Daniel and Kelly’s Extraordinary Universe - Does hot or cold water freeze faster?

Episode Date: December 28, 2023

Daniel and Jorge get the chills when they discover how little we know about water.See omnystudio.com/listener for privacy information.

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talk about vaping.org. Brought to you by the American Lung Association and the Ad Council. Hey, Daniel. kids ask you a lot of physics questions? Sometimes, but actually they're mostly interested in other stuff like horses or chemistry. Oh, sounds like they're doing experiments on horses. Not chemical experiments, fortunately.

Just the romantic chemistry kind between horses. No comment. Well, do their questions ever give you good ideas, like for your science? Not yet, but I'm waiting for the day they inspire some new physics ideas in me. ideas in me. Oh, would you give them credit? Or would you just say it called the Whiteson theory? Then it can apply to both.

No, of course I'd give them credit. I'd love to have a paper with my kids, Whiteson and Whiteson. Double Whiteson. Yeah, though. I guess we might have an argument about whose first author. Ooh. Or whose last author? Wouldn't your kids win though?

Don't kids always win? I always put them first, even on author lists. There you go. Hi, I'm Jorge and Cartoonist and the author of Oliver's Great Big Universe. Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I love answering kids' questions. But do kids love the answers, though? That's always the question. As long as I can keep them brief, they're pretty happy to hear them. Doesn't it depend on the kind of question?

Like, hey, Dad, can I play more video games? No. Can I play more video games? No. At some point, I don't think you enjoy those questions, do you? That's not the kind of question, I mean. I mean, when they're trying to understand something. When you can see their brains have chewed on something and it doesn't quite fit together and they want to know what the resolution is. Do they ever regret asking you questions?

Like, I have a question. I'm curious. But, oh, wait, I forgot I'm going to get a lecture from a physics professor. Anything longer than, like, 30 seconds, and you can see them start to tune me out. You can see them start to think, maybe I should have asked Wikipedia instead. Not datapedia. Exactly. But, hey, that trains me to keep my answers brief. Oh, there you go.

To get it down to yes, no answers. What is quantum gravity? Yes. Yes. And no. There you go. It's both true and false. Do they ever ask you questions about the, like, everyday life that you can't answer?

Yeah, I mean, they ask me questions about how to navigate tricky situations, and sometimes there isn't a perfect answer. No, I mean, like, everyday phenomenon that happens to them about physics. Yeah, all the time. There's lots of things in kids' lives that they don't understand, why a rainbow follows them around, or why you can smell the rain before it comes, all sorts of things inspire questions. And what if you don't know the answer?

Or what if there isn't an answer? Those are my favorite, because then I get to show them. them how little we understand about the universe and how close they are to the forefront of knowledge. What if there is an answer, but you don't know it? You have to take a little Wikipedia break? Yeah, then we try to figure it out together. Exactly.

And I show them how to find their own answers. Oh, well, there you go. How to Google together in case they don't know how to do it already. A crucial skill in today's world. But it is interesting how sometimes there are still mysteries that you find, even in our everyday lives, right? In small effects, that it kind of surprises you that scientists don't know the answer to. Yeah, a lot of people have the impression that we've mostly figured out the universe that your everyday experience is totally cracked. And it's just like tiny little questions like

what's inside a black hole or what's dark matter made out of the physicists are struggling over. But there's a lot of things in your everyday experience that are still pretty tricky. Yeah, remember we had the podcast episode about ice skates, right? Isn't that a big mystery still, how ice skates work? Yeah, ice skates and bicycles and all sorts of stuff. And sometimes we like to tackle these questions on our podcast to hopefully demystify or at least explain the mystery to people. And some of the questions that scientists are still struggling over

were inspired by actual children, teenagers even. So today on the podcast we'll be asking the question. Does hot or cold water freeze faster? This seems a bit out of left field for our podcast. Why? Because it's chemistry? Kind of. Or it doesn't involve some distant planet or some crazy microscopic effect. Well, there are crazy microscopic effects here, and it is really fascinating. But in the end, this is what physics is about is explaining our everyday world,

what we can see in the sky, but also what we see under our feet. And it's a huge challenge to bring it up from microscopic particles to explaining the fabric of our reality. So sometimes I like to show how difficult. it is to really bridge that gap. Yeah, we'd like to explain it all here. Even the things inside of your fridge, which may seem inexplicable and mysterious. And this particular story really was inspired by an experiment done by a Tanzanian teenager who wrote the first paper on the topic.

Now, this is an interesting question. Does hot or cold water freeze faster? Because I guess at first glance, it seems kind of obvious that the colder water is going to freeze faster if you put them in a freezer. Exactly, but it turns out the universe is not so simple. Or your freezer is not that simple. Your freezer is part of the universe, so yeah. Although sometimes it seems like it's from another dimension.

If you look inside my freezer, there's things growing in there and they have a supernatural color to them. I think my freezer might have additional dimensions because I keep putting ice cream in there and then it's gone. Oh, wow, yeah. It goes into a black hole maybe called your stomach. Or my teenager. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe,

a production of iHeard Radio. In which we tackle mysteries big and small, hot and cold, weird and wacky. Mysteries that you encounter every day and mysteries that sometimes nobody may ever encounter. We cover the whole range. But anyway, this is kind of a seemingly simple question, and we were wondering how many people out there had thought about this, and whether they know whether the answer is yes or no. Thanks very much to everybody who answers these questions.

We love this audience participation segment, and we'd love to hear your voice as, part of the chorus. So please write to me to questions at danielanhorpe.com and i'll set you up. So think about it for a second. Which one do you think freezes faster, hot or cold water? Here's what people have to say. I've heard that hot water freezes faster. I'm not sure why. Possibly, I think maybe the atoms have more speed and are more active. So maybe they lose their heat a little bit quicker than cold water. So hot water definitely freezes faster. And I know this because in Colorado you can take boiling water and throw it in the air on a really cold day and it turns into freezy dust really fast.

Well, I would imagine cold water would freeze faster because freezing is the process of slowing down your molecules to the point where they would be measured at 0 degrees centigrade. So hot water, a lot more energy than the molecules. They are moving a lot quicker so more energy needs to be applied over a longer duration to slow those molecules down. However, I suspect the correct answer is probably hot because it's the less obvious one. It's funny because I've seen so many science shows demonstrate this, and I clearly remember that hot water freezes faster, but I do not remember exactly why. I think it's because there's more energy in hot water to facilitate the phase transition, but that's just my guess. Well, I believe it's hot water, but I don't really know why other than it's always been a wives tale of sorts maybe because hot water is as more pressure and i know pressure is a big part

of phase changes as much as temperature well um logic would say cold water would freeze faster because it's already closer to the freezing point but you wouldn't ask this question if it would be that easy and i seem to recall that some people were chucking boiling water into freezing air on youtube a while back so my final answer is hot water freezes faster, but I cannot tell you why. I always thought that boiled water freezing faster was just a myth, but you can boil water at room temperature by lowering the pressure, so perhaps if you increase the pressure, maybe.

Alright, well let's dig into this strange question, Daniel. What does this question even mean? What's the setup? I love this question because it seems so simple, both experimentally, like actually measuring this and theoretically, but it turns out to be much more complicated in both aspects. both aspects. From a basic point of view, it's a very simple experiment you could do while you listen to this episode. I mean, take two cups of water, one of them hotter than the other, put them both in the freezer and just measure how long does it take for each one to freeze? And

that would answer the question, does hot or cold water freeze faster? Which one turns into a cube of ice first? Yeah, exactly. Or does it depend on what you mean by freeze? We're going to get into that, yeah. But I guess the question is, which of the two cups, the hot one or the cold one turns into ice first. And so intuitively, you would assume that the cold one freezes faster because it's closer to freezing temperature. Exactly. If you can describe water basically in terms of just one variable, like it's temperature, then the hot water has to travel further along that temperature line and so it should take longer. Like eventually the hot water will become the cold water and it'll still have to progress to freezing. So if the hot water has to pass through the cold water

point, then it's like riding the bus home. If you get on it a further stop, it's going to take longer to get home. Right. Like if you have hot water at 100 degrees and cold water at 50 degrees, eventually after a while, the hot water is going to be 50 degrees, at which point, it's basically at the same starting point as the cold water. Yeah. If it took time to get there, then obviously it's going to take longer overall to get to the freezing point. Right. So you would think that the cold water freezes faster because the hot water has to become the cold water first anyways. Exactly. But it sounds like physicists have other ideas.

Yeah, and not just physicists. It's sort of an old wives tale that people have been repeating for like centuries or millennia that hot water freezes faster. You hear plumbers in the northeastern part of the United States often saying things like that hot water pipes freeze more often in big snowstorms, like they will burst more often than the cold water pipes. There's writings by Aristotle in the fourth century BC who says many people when, they want to cool water quickly, begin by putting it in the sun. Interesting. Give it a sunburn first and that will freeze it faster. Now, does Aristotle count as an old wife?

Is he like the OG old wife? He's definitely one of the OG physicists. But, you know, in the end, it comes down to actually measuring this, like doing the experiment. And for a long time, this is something people sort of just discussed and assumed that the cold water freeze faster. But then there was this event in the 1960s that involved ice cream. that sort of changed the course of this question forever. Oh my goodness.

Did somebody stop to eat a snag or and accidentally dropped, left some cold water in the freezer? No, there was a Tanzanian teenager named Erasto Mpemba. He and his science class were doing the exercise of making ice cream. But apparently there weren't going to be enough slots in the refrigerator. While most students were letting the ingredients cool to room temperature, he just jammed his in the freezer to get a spot. And he saw that his concoction froze faster than other kids who put it in at the same.

same time and started cooler. So he thought, hmm, maybe hot water does freeze faster. So he did it with ice cream, but that's not really how you make ice cream, is it? You don't just freeze cream, do you? No, you have to freeze it and you have to mix it at the same time. So I'm not sure if it qualifies as ice cream. So maybe he was just making popsicles. Exactly, creamcicles, I guess. I'm not just trying to debug this story, figure out what is really true here, Daniel. We're doing some hard investigating here. That's just sort of what inspired him. And he asked his physics teacher about it and his physics teacher told him, no, no, you're confused. That cannot happen. It's physically impossible. And then later on, a physicist came to visit his school and he raised his hand

and he told this story and he asked the physicist about it. And the physicist was interested enough to invite him back to his lab where they did a bunch of experiments confirmed the result. They saw hot water freeze faster than cold water. And then they wrote a paper together. And that's why this is now called the Impenba effect. Wow. So they actually did an experiment in a physics lab. did an experiment in a physics lab. And what did this experiment look like? The experiment is just two cups of water in a freezer with thermometers in them. I see.

Pretty basic. It was pretty basic. But the paper is pretty fun to read because it's written by a teenager. Like the opening line of the paper is, my name is Erastom Pemba, and I'm going to tell you about my discovery, which was due to misusing a refrigerator. Nice. Nice and direct. Nice and direct.

As opposed to how an adult academic would do it, which would take you the seven paragraph to get to the same point. Exactly. But the question you asked a minute ago about the details of the experiment turn out to be crucial because these experiments done in the 60s sort of established the effect and lots of people trying to reproduce it in the decades following with mixed success. Wait, but if it's a simple experiment, just putting two cups into a freezer, you're saying people have done the same thing, but sometimes the cold water beats the hot water and sometimes the hot water beats the cold water to the freezing point. Exactly. The experiment seem to be very sensitive to the conditions in a way that we do not fully understand because

it's not just two cups of water in a freezer. There's like the questions of the purity of the water or the blowing of the fan through the freezer. Something is going on which makes it very difficult to reproduce. It's not just about putting two cups inside of a freezer. It's about like how they're being cooled and what they're sitting on maybe perhaps. I read one study that saw hot water freeze faster and they discovered that it was because the shelves of the freezer were covered in frost and the hot water basically melted that frost, which improved the thermal contact with the shelf, the metal shelf, and that helped it cool faster. So all sorts of little details like that can make a difference in how you do this experiment. Well, but I guess, you know, the main headline

is that this is kind of an undecided question, it seems. Like people have tried it and sometimes the hot water does beat the cold water to freezing. Yeah, it's something which is not experimentally decided. Like, we cannot reliably reproduce this result. It turned down to only happen under certain conditions and be very sensitive to those conditions, and nobody has quite isolated those and controlled them. But I guess my question is how hard have people tried? Like, have you spent billions of dollars like you have in the LHC to figure out this question? Or is this one of those questions that you only see, you know, physicists published at the, you know, sort of on their websites? No, there are real labs doing detailed studies because it turns out this is a really

interesting question on the energetics of water. And so people have really tried. I read another review of this which said, quote, there is a wealth of experimental variation in the problem. So any laboratory undertaking such investigations is guaranteed different results from all the others. So this is something serious physicists and chemists are trying to nail down because the chemistry of water is very important. It's very important to life. It's important to climate change. It's important to exoplanets. Like water's important stuff. Yeah, I hear it's important for horses too. I'll have to ask my daughter about it. All right, well, let's dig into the details of the chemistry of water

and the details of these experiments and how they might affect who wins first cold water or hot water to freezing. So let's do that, but first let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently the explosion actually impelled metal glass.

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One question you asked earlier is like, well, what do you mean by freezing, right? Is that the formation of crystals? It's possible that like hot water could start forming crystals sooner, but actually takes longer to get to zero C. Water is very complicated stuff and it can exist in different phases at the same temperature. Or do you really just mean thermodynamically getting to zero C? Well, I guess maybe that I would guess that what most people think of as freezing is when water turns into a solid. So are you saying sometimes the hot water. it turns completely into a solid first?

Yes, some of these experiments see hot water forming these crystals first, right? Remember, water is a sort of disordered crystal. It's possible for the water which starts out hot to start forming those crystals. And crystal formation is very stochastic, right? Once you get a seed going, then you can rapidly form more crystals. So it sort of depends on like when you get that first seed. So hot water might be able to like first form that seed, which gives it an advantage even if it's still at a higher temperature.

Right. And I think freezing also kind of depends on pressure as well, right? But I guess you're assuming they're both under the same amount of pressure. Yeah, I think we're assuming that they're in a refrigerator, which is basically like an infinite thermal bath and can provide the pressure. But there are these little details also like evaporation. Right. Like did you seal your container? Because hot water will also evaporate, which lowers its volume, which makes it easier to freeze. I see. So the hot water, even if you stick it in the freezer, it's going to be hot for a while. And so some of it's going to evaporate. out into the freezer, which means that the amount of water left in the cup will be less than the amount of water in the cold cup, which means that it might be easier for it to freeze. Exactly. And there's other complicated experimental issues too.

Like one study discovered that it depended on where you put the thermometer in the cup, that sometimes they could get false readings of the impemba effect because they put the thermometer like in the wrong place. What do you mean? What's the right place to put it in a cup of water? Basically, you have to have them in the same place. Really, you should put it at the core so that you're measuring the time it takes the core to get to zero C. For both cups, you mean?

For both cups. But if you don't place the thermometer exactly in the center for both of them, you can get a false reading of the impamba effect. So there's two things going on here. One is like how tricky it is to reproduce this effect. And the other is, are all the reported cases of the impemba effect actually real or are some of them experimental mismeasurements? Well, let's break it down. In the cases that we think or people have thought that hot water for you, is faster. What do you think it might be going on? It all comes down to this question of describing

water with one number temperature. You imagine what's happening is you have this cube of water and the outer layer is in contact with the freezer and so it starts to chill and then it chills the inner layer and then that chills the inner layer and eventually the whole thing cools down. That is the simple model of the temperature dropping and you're really just describing the water in terms of one number. But this is tricky because temperature is a very slippery topic and it's not actually well defined And out of equilibrium. Equilibrium means there's no heat transfer, right? Like when the water has cooled and it's no longer changing, then you can define it to be

at the same temperature as the rest of the freezer. But if things are changing, then temperature is not technically defined. It's only defined for a system in equilibrium. The out of equilibrium, things get very complicated very quickly and you need much more information to actually describe the whole system. Oh, I see what you're saying. Like the idea of temperature, it only works if nothing's changing. But when something's freezing from hot water or cold water into ice, things are changing.

So if you're just going by measuring freezing as some sort of temperature reaching a point, then you're already kind of measuring the wrong thing. Yeah, exactly. And the thing to remember is that temperature is a macroscopic thing. It's like our experience. It's something we can measure using thermometers. And we try to connect it to the microscopic to say what's actually happening in hot water or in cold water. what's the difference between those two? And there's a bunch of different descriptions, a bunch of

different ways to try to explain and understand our intuitive macroscopic experience of temperature in terms of the microscopic particles. Like one very common one is the kinetic theory. It says in hot water molecules move faster and in cold water molecules move slower. That's rough because molecules can also do other things like spin and vibrate. That's one basic idea. But zooming out from that microscopic picture of the little molecules and their speeds determining the temperature, assumes that it's in equilibrium. There's a bunch of steps there. The mathematics involved to go from like zillions and zillions of little particles

out to a single number that describes it assumes that it's an equilibrium. And if it's not, you just can't do that. So I think what you're saying is if you're going by freezing as when it reaches, for example, zero degrees Celsius, then even if you measure it to be zero degree Celsius, maybe it's not done changing or maybe the molecules are still moving around. I think I'm saying more generally that describing the whole system as like having to move through one path to get from hot to freezing is not an accurate way to think about it. In reality, there's lots of different paths. It's not like the hot water is getting on the bus further from home.

It's like the hot water might be able to take a shortcut. There's not just one path from 100 degrees to zero. It doesn't necessarily have to pass through 50 because temperature isn't even really well defined for a system that's changing. It can be 100, it can later be zero, and it could have never been 50. Well, it sounds like you're basically disqualifying temperature as a gauge for this experiment. Like, basically don't use temperature to measure whether something freezes or not. Well, I think for the starting point and the ending point, you can use it. Like, is it frozen yes or no?

But while it's out of equilibrium, as it's changing, there's a lot more complicated stuff that's going on. Oh, I see. They may trace the same history of temperature, but actually what's going on inside the cup might be totally different yeah exactly the hot water cooling and the cold water cooling might be very very different processes remember that water is very very complicated stuff it has all these strange bonds these hydrogen bonds between the molecules which create lots of counterintuitive effects like famously water is less dense when it's a solid than when it's a liquid right water floats on top of liquid water it's like one of the only substances that will do that you mean ice floats

right yes solid water floats on top of liquid water ice floats right it's one of the only things that will do that and so it has all of these weird counterintuitive effects like what how would that affect how fast it freezes or not so these hydrogen bonds the sort of weak bonds between the molecules are crucial for forming the crystal and if you heat the water up it can like destroy all the existing ones freeing them up to rearrange themselves so hot water is like more active and more loose which allows it to like explore the possible configurations more quickly Like imagine you have a box of Legos and you're shaking it around. The more you shake it around, the more likely you are for it to end up in some configuration

than if you're shaking it less because you're exploring like more combinations of Legos bumping against each other. So Hot Water sort of like explores all those configurations faster and it might find accidentally some configuration which causes a seed of structure, a little mini crystal, which then flourishes and forms a larger crystal. But if the whole thing is hotter, wouldn't those eventually burn? break? Like even if you're shaking the container of Lego, they might, you know, accidentally or coincidentally, you know, build themselves, but you're still shaking, you're still shaking the canisters. So wouldn't it break apart? Yeah, you're absolutely right. So we have to add one more little thing to our model, which is that water does like to stick to itself, right? There

are these hydrogen bonds. So it's sort of like a box of sticky Legos and you're shaking them and some pieces come together and like to stick together. And that's what happens with water. Sometimes the pieces end up in exactly the right configuration and boom, they're bound together. So even though they were hot, now they like to stick together. That's a lower energy configuration. So that's one way that maybe hot water can get to being a solid faster than cold water. Exactly. That's one idea that's out there.

And people have done a bunch of experiments to try to confirm this. They're very artificial sounding experiments. They like take beads of glass and shoot them with lasers and study these very artificial situations where the bead of glass is like different energy levels. levels it can be in. But in general, they prove the principle that like high energy beads of glass find the minimum faster. They like explore all the possible configurations more quickly and end up finding that minimum, that most relaxed state more quickly than a slow bead of glass. And so some people think that that sort of proves that that's possible in principle. Though that doesn't mean it's what's actually happening like in water. The way they don't think this is helping harder water freeze faster. A lot of people think, okay, that proves in principle. that hot things can relax faster. But, you know, water is a very complex molecule. And so like very simple models of it don't always describe the behavior in reality. I talked to one water chemist who said, you can't believe anything that doesn't have a lot more details included in the simulation. So why don't they do these more detailed simulations? They are doing these simulations

and people already do lots of simulations of water for reasons we talked about. Like how does water form? And what happens when asteroids hit the atmosphere and contain ice in them? Is there a possibility for making like basic amino acids and organic molecules. All sorts of people are studying water for lots of reasons, but it's hard because there are lots of interactions. And so it takes like supercomputers basically to model a little bit of water. I guess maybe paint this a little bit of a picture. When you say that sometimes hot water freezes faster, is it by a lot or is it like super

close to the cold water? So if you look at the plot in the original paper or the one by Mpemba, then the variation and the time to start freezing is in like tens of minutes. So if you start at like 80C, he says it takes 30 minutes to cool his glass, where if you start at like 20C, it takes 100 minutes. So it's a very strong effect, at least in this original impenba paper. Oh, wow. Yeah, that's a big difference.

And I guess it's interesting how in his experiment the hot water wasn't that much hotter. Like it wasn't boiling water. Would this happen with boiling water? He did try a bunch of different temperatures from 20 to 80C, but he didn't try boiling water. No. Boiling water is much harder to control, right? It's like actively vaporizing, and so you can't really control the volume as easily. I see.

All right. So it seems like that's one idea about what could be going on. What else has physicists thought about could explain this? There's a whole lot of little details that people are thinking about. Like it could be the impurities. Cold water tends to contain more dissolved gases in it just because of the chemistry of water. And that can help actually lower its freezing point, which means that you're not really comparing two things that are the same. You're comparing one which has a little bit more gas dissolved in it, which could totally affect how long it takes to freeze.

Wait what? Can you explain that again? So cold water can have more dissolved gas in it. Like if you try to make bubbly water and try to get CO2 dissolved into your water, it's hard to get that CO2 in unless the water is cold. So cold water will absorb CO2 more than hot water. And so cold water likely has more CO2 in it and other gases dissolved. And that will change the freezing point of that water. But wouldn't the hot water absorb gas as it cools? Yeah, absolutely.

Hot water will absorb gas once it cools, but it doesn't have as much time. So if you've had water that's been cold for a long time, it will have absorbed a bunch more CO2 than water that's just been hot like five minutes ago. And so the gas in the water might help or make it more difficult for the water. water to freeze. Yeah. Or in this case, I guess it makes it more, it makes it harder. Why would it make it harder?

Well, you know, water has to form these crystals and if there's a bunch of CO2 involved, that it inhibits the ability of those water molecules to like find each other and to make those bonds. There's just more stuff going on that's not water. Yeah, exactly. The same way that like adding salt to water will change its freezing point. So the idea is that maybe when you heat it up the water to put into your experiment, it lost a bunch of gas.

Yeah, exactly. Then there's people who argue the opposite. They say that actually having impurities in the water should seed crystals that as it cools, if one of the two glasses has more impurities in it, that those impurities become like the nucleation site for crystal formation. Remember crystal formation is sort of a stochastic thing. Like you have a bunch of molecules at different temperature and they have to sort of like click together in order to start that crystal. And we talked earlier about how maybe hot water has an advantage because it tries more combinations per second,

but could also just be a difference experimentally in the impurities in that water. And as you heat it up, you might have boiled off some of those impurities or you may be concentrating those impurities as you heated up the water. So if the hot water has more impurities in it, that could actually provide more sites

for the nucleation of those crystals, which could lead to it forming a solid faster, even if it's not at the same temperature. But I feel like maybe we're talking a lot about things that might affect the formation, of ice crystals, but from a sort of a macro point of view, doesn't the hot water just have more energy? And so wouldn't it just technically take longer to get rid of that energy? It's a compelling argument. And it's compelling because it's a simple model when it basically says there's a single

number you can use to describe the system. But imagine if instead of just having energy, you also have energy in like momentum of heat loss. What is starting from a higher temperature means that you start losing energy more quickly because there's a higher difference between the heat of the water and the freezer and that high rate of energy transfer is somehow remembered. So now when you pass through that 50 degree mark, you're losing heat faster than the cold water did when it was there. It's sort of like having somebody start a race 10 or 15 meters behind the starting line, but they get to accelerate up to their top speed before they cross the starting line. Right. That's an effect that might explain it, but it's a bit crazy, isn't it? The idea that you're going to have like temperature

inertia. Yeah, that is a bit crazy. And it totally violates our simple model where you can describe things just in terms like temperature and pressure and volume. And that's because that only applies in equilibrium. Out of equilibrium, things are crazy. And none of these approximations we use to like grapple with all the crazy details of those particles are really applicable. And so there's lots of things that can happen to complex liquids much more than can be summarized in just a few numbers. Well, I think maybe you're not saying that the water itself has some sort of temperature inertia, but you're saying that maybe like the details or the complexity of how the cub interacts with the air around it that might have some effects that look like temperature

inertia. It could be both of those things, right? It certainly could be dependent on the details of the experimental setup, but also we just do not understand out of equilibrium chemistry very well. So temperature inertia could be a real thing, but it could also depend on the details of the molecular structure. Like maybe it only happens for more complex substances. Maybe it only happens for things with very specific kinds of bonds that are possible. All right. Well, let's get into some of these other ideas for what could be making hot water freeze faster than cold water and what that means about our understanding of water, chemistry, and horses. So let's dig into that. But first, let's take another quick break.

December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism.

Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio. Radio app, Apple Podcasts, or wherever you get your podcasts. A foot washed up a shoe with some bones in it. They had no idea who it was. Most everything was burned up pretty good from the fire that not a whole lot was salvageable. These are the coldest of cold cases, but everything is about to change.

Every case that is a cold case that has DNA. Right now in a backlog will be identified in our lifetime. A small lab in Texas is cracking the code on DNA. Using new scientific tools, they're finding clues in evidence so tiny you might just miss it. He never thought he was going to get caught, and I just looked at my computer screen. I was just like, ah, gotcha. On America's Crime Lab, we'll learn about victims and survivors, and you'll meet the team behind the scenes at Othrum,

the Houston Lab that takes on the most hopeless cases, to finally solve the unsolvable. Listen to America's Crime Lab on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people and an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. We talked about her recent 40th birthday celebrations, co-hosting a podcast with her fiancé Sue Bird, watching former teammates retire and more. Never a dull moment with Pino.

Take a listen. What do you miss the most about being a pro athlete? The final. The final. And the locker room. I really, really, like, you just, you can't replicate, you can't get back, showing up to locker room every morning just to shit talk. We've got more incredible guests like the legendary Candace Parker and college superstar A.Z. Fudd.

I mean, seriously, y'all, the guest list is absolutely stacked for season two. And, you know, we're always going to keep you up to speed on all the news and happenings around the women's sports world as well. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Presented by Capital One, founding partner of IHeart Women's Sports. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about exploring human potential. I was going to schools to try to teach kids these skills, and I get eye rolling from teachers or I get students who would be like,

It's easier to punch someone in the face. When you think about emotion regulation, like, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome as a result of it if it's going to be beneficial to you. Because it's easy to say, like, go blank yourself, right? It's easy.

It's easy to just drink the extra beer. It's easy to ignore, to suppress, seeing a colleague who's bothering you and just, like, walk the other way. Avoidance is easier. Ignoring is easier. Denials is easier. drinking is easier, yelling, screaming is easy, complex problem solving, meditating, you know, takes effort.

Listen to the psychology podcast on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. and how it seems to disappear magically, as if by magical horses. That's right. When my teenager leaves the ice cream out on the counter, why does it cool faster? Wait, could he say then that he's just trying to freeze it faster? Because then he's taking it out, leaving it out, so it heats up. So then when you finally put it in the freezer, it'll freeze faster. Yeah, I'm sure he's just doing a chemistry experiment, right?

Yeah, that's right. He's maybe just trying to raise your boiling point. But you know, it's amazing to me that this is still an open territory, both theoretically and experimentally. Lots of people trying to understand under what conditions you can make this happen and a bunch of other people are trying to understand whether it makes sense and what it means about like the nature of matter and phases and being a liquid. Yeah, it's pretty interesting that we don't have an answer to this. Sounds like we need to spend a couple more billion dollars on this question. That's right, billions of dollars worth of ice cream must be purchased. That's right.

Yes, white chocolate ice cream with bananas. Okay, so then I don't think we're quite done. You said there might be other factors that might be going on that might explain why the hot water freezes faster. Yeah, another theory I was reading about, and there's like no shortage of theories and possible explanations for what might be going on here, has to do with convection. How the water, like, moves through the glass as it's cooling. So, like, as the water is cooling, it's going to definitely have some current. within it, even if it started out totally stable, because density decreases with increasing temperature. So the surface of the water is going to be warmer than the bottom, which sometimes

they call a hot top. Now, if the water primarily loses its heat to the surface, then water with a hot top will lose heat faster than we would expect based on its average temperature. When the initially warmer water then cools down a little bit to the initial temperature of the other cooler water, it's going to have a hot top and its rate of cooling will be faster than the rate of cooling of the other water at the same temperature. Anyway, it's complicated, but it has to do with, like, how the water changes density and which chunk of the water is essentially exposed to the cool air. Oh, I see what you're saying.

Like, maybe you have a hot cup and a cold cup, and you're measuring the temperature, and maybe they both have the same temperature in the middle of the cup, but you're saying maybe the warmer cup has a hotter surface or water on the surface of it, which means it's losing heat faster, which means it's basically running faster towards freezing than the cold water. Yeah, it's like the hot cup is constantly exposing the hotter water

to the surface, which helps it cool. Whether there's the colder cup, the water is moving more slowly through it, and so it's not like as efficient at exposing the hottest parts of itself. The hottest parts of itself stay in the center for the cooler cup rather than the hot cup. And that depends on like concurrence,

which depends on like fluid dynamics, which we all know is a nightmare. But then wouldn't the hot cup need a colder bottom? Yeah. And this is one of the reasons why this depends on like where are you measuring this in the cup. But how did it get a colder bottom? Well, the hot water is going to rise to the surface because density decreases with increasing temperature. So it might be like more dense than the bottom of the hot cup than at the bottom of the cold cup.

Exactly. I think there's also a theory about heat conduction, right? Like maybe that when you initially put the hot cup into the freezer like it may. like it melts the things around it a little bit more, which helps it maybe connect to the coldness in the freezer better. Exactly, because heat conduction is very different from material to material. Between water and air surfaces, it's one number. Between water and water, it's another.

And so as we were saying earlier, like if you put the cup on a frosty shelf and that melts the frost near the cup, then you now have like a water connection to that shelf. It can very rapidly cool it. And so all sorts of these little details, you can even pull frost out of the air and then melt it. You can even pull water vapor out of the air and it can accumulate on the sides of the cup. All of these things could have a big difference on the experimental measurements. So I think first we have to like nail down what are the conditions we need to make this happen.

Then we can understand on the theoretical side, like do we understand why it happens in one configuration and not another? Meaning like if you stick a cold cup in the freezer and it's like my freezer, which is full of frost. It will basically be like putting a cold cup of water on a bank of snow. And because the water is cold, it's not going to melt that snow. And so it's basically going to be sitting kind of an insulation of fluffy snow. Whereas if you put in a hot cup, it's going to be hot enough to melt that snow, which basically melts. And then it basically turns into ice around it, which means that the hot cup is going to have basically like a fast track for the heat to escape. Exactly.

for the same reason that like wet jeans will make you colder on a ski hill than snowy dry jeans, right? That water will conduct heat away from you much faster than the snow will. So if you melt the surrounding area, then very quickly your heat is going to bleed out. And that's the reason you don't ski, right? That's one reason I don't ski. Absolutely. There are so many. Well, we can fix that one pretty quick, then.

Just use a special socks. No, waterproof pants are the answer to that one. Yeah, yeah. Don't ski in jeans. But the physicist in me is more interested in like what's happening to these particles and how do you zoom out from all these tiny little particles doing their thing individually to an explanation of what's happening to the water, right? Because in the world, what we interact with is not individual particles of water in their hydrogen bonds, but like the water in your cup or you want to freeze your ice cream. And in the end, what we're trying to do is explain that universe. And it's very, very difficult sometimes to connect this picture of the microscopic particles with.

our actual experience and things we can measure. But I guess maybe I wonder if the point is that if you have a very simple model or just assume that it's like some molecules floating in a simple canister or something, then you do expect the cold water to freeze faster. But because we live in the real world and there's all these different things that can happen and the way that the water freezes and the heat conduction depends on surfaces and what those services are touching or which, direction they're pointing, then the phenomenon of freezing is much more complex.

Yeah, that's exactly right. We're trying to describe complicated emergent behavior, and we usually start with a simple model because we hope that works. And often this simple model, which just has like temperature, pressure, volume does work. It works amazingly well. It's incredible. But we can also learn from when it fails. And when it fails, this tells us that other details that we've ignored in our model are now

important. They may even be crucial. They may even determine the total outcome. And that's an opportunity to learn something, to go back and say, okay, well, what is it that we didn't include in our description that gave us that simple story and how do we need to make it more complicated to describe what we're actually doing? Science is all about that, right? Start simple and then refine, refine, refine, refine. And I feel like this question is interesting, as you said before, because it taps into the chemistry of water and the dynamics of water, which might be related to like how life started right here on earth and maybe in other planets like if if we understand more how what's happening at the molecular level with water maybe we can understand how likely or

less likely it is or necessary it is for water to be there for the molecules that make life to form yeah one theory about how organic molecules were created on earth involves like asteroids slamming into the earth and if those asteroids have ice in them then those very high temperature high pressure impacts could have created conditions needed for that kind of chemistry to happen. So understanding exactly how water works and all the weird forms that it can take is crucial for understanding how life could have started here and also what the conditions might be like on exoplanets. We're like right on this exciting cusp of being able to detect water vapor

in the atmospheres of planets around other solar systems. And understanding the chemistry of that gives us a deeper and richer picture of what it's like on those surfaces and what, it might be like to be a squiggly blob crawling around and waiting for your ice cream to cool. Yeah, or not even maybe that far. Like even in our solar system, the moon, one of the moons of Jupiter Europa, right? It's made out of ice on top and it's got an ocean of liquid water inside. So we kind of want to know, is it possible for life to exist there? Oh yeah, you're absolutely right. Even that close to home, there's exciting water chemistry

happening in our solar system. It's crazy to imagine this like frozen crust of ice under which there's like a mile deep ocean of super cold water in which maybe life has started. We just don't know. Yeah, because we know there's life underneath, like, the ice shelf in Antarctica. But maybe, like, you need some special conditions for life to start. Maybe they can't start in somewhere like Europa. Yeah. I wonder if you take two moons of Jupiter and one of them is hotter and one of them is colder.

Which one will freeze first? Yeah, you need a pretty big freezer for that, though. Like maybe space. Now imagining a moon-sized chunk of ice cream. There you go. A giant scoop to size of the moon. That's no moon. That's a giant ball of ice cream.

That'll be the death of me. I can hear the cries of a thousand whitesons or a billion whitesons crying out further ice cream. As our cholesterol rises and temperature drops. That's right. And our mass increases as well. Okay, so what would you do, Daniel, if you're doing. daughter asks you what would happen if you stuck a cold horse and a warmer horse in a freezer. Would you be concerned?

Would you be like, huh, interesting question. Sit down. Let me explain this to you. I try to summarize this entire podcast in 30 seconds and I would fail. It's hard, man. It's hard. Well, yeah, it kind of has an impact on like horses in cold places, right? Yeah, absolutely.

No, I tell her that we don't know the answer to that. That it's too complicated and maybe she should grow up and figure it out. become a horse chemist. Better than a horse particle collider. Yeah. That would be a nea career you want to pursue. That's not science. That's just horsing around.

Yeah. Yeah, don't look at gift horse in the particle collider. I don't know what that means, but I laughed anyway. Yeah, I don't know. Either. It's horse nonsense. All right. Well, another reminder that there are still mysteries.

in the universe and some of them that you could even do at home and experiment and see for yourself how weird things can happen and how complicated even something as simple as making ice can be teenagers out there your questions to your science teacher could kick off a multi-decade exploration and reveal deeper understandings of the natures of liquids and solids so keep thinking keep asking questions and keep eating ice cream we hope you enjoyed that thanks for joining us see you next time For more science and curiosity, come find us on social media where we answer questions and post videos. We're on Twitter, Discord, Insta, and now TikTok.

Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of IHeartRadio. For more podcasts from IHeartRadio, visit the IHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, everything changed. There's been a bombing at the TWA terminal, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, terrorism. Listen to the new season of Law and Order Criminal Justice System.

On the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Get fired up, y'all. Season two of Good Game with Sarah Spain is underway. We just welcomed one of my favorite people, an incomparable soccer icon, Megan Rapino, to the show. And we had a blast. Take a listen. Sue and I were, like, riding the lime bikes the other day. And we're like, we're like, we!

People ride bikes because it's fun. We got more incredible guests like Megan and Storke. plus news of the day and more. So make sure you listen to Good Game with Sarah Spain on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. Brought to you by Novartis, founding partner of IHeart Women's Sports Network.

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