Quasi-Particles - The Fundamental Particles

In empty space, it's very convenient to organize our description of what goes on in terms of different elementary particles and their interactions. For many purposes, that's an extremely useful description, especially when you're working at very small distances. When you examine a lump of silicon, that's a kind of world in itself. And the laws of what goeson inside the silicon are conveniently described also in terms of particles. But those particles are quite different from the particles that you use to construct the world models of what happens in empty space.