In contrast to a phenomenon, a noumenon is not directly accessible to observation.

So, a Penrose diagram can be used as a concise illustration of spacetime regions that are accessible to observation.

However, also the hypothesis of quantum non-equilibrium big bang gives rise to quantitative predictions for nonequilibrium deviations from quantum theory which appear to be more easily accessible to observation.

He claims that functions of the mind/soul are internal, very private experiences that are not accessible to observation by others, and therefore not accessible by science (at least not yet).

All this libidinal desire and striving is directed inward toward internal objects and he lives an intense inner life often revealed in an astonishing wealth and richness of fantasy and imaginative life whenever that becomes accessible to observation.

An additional complication was that all three of these factors were themselves consequences of decisions made at some point or other in somebody's mind; exactly when, and in what manner, the results of such decisions became accessible to observation was something that was still far from clear.