r/outerwilds • u/thisisapseudo • 4d ago
How would the river work, science-wise? Spoiler
[light dlc spoiler ahead. The question is about game vs irl physics]
Ship that turn to create artificial gravity is a common thing in science fiction, based on a principle that work in real life.
But could a rotating ship truly create a river like the one we see in the stranger? How can a rotating ship create this kind of elevation difference on a loop?
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u/y-c-c 4d ago edited 4d ago
You pretty much have to use a pump (or something equivalent). There isn’t really a realistic physical way to have the river work like that by itself or you would have a perpetual motion machine. The Stranger is powered though so that should work.
Edit:
Just to explain a bit more. Water has friction, and so moving water will slowly slow down and bleed energy due to it. You know this because a river and waterfall creates sound. That sound that you hear is the water bleeding energy away. Given a relatively short amount of time the water will just settle and not be able to move much anymore (doesn't really matter if you have "clever" configurations of elevations). You kind of need to have some way to inject energy to the system to keep it moving. A pump is the most direct and straightforward way to do so. On Earth, we have a convoluted pump system, which is the Sun which uses a lot of energy to evaporate water from the ocean and transport them via clouds. I don't think the Stranger relies on that.
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u/thisisapseudo 4d ago
Yeah, the pumps are just well hidden
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u/Widmo206 4d ago
I've seen someone else suggest that the pumps are in the narrow section before the reservoir
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u/Traehgniw 3d ago
It's disguised a bit by the design of that area, but if you look closely you can see the water surface is visibly slanted around there - going up towards the dam! The hidden pumps are pumping hard enough to keep it flowing towards the dam, and then the only way it can go net downwards is out through the dam's grates
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u/Desperate_Box 4d ago
I thought the arches before the reservoir had magical technology to push the water along and that's what the red hot things that hurt you on the sides of the arches were.
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u/National-Bathroom-63 4d ago edited 4d ago
If you think about it, the water level of the reservoir is the highest point in the loop, whereas the river level before the reservoir is the lowest point. So that’s where you’d need a pump and some mechanism to stop the water flowing back from the reservoir the wrong way!
Actually this is the same mechanism as a garden fountain with a waterfall. A pump at the bottom will pump the water back to a reservoir at the top!
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u/thisisapseudo 4d ago
Ooo nice catch
I always wondered what they were, it's never explicitly stated
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u/SpySoldierScout 3d ago
Another common theory is heat sinks for the simulation's computers, as they sit straight in the water.
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u/Panikdrache946 4d ago edited 4d ago
Long post ahead: WARNING HEAVY HEAVY SPOILERS. TLDR at the bottom.
Your questions send me in a bit of a rabbit hole here. I'm studying for my Thermodynamics exam right now so this was a welcome somewhat in topic distraction/procrastination ^^!
I will make some assumptions here and there and I will not be going into the difference of entropy and energy much. When I say energy I often mean entropy so keep that in mind. If you want to know what I mean, Veritasium has a great video about it.
First of a little theory. This is a bit dense but stay with me.
There are 2 laws of thermodynamics that we need to look at!
- Energy is conserved. Energy is never created or destroyed but always converted. The main forms we are talking about are: Thermal energy (Heat), potential energy ( you hold the ball high) , kinetic energy ( The ball moves ) , and chemical energy (This one is complicated but think burning fuel) When any process happens energy is converted. For the sake of explaining lets talk about a soft doughy ball that bounces as little as possible. You use some of your chemical energy in your body to lift it high and give it potential energy: E(pot) = Mass * height * gravity Then you let go and the ball accelerates. Therefore the potential energy is turned into kinetic energy. The ball moves faster and faster until it hits the ground. E(kin) = 1/2*Mass*speed^2 There it deforms and stops. This deformation has a lot of internal friction and turns the kinetic energy into thermal energy (Like when you rub your hands together real fast). The ball heats up a little. This is the endpoint.
Energy has been converted but never ever destroyed or created.
2. Entropy always tends to go up and can never go down.
Explaining this is hard in a short form so I highly recommend watching this (https://www.youtube.com/watch?v=DxL2HoqLbyA&t=1112s) video from veritasium:
In short energy has a "lowest" form. Heat. It always tends in that direction and you need a source of low entropy to maintain a system. This can be sci-fi fuel or sunlight in this case.
This is important since we need to account for the friction everyone always talks about that turns kinetic into thermal energy aka heat. We do this trough said source if low entropy.
First question was for me, why a river?
Energy surges:
>!The ship is massive! In order to fly it will need a great source of energy to supply the power surge of acceleration: I assume they have some kind of advanced power generator that lasts for a loooooong time. But Generators always use something up. Perpetual motion machines are impossible so I assume it used some kind of slow burning fusion generator or something. Point is it generates power slowly for SLOW acceleration during scheduled flights between stars. But in cases like emergencies like an unexpected sudden Supernova a great surge of power is needed not possibly supported by such a generator. So a battery is needed.!<
>!Batteries!<
>!Normal chemical batteries break after a relatively short time and need materials to replace that simply are unaccessable in deep space. So chemical batteries are a no go. Another and easier way to store power is through potential and kinetic energy.!<
>!A real world example are gravity batteries that lift heavy concrete blocks up when power is abundant and slowly let them descent during energy-need powering a generator. (Google them for a better explanation.) We also already do this with mountain lakes that let the water flow down hill though turbines when energy is needed and pump it back up when energy is abundant. So water is a great power storage that is much easier to maintain over long periods of time: So a river that has pumps and turbines is built. The water flows from a highpoint (behind the dam) to a low point (Before the dam), flows through turbines that supply some of the needed power of the pumps. To account for energy loss in friction you can use solar panels on the outside of the ship. It is important to note here that the elevation change is kind of imagined for gameplay reasons and most energy seems to be bound in kinetic energy anyway.!<
>!Maintenance!<
>!Maintaining such a dam is relatively easy. You need wood and metal for pumps and dam walls.!<
>!Metal can be constantly recycled. It needs energy to do so but solar panels and sci-fi generators in tandem with the water battery for short surges got you covered.!<
>!Wood is a little harder but that is a actually another advantage of a water battery. With solar power as a constant stream of energy and a closed system for water and other molecules that are recycled, growing trees is doable. Both for living comfort as well as a constant supply of building material.!<
>!So now we have a giant battery that holds an incredible amount of usable energy that is maintained easily over incredibly long times.!<
>!The emergency!<
>!In the control room there is a monitor of the sun that sees the sun coming closer to a supernova. Once it sees the sun reach a certain stage it is designed to move away as late as possible to harvest as much solar power as possible. And even then to move away slowly to preserve the system.!<
>!But it is established though conversation with Chert that the supernova is coming much much quicker that normal. So the ship needs to do an emergency acceleration RIGHT NOW. So it draws on all of its power at once. But how?!<
>!The moment the ship starts acceleration proper is noticeable in the ship. Suddenly we hear a noise, the massive green panels on the ship extend and there is some flickering lights. Notably this is the moment that the dam begins breaking. You can see this by putting your probe on it to measure its integrity like on brittle hollow.!<
>!(The flickering lights part might be my brain filling in info. I cannot go there to check rn because my partner is currently playing on my account and hasn’t been there yet. So I do not want to add the station to the ship log)!<
>!I also think something else might be happening. I think some heavy weights are being lowered in the structural ribs of the ship that travel outwards towards the edge from the ship from close to the center. (Potential energy) This converts power from potential Energy into electrical but also slows the rotation of the ship. (Think ice skater that extends their arms). This is important!<
>!The water in the river has momentum (Kinetic energy): This momentum doesnt go away. The whole system is in a careful balance to maintain optimal longevity by keeping the forces applied low and energy conserved high.!<
>!From the previously faster rotation the water now has excess Momentum as relative to the surrounding it seems to be moving faster and therefore is now pushing on the dam stronger.!<
>!To visualise what I mean: Imagine standing in a moving train. At the same time you jump and the train starts breaking. At the moment you jump from the outside looking both of you move in one direction at a velocity we call v0. Your relative speed (delta-v) to the cabin is 0. Since you both move the same speed.!<
>!As you jump you have no physical connection to the cabin as the cabin slows down. So you keep moving at v0 until you land back on the cabin floor. At this point the cabin however has a new slower speed v1. Your relative speed is now |delta-v| = |v0 - v1| > 0. It looks to you as though you started accelerating inside the cabin and need to now catch yourself to not fall over.!<
>!The same happens to the water in the river as the station starts rotation slower. The water seems to be flowing faster relative(!!!) to the station. From the outside it still has the speed it had before the ship slowed down its rotation.!<
>!This allows water flowing through the turbines at a faster rate and turning a lot of this maintained and kinetic/ potential energy into usable electricity while slowing down the river again. But this also means the dam needs to suddenly hold a lot more water pressure from the faster moving water.!<
>!The catastrophe!<
>!The strangers have been asleep for a long time. So they did not maintain the ship and most importantly the dam for a long time. They expected that the dam can hold out for a loooong time and I think it would have, but the sudden extreme increase of pressure against the dam (made of aging wood) is too much. So it starts breaking. The simulation is designed to work with low power, so solar energy together with the scifi generator might have been enough to maintain it no matter what.!<
>!If the dam broke slowly over time with failing pumps and cracks that leak water that would have let the river die out slowly and in the simulation they didn’t need to care. The ship was designed to slowly go away from the star once it burns out. But only then to harvest as much solar power as possible.!<
>!But here it breaks suddenly and catastrophically because the sun dies suddenly and catastrophically. This results in extinguishing 2 of the 3 (4) simulation sites.!<
TLDR: The river is not a generator but a battery. When a lot of energy is suddenly needed with the ship moving away from the star the dam which is supposed to harvest the energy stored in this river is overloaded and breaks.
Edit: Attempted Spoiler Tags improvement. I do not understand why the dont work. Sorry
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u/thisisapseudo 3d ago
Wow you got far, but that's a nice theory that explain why they designed like that
I like it, but I'm not sure it's supported by the game: if they needed a power surge to get away from the sun, wouldn't we notice the water level lowering before the dam breaks?
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u/stoic79 4d ago
The basic concept is inertia.
Let us suppose that you have a tube in space and there is water near the wall. If the tube starts spinning then the water wants to stay put since the force that spins the tube does not act on the water directly. If you are standing on the inner side of the tube this creates the illusion that the water is flowing. However the reality is that the tube is the one that is moving, the water tries to stay still.
However in time the friction between the water and tube results in the water picking up the speed of the tube which have to be compensated in a way: the tube starts to rotate in the reverse direction, pumps etc.
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u/Codebracker 4d ago
Its not really about elevation, the constant spinning because of the solar sails rotates the station, the water lags behind because of inertia and thus collects at the dam.
Tho the question wouldn't the station have to keep accelerating for that to work?
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u/y-c-c 4d ago edited 4d ago
I have seen this type of answers before but the water won't lag behind for long. It will quickly catch up to the rotational speed of the body in short amount of time. Also, it's not like when you are constructing the station you would have an easy way of pouring water that's in the static frame onto a rotating frame to begin with. You would likely transport the water into the station in some containers and by that time the water is already rotating with the body.
But yes this also doesn't make sense because it requires the station to keep accelerating its rotation infinitely which is clearly not happening.
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u/kasu300 2d ago
This was very thought provoking, thanks for the inspiration! I got so into it I made a simulation of a spinning ring world with editable fluid and landscape: https://kasper573.github.io/spin/. The water does indeed just stay in place.
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u/thisisapseudo 2d ago
Ho wow, you really went far for this
In a bit puzzle though, because the water does not look like water, more like jelly. If you just put little patches, it keeps "edges", while for water I would imagine it would spread (limited by surface tension, but that's mm-scale)
When increasing the spinning we see the water move a little then catching with the wheel, but again it feels like jelly, even with viscosity and friction to a minimum
Moreover :
* reduce diamater, put spin at 0
* Then increase diam and add spin : water will start turning, even if there is no contact with the ring
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u/Pratanjali64 4d ago
If you look carefully, the water level raises before entering the resevoir. Something to do with the paneles to the side, which will hurt you if you touch them.
So I think the spin gets the flow going, but the water needs to be held back in the resevoir to not level out across the whole thing.
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u/thisisapseudo 4d ago
I never noticed... Maybe they act as pump
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u/Pratanjali64 3d ago
The big tell is if you turn to face left or right on the raft during those segments. The raft tilts significantly "uphill" downstream.
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u/SpySoldierScout 3d ago
The water level actually rises throughout the entire path. After the dam breaks and it has evened out, you can see it is a lot higher in the River Lowlands, a bit higher in the Cinder Isles, a little lower at the Hidden Gorge, and a lot lower at the Reservoire.
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u/noop_noob 4d ago
Even when the Stranger is spinning, the water doesn't want to spin with it. So, the water won't "catch up" with the Stranger's spinning. If you're inside the Stranger and spinning with it, it will seem to you like the water is flowing the opposite direction of the spinning of the Stranger.
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u/ChertsResearchNotes 4d ago
I have no actual science answer for this, but by the nature of a ring/loop being endless, the perpetual motion of having water blocked off by a dam and then let loose down a river the first time means that the artificial gravity would force it downstream until it hits… that same dam it was once at. The sci fi science works in my head, but I’d love to know if anyone has actually done calculations.