ELI5: Explain Like I'm 5

Homological dimension

Homological dimension is a fancy term used in mathematics to talk about how complicated things can get. It's like trying to measure how many steps you need to take to go from one place to another.

Imagine you have a group of friends that are all holding hands and standing in a line. Each friend has their own special place where they stay. This line of friends is called a chain. The chain can be long or short, depending on how many friends there are.

Now, let's say you have a friend who can't let go of the hand of the person next to them. This friend is called a prisoner and they can't move. So, the chain can't move either because the prisoner is holding their neighbor's hand.

If you want to measure how complicated this chain is, you can count how many friends can move freely without being held back by the prisoner. This is called the homological dimension of the chain.

The homological dimension tells you how many steps you need to take to free all the friends in the chain. If the homological dimension is low, it means there are only a few steps needed to break free. But if the homological dimension is high, it means there are a lot of steps required to free all the friends.

In math, we don't just talk about friends and chains, instead, we use more complicated objects called modules. These modules are like puzzles that need to be solved. The homological dimension of a module tells us how many steps it takes to solve the puzzle and understand everything about it.

So, in short, homological dimension is a way to measure how complicated things can be and how many steps it takes to understand or solve them.