The enduring mystery of how water freezes | Hacker News Reader

The enduring mystery of how water freezes

quantamagazine.org

231 pointsTomte83 comments

Interestingly liquid water also has negative thermal expansion between 0 and 3.98°C. This means that natural convection ("heat rises") is reversed in cold water.

https://en.m.wikipedia.org/wiki/Negative_thermal_expansion

And for this reason ice floats on water as it’s one of those rare materials whose density decreases as it solidifies.

Because ice floats and is an excellent insulator rivers and lakes don’t completely freeze up enabling aquatic life to continue to thrive beneath while the surface remains frozen.

If ice didn't float, life as we know it wouldn't be possible anywhere in the universe. (It doesn't exclude life that doesn't require water, though—if that's possible.)

Ice freezing and sinking would be an issue on earth, but the habitable zone extends much closer to the sun than the earth because extremophiles can survive up to at least 122 C.

Similarly a denser atmosphere more eventually distributes temperature so planets don’t actually need to have very high surface temperatures to avoid water freezing.

> If ice didn't float, life as we know it wouldn't be possible anywhere in the universe.

I cheerfully propose this is evidence of a hacked universe. More specifically that there was a design flaw in the core structures and that water got tweaked as a band-aid - rather than rip the germ-code apart and rewrite it.

subscript: my premise requires a fallible creator. the most interesting kind, imho

Evidence and a clue are very different. Just because a scientific hypothesis us incorrect, or there is no explanation, does not mean that alternatives must be right.

Eg: disproving darwinism does not mean creationism is correct. Just that darwinism is flawed. You have to affirmatively prove alternative theories, can't just disprove something else and claim that makes you right. Yet more, creationism is not falsifiable, that's outside the scope of science. In the realm of faith, clues are taken as evidence, and this is where I quibble with you if we are talking science fact.

> Evidence and a clue are very different. Just because a scientific hypothesis us incorrect, or there is no explanation,

Evidence, clues, hypotheses and explanations are indeed different things.

> does not mean that alternatives must be right.

It was a proposal.

It was a cheerful proposal. A cheerful rebuttal seems to be called for, does it not?

My apologies for not rebutting your original statements as directly as I could. I am trying to understand better why your comment gave me a relatively visceral reaction.

I think the reason is that it feels somewhat common to see the realm of science as complementary to religion. There is tension for sure there. As a given, religion attempts to essentially explain everything. Therefore when science begins to explain more and more, religion explains less and less.

To that extent, how exactly is something working in a way we do not understand actually evidence of anything? Perhaps understanding more would finally be evidence for why exactly water freezes - but nothing more.

Last point, the logic is flawed. Seemingly you are conveying an implication relationship (ie: if A, then B) - notably: because physics & chemistry were hacked, life can exist. Looking at the truth table of the implication relationship [1], the latter being true, that life exists, the relationship no longer guarantees the former proposition (that physics and chemistry were hacked) to also be true. Which means we could equally say "because so much time passed things lined up - therefore life could exist."

The key is, you have to figure out why the preposition (ie: A, that physics & chemistry were hacked) is independently true of life existing. In other words, independent of life existing, you must prove that physics and chemistry were hacked in order for that to be evidence of why life exists. Otherwise, using the existence of life as evidence of a hacked chemistry & physics is circular reasoning.

[1] https://math.stackexchange.com/questions/4254268/implication...

Given that life exists, and life requiring improbable actualities, those actualities existing are not evidence. We are very lucky, we live in a geological era at a specific location of the universe that has hit the jackpot of actualities to allow life to be sustained.

I might be mildly autistic, I'm not sure how to say this more cheerfully.. but no - the fact water behaves slightly differently is not evidence for intelligent design. What's more, there can never be evidence for intelligent design because it is a non-falsifiable assertion. It is faith.

This just feels familiar to the intelligent design vs evolution debate. The idea being that if 'evolution' can be shown to be false, then intelligent design is true. First, intelligent design is not science, it is faith - it cannot be shown to be false and therefore a prime requirement of a scientific hypothesis fails. Further, if evolution is false in the end, then it does not mean intelligent design is correct, it just means we have no clue - we only are left with more questions and fewer answers.

if we live in a simulation, god must exist

What's the next level above hypervisor?

it's gods all the way up

water is OP

What's the reasoning here? You think that life would not have survived ice ages if ice didn't float? Life would probably have adapted even if the oceans froze bottom-up with deep sea "snow" no? It could even have led to a more consistent global temperature as the albedo of earth didn't change through colder periods.

Yes, ice floating is super important in our system. Another biggie is the surface tension effect. Surface tension [1] plays a big part in the capillary action that allows trees to transport water and nutrients from deep in the ground up to the top of their trunk and branches. Surface tension is important throughout nature and many industrial processes as well. Water is incredible.

[1] https://www.fs.usda.gov/research/treesearch/38556

> Water is incredible.

You could say that again! The more I observe and understand properties of water the more fascinating it gets.

For example, the minutest of leakages can cause a havoc in a building. That’s why I get extremely nervous when I see damp walls.

Or take flowing water. What looks like a gentle stream could easily sweep away a few tons of bus. Often times vehicle drivers misjudge this to drive through a shallow rain stream and end up in a whole lot of trouble.

So outer space is max frozen water?

My father taught us this as a simple conjecture of sorts that somehow always stuck with me: "in a frozen lake the warmest layer of water is at the bottom and it's at 4°C". Now there might be a plethora of cases where this is not exactly true, as is often the case with simplified models, but this is how I would word it to my kids :)

It is a simplified model. The obvious next question is why doesn't the entire lake freeze from the top down? Why does the ice not get progressively thicker every day? The next-level is to model the thermal insulation of the ice. Heat from beneath is insulated from the cold air above. With a constant supply of heat from below but a reduced heat transfer due to the ice/snow, along with reduced evaporation, it is theoretically possible for the depths of a lake to get warmer once frozen over.

https://en.wikipedia.org/wiki/Lake_stratification

Here's a good article if you anyone wants to learn more. There is a lot going on down there.

https://seagrant.umn.edu/news-info/featured-stories/lake-riv...

That's a bit like the atmosphere.

At low altitudes, temperature reduces with height (in daytime the atmosphere is heated by contact with the hot surface of the earth (as the atmosphere itself doesn't really get heated by the sun). The hot air rises, and expands as it ascends (pressure reduces as you climb, less air pushing down from above) and therefore cools (adiabatic expansion). Therefore, in the troposphere at least, temperature reduces with altitude due to all this vertical air movement and heating from below.

This is contrasted with the stratosphere, where the temperature begins to rise with altitude again and therefore is very stable and stratified without much vertical air movement.

Somewhat different physics at play, but funny how there are similarities.

As a child I used to main line OU lectures on Saturday mornings.

One was on Ecology, and had about thermal inversion in a lake in the Lake District when the temperature of the lake fell to 4ºC and the thermal circulation changed, between above 4ºC and below.

https://en.wikipedia.org/wiki/Lake_stratification#Definition

I wonder if that could be used to calibrate thermometers.

We already have the frozen and boiling temperature of water or any other liquid.

I remind you that boiling water is 100c and not higher as the energy is used to change phase. (at 1atm and close to the sea level)

You can use different materials for the temperature you are more interested in if you want more precision, we don't need to go under bodies of water to calibrate thermometers

I think they meant that hypothetically, presuming a case where we didn’t have access to better methods. The question might be rephrased as “would this be accurate and reliable enough to calibrate a thermometer if someone cared to try?”. I might be wrong, but it’s how I interpreted it.

I think about this way more often when I should. I'm prototyping a cooling system and currently using ice; designing tolerance for the cool reservoir to contract a little as ice warms and changes states has my brain hooked on the weird behaviors of water.

What are you cooling?

I think you can put this in much more lay friendly words if you say: water has the highest density at 3.98°C.

And vice versa! The more you try to compress water, the closer you "push" it towards 3.98 centigrade. That's why water stays liquid below a certain depth, for example in the sea. Without that fact, water would freeze at higher pressures and no life would have developed in the ocean depths.

What does that mean for extreme environments like… a black hole? Water gets sucked in, experiences ultimate gravity and compression bringing it close to stopped time… at almost perfect 3.98?

Well, no, for more than one reason. First, for the water, time doesn't stop. Chances are it wouldn't even know it surpassed the event horizon (you know, if it could actually experience anything). For an external observer, it would crawl to a halt just outside the event horizon until it simply fades from vision.

Then gravitational tidal forces aren't strictly a uniform compression, on the contrary. Since gravity increases by 1/r^2, the part of the water drop that's closest to the black hole would experience largest force. That tears everything apart, so the water would be more dispersed instead of compressed. While I haven't done the math (and don't know if I even still could), I'd assume that gravity would quickly overcome Van Der Waals forces that holds the water molecules together, so it'd probably closer to water vapour than liquid.

And lastly, once it finally reaches the singularity, all bets are off. As far as I'm aware we have no idea what happens to matter in a singularity apart from contributing to its mass.

I wonder if this is tied to the (alleged, highly dubious) effect where hot water freezes faster then cold water? I always figured if it was real, it had to be some momentum-based phenomenon. So if (a) hot water in a freezer sets up strong convection currents and (b) those currents are more useful for cooling the water than the "usual" reverse convection of cold water (by bringing warmer water to the surface where its less insulated, or at least not actively burying it) and (c) the regular convection is able to continue on momentum even when the water has cooled a lot, then it might conceivably accelerate cooling enough to win the race. Maybe in just enough of a patchwork, fragile way to match the mess of inconclusive tests about the whole phenomenon.

Does this negative thermal expansion continue for supercooled water as well?

Water has so many fascinating properties. A lot of them arise from the strong hydrogen bond network between the molecules. https://web.archive.org/web/20200427193704/http://www1.lsbu....

Edit: replaced the broken link with the archived site. RIP www1.lsbu.ac.uk/water, this used to be one of the best resources to learn about water properties when I started studying physical chemistry.

Looks like it's here now: https://water.lsbu.ac.uk/water/water_anomalies.html

I searched for a unique looking phrase and the author's name.

Ah, thank you! Glad to see the site is still available.

Water is the most interesting and fascinating molecule in my opinion. Isaac Asimov's essays on water's "strange" properties in his excellent book

https://en.wikipedia.org/wiki/The_Left_Hand_of_the_Electron

opened my eyes to the life enabling properties of this small ubiquitous molecule. Just recently when I stood at a coast watching the waves come and go I imagined all these small molecules bonded together by their electrical bonds.

Couldn't agree with this more. Essential molecule for life and its properties in both solid and gas are quite unique.

And its properties have far-reaching implications for life, climate and the physical world in general. Indeed a remarkable one

Fascinating to see how water has remained an unsolved problem for so long. In some ways we know less now than before. When I was an undergraduate physical chemistry student 137 years ago, it was a well-known fact that ice skates worked because the phase diagram for water said it would be a liquid at the pressure and temperature underneath the blade. Now, all we know is that that is not the case.

Nice to see the occasional physical chemistry article in HN (or, in Quanta for that matter.) Some of my professors and colleagues have dedicated their lives to the fundamentals of water; theory and experiment from gas phase spectroscopy of water dimers, trimers, and clusters to stat-mech of the condensed phases of which there are so many.

On the macro scale, water availability or the lack of it, will loom large in the coming years. My late father dedicated a lot of his life to the implications.

It seems that there is a pretty good explanation for the slipperiness of ice now: https://youtu.be/20zyW0qoSTE (referencing this article: https://www.nature.com/articles/s41586-024-07427-8)

Layman tl;dw: on the surface of ice the crystal structure isn't perfect, leaving some water molecules able to move around as if they were in a liquid.

Thanks for this. Lots of familiar names in the references including, in a big surprise, my undergraduate research advisor and another colleague with whom I worked closely in his lab. My first published scientific paper was with both of them. My advisor is a legendary surface scientist but I had no idea he had studied ice formation on his beloved single-crystal surfaces! I look forward to reading the full paper.

Does their work extend to snow and skiing?

Wow - "When I was an undergraduate physical chemistry student 137 years ago" - you really are the oldest guy in this club.

Ya gotta type louder, I don't see as well as I used to. ;-)

I read that absolutely credulously. I thought "137 years ago? Would that phase transition under pressure be widely known around 1890?" then after a few moments of pondering... "wait a minute!"

For me it feels more like 1000 years ago that I did. I haven’t touched physics even once after uni as I went into software dev so it was another life that feels ‘outside’ me.

How many people has software development sucked up? One of my previous coworkers has a doctorate in mathematics. He now works as a php web developer.

> Fascinating to see how water has remained an unsolved problem for so long.

Despite being a simple molecule with just three atoms

> When I was an undergraduate physical chemistry student 137 years ago

Wow! How old are you? Lol

I thought it remarkable that you can coerce water into yet a different phase ("slime phase"?) with only parts-per-million additives of proteins,

https://www.nhm.ac.uk/discover/how-much-slime-can-a-hagfish-... ("Hagfishes: how much slime can a slime eel make?")

(Is slime a viscous liquid or is it a creeping solid?)

Non-Newtonian fluid

Like ketchup or semen.

Fascinating!

Apparently, water can turn solid at room temperature (and above) as well, when seeded by a hydrophilic surface. Some researchers actually believe that all water in living cells are made up of this kind of 'solid water', and that this is responsible for a lot of cell properties and mechanisms (like cross membrane transport):

https://www.google.com/search?q=gerald+pollack

Whether there's water-weirdness or not, cellular insides are definitely hard for us to intuit. We think of them like tiny fishtanks, but they're actually a fully packed squirming stew where "body temperature" means floating proteins molecules are bouncing around at enormous velocities.

David Goodsell’s Molecular Landscapes (see https://pdb101.rcsb.org/sci-art/goodsell-gallery/mycoplasma-... or https://pdb101.rcsb.org/sci-art/goodsell-gallery/model-of-a-...) represent in a nice way the intracellular macromolecular environment.

Perhaps you've read it already, but this is a nice article on that topic: http://www.righto.com/2011/07/cells-are-very-fast-and-crowde...

One of my favorite things about the statistical physics of water is that H2O is a strong electric dipole. You'd expect this plays an important role on its nucleation, and yet we get quite good approximations when we neglect this fact.

This is all very interesting but they have to stop all this research before someone accidentally discovers ice-9.

Seriously though as i read this, I am surprised how scientifically plausible Kurt Vonnegut’s science fiction was.

If we could get an ice-9 that raises the freezing temp of water by only a couple of degrees, that might be hugely useful in a world of climate change. We could keep our glaciers and the wonderful year-round fresh water supplies (rivers) that they enable.

https://en.wikipedia.org/wiki/Mpemba_effect

This is also an interesting related read, basically hot water my in some circumstance freeze faster that the colder one.

It's even in the related articles from quanta now that I see.

Given the content in the Quanta Magazine article, I would have assumed the explanation was straightforward: the hotter the water is, the more the molecules inside are bouncing around randomly, and therefore more likely to end up randomly entering a configuration that triggers nucleation in a given period of time than the same water at a lower temperature. But I don't even see that possibility discussed in the Wikipedia article. It's such a simple explanation that I therefore also assume it's wrong for some reason, but I'm curious why it's wrong.

We can test to see what freezes faster: cold still water, cold stirred water, or hot water.

Related: ice-suppressing proteins [1].

[1] https://www.youtube.com/watch?v=l2lXiwbRhb0

Further related:

https://pdb101.rcsb.org/motm/120

Molecule of the month from the RCSB

One of my favorite class of proteins to look at. Check those neatly ordered residues at the water-binding interface!

> The process of freezing water actually releases heat, which is why you can use an infrared camera to see ice heat up as it solidifies.

If it's releasing heat, shouldn't we say it's cooling off as it solidifies?

If "releasing heat" is a confusing phrase, think of it as "generating heat".

It releases the heat into itself before the heat escapes into the environment.

I wish Quanta Magazine would fix their floating header on iOS mobile. It’s been broken for more than a year. I have the URL bar at the top of my screen. If the height of the header is Hpx, its top is positioned Hpx away from the origin. It’s infuriating. And also, reader mode sometimes doesn’t render the whole article so I can’t use it to bypass the frustrations.

If iOS mobile will run bookmarklets [1] then this bookmarklet will delete the fixed header from the page (note, this is all one long line in the bookmark URL field):

    javascript:(function () {var i,elements=document.querySelectorAll('body *'); for (i=0;i<elements.length;i++) {if (getComputedStyle(elements[i]).position==='fixed' || getComputedStyle(elements[i]).position==='sticky'){elements[i].parentNode.removeChild(elements[i]);}}})();

[1] https://en.wikipedia.org/wiki/Bookmarklet

I’m sure there is a way to get that to work, but I just tweeted at them instead. Fingers crossed they fix it. I like their articles… (To be fair, I block all their ads and don’t pay them any money.)

Well that was quite a rabbit hole on bookmarklets! Not sure how I went so long without learning about them, and now I'm not sure how I managed without them

Somewhat oddly I guess, my thesis advisor worked on both high temperature intermetallics and ice (the latter through a partnership with a US Army Lab in Hanover, NH). I actually did my thesis on a nickel-aluminide--one of the intermetallic alloys that basically didn't go anywhere commercially interesting--and went off in other directions anyway. But he established an ice lab and it's really an interesting material (which in the 80s, the US military was really interested in for obvious reasons).

I love this article: it starts out saying that proteins are great and I nodded my head, thinking, “oh yeah, that makes sense”.

Read down a bit and my intuition as to why turns out to be bogus.

For me the weird part is that they put in a gif of a researcher using a 'video wall' (apparently a projector combined with some gesture recognition?) to show one of these ice proteins...

Except the one shown looks like it is some helix-rich structure with a haeme group. Even if that is an ice-forming protein, I would have shown one with a beta helix instead, which have the properties mentioned - large surface for nucleation.

https://en.m.wikipedia.org/wiki/Beta_helix

Looks like hemoglobin (good ol’ 4HHB[1]) to me.

[1]: https://www.rcsb.org/structure/4HHB

fun-fact: heavy water freezes at 39f (3.8c) not 32f

https://en.wikipedia.org/wiki/Heavy_water#Physical_propertie...

Subspace darkmatter icebergs scratching along supercooled liquids?

Related: we also don't really know how ice skates work, at least not in detail.

[1] https://xkcd.com/1867/

Also related, the rather counterintuitive theory / myth that hot water freezes faster than cold water.

It comes up every winter here when it starts freezing and people want to leave out water for the birds. I can't help to urge people to just try it instead of simply believing it. I.e., it's not that I don't believe it's impossible under certain specific circumstances, but having tried it myself a number of times and the result always being that the cold water freezes first, it's pretty clear to me that it's a bit silly to just dismiss using warm water.

More info (but a little vague on myth vs fact): https://en.wikipedia.org/wiki/Mpemba_effect

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