ELI5: Explain Like I'm 5

Homotopy category of chain complexes

Okay kiddo, so imagine you have a bunch of blocks, each with a letter on it. You can stack these blocks on top of each other and make words or even whole sentences!

Now, let's say that instead of blocks, we have something called "chain complexes." These are just a bunch of mathematical objects called modules stacked on top of each other, with arrows between them that tell us how they connect.

The homotopy category of chain complexes is like a special club that only lets in certain chain complexes. To get in, a chain complex has to meet certain criteria. This criteria has to do with the arrows between the modules. These arrows have to be "homotopic" to each other, which basically means they can be continuously deformed into each other without changing the overall structure of the chain complex.

Think of it like having two words that use the same letters, but in a slightly different order. If you can rearrange the letters in one word to make it match the other word, then those two words are homotopic!

The homotopy category of chain complexes is important because it helps us study these mathematical objects in a more organized way. We can group them together based on their homotopy classes and compare them to each other. This helps us understand more about their properties and how they relate to each other.

So, in short, the homotopy category of chain complexes is like a special club where chain complexes can hang out if they have arrows that can be continuously deformed into each other, and it helps us study them in a more organized way.