>>14235628If you think of waves, you can break up a wave into fourier modes each with a well defined wavelength and amplitude. In quantum field theory the wavelength becomes the momentum and the amplitude becomes the particle number (roughly speaking). For a fermion field, oscillations can also be split up into different modes, but the amplitude doesn't work classically. It is like an on-off switch, either the mode is active or it is not. A fermion particle corresponds to an active mode, and you can only have one for each mode (given the on-off nature of the field).
