something like this: An enormous technological leap occurred in the decades around 1900. This advance was fired by some mixed-up combination of abstract mathematical speculation, capitalist greed, global geopolitical power struggle, and sheer mysticism. We know (roughly) how it all turned out, but if we had been living in those years it would have been impossible to sort out the fantastical possibilities from the plausible ones. Maybe we could split time and be in two places at once, or travel backward and forward at will, or maintain parallel lives in parallel universes. It turns out (so far) that we can’t. But we did split the atom — an achievement that must once have seemed equally far-fetched. "Against the Day" is a kind of inventory of the possibilities inherent in a particular moment in the history of the imagination. It is like a work of science fiction written in 1900.