Abstract (eng)
The method of projection operators in statistical mechanics describes the separation of equations of motions for properties of interest in a relevant and a fluctuating part, where the fluctuating part consists of constituents which are individually not important. With these techniques,
it is possible to derive generalised Langevin equations or generalised Fokker-Planck equations,
which extend and motivate known phenomenological equations.
In this thesis, we describe the concept of projection operators in statistical mechanics,
review four specific choices of them and show that Grabert’s formalism (Grabert (1982)) is a
generalisation of the others. Examples are given and relationships to the method of partially
solving the equations of motion as described in Zwanzig (1973) are pointed out.