Two Science/Astronomy questions

[Ravana]

Our principal problem is that subtended angle (=size, for this argument) drops off as the square of the distance, as does gravitational pull. So size and tides go together for a particular density of moon.

Keeping in mind that, as mentioned, volume is a cube, mass is derived from volume times density, and gravity is derived from mass… so the effect of gravity drops off far more rapidly than apparent size does as you reduce the actual size of the object. But other than that, yeah, I'm with ya here.

bigger than Cherryh's 'stations'

Ah, someone else who reads Cherryh–yay! Some of the best "hard" SF out there… and not at all "hard" to read. In fact, you can easily forget all about the hard science as you're caught up in the compelling characters she liberally populates her worlds with. Can't recommend her highly enough, though this might give a hint: she's one of only four authors out there whose works I buy in hardback as they come out.

Add a dimension, in which gravity propagates [etc.]

Meh… more trouble than is worth it, unless you really want an "impossible" system–say, several equally-large bodies occupying close orbits. At which point, you might as well just do it by fiat and ignore the reason, unless that reason itself is an important part of your story.

I would add, however, that while we know what gravity does, and can make reliable calculations of its effects in terms of orbits and such, we have no idea how it does what it does–nor why. That's right: as far as scientific explanation goes, it's still "magic." Oh, no scientist would say that: we know it's linked to mass somehow, and we can predict its effects to a very fine degree; we just don't have an account of why mass produces gravity in the first place. So, yeah, if you want to muck around with something, gravity's a great candidate.

I would also insert a plug for David Brin's The Practice Effect, where a character finds himself in an alternate universe where all the physical laws we know are the same… with one important exception. You might be able to guess from the title, but I won't otherwise spoil it. Read the book.

[Brin is another of the four authors I buy in hardback, by the way.]

Go to a proper fantasy universe where the Earth is flat, the stars are mounted on a crystal bowl, an down just is; no need for gravity or any of these new fangled forces.

I've done a variant on this: my nearly-flat world (it's very slightly lenticular) has a special bi-directional gravity. On the faces, gravity pulls you "down" (in this case, where your feet are pointed, not toward the center of mass); on the edges, it's reversed–it pushes outward. No one knows why. Not even the gods. The combined pull/push creates a net effect on the orbits of the celestial bodies surrounding it equivalent to what would be expected from a spherical body with normal gravity, i.e. those bodies are all in stable orbits around the world's center of mass. (Which is also where any resemblance to a real system ends–the sun, stars and other planets all differ significantly from reality–but that's beside the point.)

Who needs orbital dynamics?

Heh. But, yeah, basically what I was suggesting: unless you're really going to get "hard science" about the dynamics, or unless they're going to play a prominent part in your story, the math ain't worth it: just do what you feel like doing. I sometimes go to the trouble, but only when the physics does play an important role in the story… which, in fantasy, is going to be fairly seldom.

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Yay! Thank you so much, Ravana! This is a huge help!

Quite welcome. Glad to be of help.

 

[Steerpike]

An Aside RE: Cherryh - I've always been a fan of her Chanur books, which are a lot of fun. I'm about 1/4 of the way into Cyteen right now, which is quite good. I am confident in recommending her work to anyone.

 

[Ravana]

An Aside RE: Cherryh - I've always been a fan of her Chanur books, which are a lot of fun. I'm about 1/4 of the way into Cyteen right now, which is quite good. I am confident in recommending her work to anyone.

And that makes two votes.

As with Steerpike, I'd recommend the Chanur and Alliance/Union series to anybody. For anyone looking for an entry into the latter, Downbelow Station is the best choice, though nearly all of them can be read independently of one another and in any order, the exception being Regenesis, which is a sequel to Cyteen (be sure to pick it up, Steerpike), and to a lesser extent Hellburner, which follows the same characters from Heavy Time, though you can read the former without having read the latter. The Chanur series should ideally be read in order, particularly since the middle three books are a genuine trilogy; the trilogy can be read without the first one, and the most recent could be read without the ones which come before it, but you'd lose a fair amount of context.

I've found some of her other work less appealing, but there's only one book of hers that truly disappointed me. In general, I'd have to say her SF is better than her fantasy, but I have few quibbles even with the latter, whereas the former would, I think, interest even people who do not read SF on a regular basis. As mentioned, a lot of it has to do with her characterizations: she's a great author to learn from and emulate in that aspect.