[ELI5] Can one physically compress water, like with a cyclinder of water with a hydraulic press on the top, completely water tight, pressing down on it, and what would happen to the water?

Question

[ELI5] Can one physically compress water, like with a cyclinder of water with a hydraulic press on the top, completely water tight, pressing down on it, and what would happen to the water?

In: 1967

Answer 1

Ok, so far everyone’s given you the boring engineer answer that water is practically incompressible.

Key word *practically.* Rather than an engineer, let’s think like a physicist and assume we have an indestructible vacuum-sealed press that has no limit on how much force it can output. What would happen?

Well, as much as water seems incompressible from our limited, primitive, earth perspective, one rule of physics is that everything is basically a gas when your forces are large enough. As you increased the pressure, your liquid water would slowly transition through several increasingly exotic forms of ice, characterized by different molecular structures. (You might envision “ice” as being cold, but rest assured it would get *very* hot and glowy)

…But let’s really ramp things up. Once we’re at several hundred million times the pressure of a real hydraulic press, the ice would start to undergo nuclear fusion. In other words, the electromagnetic force pushing atoms apart would no longer be able to oppose the pressure, and nuclei would begin to merge. At this point you basically have a small star in your hydraulic press

…But let’s *really* ramp things up. If you increase the pressure another thousand trillion times or so, electrons can no longer maintain their energy levels, and their charge neutralizes with that of protons to leave only neutrons. Atoms don’t exist as a whole anymore, and now we have all this empty space between nuclei, so we keep compressing. Ultimately, we get neutron degenerate matter. This is what neutron stars are made of. We’ve now compressed our “water” to the size of a handful of atoms, and at this point we’re opposed by something called “neutron degeneracy pressure”, which arises from the nuclear forces that hold quarks together.

If we apply more pressure to overcome this force, we get a black hole. It would be a tiny black hole, and thanks to Hawking radiation would evaporate into a burst of photons and neutrinos within less than a billionth of a second of its creation.

Edit: Since this has become the top answer, let me shout out my favorite blog [XKCD What If?](https://what-if.xkcd.com/archive/). Check it out of you want more scientific answers to absurd hypotheticals (only better written and illustrated).