Why Matter Has Mass
Introduction
In an act of brilliance that smacks of the ether, physicists have a theory that explains the matter of mass. All matter has it (mass, not ether): it resists motion and produces gravity. Yet it is similar to asking why our brains think: it makes sense (that they go together), but how do they? Modern physicists believe mass is generated by interactions with a field.
Higgs Mechanism
All empty space is filled with the Higgs field (but it is still empty....well, maybe). As a particle enters this space (actually, it never enters space, because it is always in space, but still.), the Higgs field will "cluster" around it and impede its progress. This generates the effects of mass.
Higgs Particles
A side effect of this field theory would the production of "Higgs Particles". Imagine the collision between two particles, which will produce energy. This energy can also cause the Higgs field to "cluster" and give the impression of mass were there is no particle.
Supersymmetry
Supersymmetry differs from the basic Higgs Theory is several ways, one, it requires five different Higgs particles, as well as a multitude of other yet unknown particles. Two major supports of this theory are that it unites all of the forces and stands up to high energy situations. It also has one major downfall, the amount of new particles it predicts do not make nature simpler, and those and the five Higgs particle have yet to be seen.
Technicolor
Another interesting theory as two why matter has mass is the Technicolor theory. Technicolor differs from Supersymmerty in several ways. It only has two particles, called techniparticles, or techniquarks, that are bound together by a new force called Technicolor. Technicolor does not require the multitude of new particles that Supersymmerty does. Technicolor may be simpler then Supersymmetry but it is not without flaws: the theory fails to explain why the forces unit at high energy.