.

But don't mistake the Earth for looking like a donut just because it's a two-dimensional torus.

They're both in the same topology, not the same shape.

So why does the Earth have this trait?

That's because the Earth is not an object, it's a space.

Space is a relationship.

The relationship between me and you, animals and plants, wind and clouds, mountains and valleys is the space.

So, without those elements, there's no space.

The change of space is time.

So, time and space are the same thing.

So the world is a space, a time and a relationship.

Time changes periodically.

Day and night, and season show it well.

Space and time are the same, so space also changes periodically.

It's easy to think about the fact that trees change regularly according to the seasons.

Periodic change and flow is like the progression of light.

So the world is light.

So if we go straight in the world, we'll reach the cycle and get back to where we are.

The space cycle, which is equivalent to a day in time, is 40,000 kilometers.

So if we travel 40,000 kilometers, we're back in place.

In short, the Earth is a space where the sky, the earth, and all the elements in it are involved.

It's a space, so it has no shape.

But it's finite, flat and without curvature.

It's already been scientifically proven that there's no curvature in the sky.

The space has a cycle like time.

That's true world.