We know that our non-relativistic Quantum Mechanics only needed a two component spinor. We can show that, in the non-relativistic limit, two components of the Dirac spinor are large and two are quite small. To do this, we go back to the equations written in terms of and , just prior to the introduction of the matrices. We make the substitution to put the couplings to the electromagnetic field into the Hamiltonian.

- The Two Component Dirac Equation
- The Large and Small Components of the Dirac Wavefunction
- The Non-Relativistic Equation

Jim Branson 2013-04-22