 One proposal is to say that if we came across reversed cases of de facto irreversible processes, such as running a film backwards in which the cream converged in a coffee cup, such cases should be interpreted as examples of backward causation (Price 1996). Such a claim build on a common interpretation of time reversal invariance of processes according to which this descriptive feature of the dynamical equations of physics makes reversal processes symmetric in time. Many philosophers have defended such an interpretation, in particular Hans Reichenbach (1956, 1929 [1958]) and Adolf Grünbaum (1963). This also led them to argued that only de facto irreversible processes, such as those described by statistical thermodynamics, could be used to defined a physical orientation of time. Thus, it seems to be the case that the actual world consisting of mostly de facto irreversible processes on the macroscopic level due to a prevalent set of boundary conditions is temporally and causally symmetric on the microscopic level. On the macroscopic level, de facto irreversible processes emerge, because the boundary conditions are a result of the huge degree of freedom among microprocesses or coherence conditions forced upon the underlying microscopic processes.