Why does our Universe have a Cold Spot?

Daniel and Jorge explain why scientists are puzzling over a massive cold spot in the sky.

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Episode Transcript

Speaker 1 (00:08):
Hey, Jorgey, does your family cook many things in the
microwave oven? We used it to reheat stuff, but we
don't do a lot of cooking in there, so you're
not a big fan of the microwave. You're not making
Thanksgiving turkeys in there, We'll only you like turkey hot
spots and cold spots. Well, what if the hot spots
and cold spots were actually the best part? What it's

(00:29):
definitely the worst parts of cooking in the microwave. What
if I told you that sometimes the hot spots and
cold spots can hold secrets of the universe. I think
I'd still read to live in a evenly heated universe.

(00:56):
Hi am more Hammad, cartoonists and the creator of PhD comics. Hi,
I'm Daniel. I'm a particle physicist, and I actually have
a fancy microwave oven that doesn't generate hotspots and cold spots.
That's right, you have an AI powered microwave, right, I do.
It was given to me by one of our awesome
listeners who heard our episode about how microwave ovens worked,

(01:16):
and he actually developed a fancy new kind of microwave
that has a thermal camera that watches your food and
decides where to target the radiation. It's pretty awesome. Wow,
has it taken over your life now? Isn't you know?
Your new microwave overlord. The kids are worried that it's
going to tell them what to eat and win. Just
don't connect. Get to the internet, Daniel, it's probably listening

(01:39):
to podcast right now. Say something nice about it. It's
gonna scall to you in your next meal. But welcome
to our podcast. Daniel and Jorge explained the Universe State
production of Our Heart Radio, in which we think about
everything out there in the universe, the mysterious thoughts of
microwave ovens, to the interiors of black holes, to the craziest,
tiniest things happening in the microscopic level. We think about

(02:01):
the huge things in the universe and try to understand
the grand scale of the cosmos, and we think about
the tiniest little particles that make up me and you
and hamsters and microwave dinners. Yeah, because physics is all
around us. It's in our fingertips, it's in the food
we eat and how we heat it up, and it's
also out there on the vast reaches of space. It's

(02:23):
physics is everywhere, Physics is everywhere, and it's doing a
pretty good job at revealing to us the nature of reality,
letting us like pull back a layer and see what's
really going on. Sometimes the answer is staring you in
the face, like learning that the Earth goes around the
Sun rather than the other way around. But sometimes it
takes some real sleuthing to pull the clues out of

(02:44):
the cosmos. Yeah, because the universe sort of screaming at
us all the time, right with data and information. It's
sort of revealing itself to us all around us all
the time. But it's sort of recognizing what's happening. That's
the hard part. Yes, sometimes it's obvious, and sometimes you
have to look for those subtle little clues because it
doesn't seem like the universe was designed to be easy

(03:06):
to figure out. After all, has taken us some thousands
of years, and sometimes we learned that there is evidence
all around us that we didn't even know existed that
tells us a crazy story about the origins of the universe. Daniel,
do you feel like physicists are sometimes like reality detectives
that you're trying to reconstruct what happened in the universe
and what's going on and who's guilty? Yeah, exactly. Sometimes

(03:29):
in our best moments, I feel like we're Sherlock Holmes,
you know how he's famous for like figuring out exactly
what happened based on the kind of ash sprinkled on
somebody's shoe, you know, or a particular form of dirt,
or a kind of thread used by only one factory
in northern England or something. It's cases like that when
we have to figure out what happened in the universe
based on really subtle little clues that I feel like

(03:52):
physics is really doing its job. Do you keep like
a magnifying glass at your desk just in case a
clue revealed itself right next to you. I don't know.
If the universe is a murder mystery. Who's getting murdered.
Probably us? Well, technically we all get murdered by the universe.
Eventually mystery solved. There you go. We know what the
culprit is. It was the universe, with the universe in

(04:13):
the universe, with the entropy in the gamma, decay of
our courts. That's right exactly. But it's fun, right, It's
a fun mystery. Sometimes you learn something boring. You go
out there and you study, and you learn exactly what
you expected. But sometimes you go out there and you
find something exciting, something interesting, something surprising, something puzzling that
tells you there's still more to learn about this incredible cosmos. Yeah,

(04:36):
and you know, one of the biggest mysteries that you
I feel like you physicists are trying to figure out
is basically the whole universe, like where it came from,
how did it come to be, what's it made out of?
Why is it the way it is right now? Yeah, precisely,
we want to know, like how does it look? Is
it look the same way here as it does somewhere else,
How far does it go on? And where did it
all come from? It's basically the biggest mystery in human history.

(04:59):
You know, I'd put it up there is one of
the biggest questions in science and one of the biggest
questions in like, you know, human existence. Where did this
all come from? And amazingly, we actually like have some answers,
We have beginnings of ideas for how to unravel this
because we've detected clues from the very early universe. Yeah,
and so one thing that's interesting about the universe. Is

(05:21):
that there's a picture of it. I mean not just
all around us we can see the universe, but we
have a picture of it from the early beginnings of
the universe, like a baby picture of the universe. Yeah,
it's incredible. If you sniff around through all the light
that's flying around, through all the photons that are banging
into each other, you can find a certain set of
photons that were generated when the universe was very very young.

(05:42):
Put that together, and you're absolutely right. You get a
picture of the early universe. And that picture is so
rich in information that tells us about how the universe
was formed, what it looked like, how much dark energy
there is, how much dark matter there is. It's really
a treasure trove of information about how our universe came
to be and what's going to happen to it. Yeah,

(06:02):
and apparently something that sticks out about that picture of
the universe is that it's not perfectly even. It has
hot spots and cold spots. Yeah, it has wiggles, just
like our universe has hot spots and cold spots. Right
Like the Sun, for example, is hotter than a lot
of empty space. Just like that, we can backtrack to
the early universe, and we see that there are wiggles.

(06:23):
They're also there are little hot spots and little cold spots,
but they're much more subtle in the very early universe
that we've done a lot of detailed analyzes of these
hot spots and cold spots to see like what do
they mean about the distribution of matter and how did
that lead to the big structures that we see today?
And so to be on the podcast, we'll be tackling
the question does the universe have a cold spot or

(06:51):
a cold sword? Daniel? And can we put windeck kind it?
Do you want to take care of the universe since
you already figured out it's going to murder you. Well,
it also gave birth to me, so you know it's
a complicated relationship. So it's a zero moral balance overall. Well,
it's positive for me for now. I don't know if

(07:12):
the universe sees me as a net positive, but I
definitely see myself as a net positive for me. I
think you're definitely a net positive for the universe or head, Oh,
thank you at least for this podcast. You're definitely a
hot spot for the universe. Yes, I definitely have a
spot for the universe in my heart. But this cosmic
microwave background radiation, this light we study from the very

(07:34):
early universe does have hot spots and cold spots, and
in particular there's one spot that's extra big and extra cold. Yeah,
it's a big mystery in physics. And so we were wondering,
as usual, if people out there knew that the universe
had a cold spot, like a big glaring cold spot,
And so Daniel went out there and asked people on
the internet if they knew if the universe has a

(07:56):
cold spot. So thanks to everybody who participated. If you
would like to basils the speculate on difficult topics in physics,
please write to me two questions at Daniel and Jorge
dot com. So think about it for a second. Have
you heard of the universe having a cold spot? And
what would you answer? Here's what people had to say.
Sounds like a medical thing. What does the CNB? I

(08:17):
think it probably means central massive blackhole, maybe the black
hole the center of the galaxy. That's just a guess,
or it's super massive, but this the c is in
place of the that wouldn't be too off from health.
Physicists like do their acronyms. I think it's a trick question.
They don't think it has a call, but I think

(08:38):
it's all called. I actually was reading about that a
little while ago. So the CNB being cosmic microwave background radiation,
that map that was drawn up showed a dark spot
in it that would potentially denote a void of some kind,
being just a massive space where galaxies are all surrounding it,

(09:00):
but there's nothing in it, a big void. So that's
what I think it would be. But the other alternative
theory to it was that it could potentially be a
signal of another universe, so that would be where a
parallel universe would exist. But the science behind that is
completely lost on me, and it goes straight over my
head thinking of expansion and thinking of this video I

(09:24):
saw of um legos getting smashed by a hammer from
high up. There's one spot where the legos clumped together
and that was close to the point of impact. And
I you know, back to quantum fluctuations. Dark matters a
big part of the creation universe. It's fingerprints are there um.

(09:46):
So this is a part that was close to the
impact that cooled down first. Well, this cold spots might
be caused by like being really far away from where
the Bagman happened, so it has had a lot of
time to cool that. I remember hearing about it in
the movies. A lot I don't remember, but I think
it's something to do with like either time travel or

(10:09):
bending space. All right, Well, first of all, I see
you made the error of asking people with an acronym.
He asked him why does the CMB have a could spot?
And most people were like, what, what does the CMB
central massive black hole cool mega bears? Sometimes it's hard
for me to get out of my physics head and
forget that CMB, you know, might have any other meaning.

(10:32):
It's one of these acronyms we use in physics all
the time, so I forgot that it might not be
something people are familiar with. So yeah, we got some
fun interpretations. Shockingly, not everyone knows what CMB means, although
I don't know if you're watching one division they referenced
the CMB. They do reference the CMB, but they call
it the c m b R. It's like, no afterphysicists

(10:53):
would call it the c m b R because that
would be the accurate exactly, And we know how these
names work right. You call it cosmic microwave background radiation,
but the acronym is CMB right because it makes because
it makes no sense, and therefore it's a name for
astrophysics exactly. See, you're just trying to exclude more people
from knowing what you're talking about. It just shows that

(11:14):
they didn't really consult an astrophysicist when they wrote that episode,
or they did and they ignored it to correct you. Yeah,
they're like, that doesn't make any sense. Come on, this
is a Marvel movie television show. We need to make sense.
That's a new standard for Marvel apparently. Yeah, well you
know that they figured that out in The Quantum Realm.

(11:35):
I just did a whole episode on the physics of
ant Man with a fun new podcast. It's a podcast
called The Marvels of Science with Dave Reinersman. So check
it out fans of Marvel and science. I actually gave
it pretty positive reviews. You know, the physics oftment the
quantum physics is pretty well done. Nice. But anyways, the
cosmic microwave background radiation has apparently a cult spot and

(11:59):
it tells us something about the universe, So I guess
maybe step us through Daniel. First of all, for those
of us who don't know what the CNB is, what
is the cosmic microwave background radiation? With an R Oh,
you mean the CMB r Oh, Yeah, that's something totally different. No,
the CNB, the cosmic microwave background. These are just photons
right there, light like anything else, but they're light of

(12:20):
a different frequency. And these photons are particularly interesting because
they're super duper old, so they're like a picture of
the very early universe. We don't know exactly what happened
in the very beginning of the universe, but we suspected that,
like a few hundred thousand years after the universe was born,
it was still really hot. It was a nasty, wet plasma,

(12:41):
super duper burning. It hot and life most plasmas, it
was opaque, like the sun is a plasma, right, it's
a glowing ball of gas and you can't see through it,
and the light that's generated inside of it gets reabsorbed
by the stuff in it. But at some point, because
the universe was cooling and expanding, that is, mc cooled
to the point where it couldn't absorb its own light anymore.

(13:03):
It is sometimes called the surface of last scattering, There
was this moment when it was giving off light and
then all of a sudden it couldn't absorb it. So
that light that was generated by the plasma just before
it cooled is still flying around. That's the cosmic microwave background. Yeah,
it's like that moment when the universe sort of crystallized
and weighing and it became transparent. That light is still

(13:25):
flying around, but is it's still like bouncing around or
or like is the cosmic microwave radiation that we get
like the actual original photons that were started flying at
the Big Bang, they are the original photons, but it
does bounce around like it gets absorbed, it interacts with stuff,
So not every single photon that was generated back then
is still around. They can't interact with other things and

(13:47):
get absorbed, but there's plenty of them left over for
us to see. But when we see one, we typically
see it before it's interacted with anything else, And so
will exactly happened that made the universe transparent, like everything
became crystallized or glass or what does that mean? Well,
the key thing to understand is that the universe was cooling,
so you have a hot plasma, which is basically like atoms,

(14:09):
but the electrons and the nuclei are separated so much
energy that the electrons can't be trapped by the nuclei.
But then as it cools, the electrons slow down and
they get captured by the nuclei. And so this goes
from ionic it's like charge, and it's absorbing and emitting
a lot of radiation to neutral and all of a sudden,
those photons can just fly through a sea of neutral

(14:31):
atoms without getting absorbed or interacted with. Before it was
like a soup and it would get pulled in all
kinds of directions. But now everyone is just more chill,
and so photons can just fly through, yeah, exactly, and
neutral atoms they can absorb photons and they can give
off photons, but only a certain wavelengths because of the
electron energy levels. You know, free electrons can absorb and

(14:52):
emit photons of any wavelength. That's why like plasma glows
and many more frequencies than like hydrogen gas. For example,
So when the universe cooled from a plasma to just
like clouds of hydrogen gas, that gas was mostly transparent
to the light that had just been created and another
thing for people to keep in their minds. When you
think about the CMB plasma, you might be imagining like

(15:12):
a blob of gas that's burning and giving off light
like our sun. And then you think, well, that light
is now, you know, flying fourteen billion years away, must
be in a big sphere. How are we seeing it now?
How is it just like coming to us now. The
way to think about it, though, is that it was
everywhere and this plasma field the whole universe so simultaneously
making photons in every direction. The ones that we are

(15:34):
seeing now came from plasma that was really really far
away a long time ago, and it's just reaching us.
But the photons we see in one direction are not
from the same bit of plasma as the photons we
see in another direction. Those are two totally separate bits
of plasma whose photons are both reaching Earth right now,
right because this microrave radiation is coming at us from

(15:56):
all around us, right Like if you point like your
small radio at the sky, you'll sort of pick up
this this noise right. That's right, every direction of the
sky you see this radiation because it's coming from everywhere
in the universe and everywhere you look, you see it
from a different location. Just like if you look in
one direction you see a star, you're seeing light from
the star really far away. You look in another direction

(16:18):
and you're looking at a star. You're seeing light from
the star really far away in the other direction. Both
of those have had photons flying through space for billions
of years just arriving at Earth. So you're looking at
very different parts of the universe when you look out
at different parts of the sky. And that's also true
for the cosmic microwave background radiation, Like if you look left,

(16:39):
you'll be looking at a different part of the early universe,
and if you look right. But I guess the question
is if I look in one particular direction and I
keep looking there, am I getting the photons from the
same spot of the universe or is it kind of
like an observable universe thing where you know, I'm looking
at photons from the early universe further and further out
the longer I look. Yeah, you're looking for further and

(17:00):
further out the longer you look. So the CMB that
we see will change as time goes on, because we're
essentially looking at it from a larger and larger sphere
I see. So we're sort of getting a three D
picture almost the universe, yes, exactly, because it's not a
continuous source in time the way a star is. Right,
when you look at a star, you're seeing the star
where it is, and it's continuing to beam photons at

(17:22):
you every second, and so as you look at it,
you see new photons. But the CMB was generated in
one moment. It's one moment in time, and so when
you look out at the same b right now, you're
seeing like a shell around the Earth, and then ten
seconds later you see the c MB from a larger shell,
ten light seconds larger than the previous one. And it's

(17:42):
a wiggling in time, like is it sort of changing
in volume as well as in direction. There are some wiggles.
I mean, it's pretty faint and we've only been observing
it for a few years, so we don't expect to
see like variations on that kind of time scale. Al right,
So that microwave radiation tells is it's like a picture
of that early universe when it sort of crystallized and

(18:03):
cool down, and the mysteries that are hot and cold
spots on it, right, Like if you look at the
temperature of that radiation, it's not even so here physicists
are sort of playing a little game. They're saying, those
photons themselves don't have a temperature. We're talking about the
heat of the thing that made the photons. And there's
this concept in physics, this connection between the frequency of

(18:24):
light you generate and the temperature you have. And it's
pretty simple when you think about it. Hot things tend
to glow, and as they get hotter, they glow in
higher frequencies, like everything around you is actually glowing in
very low frequencies. You're giving off infrared radiation right now.
If you heat it up your body really really hot,
not recommended the thousands of degrees, you would glow red,

(18:45):
or you would glow blue, or you would glow white.
That's why the Sun, for example, glows more than the
Earth because it's much much hotter. So when we talk
about the temperature of the CMB, we really mean the
temperature of a thing that would give off light at
that frequency. So when you tell your spouse that they
have a special glow about them, really you're just saying
that they glow like everything else exactly. But if they're

(19:08):
extra hot, then maybe they are radioactive, or maybe they're
just glowing red and angry at you or something. And
so when we look at like the temperature of the
CNB really means the wavelength of the CNB, and if
something is hotter, then it's a little bit more blue shifted.
If something is colder, it's a little bit more red shifted. Right,

(19:28):
But it tells you, basically, at the end of the day,
how hot or how cold that early universe was in
different directions. Yeah, it does. It can't tell you that now.
The temperature that we measure is sort of a crazy,
crazy low temperature. It's like two point seven degrees kelvin,
which is like just above absolute zero. Right, it's really
really cold. And that seems confusing because we're saying that

(19:49):
the universe was really really hot, right it was like
a hot burning plasma. Well it was. It was like
three thousand degrees kelvin when this light was made. But
the light has gotten red shift over time because the
universe is expanding and that stretches out that light lengthens
its wavelength and lowers its effective temperature. Right, all right, Well,
so then we're noticing that it has cold spots and

(20:11):
temperature that radiation, and so there are hot and cold spots.
So let's talk about what that big cold spot is
and what it could mean. But first let's take a
quick break, all right, Daniel. We're trying to cure the

(20:35):
universe of its cold sore. The universe is going on
a date and it wants to look hot. Yeah, or
to figure out if we live in a hot spot.
It's pretty happening around here and on Earth. But who knows,
Maybe we're we're in the cold spot, or maybe our
whole universe is not that hot out there in the multiverse.
Maybe there are much hotter universes. Oh man, See now

(20:56):
you're just playing that game. You're saying that the light
is greener on the other side of the multiverse. I'm
just saying, you know, maybe our universe should get on
universe tinder and consider its options. It might choose a
different you here hoping for or worried about. No, I'm
just saying, you know, hey, get some quantum entanglement going on,
we can get some information from another universe. Boy, Now
you sound like a Marvel movie. Dan. All right, so

(21:19):
there's a cosmic microwave background radiation it's coming at us
from all directions, and it's telling us about the early universe,
and there are cold spots in it. So tell me
about these cold spots. And apparently there's one big cold spot. Yeah.
So when they first found this radiation, it was really
exciting because it was essentially proof that the universe had
once been plasma. That was really cool. And they looked

(21:40):
at it and it was pretty smooth at first, like
it's basically the same temperature everywhere. But then they made
better and better measurements of it and they found these wiggles.
They found these hot spots and these cold spots, and
these are actually really really small wiggles, like we're talking
about twenty microkelvin's or so, like one factor in a
hundred thousand. So it's almost exactly smooth, but there are

(22:03):
these little variations in temperature, kind of like a texture
almost to the light. Yeah, kind of like a texture.
And you might think, oh, well, that's just nothing, but
there are statistically significant, like we've measured enough of these
photons to tell that it's a real effect. It's not
just like noise in the data. It's fascinating because those
little wiggles tell us about wiggles in the early universe,

(22:23):
which revel really interesting and important facts about the nature
of the universe itself. And they're pretty consistent, I imagine, right,
Like if you take a picture of the microwave cosmic
background now and I take another picture of it later,
you'll see the same wiggles, Like the wiggles won't go away. Yeah, exactly.
These come from wiggles in the original plasma, and so
we're seeing those exactly, they're still there. Yeah. Like if

(22:45):
you point your antenna at one spot in the sky,
you'll get consistently a little cooler measurement there, right, or
a hotter exactly. And you need a really really refined
measurement in order to even see this, because it's like
one part in a hundred thousand. You need a very
very find instrument to capture that, right. And So what
causes these variations in the temperature of the universe, Like

(23:06):
why is it colder or hotter in some places than others? Yeah,
it's fascinating. There are two main reasons. One is that
there just were hot spots and cold spots like in
the original plasma. Quantum fluctuations. You know, you might imagine
the universe starting sort of like smoothly, like homogeneously, like
every place in the universe when he was born. However

(23:27):
that happened was the same. So then how do you
go from that to like having a star here and
not having a star there. Well, that has to begin somewhere,
and we think that quantum fluctuations in the very very
early original universe, well before this plasma then got like
blown up by cosmic inflation, this process where you take

(23:47):
the universe and you expanded by like ten to the
thirty intend of the minus thirty seconds. So you get
these random quantum wiggles in the very early universe which
then get blown up into macroscopic wiggles in a real universe,
which lead to like little hot spots and little cold
spots in this original plasma. Mm hmmm. That's because the
early universe was so small, right, Like, it was so

(24:09):
small and so compact, and everything was crunched together so
much that the quantum uncertainty of this quirk or this
particle made a big difference. It's hard to talk about
the original universe as small, because I think it was
always infinite, and so we had an infinite universe which
then got like expanded massively to an infinite universe, and

(24:30):
you know, it's harder to think about it as bigger
or smaller. Some like subtle mathematics, they're like, are there
more numbers between zero and one than they're between zero
and ten? There aren't. Actually, there's no one to one
mapping between those two things. So the universe is like
technically the same size even though it expanded. That's a
whole other mind bending discussion. But you're exactly right, little

(24:52):
like quirk to quirk fluctuations, little quantum randomness. Right, The
only way something can happen differently in one spot than
in another if of the same initial conditions is through
quantum mechanics. It's the only source of actual randomness. Usually
we don't notice that it doesn't affect anything, But if
all of a sudden, random quantum fluctuations get blown up
to the macroscopic size by inflation, then it does matter

(25:14):
that it can have a real impact on the shape
of the universe. Right. It's sort of like when you
zoom in on a picture on your phone or a
computer screen, Like you blow it up, but you can
see all the imperfections in it, right, And then we
can actually do some really amazing physics. We can model
that plasma. We can say, well, that plasma was probably
some percentage dark matter and some percentage quirks, and some
percentage light, and we understand how those things like attract

(25:38):
each other and bounce off each other. So people have
done incredibly detailed studies of like the acoustic oscillations of
that plasma, understanding how those things are bouncing against each other,
and measuring from that plasma how much dark matter there
was in the universe, because dark matter and quarks interact
very differently, so they change the shape of those oscillations

(26:00):
in that original plasma. Right. That's one of the ways
we know that dark matter exists in that it exists
at a certain percentage of the universe is because it
cosmic microrade background radiation tells you how much dark matter
there was and is in the universe exactly. And it's
those hot spots and cold spots that tell you, like,
if there was more dark matter, then you would have
different kinds of wiggles and oscillations in that original plasma,

(26:22):
and then you would see a different pattern of hot
spots and cold spots in the CNB today. So that's
one source of the hot spots and cold spots, like
the original primordial plasma itself was hotter or colder. But
then there's another super fascinating, really interesting way that this
light can get hotter and colder. What is it? Well,
it turns out that as this light flies through the

(26:42):
universe to us, it basically measures how much matter is
along the way. If that light passes through really dense
regions of the sky, it picks up some energy and
it gets bluer. If the light passes through like really
really empty regions of the sky, then it loses some
of its energy as it leaves like the obviously more
dense region, and it gets redder. So some of the

(27:03):
red and blue shifts in the CNB, the hot and
cold spots come from differences and how much stuff there
is now between us and where the lights started. So
sort of like measuring the density of the universe along
the line right, interesting, So can you tell the difference
like how much a variation in the radiation is due

(27:23):
to its original fluctuations or it's present fluctuations. Can you
tell the difference? Yeah, we can. We think that make
very different sort of scale effects like these variations due
to structure and density make very large scale effects that
have like effects of the size of like ten degrees
on the sky, whereas the other ones that indicate like
you know, the very on acoustic ostillations and the fraction

(27:46):
of dark matter make much smaller effects. And so it's
fascinating because you can sort of like pull apart this information.
You can learn very different things about the universe, what's
going on today, the density of stuff, and what happened
the very early universe by studying the hot spots and
cold spots at different scales. All right, Well, for the
most part, these variations in the cosmic microwave background are

(28:08):
sort of small, right, Like, if you look at a
picture of the cosmic microwave background radiation, it sort of
looks like almost television noise, right for the most part, Yeah, exactly,
it's pretty smooth. Like you look around the CMB and
you see typically variations of about you know, twenty microkelvin's,
and they tend to be like, you know, about one
angular degree. Sometimes there are larger effects because like we're

(28:30):
moving through the rest frame of this radiation, et cetera.
But typically we see like you know, twenty microkelvin's about
one angular degree, and that's about what you expect. You know,
you expect some variation, some hot or some cold, or
some a little cold or some a little hotter. But
we expected to follow like a pretty nice and tidy
statistical distribution. Yeah, like I was saying, it sort of
looks like television noise. But if you look in some spots, though,

(28:52):
you do see kind of bigger features in this noise, right,
almost like some ghostly features in your TV static. Yeah,
there's one spot has astrophysicists and cosmologists puzzling for like
more than a decade, and it's called the cold spot,
and it's a spot in the sky where this radiation
is surprisingly cold. It's much colder than it is anywhere else,

(29:14):
and it's a much bigger spot than you expect to see.
So this thing is like seventy or up to a
hundred and fifty microkelvin's colder than the average CNB temperature,
and it's like five angular degrees. So you can see
this thing with your eye, like, what, oh, not what
you like? If you see the picture of the costming
microwave background, Yeah, that's right. You can't see the CNB

(29:35):
with your eye, right, it's in microwave frequencies, though I
guess it does gently cook your food. But you can't
see it with your eye. But if you look at
a plot of this stuff you see this spot, you're like, oh,
there's an extra dark blue spot there where you might
not otherwise expect it. M M. Now is that a
lot of five angular degrees? How big in the sky
are we talking about? Like the size of the sun
as we will see it, or the moon or of

(29:58):
texas well, the moon is about half a degree in
the sky, and so yeah, this is a pretty big
effect I see. So like if you lived to look out,
you would see like something ten times larger than the moon.
And that's how big this could spot is, yeah, exactly.
And it's in the southern hemisphere. So you looked in
the direction of the constellation Irridanus, then that's the direction

(30:19):
from which this light is extra cold. All right, So
that there's a big cold spot in the sky, that
my may tell us that the universe had a big
cold spot when it was born. Maybe, So let's dig
into that and let's talk about what it could mean.
But first let's take another quick break, all right, the

(30:48):
early universe had a cold spot, Daniel, possibly at least
from what we can see right now. If we look
out into the sky at the cosmic microwave background radiation,
we see that there's one spot that is cold are
than the rest of the universe. So what's going on? Yeah,
it's a big cold spot. And you know, we can
never really definitively no, because there are a few possible

(31:09):
explanations and they range from like the total yawn fast
boring explanation to like the crazy, mind blowing revealing the
nature of reality kind of explanation. I mean, I guess
which one you're hoping for, Not the boring one. I'm
hoping for aliens. But there's no alien explanation for this one,
not yet. But we still got fifteen minutes on this podcast. Well,

(31:31):
we'll figure something out for you, or when we write
our pitch script to Marvel, will include aliens somehow. Oh yeah,
microwave guardians of the universe, Guardians of the micro universe.
All right, So what are these possible explanations for this
cold spot? Now? I know we see it out there
in the microwave radiation, but do we think that it's

(31:52):
like a hole through the universe or like a sphere
out there of coldness what we think it looks like.
Well there really there are two ethic explanations. One is
that like the light was generated itself from a colder
spot in the original plasma. And you know, we're talking
about quantum effects here, and quantumness is random, and sometimes

(32:13):
randomness gives you weird stuff. You know, if you flip
a coin ten times, you do have a chance, however small,
to get ten heads in a row. It can happen.
And so one possible explanation is that those original quantum
fluctuations in the early universe just happened to create a
spot with less density of stuff, a slightly colder spot
in the original plasma. Like maybe that that's just how

(32:36):
the universe rolled, you know, or like that's what they
got in their role playing character role when it determined
would look like it just happened to have a cold spot. Yeah,
it's possibility. That's one explanation. Yeah, it's sort of like
a non explanation. But you know, every time you have
random effects and you have a statistical distribution, you never
really know, and so this is pretty unlikely. We can

(32:58):
quantify how unlikely it is. We have a model for
what those quantum fluctuations should have looked like. And just
like you can calculate how likely is it to get
ten heads in a row when you flip a coin,
we can calculate how likely is it to see this
coldest spot this size in the sky. You know, it's
like a one in two hundred chants though it's like
right on the edge there where it seems kind of improbable,

(33:21):
but it's not impossible. You know, we only have this
one universe. If we had a bunch of different universes
and we have a bunch of different CMBs, we could ask,
how often do you see something like this? Is it
really wanting two hundred or is there something else going on? Right?
Like if you had two hundred universes, one of them
would probably have a cultpot just naturally exactly, yeah, And
so you never know, like, did we just get a

(33:42):
weird one? Do we have an odd universe in some way?
Or do we not have an understanding for how that
quantum random has happened and something else is going on?
We really just don't know. So the most boring vanilla
explanation is, you know, we just happen to get a
weird universe. The most boring explanation is just oh, well,
get what you get and you don't complain. And it's

(34:04):
also sort of boring because it's not really like much
to follow up on, like, well, it just is what
it is, like, you know, sometimes you get double zero
when you spind the wheel, and there's not much else
to say about it unless you can prove that it
is controlled by a different probability distribution than the one
we expected. But if it is just sort of like
a weird outlier, then hey, you know that happens, all right.
Well then what's the next more interesting explanation. Well, the

(34:26):
next more interesting explanation is that the CMB got cold
as it flew to us. Remember we talked about how
the light as it comes to us from where it
was originally generated is affected by how much stuff there
is in the universe, and so in that sense, looking
at this light is a way to probe how much
stuff there is between us and that original plasma. So

(34:48):
if there's a really big cold spot in the CMB,
it could mean that there's like a huge void of stuff.
There's like a huge blob of space between us and
that original plasma h that just like has nothing in it.
M M, I see, because like an empty void like
that would cool the MicroID background radiation. Right exactly as

(35:09):
the light enters the void, it loses some energy. It's
going to lose some energy because it's more like stuff
behind it. And you know, we expect there to be voids,
like we know that the structure of the universe is
you start from stars, which form galaxies. Those galaxies form clusters,
and those clusters themselves form these like walls and these
filaments and these huge sheets around bubbles around big voids

(35:31):
in which there is nothing, and those things are pretty big.
But those voids would not explain this gap like you
would need a super void, like a void the size
of five angular degrees basically right, Yeah, like a humongous
like multi galaxy empty space. Yeah, much bigger than multi galaxy.
We're talking about something that's like a thousand times the

(35:53):
volume of the voids. We see. This thing would have
to be like billions of light years across some rediculously
unusual spot in the universe that happens to just contain nothing. Yeah,
I guess the big question would be, then where did
this void come from, right, Because don't voids come from
those original quantum fluctuations too? They do come from that

(36:14):
exactly the way the universe gets its structure as you
have those fluctuations, which then build on themselves because anything
that has a little bit more density, that has a
little bit more gravity, and so it's tugging more stuff
in and then it gets denser and it's a runaway effect,
and so the matter sends to clump together where there
were original like over densities, and you tend to get
voids where there were under densities. But that doesn't explain

(36:37):
how you got that under density, right, sort of like
again the same question, how is it possible that we
look at and we see a bunch of voids of
a particular size, but then there's one super duper void.
How did that happen? Right? And it goes back to
the same question almost right, like was there a big
cold spot like that in the early plasma of the universe.
It's almost the same question, isn't it. Yeah, it's almost

(36:59):
the same question, but one would be even bigger. Right,
In order to create this sort of cold spot, you
need a really really massive void that would extend across
a much bigger region of the universe. Such a void
is like it's hard to gell with, Like our ideas
about dark matter and dark energy, you just don't get
this kind of thing. We've run lots of simulations of
universe is and you never see this kind of structure.

(37:22):
So this is maybe even more unlikely, but it would
be more awesome for that reason. I guess the less
likely it is, the more interesting it is scientifically to right, Yes, exactly,
we want to see something weird that we can't explain
with our current theories because that tells us how we
might be able to change our theories and learn something
new about the universe. We want to see our theories fail. Right.

(37:44):
Scientists are not out there like my theory will win out.
We're trying constantly to disprove our theories because that means
finding a clue to solving the murder mystery of the universe.
And so one thing people have done is like, well,
let's look directly for this void. I mean, if there
really is a huge gap in stuff out there, we
could literally see it. Right, this is something we can

(38:05):
see not just through the CMB, but by directly looking
to see are there a bunch of galaxies missing, right,
But we would have to be looking pretty far out, right,
We would have to be looking pretty far out, but
we can, right, we can look really far out into
the universe. This is something which would exist in the
universe between us and the edge of the observable universe.
Because remember the CNB comes from almost the edge of

(38:28):
the observable universe, and so it would have passed through
this super void. So we should be able to see it.
And how we've seen it. People looked and seen any
big empty spaces we have looked, And in two thousand
and fourteen, a study from University Hawaii actually did find
a super void, like a really massive void, and they
called it the largest individual structure identified by humanity, which

(38:52):
is sort of hilarious because, like I keep seeing that
in astronomy papers, people keep saying, this is the biggest
thing in the universe. No, now, this is the biggest
thing in the universe. It's like they're claim to fame. Yeah,
but it technically it's the largest empty space they found, right, Yeah, exactly.
It's like a bubble surrounded by galaxies and galaxy clusters
with nothing inside it. So they found a really big

(39:14):
super void roughly in the right direction, but it's not
actually big enough, and it's not sort of voidy enough,
like it needs to be like really empty of stuff
in order to explain this cold shift. And if you
take this super void and you think, well, what would
happen to photons passing through it, they don't actually get
chilled enough to explain the cold spot that we see

(39:34):
explains like twenty or thirty microkelvins of cooling, not the
full seventy to a hundred I see. So it's not
cool enough this super void, this super void is too hot,
not hot enough or cool enough sadly exactly, even though
it lives in Hawaii, exactly Hawaiian. So it doesn't really
match up like you'd love to see, like a massive

(39:56):
super void just in the same direction that explained. That
be a really sort of nice connection there, But this one,
though it's interesting, doesn't actually explain the data. The two
stories don't really fit together quite well enough. But that's
just only what we've seen. Like there could still be
a giant boyd, we just haven't seen it or been
able to make it out. Yeah, exactly. There's always more
stuff to look at in better telescopes and new ways

(40:17):
to analyze the data. But we have not found a
supervoid out there that explains this cold spot. All right,
So then what's the craziest idea we have about this
could spot? The craziest idea about this cold spot is
that maybe it comes from even earlier in the universe.
Maybe it comes from the very very birth of our universe.
People talk about how the universe was made, and one

(40:39):
possible explanation is that our universe is like a little bubble,
a bubble of some pre universe stuff that decayed into
normal matter. And here we are going way out into
like crazy, no basis speculation for how the universe might
have been formed, right, no data to support this. But
it's possible that the universe sort of turn into normal

(41:01):
matter from some sort of pre universe matter. They call
this like the Inflaton field. And you have to imagine
sort of like a meta universe filled with this stuff,
which then, like birth's individual universes, so like our entire
universe created in a little bubble inside this larger universe,
along with other little bubbles exactly along with other little bubbles.

(41:23):
Where do those bubbles get made? Well, it's quantum mechanical,
so it's random. And sometimes those bubbles might be really
close to each other and maybe bump up against each other,
and if they did that, they might leave a mark
on each other. You might get like evidence on your
bubble that you bounced against another bubble. And in some
of these theories, this effect this sort of like bruise

(41:45):
on a universe, which show up as a cold spot,
which would lead to a super void. Wait what you mean,
like the ideas that these universe are being created in
this froth of meta universe and sometimes the bubble bumping
to each other and that would create a cold spot.
When did it creates like I don't know, like a
dent maybe more a dent is basically a cold spot.

(42:08):
You know, it gets like suppressed, It gets like squeezed down,
and you would expect actually a cold spot surrounded by
like a little bit of a hot spot. You get
like a hot ring inside of it a cold spot,
And that's actually kind of what we see. Like if
you look at this cold spot, it is cold, but
the stuff around it is a little bit unusually hot,
and so it sort of looks like a bruise on

(42:30):
the cosmic microwave background from a parallel universe. And you know,
again this is speculation on speculation, on speculation. There are
many other possible explanations, and we have no evidence that
there was this meta universe or other bubble universes. But
it's sort of a fun idea, Like they have a
model of this crazy multiverse and you can actually model

(42:51):
like what happens when two universe is bumping to each other. Yeah,
they do, although you know you have to wonder, like
are these models designed to explain this cold spot? Is
not like a prediction. This is sort of like more
like a post adiction. It's not like fifty years ago
people are saying we're going to discover the CNB and
it's going to have a cold spot from the previous universe.
It's more like a cold spot. I wonder if I

(43:13):
could explain that using a parallel universe. So here's a
theory I cooked up, and you probably like tweak the
parameters until you get the cold spot, right. Yes, that's
the tricky thing. And so what you got to do
always when you make a theory that explains the data
is then you have to predict future data so you
can test your theory. Otherwise it's just an explanation. Wow. Alright, Well,

(43:34):
so this big cold spot in the sky in the
universe background radiation, it sounds like it's still a big mystery,
like nobody really knows what could be causing it. It's
still a mystery. It's still something people are puzzling over.
There even crazier ideas out there that we didn't cover,
things like cosmic texture and all sorts of weird stuff
and aliens, aliens. Let's not forget aliens. Here's here's my

(43:55):
alien theory, Daniel. They build a death star that's billions
of light year across and that's what's causing the cold spot.
It's blocking the CNB and it's coming our way. Yeah,
and there's a one percent chance that I'm totally making
it up. I love your theory. It sounds just about
as plausible as the parallel universe theory. Yeah, there you go.

(44:17):
I am right up there with the leading physicists on
this matter. Yes, absolutely, you're on the cutting edge. But
you're right, it could be nothing. It could just be
like a random quantum fluctuation. But it's not something we
currently understand, and so it could be that twenty years
from now we look back and say, oh my gosh,
that was the clue that told us something deep about
how the universe works. Because remember, the CNB is filled

(44:38):
with super rich information about how the universe came to
be and how it evolved and why it looks the
way it does today. So I wouldn't be surprised if
this really, in the end taught us something deep about
the universe. We just don't know what yet. Yeah, Or
maybe the universe just doesn't like to talk about it,
you know, maybe to lit embarrassed by that cold spot,
in which case maybe we should just look away, Daniel,
just ignore it. That's the polite thing that don't stare

(45:00):
that ZiT on your friend's head, and I just pretend
it's not there. Yeah, Yeah, that's what a good friend
of the universe would do. All right. Well, again, just
another reminder that the universe is all around us, it's
giving us clues all the time, and that there are
big cold spots of mystery in it, in that information
that it's bathing as with exactly, they're big giant voids

(45:22):
of knowledge that we still don't have about the universe. Yep.
And we have figured out the c MB is there,
but there's probably other kinds of information that we're swimming
in right now that contains incredible facts about the origins
of our universe. We just don't even know how to
look for it and how to interpret it. In later
generations will chuckle when they look back at how silly

(45:43):
and how foolish we were. Right, maybe all we have
to do is check the cmb R, not the cmb
and we would have seen the answer. And we should
have checked the CNBS and the c MBT. I mean, like,
let's follow up on these things, all the Marvel movies
right there. All right, Well, we hope you enjoyed the ad.
Thanks for joining us, see you next time. Thanks for listening,

(46:12):
and remember that Daniel and Jorge explained the universe is
a production of I Heart Radio. For more podcast For
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