Time-asymmetric quantum physics

A quantum theory that applies to the (closed) universe needs to be time asy mmetric because of the cosmological arrow of time. The preparation double r ight arrow registration arrow of time (a state must be prepared before an o bservable can be detected in it) of the quantum mechanics of measured syste ms provides a phenomenological reason for an asymmetric semigroup time evol ution. The standard theory in the Hilbert space (HS) is inadequate for eith er since the mathematics of the HS allows only reversible unitary group evo lution and time symmetric boundary conditions. The mathematical theory that describes time-asymmetric quantum physics in addition to providing the mat hematics for the Dirac kets is the rigged Hilbert space (RHS) theory. It us es a pair of RHS's of Hardy class with complementary analyticity property, one for the prepared states (''in states") and the other for the registered observables ("out states"). The RHS's contain Gamow kets which have all th e properties needed to represent decaying states and resonances. Gamow kets have only asymmetric time evolution. The neutral kaon system is used to sh ow that quasistationary microphysical systems can be experimentally isolate d if their time of preparation can be accurately identified. The theoretica l predictions for a Gamow ket have the same features as the observed decay probabilities, including the time ordering. This time ordering is the same as the time ordering in the probabilities of histories for the quantum univ erse. The fundamental quantum mechanical arrow of time represented by the s emigroup in the RHS is therefore the same as the cosmological arrow of time , assuming that the universe can be considered a closed quantum system. [S1 050-2947(99)08608-4].