Can You Float a Liquid on a Gas?
Why Worldbuilding Stack Exchange recommends it
Worldbuilding Stack Exchange answerers point people to it as real-world evidence for physically odd setups like floating lakes, ceiling oceans and flying creatures in dense atmospheres.
Recommended by 1 people across 1 different months, 2017 to 2023.
What it is
Cody's Lab seals very dense xenon in a tube under high pressure to test whether a liquid can actually float on top of a gas. The experiment explores supercritical xenon, which can reach the density of water, and shows what happens when it meets water and other liquids.
What people said
Recommends Someone Else 37 · 2018-02 · Worldbuilding Stack Exchange · on “How to put a lake on the ceiling?”
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 [this video] . 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 [LINK] , which combines properties of liquids and gases. However, to Joe A. Venture, it'll look enough like a gas for
Cites Samwise · 2017-07 · Worldbuilding Stack Exchange · on “Can lava still be red hot liquid underwater?”
Sadly Cody from *Cody's Lab* [this video] tried something like this (the water + high density xenon, not the volcano) and found that the xenon dissolved *into* the water when under high pressure and made it freeze *at room temperature*. So unless the entire ocean is Xenon, it might not work so well.
Cites Willk · 2017-08 · Worldbuilding Stack Exchange · on “How would a noble gas lake form on an earth-like world?”
Radon is a noble gas. Radon coming up from the earth could form a lake. In fact, radon pooling in low points and buildings with poor air exchange poses a real human health hazard. Maybe there are radon lakes deep in the earth! from [LINK] (bold emphasis mine) Radioactive heavy metal elements uranium and thorium are dispersed throughout the Earth's crust. They very slowly disintegrate into lighter radioactive metals, including radium, the precursor of radon gas. Since the half-life of uranium and thorium is billions of years, the Earth will produce a never-ending supply of radon gas . Radon Element When radium atoms disintegrate into alpha particles and atoms of radon, 10 to 50 percent of the
Cites Logan R. Kearsley · 2017-11 · Worldbuilding Stack Exchange · on “How dense of an atmosphere do I need to "float" an ocean of liquid at 1000 ft elevation?”
There are several pairs of liquids and gasses where the gas is more dense, and thus the liquid will float on it... for a while at least, as in many cases one will dissolve into the other, which ruins the effect! There is only one pair that I know of in which the gas will not dissolve into the liquid, and in which this effect has in fact been practically demonstrated (and in a YouTube video, no less! Can You Float a Liquid on a Gas? [this video] ): Supercritical xenon, and liquid NaK alloy. (Technically, supercritical xenon isn't actually a gas , but close enough!) This works because NaK is a super light metal with a very low melting point, xenon is a really heavy gas, xenon doesn't dissolve in or
Cites Someone Else 37 · 2019-09 · Worldbuilding Stack Exchange · on “What would be needed to scientifically be able to stand on cloud?”
Little-known science fact: It's actually possible to have a gas that's denser than water at room temperature. Well, almost. At the pressure required, it'll technically be a supercritical fluid, which will act like a gas in many ways. Specifically, you'll want to use supercritical xenon. At something like 100 atmospheres of pressure, xenon actually becomes denser than water, as demonstrated in this Cody's Lab video [this video] . Caveats: Pure water won't actually float on this, as the xenon will dissolve into it and form a clathrate, causing it to freeze. Adding alcohol to the water, though, will prevent this from happening, so you could have floating lakes of vodka. This environment will be quit
Cites Willk · 2020-03 · Worldbuilding Stack Exchange · on “In what conditions could whales fly?”
High density atmosphere. Whales can do what they do because they are neutrally buoyant. The water they are in buoys up their great mass and so they are weightless. They are not massless and so still must propel themselves around, but the great oppression of gravity is alleviated. If the mass of a thing is less than the mass of the volume of atmosphere it displaces, that thing will float. True for a whale in water, true for a helium balloon in air. Let us assume whale-like whales, not some hydrogen balloon creatures which although awesome would be unwhalelike. Venus has a high pressure atmosphere [LINK] - 93 bar so about 93x our atmospheric pressure. But that still yields gas only about 5% th
Cites Mark Morgan Lloyd · 2023-09 · Worldbuilding Stack Exchange · on “An atmosphere that gets denser with increasing altitude, to support these flying creatures”
This [this video] from Cody's Lab on YouTube demonstrates that it might be possible to float a layer of water (etc.) above gaseous Xenon, but it needs silly pressures to do so. But you might be better off simply waving your hands along the lines of "while the antigravapods are able to float a few feet above the ground they lost their sentience billions of years ago, so it's not possible to ask them how they do it".