Bach tensor

Okay kiddo, let's talk about bach tensor. Imagine you have a ball, and you want to know how curved its surface is. If you look at the ball from really close up, each point on the surface will have a certain amount of curvature. Now, imagine you have a bunch of little people standing on the surface of the ball. Each of them can feel the curvature at the point they are standing on. The bach tensor is like a special tool that combines the feelings of all those little people and tells you how much the overall surface of the ball is curved. It helps scientists understand things like how gravity works and how objects move through space.