For every particle of matter that’s known to exist in the Universe, there’s an antimatter counterpart. Antimatter has many of the same properties as normal matter, including the types of interaction it undergoes, its mass, the magnitude of its electric charge, and so on. But there are a few fundamental differences as well. Yet two things are certain about matter-antimatter interactions: if you collide a matter particle with an antimatter counterpart, they both immediately annihilate away to pure energy, and if you undergo any interaction in the Universe that creates a matter particle, you must also create its antimatter counterpart. So what makes antimatter so “anti,” anyway?