In Depth Quantum Mechanics

In Quantum mechanics, an energy level is said to be degenerate if it corresponds to two or more different measurable states of a quantum system. Conversely, two or more different states of a Quantum mechanical system are said to be degenerate if they give the same value of energy upon measurement. The exchange interaction is a Quantum mechanical effect between identical particles. (Actually, one should better speak only of the exchange energy, or the exchange term, to avoid the incorrect idea that this effect corresponds to a classical force or potential.) In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interacts and is the first theory where full agreement between Quantum mechanics and special relativity is achieved. Recently, it has been discovered that a quantum particle is described by a non-conventional wave packet which, instead of the Hamiltonian includes the Lagrangian in the time dependent phase of the wave functions. Adopting a quantum relativistic principle which asserts that the time dependent phase of a quantum particle is invariant for an arbitrary exchange of coordinates, the relativistic mechanics of the particle and the electrodynamics of a field interacting with this particle are obtained.