Science fiction is largely based on some form of science fact. I mean... wildly divergent and largely incorrect and generally criminally uninformed, but definitely based on.

[He can and will talk about Star Trek and Whovian science for hours, if you let him.]

Going by the actual content of the Network there are about three predominant theories that people have considered. That this is the afterlife, that it's a pocket dimension, or that they themselves have gone - um, crazy.