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Speaker 1: Hey Orge, do you have any concerns about raising your

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Speaker 1: kids in southern California.

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Speaker 4: I don't. It's pretty great out here, although I do

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Speaker 4: feel like they miss out on some things they do.

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Speaker 1: What's missing in southern California.

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Speaker 4: Well, definitely not plastic surgery.

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Speaker 1: We got that covered for sure.

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Speaker 4: But you know, there are experiences kids growing up here

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Speaker 4: that they don't get that other kids do. Yeah, like

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Speaker 4: what you know, like experiencing winter, snowfall.

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Speaker 1: I mean, I guess I'm miss winter, but I wouldn't

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Speaker 1: say I'm missing winter.

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Speaker 4: Would you say, you know, misshoveling snow? Putting on multiple

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Speaker 4: layers of clothes.

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Speaker 1: Multiple layers of clothes? What does that even mean?

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Speaker 4: Man, You're like layers of clothes, What does that even mean?

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Speaker 4: I'm recording this naked. You don't think kids you know

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Speaker 4: about winter?

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Speaker 1: No, I'm definitely anti winter. That's what I'm teaching my

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Speaker 1: kids about winter avoided at all costs.

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Speaker 4: But what if they don't, What if they end up

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Speaker 4: living there? And then are you going to go visit them?

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Speaker 1: Depends how cute the grand kids are. I guess that's

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Speaker 1: pretty cold.

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Speaker 4: Daniel Hi I am Hoorham made cartoonist and the co

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Speaker 4: author of Frequently Asked Questions about the Universe.

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Speaker 1: Hi I'm Daniel. I'm a physics professor at UC Irvine

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Speaker 1: and a high energy physicist, and I definitely prefer high

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Speaker 1: energy air molecules.

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Speaker 4: You don't like low energy air?

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Speaker 5: No?

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Speaker 1: I like it hot outside. You know, when I moved

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Speaker 1: to California, I discovered that sunshine makes me happy.

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Speaker 4: Do you think maybe that's your upbringing? You grew up

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Speaker 4: in New Mexico, right, and then you went to school

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Speaker 4: in Texas.

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Speaker 1: I did. I'm a desert person, but you know, New

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Speaker 1: Mexico was pretty cold. Los Almos is seven thousand feet

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Speaker 1: in elevation, and so we got a lot of snow.

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Speaker 1: I remember one year we got fifty five inches overnight.

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Speaker 1: I was not a happy camper.

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Speaker 4: Whoa a desert person or a dessert person?

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Speaker 1: Dessert in the desert?

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Speaker 4: And do you like your desserts hot or cold?

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Speaker 1: Oh? I like them both. I'm not picky.

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Speaker 4: But anyways, Welcome to our podcast, Daniel and Jorge Explain

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Speaker 4: the Universe, a production of iHeartRadio.

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Speaker 1: In which we are hot on the mysteries of the

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Speaker 1: universe and we think that everything about it is pretty cool.

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Speaker 1: We want to understand how the universe works, what the

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Speaker 1: rules are that govern how it operates and whether or

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Speaker 1: not we can understand them. We think one of the

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Speaker 1: most fundamental questions about being alive, about being human, is

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Speaker 1: why are things the way that they are and what

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Speaker 1: else could happen in this universe.

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Speaker 4: It's right, we don't give a cold shoulder to the

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Speaker 4: big questions out there because it is a wonderful universe

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Speaker 4: full of amazing things, and sometimes we wish we could

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Speaker 4: freeze it all so we can study it a little

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Speaker 4: bit better.

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Speaker 1: That's right. These are hot topics for us to understand,

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Speaker 1: and as we look out around us in the universe,

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Speaker 1: we want to understand why some things are the way

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Speaker 1: they are, Why some things are hot, why some things

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Speaker 1: are cold, Why hot things tend to heat up cold things,

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Speaker 1: why cold things tend to cool down hot things.

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Speaker 4: Yeah, I guess we want people to warm up to

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Speaker 4: the extremes of the universe and all the amazing things

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Speaker 4: that can happen and many different temperatures out there. The

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Speaker 4: universe has a pretty wide range from super hot, explosive

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Speaker 4: supernovas and hearts of neutron stars really vast voids of empty.

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Speaker 1: Space exactly, and one of the best ways to understand

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Speaker 1: how the universe works to make it reveal its underlying truth,

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Speaker 1: the rules that govern it. Is to look at the

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Speaker 1: extremes to find out what is the most of something

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Speaker 1: that can happen. How bright can things get, how fast

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Speaker 1: can they spin? How empty can space be? How dense

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Speaker 1: can matter be? So on this podcast, we'd like to

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Speaker 1: explore those extremes because we think those are the places

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Speaker 1: that the universe is cornered, is forced to tell us

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Speaker 1: something about how the rules work. These are the edge cases,

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Speaker 1: the ones where we hope the truth will reveal itself.

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Speaker 4: Yeah, we have a whole series of episodes where we

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Speaker 4: talk about extreme things in the universe, the coldest, the brightest,

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Speaker 4: the biggest. Daniel have we done the most delicious thing

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Speaker 4: in the universe yet?

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Speaker 1: That's just been a side research project of mine for

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Speaker 1: a long time.

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Speaker 4: You're just gathering data more and more every year.

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Speaker 1: Yeah, you know, I'm not trying to mine my personal

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Speaker 1: experience for podcast episodes, but that's a good idea.

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Speaker 4: Or maybe the most delicious thing in the universe is

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Speaker 4: the universe. It's a pretty tasty place.

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Speaker 1: Well, the universe is the only thing in the universe, right,

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Speaker 1: so it's both the most delicious and the most disgusting

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Speaker 1: thing to eat in.

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Speaker 4: The universe, also the most filling I guess. We have

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Speaker 4: done a whole series of episodes on extremes and we

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Speaker 4: encourage you to go back through the archive and check

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Speaker 4: them out. But we did do those sort of the

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Speaker 4: hottest and coldest things in the universe. Those are two

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Speaker 4: episodes you can download, right.

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Speaker 1: Yeah, that's right. And we recently organized a curated list

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Speaker 1: of all of our episodes on our website. Listeners have

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Speaker 1: been asking for us to sort the episodes by topic,

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Speaker 1: and so now we have them grouped by cosmology or

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Speaker 1: particle physics, or science fiction or extreme universe. So go

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Speaker 1: to our website Danielandjorge dot com and look at the

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Speaker 1: list of episodes by topic.

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Speaker 4: Yeah, so it's kind of like a menu. So if

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Speaker 4: you're feeling like, hey, you know, I could use a

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Speaker 4: little cosmology today, or I could use a little fundamental

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Speaker 4: particles with my meal, you can go and help yourselves.

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Speaker 1: That's right, Order up a side dish of black holes.

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Speaker 4: So we have talked about temperature a lot in this podcast,

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Speaker 4: but recently you've gotten a few questions about a new

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Speaker 4: and interesting topic that's kind of floating out there.

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Speaker 1: Right, exactly. Folks are interested in the extremes of temperature,

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Speaker 1: all the way down to absolute zero, or all the

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Speaker 1: way up to absolute hot, the hottest that things can

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Speaker 1: get in the universe before temperature doesn't even make any sense.

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Speaker 1: But over the last year so I've gotten a few

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Speaker 1: emails asking me to talk about something that sounds like

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Speaker 1: it makes no sense at all, something that has been

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Speaker 1: bouncing around on the Internet and inspire the curiosity of

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Speaker 1: several listeners whether or not it's possible to go even

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Speaker 1: below absolute zero.

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Speaker 4: So today on the podcast, we'll be asking the question,

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Speaker 4: what is negative temperature?

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Speaker 1: Negative temperature?

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Speaker 4: What now, Daniel, is this temperature that is not an

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Speaker 4: optimist or what always looks on the dark side of things?

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Speaker 1: Yeah, this is grumpy temperature exactly, whatever makes you feel bad.

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Speaker 4: It's not a positive temperature. Yeah, this is a weird concept.

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Speaker 4: I guess, well, I guess people are familiar with negative temperature, right,

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Speaker 4: Like in some places it gets so cold it's like

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Speaker 4: minus fifteen degrees.

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Speaker 1: Right, yeah, and like negative forty is where celsius and

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Speaker 1: fahrenheit meet, so on some scales, negative temperature is a

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Speaker 1: pretty common experience. But I think people are probably thinking

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Speaker 1: about Kelvin.

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Speaker 4: You mean this physical concept is more about absolute temperature

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Speaker 4: and whether or not it can be negative.

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Speaker 1: Yeah, the Kelvin scale goes from zero, which is supposed

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Speaker 1: to be this scenario where nothing is moving and everything

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Speaker 1: is basically frozen, up to very high values when things

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Speaker 1: are wriggling around. So from that perspective, you know, like,

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Speaker 1: what does it mean to have negative temperature? Can you

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Speaker 1: move less and not moving at all?

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Speaker 4: Right, that is pretty weird. But is that maybe just

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Speaker 4: the scaler thing, like we used the wrong scale. But no,

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Speaker 4: because it's absolute temperature, right, there are like hard limits

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Speaker 4: or at least I thought there were hard limits to

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Speaker 4: absolute temperature or the Kelvin scale, right, zero two infinity

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Speaker 4: kind of zero.

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Speaker 1: To the plank temperature. Actually, there is this maximum temperature

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Speaker 1: beyond which we think that gravity will take over. In

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Speaker 1: quantum gravity effects will be important. And we don't even

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Speaker 1: know what temperature means there, Wait, what that's called absolute hot?

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Speaker 4: Absolute hot or absolutely hot?

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Speaker 1: Absolute hot is absolutely hot.

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Speaker 4: For sure, sounds like a new vodka brand.

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Speaker 1: But it touches on these interesting questions of like what

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Speaker 1: is temperature? Anyway? You know, as humans, we have experiences

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Speaker 1: in the world, and then we try to build models,

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Speaker 1: physical ideas that describe those things. Then we have to

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Speaker 1: find a way to like mathematically express some things that

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Speaker 1: we experience temperature, something that's like very intuitive to us.

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Speaker 1: But in our physical models we need like equations and

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Speaker 1: numbers to describe these things. And sometimes that's easy to do,

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Speaker 1: like velocity or location, and sometimes it's a little bit fuzzy,

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Speaker 1: And so we're going to get into like what does

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Speaker 1: temperature really mean anyway?

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Speaker 5: Man?

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Speaker 4: Yeah, So we have this temperature in the of absolute

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Speaker 4: temperature within the Kelvin scale, and so for example, like

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Speaker 4: what is room temperature in kelvin.

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Speaker 1: Zero and celsius corresponds to two hundred and seventy three

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Speaker 1: in kelvin, So comfortable temperature in celsius is like twenty

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Speaker 1: twenty five, which would be like two hundred and ninety

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Speaker 1: something in kelvin.

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Speaker 4: Okay, So room temperature is two hundred and ninety eight,

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Speaker 4: let's say in kelvin, and then freezing is two hundred

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Speaker 4: and seventy three, And I guess what temperature does water boil?

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Speaker 4: So it'd be three hundred and seventy three.

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Speaker 1: Three seventy three or one hundred celsius.

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Speaker 4: Okay, So then as you start to cool things and

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Speaker 4: make things colder, the kelvin goes down and down and

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Speaker 4: down and down. And I think we talked about what

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Speaker 4: is the coldest thing we've gone in? Something here on Earth?

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Speaker 1: Right, Yeah, we have done the coldest thing in the

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Speaker 1: universe and the coldest thing on Earth. And physicists regularly

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Speaker 1: do experiments with super duper cold objects, things that like

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Speaker 1: the microkelvin temperature just above what we thought was the

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Speaker 1: absolute minimum temperature, which is actually a tiny little bit

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Speaker 1: above absolute.

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Speaker 4: Zero, that's right. We talked about how maybe the coldest

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Speaker 4: thing in the universe is something here on Earth that

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Speaker 4: scientists have been able to cool down to almost zero

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Speaker 4: kelvin zero point zero zero zero zero zero zero one kelvin.

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Speaker 4: And so the question is can you actually go below? Right?

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Speaker 4: Is there such a thing as negative absolute temperature exactly?

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Speaker 1: That is the question today?

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Speaker 4: Or is it even possible? I guess?

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Speaker 1: And what are physicists thinking?

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Speaker 4: So, as usual, we were wondering how many people out

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Speaker 4: there had thought about this question or wondered whether temperature

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Speaker 4: can go negative? And so Daniel went out there into

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Speaker 4: the internet or your campus.

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Speaker 1: These are Internet answers, and thanks again everybody who volunteers

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Speaker 1: to answer these weird email the questions. If you'd like

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Speaker 1: to receive some strange questions for future podcast episodes in

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Speaker 1: your inbox, please please don't be shy or write to

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Speaker 1: us to questions at daniel Aandhorge dot com.

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Speaker 4: That's right, and you can be as positive or as

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Speaker 4: negative as you want in your answers. But think about

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Speaker 4: it for a second, right now. Do you think absolute

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Speaker 4: temperature can be negative? Here's what people have to say.

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Speaker 4: This is a loaded question.

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Speaker 6: But if my bank account can have a negative balance,

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Speaker 6: so too can as themometer.

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Speaker 4: Unless it's measuring in kelvin, he never goes below zero.

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Speaker 7: Well, because you're asking this, I'm going to assume that

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Speaker 7: that's what the topic is. But my first I think

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Speaker 7: would be, no, you can't have a negative temperature because

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Speaker 7: I'm thinking like kelvin, right, I mean, obviously you can

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Speaker 7: have like a negative celsius or something, but like you

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Speaker 7: can't have like a negative like kelvin amount of temperature.

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Speaker 4: So no, I don't think you can.

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Speaker 8: I think at zero kelvin, the molecules actually stop moving.

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Speaker 8: Not molecules, I mean particles actually stop moving as far

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Speaker 8: as I know, probably wrong, but that's my understanding.

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Speaker 9: Well, on the Celsius and fahrenheit's scales, you can have

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Speaker 9: a negative value for your timerture. But on the Kelvin

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Speaker 9: or Rankin scales, with positive temperature being amount of energy

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Speaker 9: and zero absolute zero being no heat energy. In that case,

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Speaker 9: for a negative temperature you would have to have this

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Speaker 9: you'd be like a black hole of energy or just

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Speaker 9: the potential to absorb energy from somewhere else. But maybe

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Speaker 9: you don't actually exist and you're just something mathematicians use.

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Speaker 10: Like I my first impression would be no, I don't

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Speaker 10: think you can, since if your particles are static, then

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Speaker 10: your temperature would be absolute zero.

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Speaker 1: I don't know.

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Speaker 10: Maybe unless the particles are moving back in time some way,

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Speaker 10: then you could have negative temperature.

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Speaker 1: I really don't know.

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Speaker 11: I'm making this up as I go, Danielle, I think

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Speaker 11: you forgot about Chicago. You moved in Kali, Na, and

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Speaker 11: you forgot that you can go negative during the year.

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Speaker 12: I do not believe it's possible to have a negative temperature.

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Speaker 12: There is a reason why absolute zero is called. Absolute

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Speaker 12: temperature is the sum of the kinetic energy of the

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Speaker 12: particles of the objects being measured. And I don't believe

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Speaker 12: something can have negative motion unless there is some oddity

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Speaker 12: in the fact that measuring motion requires the existence of

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Speaker 12: a reference point, and with a boundless, infinite universe, where

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Speaker 12: is that absolute reference point? But otherwise there is no

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Speaker 12: possibility for negative temperature.

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Speaker 6: I'm going to go with no. And also it depends

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Speaker 6: on what context we're talking about this. And for example,

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Speaker 6: if you're dead, I think your temperature can be negative

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Speaker 6: because you'd be frozen in a refrigerator or something. But

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Speaker 6: as a living human being, having a negative temperature I

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Speaker 6: think would be impossible because we are made up of

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Speaker 6: water and that water would freeze if it was a

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Speaker 6: negative temperature, meaning we wouldn't be able to be alive,

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Speaker 6: blood would not be able to move, our heart couldn't beat,

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Speaker 6: and things like that.

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Speaker 4: Hmm, Okay, a lot of negative responses, not a lot

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Speaker 4: of positive yeses.

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Speaker 1: No, not a lot of believers in negative temperature, but

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Speaker 1: some good creative answers.

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Speaker 4: You think they should have been more positive, like, yes,

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Speaker 4: maybe it can. I believe in you, universe, You're beautiful.

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Speaker 1: I think that they should have had more faith in

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Speaker 1: physicists to break the rules and think outside the bounds

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Speaker 1: of what is normally possible.

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Speaker 4: There should have been more temperature positive that it can

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Speaker 4: be negative.

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Speaker 1: Exactly because you know, the history of physics is littered

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Speaker 1: with examples of doing things that we thought were once impossible,

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Speaker 1: of discovering the universe works in a way different from

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Speaker 1: the way that we had imagined, of breaking the rules

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Speaker 1: that we once thought were ironclad.

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Speaker 4: Are you saying physicists basically do things on a dare

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Speaker 4: like you have some kind of chip on your shoulder, Hey, Daniel,

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Speaker 4: I dare you to understand the universe?

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Speaker 1: I think it's exciting to imagine what's impossible might be possible,

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Speaker 1: to think about it. That's the job of science fiction

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Speaker 1: authors to think, could we get to a nearby star

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Speaker 1: faster than the speed of light? How might that be possible.

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Speaker 1: It's also the job of physicists to think, like, what

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Speaker 1: are the actual rules of the universe? Which ones can

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Speaker 1: be broken, which ones can be bent, Which ones seem

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Speaker 1: like rules but only in certain circumstances and actually aren't

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Speaker 1: fundamentally rules at all.

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Speaker 4: Although I guess you have to be careful where you

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Speaker 4: don't want to dare a Physicists to find a way

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Speaker 4: to blow up the world or create a black hole

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Speaker 4: at the center of the of our planet.

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Speaker 1: Yeah, I think we've tried that already.

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Speaker 4: Actually, Oh, I see you were there and that what

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Speaker 4: I guess you gave up? You well, I hope or failed.

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Speaker 1: No, we are still trying to create black holes. It's

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Speaker 1: a large Hadren collider. In fact, we recently turned the

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Speaker 1: collider back on a few weeks ago.

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Speaker 4: Oh man, you're not going to give up, are you.

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Speaker 1: You know, just after we turned on the collider the

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Speaker 1: government of the UK collapsed and Boris Johnson was forced

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Speaker 1: to resign as Prime minister.

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Speaker 4: Really do you think there's a correlation there?

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Speaker 1: There's definitely a correlation. I don't know, boy, causation. Have

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Speaker 1: to turn the thing on and off a few times

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Speaker 1: and see what other governments fall.

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Speaker 4: I think there are other things going on besides you

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Speaker 4: switching on the collider, just you know, a few things

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Speaker 4: here on our world stage.

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Speaker 1: I don't know. I don't keep up with politics, man, So.

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Speaker 4: I see you just flip on the switch, all right. Well,

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Speaker 4: this is a fascinating question. Can absolute temperature go negative?

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Speaker 4: Can it be minus something degrees absolute? And so, Daniel,

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Speaker 4: that is a weird phrase negative temperature, What does it mean?

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Speaker 1: It all comes down to what we mean by temperature.

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Speaker 1: And normally when we talk about temperature, we're talking about

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Speaker 1: how hot something feels. You know, you touch something it

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Speaker 1: feels hot, you touch something it feels cold. You have

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Speaker 1: a sense for whether it's hot or cold outside. That's

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Speaker 1: about like the energy flow between you and some other object.

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Speaker 1: But we also have a concept for like what's going

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Speaker 1: on inside the like microphysical picture of why some things

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Speaker 1: are hot and some things are cold. What's going on

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Speaker 1: inside something that's hot that makes it different from something

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Speaker 1: that's cold. And this microphysical picture mostly is about like

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Speaker 1: how much the atoms inside are moving. Like if they're

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Speaker 1: zooming around a lot and jiggling a lot, they have

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Speaker 1: a lot of energy, then the thing they make up

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Speaker 1: feels hot. If they're mostly not moving, they're not jiggling

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Speaker 1: or whizzing around, then the thing they make up feels cold.

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Speaker 4: Right, And we have ways to measure that, right, Like

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Speaker 4: we have devices that called thermometers, as you probably know,

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Speaker 4: that kind of tell you a little bit about that

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Speaker 4: kind of internal moving around of things.

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Speaker 1: Yeah, And what's interesting is that thermometers measure things that

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Speaker 1: are related to temperature. None of them actually directly measure

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Speaker 1: temperature itself.

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Speaker 4: Wait, what a thermometer does not meter metter temperature?

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Speaker 1: I know it's called a thermometer, but it doesn't actually

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Speaker 1: meter thermo. I mean, take, for example, the classic bulb thermometer.

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Speaker 1: What is it. It's a little pot of liquid with

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Speaker 1: a tube above it, and what it's really measuring is

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Speaker 1: the volume of the liquid, because there's a relationship. As

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Speaker 1: the liquid gets hotter, its volume increases and so it

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Speaker 1: climbs up that cylinder. So you're not directly measuring temperature.

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Speaker 1: You're measuring the volume, which is you think related to

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Speaker 1: the temperature.

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Speaker 4: Right, It's like those glass tubes with the little red line.

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Speaker 4: What's actually happening is that when you stick it into

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Speaker 4: like let's say, boiling water, it heats up the little

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Speaker 4: red liquid and it expands, and the more it expands,

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Speaker 4: I guess, the harder the water was. But you're saying

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Speaker 4: it's not actually measuring the temperature of the water.

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Speaker 1: No, it's measuring the volume of that little red liquid

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Speaker 1: inside the thermometer, which of course is related to temperature,

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Speaker 1: but it's indirect. Right. There are other ways that are

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Speaker 1: also indirect that you can measure temperature. Like the thermostat

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Speaker 1: in your house, the one that decides whether or not

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Speaker 1: to turn on the air conditioning, that doesn't have a

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Speaker 1: little ball of liquid in it. It has something called

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Speaker 1: a bimetallic strip and has two kinds of metal bonded together.

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Speaker 1: And the two kinds of metal have different properties. One

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Speaker 1: of them expands faster when they heat up than the

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Speaker 1: other one. So if the metallic strip heats up, then

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Speaker 1: it tends to bend in one direction because half of

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Speaker 1: it is expanding faster than the other one, and then

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Speaker 1: it like closes some circuit and decide to turn on

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Speaker 1: your air conditioning. So that's measuring the bending of this

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Speaker 1: piece of metal, which again is related to the temperature.

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Speaker 1: But it's one step indirect, right.

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Speaker 4: Well, I mean maybe it depends on what you mean

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Speaker 4: by measure, but it does sort of measure the temperature

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Speaker 4: of the metallic strip, right, which is I guess related

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Speaker 4: to the temperature of the air around it.

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Speaker 1: Yeah, I mean it's measuring the bending of the metallic strip,

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Speaker 1: which is related to the temperature. Right, Like, how would

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Speaker 1: you actually measure the temperature directly? You'd have to go

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Speaker 1: like measure the velocity of those particles themselves inside the object,

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Speaker 1: how much they're wiggling, and that would tell you the temperature. Instead,

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Speaker 1: you're measuring something which is determined by that property. So,

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Speaker 1: I mean, I'm not criticizing thermometers. I'm not saying the

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Speaker 1: whole thing's a hoax. It's not a scam.

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Speaker 4: Are you anti thermometer?

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Speaker 1: No, I'm pro thermometer.

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Speaker 4: You're saying it's all a big pharma conspiracy.

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Speaker 1: No, But if we're gonna think carefully about what temperature means,

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Speaker 1: then let's think about what our devices are actually measuring,

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Speaker 1: what they're really proing, and not just what numbers they're

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Speaker 1: reading out.

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Speaker 4: Maybe we should have a disclaimer. You know, you should

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Speaker 4: trust your thermometer. If it says you have one hundred

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Speaker 4: and sixty degree fever, maybe you should call a doctor.

440
00:21:10,359 --> 00:21:13,119
Speaker 1: Yeah, I'm not a thermometer denier or anything like that.

441
00:21:14,680 --> 00:21:17,280
Speaker 4: Yeah you're a temperature denier.

442
00:21:17,440 --> 00:21:19,600
Speaker 1: No, I'm not like that guy who says birds aren't real.

443
00:21:20,119 --> 00:21:22,879
Speaker 4: All right, Well, that so what you were saying. Usually

444
00:21:22,920 --> 00:21:25,760
Speaker 4: we measure things like the effects of temperature and not

445
00:21:25,960 --> 00:21:28,520
Speaker 4: maybe what we define temperature to be exactly.

446
00:21:28,680 --> 00:21:30,680
Speaker 1: Yeah, that's right, But we do have a model again

447
00:21:30,720 --> 00:21:33,080
Speaker 1: for what temperature is. We imagine that what's going on

448
00:21:33,280 --> 00:21:35,800
Speaker 1: inside that liquid or inside the metal is that they're

449
00:21:35,800 --> 00:21:38,480
Speaker 1: made of atoms, and those atoms wiggle and move or

450
00:21:38,520 --> 00:21:41,680
Speaker 1: they fly around or they flow around, and the degree

451
00:21:41,720 --> 00:21:44,840
Speaker 1: of that motion is usually what we talk about for temperature.

452
00:21:44,880 --> 00:21:47,040
Speaker 1: But this is a model of temperature. We call this

453
00:21:47,119 --> 00:21:51,040
Speaker 1: the kinetic model of temperature. This idea that something is

454
00:21:51,080 --> 00:21:54,520
Speaker 1: hot when the atoms inside of it have more kinetic energy,

455
00:21:54,520 --> 00:21:56,600
Speaker 1: and something is cold when the atoms inside of it

456
00:21:56,760 --> 00:21:59,600
Speaker 1: have less kinetic energy. And it's not just motion like,

457
00:21:59,640 --> 00:22:02,199
Speaker 1: it's not just velocity. You can also have spinning and

458
00:22:02,320 --> 00:22:04,680
Speaker 1: vibrating and all this kind of stuff. And so it's

459
00:22:04,760 --> 00:22:08,000
Speaker 1: related to this idea of kinetic energy, right, how fast

460
00:22:08,040 --> 00:22:11,320
Speaker 1: things are moving. So from that perspective, you might imagine like,

461
00:22:11,600 --> 00:22:15,200
Speaker 1: if temperature is related to kinetic energy, well, kinetic energy

462
00:22:15,440 --> 00:22:18,760
Speaker 1: is either zero or more than zero. So how could

463
00:22:18,800 --> 00:22:21,639
Speaker 1: you possibly have negative temperature? Right? It seems like that

464
00:22:21,720 --> 00:22:25,200
Speaker 1: should tell you that temperature is zero or above zero.

465
00:22:25,480 --> 00:22:27,760
Speaker 4: Right, Because you're saying it's sort of a measure of

466
00:22:27,800 --> 00:22:31,199
Speaker 4: the I guess the average kinetic energy of something, and

467
00:22:31,400 --> 00:22:34,080
Speaker 4: I guess if it's air you're measuring the kinetic energy

468
00:22:34,240 --> 00:22:37,840
Speaker 4: of the air particles flying around. Those have kinetic energy.

469
00:22:37,840 --> 00:22:39,679
Speaker 4: But if it's like a block of wood or a

470
00:22:39,680 --> 00:22:42,600
Speaker 4: block of metal, then I guess the atoms aren't moving around,

471
00:22:42,600 --> 00:22:45,320
Speaker 4: but they're still vibrating and bumping against each other. Right,

472
00:22:45,400 --> 00:22:47,359
Speaker 4: And so if you kind of were to measure all

473
00:22:47,400 --> 00:22:50,760
Speaker 4: of those particles and take the average velocity and I

474
00:22:50,760 --> 00:22:54,000
Speaker 4: guess squared it and all that, then you would get

475
00:22:54,080 --> 00:22:54,720
Speaker 4: the temperature.

476
00:22:54,840 --> 00:22:57,199
Speaker 1: Yeah, and there's some mathematics you can look up about

477
00:22:57,359 --> 00:22:59,960
Speaker 1: exactly how temperature is defined based on the number of degrees.

478
00:23:00,080 --> 00:23:02,320
Speaker 1: He's a freedom, the number of ways you can move

479
00:23:02,520 --> 00:23:04,400
Speaker 1: or wiggle and all this kind of stuff. But that's

480
00:23:04,400 --> 00:23:07,520
Speaker 1: the basic idea for your classic definition of temperature.

481
00:23:07,720 --> 00:23:10,679
Speaker 4: Right. The average energy, and in fact, kinetic energy you

482
00:23:10,920 --> 00:23:15,240
Speaker 4: calculated by squaring the velocity of something, right, which means

483
00:23:15,240 --> 00:23:16,760
Speaker 4: that it should always be positive.

484
00:23:16,880 --> 00:23:19,480
Speaker 1: Yeah, kinetic energy is always positive.

485
00:23:19,320 --> 00:23:22,520
Speaker 4: Right, unless I guess you have imaginary energy.

486
00:23:22,720 --> 00:23:26,679
Speaker 1: Let's see if imaginary velocity like I imagined, I went

487
00:23:26,680 --> 00:23:28,600
Speaker 1: to the post office today, but I didn't.

488
00:23:29,040 --> 00:23:30,720
Speaker 4: Because you had negative energy because.

489
00:23:30,480 --> 00:23:32,679
Speaker 1: I didn't eat enough dessert in the desert to fuel

490
00:23:32,720 --> 00:23:33,160
Speaker 1: my trip.

491
00:23:33,240 --> 00:23:36,000
Speaker 4: There. You go easy, solution. All right, Well, let's get

492
00:23:36,000 --> 00:23:40,080
Speaker 4: into what exactly is temperature, whether that definition of temperature

493
00:23:40,119 --> 00:23:43,840
Speaker 4: as kin energy makes sense, and whether or not it's

494
00:23:43,880 --> 00:23:46,480
Speaker 4: possible for it to be negative. But first, let's take

495
00:23:46,520 --> 00:23:47,240
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496
00:23:51,440 --> 00:23:54,440
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549
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564
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Speaker 4: All right, we're asking a pretty triviy question, which is

565
00:27:32,000 --> 00:27:36,359
Speaker 4: can you have negative absolute temperature? Which is sort of

566
00:27:36,600 --> 00:27:40,080
Speaker 4: a oxymorn right, negative absolute because absolute usually means it

567
00:27:40,119 --> 00:27:41,120
Speaker 4: can only be positive.

568
00:27:41,320 --> 00:27:41,680
Speaker 5: Mm hmm.

569
00:27:41,920 --> 00:27:45,480
Speaker 1: Yeah. It's a pretty psycho kind of idea negative temperature,

570
00:27:45,640 --> 00:27:47,480
Speaker 1: and it really gets at the heart of this question,

571
00:27:47,640 --> 00:27:51,120
Speaker 1: like what is temperature anyway? You know, which we've talked

572
00:27:51,160 --> 00:27:53,639
Speaker 1: about several times on the podcast, because it's kind of

573
00:27:53,680 --> 00:27:54,880
Speaker 1: a slippery idea.

574
00:27:55,040 --> 00:27:57,080
Speaker 4: Yeah, and I know you sort of hate talking about it, right,

575
00:27:57,880 --> 00:28:00,480
Speaker 4: you're not a fan of thermodynamics. Wait, is it because

576
00:28:00,480 --> 00:28:03,000
Speaker 4: you're a thermal denier? Is it? Is this all making

577
00:28:03,040 --> 00:28:04,439
Speaker 4: sense now?

578
00:28:04,840 --> 00:28:09,080
Speaker 1: It's because it's complicated and thermodynamics involves like thousands and

579
00:28:09,160 --> 00:28:12,480
Speaker 1: thousands or millions or billions of particles. I like thinking

580
00:28:12,480 --> 00:28:15,720
Speaker 1: about individual particles bouncing off each other, really reducing the

581
00:28:15,760 --> 00:28:18,560
Speaker 1: universe down to the simplest little bits and their rules.

582
00:28:18,600 --> 00:28:20,720
Speaker 1: It's hard to think about swarms, you.

583
00:28:20,680 --> 00:28:23,240
Speaker 4: Know, Right, does that mean you're anti democracy?

584
00:28:23,359 --> 00:28:27,480
Speaker 1: Daniel, I don't pay attention to politics, right, that's the

585
00:28:27,560 --> 00:28:28,200
Speaker 1: official line.

586
00:28:28,359 --> 00:28:32,400
Speaker 4: Oh that's right, we forgot for akda. We established that earlier. Yeah.

587
00:28:32,440 --> 00:28:34,280
Speaker 4: So it kind of gets into the question of what

588
00:28:34,440 --> 00:28:37,439
Speaker 4: is temperature anyway? Like is it really the kinetic energy

589
00:28:37,440 --> 00:28:39,360
Speaker 4: of the particles inside of it? And what does that

590
00:28:39,400 --> 00:28:39,840
Speaker 4: even mean?

591
00:28:40,000 --> 00:28:42,120
Speaker 1: It is really interesting question and we talked about it

592
00:28:42,160 --> 00:28:44,960
Speaker 1: several times. Even in this idea of temperature as like

593
00:28:45,000 --> 00:28:48,320
Speaker 1: the kinetic energy of particles, you can ask weird questions

594
00:28:48,400 --> 00:28:51,440
Speaker 1: like what's the kinetic energy of one particle? Can a

595
00:28:51,480 --> 00:28:54,040
Speaker 1: single particle have kinetic energy, Well.

596
00:28:53,880 --> 00:28:56,400
Speaker 4: A single particle can, right, you're wondering if it can

597
00:28:56,480 --> 00:28:57,080
Speaker 4: have temperature.

598
00:28:57,200 --> 00:28:59,880
Speaker 1: Yes, can a single particle have temperature, because it can

599
00:29:00,120 --> 00:29:02,600
Speaker 1: have kinetic energy. And that sort of shows you something

600
00:29:02,640 --> 00:29:06,400
Speaker 1: about the limits of this idea of temperature as kinetic energy.

601
00:29:06,760 --> 00:29:09,840
Speaker 1: Because we mean more by temperature than just like how

602
00:29:09,920 --> 00:29:12,600
Speaker 1: much energy is in something. We also mean something about

603
00:29:12,640 --> 00:29:16,160
Speaker 1: how heat flows. Right. We have this intuitive experience that

604
00:29:16,200 --> 00:29:18,480
Speaker 1: we want to somehow describe. That's if you put like

605
00:29:18,520 --> 00:29:21,560
Speaker 1: a block of ice in your coffee, then the ice

606
00:29:21,640 --> 00:29:24,040
Speaker 1: will melt, right because the heat will flow from the

607
00:29:24,080 --> 00:29:27,280
Speaker 1: coffee to the ice cube. So temperature is also about

608
00:29:27,320 --> 00:29:30,160
Speaker 1: how heat flows. Heat tends to flow from hot things

609
00:29:30,160 --> 00:29:32,960
Speaker 1: to cold things. So when we define temperature, we also

610
00:29:33,000 --> 00:29:35,080
Speaker 1: want this idea of heat flow.

611
00:29:35,320 --> 00:29:35,480
Speaker 5: Right.

612
00:29:35,520 --> 00:29:37,360
Speaker 4: I guess you're saying there's some sort of tension between

613
00:29:37,400 --> 00:29:41,520
Speaker 4: our intuitive understanding of temperature and maybe the official physics

614
00:29:41,520 --> 00:29:43,760
Speaker 4: definition of it, because I guess you know, we talked

615
00:29:43,800 --> 00:29:45,560
Speaker 4: about the hottest things in the universe, and one of

616
00:29:45,600 --> 00:29:47,520
Speaker 4: the hottest things in the universe is kind of an

617
00:29:47,560 --> 00:29:51,000
Speaker 4: empty space, right, or at least mostly empty space. Because

618
00:29:51,440 --> 00:29:53,480
Speaker 4: it's mostly empty, there's not much in it, but there

619
00:29:53,520 --> 00:29:56,160
Speaker 4: are particles in it that are moving really fast, and

620
00:29:56,200 --> 00:29:59,440
Speaker 4: so it does technically have a high temperature empty space,

621
00:29:59,480 --> 00:30:01,719
Speaker 4: but if you were there, you would freeze. And so

622
00:30:02,160 --> 00:30:03,680
Speaker 4: I think that's what you're saying, is that, like, well,

623
00:30:03,680 --> 00:30:05,880
Speaker 4: that's kind of counterintuitive. How can I freeze if it's

624
00:30:05,920 --> 00:30:07,440
Speaker 4: one of the hottest things in the universe, And so

625
00:30:07,560 --> 00:30:09,280
Speaker 4: it kind of makes your brain pop a little bit.

626
00:30:09,400 --> 00:30:11,239
Speaker 1: Yeah, out in the middle of empty space there are

627
00:30:11,320 --> 00:30:14,280
Speaker 1: very fast moving particles, but not very many of them.

628
00:30:14,400 --> 00:30:17,280
Speaker 1: So if you went into empty space, those particles would

629
00:30:17,280 --> 00:30:20,080
Speaker 1: give you energy, but you'd be losing energy more quickly

630
00:30:20,080 --> 00:30:22,400
Speaker 1: than you'd be gaining energy because you'd be radiating it

631
00:30:22,440 --> 00:30:25,840
Speaker 1: out into space. You would freeze. That's counterintuitive. There's another

632
00:30:25,920 --> 00:30:28,400
Speaker 1: idea here, though, which is the idea of equilibrium. We

633
00:30:28,440 --> 00:30:31,440
Speaker 1: talk about temperature in terms of many particles rather than

634
00:30:31,440 --> 00:30:35,480
Speaker 1: a single particle, because temperature really is about like an object.

635
00:30:35,520 --> 00:30:38,640
Speaker 1: In equilibrium, it's like settled. It's a statement about many

636
00:30:38,720 --> 00:30:42,200
Speaker 1: many things. It's an emergent property, not the property of

637
00:30:42,200 --> 00:30:45,440
Speaker 1: an individual object. The way, for example, like the cost

638
00:30:45,520 --> 00:30:48,640
Speaker 1: of something, the value of something is an emergent property

639
00:30:48,720 --> 00:30:50,840
Speaker 1: of the market. You can say I'm gonna make some

640
00:30:50,960 --> 00:30:53,520
Speaker 1: piece of art, and I'm going to claim it's worth

641
00:30:53,520 --> 00:30:55,640
Speaker 1: a billion dollars. Well, if you can only sell it

642
00:30:55,680 --> 00:30:58,120
Speaker 1: for seventy four dollars, then what is its value. Its

643
00:30:58,160 --> 00:31:01,680
Speaker 1: value really is seventy four dollars. So the value of

644
00:31:01,720 --> 00:31:03,880
Speaker 1: your art is really determined sort of by like the

645
00:31:03,920 --> 00:31:06,040
Speaker 1: market price for what it is willing to bear. The

646
00:31:06,080 --> 00:31:08,480
Speaker 1: same way, temperature isn't really the property of a particle.

647
00:31:08,560 --> 00:31:11,400
Speaker 1: It's like the property of a system of objects. It's

648
00:31:11,440 --> 00:31:13,240
Speaker 1: an average emergent quantity.

649
00:31:13,400 --> 00:31:16,160
Speaker 4: Well, are you saying that that's one way to measure temperature,

650
00:31:16,200 --> 00:31:18,720
Speaker 4: because right before you said that you can calculate it

651
00:31:18,760 --> 00:31:21,920
Speaker 4: as the average kinetic energy of the particles inside of something.

652
00:31:22,040 --> 00:31:24,840
Speaker 1: Yeah, but you can't define a temperature for a single particle.

653
00:31:24,960 --> 00:31:27,360
Speaker 1: Even for this kinetic theory of temperature, you can't define

654
00:31:27,400 --> 00:31:29,600
Speaker 1: temperature for a single particle. It has to do more

655
00:31:29,720 --> 00:31:32,120
Speaker 1: with equilibrium sets of particles.

656
00:31:32,720 --> 00:31:34,840
Speaker 4: But what if I have empty space and there's only

657
00:31:34,880 --> 00:31:37,320
Speaker 4: one particle in it, would in the kinetic energy of

658
00:31:37,360 --> 00:31:40,480
Speaker 4: that particle basically define the temperature of that empty space.

659
00:31:40,600 --> 00:31:42,239
Speaker 1: Well, in the same way that like if you are

660
00:31:42,280 --> 00:31:44,320
Speaker 1: the only person in the world and you create some

661
00:31:44,480 --> 00:31:46,520
Speaker 1: art and you say it's worth a billion dollars. Are

662
00:31:46,520 --> 00:31:48,600
Speaker 1: you're defining the value of that. You can't really sell

663
00:31:48,640 --> 00:31:51,760
Speaker 1: it for a billion dollars as nobody else in that universe.

664
00:31:52,160 --> 00:31:54,480
Speaker 1: So in that same way, like a single particle doesn't

665
00:31:54,520 --> 00:31:56,600
Speaker 1: really have a temperature.

666
00:31:56,040 --> 00:31:57,960
Speaker 4: I guess I'm not sure what you're saying. You're saying

667
00:31:57,960 --> 00:32:01,000
Speaker 4: that our definition of particle temperate doesn't make sense. Is

668
00:32:01,000 --> 00:32:02,560
Speaker 4: that what you're saying, or that it breaks down?

669
00:32:02,680 --> 00:32:03,440
Speaker 1: Yeah, it breaks down.

670
00:32:03,560 --> 00:32:06,280
Speaker 4: It breaks down intuitively or in actual like math.

671
00:32:06,520 --> 00:32:09,160
Speaker 1: I guess it breaks down intuitively, not an actual math.

672
00:32:09,200 --> 00:32:11,920
Speaker 1: I mean an individual particle can hit an object and

673
00:32:11,960 --> 00:32:15,440
Speaker 1: deposit its energy, right, that can happen, There's no problem there.

674
00:32:15,520 --> 00:32:18,240
Speaker 1: We can calculate how that happens. But that doesn't mean

675
00:32:18,280 --> 00:32:20,960
Speaker 1: that we can talk about the temperature of this object temperature.

676
00:32:21,000 --> 00:32:23,880
Speaker 1: In the end, it is a macroscopic quantities, not a

677
00:32:23,880 --> 00:32:27,840
Speaker 1: microscopic quantity. It emerges the way like consciousness does. Like

678
00:32:27,880 --> 00:32:30,880
Speaker 1: can you say that an individual neuron in your brain

679
00:32:31,040 --> 00:32:34,440
Speaker 1: is conscious? No, but somehow they come together to make

680
00:32:34,480 --> 00:32:37,520
Speaker 1: your brain self aware. Not a process we understand. But

681
00:32:37,760 --> 00:32:40,960
Speaker 1: individual neurons we don't think are self aware. In the

682
00:32:40,960 --> 00:32:43,600
Speaker 1: same way, like a particle doesn't have a temperature, and

683
00:32:43,600 --> 00:32:45,880
Speaker 1: so it's a little bit slippery because temperature is this

684
00:32:46,000 --> 00:32:48,880
Speaker 1: like intuitive thing we want to describe and not something

685
00:32:49,160 --> 00:32:51,160
Speaker 1: hard and fixed about individual particles.

686
00:32:51,440 --> 00:32:53,239
Speaker 4: Oh okay, So I think what you're saying is that

687
00:32:53,280 --> 00:32:56,280
Speaker 4: our intuitive sense of what temperature is and the official

688
00:32:56,280 --> 00:32:59,200
Speaker 4: physics definition of what temperature is kind of matches up

689
00:32:59,320 --> 00:33:01,600
Speaker 4: or makes sense if you have a lot of particles

690
00:33:01,640 --> 00:33:04,480
Speaker 4: in something, or something is dense put in some of

691
00:33:04,520 --> 00:33:07,680
Speaker 4: these extreme cases, like if you're down to one particle

692
00:33:07,720 --> 00:33:11,000
Speaker 4: in empty space, then our intuitive definition and the official

693
00:33:11,000 --> 00:33:14,800
Speaker 4: definition sort of like start to diverge or don't start

694
00:33:14,840 --> 00:33:15,800
Speaker 4: to match well together.

695
00:33:16,000 --> 00:33:18,480
Speaker 1: Yeah, that's right. And to make it even more confusing,

696
00:33:18,640 --> 00:33:22,680
Speaker 1: we have more than one official definition of temperature. Like

697
00:33:22,720 --> 00:33:24,640
Speaker 1: we have one definition of temperature, which is what we

698
00:33:24,680 --> 00:33:27,920
Speaker 1: talked about earlier, related to the average kinetic energy of

699
00:33:27,920 --> 00:33:32,280
Speaker 1: the particles. But we have another completely separate definition of temperature.

700
00:33:32,400 --> 00:33:35,360
Speaker 4: Wait, what we have a second definition of temperature?

701
00:33:35,400 --> 00:33:38,840
Speaker 1: We do. We have a thermodynamic definition of temperature. So

702
00:33:39,040 --> 00:33:41,720
Speaker 1: one earlier we call that the kinetic theory of temperature

703
00:33:42,160 --> 00:33:44,400
Speaker 1: relates to the motion of the particles. Now we have

704
00:33:44,440 --> 00:33:48,880
Speaker 1: another one thermodynamic definition, which is about how heat flows.

705
00:33:49,000 --> 00:33:51,320
Speaker 1: This one comes from the observation that heat flows from

706
00:33:51,400 --> 00:33:54,160
Speaker 1: hot things too cold things, and so this one tries

707
00:33:54,200 --> 00:33:56,920
Speaker 1: to build a definition of temperature that says, if two

708
00:33:57,040 --> 00:33:59,960
Speaker 1: things are at the same temperature, no heat flows between them.

709
00:34:00,520 --> 00:34:02,200
Speaker 1: And if one thing is a higher temperature and the

710
00:34:02,240 --> 00:34:04,240
Speaker 1: other one has a lower temperature, he will flow from

711
00:34:04,280 --> 00:34:06,720
Speaker 1: the higher temperature thing to the lower temperature thing. So

712
00:34:06,800 --> 00:34:10,520
Speaker 1: trust and build a theory of temperature that matches that experience.

713
00:34:11,280 --> 00:34:13,000
Speaker 4: I see you're saying, like it's a different way to

714
00:34:13,480 --> 00:34:16,320
Speaker 4: basically think about temperature, Like temperature is not. Maybe the

715
00:34:16,400 --> 00:34:18,840
Speaker 4: kinetic energy of the particles is just kind of like

716
00:34:18,880 --> 00:34:22,600
Speaker 4: a relative property or relative quantity, Like you know, something

717
00:34:22,719 --> 00:34:25,480
Speaker 4: has more temperature than something else if the heat flows

718
00:34:25,480 --> 00:34:27,279
Speaker 4: from the first thing to the second thing, that's kind

719
00:34:27,280 --> 00:34:28,919
Speaker 4: of what you're saying. I guess zero would be if

720
00:34:28,960 --> 00:34:32,480
Speaker 4: heat can't flow from this thing to anything, then it

721
00:34:32,560 --> 00:34:34,600
Speaker 4: must be at zero. That's kind of what you're saying, Like,

722
00:34:34,680 --> 00:34:36,760
Speaker 4: let's measure zero to be that exactly.

723
00:34:36,760 --> 00:34:38,560
Speaker 1: And so then you can come up with a new

724
00:34:38,640 --> 00:34:42,400
Speaker 1: mathematical expression or how to measure this other idea of

725
00:34:42,440 --> 00:34:45,120
Speaker 1: temperature thermo dynamic temperature the same way that for the

726
00:34:45,200 --> 00:34:47,560
Speaker 1: kinetic theory, you can say, oh, it's about the motion

727
00:34:47,680 --> 00:34:49,359
Speaker 1: of the particles, and then you can go and write

728
00:34:49,360 --> 00:34:51,839
Speaker 1: the math and say, here's the kinetic energy and vibrational energy,

729
00:34:51,880 --> 00:34:54,120
Speaker 1: and I can actually calculate it constructive. And that same

730
00:34:54,120 --> 00:34:58,759
Speaker 1: way you can write down mathematical expressions for thermodynamic temperature

731
00:34:58,840 --> 00:35:02,080
Speaker 1: and they relate to entropy and to energy and help

732
00:35:02,120 --> 00:35:05,400
Speaker 1: you understand like why heat flows from hot things to

733
00:35:05,480 --> 00:35:08,680
Speaker 1: cold things. So it gives you a really interesting thermodynamic

734
00:35:08,880 --> 00:35:11,240
Speaker 1: insight into like why these things happen.

735
00:35:11,440 --> 00:35:13,880
Speaker 4: But is that really sort of different in the kinetic

736
00:35:13,960 --> 00:35:16,960
Speaker 4: I guess a view of things because I imagine if you

737
00:35:17,000 --> 00:35:19,239
Speaker 4: have something where all the particles are moving a lot

738
00:35:19,520 --> 00:35:22,040
Speaker 4: that would be hot, and something that's not moving a

739
00:35:22,040 --> 00:35:24,280
Speaker 4: lot that would be cold, and be put in together.

740
00:35:24,400 --> 00:35:26,480
Speaker 4: The moving things would you know, bump up against the

741
00:35:26,520 --> 00:35:28,560
Speaker 4: other things. And that's why that's what kind of what

742
00:35:28,600 --> 00:35:31,319
Speaker 4: heat flow is. It's like the energy of one thing

743
00:35:31,360 --> 00:35:31,920
Speaker 4: going to the other.

744
00:35:32,000 --> 00:35:34,120
Speaker 1: Most of the time, these two definitions agree about what

745
00:35:34,160 --> 00:35:38,000
Speaker 1: temperature is and also how energy flows from hot things

746
00:35:38,040 --> 00:35:41,200
Speaker 1: to cold things. So in many scenarios you could use

747
00:35:41,239 --> 00:35:45,120
Speaker 1: either one. But as we'll see thermodynamic temperature has some

748
00:35:45,160 --> 00:35:49,440
Speaker 1: weird behaviors in strained systems at extremes that might allow

749
00:35:49,480 --> 00:35:51,680
Speaker 1: the existence of negative temperatures.

750
00:35:51,960 --> 00:35:54,200
Speaker 4: So I guess if you go keep going and keep

751
00:35:54,239 --> 00:35:57,879
Speaker 4: defining temperature in terms of heat flow, then that's when

752
00:35:57,920 --> 00:35:59,280
Speaker 4: you might get into trouble.

753
00:35:59,360 --> 00:36:03,319
Speaker 1: Yeah, or into this weird territory where temperature can have

754
00:36:03,440 --> 00:36:06,799
Speaker 1: non zero negative values, and like what does that mean?

755
00:36:07,000 --> 00:36:09,160
Speaker 1: And in the end it reflects something about you know

756
00:36:09,280 --> 00:36:12,480
Speaker 1: what temperature means? What question are you asking about the

757
00:36:12,560 --> 00:36:14,640
Speaker 1: universe when you calculate this number?

758
00:36:14,880 --> 00:36:17,920
Speaker 4: So then you're saying this different definition of temperature is

759
00:36:17,960 --> 00:36:21,759
Speaker 4: the thermodynamic version. Uh, and it's related to entropy. What

760
00:36:21,760 --> 00:36:22,200
Speaker 4: does that mean?

761
00:36:22,360 --> 00:36:24,840
Speaker 1: So thermodynamic temperature tries to give us a sense for

762
00:36:24,920 --> 00:36:26,600
Speaker 1: like why things flow from one thing to the other.

763
00:36:26,680 --> 00:36:28,480
Speaker 1: You know why when you put that ice cube in

764
00:36:28,520 --> 00:36:30,880
Speaker 1: your cup of coffee and you come back in an hour,

765
00:36:31,160 --> 00:36:33,919
Speaker 1: everything is about an even temperature, right? Why do things

766
00:36:34,080 --> 00:36:36,440
Speaker 1: like to even out? And the answer is entropy. The

767
00:36:36,480 --> 00:36:40,080
Speaker 1: second law of thermodynamics says that entropy always increases. And

768
00:36:40,160 --> 00:36:42,840
Speaker 1: people sometimes think about entropy is like the amount of

769
00:36:42,880 --> 00:36:46,680
Speaker 1: disorganization in the universe, the messiness in the universe, and like,

770
00:36:46,719 --> 00:36:49,480
Speaker 1: you know that works in some certain circumstances, But that

771
00:36:49,640 --> 00:36:52,800
Speaker 1: more accurate description of entropy is like how many ways

772
00:36:52,840 --> 00:36:56,759
Speaker 1: can you arrange something? How many different configurations of an

773
00:36:56,760 --> 00:36:59,759
Speaker 1: object can you have, like in the different microscopic particles

774
00:37:00,040 --> 00:37:02,640
Speaker 1: that match the things that you're measuring about it. And

775
00:37:02,719 --> 00:37:06,880
Speaker 1: a basic concept in thermodynamics is that every configuration is

776
00:37:06,960 --> 00:37:09,680
Speaker 1: equally likely. And so if you have some state, some

777
00:37:09,880 --> 00:37:12,719
Speaker 1: condition that has lots of possible ways to achieve it,

778
00:37:12,760 --> 00:37:16,560
Speaker 1: many possible internal configurations, you're just more likely to end

779
00:37:16,680 --> 00:37:19,560
Speaker 1: up in that state. Say, for example, you have a

780
00:37:19,600 --> 00:37:22,200
Speaker 1: bunch of coins and you throw them all on the floor, right,

781
00:37:22,280 --> 00:37:24,440
Speaker 1: how many ways are there to get all heads up?

782
00:37:24,520 --> 00:37:26,719
Speaker 1: There's only one way. How many ways are there to

783
00:37:26,760 --> 00:37:29,200
Speaker 1: get all heads down? There's only one way. There's lots

784
00:37:29,239 --> 00:37:31,200
Speaker 1: of ways to get fifty percent heads up and fifty

785
00:37:31,239 --> 00:37:33,200
Speaker 1: percent heads down. So if you throw a bunch of

786
00:37:33,200 --> 00:37:35,600
Speaker 1: coins on the floor, you're much more likely to end

787
00:37:35,680 --> 00:37:38,839
Speaker 1: up in that state. Those states have higher entropy, So

788
00:37:38,960 --> 00:37:42,560
Speaker 1: the universe tend towards these arrangements with there's lots of ways,

789
00:37:42,600 --> 00:37:45,759
Speaker 1: lots of configurations to get the same value. So that's

790
00:37:45,760 --> 00:37:46,600
Speaker 1: what entropy is.

791
00:37:46,840 --> 00:37:47,000
Speaker 5: Right.

792
00:37:47,040 --> 00:37:49,040
Speaker 4: I guess in terms of that coffee cup and the

793
00:37:49,080 --> 00:37:51,160
Speaker 4: ice cube, it's almost like you were saying, like, if

794
00:37:51,200 --> 00:37:53,920
Speaker 4: I take some water and I take some coffee, and

795
00:37:53,960 --> 00:37:56,560
Speaker 4: I imagine water and coffee in a cup, it's much

796
00:37:56,600 --> 00:37:58,880
Speaker 4: more likely for it to be all mixed up together

797
00:37:59,360 --> 00:38:03,480
Speaker 4: in the tippit temperature. Right, then it would be likely

798
00:38:03,680 --> 00:38:06,440
Speaker 4: for all the water to be congregated in one place,

799
00:38:06,560 --> 00:38:09,080
Speaker 4: locked together into an ice cube, and then all of

800
00:38:09,120 --> 00:38:12,680
Speaker 4: the coffee to be hot surrounding that block. That's kind

801
00:38:12,680 --> 00:38:14,319
Speaker 4: of what you're saying. And I think you're saying that

802
00:38:14,360 --> 00:38:18,399
Speaker 4: the melted ice cube teppit coffee, watery coffee is more

803
00:38:18,560 --> 00:38:21,560
Speaker 4: likely to happen, and therefore it's a state of higher entropy.

804
00:38:21,800 --> 00:38:25,400
Speaker 1: Exactly, if you let the energy flow from the hot

805
00:38:25,440 --> 00:38:29,359
Speaker 1: coffee into the ice cube, then it opens up more configurations, right,

806
00:38:29,360 --> 00:38:31,800
Speaker 1: You can arrange that in many, many more ways. Now,

807
00:38:31,920 --> 00:38:34,960
Speaker 1: that's why energy flows from hot things to cold things,

808
00:38:35,040 --> 00:38:37,680
Speaker 1: because when it does so, it increases the entropy. It

809
00:38:37,760 --> 00:38:40,400
Speaker 1: opens up the number of ways you can arrange the

810
00:38:40,520 --> 00:38:42,040
Speaker 1: little internal bits.

811
00:38:42,000 --> 00:38:44,239
Speaker 4: Right, But that's not why it does it, right. I

812
00:38:44,239 --> 00:38:46,680
Speaker 4: think what you're saying is that's how thermodynamic says it

813
00:38:46,920 --> 00:38:48,600
Speaker 4: why it does it right, Like, if you were to

814
00:38:48,640 --> 00:38:50,719
Speaker 4: look at it from a totally different perspective, you would

815
00:38:50,760 --> 00:38:53,280
Speaker 4: see the molecules of the ice and the coffee interacting

816
00:38:53,360 --> 00:38:55,640
Speaker 4: and bumping against against each other, and that's why you

817
00:38:55,680 --> 00:38:58,160
Speaker 4: would say that the heat, the energy goes from one

818
00:38:58,160 --> 00:38:59,759
Speaker 4: place to the other. But if you were to put

819
00:38:59,800 --> 00:39:02,759
Speaker 4: on your thermodynamic glasses, you would kind of ignore all

820
00:39:02,920 --> 00:39:05,319
Speaker 4: those interactions and just say, oh, yeah, of course it's

821
00:39:05,360 --> 00:39:07,880
Speaker 4: because of the entropy that it's going up exactly.

822
00:39:08,120 --> 00:39:10,200
Speaker 1: Yeah. So it's another way to explain it. It's like

823
00:39:10,239 --> 00:39:13,680
Speaker 1: a completely different approach, a different set of ideas, and

824
00:39:13,760 --> 00:39:16,120
Speaker 1: most of the time they predict the same thing. And

825
00:39:16,200 --> 00:39:19,239
Speaker 1: so in this thermodynamic context where you're thinking about the

826
00:39:19,320 --> 00:39:22,680
Speaker 1: energy flow and the entropy, then it's this relationship between

827
00:39:22,840 --> 00:39:26,520
Speaker 1: energy and entropy that tells us what temperature is. If

828
00:39:26,520 --> 00:39:28,799
Speaker 1: two things have the same temperature, then we don't want

829
00:39:28,840 --> 00:39:31,160
Speaker 1: any energy to flow between them. So what we want

830
00:39:31,280 --> 00:39:34,560
Speaker 1: is if two things have the same relationship between energy

831
00:39:34,600 --> 00:39:38,319
Speaker 1: and entropy, then we shouldn't have any more energy flow. Like,

832
00:39:38,400 --> 00:39:41,880
Speaker 1: for example, if moving some energy from the ice cube

833
00:39:41,880 --> 00:39:45,480
Speaker 1: to the coffee cup doesn't increase the entropy anymore, then

834
00:39:45,719 --> 00:39:49,640
Speaker 1: energy won't flow. So the definition of temperature for thermodynamics

835
00:39:49,760 --> 00:39:52,000
Speaker 1: doesn't have to do with the kinetic energy objects. It

836
00:39:52,080 --> 00:39:54,880
Speaker 1: has to do with the derivative of energy with respect

837
00:39:55,040 --> 00:39:58,120
Speaker 1: to entropy. How the energy and entropy are related to

838
00:39:58,200 --> 00:39:58,640
Speaker 1: each other.

839
00:39:59,160 --> 00:40:01,719
Speaker 4: I feel like you're saying that maybe temperature is relative

840
00:40:02,040 --> 00:40:04,319
Speaker 4: if you look at it from a thermodynamic point of view.

841
00:40:04,320 --> 00:40:06,720
Speaker 4: And so let's get dig into this connection between energy

842
00:40:06,920 --> 00:40:10,359
Speaker 4: heat and temperature and entropy. But first, let's take another

843
00:40:10,440 --> 00:40:10,920
Speaker 4: quick break.

844
00:40:15,200 --> 00:40:17,000
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845
00:40:17,120 --> 00:40:20,240
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846
00:40:20,280 --> 00:40:24,320
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847
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848
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849
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Speaker 4: All right, we are getting hot and heavy here talking

894
00:42:54,520 --> 00:42:59,920
Speaker 4: about possibly negative temperature. Can you have negative absolute temperature?

895
00:43:00,040 --> 00:43:03,000
Speaker 4: And it may be possible depends on how you define temperature.

896
00:43:03,080 --> 00:43:04,840
Speaker 4: I guess most people know that, right, Like, if you

897
00:43:04,880 --> 00:43:07,640
Speaker 4: define temperature in terms of fahrenheit, then yeah, you can

898
00:43:07,680 --> 00:43:10,239
Speaker 4: have negative temperature or it's celsius, Yeah you can have

899
00:43:10,320 --> 00:43:13,120
Speaker 4: negative temperature. But you're saying this is something more fundamental,

900
00:43:13,320 --> 00:43:17,520
Speaker 4: like maybe the universe can allow negative absolute temperature.

901
00:43:17,600 --> 00:43:19,359
Speaker 1: Yeah, And it goes to the heart of this question

902
00:43:19,480 --> 00:43:22,239
Speaker 1: or like what do we mean by temperature anyway? And

903
00:43:22,280 --> 00:43:24,719
Speaker 1: you know, we define these things to describe our experience

904
00:43:24,760 --> 00:43:27,080
Speaker 1: and then we explore their extreme to say where does

905
00:43:27,080 --> 00:43:29,360
Speaker 1: this break down? Does this really make sense? Is this

906
00:43:29,680 --> 00:43:33,920
Speaker 1: something that's universal or only something that's useful in certain contexts.

907
00:43:34,080 --> 00:43:37,280
Speaker 1: So we came up with this idea of thermodynamic temperature

908
00:43:37,360 --> 00:43:41,600
Speaker 1: that basically tells you how energy flows around to maximize entropy.

909
00:43:41,719 --> 00:43:44,479
Speaker 1: If two things have the same temperature, then we don't

910
00:43:44,480 --> 00:43:46,719
Speaker 1: expect energy to flow between them. And you know, you

911
00:43:46,760 --> 00:43:48,719
Speaker 1: can have two things that are very different. One thing

912
00:43:48,719 --> 00:43:51,920
Speaker 1: could have a lot more capacity for different configurations than

913
00:43:51,960 --> 00:43:54,520
Speaker 1: the other one, and whether energy flows from one object

914
00:43:54,560 --> 00:43:57,000
Speaker 1: to another depends on like are you going to increase

915
00:43:57,040 --> 00:44:00,520
Speaker 1: the entropy by moving that energy along? And so it's

916
00:44:00,560 --> 00:44:04,400
Speaker 1: this relationship between energy and entropy. That is the thermodynamic

917
00:44:04,440 --> 00:44:08,239
Speaker 1: definition of temperature. Technically, it's the derivative of energy with

918
00:44:08,360 --> 00:44:12,120
Speaker 1: respect to entropy. So do you increase the energy as

919
00:44:12,320 --> 00:44:13,320
Speaker 1: entropy increases.

920
00:44:13,719 --> 00:44:16,120
Speaker 4: That's the temperature I see, And I guess maybe my

921
00:44:16,239 --> 00:44:19,640
Speaker 4: question is why would you do that? Like why would

922
00:44:19,640 --> 00:44:22,120
Speaker 4: you define it this way? Is it because it matches

923
00:44:22,480 --> 00:44:25,439
Speaker 4: usually with our other definition of temperature, or like why

924
00:44:25,440 --> 00:44:26,840
Speaker 4: would you call this temperature?

925
00:44:26,880 --> 00:44:30,000
Speaker 1: Also, it's a totally different approach, and it's the macroscopic approach,

926
00:44:30,000 --> 00:44:32,719
Speaker 1: and it has some advantages. You know. The microscopic one

927
00:44:33,000 --> 00:44:36,640
Speaker 1: is weirdly time invariant. The laws of physics governing how

928
00:44:36,680 --> 00:44:39,680
Speaker 1: things bounce against each other, those look the same forward

929
00:44:39,760 --> 00:44:42,279
Speaker 1: and backwards, and so it's hard to go from like

930
00:44:42,320 --> 00:44:45,960
Speaker 1: a microscopic picture of atoms as like little balls, to

931
00:44:46,040 --> 00:44:49,160
Speaker 1: an understanding of how a state evolves forward in time

932
00:44:49,600 --> 00:44:52,759
Speaker 1: with entropy. It's complicated to go from one to the other.

933
00:44:52,920 --> 00:44:55,319
Speaker 1: This is a picture of thermodynamics that deals directly with

934
00:44:55,400 --> 00:44:58,439
Speaker 1: the macroscopic quantities, that says, look, these are the things

935
00:44:58,520 --> 00:45:00,759
Speaker 1: we can measure, the entropy, energy, these are the things

936
00:45:00,800 --> 00:45:03,879
Speaker 1: we're interested in. Not all of science has to be reductionists.

937
00:45:03,880 --> 00:45:07,160
Speaker 1: There are other ways to gain understanding and explanation than

938
00:45:07,239 --> 00:45:10,080
Speaker 1: just to tear things apart into their tiny bits. Sometimes

939
00:45:10,080 --> 00:45:12,279
Speaker 1: you do that and you don't get any understanding. Like

940
00:45:12,320 --> 00:45:15,000
Speaker 1: when you look at the brain, psychology is valuable even

941
00:45:15,040 --> 00:45:17,160
Speaker 1: if neuroscience can't yet explain it.

942
00:45:17,360 --> 00:45:19,400
Speaker 4: Right, right, Well, let's dig into this a little bit

943
00:45:19,440 --> 00:45:21,600
Speaker 4: because I am a little bit confused. So you're saying,

944
00:45:21,880 --> 00:45:25,520
Speaker 4: the thermodynamic definition of temperature is the derivative Oh say

945
00:45:25,520 --> 00:45:28,000
Speaker 4: it again, energy flow divided by entropy.

946
00:45:28,120 --> 00:45:31,840
Speaker 1: Yeah, it's the derivative of energy with respect to entropy.

947
00:45:32,000 --> 00:45:35,200
Speaker 1: So energy is E and entropy is S. So temperature

948
00:45:35,200 --> 00:45:39,200
Speaker 1: in this sense is d DS. I apologize for introducing

949
00:45:39,200 --> 00:45:40,400
Speaker 1: math to the podcast.

950
00:45:41,360 --> 00:45:45,080
Speaker 4: What are you doing to me here? Okay? So it's

951
00:45:45,200 --> 00:45:49,040
Speaker 4: kind of like saying how energy changes if you change.

952
00:45:48,880 --> 00:45:52,640
Speaker 1: Entropy exactly, because the key idea again is that entropy

953
00:45:52,680 --> 00:45:55,799
Speaker 1: is always going to be maximized, and so what arrangement

954
00:45:56,000 --> 00:45:58,400
Speaker 1: of the stuff, what arrangement of the energy is going

955
00:45:58,480 --> 00:46:01,279
Speaker 1: to give you the most entropy. And so to know

956
00:46:01,320 --> 00:46:03,680
Speaker 1: whether something is going to flow from one object to another,

957
00:46:03,960 --> 00:46:05,799
Speaker 1: you have to know, like how much energy does some

958
00:46:06,040 --> 00:46:08,879
Speaker 1: entropy cost? If I want to increase the entropy over here?

959
00:46:08,880 --> 00:46:10,920
Speaker 1: How much energy does it cost me? If I'm going

960
00:46:10,960 --> 00:46:13,200
Speaker 1: to gain more entropew by moving the energy over then

961
00:46:13,239 --> 00:46:16,359
Speaker 1: I lose where the energy came from. Then let's do it.

962
00:46:16,480 --> 00:46:18,800
Speaker 1: So you have to understand, like how much entropy do

963
00:46:18,840 --> 00:46:22,239
Speaker 1: you get per energy? And that's basically what temperature is.

964
00:46:22,520 --> 00:46:24,080
Speaker 4: Right, But then what are you trying to measure the

965
00:46:24,120 --> 00:46:26,920
Speaker 4: temperature of like one thing or two things? You know

966
00:46:26,960 --> 00:46:28,359
Speaker 4: what I mean? Like if I tell you what's the

967
00:46:28,360 --> 00:46:32,080
Speaker 4: thermodynamic temperature of an ice cube, how would you calculate that?

968
00:46:32,160 --> 00:46:36,280
Speaker 1: Well, I would measure how quickly it gains new possible

969
00:46:36,320 --> 00:46:38,759
Speaker 1: configurations as I increase its.

970
00:46:38,760 --> 00:46:40,200
Speaker 4: Energy as you put it in coffee.

971
00:46:40,200 --> 00:46:42,560
Speaker 1: I can measure the energy of the atoms in the

972
00:46:42,600 --> 00:46:44,560
Speaker 1: ice cube or in some other way.

973
00:46:44,719 --> 00:46:46,239
Speaker 4: Yeah, I guess the question is just like if I

974
00:46:46,320 --> 00:46:48,439
Speaker 4: give you an ice cube, how would you measure the

975
00:46:48,440 --> 00:46:50,120
Speaker 4: thermodynamic temperature of it?

976
00:46:50,280 --> 00:46:53,040
Speaker 1: I would measure how it's entropy changes as I change

977
00:46:53,040 --> 00:46:55,960
Speaker 1: its energy. Right, So the temperature there is the relationship

978
00:46:56,160 --> 00:46:59,319
Speaker 1: between the energy and the entropy, So you change one

979
00:46:59,360 --> 00:47:00,240
Speaker 1: and you measure the.

980
00:47:00,080 --> 00:47:02,120
Speaker 4: Other, Right, But how would you measure its entropy?

981
00:47:02,200 --> 00:47:04,719
Speaker 1: Well, you know you can measure entropy by measuring temperature

982
00:47:04,760 --> 00:47:07,719
Speaker 1: and energy, because it's a relationship between the three. And

983
00:47:07,760 --> 00:47:10,200
Speaker 1: that's the thing I always hated about thermodynamics is that

984
00:47:10,280 --> 00:47:12,680
Speaker 1: you feel like you just going in circle. Sometimes.

985
00:47:12,960 --> 00:47:15,320
Speaker 4: Well, it's good, we're spending an hour here discussing something

986
00:47:15,320 --> 00:47:19,839
Speaker 4: you hate. I'm sure people are are following along, right

987
00:47:19,920 --> 00:47:22,759
Speaker 4: right along. All right, Well, let's maybe take a step back.

988
00:47:22,800 --> 00:47:25,440
Speaker 4: I think what you're saying is that temperature is kind

989
00:47:25,440 --> 00:47:27,319
Speaker 4: of this weird thing, and if you look at it

990
00:47:27,320 --> 00:47:29,520
Speaker 4: from a thermodynamic point of view, you can look at

991
00:47:29,560 --> 00:47:32,320
Speaker 4: it in terms of how it changes with respect to entropy.

992
00:47:32,760 --> 00:47:35,920
Speaker 4: Like if something has a lot of temperature, something is

993
00:47:35,960 --> 00:47:39,560
Speaker 4: hot in a thermodynamic sense, that means what it takes

994
00:47:39,600 --> 00:47:41,759
Speaker 4: a lot of entropy, or it doesn't take a lot

995
00:47:41,760 --> 00:47:42,160
Speaker 4: of entropy.

996
00:47:42,400 --> 00:47:45,360
Speaker 1: If something is hot in a thermodynamic sense, it means

997
00:47:45,360 --> 00:47:48,360
Speaker 1: that it costs a lot of energy to change its entropy.

998
00:47:48,600 --> 00:47:50,520
Speaker 1: And so if you want to take some of that

999
00:47:50,640 --> 00:47:54,080
Speaker 1: energy away, it doesn't reduce its entropy very very much.

1000
00:47:54,239 --> 00:47:56,040
Speaker 1: So if you have a really hot liquid surround your

1001
00:47:56,080 --> 00:47:58,520
Speaker 1: ice cube, you can take some of that energy out

1002
00:47:58,560 --> 00:48:00,560
Speaker 1: of the liquid and put it into the eye ice cube,

1003
00:48:00,560 --> 00:48:02,200
Speaker 1: and you're not going to lose a whole lot of

1004
00:48:02,320 --> 00:48:06,360
Speaker 1: entropy from the liquid. Right, high temperature means high DEDs,

1005
00:48:06,440 --> 00:48:08,600
Speaker 1: so you can take energy away without losing a whole

1006
00:48:08,640 --> 00:48:11,719
Speaker 1: lot of entropy. And because the ice cube is cold, right,

1007
00:48:11,719 --> 00:48:14,960
Speaker 1: it has load DEDs and as you add energy to it,

1008
00:48:15,000 --> 00:48:17,200
Speaker 1: you get a lot more entropy. So you lose a

1009
00:48:17,200 --> 00:48:19,200
Speaker 1: little bit of entropy from the hot liquid and you

1010
00:48:19,239 --> 00:48:22,400
Speaker 1: gain a lot of entropy into the cold ice cube

1011
00:48:22,600 --> 00:48:24,040
Speaker 1: for the same amount of energy.

1012
00:48:24,160 --> 00:48:27,200
Speaker 4: I see. It's almost like the cost of entropy for

1013
00:48:27,280 --> 00:48:28,160
Speaker 4: something exactly.

1014
00:48:28,200 --> 00:48:29,320
Speaker 1: It's like exchange rates.

1015
00:48:29,520 --> 00:48:32,160
Speaker 4: Yeah, it's like how much bang for your buck does

1016
00:48:32,320 --> 00:48:36,319
Speaker 4: energy give you in the entropy of something Like if

1017
00:48:36,320 --> 00:48:39,279
Speaker 4: something an ice cube which is cold, you get a

1018
00:48:39,360 --> 00:48:42,440
Speaker 4: lot of entropy just by you know, breathing on it

1019
00:48:42,480 --> 00:48:46,520
Speaker 4: with your warm breath. But a cold cup of coffee

1020
00:48:46,640 --> 00:48:49,800
Speaker 4: you need a lot of energy to reduce its entropy.

1021
00:48:49,920 --> 00:48:52,920
Speaker 1: Yes, so now we have Jorge's economic theory of temperature.

1022
00:48:53,160 --> 00:48:55,080
Speaker 4: Yes, my coffee theory.

1023
00:48:55,000 --> 00:48:58,160
Speaker 1: Yes, you can buy entropy cheap from a hot liquid,

1024
00:48:58,239 --> 00:49:00,440
Speaker 1: and you can sell it at a high price in

1025
00:49:00,480 --> 00:49:02,480
Speaker 1: your cold ice cube. Exactly.

1026
00:49:02,600 --> 00:49:05,840
Speaker 4: Okay, So that's the thermodynamic definition, and it matches up

1027
00:49:05,880 --> 00:49:08,040
Speaker 4: with the regular definition because I guess if something is

1028
00:49:08,160 --> 00:49:10,839
Speaker 4: zero Calvin, entropy is cheap for something like that, right,

1029
00:49:10,920 --> 00:49:12,160
Speaker 4: Like I just got to put in a little bit

1030
00:49:12,200 --> 00:49:14,360
Speaker 4: of energy and I get a whole bunch of entropy.

1031
00:49:14,760 --> 00:49:17,560
Speaker 4: But if something is like a million degrees Calvin, you

1032
00:49:17,560 --> 00:49:19,240
Speaker 4: know it's going to take me a lot of energy

1033
00:49:19,280 --> 00:49:22,560
Speaker 4: to increase the entropy of something that's already super entropic.

1034
00:49:22,640 --> 00:49:24,719
Speaker 1: And it's also about the relationship. Like this makes a

1035
00:49:24,760 --> 00:49:27,440
Speaker 1: lot of sense for most things, because for most things,

1036
00:49:27,760 --> 00:49:30,400
Speaker 1: as you add energy, you get more entropy. As you

1037
00:49:30,400 --> 00:49:33,400
Speaker 1: add energy to a liquid, you free the particles and

1038
00:49:33,400 --> 00:49:35,120
Speaker 1: then they become gas and they can move in new

1039
00:49:35,120 --> 00:49:38,319
Speaker 1: ways and find new arrangements. And as you cool things down,

1040
00:49:38,360 --> 00:49:42,160
Speaker 1: they get less entropy. So if entropy is always increasing

1041
00:49:42,200 --> 00:49:44,520
Speaker 1: with energy, then this makes perfect sense. And that's what

1042
00:49:44,560 --> 00:49:46,760
Speaker 1: it does for the ideal gas and your like kinetic

1043
00:49:46,800 --> 00:49:50,080
Speaker 1: theory of temperature, and they line up as you say.

1044
00:49:49,920 --> 00:49:52,160
Speaker 4: You mean, like you always get something for your money.

1045
00:49:51,960 --> 00:49:55,880
Speaker 1: Mm hmm, exactly. But condensed matter physicists can imagine some

1046
00:49:56,280 --> 00:50:00,560
Speaker 1: kinds of weird materials where this isn't true, some kind

1047
00:50:00,560 --> 00:50:03,600
Speaker 1: of weird materials where as you add more energy you

1048
00:50:03,640 --> 00:50:07,960
Speaker 1: actually get fewer micro states, do you get decreasing entropy,

1049
00:50:08,080 --> 00:50:10,640
Speaker 1: So as the thing has more and more energy, there

1050
00:50:10,680 --> 00:50:13,600
Speaker 1: might be fewer ways to arrange it, and that would

1051
00:50:13,680 --> 00:50:15,320
Speaker 1: lead to negative temperature.

1052
00:50:15,800 --> 00:50:18,719
Speaker 4: M all right, now we're getting to the question of

1053
00:50:18,760 --> 00:50:21,680
Speaker 4: the episode, which is you're saying that if you define

1054
00:50:21,840 --> 00:50:27,879
Speaker 4: temperature in the thermodynamic way, there are things potentially or theoretically,

1055
00:50:27,920 --> 00:50:31,120
Speaker 4: I guess that could have negative temperature because when you

1056
00:50:31,160 --> 00:50:34,280
Speaker 4: put energy into them, they actually sort of get neaterer,

1057
00:50:34,719 --> 00:50:35,640
Speaker 4: right or colder?

1058
00:50:35,760 --> 00:50:39,600
Speaker 1: Exactly, they get neater they have fewer ways to arrange themselves.

1059
00:50:40,040 --> 00:50:43,520
Speaker 1: And here's an example. Imagine a bunch of particles in

1060
00:50:43,560 --> 00:50:46,439
Speaker 1: a line, and these particles are fixed on the line.

1061
00:50:46,440 --> 00:50:48,120
Speaker 1: They can't move it all. The only thing they can

1062
00:50:48,160 --> 00:50:50,319
Speaker 1: do is be spin up or spin down. Put these

1063
00:50:50,360 --> 00:50:52,719
Speaker 1: particles in a magnetic field so that like, spin up

1064
00:50:52,920 --> 00:50:55,840
Speaker 1: has more energy than spin down for example.

1065
00:50:55,520 --> 00:50:57,800
Speaker 4: Meaning more energy meaning like it ten just want to

1066
00:50:57,800 --> 00:50:58,319
Speaker 4: spin down?

1067
00:50:58,400 --> 00:51:01,440
Speaker 1: Yeah exactly. It costs more energy to spin up than

1068
00:51:01,480 --> 00:51:02,440
Speaker 1: to spin down.

1069
00:51:02,280 --> 00:51:03,440
Speaker 4: Like trying to stand up a stick.

1070
00:51:03,600 --> 00:51:06,880
Speaker 1: Yeah exactly. So now imagine all these particles spin down,

1071
00:51:07,080 --> 00:51:10,640
Speaker 1: right minimum energy, there'd be no entropy because there's only

1072
00:51:10,680 --> 00:51:13,520
Speaker 1: one way to arrange all of these things. It's just

1073
00:51:13,560 --> 00:51:15,839
Speaker 1: like getting all heads when you flip a bunch of coins,

1074
00:51:15,920 --> 00:51:18,640
Speaker 1: or getting all tails. Right, there's only one way to

1075
00:51:18,760 --> 00:51:21,479
Speaker 1: arrange them so that they're all spin down, so there's

1076
00:51:21,680 --> 00:51:23,520
Speaker 1: zero entropy, it's minimum entropy.

1077
00:51:23,600 --> 00:51:25,880
Speaker 4: It's like the block of ice. Right, everything's like neatly

1078
00:51:26,080 --> 00:51:28,719
Speaker 4: ordered in a state that it wants to be in.

1079
00:51:28,760 --> 00:51:32,040
Speaker 1: Exactly Now, as you add energy, some atoms start to

1080
00:51:32,040 --> 00:51:35,560
Speaker 1: flip right, and you quickly add entropy. There's lots of

1081
00:51:35,600 --> 00:51:38,160
Speaker 1: ways to arrange it. Now, if you say, well, I

1082
00:51:38,160 --> 00:51:40,600
Speaker 1: have enough energy to flip one atom, well, there's a

1083
00:51:40,640 --> 00:51:42,320
Speaker 1: bunch of different ways to do that. You can flip

1084
00:51:42,360 --> 00:51:44,520
Speaker 1: any of the atoms. If you want to flip five atoms,

1085
00:51:44,520 --> 00:51:46,640
Speaker 1: you have enough energy to flip five atoms right, Then

1086
00:51:46,680 --> 00:51:48,560
Speaker 1: there's lots and lots of ways, and so as you

1087
00:51:48,560 --> 00:51:52,120
Speaker 1: add energy, the entropy increases. Totally normal so far. But

1088
00:51:52,160 --> 00:51:56,160
Speaker 1: what happens once you pass the halfway point, once more

1089
00:51:56,239 --> 00:51:58,600
Speaker 1: than half of the atoms are flipped up, and as

1090
00:51:58,600 --> 00:52:02,120
Speaker 1: you keep adding energy, you're reducing the number of ways

1091
00:52:02,120 --> 00:52:04,279
Speaker 1: you can arrange the system until all the way up

1092
00:52:04,280 --> 00:52:07,279
Speaker 1: to the maximum energy. When everything is flipped up, there's

1093
00:52:07,320 --> 00:52:11,240
Speaker 1: only one way to arrange the system at the maximum energy.

1094
00:52:11,360 --> 00:52:13,840
Speaker 1: So in the second half there after you pass the

1095
00:52:13,880 --> 00:52:18,520
Speaker 1: halfway point, as you're adding energy, you're losing entropy, so

1096
00:52:18,560 --> 00:52:21,520
Speaker 1: you have the opposite relationship between energy and entropy.

1097
00:52:21,800 --> 00:52:24,480
Speaker 4: WHOA, Okay, So it's kind of like the coins, like

1098
00:52:24,480 --> 00:52:27,200
Speaker 4: you're saying right like, if all the coins are heads up,

1099
00:52:27,840 --> 00:52:31,000
Speaker 4: that's minimum entropy.

1100
00:52:31,160 --> 00:52:33,399
Speaker 1: Yeah, that's zero entropy, and half of.

1101
00:52:33,360 --> 00:52:36,359
Speaker 4: Them heads up heads down is maximum entropy. But then

1102
00:52:36,560 --> 00:52:38,880
Speaker 4: if you go all the way, keep going, and somehow

1103
00:52:38,920 --> 00:52:41,520
Speaker 4: you're able to flip all of the coin's tails up,

1104
00:52:41,840 --> 00:52:43,480
Speaker 4: then that's also zero entropy.

1105
00:52:43,600 --> 00:52:48,920
Speaker 1: Yeah, exactly, And so you have maximum energy and zero entropy.

1106
00:52:49,400 --> 00:52:51,319
Speaker 1: And this is a really weird system and not something

1107
00:52:51,320 --> 00:52:54,279
Speaker 1: we actually see in nature, but in principle because you

1108
00:52:54,320 --> 00:52:59,719
Speaker 1: are adding energy but reducing entropy. That's technically negative temperature.

1109
00:53:00,160 --> 00:53:03,960
Speaker 1: So everything above the halfway point there has negative temperature.

1110
00:53:04,320 --> 00:53:07,160
Speaker 1: It has dedes is a negative.

1111
00:53:06,800 --> 00:53:10,600
Speaker 4: Value I see in this weird situation. After all the

1112
00:53:10,640 --> 00:53:14,440
Speaker 4: coins are fifty percent heads and tails up, you're saying,

1113
00:53:14,520 --> 00:53:17,880
Speaker 4: it actually starts to have negative temperature again because the

1114
00:53:18,000 --> 00:53:20,760
Speaker 4: entropy is going down again as I put more energy into.

1115
00:53:20,600 --> 00:53:22,959
Speaker 1: It, exactly, And so the system would prefer less energy,

1116
00:53:22,960 --> 00:53:26,480
Speaker 1: you would flow towards a higher entropy situation, which is

1117
00:53:26,520 --> 00:53:27,600
Speaker 1: more of a mix.

1118
00:53:27,480 --> 00:53:29,880
Speaker 4: Right, Like you try to buy more entropy with your energy,

1119
00:53:29,880 --> 00:53:32,839
Speaker 4: but you actually lose entropy. That's what it means to

1120
00:53:32,880 --> 00:53:36,680
Speaker 4: be cold in this definition of temperature.

1121
00:53:37,360 --> 00:53:39,840
Speaker 1: And this gets really weird. Like let's say you have

1122
00:53:39,880 --> 00:53:41,640
Speaker 1: two of these things. Now you have two of these

1123
00:53:41,680 --> 00:53:43,920
Speaker 1: lines of atoms, and you put them in touch so

1124
00:53:43,960 --> 00:53:47,160
Speaker 1: they can share energy. Right, where's the energy going to go?

1125
00:53:47,680 --> 00:53:50,759
Speaker 1: Say one of them has a higher value of temperature

1126
00:53:50,880 --> 00:53:52,840
Speaker 1: than the other one. Well, in this case, something with

1127
00:53:52,920 --> 00:53:57,480
Speaker 1: negative temperature actually has more energy than the thing with

1128
00:53:57,760 --> 00:54:01,960
Speaker 1: positive temperature, right, because they get negative temperature you have

1129
00:54:02,000 --> 00:54:04,239
Speaker 1: to go above the halfway point, so half of them

1130
00:54:04,440 --> 00:54:07,160
Speaker 1: are flipped up. So in this case, the heat actually

1131
00:54:07,239 --> 00:54:12,120
Speaker 1: flows from the higher energy negative temperature system to the

1132
00:54:12,160 --> 00:54:15,880
Speaker 1: positive temperature system, which sounds kind of bonkers and backwards.

1133
00:54:15,920 --> 00:54:19,040
Speaker 4: Well yeah, yeah, it doesn't cound bonkers, but I feel

1134
00:54:19,040 --> 00:54:21,279
Speaker 4: like you're trying to maybe trying to fudge some of

1135
00:54:21,320 --> 00:54:24,600
Speaker 4: these definitions, right, because like these things, these coins only

1136
00:54:24,640 --> 00:54:27,040
Speaker 4: have this weird property because you're kind of introducing this

1137
00:54:27,120 --> 00:54:30,520
Speaker 4: bias with the magnet, right, it's not actually heat or energy, Right,

1138
00:54:30,600 --> 00:54:33,000
Speaker 4: it's sort of something different that's going from one to

1139
00:54:33,040 --> 00:54:33,319
Speaker 4: the other.

1140
00:54:33,480 --> 00:54:36,279
Speaker 1: It is energy, right. It takes energy to be like

1141
00:54:36,440 --> 00:54:39,320
Speaker 1: misaligned with the magnet, for example, and so it really

1142
00:54:39,360 --> 00:54:41,839
Speaker 1: is energy. The question really is like, what does this

1143
00:54:41,920 --> 00:54:46,080
Speaker 1: mean by temperature? We introduce this definition of thermodynamic temperature

1144
00:54:46,440 --> 00:54:48,440
Speaker 1: so that we could describe the kind of things we

1145
00:54:48,480 --> 00:54:51,520
Speaker 1: see in the world, right, heat flowing from high temperature

1146
00:54:51,520 --> 00:54:53,880
Speaker 1: objects to low temperature objects. And this is just an

1147
00:54:53,920 --> 00:54:56,440
Speaker 1: example of this definition pushed to the extreme where it

1148
00:54:56,480 --> 00:54:59,120
Speaker 1: really doesn't make any sense anymore. The same way we

1149
00:54:59,160 --> 00:55:02,560
Speaker 1: push the definition kinetic temperature to the extreme, basking what

1150
00:55:02,719 --> 00:55:05,080
Speaker 1: is the temperature of one particle? In this case, while

1151
00:55:05,120 --> 00:55:08,440
Speaker 1: you can get technically negative temperature, it really shows the

1152
00:55:08,480 --> 00:55:12,400
Speaker 1: breakdown of this idea of thermodynamic temperature more than like

1153
00:55:12,800 --> 00:55:15,200
Speaker 1: actually being negative in any meaningful way.

1154
00:55:16,320 --> 00:55:18,680
Speaker 4: I see you're saying it, like if I define temperature

1155
00:55:18,719 --> 00:55:22,560
Speaker 4: as the cost of entropy per bank per buck for energy,

1156
00:55:23,520 --> 00:55:25,480
Speaker 4: that doesn't work if you have a situation where it

1157
00:55:25,560 --> 00:55:27,800
Speaker 4: actually like if you put in more energy, it actually

1158
00:55:27,800 --> 00:55:29,200
Speaker 4: loses entropy exactly.

1159
00:55:29,280 --> 00:55:31,600
Speaker 1: Yeah, it just doesn't really work. And you can see

1160
00:55:31,640 --> 00:55:35,800
Speaker 1: that because it predicts that things flow from negative temperature

1161
00:55:35,840 --> 00:55:38,440
Speaker 1: to positive temperature. What's the point of temperature then if

1162
00:55:38,440 --> 00:55:40,680
Speaker 1: it doesn't even align with our ideas and our experience?

1163
00:55:40,920 --> 00:55:42,719
Speaker 4: All right, Well, I mean it's sort of like kind

1164
00:55:42,719 --> 00:55:45,320
Speaker 4: of I feel like it's almost kind of like going

1165
00:55:45,360 --> 00:55:48,120
Speaker 4: to celsius or fahrenheit, Right, you're sort of changing the

1166
00:55:48,160 --> 00:55:51,600
Speaker 4: scale of things maybe, and so then therefore you can

1167
00:55:51,680 --> 00:55:54,919
Speaker 4: have negative temperatures if you define things this way.

1168
00:55:55,120 --> 00:55:57,319
Speaker 1: Yeah, that's true. You could always define temperatures to be

1169
00:55:57,440 --> 00:56:00,640
Speaker 1: negative as well. I think this one is interesting because

1170
00:56:00,680 --> 00:56:03,759
Speaker 1: it shows you, not like that the universe breaks the

1171
00:56:03,840 --> 00:56:06,240
Speaker 1: rules or anything, but it shows you that these ideas

1172
00:56:06,320 --> 00:56:08,560
Speaker 1: that we invent to try to describe by our experience,

1173
00:56:08,719 --> 00:56:11,719
Speaker 1: they have limits. And those limits aren't physical limits, they're

1174
00:56:11,760 --> 00:56:15,000
Speaker 1: like conceptual limits. So like this idea doesn't really work

1175
00:56:15,040 --> 00:56:17,960
Speaker 1: in that circumstance. The whole concept of temperature doesn't really

1176
00:56:18,040 --> 00:56:20,200
Speaker 1: make sense for this weird invented system.

1177
00:56:20,320 --> 00:56:20,520
Speaker 5: Right.

1178
00:56:20,719 --> 00:56:23,480
Speaker 4: It's like maybe we have a way of describing and

1179
00:56:23,560 --> 00:56:26,280
Speaker 4: calling things in the universe and calculating things, but maybe

1180
00:56:26,280 --> 00:56:28,560
Speaker 4: that's not really how the universe works. Like, maybe the

1181
00:56:28,640 --> 00:56:30,759
Speaker 4: universe has its own way of doing things that are

1182
00:56:30,960 --> 00:56:34,000
Speaker 4: beyond what we're able to describe, kind of or define.

1183
00:56:34,080 --> 00:56:34,759
Speaker 4: Is that what you're saying.

1184
00:56:34,840 --> 00:56:36,680
Speaker 1: Yeah, it's like the way you can talk about feelings

1185
00:56:36,680 --> 00:56:38,759
Speaker 1: for a person, but can you talk about feelings for

1186
00:56:38,920 --> 00:56:41,440
Speaker 1: like a rock or a river. You know, it's an

1187
00:56:41,520 --> 00:56:44,439
Speaker 1: idea but doesn't really make sense in the same way

1188
00:56:44,480 --> 00:56:48,160
Speaker 1: that like temperature makes sense in certain contexts or certain

1189
00:56:48,200 --> 00:56:51,520
Speaker 1: behaviors emerge and have relationships, but not in all context

1190
00:56:51,680 --> 00:56:54,840
Speaker 1: You can't ask what is the temperature of every arbitrary

1191
00:56:54,880 --> 00:56:57,200
Speaker 1: system that you invent? It doesn't always make sense.

1192
00:56:58,280 --> 00:57:00,879
Speaker 4: I see, But what if I imagine andary friend Rob,

1193
00:57:01,560 --> 00:57:04,040
Speaker 4: can I still assign thermodynamic happiness to it?

1194
00:57:04,080 --> 00:57:06,759
Speaker 1: Depends how much it's willing to spend to get more entropy.

1195
00:57:06,880 --> 00:57:09,560
Speaker 4: Yeah, you flip it and it lands heads up, But

1196
00:57:09,600 --> 00:57:10,239
Speaker 4: what does that mean?

1197
00:57:12,200 --> 00:57:14,040
Speaker 1: It means it's time for dessert, all right.

1198
00:57:13,880 --> 00:57:16,160
Speaker 4: So then that's kind of where this idea of negative

1199
00:57:16,160 --> 00:57:19,000
Speaker 4: temperature is. I think what you're saying is that some physicists,

1200
00:57:19,280 --> 00:57:21,960
Speaker 4: if they go by this definition, are allowed to call

1201
00:57:22,040 --> 00:57:25,720
Speaker 4: things as having negative temperature. Right, So maybe, like most

1202
00:57:25,760 --> 00:57:28,480
Speaker 4: people will say, no, that's impossible, you can't have negative temperature.

1203
00:57:28,480 --> 00:57:30,320
Speaker 4: You would say, well, it depends on who you talk

1204
00:57:30,400 --> 00:57:31,880
Speaker 4: to and what you mean by temperature?

1205
00:57:32,000 --> 00:57:34,480
Speaker 1: Yeah, exactly, and whether you think it even makes sense

1206
00:57:34,480 --> 00:57:38,240
Speaker 1: to apply temperature to these crazy, bonkers, weird situations that

1207
00:57:38,320 --> 00:57:40,160
Speaker 1: will never arise in our universe?

1208
00:57:40,440 --> 00:57:42,880
Speaker 4: So does that mean I can be a thermoidynamic temperature

1209
00:57:42,920 --> 00:57:46,480
Speaker 4: denier but still a regular temperature positivitist.

1210
00:57:48,080 --> 00:57:50,440
Speaker 1: You can be whatever you want, man. So thanks to

1211
00:57:50,440 --> 00:57:52,439
Speaker 1: everybody who wrote in to ask us to talk about

1212
00:57:52,520 --> 00:57:55,120
Speaker 1: that tricky concept. I hope that was useful.

1213
00:57:55,240 --> 00:57:57,120
Speaker 4: Yeah, we hope you enjoyed that and maybe made you

1214
00:57:57,120 --> 00:57:59,200
Speaker 4: think about what it actually means for something to be

1215
00:57:59,240 --> 00:58:01,680
Speaker 4: hot and cold. Like, maybe what we experience in our

1216
00:58:01,720 --> 00:58:05,080
Speaker 4: everyday lives is just what we experience in our everyday lives.

1217
00:58:05,080 --> 00:58:07,880
Speaker 4: Maybe it doesn't always apply to everything in the universe.

1218
00:58:08,080 --> 00:58:10,280
Speaker 4: Thanks for joining us, See you next time.

1219
00:58:18,120 --> 00:58:20,920
Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain

1220
00:58:21,000 --> 00:58:25,000
Speaker 1: the Universe is a production of iHeartRadio. For more podcasts

1221
00:58:25,000 --> 00:58:29,640
Speaker 1: from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever

1222
00:58:29,720 --> 00:58:42,880
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1227
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1247
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1248
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