So I learned about the Dirac equation which describes a relativistic free particle with spin $\frac{1}{2}$. I get the mathematics but what i can't find nowhere:
What are the observables of this theory?
Surely since the aim is to describe a relativistic particle there has to be some form of obtaining the probability of finding the particle in some region. Similarily, how can one obtain the momentum (or rather its probability distribution) given that the particle is in a fixed state described by some spinor satisfying the Dirac equation?