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World building idea: Jupiter-sized Earth

At this scale, planetary circumnavigation is not something that can be accomplished within a single human lifespan, absent magic like life extension.

This raises some interesting possibilities. There might, for example, be groups dedicated to exploration that do their work over generations. You might now have the first person to circumnavigate the sphere, but a first family or lineage to do so. You could even have a terrestrial version of a generation ship. Maybe a group of pilgrims heads into the wilderness to find a new homeland, traveling for generations before settling down.
 

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Mercurius

Legend
Um... yes and no. That brings up some very hairy questions of physics, and some very weird things happen when the rules are not the same everywhere. It is likely that without the assumption that physical laws are the same throughout the universe, the result is apt to be unstable, and areas will collapse until you reach a point where the Universe has the same laws everywhere.
Well, we could extent it to "multiverse" and hypothesize parallel universes with differing laws.
No. That would be observable with current technology, and would have... repercussions that might well destroy a galaxy, as stars tried to move from one region to another, and were destroyed in the process.
Ack! We don't want that (or do we?)

But that itself sounds like an SF story, and someone has probably addressed it. A gravitation anomaly that is, at first, contained to a solar system, then begins to spread.

Anyhow, as a general rule, I tend to take the "Dear Horatio" approach to what we currently know. Not only is it always changing, but it is limited by our means of observation--that is, our technology. What seems one way now might be rather different, or symptomatic of deeper laws. So while I hear you, based upon our current tech and knowledge, as far as hypotheticals, I can't help but think, "But why not?"
 

J.Quondam

CR 1/8
This raises some interesting possibilities. There might, for example, be groups dedicated to exploration that do their work over generations. You might now have the first person to circumnavigate the sphere, but a first family or lineage to do so. You could even have a terrestrial version of a generation ship. Maybe a group of pilgrims heads into the wilderness to find a new homeland, traveling for generations before settling down.
And the Dyson sphere doesn't have to even be solid, does it? It might be more like a cage surrounding the star. It could be a great geodesic sphere with some some of the faces filled, each a separate "planet". Each of the these "planetary panels" would likely entirely different from the others. Transport along the unobtanium "struts" between planets would make for an interesting exploratory trip.
 

GuyBoy

Adventurer
This raises some interesting possibilities. There might, for example, be groups dedicated to exploration that do their work over generations. You might now have the first person to circumnavigate the sphere, but a first family or lineage to do so. You could even have a terrestrial version of a generation ship. Maybe a group of pilgrims heads into the wilderness to find a new homeland, traveling for generations before settling down.
Could be a cool campaign theme. The player characters are the ranger-guardians of a kind of generational “wagon train”, both protecting from attack and going off on expeditions away from the main group to widen the sphere of the exploration.
 

dragoner

Dying in Chargen
At this scale, planetary circumnavigation is not something that can be accomplished within a single human lifespan, absent magic like life extension.
Even with spacecraft it would take a ridiculous amount of delta v to reach escape velocity. This one is rather small, though I wonder about working the numbers to make it smaller. Interesting that it only takes a terrestrial planet's amount of material to make the sphere.
 

Umbran

Mod Squad
Staff member
Anyhow, as a general rule, I tend to take the "Dear Horatio" approach to what we currently know.

It is always good to have an open mind. The trick is to not be so open as to allow geese to get in there and wander around.

So while I hear you, based upon our current tech and knowledge, as far as hypotheticals, I can't help but think, "But why not?"

I'm a physicist. I am prepared to have a general discussion of why not, however, it would significantly derail your thread, and I don't want to do that unless you ask for it :)

And the Dyson sphere doesn't have to even be solid, does it?

Not at all. The original concept is not for a single mega-structure. The original concept of a Dyson sphere is a cloud of modest closed space habitats, each with it's own solar arrays, so numerous that seen from outside the solar system they blot out the star within. At a distance, the only tyhing you'd see was a diffuse sphere of infrared radiation.
 

doctorbadwolf

Heretic of The Seventh Circle
Very cool - so many possibilities!

I find that considering the hard science gives frameworks and considerations for choices, even if I stick within the soft sf/fantasy range of explanations.

I also like the idea of a "Swiss cheese world" that is so riddled with pockets (and perhaps micro-ecologies) that it is far lighter than a big planet would normally be.

My understanding of science is limited, but while I realize that gravity is believed to be constant throughout the universe, this is still only theoretically true. I mean, we can't know for certain, right? Perhaps there are galaxies with different degrees of gravity, or even pockets within galaxies. Perhaps even worlds that operate by different physical laws.

Although, again, I don't need to explain or rationalize this for my purposes, although it may be somewhat important in my story idea, because the protagonist--while not a scientist--is still a member of a technologically advanced civilization (Earth at the end of the 21st century), so would have some knowledge, and at least I'd want a sense of when I'm "breaking the rules."
Yeah gotta know what things the protagonist will be surprised and bewildered by.
The trick is to not be so open as to allow geese to get in there and wander around.
I don’t know about that. Best adventure I ever ran involved a fight with a flock of geese that had swooped in an stolen several people’s headgear, and one of the keys the group needed to get into a vault beneath the city.

Of course, they turned out to be quicklings in disguise as geese, but still. Good stuff. They gave the party (and several townsfolk who tried to help and were good humored about the prank) magic apples and acorns, and a riddle that would later help them get to the vault.
 

Umbran

Mod Squad
Staff member
Even with spacecraft it would take a ridiculous amount of delta v to reach escape velocity. This one is rather small, though I wonder about working the numbers to make it smaller. Interesting that it only takes a terrestrial planet's amount of material to make the sphere.

So you need to be careful with that idea.

If you read the paper in full, it says you can take about a planetary mass, and make it 10 meters thick. However, no know planetary material has the strength to hold up. It will collapse. It requires strength a couple of orders of magnitude greater than is available with chemical bonds!

So much for not needing artificial gravity!
 

Mercurius

Legend
It is always good to have an open mind. The trick is to not be so open as to allow geese to get in there and wander around.

I'm a physicist. I am prepared to have a general discussion of why not, however, it would significantly derail your thread, and I don't want to do that unless you ask for it :)
Ha, no need. But I think the fact that you are a physicist puts you in a different category of reader than most. Most don't care or won't notice the things that you notice. Meaning, it is more difficult to suspend your disbelief than mine, at least as as the science goes. In other words, you've got the problem of expertise, which isn't unlike being an audiophile: it is nice to have a developed ear, but the problem is that an audiophile can enjoy music less often than someone who doesn't have an ear for quality hifi.

On the other hand, while you lose enjoyment in one place--e.g. a SF movie with dubious science--you might gain it in other words, e.g. a SF movie with good science that you get to enjoy the subtleties of that others miss.

(As a side note, about a year ago I purchased a really nice Marantz amplifier with Elac speakers...it is wonderful to hear music with such great sound, but it has reduced my tolerance for sub-par bluetooth speakers and such, so in a way it has made me enjoy music less, unless I'm in the room with my stereo, and most of my music listening is in the kitchen, which is where that stereo isn't!)
 

Umbran

Mod Squad
Staff member
Meaning, it is more difficult to suspend your disbelief than mine

Not really. Remember, the full term is "willful suspension of disbelief". The fact that I have more technical understanding is separate from whether I choose to ignore that understanding and just enjoy the fiction for what it is.

If I couldn't turn off the technical critic, I could not enjoy Star Trek, or most of the sci-fi genre. But I can, so I do.
 

doctorbadwolf

Heretic of The Seventh Circle
Ha, no need. But I think the fact that you are a physicist puts you in a different category of reader than most. Most don't care or won't notice the things that you notice. Meaning, it is more difficult to suspend your disbelief than mine, at least as as the science goes. In other words, you've got the problem of expertise, which isn't unlike being an audiophile: it is nice to have a developed ear, but the problem is that an audiophile can enjoy music less often than someone who doesn't have an ear for quality hifi.

On the other hand, while you lose enjoyment in one place--e.g. a SF movie with dubious science--you might gain it in other words, e.g. a SF movie with good science that you get to enjoy the subtleties of that others miss.

(As a side note, about a year ago I purchased a really nice Marantz amplifier with Elac speakers...it is wonderful to hear music with such great sound, but it has reduced my tolerance for sub-par bluetooth speakers and such, so in a way it has made me enjoy music less, unless I'm in the room with my stereo, and most of my music listening is in the kitchen, which is where that stereo isn't!)
I am vehemently opposed to narratives that are basically “ADHD is really a superpower!” or whatever, but the forgetfulness that comes with my ADHD is a blessing in a couple ways, this effect being one of them. I essentially don’t ever experience what you describe except with food, and even then it is very muted.

And thank goodness because I love hifi music but also have no patience for like…ever not having music on around me. It would suck butt to not be able to enjoy music on my phone…
 

Lanefan

Victoria Rules
This is actually an idea I'm playing with for a writing project, but thought the smart folks of ENWorld could offer good advice.

The basic idea--at least relevant to discussion here--is a Jupiter-sized world, but one that is inhabitable by humans.

Some questions:

*What are some basic factors I'd need to consider? Stuff like seasons, weather, climate, yearly and daily cycles, etc.
Weather and climate would be the biggest headaches; and tides if the sun and-or any large moons are close enough.

My first major world was a bigger-than-Earth affair and I soon came to realize that the weather would end up balls-nuts crazy a lot of the time compared to what we're used to, simply due to scale and the sheer size of the different climatic zones. The hot areas, being bigger, would get hotter; the cold areas colder, and the temperate-zone interactions between the two would thus tend to be more violent.

Tides are another issue: you'd probably have a much bigger difference between high and low tide levels in many places, again due to scale.

The other thing to consider is astronomy. A bigger world is going to be a heavier world (unless it's hollow), meaning it's going to be farther from its mother star, by extension meaning a typical sun-like star won't do unless you want your world to be too cold for Human inhabitation. So, you'll need a different star type...and once you've determined that, you're right back to weather again because incoming heat from the sun is what ultimately drives almost all day-to-day weather on the planet (volcanic activity and forest fires cause the rest, a trivial but not-zero amount).
 

Umbran

Mod Squad
Staff member
Tides are another issue: you'd probably have a much bigger difference between high and low tide levels in many places, again due to scale.

Um, when we get to tides for this large, but not dense, world, things will get complicated.

On Earth, we see tides in the ocean, but the tidal forces affect the entire planet. For Earth and its moon, we don't notice the effect on the rock of the planet on a day to day basis, because there's a whole lot of strong rock. The ground only flexes a bit (about one foot, actually), while the water, being fluid, moves a lot more.

But, this low-density, large planet, is a different beast. If we are talking about a thin shell - that one foot of movement is a large flex for a 30-foot thick shell like the dyson sphere discussed above.

The other thing to consider is astronomy. A bigger world is going to be a heavier world (unless it's hollow), meaning it's going to be farther from its mother star

This is incorrect. In our own solar system, the heavy worlds are farther from the sun, but that's not a general rule, by a long shot.

1634309913855.png

In general, on this scale, for the most part we can use radius as a proxy for mass - it is hard to be 10 times bigger and not be heavier - and we won't be too far off.

The Earth is down at the lower left area of the graph (one earth radius, and 93 million miles from the sun). You'll note that Jupiter-sized worlds (along the top of the plot) exist all along the spectrum from around 1 million to a hundred million miles from their parent star.

There is a scarcity of middling sized worlds near their stars (in the "Neptune Desert" region. But big and small worlds are found all over the place.
 
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Someone mentioned pumice as a less dense rocky material. I think it'd make for a great way to get around rocky planet gravity at the scale you're talking about and create an interesting game world.

Instead of being solid, it's more of a hive or foam like structure, with massive empty spaces traversed by a lattice of stone. This would lead to a lot more verticality in the environment that could lead to some really cool features.

Underground oceans
Gliders, zip lines and cable cars as significant means of transportation
Roads that are literal highways.
 

One other somewhat general point about gravity at from a "how would people live there?" perspective though. From an anatomical perspective, you don't really have to make any kind of special allowances.

Physics for D&D is really only based on a small subset of gamist abstractions that tell you what your character can do. These abstractions exist independent of the physical characteristics of the setting. Basically characters can do what the book says they can do.

You can of course narrate special reasons for their ability to survive, but "they grew up that way" is also a perfectly adequate response. It only really matters if your PCs venture into an area with different physical characteristics.
 

Tonguez

A suffusion of yellow
Someone mentioned pumice as a less dense rocky material. I think it'd make for a great way to get around rocky planet gravity at the scale you're talking about and create an interesting game world.

Instead of being solid, it's more of a hive or foam like structure, with massive empty spaces traversed by a lattice of stone. This would lead to a lot more verticality in the environment that could lead to some really cool features.

Underground oceans
Gliders, zip lines and cable cars as significant means of transportation
Roads that are literal highways.
it would certainly be an interesting environment
but I am wondering about its formation - Pumice is formed from the explosive eruption of magma, so for a planet sized pumice you would need to have a magma core with explosive, gassy breakthroughs that then cool into a compact planet

hmmm I suppose the left over remnant of a giant planet that exploded might be feasible - but for the remnant to be jupiter-sized means the original rocky planet was of mindblowing proportions
 

it would certainly be an interesting environment
but I am wondering about its formation - Pumice is formed from the explosive eruption of magma, so for a planet sized pumice you would need to have a magma core with explosive, gassy breakthroughs that then cool into a compact planet

hmmm I suppose the left over remnant of a giant planet that exploded might be feasible - but for the remnant to be jupiter-sized means the original rocky planet was of mindblowing proportions
Maybe something like a sponge or a coral, some fantasy creature is ingesting fantasy space debris and excreting land. Maybe it was generated as a chemical byproduct of a reaction between bubbles of fantasy space gasses? Perhaps it once was solid and something (like an explosion) happened.

Each of these could have different implications and they're all fun (imho)
 



J.Quondam

CR 1/8
Maybe something like a sponge or a coral, some fantasy creature is ingesting fantasy space debris and excreting land. Maybe it was generated as a chemical byproduct of a reaction between bubbles of fantasy space gasses? Perhaps it once was solid and something (like an explosion) happened.

Each of these could have different implications and they're all fun (imho)
Or perhaps something is eating th planet way from the inside, and excreting the waste... somewhere else? Some other plane, maybe?

One of my settings is the interior surface of a massive 100 mile-diameter cavern on/in the Plane of Earth. It was carved out by elemental motes embedded within it, that eroded the earth away, leaving behind the immense cavity, including some adamantium "pillars" that crisscross the void here and there.
 

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