Speaker 1: Hey, Jorge, do you have any concerns about raising your
Speaker 1: kids in southern California? I don't. It's pretty great out here,
Speaker 1: although I do feel like they miss out on some
Speaker 1: things they do. What's missing in southern California? Well, definitely
Speaker 1: not plastic surgery, we got that covered for sure. But
Speaker 1: you know, there are experiences kids growing up here that
Speaker 1: they don't get that other kids do. Yeah, like what
Speaker 1: you know, like experiencing winter, snowfall. I mean, I guess
Speaker 1: I miss winter, but I wouldn't say I'm missing winter.
Speaker 1: Would you say, you know, misshoveling snow, putting on multiple
Speaker 1: layers of clothes, multiple layers of clothes. What does that
Speaker 1: even mean? Man? If you're like layers of clothes, what
Speaker 1: does that even mean? I'm recording this naked. You don't
Speaker 1: think kids should know about winter? No, I'm definitely anti winter.
Speaker 1: That's when I'm teaching my kids about winter avoided at
Speaker 1: all costs. But what if they don't? What if they
Speaker 1: end up living there and then are you going to
Speaker 1: go visit them? Depends how cute grandkids are. I guess
Speaker 1: that's pretty coold. Daniela, Hi, I'm or handmade cartoonists and
Speaker 1: the co author of Frequently Asked Questions about the Universe. Hi,
Speaker 1: I'm Daniel. I'm a physics professor at u C Irvine
Speaker 1: and a high energy physicist, and I definitely prefer high
Speaker 1: energy air molecules. You don't like low energy air? No?
Speaker 1: I like it hot outside. You know, when I moved
Speaker 1: to California, I discovered that sunshine makes me happy. Do
Speaker 1: you think maybe that's your upbringing? You grew up in
Speaker 1: New Mexico, right, and then you went to school in Texas.
Speaker 1: I did. I'm a desert person, but you know, New
Speaker 1: Mexico was pretty cold. Los Almos is seven thousand feet
Speaker 1: in elevation, and so we got a lot of snow.
Speaker 1: I remember one year we got fifty five inches overnight.
Speaker 1: I was not a happy camp Well, so you'm are
Speaker 1: of a desert person or a dessert person? Dessert in
Speaker 1: the desert, and do you like your desserts hot or cold?
Speaker 1: I like them both. I'm not picky. But anyways, welcome
Speaker 1: to our podcast, Daniel and Jorge Explained the Universe, a
Speaker 1: production of My Heart Radio in which we are hot
Speaker 1: on the mysteries of the universe and we think that
Speaker 1: everything about it is pretty cool. We want to understand
Speaker 1: how the universe works, what the rules are that govern
Speaker 1: how it operates, and whether or not we can understand them.
Speaker 1: We think one of the most fundamental questions about being alive,
Speaker 1: about being human, is why are things the way that
Speaker 1: they are? And what else could happen in this universe?
Speaker 1: That's right. We don't give a cold shoulder to the
Speaker 1: big questions out there because it is a wonderful universe
Speaker 1: full of amazing things, and sometimes we wish we could
Speaker 1: freeze it all so we can study it a little
Speaker 1: bit better. That's right. These are hot topics for us
Speaker 1: to understand, and as we look out around us in
Speaker 1: the universe, we want to understand why some things are
Speaker 1: the way they are, Why some things are hot, why
Speaker 1: somethings are cold, Why hot things tend to heat up
Speaker 1: cold things, Why cold things tend to cool down hot things. Yeah,
Speaker 1: because we want people to warm up to the extremes
Speaker 1: of the universe and all of the amazing things that
Speaker 1: can happen and many different temperatures out there. The universe
Speaker 1: has a pretty wide range from super hot explosive supernovas
Speaker 1: and hearts of neutron stars really vast voids of empty
Speaker 1: space exactly. And one of the best ways to understand
Speaker 1: how the universe works, to make it reveal it is
Speaker 1: underlying truth, the rules that governed it, is to look
Speaker 1: at the extremes to find out what is the most
Speaker 1: of something that can happen. How bright can things get,
Speaker 1: how fast can this spen, how empty can space be,
Speaker 1: how dense can matter be? So on this podcast, we'd
Speaker 1: like to explore those extremes because we think those are
Speaker 1: the places that the universe is cornered, is forced to
Speaker 1: tell us something about how the rules work. These are
Speaker 1: the edge cases, the ones where we hope the truth
Speaker 1: will reveal itself. Yeah, we have a whole series of
Speaker 1: episodes where talk about extreme things in the universe, the coldest,
Speaker 1: the brightest, the biggest. Daniel have we done the most
Speaker 1: delicious thing in the universe yet? That's just been a
Speaker 1: side research project of mine for a long time. You're
Speaker 1: just gathering data more and more every year. Yeah, you know,
Speaker 1: I'm not trying to mind my personal experience for podcast episodes,
Speaker 1: but that's a good idea. Or maybe the most delicious
Speaker 1: thing in the universe is the universe. It's a pretty
Speaker 1: tasty place. Well, the universe is the only thing in
Speaker 1: the universe, right, so it's both the most delicious and
Speaker 1: the most disgusting thing to eat in the universe. Also
Speaker 1: the most filling, I guess. But we have done a
Speaker 1: whole series of episodes on extremes and we encourage you
Speaker 1: to go back through the archive and check them out.
Speaker 1: But we did do those sort of the hottest and
Speaker 1: coldest things in the universe. Those are two episodes you
Speaker 1: can download, right, Yeah, that's right. And we recently organized
Speaker 1: a curated list of all of our episodes on our website.
Speaker 1: Listeners have been asking for us to sort the episodes
Speaker 1: by topic, and so now we have them grouped by
Speaker 1: cosmology or particle physics, or science fiction or extreme universe.
Speaker 1: So go to our website Daniel and Jorge dot com
Speaker 1: and look at the list of episodes by topic. Yeah,
Speaker 1: so it's kind of like a menu. So if you're
Speaker 1: feeling like, hey, you know, I could use a little
Speaker 1: cosmology today, or I could use a little you know,
Speaker 1: fundamental particles with my meal, you can go and help yourself.
Speaker 1: That's right, Order up a side dish of black holes.
Speaker 1: So we have talked about temperature a lot in this podcast,
Speaker 1: But recently you've got in a few questions about a
Speaker 1: new and interesting topic that's kind of floating out there,
Speaker 1: right exactly, Folks are interested in the extremes of temperature,
Speaker 1: all the way down to absolute zero, or all the
Speaker 1: way up to absolute hot, the hottest that things can
Speaker 1: get in the universe before temperature doesn't even make any sense.
Speaker 1: But over the last year so I've gotten a few
Speaker 1: emails asking me to talk about something that sounds like
Speaker 1: it makes no sense at all, something that has been
Speaker 1: bouncing around on the internet and inspire the curiosity of
Speaker 1: several listeners whether or not it's possible to go even
Speaker 1: below absolute zero. So today on the podcast, we'll be
Speaker 1: asking the question, what is negative temperature? Negative temperature? What now, Daniel,
Speaker 1: is this temperature that is not an optimist or what
Speaker 1: always looks on the dark side of things? Yeah, this
Speaker 1: is grumpy temperature exactly, whatever makes you feel bad. It's
Speaker 1: not how positivemperature. Yeah, this is a weird concept. I guess, well,
Speaker 1: I guess people are familiar with negative temperature, right, Like
Speaker 1: in some places it gets so cold it's like minus
Speaker 1: fifteen degrees, right, yeah, And like negative forty is where
Speaker 1: celsius and fahrenheit meat so on some scales, negative temperature
Speaker 1: is a pretty common experience. But I think people are
Speaker 1: probably thinking about Kelvin. You mean this physical concept is
Speaker 1: more about absolute temperature and whether or not it can
Speaker 1: be negative. Yeah. The Kelvin scale goes from zero, which
Speaker 1: is supposed to be this scenario where nothing is moving
Speaker 1: and everything is basically frozen up to very high values
Speaker 1: when things are wriggling around. So from that perspective, you know, like,
Speaker 1: what does it mean to have negative of temperature? Can
Speaker 1: you move less than not moving at all? Right? That
Speaker 1: is pretty weird. But is that maybe just the scaler thing,
Speaker 1: like we use the wrong scale. But no, because it's
Speaker 1: absolute temperature, right, there are like hard limits or at
Speaker 1: least I thought there were hard limits to absolute temperature
Speaker 1: or the Kelvin scale right zero to infinity kind of
Speaker 1: zero to the plank temperature. Actually, there is this maximum
Speaker 1: temperature beyond which we think that gravity will take over
Speaker 1: in quantum gravity effects will be important And we don't
Speaker 1: even know what temperature means there. Wait, what it's called
Speaker 1: absolute hot? Absolute hot or absolutely hot? Absolute hot is
Speaker 1: absolutely hot? For sure? It sounds like a new vodka brand,
Speaker 1: but it touches on these interesting questions of like what
Speaker 1: is temperature anyway? You know, as human as, we have
Speaker 1: experiences in the world, and then we try to build models,
Speaker 1: physical ideas that describe those things. And then we have
Speaker 1: to find a way to like mathematically express some things
Speaker 1: that we experience temperature or something that's like very tuitive
Speaker 1: to us. But in our physical models we need like
Speaker 1: equations and numbers to describe these things. And sometimes that's
Speaker 1: easy to do, like velocity or location, and sometimes it's
Speaker 1: a little bit fuzzy, and so we're gonna get into
Speaker 1: like what does temperature really mean anyway? Man? Yeah, So
Speaker 1: we have this temperature in the absolute temperature within the
Speaker 1: Kelvin scale, and so for example, like what is room
Speaker 1: temperature in kelvin zero and celsius corresponds to two hundred
Speaker 1: and seventy three in kelvin, So comfortable temperature in celsius
Speaker 1: is like twenty five, which would be like two hundred
Speaker 1: nineties something in kelvin. Okay, so room temperature is two
Speaker 1: hundred ninety eight, let's say in kelvin, and then freezing
Speaker 1: is two d seventy three, And I guess what temperature
Speaker 1: does water boil, so it would be three three, three
Speaker 1: seventy three or a hundred celsius. Okay. So then as
Speaker 1: you start to cool things and make things colder, the
Speaker 1: kelvin goes down and down and down and down. And
Speaker 1: I think we talked about what is the coldest thing?
Speaker 1: We've gotten something here on Earth? Right, Yeah, we have
Speaker 1: on the coldest thing in the universe and the coldest
Speaker 1: thing on Earth. And physicists regularly do experiments with super
Speaker 1: duper cold objects, things that like the micro kelvin temperature
Speaker 1: just about what we thought was the absolute minimum temperature,
Speaker 1: which is actually a tiny little bit above absolute zero,
Speaker 1: that's right. We talked about how the maybe the coldest
Speaker 1: thing in the universe is something you're on Earth that
Speaker 1: scientists have been able to cool down to almost zero
Speaker 1: kelvin zero point zero zero zero zero zero zero one kelvin.
Speaker 1: And so the question is can you actually go below? Right?
Speaker 1: Is there such a thing as negative absolute temperature exactly?
Speaker 1: That is the question today? Or is it even possible?
Speaker 1: I guess? And what are physicists thinking? So as usually
Speaker 1: were wondering how many people out there had thought about
Speaker 1: this question or wondered whether temperature can go negative? And
Speaker 1: so Daniel went out there into the internet or your campus.
Speaker 1: These are Internet answers and thanks again everybody who volunteers
Speaker 1: to answer these weird email the questions. If you'd like
Speaker 1: to receive some strange questions for future podcast as episodes
Speaker 1: in your inbox, please don't be shy or right to
Speaker 1: us two questions at Daniel and Jorge dot com. That's right,
Speaker 1: and you can be as positive or as negative as
Speaker 1: you want in your answers. But think about it for
Speaker 1: a second, right now, do you think absolute temperature can
Speaker 1: be negative? Here's what people had to say. This is
Speaker 1: a loaded question. Um, but if my bank account can
Speaker 1: have a negative balance, so too can a cemometer unless
Speaker 1: it's measuring in kelvin. He never goes Belusira. Well, because
Speaker 1: you're asking this, I'm going to assume that that's what
Speaker 1: the topic is. But right, persons think would be you
Speaker 1: can't you can't have a negative temperature because I'm thinking
Speaker 1: like kelvin, right, I mean, obviously you can have like
Speaker 1: a negative celsius or something, but like you can't have
Speaker 1: like a negative like kelvin amount of temperature. So no,
Speaker 1: I don't think you can. I think it zero Kelvin
Speaker 1: the molecules actually stopped moving. Not molecules, I mean particles
Speaker 1: actually stopped moving as far as I know, probably wrong,
Speaker 1: but that's my understanding. Well, on the Celsius and Fahrenheit scales,
Speaker 1: you can have a nick it of value for your temperature,
Speaker 1: but on the Kelvin or ranking scales, with positive temperature
Speaker 1: being amount of energy and zero absolute zero being um
Speaker 1: no heat energy. In that case, for a negative temperature,
Speaker 1: you would have to have this um. You'd be like
Speaker 1: a black hole of energy, or just the potential to
Speaker 1: absorb energy from somewhere else. But maybe you don't actually
Speaker 1: exist and you're just something mathematicians use. Like I my
Speaker 1: first impression would be no, I don't think you can,
Speaker 1: since if your particles are studic, then your temperature would
Speaker 1: be absolute zero. I don't I don't know. Maybe unless
Speaker 1: the particles are moving back in time some way, then
Speaker 1: you could have negative temperature. I really don't know. I'm
Speaker 1: making this up as I go, Daniel, I think you
Speaker 1: forgot about you how you moved in California, and you
Speaker 1: forgot that you can go negative during the year. I
Speaker 1: do not believe it's possible to have a negative temperature.
Speaker 1: There is a reason why absolute zero is called. Absolute
Speaker 1: temperature is the sum of the kinetic energy of the
Speaker 1: particles of the objects being measured. And I don't believe
Speaker 1: something can have negative motion unless there is some oddity
Speaker 1: and the fact that measuring motion requires the existence of
Speaker 1: a reference point, and with a boundless, infinite universe, where
Speaker 1: is that absolute reference point? But otherwise there is no
Speaker 1: possibility for negative temperature. I'm going to go with no.
Speaker 1: And also it depends on what context we're talking about
Speaker 1: this in. For example, if you're dead, I think your
Speaker 1: temperature can be negative because you'd be frozen in a
Speaker 1: refrigerator or something. But as a living human being, having
Speaker 1: a negative temperature I think would be impossible because we
Speaker 1: are made up of water and that water would freeze
Speaker 1: if it was a negative temperature, meaning we wouldn't be
Speaker 1: able to be alive. Um, blood would not be able
Speaker 1: to move, our heart couldn't beat, and things like that. Mmm. Okay,
Speaker 1: a lot of negative responses, not a lot of positive yeses. No,
Speaker 1: not a lot of believers in negative temperature, but some
Speaker 1: good creative answers you think they should have been more positive,
Speaker 1: like yes, maybe it can. I believe in your universe.
Speaker 1: You're beautiful. I think that they should have had more
Speaker 1: faith in physicists to break the rules and think outside
Speaker 1: the bounds of what is normally possible. It should have
Speaker 1: been more temperature positive that it can be negative exactly
Speaker 1: because you know, the history of physics is littered with
Speaker 1: examples of doing things that we thought were once impossible,
Speaker 1: of discovering the universe works in a way different from
Speaker 1: the way that we had imagined, of breaking the rules
Speaker 1: that we once thought were iron clad. Are you saying
Speaker 1: physicists just basically do things and they're like, you have
Speaker 1: some kind of chip on your shoulder, Hey, Daniel, I
Speaker 1: dare you to understand the universe. I think it's exciting
Speaker 1: to imagine what's impossible might be possible, to think about it.
Speaker 1: You know, that's the job of science fiction authors to think,
Speaker 1: could we get to a nearby star faster than the
Speaker 1: speed of light? How might that be possible. It's also
Speaker 1: the job of physicists to think, like, what are the
Speaker 1: actual rules of the universe? Which ones can be broken,
Speaker 1: which ones can be bent, which ones seem like rules
Speaker 1: but only in certain circumstances, and actually aren't fundamentally rules
Speaker 1: at all, although I guess you have to be careful, right,
Speaker 1: Like you don't want to dare a physicist to find
Speaker 1: a way to blow up the world or create a
Speaker 1: black hole in the center of the of our planet. Yeah,
Speaker 1: I think we've tried that already. Actually, I see you
Speaker 1: were there and that what. I guess you gave up?
Speaker 1: You I hope, well, I hope or failed. No, we
Speaker 1: are still trying to create black holes. It's a large
Speaker 1: hager on collider. In fact, we recently turned the collider
Speaker 1: back on a few weeks ago. Oh man, you're not
Speaker 1: gonna give up, are you? You know, just after we
Speaker 1: turned on the collider, the government of the UK collapsed
Speaker 1: and Boris Johnson was forced to resign as Prime minister. Really,
Speaker 1: do you think there's a correlation there. There's definitely a correlation.
Speaker 1: I don't know about causation. We'll have to turn the
Speaker 1: thing on and off a few times and see what
Speaker 1: other governments fall. I think there are other things going
Speaker 1: on besides you switching on the collider, just you know,
Speaker 1: a few things here and on on our world stage.
Speaker 1: I don't know. I don't keep up with politics, man,
Speaker 1: So I see you just flip on the switch. All right, Well,
Speaker 1: this is a fascinating question. Can absolutely temperature go negative?
Speaker 1: Can it be minus something degrees absolute? And so Daniel,
Speaker 1: that is a weird phrase, negative temperature. What does it mean?
Speaker 1: It all comes down to what we mean by temperature.
Speaker 1: And normally when we talk about temperature, we're talking about
Speaker 1: how hot something feels. You know, you touch something it
Speaker 1: feels hot, you touch something it feels cold. You have
Speaker 1: a sense for whether it's hot or cold outside. That's
Speaker 1: about like the energy flow between you and some other object.
Speaker 1: But we also have a concept for like what's going
Speaker 1: on inside, like micro physical picture of why some things
Speaker 1: are hot and some things are cold. What's going on
Speaker 1: inside something that's hot that makes it different from something
Speaker 1: that's cold. And this eco physical picture mostly is about
Speaker 1: like how much the atoms inside are moving, Like if
Speaker 1: they're zooming around a lot and jiggling a lot, if
Speaker 1: they have a lot of energy, then the thing they
Speaker 1: make up feels hot. If they're mostly not moving, they're
Speaker 1: not jiggling or whizzing around, then the thing they make
Speaker 1: up feels cold. Right, And we have ways to measure that, right,
Speaker 1: like we have devices that called thermometer, as you probably
Speaker 1: know that. Can I tell you a little bit about
Speaker 1: that kind of internal moving around of things. Yeah, And
Speaker 1: what's interesting is that thermometer is measure things that are
Speaker 1: related to temperature. None of them actually directly measure temperature itself. Wait,
Speaker 1: what a thermometer does not meter metter temperature? I know
Speaker 1: it's called a thermometer, but it doesn't actually meter thermo.
Speaker 1: I mean, take, for example, the classic bulb thermometer. What
Speaker 1: is it. It's a little pot of liquid with a
Speaker 1: tube above it. And what it's really measuring is the
Speaker 1: volume of the liquid because there's a relationship. As the
Speaker 1: liquid gets hotter, its volume increases and so it climbs
Speaker 1: up that cylinder and so you're not directly measuring temperature.
Speaker 1: You're measuring the volume, which is you think related to
Speaker 1: the temperature. Right. It's like those glass tubes with the
Speaker 1: little red line. What's actually happening is that when you
Speaker 1: stick it into like let's say, boiling water, it heats
Speaker 1: up the little red liquid and it expands. And then
Speaker 1: the more it expands, I guess, the hotter the water was.
Speaker 1: But you're saying it's not actually measuring the temperature of
Speaker 1: the water. No, it's measuring the volume of that little
Speaker 1: red liquid inside the thermometer, which of course is related
Speaker 1: to temperature, but it's indirect, right. There are other ways
Speaker 1: that are also indirect that you can measure temperature, like
Speaker 1: the thermostat in your house, the one that decides whether
Speaker 1: or not to turn on the air conditioning, that doesn't
Speaker 1: have a little ball of liquid in it. It has
Speaker 1: something called a bimetallic strip. It has two kinds of
Speaker 1: metal bonded together, and the two kinds of metal have
Speaker 1: different properties. One of them expands faster when the heat
Speaker 1: up than the other one. So if the metallic strip
Speaker 1: heats up, then it tends to bend in one direction
Speaker 1: because half of it is expanding faster than the other one,
Speaker 1: and then like closes some circuit and decides to turn
Speaker 1: on your air conditioning. So that's measuring the bending of
Speaker 1: this piece of metal, which again is related to the temperature,
Speaker 1: but it's one step indirect, right. Well, I mean, maybe
Speaker 1: it depends on what you mean by measure, but it
Speaker 1: does sort of measure the temperature of the metallic strip, right,
Speaker 1: which is I guess related to the temperature of the
Speaker 1: air around it. Yeah, I mean it's measuring the bending
Speaker 1: of the metallic strip, which is related to the temperature. Right, Like,
Speaker 1: how would you actually measure the temperature directly? You'd have
Speaker 1: to go, like measure the velocity of those particles themselves
Speaker 1: inside the object, how much they're wiggling, and that would
Speaker 1: tell you the temperature. Instead, you're measuring something which is
Speaker 1: determined by that property. So, I mean, I'm not criticizing thermometers.
Speaker 1: I'm not saying the whole thing is a hoax. Right,
Speaker 1: it's not a scam. Are you anti thermometer? I'm grow thermometer.
Speaker 1: You're saying it's all a big pharma conspiracy. No, But
Speaker 1: if we're going to think carefully about what temperature means,
Speaker 1: and let's think about what our devices are actually measuring,
Speaker 1: what they're really probing, and not just what numbers they're
Speaker 1: reading out, maybe we should have a disclaimer. You know,
Speaker 1: you should trust your thermometer. If it says you have
Speaker 1: a hundred and six degray fever, maybe you should call
Speaker 1: a doctor. Yeah, I'm not a thermometer denier or anything
Speaker 1: like that. You're a temperature denier. No, I'm not like
Speaker 1: that guy who says birds aren't real. All right, Well,
Speaker 1: that that so what you're saying. Usually we measure things
Speaker 1: like the effects of temperature and not maybe what we
Speaker 1: define temperature to be exactly. Yeah, that's right, But we
Speaker 1: do have a model again for what temperature is. We
Speaker 1: imagine that what's going on inside that liquid or inside
Speaker 1: the metal is that they're made of atoms, and those
Speaker 1: atoms wiggle and move or they fly around or they
Speaker 1: flow around, and the degree of that motion is we
Speaker 1: usually what we talk about for temperature, but this is
Speaker 1: a model of temperature. We call this the kinetic model
Speaker 1: of temperature. Is this idea that something is hot when
Speaker 1: the atoms inside of it have more kinetic energy, and
Speaker 1: something is cold when the atoms inside of it have
Speaker 1: less kinetic energy. And it's not just motion, like, it's
Speaker 1: not just velocity. You can also have spinning and vibrating
Speaker 1: and all this kind of stuff, And so it's related
Speaker 1: to this idea of kinetic energy, right, how fast things
Speaker 1: are moving. So from that perspective, you might imagine like
Speaker 1: if temperature is related to kinetic energy, or kinetic energy
Speaker 1: is either zero or more than zero, so how could
Speaker 1: you possibly have negative temperature? Right? It seems like that
Speaker 1: should tell you that temperature is zero or above zero, right,
Speaker 1: because you're saying it's sort of a measure of the
Speaker 1: I guess the average kinetic energy of of something, And
Speaker 1: I guess if it's air, you're measuring the kinetic energy
Speaker 1: of the air particles flying around. Those have kinetic energy.
Speaker 1: But if it's like a block of wood or a
Speaker 1: block of metal, then I guess the atoms aren't moving around,
Speaker 1: but they're still vibrating and bumping against each other. Right,
Speaker 1: And so you if you kind of were to measure
Speaker 1: all of those particles and take the average velocity and
Speaker 1: I guess squared it and all that, then you would
Speaker 1: get the temperature. Yeah, And there's some mathematics you can
Speaker 1: look up about exactly how tempered sure is defined based
Speaker 1: on the number of degrees of freedom, the number of
Speaker 1: ways you can move or wiggle and all this kind
Speaker 1: of stuff. But that's the basic idea for your classic
Speaker 1: definition of temperature. Right, average energy, and in fact, kinetic
Speaker 1: energy you calculated by squaring the velocity of something, right,
Speaker 1: which means that it should always be positive. Yeah, kinetic
Speaker 1: energy is always positive, right, unless I guess you have
Speaker 1: imaginary energy. Unless I imaginary velocity like I imagined I
Speaker 1: went to the post office today, but I didn't because
Speaker 1: he had negative energy because I didn't eat enough dessert
Speaker 1: in the desert to fuel my trip. There you go,
Speaker 1: easy solution. All right, Well, let's get into what exactly
Speaker 1: is temperature, whether that definition of temperature as kinect energy
Speaker 1: makes sense, and whether or not it's possible for it
Speaker 1: to be negative. But first, let's take a quick break
Speaker 1: or I we're asking a pretty trippy question, which is
Speaker 1: can you have negative absolute temperature? Which is sort of
Speaker 1: an oxymoron, right, negative absolute because absolute usually means it
Speaker 1: can only be positive. Mm. Yeah, it's a pretty psycho
Speaker 1: kind of idea negative temperature, and it really gets at
Speaker 1: the heart of this question, like what is temperature anyway?
Speaker 1: You know, which we talked about several times on the podcast,
Speaker 1: because it's kind of a slippery idea. Yeah, and I
Speaker 1: know you sort of hate talking about it, right, you
Speaker 1: know you're not a fan of thermodynamics. Wait, is it
Speaker 1: because you're a thermodenier? Is it? It's all making sense now,
Speaker 1: it's because it's complicated, and thermodynamics involves like thousands and
Speaker 1: thousands or millions or billions of particles. I like thinking
Speaker 1: about individual particles bouncing off each other, really reducing the
Speaker 1: universe down to the simplest little bits and their rules.
Speaker 1: It's hard to think about swarms, you know, Right, does
Speaker 1: that mean you're antidemocracy, Daniel, I don't pay attention to politics,
Speaker 1: right the official line. Oh, that's right, we forgot form.
Speaker 1: We established that earlier. Yeah, it kind of gets into
Speaker 1: the question of what is temperature anyway, Like is it
Speaker 1: really the kinetic energy of the particles inside of it?
Speaker 1: And what does that even mean? It is really interesting
Speaker 1: question and we talked about it several times. Even in
Speaker 1: this idea of temperature as like the kinetic energy of particles,
Speaker 1: you can ask weird questions like what's the kinetic energy
Speaker 1: of one particle? Can a single particle have kinetic energy? Well,
Speaker 1: a single particle can, right, You're wondering if it can
Speaker 1: have temperature? Yes, can a single particle have temperature because
Speaker 1: it can have kinetic energy. And that sort of shows
Speaker 1: you something about the limits of this idea of temperature
Speaker 1: as kinetic energy, because we mean more by temperature than
Speaker 1: just like how much energy is in something. We also
Speaker 1: mean something about how heat flows. Right, we have this
Speaker 1: intuitive experience that we want to somehow describe as if
Speaker 1: you put like a block of ice in your coffee,
Speaker 1: then the ice will melt, right because the heat will
Speaker 1: flow from the coffee to the ice cube. So temperature
Speaker 1: is also about how how heat flows. He tends to
Speaker 1: flow from hot things too cold things, So when we
Speaker 1: define temperature, we also want this idea of heat flow.
Speaker 1: But I guess you're saying there's some sort of tension
Speaker 1: between our intuitive understanding of temperature and maybe the official
Speaker 1: physics definition of it, because I guess you know, we
Speaker 1: talked about the hottest things in the universe, and one
Speaker 1: of the hottest things in the universe is is kind
Speaker 1: of empty space, right, or at least mostly empty space,
Speaker 1: because it's mostly empty, there's not much in it, but
Speaker 1: there are particles in it that are moving really fast,
Speaker 1: and so it does technically have a high temperature empty space.
Speaker 1: But if you were there, you would freeze, And so
Speaker 1: that I think that's what you're saying, is that, like, well,
Speaker 1: that's kind of kind of intuitive. How can I freeze
Speaker 1: if it's one of the hottest things in the universe,
Speaker 1: And so it kind of makes your brain pop a
Speaker 1: little bit. Yeah, out in the middle of empty space.
Speaker 1: There are very fast moving particles, but not very many
Speaker 1: of them. So if you went into empty space, those
Speaker 1: particles would give you energy, but you'd be losing energy
Speaker 1: more quickly than you beginning energy because you'd be readiating
Speaker 1: it out into spaces. You would freeze. That's counterintuitive. There's
Speaker 1: another idea here, though, which is the idea of equilibrium.
Speaker 1: We talk about temperature in terms of many particles rather
Speaker 1: than a single particle, because temperature really is about like
Speaker 1: an object in equilibrium, it's like settled. It's a statement
Speaker 1: about many many things. It's an emergent property, not the
Speaker 1: property of an individual object. The way, for example, like
Speaker 1: um the cost of something, the value of something is
Speaker 1: an emergent property of the market. You can say I'm
Speaker 1: gonna make some piece of art and I'm gonna claim
Speaker 1: it's worth a billion dollars. Well, if you can only
Speaker 1: sell it for seventy four dollars, then what is its value.
Speaker 1: It's value really is seventy four dollars. So the value
Speaker 1: of your art is really determined sort of by like
Speaker 1: the market price for what is willing to bear. In
Speaker 1: the same way, temperature isn't really the property of a particle.
Speaker 1: It's like the property of a system of objects. It's
Speaker 1: an average emergent quantity. Well, are you saying that that's
Speaker 1: one way to measure temperature, because right before you said
Speaker 1: that you can calculate it as the average kinetic energy
Speaker 1: of the particles inside of something. Yeah, but you can't
Speaker 1: define a temperature for a single particle. Even for this
Speaker 1: kinetic theory of temperature, you can't define temperature for a
Speaker 1: single particle. It has to do more with equilibrium sets
Speaker 1: of particles. But what if I have empty space and
Speaker 1: there's only one particle in it, within the kinetic energy
Speaker 1: of that particle basically define the temperature of that empty space. Well,
Speaker 1: in the same way that like if you are the
Speaker 1: only person in the world and you create some art
Speaker 1: and you say it's worth a billion dollars, you're defining
Speaker 1: the value of that. You can't really sell it for
Speaker 1: a billion dollars. Is nobody else in that universe. So
Speaker 1: in that same way, like a single particle doesn't really
Speaker 1: have a temperature. I guess I'm not sure what you're
Speaker 1: saying that our definition of particle temperature doesn't make sense.
Speaker 1: Is that what you're saying or that it breaks down. Yeah,
Speaker 1: it breaks down. It breaks down intuitively or an actual
Speaker 1: like math. I guess it breaks down intuitively, not an
Speaker 1: actual math. I mean an individual particle can hit an
Speaker 1: object and deposit its energy, right, that can happen. There's
Speaker 1: no problem there. We can calculate how that happens. But
Speaker 1: that doesn't mean that we can talk about the temperature
Speaker 1: of this object. Temperature, in the end is a macroscopic quantities,
Speaker 1: not a microscopic quantity. It emerges the way like consciousness does.
Speaker 1: Like can you say that an individual neuron in your
Speaker 1: brain is conscious? No, but somehow they come together to
Speaker 1: make your brain self aware. Not a process we understand,
Speaker 1: but individual neurons we don't think are self aware in
Speaker 1: the same way, like a particle doesn't have a temperature,
Speaker 1: and so it's a little bit slippery because temperature is
Speaker 1: is like intuitive thing we want to describe and not
Speaker 1: something hard and fixed about individual particles. Oh okay, So
Speaker 1: I think what you're saying is that our intuitive sense
Speaker 1: of what temperature is and the official physics definition of
Speaker 1: what temperature is kind of matches up or makes sense.
Speaker 1: If you have a lot of particles in something or
Speaker 1: something is dense. But in some of these extreme cases,
Speaker 1: like if you're down to one particle in empty space,
Speaker 1: then our intuitive definition and the official definition sort of
Speaker 1: like start to diverge or don't start to match well together. Yeah,
Speaker 1: that's right. And to make it even more confusing, we
Speaker 1: have more than one official definition of temperature. Like we
Speaker 1: have one definition of temperature, which is what we talked
Speaker 1: about earlier, related to the average kinetic energy of the particles,
Speaker 1: But we have another completely separate definition of temperature. Wait,
Speaker 1: what we have a second definition of temperature? We do.
Speaker 1: We have a thermodynamic definition of temperature. So one earlier
Speaker 1: we call that the kinetic theory of temperature relates to
Speaker 1: the motion of the particles. Now we have another one
Speaker 1: thermodynamic definition, which is about how heat flows. This one
Speaker 1: comes from the observation that heat flows from hot things
Speaker 1: too cold things, and so this one tries to build
Speaker 1: a definition of temperature that says if two things are
Speaker 1: at the same temperature, no heat flows between them. And
Speaker 1: if one thing is a higher temperature and the other
Speaker 1: one has a lower temperature, he will flow from the
Speaker 1: higher temperature thing to the lower temperature thing. So trust
Speaker 1: to build a theory of temperature that matches that experience.
Speaker 1: And I see you're saying, like it's a different way
Speaker 1: to basically think about temperature, Like temperature is not. Maybe
Speaker 1: the kinetic energy of the particles is just kind of
Speaker 1: like a relative property or relative quantity, Like you know,
Speaker 1: something has more temperature than something else. If the heat
Speaker 1: flows from the first thing to the second thing. That's
Speaker 1: gonna saying, I guess zero would be if heat can't
Speaker 1: flow from this thing to anything, then it must be
Speaker 1: at zero. That's kind of what you're saying, like, let's
Speaker 1: measure zero to be that exactly, And so then you
Speaker 1: can come up with a new mathematical expression or how
Speaker 1: to measure this other idea of temperature, thermodynamic temperature in
Speaker 1: the same way that for the kinetic theory. You can say, oh,
Speaker 1: it's about the motion of the particles, and then you
Speaker 1: can go and write the math and say, here's the
Speaker 1: kinetic energy and vibrational energy, and I can actually calculate
Speaker 1: and constructed. In that same way, you can write down
Speaker 1: mathematical expressions for thermodynamic temperature, and they relate to entropy
Speaker 1: into energy and they help you understand like why heat
Speaker 1: flows from hot things to cold things. So it gives
Speaker 1: you a really interesting thermodynamic insight into like why these
Speaker 1: things happen. But is that really sort of different in
Speaker 1: the kinetic I guess view of things, because I imagine
Speaker 1: if you have something where all the particles are moving
Speaker 1: a lot that would be hot, and something that's not
Speaker 1: moving a lot that would be cold, and you put
Speaker 1: it together, the moving things would you know, bump up
Speaker 1: against the other things. And that's why that's what kind
Speaker 1: of what heat flow is. It's like the energy of
Speaker 1: one thing going to the other. Most of the time,
Speaker 1: these two definitions agree about what temperature is and also
Speaker 1: how energy flows from hot things too cold things. So
Speaker 1: in many scenarios you could use either one. But as
Speaker 1: we'll see, thermodynamic temperature has some weird behaviors in strange
Speaker 1: systems at extremes that might allow the existence of negative temperatures.
Speaker 1: So I guess if you go keep going and keep
Speaker 1: defining temperature in terms of heat flow, then that's when
Speaker 1: you might get into trouble. Yeah, into trouble, or into
Speaker 1: this weird territory where temperature can have non zero negative
Speaker 1: values and like what does that mean? And in the end,
Speaker 1: it reflects something about you know, what temperature means? What
Speaker 1: question are you asking about the universe when you calculate
Speaker 1: this number. So then you're saying this different definition of
Speaker 1: temperature is the thermodynamic version. Uh, and it's related to entropy.
Speaker 1: What does that mean? So thermodynamic temperature tries to give
Speaker 1: us a sense for like why things flow from one
Speaker 1: thing to the other. You know why when you with
Speaker 1: that ice cube in your cup of coffee and you
Speaker 1: come back in an hour, everything is about an even temperature, right,
Speaker 1: why do things like to even out? And the answer
Speaker 1: is entropy. The second law of thermodynamics says that entropy
Speaker 1: always increases. And people sometimes think about entropy is like
Speaker 1: the amount of disorganization in the universe, the messiness in
Speaker 1: the universe, and that you know that works in some
Speaker 1: certain circumstances. But that more accurate description of entropy is
Speaker 1: like how many ways can you arrange something? How many
Speaker 1: different configurations of an object and you have like in
Speaker 1: the different microscopic particles that match, you know, the things
Speaker 1: that you're measuring about it. And a basic concept in
Speaker 1: thermodynamics is that every configuration is equally likely, and so
Speaker 1: if you have some state, some condition that has lots
Speaker 1: of possible ways to achieve it, many possible internal configurations.
Speaker 1: You just more likely to end up in that state. Say,
Speaker 1: for example, you have a bunch of coins and you
Speaker 1: throw them all on the floor, right, how many ways
Speaker 1: are there to get all heads up? There's only one way.
Speaker 1: How many ways are there to get all heads down?
Speaker 1: There's only one way. There's lots of ways to get
Speaker 1: fifty heads up and fifty heads down. So if you
Speaker 1: throw a bunch of coins on the floor, you're much
Speaker 1: more likely to end up in that state. Those states
Speaker 1: have higher entropy, So the universe tend towards these arrangements
Speaker 1: with there's lots of ways, lots of configurations to get
Speaker 1: the same value. So that's what entropy is, right, I
Speaker 1: guess in terms of that, that coffee cup and the
Speaker 1: ice cube, it's almost like you're saying, like, if I
Speaker 1: take some water and I take some coffee, and I
Speaker 1: imagine water and coffee in a cup, it's much more
Speaker 1: likely for it to be all mixed up together in
Speaker 1: the in the tepid temperature, right, then it would be
Speaker 1: likely for all the water to be congregated in one place,
Speaker 1: locked together into an ice cube and then all of
Speaker 1: the coffee to be hot surrounding that blog. That's kind
Speaker 1: of what you're saying. And I think you're saying that
Speaker 1: the melted ice cube, tepid coffee, watery coffee is more
Speaker 1: likely to happen, and therefore it's a state of higher entropy.
Speaker 1: Exactly if you let the energy flow from the hot
Speaker 1: coffee into the ice cube, then opens up more configurations, right,
Speaker 1: You can arrange that in many, many more ways. Now,
Speaker 1: that's why energy flows from hot things too cold things,
Speaker 1: because when it does so, it increases the entropy. It
Speaker 1: opens up the number of ways you can arrange the
Speaker 1: little internal bits, right, But that's not why it does
Speaker 1: it right. I think what you're saying is that's how
Speaker 1: thermodynamic says it. Why does it right? Like, if you
Speaker 1: were to look at it from a totally different perspective,
Speaker 1: you would see the molecules of the eyes and the
Speaker 1: coffee interacting and bumping against against each other, and that's
Speaker 1: why you would say that the heat, the energy goes
Speaker 1: from one place to the other. But if you were
Speaker 1: to put on your thermoid dynamic glasses, you would kind
Speaker 1: of ignore all those interactions. And just say, oh, yeah,
Speaker 1: of course it's because of the entropy that it's going
Speaker 1: up exactly. Yeah. So it's another way to explain it.
Speaker 1: It's like a completely different approach, a different set of ideas,
Speaker 1: and most of the time they predict the same thing.
Speaker 1: And so in this thermodynamic context where you're thinking about
Speaker 1: the energy flow and the entropy, then it's this relationship
Speaker 1: between energy and entropy that tells us what temperature is.
Speaker 1: If two things have this same temperature, then we don't
Speaker 1: want any energy to flow between them. So what we
Speaker 1: want is if two things have the same relationship between
Speaker 1: energy and entropy, then we shouldn't have any more energy flow.
Speaker 1: Like for example, if moving some energy from the ice
Speaker 1: cube to the coffee cup doesn't increase the entropy anymore,
Speaker 1: then energy won't flow. So the definition of temperature for
Speaker 1: thermodynamics doesn't have to do with the kinetic energy objects.
Speaker 1: It has to do with the derivative of energy with
Speaker 1: respect to entropy. How the energy and entropy are related
Speaker 1: to each other. I feel like you're saying that maybe
Speaker 1: temperature is relative if you look at it from a
Speaker 1: thermodynamic point of view. And so let's get dig into
Speaker 1: this connection between energy, heat and temperature and entropy. But first,
Speaker 1: let's take another quick break. All right, we are getting
Speaker 1: hot and heavy here talking about possibly negative temperature. Can
Speaker 1: you have negative absolute temperature? And it may be possible
Speaker 1: depends on how you define temperature. I guess most people
Speaker 1: know that, right, Like, if you define temperature in terms
Speaker 1: of fahrenheit, then yeah, you can have negative temperature or
Speaker 1: itself as you think, yeah, you can have negative temperature,
Speaker 1: but you're saying this is something more fundamental, like maybe, um,
Speaker 1: the universe can allow negative absolute temperature. Yeah, and it
Speaker 1: goes to the heart of this question, or like what
Speaker 1: do we mean by temperature anyway? And you know, we
Speaker 1: define these things to describe our experience and then we
Speaker 1: explore their extreme to say where does this break down?
Speaker 1: Does this really make sense? This is something that's universal
Speaker 1: or only something that's useful in certain contexts. So we
Speaker 1: came up with this idea of thermodynamic temperature that basically
Speaker 1: tells you how energy flows around to maximize entropy. The
Speaker 1: two things have the same temperature, then we don't expect
Speaker 1: energy to flow between them. And you know, you can
Speaker 1: have two things that are very different. One thing could
Speaker 1: have a lot more capacity for different configurations than the
Speaker 1: other one, and whether energy flows from one object to
Speaker 1: another depend on like are you going to increase the
Speaker 1: entropy by moving that energy along? And so it is
Speaker 1: this relationship between energy and entropy that is the thermodynamic
Speaker 1: definition of temperature. Technically, it's the derivative of energy with
Speaker 1: respect to entropy. So do you increase the energy as
Speaker 1: entropy increases? That's the temperature I see, And I guess
Speaker 1: maybe my question is why would you do that? Why
Speaker 1: would you define it this way? Is it because it
Speaker 1: matches usually with our other definition of temperature, or like
Speaker 1: why would you call this temperature? Also, it's a totally
Speaker 1: different approach, and it's the macroscopic approach, and it has
Speaker 1: some advantages. You know. The microscopic one is weirdly time invariant.
Speaker 1: The laws of physics governing how things bounce against each other,
Speaker 1: those look the same forward and backwards, and so it's
Speaker 1: hard to go from like a microscopic picture of atoms
Speaker 1: as like little balls, to an understanding of how a
Speaker 1: state evolves forward in time with entropy. It's complicated to
Speaker 1: go from one to the other. This is a picture
Speaker 1: of thermodynamics that deals directly with macroscopic quantities. It says, look,
Speaker 1: these are the things we can measure, the entropy, the energy,
Speaker 1: these are things we're interested in. Not all of science
Speaker 1: has to be reductionists. There are other ways to gain
Speaker 1: understanding and explanation than just to tear things apart into
Speaker 1: their tiny bits. Sometimes you do that and you don't
Speaker 1: get any understanding. Like when you look at the brain,
Speaker 1: psychology is valuable even if neuroscience can't yet explain it.
Speaker 1: Right right, Well, let's dig into this a little bit
Speaker 1: because I am a little bit confused. So you're saying,
Speaker 1: the thermodynamic definition of temperature is the derivative of say
Speaker 1: it again, energy flow divided by entropy. Yeah, it's the
Speaker 1: derivative of energy with respect to entropy. So energies E
Speaker 1: and entropy is S. So temperature in this sense is
Speaker 1: d E D S. Apologize for introducing math to the body. Yeah,
Speaker 1: what are you doing to me here? Okay? So it's uh,
Speaker 1: it's kind of like saying how energy changes if you
Speaker 1: change entropy exactly, because the key idea again is that
Speaker 1: entropy is always going to be maximized, and so what
Speaker 1: array angagement of the stuff? What arrangement of the energy
Speaker 1: is going to give you the most entropy, And so
Speaker 1: to know whether something is going to flow from one
Speaker 1: object to another, you have to know, like how much
Speaker 1: energy does some entropy cost? If I want to increase
Speaker 1: the entropy over here, how much energy does it cost me?
Speaker 1: If I'm gonna gain more entropy by moving the energy
Speaker 1: over than I lose where the energy came from, then
Speaker 1: let's do it. So you have to understand, like how
Speaker 1: much entropy do you get per energy? And that's basically
Speaker 1: what temperature is, right, But then what are you trying
Speaker 1: to measure the temperature of like one thing or two things?
Speaker 1: You know what I mean? Like if I told you
Speaker 1: what's the thermodynamic temperature of an ice cube, how would
Speaker 1: you calculate it? Well, I would measure how quickly it
Speaker 1: gains new possible configurations as I increase its energy as
Speaker 1: you put it in coffee. I can measure the energy
Speaker 1: of the atoms in the ice cube or in some
Speaker 1: other way. Yeah, I guess the question is just like
Speaker 1: if I give you an ice cube, how would you
Speaker 1: measure the thermodynamic temperature of it? I would measure how
Speaker 1: it's entropy changes as I change its energy, right, So
Speaker 1: the temperature there is the relate ationship between the energy
Speaker 1: and the entropy. So you change one and you measure
Speaker 1: the other. Right, But how would you measure its entropy? Well,
Speaker 1: you know, you can measure entropy by measuring temperature and energy,
Speaker 1: because it's a relationship between the three. And that's the
Speaker 1: thing I always hated about thermodynamics is that you feel
Speaker 1: like you're just going in circles. Sometimes. Well, it's good,
Speaker 1: we're spending an hour here discussing something you hate. I'm
Speaker 1: sure people are following along, right right along. All right, Well,
Speaker 1: let's maybe take a step. But I think what you're
Speaker 1: saying is that temperature is kind of this weird thing,
Speaker 1: and if you look at it from a thermodynamic point
Speaker 1: of view, you can look at it in terms of
Speaker 1: how it changes with respect to entropy. Like if it
Speaker 1: something has a lot of temperature, something is hot in
Speaker 1: the thermodynamic sense, that means what it takes a lot
Speaker 1: of entropy, or it doesn't take a lot of entropy.
Speaker 1: Something is hot in a thermodynamic sense, it means that
Speaker 1: it costs a lot of energy to change its entropy.
Speaker 1: And so if you want to take some of that
Speaker 1: energy away, it doesn't reduce its entropy very very much.
Speaker 1: So if you have a really hot link it surrounding
Speaker 1: your ice cube, you can take some of that energy
Speaker 1: out of the liquid and put it into the ice cube,
Speaker 1: and you're not going to lose a whole lot of
Speaker 1: entropy from the liquid. Right, high temperature means high D
Speaker 1: E D s, so you can take energy away without
Speaker 1: losing a whole lot of entropy. And because the ice
Speaker 1: cube is cold, right, has low D E D s
Speaker 1: and as you add energy to it, you get a
Speaker 1: lot more entropy. So you lose a little bit of
Speaker 1: entropy from the hot liquid and you gain a lot
Speaker 1: of entropy into the cold ice cube for the same
Speaker 1: amount of energy. I see. It's almost like the cost
Speaker 1: of entropy for something exactly. It's like exchange rates. Yeah,
Speaker 1: it's like how much bang for your buck does energy
Speaker 1: give you in in the entropy of something Like if
Speaker 1: something an ice cube which is cold, you get a
Speaker 1: lot of entropy just by you know, breathing on it
Speaker 1: with your warm breath, but a cold cup of coffee
Speaker 1: you need a lot of energy to reduce its entropy. Yes,
Speaker 1: So now we have Jorges economic theory of temperature. Yes,
Speaker 1: my My coffee theory is you can buy entropy cheap
Speaker 1: from a hot liquid, and you can sell it at
Speaker 1: a high price in your cold ice cube exactly. Okay,
Speaker 1: So that's the thermo dynamic definition, and it matches up
Speaker 1: with the regular definition because I guess if something is
Speaker 1: zero kelvin, entropy is cheap for something like that, right,
Speaker 1: Like I just got to put in a little bit
Speaker 1: of energy and I get a whole bunch of entropy.
Speaker 1: But if something is like a million degrees kelvin, you
Speaker 1: know it's gonna take me a lot of energy to
Speaker 1: increase the entropy or something that's already super entropic. And
Speaker 1: it's also about the relationship. Like this makes a lot
Speaker 1: of sense for most things because for most things, as
Speaker 1: you add energy, you get more entropy. As you add
Speaker 1: energy to a liquid, you free the particles and then
Speaker 1: they become gas and they can move in new ways
Speaker 1: and find new arrangements, and as you cool things down,
Speaker 1: they get less entropy. So if entropy is always increasing
Speaker 1: with energy, then this makes perfect sense. And that's what
Speaker 1: it does for the ideal gas. And you're like kinetic
Speaker 1: theory of temperature and they line up as you say,
Speaker 1: you mean like you always get something for your money, exactly.
Speaker 1: But condensed matter physicists can imagine in some kinds of
Speaker 1: weird materials where this isn't true, some kind of weird
Speaker 1: materials whereas you add more energy, you actually get fewer
Speaker 1: micro states. Do you have decreasing entropy, So as the
Speaker 1: thing has more and more energy, there might be fewer
Speaker 1: ways to arrange it, and that would lead to negative temperature.
Speaker 1: M All right, now we're getting to the question of
Speaker 1: the episode, which is you're saying that if you define
Speaker 1: temperature in the thermoidyanatic way, um, there are things potentially
Speaker 1: or theoretically I guess that could have negative temperature because
Speaker 1: when you put energy into them, they actually sort of
Speaker 1: get neater, right or colder exactly, they get neater, they
Speaker 1: have fewer ways to arrange themselves. And here's an example.
Speaker 1: Imagine a bunch of particles in a line, and these
Speaker 1: particles are fixed on the line. They can't move at all.
Speaker 1: The only thing they can do is be spin up
Speaker 1: or spin down. Put these particles in a magnetic field,
Speaker 1: so that like spin up has more energy than spin
Speaker 1: down for example, meaning more energy meaning like it that
Speaker 1: just want to spin down, Yeah exactly. Costs more energy
Speaker 1: to spin up than to spin down, like trying to
Speaker 1: stand up a stick. Yeah exactly. So now imagine all
Speaker 1: these particles spin down right minimum energy, there'd be no
Speaker 1: entropy because there's only one way to arrange all of
Speaker 1: these things. It's just like getting all heads when you
Speaker 1: flip a bunch of coins, or getting all tails. Right,
Speaker 1: there's only one way to arrange them, so they're all
Speaker 1: spin down, so there's zero entropy. It's minimum entropy, like
Speaker 1: the block of ice. Right, everything is like neatly ordered
Speaker 1: in a state that um it wants to be in exactly. Now,
Speaker 1: as you add energy, some atoms start to flip right,
Speaker 1: and you quickly add entropy. There's lots of ways to
Speaker 1: arrange it. Now, if you say, well, I have enough
Speaker 1: energy to flip one atom, well, there's a bunch of
Speaker 1: different ways to do that. You can flip any of
Speaker 1: the atoms. If you want to flip five atoms, you
Speaker 1: have enough energy to flip five atoms, right, then there's
Speaker 1: lots and lots of ways, and so as you add energy,
Speaker 1: the entropy increases. Totally normal so far, but what happens
Speaker 1: once you pass the halfway point, once more than half
Speaker 1: of the atoms are flipped up, and as you keep
Speaker 1: adding energy, you're reducing the number of ways you can
Speaker 1: arrange the system until all the way up to the
Speaker 1: maximum energy, when everything is flipped up, there's only one
Speaker 1: way to arrange the system at the maximum energy. So
Speaker 1: in the second half there after you pass the halfway point,
Speaker 1: as you're adding energy, you're losing entropy, so you have
Speaker 1: the opposite relationship between energy and entropy. WHOA, Okay, So
Speaker 1: it's kind of like the coins that like you're saying right, like,
Speaker 1: if all the coins are heads up, that's minimum entropy. Yeah,
Speaker 1: that's zero entropy, and half of them heads up heads
Speaker 1: down is maximum entropy. But then if you go all
Speaker 1: the way I even keep going, and somehow you're able
Speaker 1: to flip all of the coins tails up, then that's
Speaker 1: also zero entropy. Yeah exactly. And so you have maximum
Speaker 1: energy and zero entropy. And this is a really weird
Speaker 1: system and not something we actually see in nature, but
Speaker 1: in principle. Because you are adding energy but reducing entropy,
Speaker 1: that's technically negative temperature. So everything above the halfway point
Speaker 1: there has negative temperature. It has d E D S
Speaker 1: is a negative value. I see in this weird situation,
Speaker 1: after all the coins are heads and tails up, you're saying,
Speaker 1: it actually starts to have a negative temperature again because
Speaker 1: the entropy is going down again as I put more
Speaker 1: energy into it, exactly, And so the system would prefer
Speaker 1: less energy would flow towards a higher entropy situation, which
Speaker 1: is more of a mix, right, Like you try to
Speaker 1: buy more entropy with your energy, but you actually lose entropy.
Speaker 1: That's what it means to be cold in this definition
Speaker 1: of temperature. And this gets really weird. Like let's say
Speaker 1: you have two of these things. Now you have two
Speaker 1: of these lines of atoms, and you put them in
Speaker 1: touch so they can share energy. Right, where is the
Speaker 1: energy going to go? Say one of them has a
Speaker 1: higher value of temperature than the other one. Well, in
Speaker 1: this case, something with negative temperature actually has more energy
Speaker 1: then the thing with positive temperature, right, because they get
Speaker 1: to negative temperature you have to go above the halfway point,
Speaker 1: so half of them are flipped up. So in this case,
Speaker 1: the heat actually flows from the higher energy negative temperature
Speaker 1: system to the positive temperature system, which sounds kind of
Speaker 1: bonkers and backwards well, yeah, yeah, it does sound bankers.
Speaker 1: But I feel like you're trying to maybe trying to
Speaker 1: fudge some of these definitions, right, because like these things,
Speaker 1: these coins only have this weird property because you kind
Speaker 1: of introducing this bias with the magnet. Right, it's not
Speaker 1: actually heat or energy, right, it's sort of something different
Speaker 1: that's going from one to the other. It is energy, right.
Speaker 1: It takes energy to be like misaligned with the magnet,
Speaker 1: for example, and so it really is energy. The question
Speaker 1: really is like what does this mean by temperature? We
Speaker 1: introduce this definition of thermodynamic temperature so that we could
Speaker 1: describe the kind of things we see in the world, right,
Speaker 1: heat flowing from high temperature objects to low temperature objects.
Speaker 1: And this is just an example of this definition pushed
Speaker 1: to the extreme where it really doesn't make any sense anymore.
Speaker 1: The same way we push the definition of kinetic temperature
Speaker 1: to the extreme by asking what is the temperature of
Speaker 1: one particle? In this case, while you can get technically
Speaker 1: negative temperature, it really shows the breakdown of this idea
Speaker 1: of thermodynamic temperature more than like actually being negative in
Speaker 1: any meaningful way. M I see you're saying it like
Speaker 1: if I define temperature as the cost of entropy per
Speaker 1: bank per bug for energy. Um, that doesn't work if
Speaker 1: you have a situation where it actually like if you
Speaker 1: put in more energy, it actually lose this entropy exactly. Yeah,
Speaker 1: it just doesn't really work. And you can see that
Speaker 1: because it predicts that things flow from negative temperature to
Speaker 1: positive temperature. What's the point of temperature then? If it
Speaker 1: doesn't even align with our ideas and our experience? All right, Well,
Speaker 1: I mean it's sort of like kind of I feel
Speaker 1: like it's almost kind of like going to celsius or fahrenheit, right,
Speaker 1: you're sort of changing the scale of things maybe, and
Speaker 1: so then therefore you can have negative temperatures if you
Speaker 1: define things this way. Yeah, it's true. You could always
Speaker 1: define temperatures to be negative as well. I think this
Speaker 1: one is interesting because it shows you, not like that
Speaker 1: the universe breaks the rules or anything, but it shows
Speaker 1: you that these ideas that we invent to try to
Speaker 1: describe our experience, they have limits, and those limits aren't
Speaker 1: physical limits, they're like conceptual limits. Like this idea doesn't
Speaker 1: really work in that circumstance. The whole concept of temperature
Speaker 1: doesn't really make sense for this weird invented system right,
Speaker 1: Like it's like, maybe we have a way of describing
Speaker 1: and calling things in the universe and calculating things, but
Speaker 1: maybe that's not really how the universe works. Like, maybe
Speaker 1: the universe has its own way of doing things that
Speaker 1: are beyond what we're able to describe, kind of or define.
Speaker 1: Is that what you're saying. Yeah, it's like the way
Speaker 1: you can talk about feelings for a person, but can
Speaker 1: you talk about feelings for like a rock or a river.
Speaker 1: You know, it's an idea but doesn't really make sense
Speaker 1: in the same way that like temperature makes sense in
Speaker 1: certain contexts or certain behaviors emerge and have relationships, but
Speaker 1: not in all context You can't ask what is the
Speaker 1: temperature of every arbitrary system that you event doesn't always
Speaker 1: make sense? I see, But what if I an imaginary friend, Rob,
Speaker 1: can I still assign thermodynamic happiness to it? Depends how
Speaker 1: much it's willing to spend to get more entropy? Yeah,
Speaker 1: be flippid and it lands heads up? But what does
Speaker 1: that mean? It means it's time for dessert, all right?
Speaker 1: So then, um, that's kind of where this idea of
Speaker 1: negative temperature is. I think what you're saying is that
Speaker 1: some physicists, if they go by this definition, are allowed
Speaker 1: to call things as having negative temperature. Right, So maybe,
Speaker 1: like most people were saying, no, that's impossible, you can
Speaker 1: have negative temperature, you would say, well, it depends on
Speaker 1: who you talk to and what you mean by temperature. Yeah, exactly,
Speaker 1: and whether you think it even makes sense to apply
Speaker 1: temperature to these crazy, bonkers, weird situations that will never
Speaker 1: arise in our universe. So does that mean I can
Speaker 1: be a thermoid dynamic temperature denier but still a regular
Speaker 1: temperature positivist. You can be whatever you want, man. So
Speaker 1: thanks to everybody who wrote in to ask us to
Speaker 1: talk about that tricky concept. I hope that was useful.
Speaker 1: We hope you enjoy that and maybe made you think
Speaker 1: about what it actually means for something to be hot
Speaker 1: and cold. Like, maybe what we experience in our everyday
Speaker 1: lives is just what we experience in our everyday lives.
Speaker 1: Maybe it doesn't always apply to everything in the universe.
Speaker 1: Thanks for joining us, see you next time. Thanks for listening,
Speaker 1: and remember that. Daniel and Jorge Explain the Universe is
Speaker 1: a production of I Heart Radio For More podcast from
Speaker 1: my heart Radio, visit the i heart Radio app, Apple podcasts,
Speaker 1: or wherever you listen to your favorite shows. Yeah.