ELI5: Explain Like I'm 5

Jordan–Schwinger transformation

The Jordan-Schwinger transformation is a fancy name for a math trick that helps us understand and work with certain types of physical systems in quantum mechanics. Think of it like a magic spell that turns one type of object into another type that's easier to study.

Let's start with a fun game: imagine you have a toy car and you want to turn it into a toy plane. You can't just wish it into being a plane, but you could use your imagination to pretend that the car is actually a plane. You might hold it up in the air and make engine noises, or draw wings on the sides with a pencil.

This is kind of what the Jordan-Schwinger transformation does: it takes one type of quantum mechanical system (let's call it a "spin" system) and turns it into another type (let's call it an "angular momentum" system). It does this by using a set of special math equations that relate the two systems in a way that makes it easier to reason about them.

So, what's a "spin" system? Well, imagine you have a tiny particle, like an electron, that can spin around its own axis. This spin is a quantum mechanical property that can have certain values (like 1/2 or 1) and affects how the particle interacts with other particles and with electromagnetic fields.

Now, what's an "angular momentum" system? This is a kind of physical property that describes how objects move and spin around a central point, like the Earth orbiting the Sun. It's related to spin, but it's a little different.

The magic of the Jordan-Schwinger transformation is that it allows us to see how these two different systems are connected. It uses a set of mathematical equations that relate the spin of a particle to its angular momentum, so that we can study both properties at the same time. This is really useful because in some situations, like when we're trying to understand the behavior of a magnetic field, it's important to know both the particle's spin and its angular momentum.

So, in short, the Jordan-Schwinger transformation is a math trick that helps us turn spin systems into angular momentum systems (or vice versa) so that we can understand them better. Just like pretending a car is a plane, the transformation lets us imagine systems in a different way that makes them easier to study.