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Another user's answer to a recent question, specifically the way it was worded, gave me a vision I cannot shake.

Our intrepid adventurer, Joe A. Venture, is making his way through a subterranean network of caves and comes upon a small stream. He follows the stream and arrives in a large chamber. Here, the stream transitions from the floor by his feet to the wall and ascends to a glimmering expanse of water stretched across the ceiling, rippling and flowing as any body of water exposed to wind or current.

A quick search reveals that, maybe, it is indeed possible that the water in a cavern (or other enclosed environment) could rise up to the ceiling. The linked experiment utilizes sound waves to levitate water droplets, but can this effect be scaled (via sound or other means, naturally or artificially)?

Is it possible to put a lake on the ceiling, and how is it done?

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    $\begingroup$ Yup! Put it in glass pipes and pump it into a glass tank on the ceiling! ;P $\endgroup$ – Muuski Feb 12 '18 at 20:03
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    $\begingroup$ You tagged it with gravity, do you want gravity based answers? If not, is this tag relevant? Either way, how stable you want / need solutions to be? $\endgroup$ – Mołot Feb 12 '18 at 20:11
  • $\begingroup$ I had the thought of using a gas with a density greater than water, but according to this Chemistry SE question, even the heaviest gases are about a hundred times lighter than water. $\endgroup$ – Jakob Lovern Feb 12 '18 at 20:15
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    $\begingroup$ Joe is a human, not a crab or other thing that walks in salt water, right? There are less salty pockets that float on saltier water in some caves. $\endgroup$ – user25818 Feb 12 '18 at 20:30
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    $\begingroup$ I wonder if you'd be satisfied with an optical illusion, where the lake wasn't really above you, but appeared to be so because light was taking a strange path to your eyes? (Most obviously: just use mirrors. But that one's boring, and it's hard to get the river-up-the-wall effect. Maybe something more exotic that can smoothly curve light paths, but I'm not sure what it would be.) $\endgroup$ – Ben Millwood Feb 15 '18 at 16:14

16 Answers 16

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The River and the Lake are not water. The fluid is actually a non-Newtonian ferrofluid, which is to say it is a fluid that has magnetic properties. The ceiling of the cave is comprised out of some sort of naturally occurring magnetic lodestone. enter image description here

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    $\begingroup$ This is the one thing that might actually work. A strong magnetic field wouldn't necessarily be felt by someone a few meters away (high ceiling) and nothing about this turns the ceiling into a floor. $\endgroup$ – ShadoCat Feb 14 '18 at 0:58
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    $\begingroup$ I thought that was ferrofluid. Non-Newtonian fluids have other nifty properties, but are not necessarily magnetic. $\endgroup$ – The Spooniest Feb 14 '18 at 14:41
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    $\begingroup$ A fluid can have both properties, I kinda figured being non-newtonian as well as a ferro fluid could help prevent the "lake" from just dripping off the magnetic cieling when it got too "deep." $\endgroup$ – TCAT117 Feb 14 '18 at 15:16
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I'm going to say yes.

Joe is actually in a rotating space habitat (I don't know how he got there, that would be the story). Upon exiting the narrow tunnel he can see the water "above" him on the opposite side of the round rotating habitat, if he were to walk forward the "wall" would become the floor and then the "ceiling" would also continue to feel down from the centrifugal artificial gravity, but from his current position it looks like it is on the ceiling.

Paint picture for reference:

enter image description here

note: not to scale or otherwise accurate at all.

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    $\begingroup$ This answer was made even better by the comments on OP about if the gravity tag was out of place. $\endgroup$ – Loduwijk Feb 12 '18 at 23:40
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    $\begingroup$ That fantastic sketch really makes this answer. Such art! $\endgroup$ – Roddy of the Frozen Peas Feb 13 '18 at 0:39
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    $\begingroup$ You'd need additional relief to prevent the water from just coating around the whole circle though. $\endgroup$ – Quentin Feb 13 '18 at 13:02
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    $\begingroup$ @Quentin please see the note on the figure, but yes you would probably need some very specific topography to make the water pool in one location and look like a lake on the ceiling of a cave. Someone is obviously going to great lengths to mess with Joe. $\endgroup$ – Josh King Feb 13 '18 at 14:45
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    $\begingroup$ Is he surfing, there? $\endgroup$ – David Richerby Feb 13 '18 at 15:59
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Yep, you can definitely have a lake, or at least something that looks like a lake, on a ceiling!

Option 1: Superfluids are incredibly weird.

Basically, a superfluid, such as liquid helium-4, has zero viscosity. In other words, it can flow without losing energy. This allows it to 'flow' along all the surfaces of a container until the liquid reaches an equal level within the entire closed system that it resides in, and cover every reachable surface in the container to form something called a Rollin film. If the fluid happens to be in an open container above the equilibrium level within a larger container, then it will continuously flow along the walls and ceilings of the higher container until it escapes into the lower area. Here is an example, where the liquid in the suspended container is flowing up and over the side, dripping down into the pool below:

enter image description here

So, if you had a regular superfluid lake in a chamber of some cave, and that cave was connected to some lower chamber, then superfluid would flow down to the lower chamber, giving Joe a river to follow. Once it reach the lower chamber, it will continue flowing along the walls of the lower chamber, and then flow and ripple along the ceiling. Some of the fluid would come to rest on the ceiling as it forms the Rollin film, or continue flowing if it can escape to yet another container. If the fluid film along the ceiling was opaque/thick enough then it would certainly look like a gently rippling lake.

Unfortunately there would be a film along all the walls and floor as well, but you would at least have some amount of lake on the ceiling if the lake was a superfluid. How Joe is surviving in a cave that is only 2 kelvin is another matter, and somehow even more impressive.

Option 2: Regular fluids can look weird.

Another way to get a 'lake' on a ceiling is by having the entire cave filled with water, but the river Joe is following is saltwater and the cave has some amount of freshwater. This results in a halocline, an area where two fluids of different densities meet but do not easily mix without turbulence.

Although it might no quite be a 'lake on ceiling, air below', it certainly could look like a ceiling lake:

Halocline Example

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    $\begingroup$ What do you mean by "until it reaches an equal level within that container"? Equal to what? And "if the level is below the current, open container"? Level of what, the surface of the superfluid? And what does it mean to be "below the container"? I am trying to picture in my head some magic water in a mason jar behaving as you describe, but those sentences do not make sense in that context - I think you are missing some words. For my visual imagery: below the bottom of the jar or the top rim? I cannot understand at all what "equal level within that container" means in this case. $\endgroup$ – Loduwijk Feb 12 '18 at 23:31
  • $\begingroup$ @Aaron: if you look at the image at the end of this comment, you can see a visual of it. Essentially, the level of the fluid can flow up and out of its container and into another container, and will do so until the fluid's level in the entire closed system is equal. I'll update the answer with a bit more explanation. en.wikipedia.org/wiki/Superfluid_helium-4#/media/… $\endgroup$ – Giter Feb 13 '18 at 0:19
  • $\begingroup$ I think we can safely assume that "lake" means "body of water", not "body of supercooled helium-4", especially since Joe walks into the chamber and is not instantly snap-frozen by the near-absolute zero ambient temperature that would be required to maintain helium in a liquid state. $\endgroup$ – Bohemian Feb 13 '18 at 6:33
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    $\begingroup$ "How Joe is surviving in a cave that is only 2 kelvin is another matter, and somehow even more impressive" +1 $\endgroup$ – r41n Feb 13 '18 at 7:26
  • $\begingroup$ On the note of Option 2 in Blue Planet II they discovered a Brine lake in the sea that had formed. It definitely looks like a lake, though normal one not ceiling. Reversing the amounts i.e. more brine than sea water should reverse the effect thought and you'd have the ceiling lake. $\endgroup$ – TheLethalCarrot Feb 13 '18 at 11:55
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Not without handwavium

The video of the water levitation thing is actually a pretty cool physics effect, but it's predicated on sound wave pressure zones. Note how the water only hovers in little areas? It's because there are literal sound waves keeping them there. When droplets get too large, they rupture. I won't go into too much detail because I'll inevitably derail, but in order to use that, you'd have to make a very low pitch tone, and make it very loud. You wouldn't have the 'upside down ocean' effect, either. You'd just have a big hovering dewdrop.

Another solution would be to have something under the water that buoys it up. Unfortunately, gases are out; the highest density gases, according to the brains in Chem SE, clock in at only $13 \frac{kg}{m^3}$, while water is an even $1000\frac{kg}{m^3}$. That solution is out.

Water isn't especially ferrous, so you couldn't just pop a huge (electro)magnet on the ceiling and call it good. Even if you used ferrofluid instead of water (ooh, imagine black rivers!) you'd get the telltale signs of magnetic fields on the surface of the lake, which would spoil the effect.

As for the other three fundamental forces... Well, the weak force is weak, the strong force isn't strong enough, and gravity defines the idea of 'ceiling' for Joe.

There goes hard science. Time for...

A dash of handwavium

Really, see ShadoCat's answer for this one. Basically, you could use biology to put ceiling growing life down that appears to be a lake on the ceiling.

The other approach is to fudge some of the properties of water and use an answer from the 'no handwavium' section.

Unfortunately, these both suffer from one key issue in your vision: liquid going from a stream in the floor and dumping into the sky. This one isn't really possible without magic, because physics would use an inverse square law sort of approach to your effect (meaning that the water would become a vapor as it approached before finally transitioning to a stream on the ceiling) and biology would use tentacles or feelers or something to suck up water.

Lots of handwavium

Magic is now on the table. With magic comes area effects and effects that only target certain classes of items. Now you have a lake on the ceiling. Congratulations.

Postscript

There's one more trick you can use for the lake on the ceiling thing. Mushrooms. Specifically, hallucinogenic spore release combined with subliminal priming could initiate a lucid dream state wherein Joe believes he's encountered all the wonders you've described, but is actually tripping out and getting dissolved by a plant monster. Ah, the wonders of drugs!

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No but you might be able to make it appear that there is a lake on the ceiling.

Here's why it won't work:

There is a vast difference between levitating a water droplet and levitating enough water to create a lake. The water droplet is suspended in the wave trough of the the sound. Also, the water droplet is small enough that its surface tension is strong enough to hold it together against the forces acting on it.

Sound waves that we can create are just aren't big enough to support a water droplet the size of a lake and reflection off of the solid surface of the ceiling would likely interfere with the waveform. Also, the surface tension of a lake is not likely strong enough to hold it together under the weight of all the water.

Finally, any force that is strong enough and evenly widespread enough to push the water to the ceiling, is strong enough to make the ceiling the local "down." It wouldn't appear to be the ceiling when you are walking/swimming on it.

One thing that could make a lake appear to be on the ceiling would be to have a mold or fungus that has microscopic fine hairs. Those hairs can be hydrophilic, holding a thin layer of water. The water layer would be thin enough that the hairs could hold it against the weight of the water itself. So, no actual lake but the layer of water could look like a lake surface.

Another option would be to have a clear mold living on the ceiling. It's jelly like composition would allow it to be deeper than a thin layer of water. It might also break loose if subjected to vibration (not fun for the explorers).

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  • $\begingroup$ I have mixed feeling about this. It explains why OP can't use what he read about,but at the same time it does not tell how to really do it, $\endgroup$ – Mołot Feb 12 '18 at 20:30
  • $\begingroup$ @Mołot, I know. The closest I could come is to show how it would appear to be on the ceiling. Anything that I came up with to put a lake on the ceiling turned the ceiling into the floor. $\endgroup$ – ShadoCat Feb 12 '18 at 20:34
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Not liquid, but seemingly so.

A strata of a slightly translucent blue stone (something like thisSynthetic clinopyroxene grown from lithium vanadate flux

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  • $\begingroup$ What kind of stone is that? $\endgroup$ – Haunt_House Feb 13 '18 at 4:31
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    $\begingroup$ Synthetic clinopyroxene grown from lithium vanadate flux $\endgroup$ – SeanC Feb 13 '18 at 12:04
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You're not going to get this to work at atmospheric pressure, or if you insist on the air in the cave being composed of mostly nitrogen, but is is possible to get water to float on top of a gas. Or, at least, something close enough to a gas.

Enter supercritical xenon.

Xenon is an extremely dense gas at atmospheric pressure (as far as gases go, at least); but at pressures around 6-7 megapascals (60-70 atmospheres, roughly), its density at room temperature reaches that of water. Granted, at this pressure, xenon is not technically a gas, but rather a supercritical fluid, which combines properties of liquids and gases. However, to Joe A. Venture, it'll look enough like a gas for the water above him to look like an upside-down lake. An extremely dense gas that he may well be able to float in if his pressure suit isn't too heavy. And he will need a pressure suit- an atmospheric diving suit rated to 600-700 meters of water on Earth, to be precise, both because of the pressure and because xenon is a powerful anesthetic.

Also, pressurized xenon has a tendency to form solid clathrates with water. However, as shown in that Cody's Lab video, adding large amounts of alcohol to the water seems to prevent this- and, as a bonus, doing so lowers the density a bit and keeps the xenon from dissolving into the water-alcohol solution to the point that it becomes too dense and sinks.

So. A cave filled with xenon gas at 60-70 atmospheres of pressure, with a lake of 150-proof vodka on the ceiling. A sight to behold, I am sure.

Although I'm not sure you could have a stream of alcohol flowing along the floor of a cavern that then rises up to the ceiling at some point and continues flowing. More likely, it'd just form a floating pool at the altitude where its density exactly matches the surrounding xenon. Which would be a pretty interesting sight as well- xenon above, xenon below, and a layer of alcohol floating in the middle.

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  • $\begingroup$ Impressive thinking! $\endgroup$ – Stilez Feb 14 '18 at 10:30
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The cave could be empty and dry with ice above, and water over that. The cave-in beneath the ice could have made a cave, and above there is water on the other side of ice. A leak could allow water to flow away, but not up to the ice-bottom pond.

Of course, getting the ice on the bottom would require a body of water to have been frozen solid, and the temperature on the top would have to be greater than the temperature below, which must be kept freezing.

So a lake or pond freezes, then a sink-hole happens underneath, then the surface begins to melt. A leak forms and water pours into the cave.

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This is an out of the box answer.

Perhaps Joe's perspective is that the water is on the ceiling, when in fact, due to "reasons", he is the one on the ceiling. Some static or sticky or biological reason, his feet are being held to the surface his feet are on. Unbeknownst to him the last several meters of the tunnel leading in, he has been guided to walk up the wall to the ceiling by an optical illusion in the terrain. Now in the cavern, the water is puddled on the floor and he is suspended above it.

Holding the weight and unit count of a single human to a ceiling seems easier than a body of water particles.

Special Thanks to @Josh King for the wonderful picture![enter image description here]1

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A) Ultradense microdeposits

For gravitational attraction, distance is more important than mass. Normally small specks of matter simply aren't dense enough to override the influence or a much larger speck of matter (the planet) even though they are much closer. If however there was a material that was significantly more dense yet still stable then there would be zone around the material where its limited mass would override planetary gravity. Small pieces of this material would essentially function as gravitational magnets. A wall and ceiling lined with enough of these should allow a limited sheet of water to climb up the wall and flow along the ceiling. The water would flow to the lowest point on the ceiling and descent back to the ground there. The ascent could be helped along by capillary structures on the wall. I don't know how thick you could make that layer of water, though. And you do have to deal with the problem that these microdeposits would also be very mass rich (heavy) and thus strongly inclined to fall from the ceiling. Also this would probably have to be an artificial phenomena. Furthermore putting too many of these together could be a very bad idea.

B) Uncommon habitat shapes

A hollow sphere of sufficient mass and size could theoretically be inhabited on the inside. A sufficiently large ocean on the other side would in that case appear to float above the inhabitants. This however is on a much larger scale than you envisioned.

Similarly donut-shaped planets are mathematically possible but with some serious downsides.

C) Halocline

A diver swimming above a halocline Fully realistic (cool!) and already mentioned but covers only part of your intended scenario. It's possible for a sea of low salinity to exist on top of a sea of high salinity water. If your explorer is swimming through a underground cavern of high salinity (his natural habitat?) and enters a cave with a low salinity layer on top he would probably interpret this as a lake of (non-habitat element) at the ceiling. There's no reason why you can't have the same effect between other mediums than just different water (well, like air and water) but outside really exotic cirumstances it's not possible to have the liquid on top.

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The lake is not made of water. Or, the air is not made of nitrogen, oxygen and carbon dioxide.

Theoretically, if the shimmering, glistening liquid on the ceiling of the cave had a density that was less that of air, it would float above the air in the cave like oil on water:

water density graph

There are some ultralight materials out there already like aerogel.

Similarly there are some ultradense gases out there like sulfur hexaflouride, pictured here with a foil boat floating on top of it. Note that if the gas was indeed an ultradense gas, then when Joe steps into it he will rapidly begin to asphyxiate due to lack of oxygen.

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    $\begingroup$ There is a hard-ish SF book from the 1950s or so where a crazy atmosphere includes something, I think methane, precipitating out as snow that falls up. Or maybe CO2. Certainly there are mixes of atmospheric gases where you could arrange for a light liquid flowing up. $\endgroup$ – arp Feb 12 '18 at 22:41
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If the liquid doesn't have to be pure water, you might consider a lake of ferrofluids (and here is a link discussing creating a water based ferrofluid). A magnetic field could suspend it above your adventurer with a minimum of handwavium. If it's anything like typical ferrofluids we make, it would be black and thus quite creepy. The surface might also appear "spikey".

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If the surface of the wall and the ceiling were some sort of extreme-hydrophile you might get a very thin layer of water on the ceiling. We're talking so hydrophilic that the water prefers to stick to this surface than to other water molecules. Any less hydrophilic than that, and the water clumps together into droplets heavy enough that they fall to the ground.

The water is still not likely to actually 'flow' up the wall, unless it had a lot of momentum when it reached it. More likely, you get spray condensing into these 'microdroplets' on the ceiling and flowing down the wall - an optical illusion might make it look like it was going the other way though?

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I think Joe can achieve this by reaching the center of a coreless planet. Near its center, he will experience gravity around him, so will the water. We can now imagine that around the center, the water will flow on the walls, on the ceiling but also on the floor.

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    $\begingroup$ Coreless planet is not a planet by definition of a planet. Apart from that en.wikipedia.org/wiki/Shell_theorem says that in empty space at the center of such body he would feel no gravity at all, in any direction. That said, water would indeed probably stick to the walls. It's only that "floor" and "ceiling" are meaningless. $\endgroup$ – Mołot Feb 13 '18 at 23:29
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A combination of surface tension and static electricity might do the trick.

Imagine a ceiling made out of a mesh of thin hair like rods with the same refractive index as water. These rods are close enough so the water bonds between it due to surface tension and doesn't fall down. Same like brushes can hold liquids and it doens't fall down(below a certain volume of course) Brushesh

To help against gravity there's also a source of static electricty, pulling the water "up" against ceiling.

Water bending

natural airflow ill cause ripples and effect, and the rods will be hidden due to the refractive index.

refractive index hiding rod

This all together could work to maintain it, with a slow source feeding water into it to battle evaporation.

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  • $\begingroup$ Huge surface tension (is there anything clingier than water?) plus gecko-scale nano-hairs plus extremely cold ceiling that causes condensation to compensate for evaporation? Or some kind of oil "floating" on (under?) the water ...? $\endgroup$ – Will Crawford Feb 15 '18 at 3:17
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Gravity occurs because of huge mass. So above the ceiling there must be something that dense, that gravity turns around close to it.

Hopefully Joe doesn't get caught by the opposite gravity...

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  • $\begingroup$ This question is tagged as science based. Could you provide some science about your proposed solution? For example how dense this material would have to be, how would a cave not collapse, and how could he not get caught by the opposite gravity? Some math?.. $\endgroup$ – Mołot Feb 15 '18 at 14:07

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