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

• 0:08
  Speaker 1: Hey, Daniel, do your kids ask you a lot of
• 0:10
  Speaker 1: physics questions?
• 0:11
  Speaker 2: Mmm?
• 0:12
  Speaker 3: Sometimes, but actually they're mostly interested in other stuff, like
• 0:15
  Speaker 3: horses or chemistry.
• 0:17
  Speaker 1: Whoa, it sounds like they're doing experiments on horses.
• 0:22
  Speaker 3: Not chemical experiments, fortunately.
• 0:25
  Speaker 1: Just the romantic chemistry kind between horses.
• 0:29
  Speaker 3: No comment.
• 0:30
  Speaker 1: Well, do there questions ever give you good ideas like
• 0:33
  Speaker 1: for your science?
• 0:34
  Speaker 3: Not yet, but I'm waiting for the day they inspire
• 0:37
  Speaker 3: some new physics ideas in me.
• 0:39
  Speaker 1: Would you give them credit or did you just say
• 0:41
  Speaker 1: called the whites in theory? Then it can apply to both.
• 0:45
  Speaker 3: No, of course I'd give them credit. I'd love to
• 0:47
  Speaker 3: have a paper with my kids.
• 0:48
  Speaker 1: Whitesin and whiteson doubule whites in.
• 0:51
  Speaker 3: Yeah, though I guess we might have an argument about
• 0:53
  Speaker 3: whose first author ooh.
• 0:56
  Speaker 1: Or whose last author? What are your kids? Window? Don't
• 0:59
  Speaker 1: kids always when.
• 1:00
  Speaker 3: I always put them first, even on author lists.
• 1:03
  Speaker 1: There you go.
• 1:19
  Speaker 4: Hi.
• 1:19
  Speaker 1: I'm hoora ma cartoonists and the author of Oliver's Great
• 1:22
  Speaker 1: Big Universe.
• 1:23
  Speaker 3: Hi, I'm Daniel. I'm a particle physicist and a professor
• 1:26
  Speaker 3: at uc R Vine, and I love answering kids' questions.
• 1:29
  Speaker 1: But do kids love the answers? Though that's always the question.
• 1:33
  Speaker 3: As long as I can keep them brief, they're pretty
• 1:35
  Speaker 3: happy to hear them.
• 1:38
  Speaker 1: Doesn't it depend on the kind of question, like, Hey, Dick,
• 1:41
  Speaker 1: can I play more Vita games?
• 1:42
  Speaker 2: No?
• 1:43
  Speaker 1: Can I play more Vida games? No? At some point,
• 1:46
  Speaker 1: I don't think you enjoyed those questions, do you.
• 1:48
  Speaker 3: That's not the kind of question I mean. I mean
• 1:50
  Speaker 3: when they're trying to understand something, when you can see
• 1:53
  Speaker 3: their brains have chewed on something and it doesn't quite
• 1:55
  Speaker 3: fit together and they want to know what the resolution is.
• 1:58
  Speaker 1: Do they ever regret asking questions like I have a question,
• 2:01
  Speaker 1: I'm curious, but oh wait, I forgot I'm going to
• 2:04
  Speaker 1: get a lecture from a physics professor.
• 2:05
  Speaker 3: Anything longer than like thirty seconds. And you can see
• 2:08
  Speaker 3: them start to tune me out.
• 2:11
  Speaker 1: You can see them start to think, maybe I should
• 2:13
  Speaker 1: have asked Wikipedia instead, not that Apedia.
• 2:19
  Speaker 3: Exactly. But hey, that trains me to keep my answers brief.
• 2:22
  Speaker 1: Oh there you go, to get it down to yes,
• 2:24
  Speaker 1: no answers.
• 2:26
  Speaker 3: What is quantum gravity? Yes?
• 2:28
  Speaker 1: Yes and no. There you go. It's about true and false.
• 2:33
  Speaker 1: Do they ever ask you questions about the like everyday
• 2:35
  Speaker 1: life that you can't answer.
• 2:37
  Speaker 3: Yeah, I mean they asked me questions about how to
• 2:38
  Speaker 3: navigate tricky situations, and sometimes there isn't the perfect answer.
• 2:42
  Speaker 1: No, I mean like everyday phenomenon that happens to them
• 2:44
  Speaker 1: about physics.
• 2:45
  Speaker 3: Yeah, all the time. There's lots of things in kids'
• 2:47
  Speaker 3: lives that they don't understand. Why a rainbow follows them around,
• 2:51
  Speaker 3: or why you can smell the rain before it comes.
• 2:54
  Speaker 3: All sorts of things inspire questions.
• 2:56
  Speaker 1: And what if you don't know the answer, or what
• 2:57
  Speaker 1: if there isn't an answer?
• 2:59
  Speaker 3: Those are my favorite because then I get to show
• 3:01
  Speaker 3: them how little we understand about the universe and how
• 3:03
  Speaker 3: close they are to the forefront of knowledge.
• 3:06
  Speaker 1: What if there is an answer but you don't know it,
• 3:09
  Speaker 1: you have to take a little Wikipeda break.
• 3:11
  Speaker 3: Yeah, then we try to figure it out together exactly,
• 3:13
  Speaker 3: and I show them how to find their own answers.
• 3:15
  Speaker 1: Oh, well, there you go, how to google together in
• 3:17
  Speaker 1: case they don't know how to do it already.
• 3:21
  Speaker 3: A crucial skill in today's world.
• 3:23
  Speaker 1: But it is interesting how sometimes there are still mysteries
• 3:26
  Speaker 1: that you find even in our everyday lives, right in
• 3:29
  Speaker 1: small effects that it kind of surprises you. The scientists
• 3:32
  Speaker 1: don't know the answer to.
• 3:33
  Speaker 3: Yeah, a lot of people have the impression that we've
• 3:35
  Speaker 3: mostly figured out the universe, that your everyday experience is
• 3:39
  Speaker 3: totally cracked and it's just like tiny little questions like
• 3:42
  Speaker 3: what's inside a black hole or what's dark matter made
• 3:44
  Speaker 3: out of the physicists are struggling over. But there's a
• 3:47
  Speaker 3: lot of things in your everyday experience that are still
• 3:50
  Speaker 3: pretty tricky.
• 3:51
  Speaker 5: Yeah.
• 3:51
  Speaker 1: I remember we had the podcast episode about ice skates, right,
• 3:55
  Speaker 1: isn't that a big mystery still how ice skates work?
• 3:57
  Speaker 3: Yeah, ice skates and bicycles and all sorts of stuff.
• 4:01
  Speaker 1: And sometimes we like to tackle these questions on our
• 4:03
  Speaker 1: podcast to hopefully demystify or at least explain the mystery
• 4:08
  Speaker 1: to people.
• 4:09
  Speaker 3: And some of the questions that scientists are still struggling
• 4:12
  Speaker 3: over we're inspired by actual children, teenagers.
• 4:15
  Speaker 1: Even so, today on the podcast, we'll be asking the
• 4:17
  Speaker 1: question does hot or cold water freeze faster? This seems
• 4:28
  Speaker 1: a bit a left field for our podcast, why because
• 4:30
  Speaker 1: it's chemistry kind of or it doesn't involve some distant
• 4:35
  Speaker 1: planet or some crazy microscopic effect.
• 4:38
  Speaker 3: Well, there are crazy microscopic effects here, and it is
• 4:40
  Speaker 3: really fascinating, But in the end, this is what physics
• 4:43
  Speaker 3: is about, is explaining our everyday world, what we can
• 4:45
  Speaker 3: see in the sky, but also what we see under
• 4:48
  Speaker 3: our feet. And it's a huge challenge to bring it
• 4:51
  Speaker 3: up from microscopic particles to explaining the fabric of our reality.
• 4:55
  Speaker 3: So sometimes I'd like to show how difficult it is
• 4:58
  Speaker 3: to really bridge that gap.
• 5:00
  Speaker 1: To explain it all here, even the things inside of
• 5:02
  Speaker 1: your fridge which may seem inexplicable and mysterious.
• 5:07
  Speaker 3: And this particular story really was inspired by an experiment
• 5:11
  Speaker 3: done by a Tanzanian teenager who wrote the first paper
• 5:14
  Speaker 3: on the topic.
• 5:16
  Speaker 1: Now, this is an interesting question. Does hot or cold
• 5:18
  Speaker 1: water freeze faster? Because I guess, at first glance, it
• 5:21
  Speaker 1: seems kind of obvious that the colder water is going
• 5:24
  Speaker 1: to freeze faster if you put them in a freezer.
• 5:27
  Speaker 3: Exactly, But it turns out the universe is not so simple,
• 5:30
  Speaker 3: or your freezer is not that simple. Your freezer is
• 5:32
  Speaker 3: part of the universe.
• 5:32
  Speaker 1: So yeah, although sometimes it seems like it's from another dimension.
• 5:36
  Speaker 1: If you look inside my freezer, there's things going in
• 5:38
  Speaker 1: there that have a supernatural color to them.
• 5:42
  Speaker 3: I think my freezer might have additional dimensions because I
• 5:44
  Speaker 3: keep putting ice cream in there and then it's gone.
• 5:47
  Speaker 1: Oh wow, yeah, it goes into a black hole maybe
• 5:50
  Speaker 1: called your stomach or my teenager. But anyways, welcome to
• 5:53
  Speaker 1: our podcast, Daniel and Jorge Explain the Universe, a production
• 5:56
  Speaker 1: of iHeartRadio.
• 5:57
  Speaker 3: In which we tackle mysteries big and small, all hot
• 6:00
  Speaker 3: and cold, weird and.
• 6:02
  Speaker 1: Wacky mysteries that you encounter every day, and mysteries that
• 6:06
  Speaker 1: sometimes nobody may ever encounter. We cover the whole range.
• 6:09
  Speaker 1: But anyways, this is kind of a seemingly simple question,
• 6:12
  Speaker 1: and we were wondering how many people out there had
• 6:14
  Speaker 1: thought about this and whether they know whether the answer
• 6:18
  Speaker 1: is yes or no.
• 6:19
  Speaker 3: Thanks very much to everybody who answers these questions. We
• 6:21
  Speaker 3: love this audience participation segment and we'd love to hear
• 6:24
  Speaker 3: your voice as part of the chorus. So please write
• 6:27
  Speaker 3: to me two questions at Danielanhorge dot com and I'll
• 6:30
  Speaker 3: set you up.
• 6:31
  Speaker 1: So think about it for a second. Which one do
• 6:33
  Speaker 1: you think freezes faster? Hot or cold water. Here's what
• 6:36
  Speaker 1: people have to say.
• 6:37
  Speaker 4: I've heard that hot water phrases faster. I'm not sure why. Possibly,
• 6:42
  Speaker 4: I think maybe the atoms have more speed and are
• 6:47
  Speaker 4: more active, so maybe they lose their heaked a little
• 6:50
  Speaker 4: bit quicker than colder water.
• 6:52
  Speaker 3: So hot water definitely freezes faster.
• 6:55
  Speaker 6: And I know this because in Colorado you can take
• 6:58
  Speaker 6: boiling water and throw it in the air on a
• 7:00
  Speaker 6: really cold day and it turns into freezy dusts really fast.
• 7:04
  Speaker 2: Well, I would imagine cold water freeze faster because freezing
• 7:09
  Speaker 2: is the process of slowing down your molecules to the
• 7:13
  Speaker 2: point where they would be measured cynthigrade. So hot water
• 7:18
  Speaker 2: a lot more energy than the molecules they are moving
• 7:21
  Speaker 2: a lot quicker, so more energy needs to be applied
• 7:24
  Speaker 2: over a longer duration to slow those molecules down. However,
• 7:27
  Speaker 2: I suspect the correct answer is probably hot because it's
• 7:30
  Speaker 2: the less obvious one.
• 7:31
  Speaker 5: It's funny because I've seen so many science shows demonstrate this,
• 7:35
  Speaker 5: and I clearly remember that hot water freezes faster, but
• 7:39
  Speaker 5: I do not remember exactly why. I think it's because
• 7:43
  Speaker 5: there's more energy in hot water to facilitate the phase transition,
• 7:47
  Speaker 5: but that's just my guess.
• 7:48
  Speaker 7: Well, I believe it's hot water, but I don't really
• 7:52
  Speaker 7: know why, other than it's always been a wives tale
• 7:55
  Speaker 7: of sorts. Maybe because of hot water is as more pressure,
• 8:00
  Speaker 7: and I know pressure is a big part of phase
• 8:02
  Speaker 7: changes as much as temperature.
• 8:04
  Speaker 8: Well, logic would say cold water freeze faster because it's
• 8:08
  Speaker 8: already closer to the freezing point. But you wouldn't ask
• 8:12
  Speaker 8: this question if it would be that easy.
• 8:15
  Speaker 9: And I seem to recall that some people were chutting
• 8:17
  Speaker 9: boiling water into freezing air on YouTube a while back.
• 8:22
  Speaker 9: So my final answer is hot water freezes faster. But
• 8:26
  Speaker 9: I cannot tell you why.
• 8:28
  Speaker 6: I always thought that boiled water freezing faster was just
• 8:31
  Speaker 6: a myth. But you can boil water at room temperature
• 8:34
  Speaker 6: by lowering the pressure, so perhaps if you increase the
• 8:36
  Speaker 6: pressure maybe.
• 8:38
  Speaker 1: All right, well, let's dig into this strange question, Daniel,
• 8:42
  Speaker 1: What does this question even mean? What's the setup?
• 8:44
  Speaker 3: I love this question because it seems so simple, both experimentally,
• 8:48
  Speaker 3: like actually measuring this and theoretically, but it turns out
• 8:52
  Speaker 3: to be much more complicated in both aspects. From a
• 8:54
  Speaker 3: basic point of view, it's a very simple experiment you
• 8:57
  Speaker 3: could do while you listen to this episode. I mean,
• 9:00
  Speaker 3: take two cups of water, one of them hotter than
• 9:03
  Speaker 3: the other, put them both in the freezer and just
• 9:05
  Speaker 3: measure how long does it take for each one to freeze?
• 9:09
  Speaker 3: And now what answer the question? Does hot or cold
• 9:11
  Speaker 3: water freeze faster?
• 9:12
  Speaker 1: Which one turns into a cube of ice first?
• 9:15
  Speaker 3: Yeah?
• 9:15
  Speaker 1: Exactly does it depend on what you mean by freeze?
• 9:18
  Speaker 3: M We're going to get into that.
• 9:19
  Speaker 1: Yeah, But I guess the question is which of the
• 9:21
  Speaker 1: two cups, the hot one or the cold one, turns
• 9:24
  Speaker 1: into ice first? And so intuitively you'd assume that the
• 9:28
  Speaker 1: cold one freezes faster because it's closer to freezing temperature.
• 9:32
  Speaker 3: Exactly, if you can describe water basically in terms of
• 9:34
  Speaker 3: just one variable, like it's temperature, then the hot water
• 9:38
  Speaker 3: has to travel further along that temperature line, and so
• 9:40
  Speaker 3: it should take longer. Like eventually the hot water will
• 9:42
  Speaker 3: become the cold water, and they'll still have to progress
• 9:45
  Speaker 3: to freezing. So if the hot water has to pass
• 9:47
  Speaker 3: through the cold water point, then it's like riding the
• 9:50
  Speaker 3: bus home. If you get on at a further stop,
• 9:52
  Speaker 3: it's going to take longer to get home.
• 9:54
  Speaker 1: Right, Like, if you have hot water one hundred degrees
• 9:56
  Speaker 1: and cold water at fifty degrees, Eventually, after a while,
• 10:00
  Speaker 1: the hot water is going to be fifty degrees, at
• 10:02
  Speaker 1: which point it's basically the same starting point as the
• 10:05
  Speaker 1: cold water.
• 10:05
  Speaker 3: Yeah, and if it took time to get there, then
• 10:07
  Speaker 3: obviously it's going to take longer overall to get to
• 10:10
  Speaker 3: the freezing point.
• 10:11
  Speaker 1: Right. So you would think that the cold water freezes
• 10:14
  Speaker 1: faster because the hot water has to become the cold
• 10:17
  Speaker 1: water first anyways, exactly, But it sounds like physicists have
• 10:21
  Speaker 1: other ideas.
• 10:22
  Speaker 3: Yeah, and not just physicists. It's sort of an old
• 10:25
  Speaker 3: wives tale that people have been repeating for like centuries
• 10:29
  Speaker 3: or millennia that hot water freezes faster. You hear plumbers
• 10:33
  Speaker 3: in the northeastern part of the United States often saying
• 10:36
  Speaker 3: things like that hot water pipes freeze more often in
• 10:39
  Speaker 3: big snowstorms, like they will burst more often than the
• 10:42
  Speaker 3: cold water pipes. There's writings by Aristotle in the fourth
• 10:45
  Speaker 3: century BC who says, many people, when they want to
• 10:49
  Speaker 3: cool water quickly, begin by putting it in the sun.
• 10:52
  Speaker 2: Mm.
• 10:52
  Speaker 1: Interesting, give it a sunburned first, and that will freeze
• 10:56
  Speaker 1: it faster. Now does Aristotle count as an old wife?
• 11:00
  Speaker 1: Is he like the og old wife?
• 11:02
  Speaker 3: He's definitely one of the og physicists. But you know,
• 11:05
  Speaker 3: in the end it comes down to actually measuring this,
• 11:07
  Speaker 3: like doing the experiment. And for a long time this
• 11:09
  Speaker 3: is something people sort of just discussed and assumed that
• 11:12
  Speaker 3: the cold water freezed faster. But then there was this
• 11:15
  Speaker 3: event in the nineteen sixties that involved ice cream that
• 11:18
  Speaker 3: sort of changed the course of this question forever.
• 11:21
  Speaker 1: Oh my goodness, did somebody stop to eat a snag
• 11:23
  Speaker 1: er and accidentally drop that left some cold water in
• 11:26
  Speaker 1: the freezer.
• 11:27
  Speaker 3: No, there was a Tanzanian teenager named Erasto Pemba. He
• 11:31
  Speaker 3: and his science class were doing the exercise of making
• 11:33
  Speaker 3: ice cream, but apparently there weren't going to be enough
• 11:36
  Speaker 3: slots in the refrigerator. While most students were letting the
• 11:39
  Speaker 3: ingredients cool to room temperature, he just jammed his in
• 11:42
  Speaker 3: the freezer to get a spot, and he saw that
• 11:45
  Speaker 3: his concoction froze faster than other kids who put it
• 11:48
  Speaker 3: in at the same time and started cooler. So he thought, hmm,
• 11:51
  Speaker 3: maybe hot water does freeze.
• 11:53
  Speaker 1: Faster, so he did it with ice cream. But that's
• 11:55
  Speaker 1: not really how you make ice cream, is it. You
• 11:57
  Speaker 1: don't just freeze cream, do you know.
• 11:59
  Speaker 3: You have to freeze it and you have to mix
• 12:00
  Speaker 3: it at the same time. So I'm not sure if
• 12:02
  Speaker 3: he qualifies as ice cream.
• 12:04
  Speaker 1: So maybe he was just making popsicles exactly creamsicles. I
• 12:07
  Speaker 1: guess I'm not just trying to debug this story figure
• 12:10
  Speaker 1: out what is really true here, Daniel. We're doing some
• 12:13
  Speaker 1: heart investigating here.
• 12:14
  Speaker 3: That's just sort of what inspired him. And he asked
• 12:16
  Speaker 3: his physics teacher about it, and his physics teacher told him, no, no, no,
• 12:19
  Speaker 3: you're confused. That cannot happen, is physically impossible. And then
• 12:23
  Speaker 3: later on a physicist came to visit his school, and
• 12:25
  Speaker 3: he raised his hand and he told his story, and
• 12:27
  Speaker 3: he asked the physicist about it, and the physicist was
• 12:30
  Speaker 3: interested enough to invite him back to his lap where
• 12:31
  Speaker 3: they did a bunch of experiments confirmed the result. They
• 12:34
  Speaker 3: saw hot water freeze faster than cold water, and then
• 12:38
  Speaker 3: they wrote a paper together and that's why this is
• 12:40
  Speaker 3: now called the Pemba effect.
• 12:42
  Speaker 1: WHOA, So they actually did an experiment in a physics lab.
• 12:46
  Speaker 3: They actually did an experiment in a physics lab.
• 12:48
  Speaker 1: And what did this experiment look like?
• 12:50
  Speaker 3: The experiment is just two cups of water in a
• 12:52
  Speaker 3: freezer with thermometers in them.
• 12:54
  Speaker 1: M I see, pretty basic.
• 12:55
  Speaker 3: It was pretty basic but the paper is pretty fun
• 12:57
  Speaker 3: to read because it's written by a teenager. Like the
• 12:59
  Speaker 3: opening line of the paper is my name is Erastum Pemba,
• 13:03
  Speaker 3: and I'm going to tell you about my discovery, which
• 13:05
  Speaker 3: was due to misusing a refrigerator.
• 13:09
  Speaker 1: Nice, nice and direct, nice and direct, opposed to how
• 13:12
  Speaker 1: an adult academic would do it, which is would take
• 13:16
  Speaker 1: you the seven paragraphs to get to the same point exactly.
• 13:19
  Speaker 3: But the question you asked a minute ago about the
• 13:21
  Speaker 3: details of the experiment turn out to be crucial because
• 13:25
  Speaker 3: these experiments done in the sixties sort of established the effect,
• 13:28
  Speaker 3: and lots of people have tried to reproduce it in
• 13:30
  Speaker 3: the decades following with mixed success.
• 13:33
  Speaker 1: Wait, but if it's a simple experiment just putting two
• 13:36
  Speaker 1: cups into a freezer, you're saying people have done the
• 13:39
  Speaker 1: same thing, but some of sometimes the cold water beats
• 13:41
  Speaker 1: the hot water, and sometimes the hot water beats the
• 13:43
  Speaker 1: cold water to the freezing point.
• 13:45
  Speaker 3: Exactly. The experiments seem to be very sensitive to the
• 13:48
  Speaker 3: conditions in a way that we do not fully understand
• 13:51
  Speaker 3: because it's not just two cups of water in a freezer.
• 13:54
  Speaker 3: It's like the questions of the purity of the water
• 13:57
  Speaker 3: or the blowing of the fan through the freezer. Something
• 14:00
  Speaker 3: is going on which makes this very difficult to reproduce.
• 14:03
  Speaker 1: It's not just about putting two cups inside of a freezer.
• 14:05
  Speaker 1: It's about like how they're being cooled and what they're
• 14:08
  Speaker 1: sitting on.
• 14:08
  Speaker 3: Maybe perhaps I read one study that saw hot water
• 14:11
  Speaker 3: freeze faster and they discovered that it was because the
• 14:14
  Speaker 3: shelves of the freezer were covered in frost, and the
• 14:17
  Speaker 3: hot water basically melted that frost, which improved the thermal
• 14:21
  Speaker 3: contact with the shelf, the metal shelf, and that helped
• 14:25
  Speaker 3: it cool faster. So all sorts of little details like
• 14:28
  Speaker 3: that can make a difference in how you do this experiment.
• 14:31
  Speaker 1: Well, but I guess you know, the main headline is
• 14:34
  Speaker 1: that this is kind of an undecided question. It seems
• 14:36
  Speaker 1: like people have tried it, and sometimes the hot water
• 14:40
  Speaker 1: does beat the cold water to freezing.
• 14:42
  Speaker 3: Yeah, it's something which is not experimentally decided, like we
• 14:46
  Speaker 3: cannot reliably reproduce this result. It turns out to only
• 14:49
  Speaker 3: happen under certain conditions and be very sensitive to those conditions,
• 14:52
  Speaker 3: and nobody has quite isolated those and controlled them.
• 14:55
  Speaker 1: But I guess my question is how hard have people tried, Like,
• 14:58
  Speaker 1: have you spent billions of dollars you have in the
• 15:00
  Speaker 1: leec to figure out this question? Or is this one
• 15:04
  Speaker 1: of those questions that you only see, you know, physicists
• 15:07
  Speaker 1: publish at the on their websites.
• 15:10
  Speaker 3: No, there are real labs doing detailed studies because it
• 15:12
  Speaker 3: turns out this is a really interesting question on the
• 15:15
  Speaker 3: energetics of water, and so people have really tried. I
• 15:19
  Speaker 3: read another review of this which said, quote, there is
• 15:21
  Speaker 3: a wealth of experimental variation in the problem. So any
• 15:24
  Speaker 3: laboratory undertaking such investigations is guaranteed different results from all
• 15:28
  Speaker 3: the others. So this is something serious physicists and chemists
• 15:32
  Speaker 3: are trying to nail down because the chemistry of water
• 15:35
  Speaker 3: is very important. It's very important to life, it's important
• 15:37
  Speaker 3: to climate change, it's important to exoplanets like water is
• 15:40
  Speaker 3: important stuff.
• 15:41
  Speaker 1: Yeah, I hear, it's important for horses too.
• 15:45
  Speaker 3: I'll have to ask my daughter about it.
• 15:49
  Speaker 1: All right, Well, let's dig into the details of the
• 15:51
  Speaker 1: chemistry of water and the details of these experiments and
• 15:54
  Speaker 1: how they might affect who wins first cold water or
• 15:58
  Speaker 1: hot water to freezing. So let's do that. But first
• 16:01
  Speaker 1: let's take a quick break or right, we're asking the
• 16:16
  Speaker 1: simple question does hot or cold water freeze faster? And
• 16:19
  Speaker 1: it seems like the answer is it depends, which is
• 16:23
  Speaker 1: wild like the idea that hot water can freeze faster
• 16:27
  Speaker 1: than cold water.
• 16:28
  Speaker 3: It comes down to lots of tricky little details. One
• 16:31
  Speaker 3: question you asked earlier is like, well, what do you
• 16:33
  Speaker 3: mean by freezing? Right? Is that the formation of crystals.
• 16:37
  Speaker 3: It's possible that like hot water could start forming crystals sooner,
• 16:41
  Speaker 3: but actually takes longer to get to zero C. Water
• 16:45
  Speaker 3: is very complicated stuff and it can exist in different
• 16:47
  Speaker 3: phases at the same temperature. Or do you really just
• 16:50
  Speaker 3: mean thermodynamically getting to zero C?
• 16:53
  Speaker 1: Well, I guess maybe I would guess that what most
• 16:55
  Speaker 1: people think of as freezing is when water turns into
• 16:58
  Speaker 1: a solid. So are you saying sometimes the hot water
• 17:00
  Speaker 1: turns completely into a solid.
• 17:02
  Speaker 3: First, Yeah, some of these experiments see hot water forming
• 17:05
  Speaker 3: these crystals first, right, number water is a sort of
• 17:08
  Speaker 3: a disordered crystal. It's possible for the water, which starts
• 17:12
  Speaker 3: out hot, to start forming those crystals, and crystal formation
• 17:15
  Speaker 3: is very stochastic.
• 17:16
  Speaker 2: Right.
• 17:16
  Speaker 3: Once you get a seed going, then you can rapidly
• 17:19
  Speaker 3: form more crystals, So it sot of depends on like
• 17:21
  Speaker 3: when you get that first seed. So hot water might
• 17:24
  Speaker 3: be able to like first form that seed, which gives
• 17:27
  Speaker 3: it an advantage even if it's still at a higher temperature.
• 17:30
  Speaker 1: Right. And I think freezing also kind of depends on
• 17:32
  Speaker 1: pressure as well, Right, But I guess you're assuming they're
• 17:35
  Speaker 1: both under the same amount of pressure.
• 17:37
  Speaker 3: Yeah, I think we're assuming that they're in a refrigerator,
• 17:39
  Speaker 3: which is basically like an infinite thermal bath and can
• 17:42
  Speaker 3: provide the pressure. But there are these little details also
• 17:45
  Speaker 3: like evaporation, right, like did you seal your container, because
• 17:48
  Speaker 3: hot water will also evaporate, which lowers its volume, which
• 17:51
  Speaker 3: makes it easier to freeze.
• 17:54
  Speaker 1: I see, So the hot water, even if you stack
• 17:56
  Speaker 1: it in the freezer, it's going to be hot for
• 17:57
  Speaker 1: a while, and so some of it's going to vapor
• 18:00
  Speaker 1: rate out into the freezer, which means that the amount
• 18:02
  Speaker 1: of water left in the cup will be less than
• 18:04
  Speaker 1: the amount of water in the cold cup, which means
• 18:07
  Speaker 1: that it might be easier for it to freeze.
• 18:09
  Speaker 3: Mm exactly. And there's other complicated experimental issues too, like
• 18:14
  Speaker 3: one study discovered that it dependent on where you put
• 18:16
  Speaker 3: the thermometer in the cup that sometimes they could get
• 18:20
  Speaker 3: false readings of the Impemba effect because they put the
• 18:23
  Speaker 3: thermometer like in the wrong place.
• 18:25
  Speaker 1: What do you mean, what's the right place to put
• 18:27
  Speaker 1: it in the cup of water?
• 18:28
  Speaker 3: Basically you have to have them in the same place. Really,
• 18:30
  Speaker 3: you should put it at the core so that you're
• 18:32
  Speaker 3: measuring the time it takes the core to get to
• 18:34
  Speaker 3: zero C for both cups. You mean for both cups.
• 18:36
  Speaker 3: But if you don't place the thermometer exactly in the
• 18:39
  Speaker 3: center for both of them, you can get a false
• 18:41
  Speaker 3: reading of the Impemba effect. So there's two things going
• 18:44
  Speaker 3: on here. One is like how treaty it is to
• 18:46
  Speaker 3: reproduce this effect? And the other is are all the
• 18:49
  Speaker 3: reported cases of the Mpemba effect actually real or are
• 18:53
  Speaker 3: some of them experimental mismeasurements.
• 18:55
  Speaker 1: Well, let's break it down. In the case is that
• 18:57
  Speaker 1: we think or people have thought that hot water fast
• 19:00
  Speaker 1: or what do you think might be going on?
• 19:02
  Speaker 3: It all comes down to this question of describing water
• 19:05
  Speaker 3: with one number temperature. You imagine what's happening is you
• 19:07
  Speaker 3: have this cube of water and the outer layers in
• 19:10
  Speaker 3: contact with a freezer, and so it starts to chill,
• 19:12
  Speaker 3: and then it chills the inner layer, and then that
• 19:14
  Speaker 3: chills the inner layer, and eventually the whole thing cools down.
• 19:17
  Speaker 3: That is the simple model of the temperature dropping, and
• 19:19
  Speaker 3: you're really just describing the water in terms of one number.
• 19:22
  Speaker 3: But this is tricky because temperature is a very slippery
• 19:26
  Speaker 3: topic and it's not actually well defined. Out of equilibrium,
• 19:31
  Speaker 3: equilibrium means there's no heat transfer, right Like, when the
• 19:34
  Speaker 3: water is cool and it's no longer changing, then you
• 19:37
  Speaker 3: can define it to be at the same temperature as
• 19:39
  Speaker 3: the rest of the freezer. But if things are changing,
• 19:41
  Speaker 3: then temperature is not technically defined. It's only defined for
• 19:43
  Speaker 3: a system in equilibrium. Out of equilibrium, things get very
• 19:47
  Speaker 3: complicated very quickly, and you need much more information to
• 19:50
  Speaker 3: actually describe the whole system.
• 19:51
  Speaker 1: Well, I see, we're saying, like the idea of temperature
• 19:55
  Speaker 1: it only works if nothing's changing. But when something's freezing
• 20:00
  Speaker 1: from hot water or cold water into ice, things are changing.
• 20:04
  Speaker 1: So if you're just going by measuring freezing as some
• 20:08
  Speaker 1: sort of temperature reaching a point, then you're already kind
• 20:11
  Speaker 1: of measuring the wrong thing.
• 20:13
  Speaker 3: Yeah, exactly. And the things you remember is that temperature
• 20:17
  Speaker 3: is a macroscopic thing. It's like our experience. It's something
• 20:20
  Speaker 3: we can measure using thermometers, and we try to connect
• 20:23
  Speaker 3: it to the microscopic to say, what's actually happening in
• 20:26
  Speaker 3: hot water or in cold water? What's the difference between
• 20:29
  Speaker 3: those two. And there's a bunch of different descriptions, a
• 20:31
  Speaker 3: bunch of different ways to try to explain and understand
• 20:35
  Speaker 3: our intuitive macroscopic experience of temperature in terms of the
• 20:39
  Speaker 3: microscopic particles. Like one very common one is the kinetic
• 20:42
  Speaker 3: theory says in hot water molecules move faster and in
• 20:45
  Speaker 3: cold water molecules move slower. That's rough because molecules can
• 20:49
  Speaker 3: also do other things like spin and vibrate. That's one
• 20:51
  Speaker 3: basic idea. But zooming out from that microscopic picture of
• 20:55
  Speaker 3: the little molecules and their speeds determined in the temperature
• 20:58
  Speaker 3: assumes that it's in equilibrium. There's a bunch of steps there,
• 21:01
  Speaker 3: the mathematics involved to go from like zillions and zillions
• 21:05
  Speaker 3: of little particles out to a single number that describes it.
• 21:08
  Speaker 3: Assumes that it's an equilibrium, and if it's not, it
• 21:11
  Speaker 3: just can't do that.
• 21:12
  Speaker 1: So I think what you're saying is if you're going
• 21:15
  Speaker 1: by freezing as when it reaches, for example, zero degree celsius,
• 21:18
  Speaker 1: then even if you measure it to be zero degree celsius,
• 21:21
  Speaker 1: maybe it's not done changing, or maybe the molecules are
• 21:25
  Speaker 1: still moving around.
• 21:26
  Speaker 3: I think I'm saying more generally that describing the whole
• 21:30
  Speaker 3: system as like having to move through one path to
• 21:32
  Speaker 3: get from hot to freezing is not an accurate way
• 21:36
  Speaker 3: to think about it. In reality, there's lots of different paths.
• 21:38
  Speaker 3: It's not like the hot water is getting on the
• 21:40
  Speaker 3: bus further from home. It's like the hot water might
• 21:43
  Speaker 3: be able to take a short cut. There's not just
• 21:45
  Speaker 3: one path. From one hundred degrees to zero doesn't necessarily
• 21:49
  Speaker 3: have to pass through fifty because temperature isn't even really
• 21:53
  Speaker 3: well defined for a system that's changing. It can be
• 21:55
  Speaker 3: one hundred, it can later be zero, and it could
• 21:57
  Speaker 3: have never been fifty.
• 21:58
  Speaker 1: Well, it sounds like you you're basically disqualifying temperature as
• 22:02
  Speaker 1: a gauge for this experiment, like basically don't use temperature
• 22:06
  Speaker 1: to measure whether something freezes or not.
• 22:09
  Speaker 3: Well, I think if for the starting point and the
• 22:11
  Speaker 3: ending point, you can use it like is it frozen,
• 22:13
  Speaker 3: yes or no? But while it's out of equilibrium. As
• 22:16
  Speaker 3: it's changing. There's a lot more complicated stuff that's going on.
• 22:19
  Speaker 1: Oh I see, they may trace the same history of temperature,
• 22:23
  Speaker 1: but actually what's going on inside the cup might be
• 22:25
  Speaker 1: totally different.
• 22:26
  Speaker 3: Yeah, exactly. The hot water cooling and the cold water
• 22:28
  Speaker 3: cooling might be very very different processes. Remember that water
• 22:32
  Speaker 3: is very very complicated stuff. It has all these strange bonds,
• 22:35
  Speaker 3: these hydrogen bonds between the molecules, which create lots of
• 22:40
  Speaker 3: counterintuitive effects. Like famously, water is less dense when it's
• 22:43
  Speaker 3: a solid than when it's a liquid. Right, water floats
• 22:46
  Speaker 3: on top of liquid water. It's like one of the
• 22:48
  Speaker 3: only substances that will do that. You mean ice floats, right, Yes,
• 22:52
  Speaker 3: solid water floats on top of liquid water. Ice floats, right,
• 22:55
  Speaker 3: It's one of the only things that will do that.
• 22:58
  Speaker 3: And so it has all of these weird counter into effects.
• 23:01
  Speaker 1: Like what, how would that affect how fast it freezes
• 23:03
  Speaker 1: or not.
• 23:04
  Speaker 3: So these hydrogen bonds, the sort of weak bonds between
• 23:06
  Speaker 3: the molecules, are crucial for forming the crystal, and if
• 23:10
  Speaker 3: you heat the water up, it can like destroy all
• 23:12
  Speaker 3: the existing ones, freeing them up to rearrange themselves. So
• 23:16
  Speaker 3: hot water is like more active and more loose, which
• 23:18
  Speaker 3: allows it to like explore the possible configurations more quickly.
• 23:23
  Speaker 3: Like imagine you have a box of legos and you're
• 23:25
  Speaker 3: shaking it around. The more you shake it around, the
• 23:27
  Speaker 3: more likely you are for it to end up in
• 23:30
  Speaker 3: some configuration. Then if you're shaking it less because you're
• 23:33
  Speaker 3: exploring like more combinations of legos bumping against each other.
• 23:37
  Speaker 3: So hot water sort of like explores all those configurations faster,
• 23:40
  Speaker 3: and it might find accidentally some configuration which causes a
• 23:44
  Speaker 3: seed of structure, a little mini crystal, which then flourishes
• 23:48
  Speaker 3: and forms a larger crystal.
• 23:49
  Speaker 1: But if the whole thing is hotter wooden, those eventually break.
• 23:54
  Speaker 1: Like even if if you're shaking the container of lego,
• 23:57
  Speaker 1: they might you know, accidentally or coincidentally you know, build themselves,
• 24:01
  Speaker 1: but you're still shaking, you're still shaking the canisters, they
• 24:05
  Speaker 1: wouldn't break apart.
• 24:06
  Speaker 3: Yeah, you're absolutely right. So we have to add one
• 24:08
  Speaker 3: more little thing to our model, which is that water
• 24:10
  Speaker 3: does like to stick to itself, right, there are hydrogen bonds,
• 24:13
  Speaker 3: So it's sort of like a box of sticky legos
• 24:16
  Speaker 3: and you're shaking them and some pieces come together and
• 24:18
  Speaker 3: like to stick together, and that's what happens with water.
• 24:21
  Speaker 3: Sometimes the pieces end up in exactly the right configuration
• 24:24
  Speaker 3: and boom, they're bound together. So even though they were hot,
• 24:27
  Speaker 3: now they like to stick together. That's a lower energy configuration.
• 24:30
  Speaker 1: So that's one way that maybe hot water can get
• 24:33
  Speaker 1: to being a solid faster than cold water exactly.
• 24:35
  Speaker 3: That's one idea that's out there, and people have done
• 24:38
  Speaker 3: a bunch of experiments to try to confirm this. They're
• 24:40
  Speaker 3: very artificial sounding experiments. They like take beads of glass
• 24:45
  Speaker 3: and shoot them with lasers and study these very artificial
• 24:48
  Speaker 3: situations where the bead of glass is like different energy
• 24:51
  Speaker 3: levels it can be in, but in generally prove the
• 24:53
  Speaker 3: principle that like high energy beads of glass find the
• 24:57
  Speaker 3: minimum faster. They like explore all the possible figurations more quickly,
• 25:01
  Speaker 3: and end up finding that minimum that most relaxed state
• 25:04
  Speaker 3: more quickly than a slow bead of glass. And so
• 25:07
  Speaker 3: some people think that that sort of proves that that's
• 25:10
  Speaker 3: possible in principle, though that doesn't mean it's what's actually happening,
• 25:14
  Speaker 3: like in water.
• 25:15
  Speaker 1: The way they don't think this is helping hot water
• 25:18
  Speaker 1: freeze faster.
• 25:18
  Speaker 3: A lot of people think, okay, that proves in principle
• 25:21
  Speaker 3: that hot things can relax faster. But you know, water
• 25:24
  Speaker 3: is a very complex molecule, and so like very simple
• 25:27
  Speaker 3: models of it don't always describe the behavior in reality.
• 25:30
  Speaker 3: I talked to one water chemist who said, you can't
• 25:33
  Speaker 3: believe anything that doesn't have a lot more details included
• 25:35
  Speaker 3: in the simulation.
• 25:37
  Speaker 1: So why don't they do these more detailed simulations.
• 25:39
  Speaker 3: They are doing these simulations, and people already do lots
• 25:42
  Speaker 3: of simulations of water for reasons We talked about like
• 25:45
  Speaker 3: how does water form, and what happens when asteroids hit
• 25:48
  Speaker 3: the atmosphere and contain ice in them? Is there a
• 25:50
  Speaker 3: possibility for making like basic amino acids and organic molecules.
• 25:55
  Speaker 3: All sorts of people are studying water for lots of reasons,
• 25:57
  Speaker 3: but it's hard because there are lots of interaction actions,
• 26:00
  Speaker 3: and so it takes like supercomputers basically to model a
• 26:03
  Speaker 3: little bit of water.
• 26:05
  Speaker 1: I guess maybe paint us a little bit of a picture.
• 26:07
  Speaker 1: When you say that sometimes hot water freezes faster, is
• 26:10
  Speaker 1: it by a lot or is it like super close
• 26:14
  Speaker 1: to the cold water.
• 26:15
  Speaker 3: So if you look at the plot in the original
• 26:16
  Speaker 3: paper or the one by in Pemba. Then the variation
• 26:20
  Speaker 3: in the time to start freezing is in like tens
• 26:24
  Speaker 3: of minutes. So if you start it like eighty C,
• 26:28
  Speaker 3: he says, it takes thirty minutes to cool his glass,
• 26:31
  Speaker 3: where if you start it like twenty C, it takes
• 26:33
  Speaker 3: one hundred minutes. So it's a very strong effect, at
• 26:37
  Speaker 3: least in this original and Pemba paper.
• 26:39
  Speaker 1: Oh wow, Yeah, that's a big difference. And I guess
• 26:43
  Speaker 1: it's interesting how in his experiment the hot water wasn't
• 26:47
  Speaker 1: that much harder, Like it wasn't boiling water. Would this
• 26:49
  Speaker 1: happen with boiling water?
• 26:50
  Speaker 3: He did try a bunch of different temperatures from twenty
• 26:52
  Speaker 3: to eighty C, but he didn't try boiling water. No,
• 26:55
  Speaker 3: Boiling water is much harder to control, right, It's like
• 26:57
  Speaker 3: actively vaporizing, and so you can't really control the volume
• 27:00
  Speaker 3: as easily.
• 27:02
  Speaker 1: I see, all right, So it seems like that's one
• 27:04
  Speaker 1: idea about what could be going on. What else physicists
• 27:06
  Speaker 1: thought about could explain this.
• 27:08
  Speaker 3: There's a whole lot of little details that people are
• 27:10
  Speaker 3: thinking about, Like it could be the impurities cold water
• 27:13
  Speaker 3: tends to contain more dissolved gases in it just because
• 27:18
  Speaker 3: of the chemistry of water, and that can help actually
• 27:20
  Speaker 3: lower its freezing point, which means that you're not really
• 27:23
  Speaker 3: comparing two things that are the same. You're comparing one
• 27:27
  Speaker 3: which has a little bit more gas dissolved in it,
• 27:29
  Speaker 3: which can totally affect how long it takes to freeze.
• 27:32
  Speaker 1: Wait, what can you explain that again?
• 27:33
  Speaker 3: So cold water can have more dissolved gas in it,
• 27:37
  Speaker 3: Like if you try to make bubbly water and try
• 27:39
  Speaker 3: to get CO two dissolved into your water, it's hard
• 27:42
  Speaker 3: to get that CO two in unless the water is cold.
• 27:45
  Speaker 3: So cold water will absorb COEO two more than hot water,
• 27:48
  Speaker 3: and so cold water likely has more CO two in
• 27:51
  Speaker 3: it and other gases dissolved, and that will change the
• 27:54
  Speaker 3: freezing point of that water.
• 27:57
  Speaker 1: Wouldn't the hot water absorb gas? Is it cool?
• 28:00
  Speaker 2: Yeah?
• 28:00
  Speaker 3: Absolutely. Hot water will absorb gas once it cools, but
• 28:03
  Speaker 3: it doesn't have as much time. So if you've had
• 28:05
  Speaker 3: water that's been cold for a long time, it will
• 28:07
  Speaker 3: have absorbed a bunch more CO two then water that's
• 28:11
  Speaker 3: just been hot, like five minutes ago.
• 28:14
  Speaker 1: And so the gas in the water might help or
• 28:17
  Speaker 1: make it more difficult for the water to freeze. Yeah,
• 28:19
  Speaker 1: or this is I guess it makes it more, it
• 28:21
  Speaker 1: makes it harder. Why would it make it harder.
• 28:23
  Speaker 3: Well, you know, if water has to form these crystals,
• 28:25
  Speaker 3: and if there's a bunch of CO two involved, then
• 28:27
  Speaker 3: it inhibits the ability of those water molecules to like
• 28:30
  Speaker 3: find each other and to make those bonds.
• 28:32
  Speaker 1: There's just more stuff going on that's not water.
• 28:35
  Speaker 3: Yeah, exactly, the same way that like adding salt to
• 28:37
  Speaker 3: water will change its freezing point.
• 28:39
  Speaker 1: So the idea is that maybe when you heat it
• 28:41
  Speaker 1: up the water to put into your experiment, it lost
• 28:43
  Speaker 1: a bunch of gas.
• 28:44
  Speaker 3: Yeah exactly. Then there's people who argue the opposite, say
• 28:48
  Speaker 3: that actually having impurities in the water should seed crystals
• 28:53
  Speaker 3: that as it cools, if one of the two glasses
• 28:56
  Speaker 3: has more impurities in it, that those impurities become like
• 28:59
  Speaker 3: the nucleation side for crystal formation. Remember, crystal formation is
• 29:03
  Speaker 3: sort of a stochastic thing, Like you have a bunch
• 29:06
  Speaker 3: of molecules at different temperature and they have to sort
• 29:08
  Speaker 3: of like click together in order to start that crystal.
• 29:11
  Speaker 3: And we talked earlier about how maybe hot water has
• 29:14
  Speaker 3: an advantage because it tries more combinations per second, but
• 29:17
  Speaker 3: could also just be a difference experimentally in the impurities
• 29:21
  Speaker 3: in that water, And as you heat it up, you
• 29:23
  Speaker 3: might have boiled off some of those impurities, or you
• 29:25
  Speaker 3: may be concentrating those impurities as you heat it up
• 29:28
  Speaker 3: the water. So if the hot water has more impurities
• 29:31
  Speaker 3: in it, that could actually provide more sites for the
• 29:33
  Speaker 3: nucleation of those crystals, which would lead to it forming
• 29:36
  Speaker 3: a solid faster, even if it's not at the same temperature.
• 29:39
  Speaker 1: But I feel like maybe we're talking a lot about
• 29:42
  Speaker 1: things that might affect the formation of ice crystals. But
• 29:46
  Speaker 1: from a sort of a macro point of view, doesn't
• 29:49
  Speaker 1: the hot water just have more energy, and so wouldn't
• 29:52
  Speaker 1: it just technically take longer to get rid of that energy.
• 29:56
  Speaker 3: It's a compelling argument, and it's compelling because it's a
• 29:59
  Speaker 3: simple model when it basically says is a single number
• 30:01
  Speaker 3: you can use to describe the system. But imagine if
• 30:05
  Speaker 3: instead of just having energy, you also have energy in
• 30:08
  Speaker 3: like momentum of heat loss. What is starting from a
• 30:11
  Speaker 3: higher temperature means that you start losing energy more quickly
• 30:16
  Speaker 3: because there's a higher difference between the heat of the
• 30:18
  Speaker 3: water and the freezer, and that high rate of energy
• 30:21
  Speaker 3: transfer is somehow remembered. So now when you pass through
• 30:24
  Speaker 3: that fifty degree mark, you're losing heat faster than the
• 30:27
  Speaker 3: cold water did when it was there. It's sort of
• 30:30
  Speaker 3: like having somebody start a RaSE ten or fifteen meters
• 30:33
  Speaker 3: behind the starting line, but they get to accelerate up
• 30:36
  Speaker 3: to their top speed before they cross the starting line.
• 30:39
  Speaker 1: Right. That's an effect and might explain it. But it's
• 30:41
  Speaker 1: a bit crazy, isn't it. The idea that you can
• 30:43
  Speaker 1: have like temperature inertia.
• 30:45
  Speaker 3: Yeah, that is a bit crazy, and it totally violates
• 30:48
  Speaker 3: our a simple model where you can describe things just
• 30:49
  Speaker 3: in terms of like temperature and pressure and volume. And
• 30:52
  Speaker 3: that's because that only applies in equilibrium. Out of equilibrium,
• 30:56
  Speaker 3: things are crazy, and none of these approximations we used to,
• 30:59
  Speaker 3: like apple with all the crazy details of those particles,
• 31:02
  Speaker 3: are really applicable. And so there's lots of things that
• 31:05
  Speaker 3: can happen to complex liquids, much more than can be
• 31:08
  Speaker 3: summarized in just a few numbers.
• 31:10
  Speaker 1: Well, I think maybe you're not saying that the water
• 31:13
  Speaker 1: itself has some sort of temperature inertia, but you're saying
• 31:15
  Speaker 1: that maybe like the details or the complexity of how
• 31:18
  Speaker 1: the cup interacts with the air or around it, that
• 31:21
  Speaker 1: might have some effects that look like temperature inertia.
• 31:26
  Speaker 3: It could be both of those things, right. It certainly
• 31:28
  Speaker 3: could be dependent on the details of the experimental setup.
• 31:32
  Speaker 3: But also we just do not understand out of equilibrium
• 31:35
  Speaker 3: chemistry very well, So temperature inertia could be a real thing.
• 31:38
  Speaker 3: But it could also depend on the details of the
• 31:41
  Speaker 3: molecular structure, like maybe only happens for more complex substances,
• 31:45
  Speaker 3: maybe only happens for things with very specific kinds of
• 31:48
  Speaker 3: bonds that are possible.
• 31:49
  Speaker 1: All right, well, let's get into some of these other
• 31:51
  Speaker 1: ideas for what could be making hot water freeze faster
• 31:54
  Speaker 1: than cold water and what that means about our understanding
• 31:57
  Speaker 1: of water chemistry and horses. So to dig into that,
• 32:02
  Speaker 1: but first let's take another quick break. All right, we're
• 32:18
  Speaker 1: talking about Daniel raiding the freezer for ice cream and
• 32:23
  Speaker 1: how it seems to disappear magically, as if by magical horses.
• 32:28
  Speaker 3: That's right, when my teenager leaves ice cream out on
• 32:31
  Speaker 3: the counter, why does it cool faster?
• 32:33
  Speaker 1: M Wait, could he say then that he's just trying
• 32:36
  Speaker 1: to freeze it faster, because then he's taking it out,
• 32:39
  Speaker 1: leaving it out so it heats up, so then when
• 32:41
  Speaker 1: you finally put it in the freezer, it'll freeze faster.
• 32:46
  Speaker 3: Yeah, I'm sure he's just doing a chemistry experiment, right.
• 32:49
  Speaker 1: Yeah, that's right. He's maybe just trying to raise your
• 32:51
  Speaker 1: boiling point.
• 32:53
  Speaker 3: But you know, it's amazing to me that this is
• 32:55
  Speaker 3: still an open territory, both theoretically and experimentally. Lots of
• 33:00
  Speaker 3: people trying to understand under what conditions you can make
• 33:02
  Speaker 3: this happen, and a bunch of other people are trying
• 33:05
  Speaker 3: to understand whether it makes sense and what it means
• 33:07
  Speaker 3: about like the nature of matter and phases and being
• 33:10
  Speaker 3: a liquid.
• 33:11
  Speaker 1: Yeah, it's pretty interesting that we don't have an answer
• 33:13
  Speaker 1: to this. It sounds like we need to spend a
• 33:16
  Speaker 1: couple more billion dollars on this question.
• 33:18
  Speaker 3: That's right, billions of dollars. Where of ice cream must
• 33:20
  Speaker 3: be purchased.
• 33:23
  Speaker 1: That's right, Yes, white chocolate ice cream with bananas. Okay,
• 33:28
  Speaker 1: So then I don't think we're quite done. You said
• 33:30
  Speaker 1: there might be other factors that might be going on
• 33:32
  Speaker 1: that might explain why the hot water freezes faster.
• 33:35
  Speaker 3: Yeah, another theory I was reading about, and there's like
• 33:37
  Speaker 3: no shortage of theories impossible at Explanations for what might
• 33:40
  Speaker 3: be going on here has to do with convection, how
• 33:44
  Speaker 3: the water moves through the glass as it's cooling. So like,
• 33:48
  Speaker 3: as the water is cooling, it's going to definitely have
• 33:51
  Speaker 3: some currents within it, even if it started out totally stable,
• 33:54
  Speaker 3: because density decreases with increasing temperature. So the surface of
• 33:58
  Speaker 3: the water is going to be warmer than the bottom,
• 34:01
  Speaker 3: which sometimes they call it hot top. Now the water
• 34:03
  Speaker 3: primarily loses its heat to the surface, then water with
• 34:06
  Speaker 3: the hot top will lose heat faster than we would
• 34:09
  Speaker 3: expect based on its average temperature. When they initially warmer
• 34:12
  Speaker 3: water then cools down a little bit to the initial
• 34:15
  Speaker 3: temperature of the other cooler water, it's going to have
• 34:18
  Speaker 3: a hot top, and its rate of cooling will be
• 34:20
  Speaker 3: faster than the rate of cooling of the other water
• 34:22
  Speaker 3: at the same temperature. Anyway, it's complicated, but it has
• 34:26
  Speaker 3: to do with like how the water changes density in
• 34:28
  Speaker 3: which chunk of the water is essentially exposed to the
• 34:31
  Speaker 3: cool air.
• 34:32
  Speaker 1: Oh, I see what you're saying. Like maybe you have
• 34:34
  Speaker 1: a hot cup and a cold cup, and you're measuring
• 34:37
  Speaker 1: the temperature, and maybe they both have the same temperature
• 34:40
  Speaker 1: in the middle of the cup, but you're saying maybe
• 34:41
  Speaker 1: the warmer cup has a hotter surface or water on
• 34:46
  Speaker 1: the surface of it, which means it's losing heat faster,
• 34:49
  Speaker 1: which means it's you know, basically running faster towards freezing
• 34:53
  Speaker 1: than the cold water.
• 34:54
  Speaker 3: Yeah. It's like the hot cup is constantly exposing the
• 34:57
  Speaker 3: hotter water to the surface, which helps cool Where there's
• 35:01
  Speaker 3: the colder cup, the water is moving more slowly through it,
• 35:03
  Speaker 3: and so it's not like as efficient at exposing the
• 35:06
  Speaker 3: hottest parts of itself. The hottest parts of itself stay
• 35:09
  Speaker 3: in the center for the cooler cup rather than the
• 35:11
  Speaker 3: hot cup. And that depends on like concurrence, which depends
• 35:14
  Speaker 3: on like fluid dynamics, which we all know is a nightmare.
• 35:18
  Speaker 1: But then wouldn't the hot cup need a colder bottom?
• 35:21
  Speaker 3: Yeah, and this is one of the reasons why this
• 35:22
  Speaker 3: depends on like where are you measuring this in the cup?
• 35:25
  Speaker 1: But how did it get a colder bottom?
• 35:27
  Speaker 3: Well, the hot water is going to rise to the
• 35:29
  Speaker 3: surface because density decreases with increasing temperature.
• 35:32
  Speaker 1: Hmmm, So it might be like more dense than at
• 35:36
  Speaker 1: the bottom of the hot cup than at the bottom
• 35:38
  Speaker 1: of the cold cup, exactly. I think there's also a
• 35:40
  Speaker 1: theory about heat conduction, right, like maybe that when you
• 35:44
  Speaker 1: initially put the cup into the freezer, like, it melts
• 35:48
  Speaker 1: the things around it a little bit more, which helps
• 35:51
  Speaker 1: it maybe connect to the coldness in the freezer better.
• 35:56
  Speaker 3: Exactly, because heat conduction is very different from material to material.
• 36:00
  Speaker 3: Between water and air surfaces it's one number. Between water
• 36:03
  Speaker 3: and water it's another. And so as we were saying earlier,
• 36:06
  Speaker 3: like if you put the cup on a frosty shelf
• 36:08
  Speaker 3: and that melts the frost near the cup, then you
• 36:11
  Speaker 3: now have like a water connection to that shelf. It
• 36:14
  Speaker 3: can very rapidly cool it. And so all sorts of
• 36:17
  Speaker 3: these little details. You can even pull frost out of
• 36:19
  Speaker 3: the air and then melt it. You can even pull
• 36:21
  Speaker 3: water vapor out of the air and it can accumulate
• 36:24
  Speaker 3: on the sides of the cup. All these things could
• 36:26
  Speaker 3: have a big difference on the experimental measurements. So I
• 36:29
  Speaker 3: think first we have to like nail down what are
• 36:31
  Speaker 3: the conditions we need to make this happen. Then we
• 36:34
  Speaker 3: can understand on the theoretical side like, do we understand
• 36:37
  Speaker 3: why it happens in one configuration and not another.
• 36:40
  Speaker 1: Meaning like, if you stick a cold cup in the
• 36:43
  Speaker 1: freezer and it's like my freezer, which is full of frost,
• 36:46
  Speaker 1: it will basically be like putting a cold cup of
• 36:48
  Speaker 1: water on a bank of snow, and because the water
• 36:51
  Speaker 1: is cold, it's not going to melt the snow, and
• 36:54
  Speaker 1: so it's basically going to be sitting kind of an
• 36:56
  Speaker 1: insulation of fluffy snow. Whereas if you put in a
• 37:00
  Speaker 1: hot cup, it's going to be hot enough to melt
• 37:02
  Speaker 1: that snow, which basically melts and then it basically it
• 37:06
  Speaker 1: turns into ice around it, which means that the hot
• 37:09
  Speaker 1: cup's going to have basically like a fast track for
• 37:13
  Speaker 1: the heat to escape.
• 37:14
  Speaker 3: Exactly for the same reason that like wet jeans will
• 37:17
  Speaker 3: make you colder on a ski hill than snowy dry jeans, right,
• 37:21
  Speaker 3: that water will conduct heat away from you much faster
• 37:24
  Speaker 3: than the snow will. So if you melt the surrounding area,
• 37:27
  Speaker 3: then very quickly your heat is going to bleed out.
• 37:29
  Speaker 1: And that's the reason you don't ski, right.
• 37:31
  Speaker 3: That's one reason I don't ski. Absolutely. There are so.
• 37:34
  Speaker 1: Many Well we can fix that one pretty quick then
• 37:39
  Speaker 1: and just use a special socks.
• 37:41
  Speaker 3: No waterproof pants are the answer to that one.
• 37:43
  Speaker 1: Yeah, yeah, those ski and jeans.
• 37:44
  Speaker 3: But the physicist in me is more interested in, like,
• 37:47
  Speaker 3: what's happening to these particles, and how do you zoom
• 37:50
  Speaker 3: out from all these tiny little particles doing their thing
• 37:53
  Speaker 3: individually to an explanation of what's happening to the water,
• 37:58
  Speaker 3: right because in the world enteract with, there's not individual
• 38:01
  Speaker 3: particles of water in their hydrogen bonds, but like the
• 38:04
  Speaker 3: water in your cup, or you want to freeze your
• 38:05
  Speaker 3: ice cream. And in the end, what we're trying to
• 38:07
  Speaker 3: do is explain that universe. And it's very very difficult
• 38:11
  Speaker 3: sometimes to connect this picture of the microscopic particles with
• 38:14
  Speaker 3: our actual experience and like things we can measure.
• 38:17
  Speaker 1: But I guess maybe I wonder if the point is
• 38:20
  Speaker 1: that if you have a very simple model, or just
• 38:24
  Speaker 1: assume that it's like some molecules floating in a simple
• 38:27
  Speaker 1: canister or something, then you do expect the cold water
• 38:31
  Speaker 1: to freeze faster. But because we live in the real
• 38:33
  Speaker 1: world and there's all these different things that can happen,
• 38:36
  Speaker 1: and the way that the water freezes and you know,
• 38:39
  Speaker 1: the heat conduction depends on surfaces and what those surfaces
• 38:43
  Speaker 1: are touching or which direction they're pointing. Then the phenomenon
• 38:48
  Speaker 1: of a freezing is much more complex.
• 38:50
  Speaker 3: Yeah, that's exactly right. We're trying to describe a complicated
• 38:54
  Speaker 3: emergent behavior, and we usually start with a simple model
• 38:57
  Speaker 3: because we hope that works. And often this simple model,
• 39:00
  Speaker 3: which just has like temperature, pressure, volume, does work. It
• 39:03
  Speaker 3: works amazingly well, it's incredible. But we can also learn
• 39:06
  Speaker 3: from when it fails. And when it fails this tells
• 39:08
  Speaker 3: us that other details that we've ignored in our model
• 39:11
  Speaker 3: are now important. They may even be crucial. They may
• 39:14
  Speaker 3: even determine the total outcome. And that's an opportunity to
• 39:17
  Speaker 3: learn something, to go back and say, Okay, well, what
• 39:20
  Speaker 3: is it that we didn't include in our description that
• 39:22
  Speaker 3: give us that simple story, and how do we need
• 39:24
  Speaker 3: to make it more complicated to describe what we're actually doing.
• 39:27
  Speaker 3: Science is all about that, right, Start simple, and then refine, refine, refine.
• 39:31
  Speaker 1: And I feel like this question is interesting, as you
• 39:33
  Speaker 1: said before, because it taps into the chemistry of water
• 39:37
  Speaker 1: and the dynamics of water, which might be related to
• 39:40
  Speaker 1: how life started right here on Earth. And maybe in
• 39:43
  Speaker 1: other planets. Like, if we understand more how what's happening
• 39:47
  Speaker 1: at the molecular level with water, maybe we can understand
• 39:50
  Speaker 1: how likely or less likely it is or necessary it
• 39:52
  Speaker 1: is for water to be there for the molecules that
• 39:55
  Speaker 1: make life deform.
• 39:57
  Speaker 3: Yeah. One theory about how organic molecules we're created on
• 40:01
  Speaker 3: Earth involves like asteroids slamming into the Earth, and if
• 40:04
  Speaker 3: those asteroids have ice in them, then those very high temperature,
• 40:08
  Speaker 3: high pressure impacts could have created conditions needed for that
• 40:12
  Speaker 3: kind of chemistry to happen. So understanding exactly how water
• 40:15
  Speaker 3: works and all the weird forms that it can take
• 40:18
  Speaker 3: is crucial for understanding how life could have started here
• 40:21
  Speaker 3: and also what the conditions might be like on exoplanets.
• 40:24
  Speaker 3: We're like right on this exciting cusp of being able
• 40:27
  Speaker 3: to detect water vapor in the atmospheres of planets around
• 40:31
  Speaker 3: other Solar systems, and understanding the chemistry of that gives
• 40:34
  Speaker 3: us a deeper and richer picture of what it's like
• 40:37
  Speaker 3: on those surfaces and what it might be like to
• 40:40
  Speaker 3: be a squigly blob crawling around and waiting for your
• 40:43
  Speaker 3: ice cream to cool.
• 40:44
  Speaker 1: Yeah, or not even maybe that far like even in
• 40:47
  Speaker 1: our solar system. The moon, one of the moons of
• 40:49
  Speaker 1: Jupiter Europa, Right, it's made out of ice on top,
• 40:52
  Speaker 1: and it's got an ocean of liquid water inside. So
• 40:55
  Speaker 1: we kind of want to know, is it possible for
• 40:57
  Speaker 1: life to exist there?
• 40:58
  Speaker 3: Oh yeah, you're absolutely right. I'm that close to home.
• 41:01
  Speaker 3: There's exciting water chemistry happening in our solar system. It's
• 41:05
  Speaker 3: crazy to imagine this, like frozen crust of ice under
• 41:08
  Speaker 3: which there's like a mile deep ocean of super cold
• 41:11
  Speaker 3: water in which maybe life has started.
• 41:14
  Speaker 1: We just don't know, Yeah, because we know there's life underneath,
• 41:17
  Speaker 1: like the ice shelf in Antarctica. But maybe, like you
• 41:22
  Speaker 1: need some special conditions for life to start. Maybe they
• 41:25
  Speaker 1: can start in somewhere like EUROPEA.
• 41:28
  Speaker 3: Yeah, I wonder if you take two moons of Jupiter
• 41:30
  Speaker 3: and one of them is hotter and one of them
• 41:31
  Speaker 3: is colder, which one will freeze first?
• 41:33
  Speaker 1: Yeah, you need a pretty big freezer for that bo
• 41:36
  Speaker 1: like maybe space.
• 41:39
  Speaker 3: Now, imagining a moon size chunk of ice cream.
• 41:42
  Speaker 1: There you go, a giant scoop the ship the size
• 41:46
  Speaker 1: of the moons. That's no moon, that's a giant ball
• 41:49
  Speaker 1: of ice cream.
• 41:51
  Speaker 3: That'll be the death of me.
• 41:53
  Speaker 1: I can hear the cries of a thousand white suns
• 41:56
  Speaker 1: or a billion white sons crying out fur their ice.
• 41:59
  Speaker 3: Cream as our cholesterol rises and temperature drops.
• 42:03
  Speaker 1: That's right, and our mass increases as well. Okay, So
• 42:07
  Speaker 1: what would you do, Daniel if your daughter asks you
• 42:09
  Speaker 1: what would happen if you stuck a cold horse and
• 42:12
  Speaker 1: a warmer horse in a freezer? Would you be concerned?
• 42:16
  Speaker 1: Would you be like, oh, interesting questions? Sit down, let
• 42:19
  Speaker 1: me explain this to you.
• 42:20
  Speaker 3: I try to summarize this entire podcast in thirty seconds,
• 42:23
  Speaker 3: and I would fail. It's hard, man, it's hard.
• 42:27
  Speaker 1: Well, yeah, it kind of has an impact on horses
• 42:30
  Speaker 1: and cold laces, right.
• 42:31
  Speaker 3: Yeah, absolutely No. I tell her that we don't know
• 42:34
  Speaker 3: the answer to that, that it's too complicated, and maybe
• 42:36
  Speaker 3: she should grow up and figure it out.
• 42:38
  Speaker 1: Mmm, become a horse chemist.
• 42:42
  Speaker 3: Better than a horse particle collider.
• 42:44
  Speaker 1: Yeah, that would be a nea career you want to pursue.
• 42:51
  Speaker 3: That's not science, that's just horsing around.
• 42:53
  Speaker 1: Yeah. Yeah, don't look at gift horse and the particle collider.
• 42:58
  Speaker 3: I don't know what that means, but I laughed anyway.
• 43:01
  Speaker 1: I don't know either, it's horse nonsense, all right. Well,
• 43:05
  Speaker 1: another reminder that there are still mysteries in the universe,
• 43:09
  Speaker 1: and some of them that you could even do at
• 43:11
  Speaker 1: home and experiment and see for yourself how weird things
• 43:14
  Speaker 1: can happen and how complicated even something as simple as
• 43:17
  Speaker 1: making ice can be.
• 43:18
  Speaker 3: Teenagers out there, your questions to your science teacher could
• 43:22
  Speaker 3: kick off a multi decade exploration and reveal deeper understandings
• 43:27
  Speaker 3: of the natures of liquids and solids. So keep thinking,
• 43:30
  Speaker 3: keep asking questions, and keep eating ice cream.
• 43:33
  Speaker 1: We hope you enjoyed that. Thanks for joining us, See
• 43:36
  Speaker 1: you next time.
• 43:41
  Speaker 3: For more science and curiosity, come find us on social
• 43:44
  Speaker 3: media where we answer questions and post videos. We're on Twitter, Discboard,
• 43:49
  Speaker 3: Instant and now TikTok. Thanks for listening and remember that
• 43:52
  Speaker 3: Daniel and Jorge Explain the Universe is a production of iHeartRadio.
• 43:56
  Speaker 3: For more podcasts from iHeartRadio, visit the iheartradi, your app,
• 44:00
  Speaker 3: Apple Podcasts, or wherever you listen to your favorite shows.
• 44:08
  Speaker 4: Mm hmm.