A typical statement of Captain Mitchell's ignorance, but with an added twist. Note that Mitchell seeks an answer to this (quite philosophical) question by going out into the sunshine, i.e., into the realm of unfiltered reality. There his answer to this (quite philosophical) question is the screaming of Hirsch, a reality of torture and agony which has already been given metaphysical significance via the metaphor of Plato's cave. Mitchell then "retreat[s]" indoors, i.e., back into the shade of his comfortable illusion, though not without "blanched cheeks."