Physics of a World Tree

[D. Gray Warrior]

I'm kicking around the idea of a world that is supported by a tree, kinda like Yggdrasil from Norse mythology.

The world is just a flat disk that sits upon the branches of the tree, with an atmospheric dome.

What I'm wondering is the exact physics of the world, what would realistically change from our world?

Since the tree has roots, perhaps it should have some kind of soil to support it, unless it's somehow immortal.

I would also need to figure out how the sun and moon would work. Would the tree orbit the sun much like how our earth does, while the moon orbits the tree?

 

[WooHooMan]

I think the idea of a world tree is inherently unscientific so trying to apply physics to it or doing things “realistically” is kind of a wasted effort.

I got a world tree in a story I’m working on now and I’ve had to throw physics out the window and have things like an ocean hovering over the tree with water dripping through its branches and onto the roots while the sun is logged in the trunk. All in order to make the concept have some semblance of internal logic.

It’s a symbolic thing so you need to approach it as such for it to work. That’s my perspective anyways. Maybe there is a realistic way to do it but I can’t even conceive of one.

 

[Riva]

As the answer above, I think it would be easier to not consider too much the realism factor here.
But if you want to it depends on the dimensions.
If it is small enough, gravitational rounding of the object can be avoided. I'm thinking asteroid size should still work, but even so "asteroid" encompasses a farly large collection of sizes. I'm thinking somewhere between 0 and 100 km should be it but it really depends on the characteristics of the material it is made of. Consider that on the larger side it will get rounder.
So if it's the kind of three we're used to it will need soil, some solvent (most likely water, but it can vary), sunlight, and air (well, oxygen and CO2 at least).
The only way I can see to have those is having the tree on a planet, so you would have a world with a world tree with a world on top.
The problem with having it on a planet is that its size would have to be limited (depending on the size of the planet), and it would get more pyramidal the larger the planet is (to not collapse).
An alternative would be to have a planet almost entirely made out of wood. Straying a bit away from what we've ever observed but imagine a vegetal superorganism that took over the entirety of the surface of the planet, that is capable of processing any kind of unorganic substance it finds in the ground to its advantage. Maybe besides the sun it is also capable of using the planets core heat as a source of energy.
More than a world tree it would be a tree-world though.
The last thing I can maybe think of is a plant-like organism that spans an entire asteroid belt that is situated in the habitable zone. It may be carbon based or silicon based, or both why not. This environment would lack water and an atmosphere. Water and carbon dioxide could be provided in little quantities by comets. The plant organism would have to have some kind of large surface to maximize nutrient absorption from space, which could be the start of it growing leaf or coral like extrusions eventually reaching other asteroids (I know they are very far apart and the substance quantity of the asteroids is comparatively small to the volume of space they occupy, but eh ).
Lacking oxygen the plant could use a hybrid of phototrophy and chemotrophy to produce energy (I don't know of any organism that do both but I think there could be). It could have photosynthetic centres spread along its lenght, dome or button shaped and facing the sun. In them there could be water and carbon dioxide in liquid form, harvested from the leaf-like complexes in other parts of the plant. Through photosynthesis there would be a production of oxygen, but I doubt it could sustain cellular respiration throughout the whole organism. It could be coupled with chemosynthesis.
To be honest I don't know if there are elemnts like sulfur in order to perform chemosynthesis in space, so I'm guessing a bit that there would be a metabolical way to produce energy from asteroid stuff ecc..
So this photosynthetic domes could be your worlds, it would be a bit alien but not too much, you would have water, oxygen, carbon dioxide ecc..
This last one is the most speculative but I thought it may be fun to try imagining something along those lines.

These were my considerations, I'm sure that there are people here who are more knowledgeable than me on the subject and might correct/expand on this.
Hope you can get some ideas out of this, have a nice day.

 

[Prince of Spires]

You could simply go full-on Discworld and explain everything with "because magic". It worked well enough for Discworld.

If you want actual pseudo-physics then I would suggest you look into flat-earth theory. There is a whole group of people who believe the earth is flat (hence flat-earth theory), and they have developed a physics system in which this would work (if you don't look too closely). You could "borrow" from them.

The main question I have, if you want to go the physics route, about the world tree is "What does the tree sit on"?

 

[Maker of Things Not Kings]

I'd agree with the suggestions to not worry over the actual technical physics of it unless it absolutely pertains to your story and plot. I've read books with floating land masses, cities in clouds etc etc and I cannot recall any of them being explained (other than as a magical creation) and that never stopped me from reading on, nor did I feel cheated. The choice you have is between what reader audience you want. I think of sci-fi here. I myself can't get through two chapters of most hard sci fi. I'm not interested in the factual reality of space science, life on another planet, etc only that, within the story, it makes sense.

Here's a real world example.

I live near to a tidal estuary/bay. The town I live in has maybe 700 people. No one along this bay, if it weren't for the books and info written on how and why the tides, rivers and oceans here combine to do what they do, would have any way or real reason to understand the workings of it. It's natural science but it's not, among the local residents, common knowledge. Even with the science out there to explain it, most aren't interested or could care less. Fisherman understand the tides but only as far as what times and under what conditions it's safe to take their boats over the bar. Clammers know when the low clam tides are, salmon fishermen know when the salmon run is on. The science we can google or read about is an outside introduction/force. Someone, sometime, studied it all and wrote a book or two about it but, if they hadn't, the tides would do what they do and the bay would empty and fill accordingly as it always has with or without us understanding it. What i'm saying is, unless its necessary for your characters to understand why the tree supports them, or unless someone else has done the research in your world and made it public, then it just is, and as long as that makes sense within the story, then I, as a reader, have no need to know it either.

And that sort of ignorance is bliss lends itself to all sorts of plot twists.

Certainly, no one here understood the ramifications when in the 1920's-30's they built a single jetty (against the recommendation of the army corps of engineers to build two or them) at the mouth of the bay to make for an easier passage for the steamship that brought people to the land spit on which a booming resort town had begun to emerge. In just a few years, the once wide and desirable spit ended up being eroded away and the buildings were reclaimed into the ocean because that jetty changed the flow and effects of the tides on the existing sand bar and currents. At that time, even the Ary Caps couldn't have imagined that result.

So if your world is not populated with scientists and researchers, then the world tree would just "be". There will certainly be lore and origin stories etc, of course, but there doesn't have to be a solid "and here is how this is possible" in there at all. Could be they are just discovering the truth or that someone does something to damage the tree. (that would be more interesting to me as a reader than hearing how the tree manages to exist!) Maybe that requires the first expedition outside of the dome to see what has happened.

When you say "world on a tree" thats the part I have trouble imagining in any fashion because I'm thinking of it as planet sized itself. A city, or a series of small towns under the dome, yes, that I can see. That would seem to be much like how the "world", to many ancient people, was only what they knew existed within a few miles or days travel around them.

Sun, moon etc. All can be the stuff of myth and legend to your people too. Stories told, perhaps, with a grain of truth in them.

I like to think of going back to the source material. Remembering that many of those world tree myths existed before there was any knowledge of the Earth as a sphere that existed in space and that orbited a fireball of a sun! Would they ever have created such a tree story if they knew the larger truth back then? I think, depending on the level of development in your world, that would inform where they might be as far as their own understanding of their existence and that is what I would try to stay true to. The dome does suggest high tech, but maybe that was a previous civilization?

Anyway, those are my first thoughts. I hope they can help!

Good luck!!

 

[enoch driscoll]

You could simply go full-on Discworld and explain everything with "because magic". It worked well enough for Discworld.

If you want actual pseudo-physics then I would suggest you look into flat-earth theory. There is a whole group of people who believe the earth is flat (hence flat-earth theory), and they have developed a physics system in which this would work (if you don't look too closely). You could "borrow" from them.

The main question I have, if you want to go the physics route, about the world tree is "What does the tree sit on"?

the flat earth society has followers all around the world.

 

[WooHooMan]

the flat earth society has followers all around the world.

What’s more: they’ve come up with their own ridiculous system of physics to justify their goofy nonsense. So, maybe that would be a good area to research?

 

[Avery Moore]

Definitely with the others in that, if the world exists in the branches of a tree, then you don't really need to worry about the physics of orbit and stuff like that. In fact, I'd suggest making the universe more fantastical by coming up with legends surrounding the sun and moon as well.

For instance, the sun and moon could be the spirits of a gold and silver dragon, locked forever in a mating ritual where the sun torments the moon by flying around the world to elude him, and the love stricken moon forever chases her, but is never able to catch up. The stars can be a vast collection of smaller female dragons who follow the moon in an attempt to gain his attention, but none of them can distract him from the beautiful sun.

... Or something like that. maybe research some old legends about the sun and moon and see if you can find something you like.

As for the tree having soil to support it, I'm not sure. From any images I can find of Yggdrasil, it typically doesn't seem to have any soil, but if you decide that the tree does grow in soil, you'd probably have to ask yourself the question, what would that soil be? Is it another planet? And if so, how does that planet effect your world. Maybe whenever an animal eats leaves from the tree, it causes an earthquake in your world? Or maybe the rain is really tears of a lonely giant standing over the tree? Fantastical worlds have so many possibilities. ^_^

 

[Riva]

Oh, just had another idea.
What if it's a normal tree and your world is like, very small; like a little fishtank stuck on a tree with insects and little people in it?

 

[Patrick-Leigh]

Maybe the tree roots are connected to some kind of primordial sea of chaotic energy that looks a bit like a nebula. As for the physics, if the tree is able to support an entire disk-shaped world, then just have it generate it's own gravity field that simply doesn't follow the normal rules. It's your story universe; you set the rules. I'm doing the same thing with the Transitory Planes in my own story setting. Each one has it's own laws of gravity that aren't like the laws of gravity in other planes. For example, in the Plane of Earth, gravity doesn't pull toward the center of mass, it pulls towards the walls of the tunnels and caverns. It's like being inside an O'Neill cylinder except the gravity is actual gravity, not a product of centrifugal force. Nobody (other than the gods) can account for why gravity works like that on the Plane of Earth beyond "it's a different universe with different rules."

I don't have a problem suspending my disbelief when it comes to stuff like that, especially when the concept is cool and fun. I say that having a disk-shaped world set atop a tree is too fun not to do, realistic physics be damned.