Speak physics: What is a cross section?

Cross sections tell physicists how likely particles are to interact in a given way. Imagine two billiard balls rolling toward one another. The likelihood of a collision depends on easy-to-grasp concepts: How big are they? How precisely are they aimed? When you start talking about the likelihood of particles colliding, things get trickier. That's why physicists use the term "cross section." Unlike solid objects, elementary particles themselves behave as tiny waves of probability. And their intera...