  It is brought forward that viable theories of the physical world that have no
variable at all that can play the role of time, do not exist; some notion of
time is one of the very first ingredients a candidate theory should possess.
Almost by definition, time has an arrow. In contrast, time reversibility, or
even the possibility to run the equations of motion backwards in time, is not
at all a primary requirement. This means that the direction of the arrow of
time may well be uniquely defined in the theory, even locally. We explain these
statements in terms of the author's favoured deterministic cellular automaton
interpretation of quantum mechanics, also to be referred to as `vector space
analysis', and expand on these ideas.
