  Arno Bohm and Ilya Prigogine's Brussels-Austin Group have been working on the
quantum mechanical arrow of time and irreversibility in rigged Hilbert space
quantum mechanics. A crucial notion in Bohm's approach is the so-called
preparation/registration arrow. An analysis of this arrow and its role in
Bohm's theory of scattering is given. Similarly, the Brussels-Austin Group uses
an excitation/de-excitation arrow for ordering events, which is also analyzed.
The relationship between the two approaches is initially discussed focusing on
their semi-group operators and time arrows. Finally a possible realist
interpretation of the rigged Hilbert space formulation of quantum mechanics is
considered.
