ELI5: Explain Like I'm 5

Plane at infinity

Imagine you are playing with toy planes on a big flat surface, like a table. You can move the planes anywhere on the table and they can go really far away from you. Now, if you look at the planes that are really, really far away from you, they start to look very, very small. It's almost as if they are shrinking and going away to a special place that you can't reach. This special place is called the "plane at infinity."

The plane at infinity is like the farthest point you can see where everything becomes very small. It's like the end of your vision where things start to disappear. But, don't worry, they are not really disappearing, they are just going very far away.

Now, when we talk about the plane at infinity in math, we are not really talking about a physical place. It's more like a concept that helps us understand some interesting ideas. In math, we often imagine things that are not real, but they can still be very useful.

In geometry, the plane at infinity helps us think about shapes and lines that go on forever, like the horizon you see when you look at the sky and the ground meeting. These shapes and lines don't have an ending point, they just keep going and going. So, we use the plane at infinity to help us think about these never-ending shapes and lines.

When we draw a picture of the plane at infinity, we usually draw a straight line that goes all the way across the paper. This line represents the horizon or the farthest point we can see. Everything below this line is like the regular world we live in, and everything above this line is like the plane at infinity.

So, the plane at infinity is a special way we think about things that are very, very far away and never-ending. It helps us understand shapes and lines that go on forever and imagine things that are beyond what we can see with our eyes.