ELI5: Explain Like I'm 5

Eilenberg–Moore spectral sequence

The Eilenberg-Moore spectral sequence is a way to understand how different parts of a complicated mathematical object (called a "fiber bundle") fit together.

Imagine you have a bunch of toy blocks that can be stacked on top of each other to make a castle. Each block represents a part of the castle, like a tower or a wall. But sometimes the order you stack the blocks matters - maybe one block needs to be at the bottom to hold everything else up!

The Eilenberg-Moore spectral sequence helps us understand the order of the blocks in a fiber bundle. Here, the "blocks" are mathematical objects called "sheaves", which describe how a space varies over different scales. A "fiber bundle" is a way of stacking these sheaves on top of each other, so that they fit together in the right way.

The spectral sequence works by breaking down the fiber bundle into smaller pieces, kind of like taking apart the castle into individual blocks. Then, it looks at how each piece fits together with the others, and uses that information to build up a bigger picture of the object as a whole.

It's like building the castle by starting with one tower, and then slowly adding on other pieces one by one, checking each time to make sure they fit and support each other. By the end, you have a full castle - or, in the case of the spectral sequence, a full understanding of how the fiber bundle is put together.