ELI5: Explain Like I'm 5

Riemann–Cartan geometry

Alright kiddo, let me tell you about Riemann-Cartan Geometry in a way that you can understand.

Do you know what Geometry means? It's all about shapes and the way they fit together. Like a puzzle, every shape has a different size, angle, and location, and they can all fit together differently.

Now, Riemann-Cartan geometry is all about shapes in space that are constantly changing. Imagine you have a piece of rubber that you can stretch, bend, and twist in any direction - this is called a "manifold". This manifold is like space that can change and move around.

Now, let's say you have a tiny bug on this piece of rubber, and it starts walking around. As it moves, it can sense the changes in the shape of the rubber, and it can also feel the force of gravity pulling it down.

That's where Riemann-Cartan geometry comes in - it's a way of describing how shapes change in space and how forces like gravity affect them. It does this by using something called a "connection", which is like a map that tells you how to move from one point to another on the manifold.

The connection is special because it can also tell you how the manifold is curved, twisted, or stretched. It's like having a GPS that not only gives you directions, but also tells you about bumpy roads or steep hills.

So, Riemann-Cartan geometry is really useful for physicists and mathematicians who study things like black holes, the universe, or even tiny particles, because it helps them understand how they move and interact in a constantly shifting and curved space.

That's it kiddo, I hope you have a better understanding of Riemann-Cartan geometry now.