ELI5: Explain Like I'm 5

Purification theorem (physics)

Imagine you have a bunch of toy blocks that are all different shapes, colors, and sizes. You want to organize them into separate groups of blocks that are all the same shape, color, and size. This is kind of like what the purification theorem in physics does, but with atoms and electrons instead of toy blocks.

In physics, everything is made up of atoms, which are like tiny building blocks. Atoms have a bunch of different parts, including electrons, which are like little particles that orbit around the atom's nucleus, kind of like a planet orbiting around a star.

The purification theorem says that if you have an atom in a certain state, you can use a process called purification to make sure it's in the same state every time you measure it. It's kind of like sorting your toy blocks – you want to make sure that all the blue blocks are in one group, all the red blocks are in another group, and so on.

The way purification works is by measuring the atom's state and then using that measurement to "filter" out any unwanted states. It's like using a strainer to separate the noodles from the water when you're cooking spaghetti – you want to keep the noodles and get rid of the water.

So, let's say you have an atom that can be in one of two states – let's call them A and B. When you measure the atom's state, you might find that it's sometimes in state A and sometimes in state B. But if you use the purification theorem, you can "filter out" the unwanted state every time you measure the atom.

This is really important in physics because it means that you can control the state of atoms and electrons very precisely. It's kind of like having a bunch of toy blocks that are all exactly the same color, shape, and size – it makes it easier to study them and figure out how they work.

So, the purification theorem is like a process for making sure that atoms and electrons are in a specific state every time you measure them. This helps physicists study these tiny building blocks more carefully and understand how they work together to make everything in the universe.