The human world is the world of language, i.e. of knowledge. To know means to formulate a hypothesis, to then be either verified or falsified. This also means that the "boundaries' of the world are not fixed but shift with the progress of knowledge. But this also entails that it is knowledge itself that produces the unknown. Prodi calls this movable field of experience, shifting along with the process of knowledge, "darkness" [buio]. The problem of "darkness' is the problem of the internal limits of language. Such "darkness", indeed, is by definition unrecognizable, since it is an inevitable collateral effect of knowledge. There is no science of "darkness", but this does not mean that it cannot be thinkable via other means. Aesthetic experience and the experience of the sacred are non-scientific ways to "think" the "darkness".