(P van Dokkum/NASA/ESA via AP) One of the most subtle threats to any civilization is a decline in its ability to approach the unknown. The undiscovered is as important as the known. If the knowns are compiled in an encyclopedia, the compendium of things “we don’t know about” has been called by some the reversopedia. Vital as it is, how one may reasonably ask, is whether it’s possible to a map of the terra incognita? The lists of unsolved problems that every field of inquiry– astronomy, biology, chemistry, computer science, physics, etc.– seems to throw up continuously, allows us to trace the boundaries of ignorance. Mathematics, for example, generates questions in each branch (i.e. algebra, analysis, game theory, topology) for which no one yet knows the answer. Indeed, the process of inquiry seems to create more questions for each one it answers. It seems impossible to expand the encyclopedia without simultaneously enlarging the reversopedia.