We see this interesting phenomenon with water bottles in cold chillers left undisturbed for a long time; the water within remains a liquid, but a small kinetic shock, such as a tap, shake or pour, causes the water to freeze rapidly before our eyes.
A friend of mine wanted to know; is this phenomenon possible with water cooled to absolute zero, or very near it? Can water remain liquid at these temperatures if left undisturbed?
The phenomenon is called supercooling:
A liquid crossing its standard freezing point will crystalize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid. Lacking any such nuclei, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs.[4]
Homogeneous nucleation can occur above the glass transition temperature, but if homogeneous nucleation has not occurred above that temperature, an amorphous (non-crystalline) solid will form.
This video illustrates experiment similar to the one discussed in the OP
However, as the second paragraph in the quote says, if cooled to a sufficiently low temperature the water would eventually freeze:
Water normally freezes at 273.15 K (0.0 °C; 32 °F), but it can be "supercooled" at standard pressure down to its crystal homogeneous nucleation at almost 224.8 K (−48.3 °C; −55.0 °F).[5][6] The process of supercooling requires water to be pure and free of nucleation sites, which can be achieved by processes like reverse osmosis or chemical demineralization, but the cooling itself does not require any specialised technique. If water is cooled at a rate on the order of 106 K/s, the crystal nucleation can be avoided and water becomes a glass—that is, an amorphous (non-crystalline) solid. Its glass transition temperature is much colder and harder to determine, but studies estimate it at about 136 K (−137 °C; −215 °F).[7] Glassy water can be heated up to approximately 150 K (−123 °C; −190 °F) without nucleation occurring.[6] In the range of temperatures between 150 and 231 K (−123 and −42.2 °C; −190 and −43.9 °F), experiments find only crystal ice.
Remark
In response to comments:
Supercooling should not be confused with freezing-point depression. Supercooling is the cooling of a liquid below its freezing point without it becoming solid. Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute; an example of this is the freezing point depression that occurs when salt is added to pure water.
Thus the example of sugar diluted in water and crystallizing on a spoon or the cup is freezing point depression. Note that the sugar here is below its melting temperature of about 185C.
NON-SOLID WATER BELOW 0 degrees Celsius
I assume you intended to say "absolute zero" as it would be explained by thermodynamics--as opposed to simply "freezing point."
From a theoretical perspective, technically, no it can't without defying the laws of physics. But someone did offer a practical explanation that resurrected the worst memories of Calculus I - wherein the limit approaches infinity as your value reaches zero. Of course, calculus makes it clear that it's technically impossible to reach zero; but immediately declares that any value that has reached its limit at nearly 0 is--for all intents & purposes--negligible and therefore zero.
I immediately think of Chemistry's "Heisenberg Uncertainty Pricinple" relating the speed of electrons (in orbit) to their known location within their shell. If we know their location, we don't know their speed; and knowing their speed prevents us from knowing their location. For kinematic measurements to work when [velocity=d1-d2/t], t, or time, must be a positive number. Unfortunately that means we don't know exactly where the electron is--simply that it exists somewhere between d1 & d2 like a blurred olympic sprinter during a photo finish. Alternatively, in order to know both the velocity & exact location of an electron in space & time, then time MUST equal zero. As the denominator...that's not ideal, because if t=0, the equation is 'undefined'; but mildly more upsetting is the fact that 'undefined' equations render time impossible with humans trapped in the void between 2 broken dimensions where objects neither travel, accelerate, or experience gravity--let alone perceive.
So for our world to function without our existence being unrecorded, we believe 2 measureable truths can coexist simultaneously and equally--albeit with some statistical probabilities sprinkled in to inch us closer to that pesky 'zero.'
Anyway...potassium & sodium salts are added to water (ice) across most roads in the world because road salt "lowers waters freezing point so that it is no longer capable of freezing at 0C. Thats a magical way of saying salts ionic bonds complex with ice molecules in a manner that disrupts their crystalline structure alignment across every dipole or hydrogen bond. Salt will then increase ice's density to a level thats higher than solid water and liquid fresh water--hence the bouyancy of salt water. If youve cooked, youve likely put salt in a pot of water to change when it boils. Pressure is a whole other essay, but obviously altitude (~atmospheric pressure) and closed pressure systems will have additional effects on water's molecular kinetic energy (prop. to speed & heat).
Also...Mg-based salts are used but they actually melt the salt via the heat emitted from resulting chemical reaction--which is entirely unlike typical road salt that doesn't change temp.
Physics cannot really answer that question, because:
a) nothing can ever be cooled down to absolute zero at the first place, therefore the subject of supercooling is undefined in that sense;
b) the distinction between solids (which have a definite shape and volume) and liquids (which have a definite volume, but take the shape of the container) would be lost at the absolute zero, as at that temperature all the movement of the molecules stops.
Even we consider temperatures near the absolute zero, it would also impossible to supercool water down there. Supercooled water could remain in the metastable liquid state because the density of liquid water in that temperature is higher than the density of ice. As we chill the water down more and more, its density lowers below the density of ice at the equivalent temperature and the supercooled water spontaneously crystallizes to hexagonal ice almost immediately since the energy barrier allowing the metastable state's existence disappears. Here is the plot of liquid water's density vs temperature:
By modifying the ambient pressure, the lowest supercooling could ever go down to is at around -92°C.
