Count to a Trillion — John C. Wright

Hundreds of years in the future, after the collapse of the Western world, young Menelaus Illation Montrose grows up in what was once Texas as a gunslinging duelist for hire. But Montrose is also a mathematical genius -- and a romantic who dreams of a future in which humanity rises from the ashes to take its place among the stars.

The chance to help usher in that future comes when Montrose is recruited for a manned interstellar mission to investigate an artifact of alien origin. Known as the Monument, the artifact is inscribed with data so complex, only a posthuman mind can decipher it. So Montrose does the unthinkable: he injects himself with a dangerous biochemical drug designed to boost his already formidable intellect to superhuman intelligence. It drives him mad.

Nearly two centuries later, his sanity restored, Montrose is awakened from cryo-suspension with no memory of his posthuman actions, to find Earth transformed in strange and disturbing ways, and learns that the Monument still carries a secret he must decode -- one that will define humanity's true future in the universe.