In his "Tower of Babylon" story, Ted Chiang describes his square tower having two "intertwined" and recessed ramps, one going up, the other going down. He said that:
The upward and downward ramps wound around each other without touching, but they were joined by the corridors through the tower's body.
Can anyone explain how this is possible? The ramps are intertwined, but don't touch? If they are intertwined, don't they have to touch at the points where they intersect in a figure-8 pattern? If they are only joined by corridors linking them across the tower, then how are they intertwined? Granted, I'm a mathematically-challenged liberal-arts guy, but this doesn't seem possible. Is the tower's geometry somehow bent into a strange shape, like the fabric of the universe in the story (per the ending)? That doesn't seem to hold water, because the characters seem to view the world beneath the vault of heaven with the same geometrical perspectives and rules that we do. What, again, am I missing! Ack.