From this new point of view, the universe I had inhabited became an object I could perceive in its entirety. It was a hypersphere embedded in a cloud of alternative states—the sum of all possible quantum trajectories from the big bang to the decay of matter. Reality —history as we had known or inferred it—was only the most likely of these possible trajectories. There were countless others, real in a different sense: a vast but finite set of paths not taken, a ghostly forest of quantum alternatives, the shores of an unknown sea.

Chapter 32 (p. 327) - Vortex (2011)