ELI5: Explain Like I'm 5

Pontryagin-Thom construction

The Pontryagin-Thom construction is like a special way to turn a shape or space, called a manifold, into a point. It's like taking a 3D object, like a toy car, and crushing it down until it becomes a single point on the ground.

To do this, we start with a special type of shape called a smooth manifold, which is like a stretchy, rubbery object that can be bent and twisted in different directions. We can think of the different parts of the manifold as being made up of different types of curves, like circles or smooth lines.

Now imagine we want to turn this manifold into a point. To do this, we smash all the different parts of the manifold together in a special way. We pick a particular type of curve that goes through every part of the manifold, kind of like drawing a line through every point on a map. We then attach all these curves together to create a new object that looks like a mesh or web, with all the curves weaving in and out of each other.

This new object is called the Thom space of the original manifold. It's kind of like a "ghost" or "shadow" of the original shape, because it captures all the important information about how the original manifold was shaped and twisted.

The Pontryagin-Thom construction is important in mathematics because it allows us to study the properties of manifolds by looking at this "ghost" or "shadow" object instead. We can use tools from topology and algebra to study the Thom space and learn more about the original manifold.