November 26, 2019 • 39 mins
EXTREME UNIVERSE: Where is the coldest place in the Universe?
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Speaker 1 (00:08):
Hey, Daniel, what's your least favorite topic in physics? Oh, man,
don't make me say something negative about physics. Well, now
I really want to know. Fine, Fine, it's thermodynamics. You
don't like thermodynamics. But it's such a hot field, Daniel,
or cold, depending on the state. It's just too hard
(00:29):
to get my mind around. There's so many particles involved,
you know, So you don't know much about thermodynamics, then
I wouldn't say I know that much. Really, like you
know zero about it? You're getting close. What if we
talk about absolute zero? That's a reasonable approximation of how
much I like thermodynamics. I am or handmade cartoonists and
(01:04):
the creator of PhD comics. Hi, I'm Daniel. I'm a
particle physicist, and I'm not a lover of thermodynamics. Now,
welcome to our podcast, Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we find
all the amazing and crazy things about the universe, the
extreme things, the fast things, the hot things, the cold things,
(01:24):
and we explain them all to you. That's right. We
explore all of the hot topics in physics and science
out there in the universe, but also the coldest thing sometimes,
that's right. We try to touch on the hot topics
and we try to be cool at the same time.
We are. We are pretty cool for a physics podcast.
We're definitely cool. Yeah, all all three of them were
(01:48):
probably the coolest, but yeah. This is part of a
series of podcast episodes about the extremes of the universe.
Should we cue the heavy metal sounds, Danny Wild Stallions,
where we're gonna get Bill and Ted on the podcast,
Oh we should build or Ted just before their reunion tour.
(02:08):
We like talking about the crazy bits of the universe
because where the extremes are sort of where you learn
the most about the universe. How hot can things get?
What is the densest thing, what is the strongest magnetic field?
And that's why we explored all those topics in previous episodes. Yeah,
it really makes you kind of push or stretch the
boundaries of your mind, you know, to think of the
(02:28):
hottest things, the dancest things, the brightest things. Those are
all things we've covered in other episodes, and today we'll
be talking about another one of those extremes in the universe.
So today on the podcast, we'll be talking about what
is the coldest place in the universe. Instead of heavy
(02:51):
metal guitar, we should just have a cold wind or something. No,
we should have the theme music from Frozen, of course,
come on, just let it go, Just let it go. No.
I love the extremes of the universe because they remind
us that where we live is not usual. And this
is this big lesson in physics that you can't just
(03:12):
look the stuff around you and then try to generalize
to the whole universe. You can't assume that everything around
you is typical, that things on other planets and other
parts of the universe follow the same rules. We've often
made that mistake in physics and then learned that the
universe works in totally different ways. And we learned that
when we look far and wide, we explore the extremes,
we look for the hottest, the fastest, the brightest, the
(03:35):
weirdest stuff. That's where lessons lie, that's where we find
new physics. And so today we'll be talking about what
is the coldest place in the universe, And um, I
hear it that it's probably not what most people expect.
I hear it's not Nancy Pelosi's cold Stare that was
pretty chilling though, But yeah, this is a topic in
(03:57):
statistical and thermodynamics, and I to admit this is not
my number one favorite field of physics. Not because I
don't think it's awesome. It is really awesome, and the
kind of things that people have developed are really pretty cool,
but it's it can be sort of frustrating to think about,
and I particularly find it um sort of intimidating as
a topic to talk about coldness or or just temperature
(04:20):
and thermodynamics in general. Well, just thinking about like systems
of particles. I mean, let me reaf you. And as
an example, the opening paragraph of the Statistical Mechanics book
from grad school. Oh please, no, I know it doesn't
sound riveting, but whole lover a moment, all right, all right.
Ludwind Boltzmann, who spent much of his life studying statistical mechanics,
(04:43):
died in nineteen o six by his own hand. Paul Aaronfest,
carrying on his work, died similarly in three Now it
is our turn to study statistical mechanics. That's that's the
scene right there. You know, the legends of the field
killed themselves thinking about this, So now let's study it.
(05:04):
Do you think because it was just such an intense
topic or that, um, it's a dangerous thing to study.
I don't think. I don't think the topic itself is dangerous.
Something you're like summoning demons from below that infest your
mind or anything. But it is hard. It's tricky stuff.
You have to understand. You know, how gases move and
how they flow in terms of these tiny, little microscopic particles,
(05:27):
and so there's a lot of complicated statistics and difficult mathematics.
It's amazing what they have achieved. And one of the
greatest accomplishments, of course, is understanding like our experience of temperature.
You know, you touch something it feels hot, you touch
something feels cold, understand that in terms of what that
means for the microscopic particles. That connection kind of makes
you uncomfortable. Yeah, well it's it's not makes me uncomfortable.
(05:50):
It's just sort of difficult sometimes to think about what
it means mathematically. But it's also awesome because it lets
you understand how things around you arise from the most
you know, those microscopic particles. We'll dig into into that
in a moment, but you know, this, this fascinating extension
is like how cold can things get? How much can
you push that? You know, if coldness really is about
(06:11):
the motion of the particles inside something slowing down, then
like can you push it as far as you can go?
And how far exactly can the universe take you on
the temperature scale. Yeah, So part of what we'll be
talking about today is this concept of absolute zero, as
in that is theoretically possibly the coldest that you could
(06:32):
possibly ever get in the universe. And so the question
is there such a place out there in the universe?
Can there be such a place out there in the universe?
That's the question we'll be tackling today. And so I
was wondering if people had heard about this phrase. It
seems sort of common and awesome. You know, it's got
a nice zing too. It's got pizzazz right as most
(06:52):
physics terms don't. And just to be clear, this is
not an endorsement for a vodka drink. It also not
not an endorsement for vodka, though we're not anti vodka
on this show. Are you saying are you saying call us?
Are you saying to absolute callus? Well, we'll totally take
a case of your vodka. We're saying absolute zero about vodka. Right,
(07:16):
we're not saying anything positive. We're not saying anything negative
about vodka. But maybe the podcast would be funnier if
sample there is that drunk history show, which is pretty funny.
I don't think there's a drunk physics show yet, So yeah,
put that on the list of projects. We should start
a new series of episodes physics. Daniel and Jorge slur
(07:39):
their way through the universe. But which one would be drunk?
Do you or me? The audience should be drunk so
they can understand us, or so they can like our jokes.
Daniel and Jorge drinking game. Every time Daniel says that's right,
or every time Jorge says bananas, somebody takes a shot.
I can see this being all the rage in college
(08:00):
Fra Trinity houses. Speaking of colleges, I walked around campus
that you see Irvine, and I asked people what they
knew about absolute zero and if they thought it was
just sort of a crazy theoretical idea or something we
could possibly achieve. So, as usual, Daniel went around and
asked the question what is absolute zero? So before you
hear the answers, think about it for a second. If
(08:20):
someone approached you out of the blue and ask you
what absolute zero is, what would you answer. Here's what
people had to say, absolute zero. It's something that I
can't recalltop my head. I've heard it before. Temperature zero kelvin.
Is it possible for anything to actually get to absolute zero?
I don't think so. I believe that's like a measure
(08:41):
of temperature. I think if we were measuring in kelvin,
that's like the lowest anything could ever go. Can something
actually get to absolute zero? Uh? Theoretically yes, but physically
we haven't gone there yet. Of some understanding, I actually
don't know, but it sounds somewhat familiar. Absolute zero is
zero kelvin. It's the coldest possible temperatures, eat, death of
(09:03):
the universe, or however you want to say it. So
is it possible for something to physically achieved zero? Uh? So.
I believe it is extremely difficult to get to absolute
zero properly, but people have achieved some number of desmal
places very very close to this. But I think that
(09:24):
some of the matter based effects can be realized at
maybe higher temperatures and capsolute zero, like the helium three
and things like that. Superfluidity, Yes, superfluid. It's the coldest
possible temperature when everything stops moving and we've never gotten there.
So is it physically possible to get something absolute zero? Uh?
(09:45):
I don't know. I'm the wrong person as zero on
the Kelvin scale just no movement, no energy. Is that
physically achieved? Just theoretical? I believe theoretic here, So it's
impossible to get to epsoide zero. I don't think so.
All right, some pretty good answers. I thought, no mentions
of vodka. Yeah, I guess vodka is pretty expensive for
(10:05):
college students. Well, you see, Irvine does have the reputation
of being sort of the nerdy you see campus, like,
that's where you go if you want to really be
serious about your studies. I think, Santa Barbara, you might
to get different answers. All right, so you're saying, um,
that you're not surprised then that people a lot of
people knew what absolute zero was, and some people evedn't
talked about the heat death of the universe and how
(10:28):
it's sort of theoretical as well. Yeah, these were some
seriously good answers, and I think there's a lot of
interest there so I think, um, let's dig into it
and talk to people about what absolute zero is and
how cold we can actually get and if we can
find it somewhere in the universe. I think the answer
is might be pretty surprising. I guess maybe let's just
start with what is coldness? Like, what does it mean
(10:49):
for something to be cold at all? Yeah, it's sort
of fascinating. Um, whether like coldness or heat is a thing? Right, Like,
if heat is a thing, then coldness is sort of
like the sense of that thing. But if you were
sort of like an early person thinking about thermodynamics, it
could have been that like coldness was a thing and
heat was the opposite of it. But it turns out
(11:09):
that like heat is a thing, heat is the motion
of particles. We were talking earlier about this connection between
your experience of temperature and that what's happening for the
microscopic particles, and that's really what it is. Temperature is
a measurement of sort of the speed of how fast
these particles are moving or shaking. That sounds like a
really deep question, like is heat the absence of coldness
(11:31):
or is coldness the absence of heat? Yeah? What is
the sound of one thermometer measuring. Yeah, it's a it's
a fascinating question. But it turns out that heat is
the thing, right. Heat is the motion of particles and
coldness is the absence of that motion, and so there's
all sorts of fascinating consequences of that. And we really
got into this when we talked about um we had
(11:53):
an episode about temperature about and I got really confused
about how you know, you were saying temperature is actually
not like it's a thing, but it's sort of an
average thing. Like you can't measure the temperature of a
single particle. That's really weird to me. Yeah, in our
episode about what is the hottest thing in the universe,
we got into that because there's a lot of weird
stuff that's like really hot things that are three d
(12:15):
million degrees, but if you went inside them you would
freeze to death because they're really dilute um. So the
concept of temperature is very confusing, especially as you get
two very high energies. And you're right, temperature is not
the property of a single particle to property of a
system of particles. That has to do with the essentially
the average motion. And I got really hung up on
like um. So you can't take the temperature of a
(12:36):
single particle. Can you take the temperature of two particles?
You can't take the temperature of a single particle. In theory,
you can only take the temperature of an infinite number
of particles. But in practice a large number of particles
approximated infinite number pretty quickly, So to definitely not a billion,
probably a million, almost certainly a thousand, maybe circumstances. It's
(13:01):
one of these fuzzy things, you know, like when does
the practical match the theoretical. It's like saying, like, what's
the death of an ocean? You know, you can't apply
that to a single water molecule. You have to apply
to a huge number of water particles. It's a concept
that only exists for a system of particles, bunch of things, Yeah,
not for an individual. Yeah. And so for coldness, it's
(13:23):
the it's not the emotion of the stuff, it's the
lack of motion. So I guess maybe coldness is not
a thing. Then you're saying heat. Heat is a thing
because you can measure it, but coldness is just like
if the thing is not there, there's no motion of
the particles. Yeah, coldness is to heat, what like silence
is to noise. Right, is silence a thing or it's
(13:44):
the lack of noise In the same way, coldness is
the lack of heat. You know, heat is the motion
of these particles. They can move, they can spin, they
can vibrate. All that stores energy, right, and that energy
is the heat of the system. And as that energy
leaves that the object gets colder and colder, those little
particles move less and less. I feel like we're asking
(14:05):
some really deep questions, Daniel. Well, this is what I
love about physics, you know. It touches on really simple,
basic d questions. And this is why we're always bumping
into sort of philosophy questions because physics is important. And
so if you think about you know, this is like
the motion of particles. You can imagine the particles like
moving more and more and more and getting hotter and
hotter and hotter, and that's sort of continuing off to infinity. Right,
(14:27):
there's no limit to how much these particles can shake
or wiggle or whatever. But the other direction, as things
get colder and colder, things move less and less. It's
fascinating if there is sort of a negative limit there
that you approach like zero motion like silence, right, Like
you can have zero silence, but you can't have negative silence. Yeah,
(14:48):
you can't have negative silence or like super silence. You know,
you can't have like extra extra silence a silence. You
can't have negative noise. I guess, yeah, yeah, And that's
what it is for amperature, right, it's um. Once you
had zero, you can't get any colder. It's that's what
it's called absolute zero. Yeah. Absolute zero is the idea
(15:09):
that maybe you have a bunch of particles together and
then they just stopped moving, that they formed like a
perfect crystal. There's no entry be left at all. There's
only one way to arrange the system. There's no motion,
there's no rotation, there's no vibration. So that's the idea
of it, right, that every particle in your system is
not moving at all. Zero right now, kinetic energy, if
(15:33):
you could achieve that, then that would be absolute zero.
And it's it's really a fascinating topic if you look
in the history of this concept, like people start first
started thinking like huh, could this be possible? Even before
people try to make things super duper cold, to try
to achieve it. They started to think about is it
theoretically possible? And one thing they noticed was they were like,
let's look at how things change as a function temperature.
(15:55):
And you know, different substances like have different melting boiling points,
and that depends on the substance. Water melts or boils
at different temperatures than you know, oil or other substances. Right, Like,
let's just play around with sticking things in the freezer
and see what happens. Yeah, but all of these things
all point towards the same zero point, right, water or
(16:15):
hydrogen or oil or whatever, they all have the same
same absolute zero. This concept of an absolute zero is universal.
Would be the same temperature for every substance at zero.
Like it's you're saying, it's just when everything, no matter
what substance you are or what you're made out of,
you at some point might or could reach zero. Precisely,
(16:36):
it doesn't vary depending on what you are, Like when
you're freezing or boiling. It's like it's it's there for everybody,
including you and me and everyone listening. Because those other
transitions like melting and boiling, those have to do with
like how the molecules are sticking together or not sticking together, whatever.
So they're really dependent on the structure in the shape
of those molecules. That's why water and other materials boil
(16:58):
at different temperatures. But when it comes to not moving
at all, it doesn't really matter what shape you are
or what size you are, and you're just doing nothing,
and everybody does nothing in the same way. Right, what
about absolute vodka? Would that also have an absolute zero? Absolutely? Absolutely?
All right? So that's that's coldness, and that's absolute zero.
(17:19):
It's this theoretical limit of when everything is no longer moving.
And so let's get into have we reached absolute zero
and we if we can even get there, or if
there are places in the universe that are that have
absolute zero temperature. But first let's take a quick break,
(17:49):
all right, Daniel, how cold are physicists or how cold
have physicists gone? We're a pretty cool group of dudes. Um.
But there's this, really there's a really fun sort of history,
a race to the bottom or everybody was wondering like
how cold can you get something? And people were developing
(18:12):
technology try to make stuff colder and colder, and it's
not that easy, right, You want to make something really cold,
you need something else really cold. And so to make
something colder than anything you've ever seen before, take some cleverness, right,
because you're trying to take away To make something colder,
you have to take away energy, right, And to take
away energy you have to kind of like grab it, right.
(18:34):
You need something that is colder to take it away
from the thing you're trying to cool down. So it's
a it's a tough problem, I guess. Yeah, if you
want to freeze your ice cream, you put it in
the freezer, and the freezer the stuff around the ice
cream and the freezer is colder, so the heat leaks
out of that ice cream um into this stuff in
the freezer warms up the air and the freezer a
little bit. It doesn't come back. And I think it's
(18:55):
the key. Like if you leave ice cream out in
outside of the freezer, there's you know, there's energy going
into it and out of it, into it and out
of it, but mostly going into it. But in the freezer,
it just leaves the ice cream and it doesn't come back, Yeah,
because the freezer is actively cooling it down. But you
can also do it in a cooler, right, say, just
pack ice cream surrounded by really cold stuff and a
(19:17):
cooler so it's all sealed off. Then if the stuff
around the ice cream is colder, then they'll tend to equilibrate.
The heat will flow out of the ice cream and
into the colder stuff. So classic way to make something
colder is to put it next to something that's even
colder than it. Right, But if you're trying to make
the coldest thing ever, you can't do that because you
would need something even colder. And so the race to
(19:39):
reach the coldest temperature started a long time ago. It
seems you wrote here that it started in the eighteen hundreds. Yeah,
people were trying to make stuff really cold. Back in
eight It was Michael Faraday. He's a famous guy in physics,
and he achieved a temperature of negative a hundred and
thirty degrees celsius. That's a hundred and forty three degrees calvin.
(20:02):
That's really cold. It's pretty impressive for the eight hundreds,
isn't it. I mean they didn't even have telephones. They
couldn't call each other and brag about how I got
some ice cream on guys coming over. Nope, you have
to send a letter. Yeah, the first thing they tried
to do is to take gases from the air, hydrogen
(20:24):
or oxygen and stuff like this, and to liquefy it
to make it, you know, liquefied or even solid. He
was the first one to do that, to liquify any gas.
And then thirty years later some French guys whose names
I can't pronounce because I can't read French very well,
they liquefied air. They got it down to negative a
hundred and ninety five degrees celsius. That's just seventy eight
(20:44):
degrees kelvin, right, and for those of us who are
in fahrenheit, that means um also a negative large number exactly.
And you might wonder, like, how are these guys doing this,
how are they making this cold? Well, the the basic
trick they were doing is they're lowering the pressure, because
these gases are complicated things, and if you lower the
(21:06):
pressure of a gas, it ends up cooling down. If
you keep like the amount of gas constant and use
and you somehow stretch it or lower the pressure, then
it automatically gets colder. Right, yeah, precisely. And that's the
kind of stuff that always melted my brain, you know,
like you have the same amount of frozer brain and
gave your brain freeze or melted your brain, both at
the same time. And that's why. But then we have
(21:30):
a series of guys making advancements. In eighty three, somebody
liquefied oxygen down to fifty five degrees kelvin and then
in door liquefied hydrogen, and of course he's famous for
inventing the doer, right, which is this like cold flask.
You've probably seen a lot of laboratories that's down to
(21:50):
twenty one degrees kelvin. So they're little by little, sort
of one up in each other, you know, getting colder
and colder because they use different gases or did they
just have better techniques. They just sort of expanded on
this technique of figuring out ways to suck heat out
by expanding the volume and then pulling out the coldest parts,
and then expanding that and then pulling out the coldest parts.
(22:12):
So it's all about this sort of experimental chemistry cleverness.
And this is way before you know, any sort of
advanced technologies, right. So these guys were just kind of
like you know, experimenting with um like flasks and boilers
and things like that, right, pretty basic, you know chemistry setups. Yeah,
they had you know, glass tubes and rubber valves and
(22:34):
this kind of stuff, and they had no complicated technology
at all. Um And then it was in nineteen o
eight they finally liquefied helium that brought them down to
four degrees kelvin and then even further down to one
and a half degrees calvin. And this guy who did it,
he won the Nobel Prize for that. It was like
such an achievement to get such cold temperatures. That was
(22:55):
like the forefront of exploration because he went from like
twenty calvin to one kelvin. Yeah, that's a huge jump. Yeah,
that's a pretty big change fractutionally, and it gets you
pretty close to absolute zero. Did they have a sense
that there was an absolute zero? You know? Do you
know what I mean? Like, did they know that at
some point you would hit rock bottom? Yeah? They had
this idea because they were studying sort of the temperature
(23:18):
as a function of pressure and volume and all this stuff,
and you know, these temperature curves all point in the
same direction, and no matter what gas you're talking about, helium, hydrogen, oxygen,
all those lines were sort of converging at the same
point at absolute zero. So they had the idea that
this existed, and they were sort of pushing to see
how close they could get. But they were all wondering, like,
(23:39):
is it possible to actually achieve something at absolute zero's
just sort of a theoretical concept, or can it actually
exist in and how is it you could have this
like theoretical concept that you could never actually achieve in practice.
That's sort of weird, right, if you can or cannot
achieve it, right, it's sort of it's a big unknown, Yeah,
but it would it would be weird to have this
theoretical a concept that's a just a straightforward extrapolation of
(24:02):
things we observe, but then have it be sort of unachievable.
If that's the case, it tells you something pretty deep
about the universe. And so people kept going, right, people,
and nowadays, what's like, what's the record lowest temperature we
can get to? Yeah, so people work really hard on
this now and the current record is much better than
like the Nobel Prize winning record at one point five
(24:25):
degrees kelvin. Right now we're at a hundred pico Kelvin's
Pico Kelvin's that's like one with nine zeros in front
of it or behind it. Yeah. Yeah, it's a zero
point zero zor zero zero or zero zero zero zero
one kelvin. Wow. So we've been able to cool something
down that cold. Yeah, well, I mean not me and
(24:48):
not you. Some people out there working really hard and
it's the collective we a is in the part of
humanity that I'm proud to call myself a part of. Yeah.
So that's the current record, and you know, the is
fascinating theoretically, but it's also it's hard to do. You know,
it's it's hard to accomplish this. As we were saying before,
Like you get something super duper cold, you need clever tricks.
(25:10):
Do they use something kind of special trick there? Yeah,
they do this thing which is really fascinating. It sounds
um counterintuitive. They use laser cooling like a cold ray. No, No,
it's a hot ray, just like normal, right, it's not
like a cold laser. That would be awesome. And in
the comic book version of US, I definitely want eyeballs
that shoot out cold lasers that can freeze things. There's
(25:30):
a Batman villain called Mr. Freeze. Yeah, precisely. But okay,
but this is not This isn't like a regular you know,
zapping laser, and somehow that cools things. And the way
it makes things cold is not by touching them and
taking away their heat. It's by selecting the hot stuff
and pushing it out of the way. So imagine you
(25:51):
have a big blob of gas. Not every atom in
that blob of gas is moving at the same speed.
That's a distribution. Some are moving after some removing colder.
If you could just select the cold ones, then the
average temperature would go down. Oh, I see, but you
can actually aim this laser or how does that work?
Or like the lasers some somehow only picks out the
(26:13):
fast moving atoms. Yeah, it's pretty complicated, but essentially the
idea is to get the fast moving atoms in the
path of the laser and so they didn't knocks them
out of the way. And you use a laser because
it's you can't just like go in there and flick
out individual atoms with a mechanical object. The laser is
the best way to interact with an individual atom. You
can just like blow on it. They tried that six
(26:34):
years later that guy still hadn't graduated. No Nobel prize
for no PhD even No. So that's the idea instead
of trying to cool down the whole sample, right, which
is what you do when you put your ice cream
in the freezer, instead they just pick out the cold bits.
It's like if I gave you a bowl of ice
cream and you're like, hey, it's kind of melted, and
I just sort of scooped out the hot bits and
(26:55):
left you with the colder bits of ice cream. You know,
that's not really cooling down your ice cream, but the
temperature of the ice cream you're left with is colder.
And so that's the current record right now, is that
the cold is that humans have been able to cool
something down is a hundred pico kelvin. Yeah, and that's
colder than outer space. You know, the average temperature out
there in space is like two point seven three degrees kelvin,
(27:18):
which sounds kind of hot in comparison. Yeah a minute
ago that sounded chili, right, but compared to a hundred
peeko kelvin's it's like bust out your swimsuit. Um. And
that's the temperature average temperature out there in space there's
some spots out there in space where lots of gases
have been like blowing out of a star, and that
expansion cools it down to maybe one degree kelvin. But
(27:39):
the coldest natural thing, we think is one degree kelvin
and the current record is a hundred peco kelvins. But
humans are not finished. You think we can go further
colder than Yeah, there's a there's an instrument right now
on the International Space Station. That's where they're doing this experiment.
And it's like you've got to be surrounded by m
(28:00):
D space just to even have a chance to do this.
And it's called the Cold Atom Lab, and their goals
to get down to one pico calvin down from a
hundred which is the current record. Maybe helped me paint
a picture here what's going on at that temperature like
or the atoms? Not very much? All right, that's that's about.
It's like the conversation at your average physics party, you know,
(28:21):
just like nobody's talking, everybody just sitting there, everyone's just
thinking about absolute zero. Now, there is some wiggling. If
you were to zoom down microscopically and look at these things,
there would be some energy. There's some motion of these particles,
like like each atom is maybe not moving across the room,
but they are sort of wiggling and vibrating. And these
(28:42):
are all crystals, right, so you imagine they have bonds
with each other. They're not totally separate atoms. Imagine like
a lattice and you have these atoms with these bonds
holding them in place, and then occasionally you get like
a little wiggle, a little bit of sound goes through
the material. Hey, that's a cool connection actually between temperature
and sound. Right. Sound probably does have a temperature because
(29:02):
it's the wiggling and motion of these of the material.
I never thought about that. Man, I'm gonna need another
shot just to consider that question, Daniel. When you get
down to those temperatures, things form into a crystal, because
what else are they going to do. Can you take
a gas down to that cold of a temperature or
does it have to form into a solid by that?
(29:23):
I think it has to form into a solid idea.
And I'm not a chemist, So maybe somebody out there
who knows more chemistry than I do knows whether or
not you could keep something a gas and still make
it really cold. I think it would have to be
super duper dilute, right, But essentially, you know, these molecules
have no vibrational energy, no rotational energy anymore, and no
translational energy. They're not moving, so they're just all sitting
(29:46):
in place. Whether or not it's a crystal or a gas,
I guess just depends on how tightly you're packing them.
But effectively this becomes how you define a gas or
a solid, right, yeah, and probably an absolute zero. You know,
it's one of those places where the phases are not
well to find, you know, how the chemistry they have
these like triple points where something is like, what is
(30:06):
it exactly if you're right at the triple point? Absolute
zero is probably like that. But you know, the fascinating
question is like how close absolute zero could you experimentally get,
Like is it possible to make a material with exactly
zero motion? All right, well, let's get into that, whether
it's even possible to reach absolute zero. And I think
for me, the more the interesting question is if there
(30:28):
are places in the universe that are absolute zero. So
let's get into that. But first let's take another break.
All right, Daniel, can we get there? Can we get
(30:49):
to absolute zero? Without drinking absolute vodka. I think it is.
They're totally not sponsored by liquor company um. But yeah,
can we get too absolutely Is it even possible or
like many of the people you interviewed on the street,
isn't only theoretical that you can get to absolute zero?
(31:10):
I think unfortunately, there is no amount of you can
drink to get us down to absolute zero. I think
theoretically it's impossible. It's impossible. Yeah, it's just not possible.
I think in the sort of the classical theory that
the folks who were first coming up with thermodynamics thought about,
you know, they're thinking about particles is a lot of
tiny little balls, and so you can talk about their
(31:31):
motion and their location in that context. It is possible.
But we know better now. We know that when you
get down to tiny particles, there are different rules that apply.
These particles don't have classical paths, they don't move in
a way that makes sense to us. Their quantum mechanical
Maybe even the idea of energy at that point gets fuzzy, right,
like the idea of kinetic energy, whether there's something's moving
(31:53):
or not. At the quantum level, it's sort of like undefined, right, yeah, well,
we'll dig into that in a whole separate episode of energy.
I gotta say, if several folks, like maybe dozens of
folks have written in asking us to do a podcast
episode about energy and what does it mean? And how
do you transfer one form to the other and quantum
mechanically doesn't make any sense. So we'll dig into that
a whole separate episode when we get the energy to
(32:14):
do it will after we're done drinking that bottle of vodka.
But the problem is that as you get really really cold,
you come down to this zero point energy. Right. Quantum
mechanics says that there are fluctuations everywhere, even in empty space.
There's a small amount of energy, and that energy is
constantly fluctuating. You have these quantum fields that are going
(32:35):
up and down, so you have particles being created, and
so it's impossible to get down to zero energy because
there's always some energy even in empty space. But is
it fluctuations or is it just uncertainty? Do you know?
Do you know what I mean? Like it's or like
randomness or is there even a difference? Well, there's both.
There's you know, we think that the mean energy of
(32:55):
empty space is not zero, that there is energy stored
in empty space, and so you just can get rid
of this is just a property of space itself to
have energy. Not even nothingness is absolute zero, yeah, because
there is no such thing as nothingness. You can't have
space without nothing. That's the property of space is that
it has quantum fields. And these quantum fields that we
talked about the Higgs Boson episode don't settle at zero.
(33:17):
They settle it's some energy above zero. Space is something,
space is something. So there so there's no nothingness. Actually yeah, well,
and that's a whole other concept. You know, how do
you get something from nothing? And what is nothingness? Or
maybe maybe it's fair to say space without anything in
it still has energy. Space can't have nothing because it
always have quantum fields which have energy. Yeah, there's no nothing, Yeah,
(33:40):
there's no nothing. That's the zero point energy concept. That's
like you can't get down to zero energy. But even
if somehow the universe, you know, even if we like
destroy the Higgs field and we got down to a
state or vacuum energy of zero, and we talked about
that in a separate episode, um, even still there would
be quantum mechanical problems because imagine what you do there.
You're taking a particle and you're setting its location, right,
(34:03):
has no motion, so you have to know its location,
and that means you also know it's momentum. But the
Heisenberg uncertainty principle says you have a minimum uncertainty in
the location and the motion. But when now we're talking
about a state where we know exactly the location and
the motion, and so that seems like it would violate
the uncertainty principle. Well, maybe that just means that there's
no like, the absolute coldness of the universe is not
(34:26):
zero point zero zero zero zero zero, But could there
still be like a minimum temperature of the universe, like
a point oh you know one pico pico, pico Keilen
or something like that. Oh, that's fascinating. You're saying the
minimum might not be zero, but there could be a
zero or could you or pretty much zero? I want
to hear that announcement scientists announce the achievement of pretty
(34:50):
much zero. We did it, We got pretty much nothing. No,
that's a really interesting question. Can you ask them topically
a pro absolutely zero getting closer and closer forever, or
is there a minimum non zero temperature. I think because
of the zero point energy of space, there must be
a minimum temperature. But if you somehow collapsed the Higgs
(35:13):
field and got rid of that minimum energy, then I
think you could ask some topically approach zero forever. You're saying,
unless the universe destroys itself, there is a limit. And
I'm not encouraging anybody to destroy the universe just to
win that Nobel prize, just to ask for Horace question,
We're going to destroy the universe. That is physicists being
(35:34):
drunk with power. Okay, So then, uh so there might
be sort of a minimum and you're saying, it's really
difficult to get there because space itself doesn't get to zero.
So that does that mean that nowhere in the universe
do we get that cold or like there's nowhere in
the universe that's actually zero. That's right. We think that
there is nowhere in the universe it's actually zero, and
(35:55):
absent physics labs here on Earth and on the space station,
we think the coldest thing in the universe is a
out just one kelvin out there in you know, the
heart of a frozen planet in the middle of nowhere.
It's still about one kelvin. Yeah, most of the stuff
out there is about two point seven degrees kelvin. If
you really work hard, you might be able to find
(36:15):
something at one degree kelvin. But here on Earth we
have stuff that's like a hundred Pego Calvin's going down
to one Pico Calvin. We hope. Wow. So the coldest
place in the entire universe might be here on Earth
in somebody's lab, depending of course, on whether there are aliens.
So basically we're in a race with alien physicists to
(36:37):
get the coldest place on Earth to see who has
the who's the coolest species in the universe. You knew
I was going to have to bring it back to aliens. Eventually.
Every topic has to touch on aliens, right, Yeah, there
could be aliens out there who have a lab because
they would have to do this on purpose, right, they
have a lab that maybe goes down to even colder
(36:59):
than us at a hundred people Calevin. Yeah, there could
be alien civilizations out there that have been doing physics
for a billion years, and you know, to them, like
a hundred Pekokelevins is laughable, man, That's like a kindergarten
science fair project. For them. Really, they could be way
way down further in the cold spectrum. Wow, But we
won't know until those aliens come and visit. All right,
(37:21):
But as far as we know, barring super advance cool aliens,
the coldest place in the universe is here, probably in
in the United States, or in the lab in Europe
or something. Right, Yeah, and very soon the coldest place
in the universe, we think, will be on the International
Space Station at the Cold Atom Lab. All right, Well,
I think we answered the question pretty well. Where is
(37:43):
the coldest place in the universe and whether we could
maybe get even colder might not be possible unless we
destroy the universe, it seems. But absolute zero is a
fascinating topic theoretically, and it's a fascinating goal. We keep
pushing more and more, and as we do so, we
learn more and more about cooling technology and how to
achieve that, and and how things operate into very extremes
(38:07):
of the universe, which is where we hope to reveal
some new secrets about how the universe works. So the
next time you have a scoop of ice cream, think
think about how how cold it is and how cold
you could get it if you went to your local
physics lab and recruited some physicist to give you a
better ice cream. Thanks for tuning in for this tasty topic.
See you next time. Before you still have a question
(38:36):
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
on Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or email us at Feedback at Daniel and
Jorge dot com. Thanks for listening and remember that Daniel
and Jorge Explain the Universe is a production of I
Heart Radio from more podcast from my Heart Radio. Visit
(38:59):
the I Heart Radio, a Apple Podcasts, or wherever you
listen to your favorite shows. Yeah h
Hey, Daniel, what's your least favorite topic in physics? Oh, man,
don't make me say something negative about physics. Well, now
I really want to know. Fine, Fine, it's thermodynamics. You
don't like thermodynamics. But it's such a hot field, Daniel,
or cold, depending on the state. It's just too hard
(00:29):
to get my mind around. There's so many particles involved,
you know, So you don't know much about thermodynamics, then
I wouldn't say I know that much. Really, like you
know zero about it? You're getting close. What if we
talk about absolute zero? That's a reasonable approximation of how
much I like thermodynamics. I am or handmade cartoonists and
(01:04):
the creator of PhD comics. Hi, I'm Daniel. I'm a
particle physicist, and I'm not a lover of thermodynamics. Now,
welcome to our podcast, Daniel and Jorge Explain the Universe,
a production of I Heart Radio in which we find
all the amazing and crazy things about the universe, the
extreme things, the fast things, the hot things, the cold things,
(01:24):
and we explain them all to you. That's right. We
explore all of the hot topics in physics and science
out there in the universe, but also the coldest thing sometimes,
that's right. We try to touch on the hot topics
and we try to be cool at the same time.
We are. We are pretty cool for a physics podcast.
We're definitely cool. Yeah, all all three of them were
(01:48):
probably the coolest, but yeah. This is part of a
series of podcast episodes about the extremes of the universe.
Should we cue the heavy metal sounds, Danny Wild Stallions,
where we're gonna get Bill and Ted on the podcast,
Oh we should build or Ted just before their reunion tour.
(02:08):
We like talking about the crazy bits of the universe
because where the extremes are sort of where you learn
the most about the universe. How hot can things get?
What is the densest thing, what is the strongest magnetic field?
And that's why we explored all those topics in previous episodes. Yeah,
it really makes you kind of push or stretch the
boundaries of your mind, you know, to think of the
(02:28):
hottest things, the dancest things, the brightest things. Those are
all things we've covered in other episodes, and today we'll
be talking about another one of those extremes in the universe.
So today on the podcast, we'll be talking about what
is the coldest place in the universe. Instead of heavy
(02:51):
metal guitar, we should just have a cold wind or something. No,
we should have the theme music from Frozen, of course,
come on, just let it go, Just let it go. No.
I love the extremes of the universe because they remind
us that where we live is not usual. And this
is this big lesson in physics that you can't just
(03:12):
look the stuff around you and then try to generalize
to the whole universe. You can't assume that everything around
you is typical, that things on other planets and other
parts of the universe follow the same rules. We've often
made that mistake in physics and then learned that the
universe works in totally different ways. And we learned that
when we look far and wide, we explore the extremes,
we look for the hottest, the fastest, the brightest, the
(03:35):
weirdest stuff. That's where lessons lie, that's where we find
new physics. And so today we'll be talking about what
is the coldest place in the universe, And um, I
hear it that it's probably not what most people expect.
I hear it's not Nancy Pelosi's cold Stare that was
pretty chilling though, But yeah, this is a topic in
(03:57):
statistical and thermodynamics, and I to admit this is not
my number one favorite field of physics. Not because I
don't think it's awesome. It is really awesome, and the
kind of things that people have developed are really pretty cool,
but it's it can be sort of frustrating to think about,
and I particularly find it um sort of intimidating as
a topic to talk about coldness or or just temperature
(04:20):
and thermodynamics in general. Well, just thinking about like systems
of particles. I mean, let me reaf you. And as
an example, the opening paragraph of the Statistical Mechanics book
from grad school. Oh please, no, I know it doesn't
sound riveting, but whole lover a moment, all right, all right.
Ludwind Boltzmann, who spent much of his life studying statistical mechanics,
(04:43):
died in nineteen o six by his own hand. Paul Aaronfest,
carrying on his work, died similarly in three Now it
is our turn to study statistical mechanics. That's that's the
scene right there. You know, the legends of the field
killed themselves thinking about this, So now let's study it.
(05:04):
Do you think because it was just such an intense
topic or that, um, it's a dangerous thing to study.
I don't think. I don't think the topic itself is dangerous.
Something you're like summoning demons from below that infest your
mind or anything. But it is hard. It's tricky stuff.
You have to understand. You know, how gases move and
how they flow in terms of these tiny, little microscopic particles,
(05:27):
and so there's a lot of complicated statistics and difficult mathematics.
It's amazing what they have achieved. And one of the
greatest accomplishments, of course, is understanding like our experience of temperature.
You know, you touch something it feels hot, you touch
something feels cold, understand that in terms of what that
means for the microscopic particles. That connection kind of makes
you uncomfortable. Yeah, well it's it's not makes me uncomfortable.
(05:50):
It's just sort of difficult sometimes to think about what
it means mathematically. But it's also awesome because it lets
you understand how things around you arise from the most
you know, those microscopic particles. We'll dig into into that
in a moment, but you know, this, this fascinating extension
is like how cold can things get? How much can
you push that? You know, if coldness really is about
(06:11):
the motion of the particles inside something slowing down, then
like can you push it as far as you can go?
And how far exactly can the universe take you on
the temperature scale. Yeah, So part of what we'll be
talking about today is this concept of absolute zero, as
in that is theoretically possibly the coldest that you could
(06:32):
possibly ever get in the universe. And so the question
is there such a place out there in the universe?
Can there be such a place out there in the universe?
That's the question we'll be tackling today. And so I
was wondering if people had heard about this phrase. It
seems sort of common and awesome. You know, it's got
a nice zing too. It's got pizzazz right as most
(06:52):
physics terms don't. And just to be clear, this is
not an endorsement for a vodka drink. It also not
not an endorsement for vodka, though we're not anti vodka
on this show. Are you saying are you saying call us?
Are you saying to absolute callus? Well, we'll totally take
a case of your vodka. We're saying absolute zero about vodka. Right,
(07:16):
we're not saying anything positive. We're not saying anything negative
about vodka. But maybe the podcast would be funnier if
sample there is that drunk history show, which is pretty funny.
I don't think there's a drunk physics show yet, So yeah,
put that on the list of projects. We should start
a new series of episodes physics. Daniel and Jorge slur
(07:39):
their way through the universe. But which one would be drunk?
Do you or me? The audience should be drunk so
they can understand us, or so they can like our jokes.
Daniel and Jorge drinking game. Every time Daniel says that's right,
or every time Jorge says bananas, somebody takes a shot.
I can see this being all the rage in college
(08:00):
Fra Trinity houses. Speaking of colleges, I walked around campus
that you see Irvine, and I asked people what they
knew about absolute zero and if they thought it was
just sort of a crazy theoretical idea or something we
could possibly achieve. So, as usual, Daniel went around and
asked the question what is absolute zero? So before you
hear the answers, think about it for a second. If
(08:20):
someone approached you out of the blue and ask you
what absolute zero is, what would you answer. Here's what
people had to say, absolute zero. It's something that I
can't recalltop my head. I've heard it before. Temperature zero kelvin.
Is it possible for anything to actually get to absolute zero?
I don't think so. I believe that's like a measure
(08:41):
of temperature. I think if we were measuring in kelvin,
that's like the lowest anything could ever go. Can something
actually get to absolute zero? Uh? Theoretically yes, but physically
we haven't gone there yet. Of some understanding, I actually
don't know, but it sounds somewhat familiar. Absolute zero is
zero kelvin. It's the coldest possible temperatures, eat, death of
(09:03):
the universe, or however you want to say it. So
is it possible for something to physically achieved zero? Uh? So.
I believe it is extremely difficult to get to absolute
zero properly, but people have achieved some number of desmal
places very very close to this. But I think that
(09:24):
some of the matter based effects can be realized at
maybe higher temperatures and capsolute zero, like the helium three
and things like that. Superfluidity, Yes, superfluid. It's the coldest
possible temperature when everything stops moving and we've never gotten there.
So is it physically possible to get something absolute zero? Uh?
(09:45):
I don't know. I'm the wrong person as zero on
the Kelvin scale just no movement, no energy. Is that
physically achieved? Just theoretical? I believe theoretic here, So it's
impossible to get to epsoide zero. I don't think so.
All right, some pretty good answers. I thought, no mentions
of vodka. Yeah, I guess vodka is pretty expensive for
(10:05):
college students. Well, you see, Irvine does have the reputation
of being sort of the nerdy you see campus, like,
that's where you go if you want to really be
serious about your studies. I think, Santa Barbara, you might
to get different answers. All right, so you're saying, um,
that you're not surprised then that people a lot of
people knew what absolute zero was, and some people evedn't
talked about the heat death of the universe and how
(10:28):
it's sort of theoretical as well. Yeah, these were some
seriously good answers, and I think there's a lot of
interest there so I think, um, let's dig into it
and talk to people about what absolute zero is and
how cold we can actually get and if we can
find it somewhere in the universe. I think the answer
is might be pretty surprising. I guess maybe let's just
start with what is coldness? Like, what does it mean
(10:49):
for something to be cold at all? Yeah, it's sort
of fascinating. Um, whether like coldness or heat is a thing? Right, Like,
if heat is a thing, then coldness is sort of
like the sense of that thing. But if you were
sort of like an early person thinking about thermodynamics, it
could have been that like coldness was a thing and
heat was the opposite of it. But it turns out
(11:09):
that like heat is a thing, heat is the motion
of particles. We were talking earlier about this connection between
your experience of temperature and that what's happening for the
microscopic particles, and that's really what it is. Temperature is
a measurement of sort of the speed of how fast
these particles are moving or shaking. That sounds like a
really deep question, like is heat the absence of coldness
(11:31):
or is coldness the absence of heat? Yeah? What is
the sound of one thermometer measuring. Yeah, it's a it's
a fascinating question. But it turns out that heat is
the thing, right. Heat is the motion of particles and
coldness is the absence of that motion, and so there's
all sorts of fascinating consequences of that. And we really
got into this when we talked about um we had
(11:53):
an episode about temperature about and I got really confused
about how you know, you were saying temperature is actually
not like it's a thing, but it's sort of an
average thing. Like you can't measure the temperature of a
single particle. That's really weird to me. Yeah, in our
episode about what is the hottest thing in the universe,
we got into that because there's a lot of weird
stuff that's like really hot things that are three d
(12:15):
million degrees, but if you went inside them you would
freeze to death because they're really dilute um. So the
concept of temperature is very confusing, especially as you get
two very high energies. And you're right, temperature is not
the property of a single particle to property of a
system of particles. That has to do with the essentially
the average motion. And I got really hung up on
like um. So you can't take the temperature of a
(12:36):
single particle. Can you take the temperature of two particles?
You can't take the temperature of a single particle. In theory,
you can only take the temperature of an infinite number
of particles. But in practice a large number of particles
approximated infinite number pretty quickly, So to definitely not a billion,
probably a million, almost certainly a thousand, maybe circumstances. It's
(13:01):
one of these fuzzy things, you know, like when does
the practical match the theoretical. It's like saying, like, what's
the death of an ocean? You know, you can't apply
that to a single water molecule. You have to apply
to a huge number of water particles. It's a concept
that only exists for a system of particles, bunch of things, Yeah,
not for an individual. Yeah. And so for coldness, it's
(13:23):
the it's not the emotion of the stuff, it's the
lack of motion. So I guess maybe coldness is not
a thing. Then you're saying heat. Heat is a thing
because you can measure it, but coldness is just like
if the thing is not there, there's no motion of
the particles. Yeah, coldness is to heat, what like silence
is to noise. Right, is silence a thing or it's
(13:44):
the lack of noise In the same way, coldness is
the lack of heat. You know, heat is the motion
of these particles. They can move, they can spin, they
can vibrate. All that stores energy, right, and that energy
is the heat of the system. And as that energy
leaves that the object gets colder and colder, those little
particles move less and less. I feel like we're asking
(14:05):
some really deep questions, Daniel. Well, this is what I
love about physics, you know. It touches on really simple,
basic d questions. And this is why we're always bumping
into sort of philosophy questions because physics is important. And
so if you think about you know, this is like
the motion of particles. You can imagine the particles like
moving more and more and more and getting hotter and
hotter and hotter, and that's sort of continuing off to infinity. Right,
(14:27):
there's no limit to how much these particles can shake
or wiggle or whatever. But the other direction, as things
get colder and colder, things move less and less. It's
fascinating if there is sort of a negative limit there
that you approach like zero motion like silence, right, Like
you can have zero silence, but you can't have negative silence. Yeah,
(14:48):
you can't have negative silence or like super silence. You know,
you can't have like extra extra silence a silence. You
can't have negative noise. I guess, yeah, yeah, And that's
what it is for amperature, right, it's um. Once you
had zero, you can't get any colder. It's that's what
it's called absolute zero. Yeah. Absolute zero is the idea
(15:09):
that maybe you have a bunch of particles together and
then they just stopped moving, that they formed like a
perfect crystal. There's no entry be left at all. There's
only one way to arrange the system. There's no motion,
there's no rotation, there's no vibration. So that's the idea
of it, right, that every particle in your system is
not moving at all. Zero right now, kinetic energy, if
(15:33):
you could achieve that, then that would be absolute zero.
And it's it's really a fascinating topic if you look
in the history of this concept, like people start first
started thinking like huh, could this be possible? Even before
people try to make things super duper cold, to try
to achieve it. They started to think about is it
theoretically possible? And one thing they noticed was they were like,
let's look at how things change as a function temperature.
(15:55):
And you know, different substances like have different melting boiling points,
and that depends on the substance. Water melts or boils
at different temperatures than you know, oil or other substances. Right, Like,
let's just play around with sticking things in the freezer
and see what happens. Yeah, but all of these things
all point towards the same zero point, right, water or
(16:15):
hydrogen or oil or whatever, they all have the same
same absolute zero. This concept of an absolute zero is universal.
Would be the same temperature for every substance at zero.
Like it's you're saying, it's just when everything, no matter
what substance you are or what you're made out of,
you at some point might or could reach zero. Precisely,
(16:36):
it doesn't vary depending on what you are, Like when
you're freezing or boiling. It's like it's it's there for everybody,
including you and me and everyone listening. Because those other
transitions like melting and boiling, those have to do with
like how the molecules are sticking together or not sticking together, whatever.
So they're really dependent on the structure in the shape
of those molecules. That's why water and other materials boil
(16:58):
at different temperatures. But when it comes to not moving
at all, it doesn't really matter what shape you are
or what size you are, and you're just doing nothing,
and everybody does nothing in the same way. Right, what
about absolute vodka? Would that also have an absolute zero? Absolutely? Absolutely?
All right? So that's that's coldness, and that's absolute zero.
(17:19):
It's this theoretical limit of when everything is no longer moving.
And so let's get into have we reached absolute zero
and we if we can even get there, or if
there are places in the universe that are that have
absolute zero temperature. But first let's take a quick break,
(17:49):
all right, Daniel, how cold are physicists or how cold
have physicists gone? We're a pretty cool group of dudes. Um.
But there's this, really there's a really fun sort of history,
a race to the bottom or everybody was wondering like
how cold can you get something? And people were developing
(18:12):
technology try to make stuff colder and colder, and it's
not that easy, right, You want to make something really cold,
you need something else really cold. And so to make
something colder than anything you've ever seen before, take some cleverness, right,
because you're trying to take away To make something colder,
you have to take away energy, right, And to take
away energy you have to kind of like grab it, right.
(18:34):
You need something that is colder to take it away
from the thing you're trying to cool down. So it's
a it's a tough problem, I guess. Yeah, if you
want to freeze your ice cream, you put it in
the freezer, and the freezer the stuff around the ice
cream and the freezer is colder, so the heat leaks
out of that ice cream um into this stuff in
the freezer warms up the air and the freezer a
little bit. It doesn't come back. And I think it's
(18:55):
the key. Like if you leave ice cream out in
outside of the freezer, there's you know, there's energy going
into it and out of it, into it and out
of it, but mostly going into it. But in the freezer,
it just leaves the ice cream and it doesn't come back, Yeah,
because the freezer is actively cooling it down. But you
can also do it in a cooler, right, say, just
pack ice cream surrounded by really cold stuff and a
(19:17):
cooler so it's all sealed off. Then if the stuff
around the ice cream is colder, then they'll tend to equilibrate.
The heat will flow out of the ice cream and
into the colder stuff. So classic way to make something
colder is to put it next to something that's even
colder than it. Right, But if you're trying to make
the coldest thing ever, you can't do that because you
would need something even colder. And so the race to
(19:39):
reach the coldest temperature started a long time ago. It
seems you wrote here that it started in the eighteen hundreds. Yeah,
people were trying to make stuff really cold. Back in
eight It was Michael Faraday. He's a famous guy in physics,
and he achieved a temperature of negative a hundred and
thirty degrees celsius. That's a hundred and forty three degrees calvin.
(20:02):
That's really cold. It's pretty impressive for the eight hundreds,
isn't it. I mean they didn't even have telephones. They
couldn't call each other and brag about how I got
some ice cream on guys coming over. Nope, you have
to send a letter. Yeah, the first thing they tried
to do is to take gases from the air, hydrogen
(20:24):
or oxygen and stuff like this, and to liquefy it
to make it, you know, liquefied or even solid. He
was the first one to do that, to liquify any gas.
And then thirty years later some French guys whose names
I can't pronounce because I can't read French very well,
they liquefied air. They got it down to negative a
hundred and ninety five degrees celsius. That's just seventy eight
(20:44):
degrees kelvin, right, and for those of us who are
in fahrenheit, that means um also a negative large number exactly.
And you might wonder, like, how are these guys doing this,
how are they making this cold? Well, the the basic
trick they were doing is they're lowering the pressure, because
these gases are complicated things, and if you lower the
(21:06):
pressure of a gas, it ends up cooling down. If
you keep like the amount of gas constant and use
and you somehow stretch it or lower the pressure, then
it automatically gets colder. Right, yeah, precisely. And that's the
kind of stuff that always melted my brain, you know,
like you have the same amount of frozer brain and
gave your brain freeze or melted your brain, both at
the same time. And that's why. But then we have
(21:30):
a series of guys making advancements. In eighty three, somebody
liquefied oxygen down to fifty five degrees kelvin and then
in door liquefied hydrogen, and of course he's famous for
inventing the doer, right, which is this like cold flask.
You've probably seen a lot of laboratories that's down to
(21:50):
twenty one degrees kelvin. So they're little by little, sort
of one up in each other, you know, getting colder
and colder because they use different gases or did they
just have better techniques. They just sort of expanded on
this technique of figuring out ways to suck heat out
by expanding the volume and then pulling out the coldest parts,
and then expanding that and then pulling out the coldest parts.
(22:12):
So it's all about this sort of experimental chemistry cleverness.
And this is way before you know, any sort of
advanced technologies, right. So these guys were just kind of
like you know, experimenting with um like flasks and boilers
and things like that, right, pretty basic, you know chemistry setups. Yeah,
they had you know, glass tubes and rubber valves and
(22:34):
this kind of stuff, and they had no complicated technology
at all. Um And then it was in nineteen o
eight they finally liquefied helium that brought them down to
four degrees kelvin and then even further down to one
and a half degrees calvin. And this guy who did it,
he won the Nobel Prize for that. It was like
such an achievement to get such cold temperatures. That was
(22:55):
like the forefront of exploration because he went from like
twenty calvin to one kelvin. Yeah, that's a huge jump. Yeah,
that's a pretty big change fractutionally, and it gets you
pretty close to absolute zero. Did they have a sense
that there was an absolute zero? You know? Do you
know what I mean? Like, did they know that at
some point you would hit rock bottom? Yeah? They had
this idea because they were studying sort of the temperature
(23:18):
as a function of pressure and volume and all this stuff,
and you know, these temperature curves all point in the
same direction, and no matter what gas you're talking about, helium, hydrogen, oxygen,
all those lines were sort of converging at the same
point at absolute zero. So they had the idea that
this existed, and they were sort of pushing to see
how close they could get. But they were all wondering, like,
(23:39):
is it possible to actually achieve something at absolute zero's
just sort of a theoretical concept, or can it actually
exist in and how is it you could have this
like theoretical concept that you could never actually achieve in practice.
That's sort of weird, right, if you can or cannot
achieve it, right, it's sort of it's a big unknown, Yeah,
but it would it would be weird to have this
theoretical a concept that's a just a straightforward extrapolation of
(24:02):
things we observe, but then have it be sort of unachievable.
If that's the case, it tells you something pretty deep
about the universe. And so people kept going, right, people,
and nowadays, what's like, what's the record lowest temperature we
can get to? Yeah, so people work really hard on
this now and the current record is much better than
like the Nobel Prize winning record at one point five
(24:25):
degrees kelvin. Right now we're at a hundred pico Kelvin's
Pico Kelvin's that's like one with nine zeros in front
of it or behind it. Yeah. Yeah, it's a zero
point zero zor zero zero or zero zero zero zero
one kelvin. Wow. So we've been able to cool something
down that cold. Yeah, well, I mean not me and
(24:48):
not you. Some people out there working really hard and
it's the collective we a is in the part of
humanity that I'm proud to call myself a part of. Yeah.
So that's the current record, and you know, the is
fascinating theoretically, but it's also it's hard to do. You know,
it's it's hard to accomplish this. As we were saying before,
Like you get something super duper cold, you need clever tricks.
(25:10):
Do they use something kind of special trick there? Yeah,
they do this thing which is really fascinating. It sounds
um counterintuitive. They use laser cooling like a cold ray. No, No,
it's a hot ray, just like normal, right, it's not
like a cold laser. That would be awesome. And in
the comic book version of US, I definitely want eyeballs
that shoot out cold lasers that can freeze things. There's
(25:30):
a Batman villain called Mr. Freeze. Yeah, precisely. But okay,
but this is not This isn't like a regular you know,
zapping laser, and somehow that cools things. And the way
it makes things cold is not by touching them and
taking away their heat. It's by selecting the hot stuff
and pushing it out of the way. So imagine you
(25:51):
have a big blob of gas. Not every atom in
that blob of gas is moving at the same speed.
That's a distribution. Some are moving after some removing colder.
If you could just select the cold ones, then the
average temperature would go down. Oh, I see, but you
can actually aim this laser or how does that work?
Or like the lasers some somehow only picks out the
(26:13):
fast moving atoms. Yeah, it's pretty complicated, but essentially the
idea is to get the fast moving atoms in the
path of the laser and so they didn't knocks them
out of the way. And you use a laser because
it's you can't just like go in there and flick
out individual atoms with a mechanical object. The laser is
the best way to interact with an individual atom. You
can just like blow on it. They tried that six
(26:34):
years later that guy still hadn't graduated. No Nobel prize
for no PhD even No. So that's the idea instead
of trying to cool down the whole sample, right, which
is what you do when you put your ice cream
in the freezer, instead they just pick out the cold bits.
It's like if I gave you a bowl of ice
cream and you're like, hey, it's kind of melted, and
I just sort of scooped out the hot bits and
(26:55):
left you with the colder bits of ice cream. You know,
that's not really cooling down your ice cream, but the
temperature of the ice cream you're left with is colder.
And so that's the current record right now, is that
the cold is that humans have been able to cool
something down is a hundred pico kelvin. Yeah, and that's
colder than outer space. You know, the average temperature out
there in space is like two point seven three degrees kelvin,
(27:18):
which sounds kind of hot in comparison. Yeah a minute
ago that sounded chili, right, but compared to a hundred
peeko kelvin's it's like bust out your swimsuit. Um. And
that's the temperature average temperature out there in space there's
some spots out there in space where lots of gases
have been like blowing out of a star, and that
expansion cools it down to maybe one degree kelvin. But
(27:39):
the coldest natural thing, we think is one degree kelvin
and the current record is a hundred peco kelvins. But
humans are not finished. You think we can go further
colder than Yeah, there's a there's an instrument right now
on the International Space Station. That's where they're doing this experiment.
And it's like you've got to be surrounded by m
(28:00):
D space just to even have a chance to do this.
And it's called the Cold Atom Lab, and their goals
to get down to one pico calvin down from a
hundred which is the current record. Maybe helped me paint
a picture here what's going on at that temperature like
or the atoms? Not very much? All right, that's that's about.
It's like the conversation at your average physics party, you know,
(28:21):
just like nobody's talking, everybody just sitting there, everyone's just
thinking about absolute zero. Now, there is some wiggling. If
you were to zoom down microscopically and look at these things,
there would be some energy. There's some motion of these particles,
like like each atom is maybe not moving across the room,
but they are sort of wiggling and vibrating. And these
(28:42):
are all crystals, right, so you imagine they have bonds
with each other. They're not totally separate atoms. Imagine like
a lattice and you have these atoms with these bonds
holding them in place, and then occasionally you get like
a little wiggle, a little bit of sound goes through
the material. Hey, that's a cool connection actually between temperature
and sound. Right. Sound probably does have a temperature because
(29:02):
it's the wiggling and motion of these of the material.
I never thought about that. Man, I'm gonna need another
shot just to consider that question, Daniel. When you get
down to those temperatures, things form into a crystal, because
what else are they going to do. Can you take
a gas down to that cold of a temperature or
does it have to form into a solid by that?
(29:23):
I think it has to form into a solid idea.
And I'm not a chemist, So maybe somebody out there
who knows more chemistry than I do knows whether or
not you could keep something a gas and still make
it really cold. I think it would have to be
super duper dilute, right, But essentially, you know, these molecules
have no vibrational energy, no rotational energy anymore, and no
translational energy. They're not moving, so they're just all sitting
(29:46):
in place. Whether or not it's a crystal or a gas,
I guess just depends on how tightly you're packing them.
But effectively this becomes how you define a gas or
a solid, right, yeah, and probably an absolute zero. You know,
it's one of those places where the phases are not
well to find, you know, how the chemistry they have
these like triple points where something is like, what is
(30:06):
it exactly if you're right at the triple point? Absolute
zero is probably like that. But you know, the fascinating
question is like how close absolute zero could you experimentally get,
Like is it possible to make a material with exactly
zero motion? All right, well, let's get into that, whether
it's even possible to reach absolute zero. And I think
for me, the more the interesting question is if there
(30:28):
are places in the universe that are absolute zero. So
let's get into that. But first let's take another break.
All right, Daniel, can we get there? Can we get
(30:49):
to absolute zero? Without drinking absolute vodka. I think it is.
They're totally not sponsored by liquor company um. But yeah,
can we get too absolutely Is it even possible or
like many of the people you interviewed on the street,
isn't only theoretical that you can get to absolute zero?
(31:10):
I think unfortunately, there is no amount of you can
drink to get us down to absolute zero. I think
theoretically it's impossible. It's impossible. Yeah, it's just not possible.
I think in the sort of the classical theory that
the folks who were first coming up with thermodynamics thought about,
you know, they're thinking about particles is a lot of
tiny little balls, and so you can talk about their
(31:31):
motion and their location in that context. It is possible.
But we know better now. We know that when you
get down to tiny particles, there are different rules that apply.
These particles don't have classical paths, they don't move in
a way that makes sense to us. Their quantum mechanical
Maybe even the idea of energy at that point gets fuzzy, right,
like the idea of kinetic energy, whether there's something's moving
(31:53):
or not. At the quantum level, it's sort of like undefined, right, yeah, well,
we'll dig into that in a whole separate episode of energy.
I gotta say, if several folks, like maybe dozens of
folks have written in asking us to do a podcast
episode about energy and what does it mean? And how
do you transfer one form to the other and quantum
mechanically doesn't make any sense. So we'll dig into that
a whole separate episode when we get the energy to
(32:14):
do it will after we're done drinking that bottle of vodka.
But the problem is that as you get really really cold,
you come down to this zero point energy. Right. Quantum
mechanics says that there are fluctuations everywhere, even in empty space.
There's a small amount of energy, and that energy is
constantly fluctuating. You have these quantum fields that are going
(32:35):
up and down, so you have particles being created, and
so it's impossible to get down to zero energy because
there's always some energy even in empty space. But is
it fluctuations or is it just uncertainty? Do you know?
Do you know what I mean? Like it's or like
randomness or is there even a difference? Well, there's both.
There's you know, we think that the mean energy of
(32:55):
empty space is not zero, that there is energy stored
in empty space, and so you just can get rid
of this is just a property of space itself to
have energy. Not even nothingness is absolute zero, yeah, because
there is no such thing as nothingness. You can't have
space without nothing. That's the property of space is that
it has quantum fields. And these quantum fields that we
talked about the Higgs Boson episode don't settle at zero.
(33:17):
They settle it's some energy above zero. Space is something,
space is something. So there so there's no nothingness. Actually yeah, well,
and that's a whole other concept. You know, how do
you get something from nothing? And what is nothingness? Or
maybe maybe it's fair to say space without anything in
it still has energy. Space can't have nothing because it
always have quantum fields which have energy. Yeah, there's no nothing, Yeah,
(33:40):
there's no nothing. That's the zero point energy concept. That's
like you can't get down to zero energy. But even
if somehow the universe, you know, even if we like
destroy the Higgs field and we got down to a
state or vacuum energy of zero, and we talked about
that in a separate episode, um, even still there would
be quantum mechanical problems because imagine what you do there.
You're taking a particle and you're setting its location, right,
(34:03):
has no motion, so you have to know its location,
and that means you also know it's momentum. But the
Heisenberg uncertainty principle says you have a minimum uncertainty in
the location and the motion. But when now we're talking
about a state where we know exactly the location and
the motion, and so that seems like it would violate
the uncertainty principle. Well, maybe that just means that there's
no like, the absolute coldness of the universe is not
(34:26):
zero point zero zero zero zero zero, But could there
still be like a minimum temperature of the universe, like
a point oh you know one pico pico, pico Keilen
or something like that. Oh, that's fascinating. You're saying the
minimum might not be zero, but there could be a
zero or could you or pretty much zero? I want
to hear that announcement scientists announce the achievement of pretty
(34:50):
much zero. We did it, We got pretty much nothing. No,
that's a really interesting question. Can you ask them topically
a pro absolutely zero getting closer and closer forever, or
is there a minimum non zero temperature. I think because
of the zero point energy of space, there must be
a minimum temperature. But if you somehow collapsed the Higgs
(35:13):
field and got rid of that minimum energy, then I
think you could ask some topically approach zero forever. You're saying,
unless the universe destroys itself, there is a limit. And
I'm not encouraging anybody to destroy the universe just to
win that Nobel prize, just to ask for Horace question,
We're going to destroy the universe. That is physicists being
(35:34):
drunk with power. Okay, So then, uh so there might
be sort of a minimum and you're saying, it's really
difficult to get there because space itself doesn't get to zero.
So that does that mean that nowhere in the universe
do we get that cold or like there's nowhere in
the universe that's actually zero. That's right. We think that
there is nowhere in the universe it's actually zero, and
(35:55):
absent physics labs here on Earth and on the space station,
we think the coldest thing in the universe is a
out just one kelvin out there in you know, the
heart of a frozen planet in the middle of nowhere.
It's still about one kelvin. Yeah, most of the stuff
out there is about two point seven degrees kelvin. If
you really work hard, you might be able to find
(36:15):
something at one degree kelvin. But here on Earth we
have stuff that's like a hundred Pego Calvin's going down
to one Pico Calvin. We hope. Wow. So the coldest
place in the entire universe might be here on Earth
in somebody's lab, depending of course, on whether there are aliens.
So basically we're in a race with alien physicists to
(36:37):
get the coldest place on Earth to see who has
the who's the coolest species in the universe. You knew
I was going to have to bring it back to aliens. Eventually.
Every topic has to touch on aliens, right, Yeah, there
could be aliens out there who have a lab because
they would have to do this on purpose, right, they
have a lab that maybe goes down to even colder
(36:59):
than us at a hundred people Calevin. Yeah, there could
be alien civilizations out there that have been doing physics
for a billion years, and you know, to them, like
a hundred Pekokelevins is laughable, man, That's like a kindergarten
science fair project. For them. Really, they could be way
way down further in the cold spectrum. Wow, But we
won't know until those aliens come and visit. All right,
(37:21):
But as far as we know, barring super advance cool aliens,
the coldest place in the universe is here, probably in
in the United States, or in the lab in Europe
or something. Right, Yeah, and very soon the coldest place
in the universe, we think, will be on the International
Space Station at the Cold Atom Lab. All right, Well,
I think we answered the question pretty well. Where is
(37:43):
the coldest place in the universe and whether we could
maybe get even colder might not be possible unless we
destroy the universe, it seems. But absolute zero is a
fascinating topic theoretically, and it's a fascinating goal. We keep
pushing more and more, and as we do so, we
learn more and more about cooling technology and how to
achieve that, and and how things operate into very extremes
(38:07):
of the universe, which is where we hope to reveal
some new secrets about how the universe works. So the
next time you have a scoop of ice cream, think
think about how how cold it is and how cold
you could get it if you went to your local
physics lab and recruited some physicist to give you a
better ice cream. Thanks for tuning in for this tasty topic.
See you next time. Before you still have a question
(38:36):
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
on Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or email us at Feedback at Daniel and
Jorge dot com. Thanks for listening and remember that Daniel
and Jorge Explain the Universe is a production of I
Heart Radio from more podcast from my Heart Radio. Visit
(38:59):
the I Heart Radio, a Apple Podcasts, or wherever you
listen to your favorite shows. Yeah h
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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