Renormalization group

Imagine you have a big puzzle with lots and lots of pieces. Each piece represents a tiny little thing that makes up the whole puzzle. You want to understand how the puzzle is put together, but it's hard to see how all the pieces fit together when you look at each tiny piece individually.

Renormalization group (RG) is like taking a step back from looking at the tiny pieces and instead looking at the big picture. You group the tiny pieces together into bigger chunks, and then group those chunks together into even bigger chunks. By doing this, you start to see patterns emerge that you didn't see before when you were looking at the tiny pieces.

For example, imagine you have a bunch of atoms that make up a solid piece of metal. Each atom has its own set of properties, like how much it weighs and how much it attracts other atoms. But when you group a bunch of atoms together, you start to see new properties emerge, like how the metal conducts electricity or how strong it is. These properties can't be seen by just looking at a single atom by itself.

In physics, we use RG to study really complex systems, like how a bunch of particles interact with each other in a material, or how a bunch of stars interact with each other in a galaxy. By grouping the particles or stars together, we can start to see how the system as a whole behaves, and we can make predictions about what we expect to happen under different circumstances.

RG helps scientists simplify complex problems and find solutions that wouldn't have been possible without seeing the big picture.