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Author Topic: Hypothetical physics question concerning a story I wish to write.  (Read 1037 times)
Shadow Of The Tower
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« on: November 09, 2015, 04:44:53 am »

I've had an idea for story for some time and recently have felt like it may be time to make a serious attempt at writing it.

The issue I am having is with the physics of world building.

The story is meant to be a Journey to the center of the earth type story. I've always loved such stories and wondered if it was possible for such a journey to take place given the right world for it to take place in.

Obviously, it is impossible to journey to the center of our earth or any earth like it because of the extreme temperatures and liquid nature of our planets interior.

My first thought was that my story could take place on  world composed mostly of metal with a dead, cold core. The tunnel where the story takes place could be an artifact from an super advanced previous culture, perhaps the ancestors of the current steampunk level culture of the story.

The solid metallic structure would make it possible for a extremely deep tunnel to exist without collapsing and the cold dead nature of the planet would eliminate the problems of heat and molten lava at great depth.

The journey would take place primarily in nuclear steam powered ship that would descend down the tunnel, clinging to the walls by some means or possibly lowered on a cable of super strong material. Imagine a combination of the Nautilus and a mining elevator lift. Ideally the journey would take place over several months and cover several thousand kilometers of vertical distance, encountering many hazards both natural an manmade while learning the secrets of the ancient civilization that built the tunnel (perhaps created by firing a small black hole through the planet at high speed)

This story is not intended to be 'hard' sci-fi but I do want it to at least pass a back of the napkin test when it comes to the physics.

My first question was what kind of air pressure would exist at the bottom of a hypothetical tunnel to a point near the center of an earth sized world.  It turns out, this is an extremely complicated problem. Although it is easy to calculate air pressure at altitude, air pressure at depth is another matter. The deeper into the earth you travel, the lower your weight as you can ignore all the mass of the earth at any point above you.  Pressure would rise, but not in a linear fashion and at some point the curve would flatten out to the point where pressure would not increase very much even with a great change in depth.

I was hoping that this effect would take place at a reasonable pressure so that the characters in this story would be able to survive at great depth. However doing the math, it seems that on an earth mass world, even with half our current atmospheric pressure and even giving the people of biological adaptations equal to that of a sperm whale AND pressure suits, the deepest they could travel is a mere 70 some kilometers before they would experience pressures greater than any reasonable person could be expected to survive without extreme sci-fi tropes like personal forcefields.

This is just using straight up atmospheric pressure calculations which do not take into account the lessening effect of gravity in a deep hole but at only 70KM this effect cannot possible be enough to make a difference.

Now, this may seem deep but in terms of an epic steampunk style voyage of discovery its not very far and if you give my tunnel ship a top speed of only 5KPH your still talking about a journey of less than a day to the bottom of the pit.

Soooo....I am left with a big problem with the story before it even gets off the ground. It seems such a journey could not take place on anything resembling a habitual planet.

My next idea was that instead of this journey taking places on a planet it could take place on some kind of constructed megastructure, a journey through the substance of a Dysons sphere, Ringworld, etc. Some kind of ancient ultra advanced construct which the characters of the story live upon but do not understand. A construct which by its nature would allow a basically vertical journey of many thousands of kilometers inside an atmospheric environment without the atmospheric pressure ever reaching ludicrous levels.

Gravity need not be a constant but it should exist in some way so that a feeling of"verticality" is maintained in the story. There would be no problem of pressure inside a long tunnel in a weightless megastructure for example but there would also be no sense of up or down and all the potential peril of falling, the feeling of depth, energy needed to pull something upwards, etc would be gone. It would be the story of people traveling through space rather than of people clinging to the walls of a bottomless pit.

For purposes of suspension of disbelief super strong materials and plausibly advanced technology (on the part of the world builders) are allowed within reason but simply ignoring existing laws of physics is not. In other words, Unobtainium is allowed but Handwaveium is not. The technology needed by the voyagers should not be the answer as it must be limited by usual steampunk tropes and be essentially limited to turn of the century technologies and materials with a few twists. The technology needed to build the world can be almost limitless but must be logical and preferably solid state enough that it could have managed itself for thousands of years in order for its use to be forgotten by the current inhabitants.

So any ideas on what kind of 'world' such a journey could take place in?

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« Reply #1 on: November 09, 2015, 05:53:12 am »

My first question was what kind of air pressure would exist at the bottom of a hypothetical tunnel to a point near the center of an earth sized world.  It turns out, this is an extremely complicated problem. Although it is easy to calculate air pressure at altitude, air pressure at depth is another matter. The deeper into the earth you travel, the lower your weight as you can ignore all the mass of the earth at any point above you.  Pressure would rise, but not in a linear fashion and at some point the curve would flatten out to the point where pressure would not increase very much even with a great change in depth.

I was hoping that this effect would take place at a reasonable pressure so that the characters in this story would be able to survive at great depth. However doing the math, it seems that on an earth mass world, even with half our current atmospheric pressure and even giving the people of biological adaptations equal to that of a sperm whale AND pressure suits, the deepest they could travel is a mere 70 some kilometers before they would experience pressures greater than any reasonable person could be expected to survive without extreme sci-fi tropes like personal forcefields.

This is just using straight up atmospheric pressure calculations which do not take into account the lessening effect of gravity in a deep hole but at only 70KM this effect cannot possible be enough to make a difference.


For your original proposal, it's actually a complicated problem, but it should have a solution - it just requires a bit of calculus and may involve a differential equation.

WARNING: TANGENTIAL SUBJECT AND NOT FOR PEOPLE WHO DON'T LIKE MATH
Spoiler (click to show/hide)

Assuming no variation in gravity the pressure turns out to be a function of a power of y, like

P(y) = C [H-y]-(gH)/(RTo)

Where H is the height of the air column above your head and C is a constant to be determined from boundary conditions

So everything above applies for the air in the tunnel, but now you have to add one more complication to this calculation: the gravitational attraction g, is changing as a function of altitude/radius. I have to rewrite this whole mess, and see what kind of differential equation I get.

So we need to insert

g(y) = ρsolid(4/3) πy3

into

Po = (1/R) ∫ [g(y) P(y)/T(y) ]dy

where ρsolid is the assumed constant density of the planet (remember the density of air changes but not the rock).

And turn the crank from the top, to re-develop the differential equation.  See what we get, and try to solve that differential equation.

As you stated, you may assume the curves shown "flatten out" faster as you approach the center of the planet.  But you have to divide the pressure function outside of the surface of the planet from that on the inside of the planet.

P(y) = Some other power of y function

 Grin


PS:

This is the way a mathematician explained the reasons why it couldn’t work:

http://www.askamathematician.com/2012/08/q-if-you-could-drill-a-tunnel-through-the-whole-planet-and-then-jumped-down-this-tunnel-how-would-you-fall/

My favorite quote:

Quote
But! Assuming that there’s no air in the tube, you’re still in trouble. If the Earth is rotating, then in short order you’d be ground against the walls of the tunnel, and would either be pulverized or would slow down and slide to rest near the center of the Earth....

This is an effect of “coriolis forces” which show up whenever you try to describe things moving around on spinning things (like planets).

For example, the top of a ten story building is moving about 0.001 mph faster than the ground (ever notice that?), so an object nudged off of the roof can expect to land about 1 millimeter off-target. But over large changes in altitude (and falling through the Earth counts) the effect is very noticeable: about halfway to the center of the Earth you’ll find that you’re moving sideways about 1,500 mph faster than the walls of your tube, which is unhealthy.


I guess he forgot that you don't necessarily have that room to move about. In free-fall you'll reach some terminal velocity and touch the wall of the tunnel very quickly- and after that you'll roll along the surface - slowing you down, unless the tunnel is very wide. It's the orbital elevator problem in reverse.  You have a tangential Coriolis acceleration that keeps the orbital elevator cable in tension, but downward the Earth is slowly decelerating you as well through that acceleration. You're not going to smash to death at 1500 mph, as you never get the chance to accelerate to that speed- the difference between a physicist and a mathematician?



« Last Edit: November 09, 2015, 07:21:17 am by J. Wilhelm » Logged

Shadow Of The Tower
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« Reply #2 on: November 09, 2015, 06:28:15 am »

Quote
For your original proposal, it's actually a complicated problem, but it should have a solution - it just requires a bit of calculus and may involve a differential equation.

Yes. I spent many frustrated hours on the internet trying to find someone who had solved this and sadly most of them where hopelessly obtuse and obsessed on temperatures and state changes rather than just simply doing the math, which should be solvable and not really that hard for someone with calculus skills (which I lack) It seems the concept of reduced gravity due to any mass above you acting as the hollow shell and having no effect on you was beyond many people, as was the fact that even though there would be no weight at the center of the earth the pressure caused by the column of air above you that did have weight would still be present.

But although it would be interesting to know the air pressure at the bottom of such a hole just simple calculations show that its far beyond the limits of biology and engineering at just a few tens of kilometers depth, well before the interesting physics of a deep hole are able to take effect.

One interesting thing I did learn, if you drilled a hole to the center of the earth about ten miles in diameter all the existing atmosphere would drain down it and leave the surface of the earth in vacuum. (temporarily of course)


One idea I have for my story is that if your tunnel had airlocks placed every 50KM or so you could keep the pressure reasonable the entire length although how this would fit in a story I don't yet know.
« Last Edit: November 09, 2015, 06:33:57 am by Shadow Of The Tower » Logged
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« Reply #3 on: November 09, 2015, 07:08:24 am »

One interesting thing I did learn, if you drilled a hole to the center of the earth about ten miles in diameter all the existing atmosphere would drain down it and leave the surface of the earth in vacuum. (temporarily of course)

This sounds like a great plot for a James Bond movie.  Mwahahaha!  Grin

The mathematician above does make a good point though.  Temperatures will be very high - I guess that is where the preoccupation with temperatures and changes in state came from.

Really the problem is that Earth is really big, and the way planets form there is very little chance of making such a tunnel.

Having said that, there is no problem on making very shallow secant-line tunnels (actually hypocycloid curves) closer to the surface of the planet. The very old idea of gravity accelerated trains connecting two points on earth along a secant line. Why not simply use that for a plot line? Why go all the way down to the centre of a planet?

Try a geodesic or polyhedral lattice network of underground tunnels.  Each vertex on the lattice is connected to another by way of secant lines, which allow gravity trains to operate.  Like a giant internal Dysons sphere it could be the superstructure developed by an advanced civilisation desperate to survive the pressures from overpopulation, climate change, or death of their star system.

« Last Edit: November 09, 2015, 08:29:54 am by J. Wilhelm » Logged
Shadow Of The Tower
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« Reply #4 on: November 09, 2015, 10:50:46 am »

Quote
This is the way a mathematician explained the reasons why it couldn’t work:


Yup, that was one of the pages I read in my research but wasn't very useful to me since he seemed more interested in showing that it couldn't be done rather that figuring out if there was any situation where it was possible. For instance, if you wanted to jump down a hole to the center of the earth the simple solution would be to drill it following a ballistic curve...or at the poles, even though there is a precession effect its slow enough not to be a problem on that scale.

Sometimes certain scientists give me the impression that they are so scared of pseudo science that they go out of their way to avoid hypothetical solutions to hypothetical problems just in case some conspiracy theorist decides to use it against them.

On the other hand, a lot of sci-fi comes from reverse engineering a problem, start with what you want to do and then build a world that allows it to happen.

Quote
Why not simply use that for a plot line? Why go all the way down to the centre of a planet?


Going to the centre isn't really important but for the reasons stated in my original post I feel the 'core' of the journey to the center of the earth type stories lies in verticality, journey not across horizontal distance the way most stories are but rather primarily on in the vertical axis. It may not be as important of a distinction as I think it is but I'd like to explore the idea at least.

I do like the way you think though.

Right now I'm thinking of perhaps a spacecraft the size earth, composed of multiple nested shells like in the old hollow earth theories. To control air pressure each shell has airlocks between it so that the surface of each shell only experiences normal air pressure on its surface. Think of nested inside out Dysons spheres, each one with a 50km ceiling so that the occupants of each layer would feel like they had whole open sky to themselves. (equiped with artificial suns of course)   In order to have reasonable earth level gravity for something that would be relatively hollow the core of the ship could be made from a neutronium sphere a hundred meters or so in diameter so that over all, the whole construct would end up with 1G of gravity on the outer layer. You end up with something with dozens of times the surface area of a planet without a giant ring world to attract curious species. Perhaps you power it by dumping matter onto the neutronium core and push the whole thing through space.

Because it seems that even unabatanium would not be enough to support that much weight they could be partially supported by continuous centrifugal trains traveling through vacuum tubes at a high enough rate of speed that the outward pressure they exert through centripetal force resists some of the shell weight. ( I didn't invent this idea, its one concept of how you could support a Dysons sphere without anti-gravity. 



hmmm....ideas abound:


Spoiler (click to show/hide)
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Miranda.T
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« Reply #5 on: November 09, 2015, 07:45:54 pm »

Very interesting premise for a story - I'm looking forwards to any further posts on its development. In terms of the structure supporting itself, I would have though that any civilisation with the technology to utilise neutron-star material could produce something strong enough to support the structure - perfect materials produced by atomic-level construction (so no flaws to weaken them) or diamond/bucky-tube type constructions?

Yours,
Miranda.
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J. Wilhelm
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« Reply #6 on: November 09, 2015, 08:19:13 pm »

[mod hat]
Ladies and gents

Just be advised.  At the moment this is a discussion on various theoretical concepts,  but since this thread is about writing a novel, some moderator may move it to the Textual section, especially if it goes beyond  conceptual or philosophical into literary.
[/mod hat]
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pakled
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« Reply #7 on: November 10, 2015, 04:35:50 am »

Feel free to ignore this, but one of the farther-out theories is the 'hollow world' theory; in that there's holes at the poles. Now obviously, it couldn't be correct, but you can still have fun with it. (The sequel to the movie Iron Sky looks like they play with the concept...Wink

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Shadow Of The Tower
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« Reply #8 on: November 10, 2015, 07:31:16 am »

Quote
Very interesting premise for a story - I'm looking forwards to any further posts on its development. In terms of the structure supporting itself, I would have though that any civilisation with the technology to utilise neutron-star material could produce something strong enough to support the structure - perfect materials produced by atomic-level construction (so no flaws to weaken them) or diamond/bucky-tube type constructions?

Good point.

And now that I think of it there really is no good reason why you couldn't just have a chunk of rock the size of say, mars and cover it with shell upon shell of habitat until the total weight is up to 1G.  The overall structure would end up larger than a solid 1G world but there is nothing wrong with that.
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« Reply #9 on: November 10, 2015, 08:32:46 am »

Quote
Very interesting premise for a story - I'm looking forwards to any further posts on its development. In terms of the structure supporting itself, I would have though that any civilisation with the technology to utilise neutron-star material could produce something strong enough to support the structure - perfect materials produced by atomic-level construction (so no flaws to weaken them) or diamond/bucky-tube type constructions?


Good point.

And now that I think of it there really is no good reason why you couldn't just have a chunk of rock the size of say, mars and cover it with shell upon shell of habitat until the total weight is up to 1G.  The overall structure would end up larger than a solid 1G world but there is nothing wrong with that.


But isn't that just a variation on what I proposed for a geodesic shell Dyson sphere on Earth?  It's basically the same, because you are using the rocky planet as a base to build a muti-level superstructure.  To me this is going to happen anyway.  In fact it could be argued that is already happening today...

http://www.dailymail.co.uk/news/article-2048395/Earth-scraper-Architects-design-65-storey-building-300-metres-ground.html

Building Down Earth Scraper 56 Floor Below in Mexico City


« Last Edit: November 10, 2015, 08:37:44 am by J. Wilhelm » Logged
Atterton
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« Reply #10 on: November 10, 2015, 09:58:20 am »

You could make it a planet-sized Malteser. Or perhaps cover the vessel in something piezoelectric and absorb some pressure that way?
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Shadow Of The Tower
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« Reply #11 on: November 10, 2015, 10:25:46 am »

Quote
But isn't that just a variation on what I proposed for a geodesic shell Dyson sphere on Earth?  It's basically the same, because you are using the rocky planet as a base to build a muti-level superstructure.

Basically. From what I understood you where thinking more of a network of straight transport tunnels and my idea is more like concentric shells but yeah, like I said, I like the way you think. Thats why I came here.

Quote
You could make it a planet-sized Malteser.

I assume you mean the candy, not the dog?

Its interesting idea and as long as the bubbles where airtight from each other you wouldn't have to deal with the crushing air pressure problem but I'm not sure how the people would move from one section to the next or why it would be made that way...not that It couldn't, just that I don't know why.
« Last Edit: November 10, 2015, 10:40:01 am by Shadow Of The Tower » Logged
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« Reply #12 on: November 10, 2015, 10:41:58 am »

Gas-filled magma, similar to what makes pumice? Though a homogenous volume of it does seem unlikely. Perhaps some form of lava tunnels?
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Shadow Of The Tower
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« Reply #13 on: November 10, 2015, 11:49:28 am »

Quote
Gas-filled magma, similar to what makes pumice? Though a homogenous volume of it does seem unlikely. Perhaps some form of lava tunnels?


The problem is that I can think of no plausible natural way such a world would form and remain that way, and it seem that an artificial world would be more structured....

But, I do kind of like the idea of bubbles instead of layered shells. They would not be as easy to live inside since there would not be much flat land, but a world filled with large bubbles with civilization built on the bottoms like an enormous steep sided valley is interesting. If all where connected by air locks my travelers could move downward from bubble to bubble following a more or less vertical course for thousands of kilometers without ever having to encounter crushing air pressure problems and each bubble could be a different environment.

It also has the benefit that I think large habituate bubbles could be more plausible than nested world sized shells wile still allowing the scale of the interior world to match what I have in mind for the story,

And smaller but still enormous by conventional construct standards bubble habitats would concentrate whatever interesting bits of the civilization that existed in them into more manageable chunks for story telling purposes. The concentric shell world would create a situation where each layer had so much surface area that it would be only by extreme coincidence that the voyagers encountered something interesting in each layer rather than just thousands of miles of empty space.

Larry Niven actually had this problem in "Ringworld" When you create a setting with millions of times the surface area of earth to work with it makes it hard for your characters to just 'happen' to find interesting settings and characters for your story. This I believe is why he had to make "luck" a real force so that even if all there random seeming movements result in interesting events its not just chance but because there was a real force pushing them to those places.

Hmmm, yes....bubble habitats of say 50KM height (for air pressure reasons) and 100KM width would be large enough to feel like a proper planetary scale mega structure but small enough that any interesting cities etc inside them could be easily found within a few days even with steampunk level technology.

I've also been thinking about gravity train tunnels. For those of you that aren't familiar with the idea ( I know J.W is) its a fact that if you could make a straight tunnel  through an portion of the earth and had suitable frictionless vehicle that gravity power alone would move you to the opposite end, regardless of the location or length of the tunnel, in about 42 minutes. This is true for a trip across the entire diameter of the planet or one just though a slice of it, its always 42 minutes and 12 seconds on a world like ours and would be the most logical way to travel in a world with an inhabited volume.

Spoiler (click to show/hide)
Spoiler (click to show/hide)


Now, I don't want to use these tunnels for the main story because if they where functional the tunnel would be in a state of vacuum, and if not functional would be filled with unsurvivable air pressure, both of which would make it hard to have much a story take place.

If shallow enough to avoid the air pressure problem would no longer have the "Journey to the center" feeling but be rather "A trip through a very long and gently sloping tunnel" (although the tunnels would be straight because of gravity you would feel like they are sloping downhill when you enter and uphill on your way out)

Spoiler (click to show/hide)

But a almost universal trope in such stories is that once they reach the climax of their journey the travelers find a active volcano or some such that launches them back to the surface in a fraction of the time it took them to reach the  bottom. A functional gravity train would be a more practical twist on this classic ending and allow everyone to travel back up to the surface in less than an hour regardless of where they end up.
 
« Last Edit: November 10, 2015, 11:52:55 am by Shadow Of The Tower » Logged
Miranda.T
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« Reply #14 on: November 10, 2015, 07:41:41 pm »

Quote
Very interesting premise for a story - I'm looking forwards to any further posts on its development. In terms of the structure supporting itself, I would have though that any civilisation with the technology to utilise neutron-star material could produce something strong enough to support the structure - perfect materials produced by atomic-level construction (so no flaws to weaken them) or diamond/bucky-tube type constructions?


Good point.

And now that I think of it there really is no good reason why you couldn't just have a chunk of rock the size of say, mars and cover it with shell upon shell of habitat until the total weight is up to 1G.  The overall structure would end up larger than a solid 1G world but there is nothing wrong with that.


But isn't that just a variation on what I proposed for a geodesic shell Dyson sphere on Earth?  It's basically the same, because you are using the rocky planet as a base to build a muti-level superstructure.  To me this is going to happen anyway.  In fact it could be argued that is already happening today...

http://www.dailymail.co.uk/news/article-2048395/Earth-scraper-Architects-design-65-storey-building-300-metres-ground.html

Building Down Earth Scraper 56 Floor Below in Mexico City




That is impressive - I really hope it gets built.

Quote
Gas-filled magma, similar to what makes pumice? Though a homogenous volume of it does seem unlikely. Perhaps some form of lava tunnels?


The problem is that I can think of no plausible natural way such a world would form and remain that way, and it seem that an artificial world would be more structured....

But, I do kind of like the idea of bubbles instead of layered shells. They would not be as easy to live inside since there would not be much flat land, but a world filled with large bubbles with civilization built on the bottoms like an enormous steep sided valley is interesting. If all where connected by air locks my travelers could move downward from bubble to bubble following a more or less vertical course for thousands of kilometers without ever having to encounter crushing air pressure problems and each bubble could be a different environment.
(snip)


Constructed by an insectoid race? The 'bubbles' are their version of honeycomb cells.

Yours,
Miranda.
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« Reply #15 on: December 25, 2015, 10:17:03 pm »

My suggestion involves your steampunk protagonists
confronting an artifact created by a post-singularity
civilization
.

Basically, a planet-sized computer or matrioshka brain
composed of utility fog  that will present itself locally to the
instruments and senses of the protagonists more-or-less as
a planet that can be drilled or descended into, with a pocket
universe
created and maintained by the "planet" at its core.

The pocket universe is accessed by a portal / wormhole  at
the bottom of the fog and, once inside, you have the classic
Pellucidar  scenario - a concave inner world, with a
( relatively ) tiny artificial sun suspended overhead, providing
constant heat and light to the world enveloping it.

You may employ various mechanisms to interrupt the
light at certain intervals, if you wish for some alteration
of day with night, but any further elaboration of the
basic idea is up to you.
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J. Wilhelm
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« Reply #16 on: December 25, 2015, 10:37:43 pm »

We  had already touched on inner cavities in planets. Assuming the inner surface is perfectly spherical,  what is there to prevent the  gravitational attraction from being exactly zero anywhere on the surface of that inner Pellucidar world? 
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« Reply #17 on: December 25, 2015, 11:07:30 pm »

We  had already touched on inner cavities in planets. Assuming the inner surface is perfectly spherical, what is there to prevent the gravitational attraction from being exactly zero anywhere on the surface of that inner Pellucidar world?  

Ah, but this is not merely an inner cavity
within a planet - it is a pocket universe,
and the physics of this universe were designed
and determined / computed at its inception.

See, for example :

Gravity Modification with Yukawa-type
Potential: Dark Matter and Mirror Gravity


Yukawa Potential

The Search for Non-Newtonian Gravity
by Ephraim Fischbach & Carrick L. Talmadge


What difference does non-Newtonian, "Yukawa"
gravity make for purposes of this story ( for those
who aren't interested in wading through the texts
mentioned above ) ?

It is not your garden variety "inverse square" sort
of gravity; it varies across the space between the
artificial sun and the surface, with a sort of "null
zone" in the sky between the sun and the surface
( that might provide some additional possibilities
for the author to exploit ).
« Last Edit: December 26, 2015, 12:24:46 am by Khem Caigan » Logged
Peter Brassbeard
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« Reply #18 on: December 27, 2015, 05:55:11 am »

Gravity attractive at short distances to hold the "sun" together, and repulsive at longer distances so everything on the inner surface of the sphere is repelled from the "sun".  Get the profile right and you can even get the sun held in the center.  Something like

|F| = k*r^(-4) - l*r^(-3)

Of course such gravity is absolutely nothing like what Newton or Einstein described.
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« Reply #19 on: December 27, 2015, 09:45:44 am »

Gravity attractive at short distances to hold the "sun" together, and repulsive at longer distances so everything on the inner surface of the sphere is repelled from the "sun".  Get the profile right and you can even get the sun held in the center.  Something like

|F| = k*r^(-4) - l*r^(-3)

Of course such gravity is absolutely nothing like what Newton or Einstein described.

Probably why this sort of gravity is referred to as 'Non-
Newtonian' or even 'Post-Newtonian' - see above.

But it was discussed and described by Einstein
- Hideki Yukawa met Albert Einstein in 1948 at
Princeton University's Institute for Advanced Study,
and they "got on like burning houses", as they say.

See also :

Beyond Einstein Gravity :
A Survey of Gravitational Theories for Cosmology
and Astrophysics

by Salvatore Capozziello, Valerio Faraoni


Actually, gravity at the surface of this 'pocket universe' can
be an attractive 'Earth normal' / 1g.

Gravity varies a great deal between the surface and solar
region, with an area of near zero gravity between the 'sun'
and the surface of the 'earth'.

And, needless to say, the surface area may be many
thousands of times that of the Earth - much like the
disparity between stepping into a certain police callbox
and discovering a much larger space inside . . .

For me, this is in large measure the attraction for positing
steampunks as the protagonists.

They possess an experimental method and instrumentation
just sophisticated enough to enable them to notice how
unusual and arbitrary some of the physical constraints of
this world they are presented with appear to be.

The trope of an environment that leads protagonists beyond
their initial expectations has been with us since Solaris
and Forbidden Planet, and protagonists possessing the
means to approach, and possibly surpass, the horizon that
they are presented with - one that is practically begging them
to do so - always make for good adventuring / reading.

And there is an entire genre that has grown up around toying
with the fundamental constants of local physics and inflicting
the consequences upon the protagonists - see Zelazny's
Nine Princes in Amber, Stirling's Dies the Fire : A Novel
of the Change
, and Steven Boyett's Ariel, for example.

Heat might rise to a certain temperature, and no higher. It
might be possible to forge metal, draw copper wire, and build
various engines, only to discover that internal combustion and
steam engines and electronics and gunpowder don't work, once
one has crossed the threshold into this "inner world".

I think Walter Jon Williams has dubbed this sub (sub?) genre
"Sword & Singularity".

There may even be a honeycomb-like lattice of pocket universes
that envelope the 'world' at their core, which provide the power
necessary to keep the portals and spheres inflated. Suns at their
core emit energy converted by thermionic and/or photovoltaic
converters lining the entire surface of the inner spheres, something
like Moseley's first atomic battery.

Pardon me while I go unpack and dust-off my old Bag of Holding
and run a few experiments . . .
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« Reply #20 on: December 27, 2015, 10:32:48 am »

Not much to add I'm afraid, certainly not on the physics side of things. I would however proffer the suggestion of my old engineering teacher back when I was studying Architecture and needed some advice on a structural conundrum; "Physics should only ever be a concern if you're actually planning on making something, for everything else you just need to concentrate on what you can make people believe will work."

A natural formation would be hard work to justify, but as you suggested saying "A Category III civilization did it and ran away" would probably work.

Also, I must recommend the Iain M Banks book 'Matter' as a great example of the layered / shell world idea.
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« Reply #21 on: December 27, 2015, 05:34:55 pm »

"Physics should only ever be a concern if you're actually planning on making something,
for everything else you just need to concentrate on what you can make people believe
will work."
That is very good advice, if you are not an Arthur
C. Clarke, Larry Niven or a Vernor Vinge. And, oh
yeah, an Iain M. Banks or Alastair Reynolds.

Some readers ( especially those of us fossils that
were weaned on Golden Age Sci-Fi ) actually
enjoy hardcore "technoporn".

That means ( for me ) an author establishing
the plausibility of their premises, and then
actually working out the details of how the
worlds and their whatzits actually function.

The rest is arguably still speculative fiction, but
I nudge it over the line from science fiction into
the realm of fantasy.

Heck, let's be generous and call it "science fantasy".

And, too, we're not dropping a Conan or a Lord
Greystoke into this puzzle - they are steampunks,
with all of the technological, methodological,
ideological and cosmological baggage that implies.

Watching the sparks fly as they grind their axes
is fun, natural fun . . .
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« Reply #22 on: December 27, 2015, 09:34:35 pm »

"Physics should only ever be a concern if you're actually planning on making something,
for everything else you just need to concentrate on what you can make people believe
will work."

That is very good advice, if you are not an Arthur
C. Clarke, Larry Niven or a Vernor Vinge. And, oh
yeah, an Iain M. Banks or Alastair Reynolds.

Some readers ( especially those of us fossils that
were weaned on Golden Age Sci-Fi ) actually
enjoy hardcore "technoporn".

That means ( for me ) an author establishing
the plausibility of their premises, and then
actually working out the details of how the
worlds and their whatzits actually function.

Oh, don't get me wrong - I love myself some proper geekout Hard Spec-Fic just as much as I love Bank's soaring Space Operas. I blame a well spent childhood ogling a fantastic couple of books filled with images of futures that seemed about to become reality, as if any-day-then we'd suddenly all find ourselves hopping aboard the mass drivers to our new orbital homes that would really look as lush and inviting as the NASA artwork showed (sadly, despite pulling apart every bookshelf in my parents house I cannot find these books any longer. Damn shame, I know we didn't have a copy of George K. O'Neill's High Frontier, but whatever we had had a lot of the artwork from it inside. Plus magrail-and-laser launched space shuttles. Loved those, wish I could find the books). Anyway, I digress (though, honestly, if you can remember any great 60s-80s books crammed full of 'this is our near future of space travel' type stuff, let me know via message).

I suspect we're both of a like mind, the reason for the quote isn't to suggest that 'space magic' is the best solution, but instead to suggest that getting bogged down in unimportant background technical detail can often have a negative impact on the presentation of a non-technical piece. But that wasn't what the OP was after and has since moved strongly in in what sounds like an intriguing direction! - I suspect I just had an early morning fatigue induced brain misfire (to many 4am starts) and wanted to plop the Banks book in as a suggestion. I'll go to sleep now.
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« Reply #23 on: December 31, 2015, 07:16:55 am »

<SNIPS>I blame a well spent childhood ogling a fantastic couple of books filled with images of futures that seemed about to become reality, as if any-day-then we'd suddenly all find ourselves hopping aboard the mass drivers to our new orbital homes that would really look as lush and inviting as the NASA artwork showed (sadly, despite pulling apart every bookshelf in my parents house I cannot find these books any longer. Damn shame, I know we didn't have a copy of George K. O'Neill's High Frontier, but whatever we had had a lot of the artwork from it inside. Plus magrail-and-laser launched space shuttles. Loved those, wish I could find the books). Anyway, I digress (though, honestly, if you can remember any great 60s-80s books crammed full of 'this is our near future of space travel' type stuff, let me know via message).
I posted the relevant links to your Inbox.

O'Neill's High Frontier was formerly available
from the Space Settlements bibliography page,
by-the-way, and was taken down due to
copyright issues.

I'll be posting a link to a High Frontier
download site momently.

If anyone else has any interest in this sort of
thing, please message me and I'll post the
links to you as well.

I suspect that many of the folks here share an
interest in space habitats of one stripe or other.
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