There are two main categories of subatomic particles - fermions and bosons. Fermions are the particles we think of as "stuff" - leptons like the electron, neutrino, and cousins, and quarks like the up quark and others in its sizable family. Gauge bosons are the particles that mediate the four fundamental forces of nature - the weak and strong nuclear forces, electromagnetism, and gravity. These include the familiar photon, and its far less-frequently-seen cousins, the W and Z bosons, gluons, and (physicists expect) the graviton, the much-sought-after particle thought to mediate gravitational interactions.

After the playing the game I learned: Gravitational force is stronger when an object is closer to it. The further away the planet the weaker the object.