ELI5: Explain Like I'm 5

Quotient space (topology)

Imagine you have a very large puzzle with lots of tiny pieces. You love puzzles, but the one you have is so big that it takes up all the space in your room! To solve the problem, you decide to make a smaller version of the same puzzle that will fit on a small table in your room.

To do this, you start by grouping some of the puzzle pieces together that are next to each other and belong to the same part of the picture. You keep doing this until you have a bunch of smaller groups of pieces, all with their own unique picture on them.

Now, instead of working on the huge puzzle, you're just working on smaller puzzle pieces that fit on your table. But the smaller puzzles still have the same picture as the bigger puzzle!

In topology, we can do something similar with a mathematical object called a quotient space. Instead of a puzzle, we have a space made up of lots of points, lines, and shapes. We can group some of these together based on certain rules or connections they have, just like we grouped the puzzle pieces together.

When we group these things together, we can think of them as being part of the same "piece" of the space. We call these pieces "equivalence classes." Each equivalence class is like a mini-version of the larger space, just like the puzzle pieces were mini-versions of the larger puzzle.

The new space we get after we group things together is called the quotient space. It has all the same points and shapes and connections as the original space, but it's been "compressed" in a way. It's like we've taken the original space and folded it up so that some parts are closer together now.

Just like with the puzzle, the quotient space is smaller than the original space, but it still has the same "picture." We can study the properties of the quotient space and use it to understand the larger space better.