Imagine a particle. What comes to mind? If you aren’t a theoretical particle physicist, chances are you picture a tiny ball, bobbing in space. But that’s not quite correct. One way to prove it: Try to imagine that tiny ball as a particle with no mass. If a particle has no mass, how can it exist?

In this 8-minute video, Don Lincoln explains how, conceptually speaking at least, there are two kinds of mass — gravitational and inertial — and how the relationship between the two has huge consequences on our understanding of the universe.

You’ve got your pole masses, and you’ve got your MC masses. DZero recently measured the top quark’s pole mass. Read on to learn the difference.