We know from the last post that phones are a pain, but there's no need to elaborate on that. I think we've all recovered from that experience.
magnetic monopole theory again, and he says that it's probably not relevant. On a macro level, we all know that if you break a magnet, you don't end up with a North piece and a South piece; what you get are two smaller magnets, each with their own pair of poles. In spite of the fact that Joseph Polchinski, a prominent string-theorist, claimed that the existence of monopoles was "one of the safest bets that one can make about physics not yet seen", Frank doubts that the Door is based on that theory. He says that it's just not logical (and if Frank is anything, he's logical).
Reimann surfaces. Those surfaces appear to be fairly normal if you only look at a small section, "but the global topology can be quite different", depending on the calculations involved. The overall impression of the shapes can be a sphere or a torus or even just a couple of sheets glued together. Frank thinks that the way the Door works is to fold our normal 3-space into a shape like those through some kind of 4-space, making two points normally distant very close together. The typical example is a folded piece of paper. (Quite a few examples of this appear all over.)
We might have more about the theory behind the Door next time, as long Frank doesn't get distracted by any other bright, shiny objects.