What might have been and what has been
Point to one end, which is always present.
Footfalls echo in the memory
Down the passage which we did not take
Towards the door we never opened.
—T. S. Eliot, "Burnt Norton"
What's up with the epigraph?
This one works on two levels.
First, T. S. Eliot is talking about the past, which just so happens to be the same thing the book is about. What a coincidence, huh? When Eliot brings up "what might have been" and "the passage we did not take," he's expressing the same sense of regret that Jason feels when he thinks about his past as a research scientist or Daniela thinks about when she thinks about her art career.
Second, the imagery used in the poem also gels nicely with the novel's depiction of the box. There are doors, passages, and echoes—oh my. While the poem's reflection on the nature of regret is probably the main reason it's used here, the fact that it works so well with Dark Matter's multidimensional imagery is just a cherry on top.