The differences between basic QM and Field Theory are these: in QM, the interactions between more than two particles are increasingly difficult to model, and the creation and destruction of particles cannot be modeled at all. In contrast, Field Theory can describe states containing arbitrary numbers of particles of different energies, masses, charges and types. Field Theory also provides an elegant framework for describing the interactions between particles, and the creation of new particles and destruction of old ones-- for example, the emission and absorption of photons by electrons, and vice versa<ref>Bjorken and Drell. <i>Quantum Field Theory</i> Chapter 3; McGraw Hill Inc. (1980)</ref>. | The differences between basic QM and Field Theory are these: in QM, the interactions between more than two particles are increasingly difficult to model, and the creation and destruction of particles cannot be modeled at all. In contrast, Field Theory can describe states containing arbitrary numbers of particles of different energies, masses, charges and types. Field Theory also provides an elegant framework for describing the interactions between particles, and the creation of new particles and destruction of old ones-- for example, the emission and absorption of photons by electrons, and vice versa<ref>Bjorken and Drell. <i>Quantum Field Theory</i> Chapter 3; McGraw Hill Inc. (1980)</ref>. |