Hollow Earth Expedition?

If that was true than the force of gravity one experienced would vary noticeably depending on where on the surface of the Earth one was, which it doesn't. Another question would be, what is the crust made of? Taking a generous figure of 50km for the thickness of the Earth's crust, then if that's all there is to the Earth, the crust must have a density 236 time greater than water, and is therefore made of no known substance, and in particular not of the substances which we know the crust is made of. Well, they've shown you videos of it. That's not quite the same thing. I can show you videos of dragons ... Well, this was a good question. And if the answer had been: "We did the math, and, dammit, you're right, if the Earth was rotating we'd all be flung off into space" then we'd all be geocentrists. Heliocentrism didn't triumph because no-one asked such questions, or because heliocentrists ignored them, but because heliocentrists answered them. Meanwhile, people have also addressed good questions to people who weren't able to answer them, and who turned out to be complete idiots. This is how we sort the men from the boys. My textbook, try reading chapter 3.Edited by Dr Adequate, : No reason given.

Well all the expanding-earthers I've seen admit sea-floor spreading. So, like that. Of course, you might ask why the magma is forced up to the surface instead of floating around inside the gravity-free hollow Earth ... you'd really have to ask them that.The best thing I can thing of is that the Earth is an artificial structure a la Ringworld. Why? Well, here's an idea. Let us suppose the existence an alien race of cosmic pariahs, who for some reason (fill in your own) have powerful enemies bent on their destruction. They construct a hollow Earth as camouflage, and live on the inside. Anyone looking at it, superficially at least, would see an ordinary planet with a bunch of harmless bipedal monkeys scurrying about on the surface. Beneath it, the race of refugees hides ... the impression that S and P waves pass through the Earth is produced by their Advanced Alien Technology, which also forces magma through the mid-ocean rifts.Of course, this doesn't explain why they'd want the planet to expand, or why they'd leave holes at the poles, but maybe you can think of something.

I don't see why --- one could stretch the Earth's crust by thinning it --- material from the inside is converted into magma and pumped out at the mid-ocean ridges.

Yes, but there isn't one, that's why they don't actually expand.In sci-fi, if you want to go beyond the limits of known scientific laws, you have to add something ad hoc. The hero can travel faster than light because he has a faster-than-light drive, and can transmute matter with his matter transmuter. And if you want planets to expand, then they do so because of the force that causes planetary expansion. You can maybe think of a snappier name for this force, but you will just have to invent it, what with it not existing.Personally, the conjuring-up of such a force would irritate me as a reader in a way that FTL drives and matter transmuters don't. Is it actually necessary for your plot that scientists should find out why planets expand? Is not not sufficient for them to find out that they do? If handled right, this would be less irritating to the reader.What I mean by "handled right" is that the reader should be given absolutely no hope that the phenomenon will be explained by the end of the book, otherwise it would be even more irritating when it wasn't. But the thing is that it would also be incredibly irritating if at the end of the book there is an "explanation" and it's along the lines of "the expansion of planets is caused by a reversal in the polarity of the neutron flow". That's worse, because the readers still aren't being provided with an explanation, but you're pretending that they have been --- a pretense which they will (a) see through and (b) be insulted by.

I'm saying I can't think of a scientific principle explaining the expansion of planets. I can think of plenty of pseudoscientific principles. It's caused by higher vibrational quantum energies in the cosmic flux. There you go. That's a pseudoscientific explanation for the expansion of planets. It's also a pseudoscientific explanation for crop circles, how dowsers find water, and why crystal healing works. The only problem with it is that if you put that at the end of a sci-fi novel as your explanation for why the Earth is expanding then you will be lynched by an infuriated mob of science-fiction fans, and rightly so.

I don't think either the quantity of these things or their plausibility (based on current) is really an issue. It's a question of the role they play in the story. An FTL drive is usually absolutely fine, its capacities and limitations are laid out at the start of the story. The same with telepathy, teleportation, whatever you like: it's OK so long as the author lays his cards on the table near the beginning, and anything the technology does subsequently can be logically inferred from the premises.

No, 'cos you don't actually have any principles. No good science fiction writer explains how a matter transmuter works either, 'cos they can't, 'cos it doesn't. (And even if they could and it did, it wouldn't improve the novel to do so --- no-one's ever spent a chapter of a novel set in modern America explaining how a television or a computer works. The fact that most of the readers have no idea is not a problem.)Now any principles you came up with couldn't be hard science, they'd have to be technobabble of the reverse-the-polarity-of-the-neutron-flow type. As such, they'd be a waste of time.Therefore, I suggest that you leave the mechanism unexplained. After all, many phenomena have been discovered prior, in some cases millennia prior, to anything remotely approaching a good theoretical explanation. You can have your expanding planets thing be one of those.However, if you do that, you'll have to be very careful that the reader knows not to expect an explanation in terms either of hard science or anything you've put on the table early in the novel and therefore might serve as the basis for a legitimate explanation at the end of it. If they're expecting a good explanation, they'll feel disappointed.I couldn't really advise you further without knowing more about the plot. I feel, however, that this is the sort of thing that is going to be hard to do. Science fiction has its own uncanny valley: I can read with pleasure a balls-out space opera with FTL travel, telepathy, and teleportation, and then have conniptions over a book where someone sliding down a zip line ends up going both higher and faster than they started out.

I just talked to God. He says the Bible is rubbish. I hope you aren't afraid of his communication.