ABSTRACT
This chapter is devoted to the problem of invariance of scattering systems with respect to time inversion. Operator T of the time inversion is introduced in such a way that its action changes the signs of the impulse and spin of all the particles of the studied system, whereas their position vectors are left unaltered. In connection with the operator T, there exists an important property, which is known as the micro-reversibility of physical processes. The relation is formally identical to the usual request for unitarity of an operator. According to the Wigner theorem, any symmetry of a quantum-mechanical system can be specified through either a unitary or anti-unitary operator in 𝓗. Let p be the collective label for the momenta of all the particles of a given quantum system and let s stands for their spin variables.
