WMG / The Great Divorce

Heaven utilizes Hyperbolic geometry.

The Narrator says upon exiting the bus that heaven is not only larger than Hell, but that it seems to have "a larger kind of space."

Now, it turns out that such a thing does exist, right here on the mortal coil. Hyperbolic geometry is a type of non-eucidian geometry wherein space has more actual space "stuffed in" if you will, such that if you were to draw two parallel lines on the ground and then extend them indefinitely in straight lines, they would diverge.

Also, fractals: because they don't exist in an even number of dimensions, their area is finite while their outline is infinite. If this sounds way abstract and impossible except in mathematics - it actually isn't: you encounter fractal geometries in living things all the time. For example, the surface of gnarled tree bark is two point seven dimensional - meaning, if you measure a length around a tree trunk with your hand; then the way along your fingers from the tip of your thumb to the tip of your index finger is a defined length (about twenty centimeters), while going exactly along the surface of the bark down to the smallest possible level, the way is infinite and undefined. If you want to give yourself a headache: something similar is true for the surface of your brain...

• Since in real life you encounter this in living things (not artificial), this could be a way of emphasising that the place where the bus goes to appears more alive than anything else the narrator has seen up to this point.

The Great Divorce is a Foil to The Screwtape Letters

The Grey Town may well be as sentient as the Valley of the Shadow of Life and the Waterfall Angel (and obfuscating stupidity) — and it is more than demonic enough. As noted there under Face of an Angel, Mind of a Demon: What's so bad, after all, about an eternally rainy, but completely normal and bleakly ordinary, "perfectly non-sentient" megalopolis where nothing exciting (and especially not anything hellish!) ever happens — that delights in psychologically torturing its denizens so subtly that they don't even notice: getting a kick out of first the effects of the torture, then out of this profound ignorance and the ignorance of the horrible deep lasting effects, then out of getting them to help do it — and most of all out of the sick joke that someone who notices and overcomes their Self-Inflicted Hell could leave at any time, yet nearly no one ever does because Hell is just that masterful at playing this game? With a side order of "this could never happen to me" (or sometimes, Then Let Me Be Evil) for extra amusement.

• Near the end of the part where he explains his economic scheme, Ikey says that "They" will come out when the night fully falls, and that part of why the ghosts make their fake houses is for the illusion of safety. So presumably Satan and his demons are still being held at bay even in the Gray Town by the last vestiges of Divine Grace... and when the last soul makes the last choice, that vestige will be withdrawn, the twilight will turn to full night, and the demons will move in.
• All you have for that is Ikey's word, though (who might well be an Unreliable Narrator here as well as for other things that are proven to be different from Ikey's idea of them later in the book) — what MacDonald explains later about the workings of hell is quite a different story (namely, that the damned shut themselves up in the Self-Inflicted Hell of their own minds) — meaning that while the fear of demons is real, the existence of demons themselves might well be a lie, rumor, or mistaken assumption. No one in hell who knows otherwise, least of all Hell itself, would correct this mistake if it were one — the denizens all are Jerks, and Hell is a Yandere master psychological abuser — so if people want to torture themselves with the fear of "them" even though "they" don't exist... Plus, it nicely keeps them from realising their hell is entirely self-inflicted and their evil is 100% their own fault (with no devils making or tempting them) if people can blame demons for either. If they realised those two things, they could get out; so the fear of demons keeps them inside even if there are no demons and no Satan at all.

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