A shattered world fantasy setting with as much hard science as I can--

[SMJB]

--squeeze into it.

Right, I've got all these shards of a shattered terrestrial planet that are encased in magic that allows them to hold atmosphere and have artificial gravity. The magic doesn't change it's gravity outside the limits of the spell, though, so the shards will interact with other celestial objects as if they were asteroids, not as if they had earthlike gravity. These shards are orbiting a Jovian world rather closely.

Right, the the most prominent thing in my mind that I'm wondering about is the relevant numbers of using gunpowder as rocket fuel. The rockets dock at towers sticking out of the shards' atmospheres (atmosphere and artificial gravity both suddenly stop at a certain height) and the distances are short in astronomical terms, so it should be at least somewhat feasible. Also, what sort of CO2 scrubbers could a relatively primitive civilization come up with?

I also have a backstory I want to float:

Once upon a time, there was a terrestrial world with a high-magitek civilization, but it shared a system with a highly unstable Jovian planet. As the seismic disturbances from its flybys got worse, it was determined that the Jovian planet was ultimately going to throw the terrestrial planet out of the system. A desperate plan was hatched. Rather than try to save their world, they would destroy it. The great sundering happened, the shards of the world began orbiting the Jovian, and by controlling the orbits they were able to stabilize the Jovian's orbit. But all the magic was being used to fuel this great spell, so civilization fell. A new civilization rose among the shards.

And, of course, any other ideas you might have in regard to this 'verse are welcome.

 

[Simon Bridge]

--squeeze into it.

Right, I've got all these shards of a shattered terrestrial planet that are encased in magic that allows them to hold atmosphere and have artificial gravity. The magic doesn't change it's gravity outside the limits of the spell, though, so the shards will interact with other celestial objects as if they were asteroids, not as if they had earthlike gravity. These shards are orbiting a Jovian world rather closely.

So start by throwing out the rulebook?
But OK - these magic bubbles are the "one-time-only exception to the rules": what are the consequences?

Right, the the most prominent thing in my mind that I'm wondering about is the relevant numbers of using gunpowder as rocket fuel. The rockets dock at towers sticking out of the shards' atmospheres (atmosphere and artificial gravity both suddenly stop at a certain height) and the distances are short in astronomical terms, so it should be at least somewhat feasible. Also, what sort of CO2 scrubbers could a relatively primitive civilization come up with?

How primitive?
Look up how scrubbers work to get an idea of what is available to your denizens.
http://en.wikipedia.org/wiki/Carbon_dioxide_scrubber

Some other considerations: climbing out of the bubble would require considerable effort as the gravitational potential energy changes abruptly at the boundary. It would take the same amount of energy to escape the surface of the bubble as it would to escape to Jupiter orbit from the surface of the Earth (without any slingshot or rotational boosting). If you were thinking your astronauts would just climb a latter, it would feel like they hit their heads on a cieling.

To make spaceflight common without adding to your burden of impossibilities you should consider reducing the strength of gravity and letting it taper off. Although, you may be able to construct a space elevator of sorts if you can arrange for a falling mass to pass through the bubble at the same time that a rising mass needs to. Still the head-cieling effect to think of.

 

[SMJB]

So start by throwing out the rulebook?
But OK - these magic bubbles are the "one-time-only exception to the rules": what are the consequences?

In another of my universes I have wizards and werewolves battling on a space station in a hollowed-out asteroid.

Still harder than Star Trek, though. :P

How primitive?
Look up how scrubbers work to get an idea of what is available to your denizens.
http://en.wikipedia.org/wiki/Carbon_dioxide_scrubber

I can't believe I didn't think to check the Wikipedia page. I guess I'm just used to Google failing to turn up relevant answers to my esoteric demands.

I suppose the quicklime would work, considering that it was apparently being produced back in the days when alchemy was considered to be a legitimate science.

Some other considerations: climbing out of the bubble would require considerable effort as the gravitational potential energy changes abruptly at the boundary. It would take the same amount of energy to escape the surface of the bubble as it would to escape to Jupiter orbit from the surface of the Earth (without any slingshot or rotational boosting). If you were thinking your astronauts would just climb a latter, it would feel like they hit their heads on a cieling.

...but they would survive the experience, right?

To make spaceflight common without adding to your burden of impossibilities you should consider reducing the strength of gravity and letting it taper off. Although, you may be able to construct a space elevator of sorts if you can arrange for a falling mass to pass through the bubble at the same time that a rising mass needs to. Still the head-cieling effect to think of.

What concerns me more than adding to the impossibility is that the primordial civilization would never have done something specifically to mitigate such an effect because it would never have occurred to them that space travel was possible in the first place. *sigh*

 

[Simon Bridge]

I suppose the quicklime would work, considering that it was apparently being produced back in the days when alchemy was considered to be a legitimate science...

That would be Newton's time then?
They could also use activated carbon - that has been in use for thousands of years.
The combination makes a nice scrubber that can be cleaned.

...but they would survive the experience, right?

Depends on how hard the hit their head. Wearing a helmet wouldn't help either.

Imagine that through some effort, someone was able to slowly force their arm through the bubble ... then would their heart be able to produce enough energy to pump blood through the barrier? If it is a 1g difference either side, then the blood in their arteries would basically need to be going at escape velocity for the surface of the Earth. Is that reasonable?
rough average speed of blood in an artery 1m/s (from ultrasound doppler)
escape velocity needed, about 11km/s

Probably just as well they didn't stick their head through then huh?
Suggests you want about 0.0001g inside the bubble, with appropriate modifications - the population would be quite weak compared with Earth norm for eg. Research the effects of low gravity and factor in some evolution? You probably don't want to go that far.

Note: didn't consider what happens to the returning blood ;)

But let's say that the same magic that makes the bubble also makes transitions to and from the bubble easy ... this is how Ender Wiggan could get in and out of the game room right?
Would it be possible to exploit the gravity difference each side of the bubble to make a perpetual motion machine? How do you imagine gravity inside the bubble working?

Maybe every time something goes out of the bubble, it takes energy from the bubble, weakening it slightly. But each time something goes in through the bubble, it gives energy to the bubble. Make the process lossy and frequent space-travel results in a gradual weakening of the bubble over time (a possible plot device) ... and it also let's you have cool light effects (where the energy goes) when someone sticks their arm through.

What concerns me more than adding to the impossibility is that the primordial civilization would never have done something specifically to mitigate such an effect because it would never have occurred to them that space travel was possible in the first place. *sigh*

Quite early civilizations considered travel to the Moon, and other planets too, as well as stories of people traveling to touch the sky. In your story, the other shards would likely be visible to the naked eye - certainly the gas giant and any other satellites would be. This would have quite an impact on the local culture.

You need someone to have tried the Tower of Babel thing and succeed in reaching the "sky" (the bubble barrier - where the going gets tough). The first people to try pushing through would report whatever effects you decide are present.

You can work out how hard it is to get through by considering how high the equivalent climb is from the Earth's surface. That climb has to happen in how ever thick the bubble is.

The main rules you want to watch for are the physical conservation laws.

 

[SMJB]

That would be Newton's time then?
They could also use activated carbon - that has been in use for thousands of years.
The combination makes a nice scrubber that can be cleaned.

Nice. I'm thinking maybe Victorian, actually, but I want this world to have a history, so really...

Depends on how hard the hit their head. Wearing a helmet wouldn't help either.

Imagine that through some effort, someone was able to slowly force their arm through the bubble ... then would their heart be able to produce enough energy to pump blood through the barrier? If it is a 1g difference either side, then the blood in their arteries would basically need to be going at escape velocity for the surface of the Earth. Is that reasonable?
rough average speed of blood in an artery 1m/s (from ultrasound doppler)
escape velocity needed, about 11km/s

Probably just as well they didn't stick their head through then huh?
Suggests you want about 0.0001g inside the bubble, with appropriate modifications - the population would be quite weak compared with Earth norm for eg. Research the effects of low gravity and factor in some evolution? You probably don't want to go that far.

Note: didn't consider what happens to the returning blood ;)

Okay, I think I get it: this is a conservation of momentum thing, right? As in, "an object is being pulled down at 1 g inside the bubble, isn't when it's outside, so where did that force go?"

But let's say that the same magic that makes the bubble also makes transitions to and from the bubble easy ... this is how Ender Wiggan could get in and out of the game room right?
Would it be possible to exploit the gravity difference each side of the bubble to make a perpetual motion machine? How do you imagine gravity inside the bubble working?

IDK, how does artificial gravity ever work? If anyone's ever bothered to explain it before, this is the first I'm hearing of it.

Maybe every time something goes out of the bubble, it takes energy from the bubble, weakening it slightly. But each time something goes in through the bubble, it gives energy to the bubble. Make the process lossy and frequent space-travel results in a gradual weakening of the bubble over time (a possible plot device) ... and it also let's you have cool light effects (where the energy goes) when someone sticks their arm through.

Well, I can't exactly imagine that the process would be gainy. Conservation of energy is one of those things I'm never going to let fall by the wayside in any of my universes--it may not always be apparent where the energy is coming from, but it's always coming from somewhere.

(That gives me an idea--a magic society having to deal with waste heat...)

Quite early civilizations considered travel to the Moon, and other planets too, as well as stories of people traveling to touch the sky. In your story, the other shards would likely be visible to the naked eye - certainly the gas giant and any other satellites would be. This would have quite an impact on the local culture.

Yeah, but that's all after the sundering. Before it wasn't a primitive world, it was a world with a developed but alien science that didn't include Newton's third law.

Which, come to think of it, is pretty messed up. I mean, firstly, they obviously have to have a fairly sophisticated understanding of how gravity works to be able to produce artificial gravity--or indeed for their plan to work at all--so someone obviously produced at least a part of his work in their world. My justification for them not having come up with the third law is them going everywhere on magic carpets which are reactionless drives, but I suddenly remember that reactionless drives are as big a violation of relativity as FTL. (Wait, is artificial gravity? I hadn't heard that, but it would make sense. If it is, I might as well continue ignoring the rest of it.)

You need someone to have tried the Tower of Babel thing and succeed in reaching the "sky" (the bubble barrier - where the going gets tough). The first people to try pushing through would report whatever effects you decide are present.

Nice.

You can work out how hard it is to get through by considering how high the equivalent climb is from the Earth's surface. That climb has to happen in how ever thick the bubble is.

The main rules you want to watch for are the physical conservation laws.

The climb out of the gravity well on Earth, right? Dammit, that was what I was trying to avoid...

 

[Simon Bridge]

Okay, I think I get it: this is a conservation of momentum thing, right?

Just conservation of energy - the PE of an object inside the boundary would be like at the surface of the Earth while outside the boundary it would be like orbit of Europa or something?
If the difference in PE were not all that great and only the direction of the gradient (force) changed, then you wouldn't have as big-a problem.

Conservation of momentum would be another complication again.

IDK, how does artificial gravity ever work?

The usual real-world solution is rotational gravity. The complications there are all about momentum ... I think John Varley does a good job of it (for fiction) in the Gaea trilogy - though he fudges a lot because Gaea is very big.

If anyone's ever bothered to explain it before, this is the first I'm hearing of it.

What I mean by how gravity works inside the bubble is not so much what the physical principles behind it are but what happens if you drop something at different places. i.e. the grav plates in Traveller define the direction of "down" as "towards them".

Is the gravity inside the bubble radial - always pointing to the center?
Maybe the bubble has an up and down oriented so a large flat part of the shard is "the ground" but you can climb over the edge? Either way, gravity won't be perpendicular to the surface of the shard everywhere.

Gravity could always point perpendicularly to the surface of the shard - which would make climbing mountains easy.

See what I mean?

Conservation of energy is one of those things I'm never going to let fall by the wayside in any of my universes--it may not always be apparent where the energy is coming from, but it's always coming from somewhere.

Working out where the energy comes from produced that extra something that can flavor a story-world. Like:

(That gives me an idea--a magic society having to deal with waste heat...)

... and other basic fallout. Magic traditionally involves a fair amount of wasted energy, in the form of colored lights and noise. Industrial scale use of magic would have pollution just like regular industry.

Larry Niven had a good riff on magic as a limit resource in his "Magic Goes Away" world.

Yeah, but that's all after the sundering. Before it wasn't a primitive world, it was a world with a developed but alien science that didn't include Newton's third law.

Um ... Newton's 3rd law gets you the conservation laws. You mean they don't know about it? They'd have a hard time working with everyday stuff like how the ground presses up as hard as you press down.

Which, come to think of it, is pretty messed up. I mean, firstly, they obviously have to have a fairly sophisticated understanding of how gravity works...

You have a precursor civilization with technology so wondrous it is basically magic - people growing up in the leftovers have a hard time developing any real physics. The challenge is to show this without actually breaking too much real physics... which is what most people end up doing sometime.

I suddenly remember that reactionless drives are as big a violation of relativity as FTL.

I don't think they get you causality violations, but they do get you closed-mill perpetual motion. You can conserve energy in the sense that you cannot get more kinetic energy than some store of energy, but where does the change in momentum come from?

But let's say the momentum gained in the vehicle is lost in some giant momentum battery?
It would something moving about - perhaps in an underground vault everyone has forgotten about?

Wait, is artificial gravity? I hadn't heard that, but it would make sense. If it is, I might as well continue ignoring the rest of it.

Nice.The climb out of the gravity well on Earth, right? Dammit, that was what I was trying to avoid...

You can't have that and Earth normal gravity inside the bubble.

I think the bubble giving and receiving energy solves that problem nicely enough for SF though.
Further, if the gravity is uniform up/down, then nobody has to climb a tower or anything: just build a ladder or, if the ground extends to the bubble: just walk.

Anything moving into/through the bubble (make it say 10m thick, or so) makes pretty lights around it like a corona discharge. Anything sufficiently inside gets sucked through to the other side ... if that is outside, they go tumbling off into space... so attach a rope.

 

[SMJB]

Okay, coronal discharge it is, then, though I have no idea how to even calculate how much light such a thing is giving off.

I'm thinking gravity is perpendicular to the surface of the shard, though I'm open to suggestions.

One more quirk I haven't mentioned is that I'm thinking that shards' atmospheres occasionally touch. I mean, we get a lot of our oxygen from the ocean, which there won't be much of on the shards where people live and such.

 

[Simon Bridge]

Okay, coronal discharge it is, then, though I have no idea how to even calculate how much light such a thing is giving off.

Why would you need to?

I'm thinking gravity is perpendicular to the surface of the shard, though I'm open to suggestions.

So consider someone piled up stone to make a pyramid - would they be able to walk up the sides like they were flat? What about up the sides of a cliff?
Or is each shard perfectly round?

Or do you mean that one surface of the shard is "the ground" and gravity is perpendicular to that?

One more quirk I haven't mentioned is that I'm thinking that shards' atmospheres occasionally touch. I mean, we get a lot of our oxygen from the ocean, which there won't be much of on the shards where people live and such.

I don't see how one follows from the other - but for the atmospheres to touch their bubbles must overlap ... which would give the possibility to climb from one shard to another without having to deal with all that stuff I talked about.

The inhabitants would think of the bubble surfaces as these weird not-crystal spheres that can open up occasionally. Nobody would ever get outside ... but there would be occasional, some periodic, contact with other worlds that way. They may try to use steerable hot air balloons to try to get through during the contact?

Some bubbles may not have a shard in them - just air, or just water.
You have quite a lot of scope there.

The main thing to think about now is what role the weird physics will have in the story.

 

[SMJB]

Why would you need to?

Well, it makes a difference if we're talking about "bright" vs. "blinding" vs. "I burned my retinas and am literally blind".

So consider someone piled up stone to make a pyramid - would they be able to walk up the sides like they were flat? What about up the sides of a cliff?

That's something I've been debating.

Or is each shard perfectly round?

Oh, definitely not. The primordials would have wanted to maximize surface area.

I don't see how one follows from the other - but for the atmospheres to touch their bubbles must overlap ... which would give the possibility to climb from one shard to another without having to deal with all that stuff I talked about.

Really? I'd have thought suddenly reversing the gravity would make everything a thousand times worse.

As to how one follows from the other, well, I'm just worried there won't be enough plants on any given shard to balance the CO2 produced by even a primitive human society.

 

[Simon Bridge]

Well, it makes a difference if we're talking about "bright" vs. "blinding" vs. "I burned my retinas and am literally blind".

Oh right - you know those plasma discharge globes?
About like that only radiating away along the surface from whatever object is moving through it.
So poke your std 10' pole into it and you get glowy stuff while the pole is moving and stops when the pole stops - but use your arm and you get bright tingly glows to about a foot while moving and cm length pulsing ones when the arm is stationary (blood is still pumping).

That's something I've been debating.

... otherwise you'd have to figure how someone distinguishes between natural and artificial structures right?

Oh, definitely not. The primordials would have wanted to maximize surface area.

So some sort of fractal surface then? That would give you infinite surface area :P

Really? I'd have thought suddenly reversing the gravity would make everything a thousand times worse.

The energy stays the same, the acceleration changes direction.

 

[SMJB]

Now I'm thinking some sort of incorporeal version of a grav plate (with "rounded edges" even though I'm imagining a 2D plane, so that gravity doesn't just stop when you step off of it lengthwise) that, from a physics standpoint, isn't so much embedded in the shard as much as the shard being the densest and most massive thing in the bubble would naturally align its center of mass with it. I don't feel like I explained that using the right words, but I'm sure you get it. This way I have real topography. And, if the shard is particularly thin, imagine the aqueducts; there will be places where it makes more sense to burrow through the ground rather than have it all on one side.

So ballooning from shard to shard when the opportunity presents itself should be no problem, then? Well, obviously you'd need to strap in and it would be hella disorienting when you make the transition from one grav field to the other, but it's perfectly viable? That's great news, actually; I can have the rocket culture descend from or be inspired by a balloon culture. (Rockets will be faster and allow you to pick your target, which will be quite a boon to trade...and conquest.)