At one point in THE GOD’S WIFE, Rebecca goes to a lecture on parallel universes. These are real constructs to physicists working in quantum string theory. Physicist Michiu Kaku writes about parallel universes in the book HYPERSPACE.
Another reason that the two women find their worlds intersect can be found in another sphere altogether—Neferet’s cosmology of magic. She believes that there are other worlds where other beings live, including the gods. She thinks that Rebecca exists on the other side of a stargate. Indeed, Rebecca’s foil, Sharif, talks about coming and going through the stargate. Maybe it’s not believable in the real world, but it’s entertaining to talk about.