What did the early Universe sound like?

Daniel and Jorge take you back to the early Universe and the sound bubbles that seeded everything.

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:08):
Hey or he. Are you a fan of boba tea?

Speaker 2 (00:11):
You mean like bubble tea?

Speaker 1 (00:12):
Yeah? Is that what the kids are calling it?

Speaker 2 (00:14):
I think they call it boba, but I think maybe
most people might not know what that is. But yeah,
I'm a fan. My kids are really into it, so
I've grown to like it.

Speaker 1 (00:22):
Well, my daughter loves it, but personally, I can't get
over the fear of being choked by a floating blob
every time they take a sip.

Speaker 2 (00:28):
Oh. Well, first of all, they don't float, which tells
me maybe you don't drink boba very often, Busty. The
other thing is they're not that big. I think they're
pretty much smaller than your throat.

Speaker 1 (00:39):
I think maybe these new trends are just not for
the faint of heart.

Speaker 2 (00:41):
So do you not like bubbles in general?

Speaker 1 (00:44):
No, I'm pro bubbles in the universe, just not in
my tea, not as a choking hazard.

Speaker 2 (00:49):
I see what about economic bubbles? Those are bad news?

Speaker 3 (00:53):
Mmm.

Speaker 1 (00:54):
I'm hoping to ride the podcast bubble until it pops.

Speaker 2 (00:56):
Yeah, there you go. Not all bubbles are bad. Hi
am Jorge Mack, cartoonist and the author of All Ours
Great Big Universe.

Speaker 1 (01:17):
Hi, I am Daniel, I'm a particle physicist and a
professor at UC Irvine, and I'm actually fascinated by the
mathematics of bubbles.

Speaker 2 (01:24):
Oh yeah, it is, and it just a sphere.

Speaker 1 (01:26):
Some bubbles are spheres, but you can also get bubbles
of all sorts of different shapes, which solve really complicated
sets of mathematical equations to like minimize surface area.

Speaker 2 (01:35):
Now is that math or is that physics.

Speaker 1 (01:37):
It's using physics to solve math. It's like using the
universe as a computer. Whoa bubble computers?

Speaker 4 (01:43):
Man?

Speaker 2 (01:43):
That sounds like an awesome topic for a podcast episode,
but I'm guessing that's not what we're talking about today.

Speaker 1 (01:49):
We are not talking about my new Bubble Computers startup,
which will be serving bubble tea in the lobby, but
we are talking about bubbles.

Speaker 2 (01:56):
You're going to ride that tech bubble. But anyways, welcome
to a podcast Daniel and Jorge Explain the Universe, a
production of iHeartRadio in.

Speaker 1 (02:04):
Which we want you to ride the bubble of understanding.
As human thought expands further and further into the universe,
we understand more and more about this incredible and crazy cosmos.
We decode the messages that come to us from all
these distant places and try to piece them together into
a fragile bubble of understanding.

Speaker 2 (02:22):
Because it is an awesome universe inflating every day with
more and more awesomeness. We like to inflate your brain
here on the podcast until it pops with an epiphany
about how the universe works.

Speaker 1 (02:32):
I don't want anybody to bring the pop man. We
want to very gently inflate it.

Speaker 2 (02:38):
I said, with an epiphany.

Speaker 1 (02:40):
Oh, that sounds terrifying, but you're right. We do want
listeners to have that moment of understanding where suddenly things
click into place and you go, oh, I get it.
This thing I used to hear in that bit, I
thought I understood. Those actually fit together into a holistic
idea about how the universe works, and that, in the end,
is the goal of this podcast.

Speaker 2 (02:58):
Yeah, we like to taggle the bit mysteries about the
universe from its large scale and what kinds of amazing
things you can find out there in the reaches of space,
but also in the smallest of scales done at the
atomic and particle sizes, from the beginning of the universe
to the end of the universe.

Speaker 1 (03:12):
Exactly, and those little bubbles at the particle level in
the early universe turn out to have a ripple effect
that create bubbles in our universe billions of years later
and millions of light years across. It turns out that
bubbles are not just the core idea between my future
billion dollar bubble computing startup or the drinks that my
daughter enjoys. They are also fundamental to understanding the early

(03:34):
universe and the structure of the universe today.

Speaker 2 (03:37):
But you mean you can tie the Big Band to boba.

Speaker 1 (03:40):
The Big Bang was basically just a bobba bubble.

Speaker 2 (03:42):
Big bubba bubble bang boom. Yes, Daniel said, a lot
of things that happened at the beginning of the universe,
even small, microscopic things that were going on, have a
huge impact in what the universe looks like today, and
maybe even might have tip things in our favor for
to be creative and for our galaxy to be the
way it is now.

Speaker 1 (04:02):
One of my favorite things in physics is figuring out
a way to sift through the clues that are left
to us about what happened in deep time, what happened
in the very early universe. If we can figure out
the signs and signals, but those early events left for us.
We can actually reconstruct a complete history of what happened
in the universe. It's like the biggest detective game ever.

Speaker 2 (04:23):
I don't think they can even trace how boba was invented,
so that would be an amazing feed if we can,
you know, trace our origin back to the Big Bang.

Speaker 1 (04:31):
Are you saying it just organically bubbled up from nothing?

Speaker 2 (04:33):
I don't know, that's the mystery. Maybe it was aliens.
I knew that NASA had secret alien technology. I just
didn't realize it was Boba technology. Well not NASA, and
NASA's is from Earth. Am saying the conspiracy runs deeper?

Speaker 1 (04:48):
Oh my gosh, wow, intergalactic Boba bubble conspiracy.

Speaker 2 (04:52):
There you go. That's what the world needs, more conspiracy theories.

Speaker 1 (04:57):
But we are here on this podcast breaking down conspiratorial
nons sense and telling you the truth about what we
do and do not know, how we trace back to
the history of the early universe and how it affects
our lives today.

Speaker 2 (05:07):
So today on the podcast, we'll be tackling the question
what did the early universe sound like? Interesting questions about
the sound of the early universe.

Speaker 1 (05:21):
Yeah, did it sound like somebody choking onbah?

Speaker 2 (05:25):
Maybe that is the origin of the universe. Maybe they're
all here because some intergalactic god choking a giant boba.

Speaker 1 (05:35):
Exactly. He took his daughter out for intergalactic boba and
the rest is history.

Speaker 2 (05:39):
Yeah, maybe black holes are like the boba of you know,
the higher beings.

Speaker 1 (05:45):
Black hole boba. I will definitely sell that in the
cafe of my bubble computing startup.

Speaker 4 (05:50):
Yeah.

Speaker 2 (05:50):
They are pretty dense right in drink, They're like thing
in the drink.

Speaker 1 (05:54):
They're terrifying.

Speaker 2 (05:55):
Oh my gosh, you're really afraid of boba.

Speaker 1 (05:58):
When I take sip of a I want to enjoy
a fresh liquid and not worry that something is going
to shoot down my throat. Yeah.

Speaker 2 (06:05):
I think we've established the bow is not for you.

Speaker 1 (06:09):
But I am a big fan of bubbles, including sound
bubbles in the early universe. People don't usually think about
what the universe sounds like because they think about space
is being mostly empty and so diffuse that sound waves
can't effectively travel through it. But that wasn't always the case.

Speaker 2 (06:25):
Yeah, so this is an interesting question, and it sounds
like the early universe sounds are related to bubbles, like
bubbles popping or bubbles forming, bubbles.

Speaker 1 (06:33):
Forming and slashing around, and even oscillating. In physics, this
whole field goes by the fancy name of baryon acoustic
oscillation b AO or bow.

Speaker 2 (06:44):
Mm oh, well we should be talking about bows then, buba.

Speaker 1 (06:49):
Bubble bow.

Speaker 2 (06:50):
Those you can't probably choke on if you try to
eat a whole one at once.

Speaker 1 (06:54):
Don't put those in your drinks, folks.

Speaker 2 (06:55):
Yeah, that that's an interesting idea, Daniel. You might have
invented the newest trend.

Speaker 1 (07:01):
Is that going to start a whole new universe?

Speaker 2 (07:03):
Maybe? Yeah, maybe somebody will struggle to swelling one and
originate a whole new universe of lawsuits, I'm guessing. But anyways,
it's an interesting question. What did the early universe sound like?
And it sounds like it's related to something called the
baryon acoustic oscillation, and so, as usual, we were wondering
how many people had heard of this concept? Do they

(07:23):
know what it is? Do they want to know.

Speaker 1 (07:26):
What it is? How could they live so long without
hearing about it? So thanks very much to everybody who
answers these questions for the podcast. If you'd like to
join the crew. Please don't be shy. Write to me
two questions at Danielandjorge dot com, or contact us on
Twitter or join our discord. We'd be happy to send
you these questions.

Speaker 2 (07:44):
So think about it for a second. Do you know
what baryon acoustic oscillations are? Here's what people have to say.

Speaker 3 (07:51):
I have no idea, but it reminds me of something
in a video game I used to play. Oscillation is
kind of like a ring of something I because in
my video game there's like a big circle ring the
boss called the ausciliator. Acoustic is like kind of like antiqueish.

Speaker 1 (08:10):
I think, I'm sorry, I'll pass. Never heard about it.

Speaker 4 (08:15):
I believe this is pressure waves in the cosmic background
radiation that is caused. We can see the slight changes
in temperature caused by pressure waves, and because the pressure
waves cannot propagate at greater than the speed of light,

(08:35):
the size of the acoustic variations gives an excellent estimate
of the distance to the cosmic background radiation source, and
therefore that, in conjunction with the red shift that we observe,
gives us a very good indication of the hubble constant

(08:57):
at that one point in time approximately four hundred thousand
years after the Big Bang.

Speaker 5 (09:03):
Based purely on the name, I would guess that baryon
acoustic castellation has something to do with either using sound
to cause beryons to bump each other or using sound
like properties to study how they behave.

Speaker 6 (09:19):
I have it in my head that baryon acoustic ostellations
has something to do with the beginning of the universe
and tower. The original quantum fluctuations prior to inflation taking
place could be seen as being like waves through the
kind of plasmi y stuff at the beginning, and then
when that gets blown out by inflation, you can still
detect and see those acoustic ostellations today.

Speaker 3 (09:41):
So Buryon's some atomic particle, and probably.

Speaker 1 (09:49):
It has acoustic.

Speaker 3 (09:51):
Oscillation to it, like having a pattern repeating over a
period of time.

Speaker 6 (09:57):
Or something like that.

Speaker 2 (09:59):
All right, and a lot of answers here. I like
the person who said, I'm sorry, I'll pass. What do
you say to that, okay next? Or do you try
to convince them that they want to know what burying
acoustic oscillations are.

Speaker 1 (10:12):
I don't want to pressure anybody. I'm just impressed that
they decided to record their passing and send it in
rather than just not responding.

Speaker 2 (10:19):
Oh, they actually like took the time to record this exactly.

Speaker 1 (10:22):
They sat down and record their answers and sent it
in even though they were passing.

Speaker 2 (10:26):
I love that, I see. Do you think what do
you think happened? Do you think they heard the question?
Were like, I don't want to say anything about burying
acoustic oscillation.

Speaker 4 (10:32):
Yeah.

Speaker 1 (10:33):
Well, the rules are no googling, no looking at the
questions ahead of time. I want people's real, spontaneous ideas
about what these topics are, because we want to get
a sense for what people out there know before they
look things up. And so this person was just reading
through the questions in real time and recording themselves, and
maybe their brain just had a bubble which popped and
they decided I got nothing.

Speaker 2 (10:51):
Okay, I see, it's more like I got nothing not
so much A.

Speaker 1 (10:55):
No, thanks, next question please.

Speaker 2 (10:59):
Well, people seem to sort of into it or know
that it's somehow related to the beginning of the universe.
And also I guess to something related to waves, right
and sound and oscillations. Nobody gets bows or boba.

Speaker 1 (11:13):
Nobody made the boba connection. That's just me, all.

Speaker 2 (11:15):
Right, well, let's jump into it, Daniel. What are baryon
acoustic oscillations.

Speaker 1 (11:19):
Yeah, baryon acoustic oscillations are really fascinating, sort of like
fossilized sound waves from very very early universe. You know,
like if somebody's playing an acoustic guitar or like an
acoustic recording. It refers to the quality and the fabrication
of the sound waves that you're hearing. So acoustic there
tells you that you're hearing sound waves, and the word
buryon tells you what you're hearing those sound waves in

(11:42):
that you're hearing it as baryons bump against each other.

Speaker 2 (11:45):
But I guess maybe not to confuse folks in this case,
acoustic doesn't mean necessarily sounds your hearers at the air.
They can also mean like sound waves and you hear
in the ocean or maybe through even a solid right.

Speaker 1 (11:55):
Yeah, exactly. Sound Waves can travel through air, but they
can also travel through water, or they can travel to steal,
they can travel through your body, They can travel through
any kind of gas or plasma. Sound Waves are just
pressure waves. If you have a bunch of molecules that
can interact with each other, that can push against each other,
then if you push on one side of that blog,
then it's going to push on the next layer, which
pushes on the next layer, which it pushes on the

(12:16):
next layer. That's what sound waves are. You're hearing us
right now because the speaker in your ear is making
sound waves that push on layers of air, which push
on the next layer of air, etc.

Speaker 2 (12:26):
I see so an acoustic wave or acoustic oscillations. They're
just like when things propagate through material, because things are
bumping into each other basically through electromagnetic forces, or can
it be other force.

Speaker 1 (12:38):
It's almost always electromagnetic forces. The crucial thing is that
they bump against each other. If they pass right through
each other, then they don't cause pressure waves. The crucial
thing is that they're bumping up against each other. That
one layer pushes the next layer, which pushes the next layer.
The microphysics of how that pushing happens is electromagnetic. You
have electrons in one atom are pushing up against the
electrons in another atom. They don't like to overlap, they

(12:59):
resist each other. It's the same reason why you don't
pass through your chair, or when you're leaning against the wall,
the wall pushes back or the Earth is pushing up
on you. Basically, anything structural is built with electromagnetic forces,
because that's the bond of chemistry.

Speaker 2 (13:13):
Now, for those of us who are not particle physicists,
can you remind us what a baryon is.

Speaker 1 (13:18):
Yeah, Baryons are anything made out of quarks, basically baryon
the shorthand for our kind of matter, stuff like protons
and neutrons, these are baryons. We call them baryons mostly
to distinguish them from the other kind of matter in
the universe, dark matter, which is some other kind of
stuff that's out there. It feels gravity, it has masks.
We think it's made of stuff. We don't know if

(13:38):
it's made of particles, but we're very sure that it's
not made of our kind of particles. And so when
we talk about the very early universe, we have a
few components to sort of like that very early universe smoothie.
There's baryons, there's photons, there's dark matter, and so we
talk about baryon acoustic oscillations because it's the sound waves
in those early universe protons mostly that we're thinking about.

Speaker 2 (14:01):
Does that include electrons as well or electrons something else?

Speaker 1 (14:04):
So electrons are not technically baryons because they're not made
out of quarks. Baryons are particles that are made out
of three quarks. Quarks are these incredible particles that feel
a strong force in order to have a neutral particle
and the strong force and that it doesn't have an
overall strong force charge the way, for example, a proton,
an electron can make a neutral atom with no overall

(14:24):
electric charge. In or for quarks to come together to
make an object that doesn't feel a strong force, it's
overall neutral. You need either three of them or two
of them, and if you put three of them together
you get a baryon like a proton or a neutron,
or there are other more exotic baryons. So technically an
electron is not a baryon, but it is included when
you talk about baryonic matter, which is like atoms made

(14:48):
out of a baryon and an electron.

Speaker 2 (14:50):
I see that makes not a lot of sense.

Speaker 1 (14:55):
Yeah. The short answer is you can lump electrons in
with baryonic matter even though technically they're not buryons.

Speaker 2 (15:01):
Okay, I see, so it's really just regular matter. You're
using that shorthand for regular matter or at least the
matter that we're made out.

Speaker 1 (15:08):
Of, exactly the matter that really matters.

Speaker 2 (15:10):
So then we're talking about the Big Bang. This is
the early moments of the universe, and now what was
going on there.

Speaker 1 (15:15):
When we talk about the Big Bang. It's also important
to clarify what we really mean by the Big Bang.
If you say that to a lot of people, they
imagine some very dense dot in space which then exploded
to make our universe. But when physicists talk about the
Big Bang, they really have a different idea in mind.
First of all, we don't go all the way back
to the creation of the universe. We don't know how
the universe was created, if it was created, if it

(15:36):
existed forever, how everything came to be. We only go
back as far as our theories can describe, which is
some moment around fourteen billion years ago when the universe
was filled with a very very hot and dense material.
Our theories go back that far, and our observations verify
that that happened. Where that stuff came from and how
it got there and all that stuff is all very speculative,

(15:59):
and we have theories about that inflation, et cetera. But
really the Big Bang, when physicists describe it, starts from
that very hot, dense state and then watches it expand
and form our universe. So the Big Bang is not
like a singularity at some point. It's a moment in
time when the universe was very hot and dense and
filled with plasma.

Speaker 2 (16:16):
Well, part of it was that there was a lot
less space back then in that those early moments of
the universe, or at least what we call the early
moments of the universe. Like space expanded a lot since then,
from then to now, and so basically maybe a way
to think about it is just like all space was
more compressed, but it had the same amount of stuff
and it so everything was hot and dense.

Speaker 1 (16:34):
Yeah, it's tricky if you think about size and use
words like smaller, because we don't know the size of
the universe. It might always have been infinite and might
still be infinite today. What we do know is about
the density. So as you say, it's more compressed, so
you should think about a universe, whether it's infinite or not,
just as filled with really hot, dense stuff and then
space expands. That's the Big Bang as we think about
it today, and makes everything more dilute. So things are

(16:57):
cooling down and getting more dilute. There's more space per
bit of stuff. That doesn't really tell you anything about
whether the universe was infinite or not. We obviously don't know.

Speaker 2 (17:07):
And so I think the early universe went through a
lot of different phases, right Like, at some point there
weren't even maybe quantum fields or the quantum fields. We're
still trying to figure it out. And then things started
to change. But as you said, at some point in
that history, everything was basically a hot plasma exactly.

Speaker 1 (17:21):
Things started out so hot and dense that we can't
even really use the physics of today to describe it.
You can't even really talk about particles because the fields
were so filled with energy. But eventually things cooled down
and particles formed, and you got quarks, and you've got electrons.
Those quarks then cooled down to make protons. And it's
really that moment that we want to zero in on today,
the moment when we had protons and electrons and photons

(17:44):
and also dark matter in this big hot plasma. But
that hot plasma is not uniform. It's not like everywhere
in space has exactly the same hot plasma, there's little
ripples in it. Some parts are denser than others, and
the baryon acoustic oscillation describes how the bears in that
hot plasma, we're sloshing around and ringing with sound waves.

Speaker 2 (18:05):
Well, I think maybe a good way to think about
plasma is that it's basically just a gas. The only
difference between the plasma and a regular gas is that
the atoms are broken up, right Like in a regular gas,
like the air we're breathing, the electrons are tied together
with the protons and neutrons into atoms. But in the plasma,
it things are so heated up that they break apart.

(18:25):
But it's still basically a gas, right Like it's just
things flying around a space.

Speaker 1 (18:29):
Yeah, exactly. It's a gas of charged particles, and it's
sort of a natural evolution of matter. You know, as
things get colder, they form more structure because they don't
have the energy to escape the power of those bonds.
So you think about an individual electron, if it has
a lot of energy, in other words, if it's in
a really hot gas, then it's going to have too
much energy to be captured by a proton. But as
things cool down, then those electrons are susceptible to being

(18:51):
captured by the proton, and then you get neutral hydrogen.
So as the universe cools, you go from having charged
plasma like you say, a charged gas, to having neutral gas.
And so, yeah, plasma is just a charged version of
a normal gas.

Speaker 2 (19:05):
Right, It's a gas made out of ions, right, electrons
and programs lying around on their own, and so like
any gas, it would have sound waves.

Speaker 1 (19:12):
In it exactly, so that hot plasma was not a
quiet place, right. It was also super dup or dense,
which means that sound propagated through it at shockingly high speeds.

Speaker 2 (19:22):
All right, well, let's get a little bit more into
this hot plasma, how it works, and how those early
sound waves in that plasma led to the universe we
see today, Boba included. So let's dig into that. But
first let's take a quick break. All right, we're talking

(19:49):
about the early sounds of the universe. Now, Daniel, what
genre of music do you think the universe sounded like
at the beginning? Was it like elevator music? Was it
like rocking, banging music? What do you think k pop?

Speaker 1 (20:01):
I think it sounded mostly like white noise and screams.

Speaker 2 (20:04):
I see, that's right, that's right, because it was some
deity choking on a giant black hole wave exactly. It
was not a pleasant sound. But yeah, you were saying
that the universe was basically at some point it evolved
into basically all hot plasma in it, and there were
sound waves in it and ripples in it, because I
guess it's just the gas. And so even the air

(20:25):
we see around us is not perfectly totally completely uniform, right.

Speaker 1 (20:30):
That's right. There are pressure waves everywhere as you talk,
and you're making pressure waves. As the wind blows and
makes pressure waves. As there are temperature variations, you've got
pressure waves, and so nothing around you is really totally uniform.

Speaker 2 (20:42):
So then what made those waves in the early universe? Like,
if I just have a room here and I leave
it alone, the gas is gonna basically all equalize, isn't it.

Speaker 1 (20:50):
Mm hmm exactly. So to get sound in the early universe,
you need a couple of things. First of all, you
need some initial over densities. You need some spots be
a little hot and a little denser than others. Then
you need a way for it to propagate or for
it to ring So what are those initial over densities
come from. Because if we're imagining the early universe just
this big hot plasma, and we say everywhere in the

(21:11):
universe is the same, there's no special location to the universe.
There's no reason why the universe would put more stuff
here and than there. Then it's hard to imagine like
where any sort of really initial ripple might come from.
And that comes just from quantum fluctuations in the very
very early universe. So way back before the plasma even formed,
much earlier on, you had just some quantum fluctuations, particles

(21:33):
popping in and out of the vacuum, just true quantum randomness.
It is true that everywhere in the universe follows the
same laws of physics, But if quantum mechanics really is random,
then it can do different things in different spots, and
that's how you get little, tiny fluctuations. But then inflation
or whatever caused the universe to expand dramatically blue those
tiny little quantum ripples up to tiny little macroscopic ripples

(21:57):
big enough that gravity could do something with them.

Speaker 2 (22:00):
Well, you call them tiny microscopic quantum fluctuations. But I
wonder if back then, when the universe was a lot smaller, basically,
like all of the quantum particles and fields were basically
more on top of each other. And for example, the
size of an electron today it does seem huge back then.
Is that a good way to look at it.

Speaker 1 (22:18):
It's definitely true that everything was much more compressed back then,
like you had the same amount of stuff with less
space between them. But those electrons probably weren't even born
yet when these ripples that were talking about were made.
Eventually that same energy did cool down and spread out
into specific particles. But the ripples we're talking about are
probably pre particle. They're just like ripples in the froth
and quantum fields before you can even really identify them

(22:41):
as particles.

Speaker 2 (22:42):
Right right. I didn't mean to say that there were
electrons back then, but I just mean like the scale
things was very different back then. Like what we might
ignore today is a quantum fluctuation because it's so small.
Back then, maybe a quantum fluctuation was huge.

Speaker 1 (22:53):
Right, Yeah, it's a really interesting comparison. I guess. Really
the only meterstick we have to compare today with back
then is the speed of light, And so you do
have this sense of like the horizon that an electron
could see, like what fraction of the universe an electron
could interact with, and then that did later get blown up.
And so back then the electron was sort of in
a smaller pond of the universe of sort of a
bigger deal.

Speaker 2 (23:14):
Then, as you said, these small ripples kind of god
stretched out as the universe expanded. So maybe take us
through a little bit of what was happening as the
universe started to expand, like what was going on with
dark matter.

Speaker 1 (23:26):
Yeah, so you have these initial ripples which create over densities,
mostly in the dark matter. Remember that there's more dark
matter than anything else. And so if your mental image
you're imagining some like hot bright plasma, add a layer
to that, an invisible layer of dark matter, which has
most of the mass of the matter in the universe
at the time, not most of the energy. Most of
the energy in the universe at this time is still

(23:47):
in photons. It's mostly radiation dominated. But most of the
stuff in the universe is dark matter. So now you
have these little ripples. You have like a little bit
more dark matter here and a little bit more dark
matter there, and dark matter has gravity of course, it
so it starts to pull things in. Because you have
a little bit more dark matter, it means it has
more gravity than everything around it. It's going to start
to pull stuff in, which gives it more density, which

(24:09):
gives it more gravity. So dark matter is starting to
form clusters, it's starting to amplify those initial quantum fluctuations.

Speaker 2 (24:16):
Well, I guess the big question is what do we
know about dark matter in those early moments, Like we
know that regular matter, it started to dissociate into protons
and electrons, and before that they dissociated even more. Did
dark matter break down too, or did it also have
quantum fluctuations or does it even have quantumness to it?

Speaker 1 (24:36):
Yeah? Wow, I wish I knew the answer to any
of those questions. We don't know, right because we don't
know what particles dark matter is made out of, if
it's even made out of particles in this theory. Instead,
we treat dark matter sort of as like a collisionless fluid,
some that has no interactions other than gravity. We think
just about its mass density and the gravitational impact of that.

(24:56):
We don't try to break it down into the microphysics
because we don't have that story at all. We don't
know if dark matter is ten different kinds of dark
particles that are all turning into each other and back
or not. But because it doesn't interact with the baryons
except for gravity, we don't really need to know those details.
I mean, we'd love to know, who wouldn't want to know,
But it doesn't change the story of the baryon acoustic

(25:17):
oscillations that we're focused on today.

Speaker 2 (25:19):
I see at this point we're just squinting at dark matter.
We're sort of waving our hands. We're like, well, I
don't care what's happening at the small microscopic level of
dark matter. It could be anything, but you just sort
of treat it as, like you said, like a cloud
or liquid of stuff.

Speaker 1 (25:35):
Yeah, it's not that we don't care. We deeply care,
and we'd love to know. But the game of physics
is trying to make progress even when you don't know things.
And so here's a question we can focus on even
without knowing what's going on with the dark matter. We
can still think clearly about what's going on with the
baryons because we think we do understand their interactions.

Speaker 2 (25:54):
Right, So then you're saying that the dark matter was
influenced by the quantum fluctuations of the regular matter. But
could dark matter itself have had its own quantum fluctuations.

Speaker 1 (26:03):
Now, they had their own quantum fluctuations for sure. Dark
matter and regular matter both come out of these initial
quantum fluctuations. So one spot in the universe we have
like an over density of energy that turns into more
dark matter and more normal matter. And it's mostly the
quantum fluctuations in the dark matter itself that spur everything
we're talking about, because it's the gravity of the dark
matter that triggers everything.

Speaker 2 (26:24):
Right, because there's more dark matter than regular matter. But
then are you assuming that, like the dark matter fluctuations
and the regular matter fluctuation, we're somehow in sync in
the early universe.

Speaker 1 (26:34):
The quantum fluctuations we're talking about again predate the formation
of the particles themselves, and this division of energy into
dark matter and normal matter, which frankly, we don't understand,
and to understand it, we'd have to have a better
idea of what particles there are and how the quantum
fields sort of filter out into the dark matter. So
we just say that there's an initial quantum fluctuation and
then at each point, if you have more stuff or

(26:55):
less stuff, you get about eighty percent of it into
dark matter and twenty percent of it into normal matter.
So from that point of view, they are correlated because
they come from the same initial quantum fluctuations, which are
independent from the dark matter or the normal matter nature.

Speaker 2 (27:08):
I see, you are sort of imagining a point in
the universe when even dark matter was maybe dissociated or
didn't exist exactly.

Speaker 1 (27:17):
Those are where the quantum fluctuations are happening before we
even have dark matter or normal matter, and then down
the road tiny fractions of a second later, when we
do have matter, some of that energy has gotten into
dark matter and some of it into normal matter.

Speaker 2 (27:29):
Okay, So then both dark matter and regular matter are
kind of have these expanding fluctuations ripples, which, as you said,
create pockets of the higher density dark matter and regular matter,
which then I guess is what creates the sound ways, right,
because when you have something more dense in one side,
it tends to try to go to the other side.

Speaker 1 (27:50):
Exactly, and sort of a push and a push back here.
So dark matter is creating these over densities. It's like
gravitationally collapsing things, and that's fine for dark matter. Dark
matter doesn't really care happy it gets pulled in by
gravity and overlap with itself whatever. But baryons are different.
Baryons and photons interact with each other, and so if
you squeeze them down, then they're going to push back.

(28:11):
Like you squeeze a bunch of baryons together, they push
against each other and they push back out. And remember
that there's a huge number of baryons but also an
enormous number of photons. So as you squeeze these protons together,
then they're effectively squeezing on the photons, which push back out.
So it's sort of like a mini version of what
happens in a star where you collapse it gravitationally and

(28:33):
then it creates fusion, and that radiation pressure from the
fusion keeps the star from collapsing. Here you have dark
matter pulling blobs of baryons and photons together, and then
those photons and baryons interacting when they get squeezed to
push back out, and that's what creates these ripples in
the baryons.

Speaker 2 (28:52):
Like it's like the dark matter collects all of the
other the regular matter tries to squeeze it down, but
then it bounces back exactly.

Speaker 1 (29:00):
It bounces back sort of like a mini weaker version
of a supernova, you know, gravitational collapse, which then bounces
back out in impollusion, which leads to an explosion. Some
way I want to get clearing people's minds, which is
sort of crazy to imagine, is the ratio of different particles,
Like there's about a billion photons for every proton and
every electron at this point at the universe, Like the

(29:21):
universe is mostly light, so there's a huge number of
photons pushing against these baryons.

Speaker 2 (29:27):
Now, are you sweeping electrons and protons into radiation here
or do you actually mean real photons that later got
transformed into electrons.

Speaker 1 (29:37):
Totally fair question, because you're right that if things are
moving near the speed of light, we just call it radiation.
But here we're talking about real radiation. We're just talking
about photons. We're treating electrons, protons, and photons separately, and
it really is mostly photons. But those photons they push
on the baryons, they push on the protons, they push
on the electrons in a way that they of course

(29:58):
don't push on the dark matter. So the dark matter
is collapsing into the center and the baryons get pushed
back out because they have this electric interaction that dark
matter doesn't have.

Speaker 2 (30:09):
But the photons are not being pulled together by gravity,
are they?

Speaker 1 (30:12):
Photons are affected by gravity? Right, Photons bend around the Sun,
or can bend around a black hole. So as dark
matter curved space, photons are also gathered into that well
together with the protons. But then they push back and
there's so many protons, so many photons that you get
a sound, right, This is the sound of the early universe.
Is this pressure wave in the buryons created by the

(30:34):
baryons and the photons being squeezed down by dark matter.

Speaker 2 (30:37):
M it's the sound of regular matter being uncomfortable, like whoa, whoa,
I don't want to be so close to my neighbors.

Speaker 1 (30:45):
Exactly, it's here, Exactly. It's the sound on the subway
when another ten people get on and squeeze you into
the back and you're like, hell, I can't breathe back here.

Speaker 2 (30:54):
It's the groan of a million introverts.

Speaker 1 (30:58):
What you're saying, Yeah, Another one rides. That was the
sound of the early universe.

Speaker 2 (31:03):
Another one gets gathered by dark matter against its well.

Speaker 1 (31:07):
Exactly, and the density of the universe is really really high,
and the density controls the speed of sound. Like sound
travels faster through water than does through air because those
molecules are more tightly packed together, so the soundwave propagates
more quickly, and their bonds are more rigid because they're denser.
So the soundwave propagates faster through denser materials like steel

(31:28):
than it does through water, than does through air, than
it does through really diffuse gases like the upper atmosphere.
And in the early universe, things are super duper crazy dense,
So the speed of sound in the early universe is
like half the speed of light.

Speaker 2 (31:42):
Whoa wouldn't you have to call it radiation wave?

Speaker 1 (31:48):
Fair point? Fair point?

Speaker 2 (31:50):
All right? So then there were these waves from the
material sort of bouncing back, and that means that like
those waves propagated at which made things more dents in
some places than others, right, because that's what a wave.

Speaker 1 (32:03):
Is, yeah, exactly, So you have this dark matter core
and then you have this density wave of baryons propagating out.
But this doesn't last forever, right, Things in the universe
are happening fast, and the universe is expanding and it's cooling,
and at some point, around three hundred and eighty thousand
years after this first moment, we can describe what we
call the beginning of the universe, or at least the
Big Bang. Things cool down enough that the protons and

(32:25):
the electrons did bond together to make neutral hydrogen. The
electrons no longer had enough energy to escape the pull
of the protons, so the universe became transparent to photons
instead of opaque. So now when photons are flying through
the universe, instead of interacting with all the protons and
the electrons, they see now they just see neutral hydrogen.
So they no longer push on it. Now they just

(32:46):
fly through it. And so the universe can expand and cool,
and these photons can dissipate, and so the sound wave
basically got frozen.

Speaker 2 (32:54):
It's sort of like if you suddenly frozy ocean, you
would see all these water molecules frozen in the shape
of a wave.

Speaker 1 (33:01):
Yeah, that's right. Or say you slap your hand in
your bathtub and it creates a wave and then you
suddenly cool it to freeze it. You can come back later.
You can still see that water wave. Otherwise it would
have kept propagating and slashing around. But now it's frozen
because your bathtub, the water has cooled so it can
no longer propagate. And the same thing happened in the universe.
The universe became transparent, it became cooler, became less dense,

(33:24):
and the photons passed through this wave overcame it. So
now that single ring of sound is like frozen in
the structure of the early universe.

Speaker 2 (33:32):
Right, But I guess maybe the confusing thing is is
that it's like a sound wave in the density of photons. Right.
It's like there were sound waves propagating because the regular
matter was interacting with photons and with itself. There were
waves in that slash. But then it's almost like you
took away the regular matter, you took all the protons
and electrons out of it, and now suddenly the light

(33:54):
was kind of stuck in these like oscillations of density.
And that's what we see today.

Speaker 1 (33:58):
The light was really powering these oscillations. It's the thing
that was pushing the baryons and the electrons along. Once
the electrons and baryons cooled so they became neutral, they're
no longer like riding this wave of the light, so
they sort of jump off the train. They get frozen
where they are, and the light continues on and it
just passes right through and it diffuses around, and that
becomes the cosmic microwave background light that we still see today.

(34:20):
So we see the echoes and the ripples of that
light today and we can measure it. But the baryons
electrons got left behind after that moment when they could
no longer ride the light train, because they became neutral.

Speaker 2 (34:31):
Right, Yeah, that's kind of what I mean is that
it's not like the photons continue to ripple with this sound.
It's more like you took out the regular matter and
so the photons that were creating those waves stayed in
those different layers of density, and.

Speaker 1 (34:45):
The photons can keep propagating out and rippling, and they did.
In truth, it's a little bit more complicated, it's like
sloshing back and forth. But basically the picture you should
have in your head is like a core of dark
matter and then these rings of frozen sound waves. At
the time, we're talking about like five hundred thousand light
years across, where you should have like more baryons, like

(35:05):
a higher density of baryons, this baryons frozen sound wave
like five hundred thousand light years across, and then the
light continuing on and slashing through the whole universe.

Speaker 2 (35:14):
Right, It's almost like the light the photons were holding
the regular matter in these wave patterns, and then you
took away the wave the water basically, and so you
have this light kind of stuck in that pattern.

Speaker 1 (35:25):
And we think that basically this seated the structure of
the whole universe. After this point, gravity takes over. In
places that you have more dark matter and more baryons,
things are going to get clustered together more and more
and more, and that's where you're going to end up
getting galaxies, and that's where you're going to end up
getting gas clouds, and then stars and planets and people
and podcasts and eventually boba.

Speaker 2 (35:46):
And bows as well. All right, well, let's dig into
how we can see this cosmic microwave background. Well, we
know about it and also what it means about how
we ended up here today, So let's dig into that.
But first let's take another quick break. All Right, we're

(36:12):
talking about the sound of the early universe, and it
sounds like. It sounded kind of uncomfortable. It was really
hot and crowded, and the regular matter in the universe
did not like it exactly.

Speaker 1 (36:23):
Very loud but very short lived early universe scream.

Speaker 2 (36:26):
And so you were saying that you had these ripples
of matter kind of bouncing back from being compressed. Things
were slashing around, things had sound waves in it. But
then at some point the regular matter kind of froze
into place. They got together into atoms, which then let
the light continue on. Does that mean that at that
point the universe went silent?

Speaker 1 (36:46):
Yeah, basically that's when the universe quieted down and the
speed of sound dropped really really fast. Right, So things
couldn't propagate nearly as fast.

Speaker 2 (36:55):
Why not, Like we wouldn't regular atoms carry those waves.

Speaker 1 (36:58):
Well, regular atoms can still carry waves the way they
do today, Like the sound we hear today is mostly
in neutral atoms in the air. Right, So neutral atoms
certainly can bump into each other and can certainly carry
sound waves. But the pressure was just a lot lower
because the photons had decoupled, and so the density was
a lot lower, and so the speed of sound just
dropped very quickly, and so there still was sound, it

(37:19):
was just much slower moving. It's no longer anywhere close
to the speed of light, and so it's effectively frozen
because soundwaves can still propagate, but just very very slowly.
So things are not going to change very fast the
way they had initially.

Speaker 2 (37:31):
I wonder if you can still measure those waves in
the regular matter, you know what I mean? Like, I
wonder if like collectively all the galaxies in the universe
still has ours kind of slashing around or being moved
around by those sound waves.

Speaker 1 (37:44):
Absolutely you can, and we have looked for this and
we have actually seen it. We can see these waves
in two different ways. One, we can look back at
those photons from the early universe and see these ripples,
like there were more photons in some places than in others.
We can look back at those photons ones that we're
created when the universe just became transparent, that's the cosmic
microwave background radiation, and we see these ripples and we

(38:06):
see exactly what we expect. But we can also see
it in the structure of the universe today. Those rings
that were five hundred thousand light years across, they expanded
as the universe expands and now we expect them to
be about five hundred million light years across. So what
people have done is they've looked at the distribution of
galaxies and they say, hm, our galaxies just like sprinkled

(38:26):
randomly everywhere, or is there a typical distance between the galaxies?
How are they clustered? So they gathered a bunch of
galaxies together, they did these redshift measurements to see how
far away they are, so we can have a three
D map of the galaxies in the universe. And then
they just like counted up what is the distance between
all the pairs of galaxies? Is there any preferred distance?

Speaker 2 (38:49):
And what did they find? Did they find that there's
so even or did they find that this distance varied
according to leg a soundwave?

Speaker 1 (38:55):
So they found that it was not smooth, that there
was a bump there, that you were more like you
have galaxies about five hundred million light years apart than
you were other distances. And this is exactly what they
expected to see because those rings the sound horizon from
the early universe was five hundred thousand light years across
at that time. But the universe has expanded since right

(39:16):
We've had deceleration and acceleration. We know the expansion history
of the universe, and we expect those rings to now
be five hundred million light years across. And when you
look at the distribution of galaxies, you see many more
at that distance apart than you do at like four
hundred million or six hundred million. So this is like
twenty years ago. In two thousand and five, they saw
this statistical evidence for the Bury on acoustic ostellations that

(39:38):
when you add up all these galaxies and compare their distances,
you tend to see the more at exactly the size
of this sound ring.

Speaker 2 (39:46):
No wait, are you saying that somehow this early sound
wave got frozen and the distances between galaxies and the
structure of the universe, or are you saying this sound
wave is still rippling through the structure of the universe.

Speaker 1 (39:58):
They got frozen in the early universe and then gravity
took over it like seeded the structure. It's like if
somebody sprinkled a bunch of seeds in a circle and
you came back one hundred years later and you found
a bunch of oak trees and you wondered, like, why
are there oak trees in a circle? It comes from
the initial distribution of seeds. And so here we're talking
about slashing around the very early universe when things were

(40:18):
still very chaotic, left this over density of baryons in
these sound rings which no longer were able to ripple
as fast because the photons the decoupled and weren't pushing
them anymore, and things got cooler and less dense. And
those are likely initial seeds which formed galaxies, which grew
up to be galaxies.

Speaker 2 (40:37):
I see. So we also see these frozen sound waves
out there exactly.

Speaker 1 (40:41):
And so about twenty years ago people saw the statistical evidence.
They're like, oh, the galaxies tend to be more far
apart at this particular distance than other distances. And that
was evidence that the baryon acoustic ostellations were real, that
we were seeing them in the universe. But very excitingly,
just a few weeks ago, people see an actual single bubble.
When you look out into the unit, you can actually
see like a ring, a huge structure, ring of galaxies

(41:04):
and superclusters lined up into a massive bubble. How big
this thing is, a ring structure about two hundred and
fifty mega parsecs around, And we're sort of near the
center of it, and at the actual center of it
is this huge supercluster called the Buches supercluster, which we
think was gathered together because there's a huge dark matter
blob at the center of this ripple. And then along

(41:26):
the edges are other superclusters that we found, like the
Slow and Great Wall and other pieces that we've been
discovering of structure here and there in the universe. Turns
out they assemble themselves into this incredible, enormous ring two
hundred and fifty mega parsex across.

Speaker 2 (41:43):
Now it's a bubble because, as you said, the early
universe dark matter brought together this barren matter, the barrion
matter bounce back, and when it bounced back, I guess
it looked like a bubble, right, that's what you're saying.
And then the universe expanded, things froze, and we still
see that bubble today exactly.

Speaker 1 (41:58):
And you can look at this paper. You can see
in this distribution of galaxies this sort of faint ring.
It's not crisp and clear.

Speaker 2 (42:05):
It's not like there're no legs a ring or a bubble.

Speaker 1 (42:07):
It's definitely a bubble. It's a sphere. But you know
this is a physics paper, which means it's two dimensional slices.
So if you look at the slices, you know, we
don't publish in three D yet, we're not three D
printing our papers. But actually, if you look online, they
have a really cool animation of which you can see
the three D version, So it definitely has a three
D structure. But in two D slices you see rings.

Speaker 2 (42:25):
I see. But was the analysis done in rings or
was it done in a bubble? Or were you saying
ring because that's how you read it in the paper.

Speaker 1 (42:31):
Well, originally they spotted it as a ring. They were
just like, hold on, is that a huge ring? And
then they started looking in three D They're like, wow,
look at that. It really is kind of a bubble.
And then they calculated the size of it and they
were like, huh, this is exactly the size you would
expect from a single baryon acoustic ostellation bubble, which nobody
had ever seen before. And these folks, they weren't looking
for this. They were doing some other studies of galaxies

(42:52):
and their distributions, and they just like spotted this visual
and they were like, hold on a second, this is
literally a frozen scream from the early universe.

Speaker 2 (43:01):
Whoa They were like, that's a big boba.

Speaker 1 (43:04):
It's a big that's when you would choke on for sure.

Speaker 2 (43:07):
Yeah, they choke Maybe they were drinking boba at the time.
They're like, well, what what is that?

Speaker 1 (43:12):
And I think it's super cool because it gives us
a way to understand not just how our universe was
formed and why we have galaxies over here and why
we have galaxies over there, but also how the universe expanded,
Like we know how big that sound wave when it
was created, because it just comes down to like the
physics of protons and photons and dark matter, how they
push on each other, and we know how big they are.

(43:33):
Now we can measure them, and so that gives us
like an independent way to measure the expansion of the universe,
which of course is a big question and a deep mystery,
like the source of dark energy and how that all works.

Speaker 2 (43:44):
I guess maybe a question is why do we see
more of these bubbles, Like wasn't the universe filled with
these sound ways and these screams of the early universe.
We aren't these bubbles more obvious?

Speaker 1 (43:54):
Yeah, great question. We haven't seen that much of the universe.
You know, our precision maps of the locations of galaxies
basically are just big enough to include one of these.
If you look online and check this thing out, you
see that this one bubble occupies a huge fraction of
the known galaxies we've seen. We just haven't looked out
far enough to see one of these things before.

Speaker 2 (44:14):
Oh wow, it's that big of a bubble, Like it's
almost the size of the observable universe.

Speaker 1 (44:18):
You're saying, it's almost the size of the set of
galaxies that we have mapped. Well, yeah, as things get
further out, it's harder and harder to map these things.
You need more and more precise measurements. Like if we
could use a James Webspace telescope and pointed in every
direction for a month, we would get an awesome map
of the galaxies in the universe. But the map we
have is really sporadic, and in some places it goes

(44:39):
really far. In some places it doesn't because we just
don't have enough telescopes and enough telescope time to do
these careful surveys.

Speaker 2 (44:46):
Well, as you said, it sort of gives us sort
of like a marker in the history of the universe
and how it expanded. And now what's the connection to
dark energy.

Speaker 1 (44:53):
Well, dark energy is our word for how the universe
expanded and how that expansion has accelerated. The picture we
have is that the early universe was dominated by matter
and radiation early on and expanded and things cooled. But
then that matter radiation starts to decelerate the expansion of
the universe, start to slow it down, because that's what
energy density does. It curves space and pulls things back together.

(45:14):
But at the same time, some new force was waking up,
something we call dark energy, was pushing the other direction
and accelerated the expansion of the universe. And this is
something we'd like to understand the detail because we don't
understand the mechanism for it, but we want to understand
the history so we can get a better sense for
what might have been causing this. So measuring the precise
rate of the expansion and how the universe has grown

(45:36):
over time is very, very valuable.

Speaker 2 (45:38):
I see, because I guess these bubbles can't just come
up randomly, right.

Speaker 1 (45:41):
Yeah, these bubbles have a fixed size in the early universe,
just determined by like the physics of acoustic oscillations which
we think we understand, and then they're stretched by dark
energy to a new size which we can measure. So
measuring the size of these bubbles now and comparing them
to the size we knew they had in the early
universe gives us a way to say how much has
the universe been stretched, which, of course is something we're

(46:03):
very interested in.

Speaker 2 (46:04):
All right, Well, another interesting exploration into our origins and
how much we can and how much we still don't
know about what was happening.

Speaker 1 (46:12):
To me, it's amazing how cosmology has gone from a
field where it's like mostly hand wavy stories with rough
numbers to a field where we can measure things and
do precise calculations and compare this and that and know
things about the early universe from these calculations. We have
filtered through crazy data to get these stories of the universe,
to find these clues to build back this history of

(46:35):
what happened and how we all got here.

Speaker 2 (46:37):
I see it's now precision handwaiting.

Speaker 1 (46:42):
Baby steps, man, baby steps, Boba steps.

Speaker 2 (46:44):
You need a thicker straw.

Speaker 1 (46:47):
Well, we need are more smart people thinking hard about
how the universe works and asking questions and listening to podcasts.

Speaker 2 (46:53):
All right, Well, the next time you're in a crowded subway,
think about how the universe felt back then, how it's
screamed out in a discomfort, and how we still see
those screams today in the shape and the distribution of
galaxies and also light.

Speaker 1 (47:07):
And please continue to enjoy your boba at your own risk.

Speaker 2 (47:10):
Well, we hope you enjoyed that. Thanks for joining us,
see you next time.

Speaker 1 (47:22):
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
from iHeartRadio, visit the iHeartRadio Apple Apple Podcasts, or wherever
you listen to your favorite shows.