 In classical physics, mass is a measure of the inertia of a body. The mass of an object causes it to resist a change in its speed or direction. The greater the mass, the greater the resistance. This is codified as force equals mass times acceleration. In quantum field theory, on the other hand, the energy of a quantum is represented by oscillations in its field. Since both mass and energy are associated with oscillations in the particle field, we can simply combine Einstein's equation for mass energy and Planck's equation for wave energy to calculate the mass of a wave. The faster a particle is oscillating, the harder it is to change its direction or speed. So this fits our common understanding of mass. Paul Dirac identified the oscillation of a particle between its right-handed incarnations and its left-handed incarnations as a mechanism for fermion mass. The faster the oscillations, the more energetic the particle, the more massive it is. It might seem strange, a particle changing its spin on the fly, but if you recall that particles travel as waves and spin can be viewed as a phase shift in the wave, it's not too hard to visualize. We'll use electrons as an example. A left-handed spinning electron has a spin one-half and carries a weak hypercharge. A right-handed spinning electron has a spin of minus one-half and carries no weak hypercharge. So for an electron to switch from left to right, it must emit a quantum of weak charge and lose a full unit of spin. And for it to switch back, it must absorb a quantum of weak charge and gain a full unit of spin. Now here we had a very large problem for particle physics. It was understood that a derivative of the Zebo-San was a candidate for the electron spin and charge transition, but there was no standard model mechanism for ejecting and absorbing weak hypercharge out of the blue. Where did it come from and where did the charge go?