Subtracting one from two times the Pauli exchange operator gives this man's namesake spin operator. In formulating the Hamiltonian of a system of photons, this man posited the existence of a zero-state from which photons could be emitted or absorbed, and calculated the probability of emission or absorption in a given state as proportional to the number of photons already present. This man used Clifford algebra elements to construct a first-order 
Subtracting one from two times the Pauli exchange operator gives this man's namesake spin operator. In formulating the Hamiltonian of a system of photons, this man posited the existence of a zero-state from which photons could be emitted or absorbed, and calculated the probability of emission or absorption in a given state as proportional to the number of photons already present. This man used Clifford algebra elements to construct a first-order and relativistically invariant wave equation. That equation led this man to posit a system of particles with negative energies whose holes were the then-undiscovered positrons, this scientist's namesake "sea." The developer of "bra-ket" notation, for 10 points, name this scientist whose eponymous delta function takes the value infinity at zero and zero everywhere else.
Subtracting one from two times the Pauli exchange operator gives this man's namesake spin operator.
Paul Dirac