What Is The Emptiest Place In The Universe?

What constitutes a vacuum? Can space ever really be empty?

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Episode Transcript

Speaker 1 (00:07):
Hey, Daniel, I've kind a dumb question. Oh, those are
always the hardest questions to answer. Why is it hard
to come with a dumb answer? He said, You know,
what people call dumb questions are sometimes really simple, deep questions,
and those are the hardest but sometimes the most fun
to tackle. Okay, here's my dumb question, Daniel. Where where
does space start? You know, like, technically we are in space,

(00:29):
but we don't think of ourselves in space. We're sort
of on Earth. There's an official definition a hundred kilometers up.
That's the official beginning of space and stuff, and that
sounds totally made up because it's a perfectly round number.
All right, Well, I guess the question is what is
a space? Right? It's it's kind of like when you
no longer have air, or when there's a vacuum. Yeah, exactly.

(00:50):
It's you know, when you're out there, like deep into space,
you know, when you're not there here on Earth, and
the boundary between them is it's a bit funny, you know,
it's sort of like growing up. You know, officially you're
grown up on you turn a team, but it's not
like a moment when you suddenly get wisdom and context
and vision and understanding and perspective, and you can make

(01:10):
grown up decisions. You know. It's something that very slowly happens.
Well Offecially, the government does give you a certificate in
your a team. That's right, Please register for the army. Congratulations,
I'm being an adult. Yeah, you saying technically, I I'm
I haven't grown up like technically you may. You may
never grow up. That's right. You and Peter Pan are
officially not grown up. There you go, Peter Pan, the

(01:31):
first thats wrong? That's probably truck too. H I am

(01:52):
or Hey, I'm a cartoonist and the creator of PhD Comics. Hi.
I'm Daniel Whitson. I'm a part of the physicist I
work at certain smashing stuff together to reveal the secrets
of the universe. And I am not a cartoonist. That's right. Also,
I forgot to mention, I'm also not if this isis
but in any case, welcome to our podcast Daniel and
Jorge Explained the Universe, a production of I Heart Radio

(02:12):
where we explain all the crazy and amazing things that
are out there in the universe and we have long
conversations about it. That's right. We're gonna take a mind
blowing tour of all the crazy stuff out there in
the universe. And the most important thing is that we're
going to do our best to explain in a way
that actually makes sense to you and hopefully entertains you
along the way. I mean, where else can you sit
for an hour and hear about nothing? Literally nothing? That's right.

(02:36):
We are going to get spacey today, folks. That's right.
Today on the program, we're gonna be asking the question
can space be empty? Truly empty? Like nothing? That's right?
What's actually out there in space? If you went out
into space and you like grabbed a big box and

(02:57):
and closed up some space, what would you capture? Is
space pretty empty? Is it mostly full of stuff that's invisible?
What's going on out there in space? And you can
think of this question for those of you keeping track
at home as part of our Extreme Universe series, This
one sort of like what is the emptiest place in
the universe? Where in the universe is space? The space

(03:19):
is yeah, I think most importantly, can it be empty?
Like is it possible to have nothingness in space? That's right? Yeah,
And that's a fun question too, like do you mean
experimentally like could we build something which makes a cubic
meter of truly empty space? Or theoretically, like is it
is it against the laws of physics for space to
be empty? Yeah? Or I mean just are there's are

(03:41):
there spots out there in the huge universe that we
live in that are really truly empty? Do you know
what I mean? Like we know that you know that
we know the stuff right here on Earth, on on
this planet, but are there parts of the universe where
there's truly nothing in there? That's right? Because the universe
is huge, it certainly a lot of space out there, right,
and not that much stuff. You know, you just look

(04:01):
up at the night sky and it's mostly space, right,
There's not that many stars, even if you have a
really amazing telescope because he really really far away, there's
a lot more space than stars. And so that makes
me wonder, and I think other people wonder, like what's
in that space? How empty is it? How much stuff
is there in space? How spacey is space? How spacious?

(04:22):
I think maybe the question is how spacious is space?
How spacious in space? Exactly? Is there room for me
to move out there and like really spread out with
my stuff? You got a lot of stuff in storage.
You're gonna take out an unpack, right, Yeah. And we
have had podcasts about how big the universe is, right,
and what's the biggest thing in the universe, But this
is the first time we're asking can't space actually be empty? Yeah? Exactly?

(04:44):
How empty is it? So as usual, before we dig
into the topic, I thought I would crowdsource of information,
and I walked around the UC Irvine campus and I
asked people, what do you think would be in a
random cubic meter of space? How empty is it? Is
there stuff out there? Or is it mostly empty? Yeah?
So thank for a moment before you hear the answers,
and ask yourself if you encountered a random physicist on

(05:07):
the street and they asked you, what do you think
is in a one cubic meter of space? What would
you answer? Here's what people had to say, what's in
a random cubic meter of empty space? Do you think of? Adams? Adams?
That's all I can think of. Jeez, I'm not too sure. Um,

(05:29):
I don't know. I know that the particles is what
I'd assume, cubic million, moleculous, preaky million. I don't know.
Guessing it depends where you're on. I mean, if you're
out in space, it'll just be filled with space. I
mean if it's space is empty, then there's nothing. I'm

(05:49):
assuming of the matter. We know, probably nothing, but there
could be dark energy and that cubic meter or dark
dark matter. Cool third reaffraightation. Awesome, thanks very much, dark matters,
dark quarters, dark matter, and yeah, I mean I'll watchally
all dark matter. What about like far between galaxies? Um,

(06:13):
is the dark matter everywhere? Or is it just near
the galaxies? No, it's I think it's like every open space.
You're like like in between like planets and stars and cool,
all right, I would say that there's stuff in there.
I wouldn't say it was like completely empty space. It's
probably a bunch of its particles or components of something.
I would say, okay, dust, there are different types of particles.

(06:37):
Is it totally empty? Vacuum energy? I guess all right, cool,
you'd probably get some particles of some swords like how
many holding up to like eight grade science? Al Right?
I like, I like, um, most people just said stuff
like I feel like, did you just say maybe? I mean,

(06:58):
you couldn't just say the Big Bang that would have
in it physics remnants of the Big Bang. I mean
that's always correct, but stuff is also pretty versatile as
as a physics answer. Well, that's sort of the question
is space have any stuff in it? And so if
you want to make it binary, like you know it's
empty or there's stuff and it, then these people were
voting for stuff. I think a lot of people have

(07:19):
the sense that space is not truly empty, that there's
always something in there, even if you can't see it. Oh,
I see you're saying that most people didn't say nothing
or vacuum. Do you know what I mean? Like, most
people assumed that they had stuff in it. Yeah, exactly.
That was the sense that I got from most people
that they weren't quite sure what was in there. They

(07:39):
thought it was mostly empty, but not truly empty. There
was still some residual stuff in there. So if you're
giving a test annual in a student, you as like, um, hey,
what is quantum physics? And the student writes stuff, what
would you would you taken a clean market wrong? Oh
for sure, yeah, but I always give credit. Um, I
always have a lot of partial it and you always

(08:00):
get some points for writting down anything like even stray
pencil marks. I will get partial credit for sometimes really,
because when it's when they leave the space empty that
you really bothers you exactly pure empty space that bothers me.
For that, you get a zero right reflecting the amount
of effort you put into the problem. But you write
down something anything, um, I'll give you some points. Maybe

(08:22):
you didn't know this. At the end of all of
my mid terms, I also do a physics cartoon contest. Really, yeah,
what do you mean? I pick a random cartoon from
the New Yorker, usually that looks a little physically like
there's a wheel or something physically in it, and I
asked them to write a physics related caption for that
cartoon related to what they learned on the exam. Well,

(08:44):
hopefully they didn't learn it on the exam hopefully before
for yeah. And then I have the ta tas always
created and I tell them if they write anything, give
them a point. If they write something that actually makes
you laugh, give them two points. And you know, sometimes
these kids are pretty funny. I can imagine being stress
stressed out student thinking, oh my gosh, should I devote

(09:06):
my last two minutes of trying to come up with
a clever caption, or should I try to solve this
quantum physics problem. Well, I hope it will get more pointive.
I hope you give them a little bit of stress relief.
But it's actually some interesting stuff in the physics education
literature that shows that making people think about the the
about physics in the context of their real lives or

(09:26):
in real life contexts helps them understand these concepts. So
it's not just a joke on my part. It's like,
I really think that it helps them understand. They have
to think about, how is this relevant to some situation?
Oh interesting, haven't kind of take a step back and
try to find a think about the context of the
stuff they learned. Yeah, exactly exactly, because we don't learn

(09:47):
everything in the vacuum, right, it's not just out there
floating in space. Right. Well, now, now I'm a little
nervous for the universe. I feel like if the universe
is truly can be truly empty, you might give it
zero points, no partial. Well, you know the universe is
making it ever um talking about being truly empty. When
I was doing some reading for this episode, I was
shocked to discover some things about what we consider empty

(10:10):
space here on Earth. You know, here on Earth, we
can do things that create vacuum in the lab, right,
people do this to to do all sorts of experiments,
and we have pretty good vacuum for example, the large
age on collider where we smash protons together. We suck
all the other stuff out because we don't want it
to interfere with the collisions. But it turns out that
that vacuum is not really empty like at all. If

(10:32):
you look at the density of air that we're breathing,
like the air that I'm breathing right now, there's about
ten to the twenty five molecules per cubic meter. So
that's a huge number, right, like ten with twenty five zeros.
I don't even know what the scientific prefixes for like.
And it's all like air molecules and gas molecules. And

(10:53):
and when they when they make vacuum, they pump the
air out, right, they suck it all out. Sometimes they
even bake it to try to get as much the
air out of it as possible. And you'd imagine they
maybe they get it down to really pretty good vacuum.
But what they call like ultra high vacuum in the
lab still has like ten to the twelve or ten
to the fifteen particles per cubic meter, which is still

(11:14):
a huge number, right, I mean it's a much smaller number.
You're down like ten or fifteen orders of magnitude, but
super high vacuum here on Earth is filled with particles.
What do you think is a limitation? Why can't they
suck out those last few particles? I mean last few
by me, I mean the last ten to the fifteen
part exactly. It's difficult. You know, you've gotta have really

(11:36):
powerful pumps, and you've gotta have no leaks. You know,
it's really pretty tricky. It's hard to get nothingness, like
to pull everything out of a space, yeah, because the
pressure on it is tremendous. Right, If there's nothing in it,
then things are pressing on it from all sides, and
then there's nothing in it to push back, right, So
things are trying to squeeze in everywhere. So you have
like the tiniest little gap, like an atom sized gap

(11:58):
in your in your well did seem or something, and
particles are going to find their way through. It's a
very powerful pressure from the outside, and you know, vacuums
don't suck, right, It's not like the vacuum inside this
machine is like actively sucking stuff in. It's all the
air outside that's pressing down, that's pushing in. Wait, what
do you mean it's not the vacuum. Well, you can

(12:20):
think about it in two ways, but I never like
thinking about the vacuum is like actively sucking stuff in.
It's not like there's something inside a vacuum chamber that's
going right. The reason things like things get sucked into
a vacuum, it's not like a black hole black holes
actively pulling stuff in. The reason things um rush into
a vacuum is because the air is being pressed into it. Right. Well,

(12:45):
you know, my grandma used to say, nature abhorts a vacuum.
Did your grandma invent that? Right? I think she invented that.
I'm not quite sure, but she used to say it. All.
My grandma used to say, I think therefore, I am wow,
that is still original. Over they are Our grammars were contemporaries,
geniuses of modern philosophy. She said, she ab pours vacuuming.

(13:08):
I'm not quite sure which one, probably probably the ladder. Okay, sorry, yeah,
exactly say you're in a spaceship, right and there's a leak, right,
then is the vacuum sucking all the air out of
the ship. No, it's the air and the ship is
like a balloon. It's under high pressure and you get

(13:30):
a leak and the air is pushing itself out. Right.
So the reason when you when they open the airlock
on a spaceship on a movie and you get that
tremendous wind, it's not the space sucking the air out
of the spaceship. It's the air pushing itself out because
it's under pressure. Okay, So we're talking about space and
whether space can be truly empty, right, and so the

(13:52):
question it is space like the perfect vacuum. Is there
really nothing out there? And the point I wanted to
make was that even super good vacuums here on Earth
are pretty terrible when it comes to when it comes
to relationships to space. So I just wanted to set
that stage right that we're gonna be talking about a
certain number of molecules per per cubic meter and the
air you breathe. This tend to the twenty five molecules

(14:13):
per cubic meter and the air and a super awesome,
fancy vacuum is like ten to the twelve particles per
cubic meter. Okay, so that that that's like the goal
you're saying, that's the gold standards for vacuum nows here
on Earth. That's right, Yeah, in terms of human engineering exactly. Yeah.
And um, so so let's take a tour, right, Let's
go up from the planet and think about and explore

(14:36):
space and and talk about how much stuff there is
in space as we leave the Earth, because the fascinating
thing to me is the amount of stuff in space.
The emptiness of space changes where you're depending on where
you are in space. So the answer to the question
is can space be empty you're saying, changes depending on
on where you are. Yeah, there's different levels of spaces. Yeah,

(14:59):
different levels of spaciness exactly. So for example, um, let's
dig into it. Like, if you take off from the
Earth and you leave the Earth's atmosphere and you're out
in space, then you're you're in this extended region we
call the heliosphere, which is where the Sun dominates and
the Sun is pumping out particles all the time. We
call it the solar wind. So yeah, you're far away

(15:20):
from the Earth's atmosphere, but you're in this region of
space that's filled with particles streaming from the Sun. And
that's basically the entire Solar system, right, I mean, basically
the entire Solar System is kind of within the heliosphere. Yeah, exactly,
the entire Solar system. And if you look, if you
Google image search heliosphere, you'll see that the heliosphere is

(15:41):
much bigger than like even the orbit of Pluto, because
the soul of the Sun dominates the local environment. At
some point, Peter's out and like the magnetic fields inside
the galaxy start to take over. But in the environment
around the Sun, you know, the the space in our
Solar system is dominated by the solar wind, and the
solar wind has all these particles that come from the

(16:02):
outer level of plasma of the Sun, which is obviously
glowing hot and shooting out light, but also shooting out
electrons and protons and other kind of radiation. So you're
saying the space in between planets, like between here and Mars,
here and Jupiter here in the Sun, it's not empty
at all. It's like it's full of sunweather exactly. It's

(16:22):
full of solar weather and it's about five to ten
million protons per cubic meter, which is still you know,
a hundred or a thousand times better than the vacuum
chambers we have on Earth. But it's not in zero.
So you said protons. Are you saying protons mostly because
that's that's those are matter particles? Yeah, exactly. Well, the
solar wind is mostly electrons and protons and a few

(16:45):
other kinds of particles, but mostly it's it's it's those
protons and electrons, and so you count them in turn.
And the protons are much heavier than the electrons, so
they dominate the calculation. Oh, I see they count of stuff,
but like photons, and do they count it stuff photons?
Do photons counts stuff? Hmm, that's a good question. Um.
You know, later when we talk about what's in in between,

(17:06):
like superclusters of galaxies and all we have is energy,
then I think you'll have to count that. Um. But
you know, photons are not matter there they are radiation though.
That's a great good question. So you're saying, within the
Solar system, the space is still not empty, it's full.
It's still full of stuff from the Sun. That's right,
And we should remember that all the stuff that we

(17:28):
know about everything that's made of atoms, right, that's a
little fraction of the universe. Right, that's only five of
all the energy in the universe, and it's about twenty
of all the matter. The stuff in the universe. The
rest of it is dark matter, and we and dark
matter normal matter both cluster into structures like you know,
planets and galaxies. Whenever those are the structures of normal matter,

(17:50):
dark matter follows those. So basically you can think of
it like anywhere you see blobs of matter, there's also
dark matter there, and about five times as much. So
there's five million protons, you're saying, there's probably twenty five
million amount of stuff of dark matter in that in
that space between planets. Yeah, and then we don't know

(18:11):
a whole lot about the structure of dark matter. We
know clumps at the center of the galaxy and then
spreads out. We don't know how clumpy it is, if
it's pretty smooth or if it's not. But on average, yeah,
you can just take the amount of matter and multiplied
by five, and that's a pretty good estimate for how
much dark matter there is. Like in this room with
me right now, you know, in the air I'm breathing,
there's what ten to the twenty five molecules of air

(18:34):
right that much mass, there's five times as much dark
matter in this room per cubic meter with me right now,
And the same is true out in space. Dark matter
follows the normal matter. So you can basically just multiply
the normal matter by five and it tells you how
much dark matter there is. So there's still a lot
of stuff out there in the Solar System. The space
is not quite into but it's sort of really empty

(18:56):
compared to what we can do on Earth, right, Like
you're saying, here on Earth, we can you tend, but
you're staying out in between the Solar System, between planets.
It's about tend to the six tend to the six,
which is much better than vacuums on Earth. But it's
not that small. And in fact, if you're an astronaut
you need you need like really really good sunscreen because
it's enough radiation to fry you and give you cancer

(19:18):
pretty quickly. So the fact that it's not empty has consequences.
Oh you're saying, if it if it was, if you
were just out there in a very really thin space,
suit without a whole lot of protection from radiation, you
would get fried from that radiation. Wow. So the fact
that it is pretty empty means that you feel those

(19:39):
that light from the Sun a lot stronger. Exactly. We
have an atmosphere between us and the Sun that protects
us from the solar wind. Right, the solar wind doesn't
come down to the surface because we're protected by the
buff or the atmosphere. But out in space you're not
shielded by that, and so you feel the full brunt
of the solar solar radiation. And uh, yeah, it's dangerous stuff.
It's dangerous stuff, is it? There's stuff out there and

(20:01):
it can kill you. Right, you'll run through traffic, folks.
It should be the title, right next book, can you
space traffic? All this stuff they can kill you. Space
can kill you. Well, let's let's take off from the
Solar System and let's go into interstellar space. But first
let's take a quick break. All right, we're talking about

(20:33):
how empty is space, and we we learned that um
that inner inner planetary space, like between us and other
planets in our Solar system, is pretty empty, but not
quite empty. Right, there's still millions of millions of protons
and stuff in like a cubic meter of space, right,
and there's a lot of cubic meters in that space.
So you're talking a huge amount of particles, Like if

(20:55):
you have to count them or number them or name them,
I mean, it's it's too big a number to really
think about, which, which is sort of strange, is cognitively
dissended from the fact that we think of it is empty. Right,
So remember it's just like chok full of particles, right,
It's like you're swimming in protons and stuff exactly, You're
literally swimming in it um. But then once you leave

(21:15):
our Solar system, you go past the heliosphere, and only
a couple of man made objects have ever done this,
like the Voyager probes. They've been traveling for decades and
they finally broke past into like the inter interstellar space,
like the stuff that the galaxy is made out of.
So you're saying that the stuff that comes out from
the Sun, all those protons and ions and stuff, at

(21:35):
some point kind of doesn't go on forever, right, like
they maybe they come back because of gravity. Is that
is that kind of what happens, Like they cluster around
the Solar system. Well, they Peter out there at the
intensity gets less and less just because the volume gets
larger and larger um. And then also they hit the
interstellar magnetic field, right, what, there's magnetic fields inside the

(21:57):
galaxy you mean, And and that's different than the one
we feel inside the solar system. Yeah, because our solar system,
the magnetic field is dominant by the magnetic field of
the Sun. Right, And the same way the Earth's magnetic
field also helps shield us from the solar wind, right,
the Sun's magnetic field helps shield us from like the
galactic wind. Whoa h yeah exactly. But then if Peter's

(22:20):
out right, and you're no longer really protected by the
Sun's magnetic field, where the point where the Sun's magnetic
field is about as strong as the magnetic field of
the galaxy, right, and you're really really far away, and
so the density of these particles the solar wind is dropping.
That's when we say you're you're in the interstellar space.
You've left the heliosphere. So who gives you a certificate

(22:40):
that at that point you can make your own certificate,
because you can do anything, because you've accomplished something nobody's
ever done before. Just bring your own printer and print
yourself a little certificate. Well, that's probably where the you know,
our our alien overlords are waiting for us. Oh, I see,
so you're saying that they're just waiting to I ne
something as as we step out there. Yeah. Sometimes I

(23:03):
think that the reason we've never heard from alien species
is that they're running some massive cosmic zoo, you know,
and they're just out there watching us, laughing at all
of our antics. And then all we need to do
to figure that out and just get out there and
say hello. And maybe they're like hanging out there waiting
for us to um, you know, get far enough away
from our planet that we're really talking to you. They're
just waiting for us to get put us back into

(23:24):
our cages. Is that don't make me use the house
exactly again for the first time. Um. So, if you
do get out there, if you do get out there
past our solar system in the in the area dominated
by the Sun, then you're in what we call the
interstellar medium. And this is mostly gas. It's like gas

(23:48):
and a little bit of dust in some cosmic rays. Okay,
what's the difference between gas and dust? Is it that
like more complex atoms and stuff. Yeah, dust is like
pulverized rock, right, So you have the stuff from the
inside of supernova and old planets that got destroyed and whatever,
and so yeah, you have like metals and and all
the silicates and all sorts of stuff. That's what dust is.

(24:11):
Gas is masic, just hydrogen, right, most of the most
of the universe is gas, and most of that is hydrogen.
So it's a proton with electron whizzing around it. Well,
and what's the concentration at that point? It actually varies
a lot once you get out of the Solar System
past the heliosphere. At the high end it's about a
million molecules per cubic meter, which is just a little
lower than the density inside the Solar System. But then

(24:33):
at the low end it goes down to about a
hundred particles per cubic meter. It's because the galaxy is
just not that smooth right there, like hot spots and
cold spots, the spots where it's more dense and spots
where it's less dense. So it varies between like a
hundred and a million molecules per cubic meter. In the
interstellar medium, the spaces between solar systems. Well, here's here's

(24:54):
a question. How do we know what spaces like out
there if we've never been there, been there present, that's
a great question. Well, we haven't been there personally, but
we have sent for example, the voyager probes, right, um.
And after that, we have models, right, we have models
that describe how galaxies are formed and how some how

(25:14):
stars work and the radiation we expect from them. And
so we can we can see you know, activity from
that gas because you know it ionizes or it or
it deflects light, and so we can probe it even
without going there, just by seeing like stuff go through it. Right, Okay, cool,
So we we're sort of guessing in a way. I mean,

(25:35):
we have models, but we think that's what the emptiness
is like up there. Yeah. Well, if there was a
lot more, for example, then we would see more absorption
of light. If there was a lot less, we would
see less absorption of light. Remember, gas absorbs photons, and
so we can have some measure of the gas and
the dust in our galaxy by just by seeing how
light is absorbed. So that's kind of the space inside

(25:57):
the galaxy between star in between solar systems that's that's
the interstellar medium, that's right. And remember to multiply by
five for a dark matter because there's a lot of
dark matter in the galaxy, and the galaxy is mostly
dark matter, and between the stars is definitely oodles and
oodles of dark matter on average, right on average. We
don't really very know very well the distribution. We know

(26:20):
again it peaks near the center of the galaxy and
that the amount of dark matter extends past the visible
edge of the galaxy, but we don't know that much
about exactly how it's distributed. So pretty empty, it starts
to drop off exactly once you get out past the
edge of the Solar System, but still pretty full of
like dark matter and and in some gas. Right, So,

(26:45):
now what happens if you keep going that, if you
keep going past our Solar system, past other solar systems
and out of the galaxy. What what do we get?
Well out there between the galaxies is something we very
cleverly call the intergalactic medium. And um, this is not
very exciting, and it's basically these it's it's mostly empty,
it's these strands of of plasma really really really dilute plasma,

(27:10):
and so it's mostly ionized hydrogen. That's what we mean
by plasma, and it's on average like one to ten
molecules of hydrogen per cubic meter. Wow. That so for
for a cubic meter, which is like a large moving box, right,
you would only see one to tend atoms of stuff. Yeah, exactly,

(27:33):
And so that's pretty empty, right. You could like take
a whole cubic meter and look all around and see
like one or two or few atoms inside the entire box.
That's so much more empty than a vacuum here on Earth.
Between galaxies, is what you're saying. Yeah, exactly, you're between galaxies.
And the thing that kind of blows my mind about
this is that, remember, the galaxies are really really really

(27:55):
far apart. So even though the density of stuff out
there is almost zero, if you add it all up,
all the stuff, all the matter between galaxies, a counter
about half the atoms in the entire universe. What Yeah,
so like half the atoms in the universe are in galaxies.
Half the atoms and the universe are not in galaxies.

(28:19):
And the reason that makes sense is that galaxies are
tiny compared to the space between galaxies. So if you
want to fill all the space between galaxies. With even
a really really low density of molecules, it takes a
lot of molecules to spread it out. It's like spreading
your frosting really thin across the cake. Wow, that's amazing
to think that there's more. There's as much stuff in

(28:41):
empty space quote unquote what we call empty space as
there are and like all those black holes and stars, stars,
the hamsters, hamsters, bananas, half of so much stuff is
just floating out in this super ultro vacuum. Yeah, exactly.
And between these galaxies also, we think they're must be
some dark matter. We don't know because it's really hard

(29:03):
to see dark matter. Remember, we only see dark matter
because of its gravitational effects, which means we can only
really see it when it's pretty dense, like the center
of a galaxy or a big blob. And so between
galaxies there might be these filaments there's a rarefied thin
strands of dark matter, but it's pretty hard to see that.
We can't see those directly. And again we know this
because it was if it was not that empty, then

(29:26):
we wouldn't be able to see other galaxies. So clearly
that's right, that's how we know, but the composition of
intergalactic space, because we can measure the absorption of photons
between here and there, and so we can sort of
like integrate over here to there and figure out how
many how much light was absorbed, how clear the spaces? Yeah, yeah,

(29:46):
And the other interesting thing that happens when you go
between galaxies is that you have to start to account
for the other crazy thing in the universe, which is
the dark energy. Right we said before that matters five
percent of the stuff in the universe. Dark of matter's
five times as much as this like of that, the
rest of it is this thing we call dark energy.
And the really weird thing about dark energy is that

(30:08):
it's not clustered at all. Right, Matter it gets pulled
together by gravity. You get planets and stars and galaxies.
Dark energy is spread uniformly, right, So it's equally present everywhere,
right even here with those right now, right right, that's
right between me and this microphone, between you and your seat, everywhere.
But because the universe is so big, spreading it uniformly

(30:29):
means it's not very dense. So, like if you added
up how much dark energy there is here on Earth
or in this room with me, there's almost none. But
once you start getting out there into really really far
stretches of space where space becomes huge, then it starts
to take over huge and empty, right, huge and emptier
and emptier. Exactly right. Yeah, I mean I think what
you're saying is that out there there's so little stuff

(30:51):
matter that basically dark energy is like that the main
thing going on out there. That's right. Once you get
outside our galaxy and then you get like outside the
cluster of galaxies that we're in, we're inside this cluster
of like thirty or fifty galaxies that are all sort
of orbiting each other, and there's these there's this plasma
between us, this intergalactic medium, um, this sort of infilaments

(31:13):
between the galaxies. Once you get past the cluster, then
you're in inter cluster space, and that's mostly dark energy.
I'm gonna I'm gonna take a wild guess and say that,
um guess that you guys call it the intercluster medium.
That did get that, and you got it right. And again,
I wish that you had been there the day that
that name was given, because I'm sure you would have

(31:34):
come up with a much better name. Um So, so
out there is mostly just dark energy, because it's really
sort of is kind of empty space, right, there's no
not very little stuff. Yeah, exactly. You can't go much
lower than one atom per cubic meter, right, you start
to get to like less than an atom per cubic meter.
And so that's what happens, like out there between the

(31:54):
clusters of galaxies, the number density of matter drops to
almost zero. So are you saying that if it drops
below one atom cubic meter, it means that there are
some cubic meters that have no atoms. There are definitely
cubic meters with no atoms. Yeah, if you have point
one atoms per cubic meter doesn't mean that every cubic
meter has a tenth of an atom. It means you

(32:16):
need ten cubic meters too, on average have one atoms,
which means it's nine of them without it. Okay, So
that that sounds pretty empty. Isn't that basically empty? It's
basically empty, But you know it's not totally empty, right,
and there's always dark energy in there. And the fascinating
thing to me is that, um, there's no box of

(32:38):
space that has no energy, right, Space itself always comes
with dark energy, right, like dark energy makes space and
space contains dark energy. We don't understand it. We don't
know what it is. We don't know where it comes
from or how it's happening, but we know it's there.
And what that means is that every place in space
has energy, and energy and mass are not that different.

(32:59):
Right equals mc squared. So what that means is that
anywhere there's energy, you can create mass. Like you have
a little density of energy, it can turn into particles
very briefly and then turn back into energy. Right. But
that that's kind of as far as we know, right,
because you're saying we don't really know that much about
dark energy. I mean, as far as you know, it

(33:20):
could maybe have little variations in it, couldn't it. It could.
The current thinking is that it's uniform, that it's spread
everywhere through space, that it's a property of space itself.
But you're right, we're pretty clueless, and so it could
be the dark energy is totally something different and that
we're wrong, and it has interesting structure. I suppose that
would be amazing, But the current thinking is that it's uniform.

(33:42):
All right, We've gone all the way from the planet
Earth vacuums and emptyness and planet on planet Earth all
the way to solar systems and galaxies and intercluster space.
So let's let's go even beyond that, Daniel, Let's go
way past that um. But first let's take another break. Okay.

(34:11):
So we we've gone from the earth emptiness of space
on Earth, to the Solar System, to the galaxies, to
inner clusters of galaxies, and we get pretty empty. You're saying,
you know, maybe less than one atom per cubic meter
out there between clusters, but you're saying that there's still
kind of an inherent energy and inherent stuff to space itself.

(34:33):
That's right. If you zoom out even further, remember that
clusters form their own kind of clusters that we call
cleverly superclusters, right, and that these superclusters then form these
big sheets, these big, these vast stretches which enclose enormous voids,
so they're really like frothing bubbles right where the edges
of the bubbles are all these superclusters of clusters of

(34:55):
galaxies of stars. And to what's inside those voids, well,
this essentially no matter. I mean, we don't know. We can't,
like we haven't measured it the way we've measured these
other things, so we know it's a very very very
small amount of matter, like a number of protons is tiny.
But you know there's dark energy there, and there's energy
in space itself. You know, for example, the Higgs boson

(35:18):
the Higgs field is something which even if there's no
particles there, it still has energy. Something we call the
vacuum expectation value is non zero, like the ground state
of the Higgs field is not at zero, which means
this energy in every space and energy can get turned
into mass. There's this fun thing about quantum mechanics where

(35:38):
you can create virtual particles. You have energy, you can
briefly create mass out of it and then back into energy,
and so that's probably happening everywhere in the universe. You
take a random box of space inside one of these
super voids inside the bubble, and briefly particles will be
being created and then destroyed. But that's a quantum physics thing, right,
isn't it. Yeah, exactly, that's kantom mechanical. There's this uncertainty

(36:02):
and this randomness, and some particles are always fluctuating in
and out of the vacuum. So you're saying, theoretically you
might be able to have truly empty space, but it's
sort of not empty all the time forever. Yeah, say
you like did the painstaking job or removing every single
particle you found from a cubic meter, then you go
back to be like, wait a second, I just found

(36:22):
another particle. What it disappeared? Oh wait, there's another one
over here. It's sort of like playing quantum Waca mole
because you can never get all the energy out of
that box and say you can effectively not ensure that
there's no matter, right, you can't ensure there's zero matter
in there because you can't get all the energy out,
and energy you can always fluctuate back into matter. And
that's a property you're saying, a property of space itself,

(36:45):
Like space by itself has energy to it meat we
need has the propensity to make matter always. Yeah, and
remember that space is a thing, right, It's not like emptiness. Right,
Space itself is a thing. It can ripple, it can expand, end,
it can um, it can bend, and so there's some
has properties, right, And it's not nothingness. I'm not saying

(37:08):
nothing has energy. I'm saying space has energy. And we're
only just now beginning to grapple with what space itself is.
So if you think space having energy sounds weird, then
remember that space is a thing. It's like, you know,
fish scientists swimming through water and discovering that water is
a thing. Space is definitely a thing that has some energy. Now,
another deeper question is are there places without space? Right?

(37:32):
Is there past the edge of the universe? If the
universe's finite, are there places where there is no space,
no energy, and therefore no energy. That might be possible,
but that wouldn't be empty space. That would be emptyness
or nothingness or something. But that's pretty hard to grapple with,
you know. Conceptually, you're saying, it's sort of like if

(37:52):
fish scientists would be like asking having a podcast, a
couple of fish talking to the podcast, asking themselves it
and water be empty, and basically the answer is ridiculous
because we know water is stuff. That's right, And then
they're having trouble thinking about like is there an edge
to the pond? Like what's above the surface of the pond? Man,

(38:14):
what does it mean to not have water? I think
they would be sort of what they mean by antwer
would be sort of like, can can you have water?
Pure water? Right? Like water with noth no, no containmants
and it just pure h two oh. That that would
be the question for them that we are sort of asking,
can if space can be empty? Yeah? Exactly, And then
the deeper question for them would be can you have

(38:35):
places without water? And so we would ask can you
have places without space? Does that even mean anything? And
that's pretty hard to think about. So I think the
answer is we're pretty sure you can't have totally empty
space because of quantum mechanics and dark energy and the
Higgs Boson vacuum expectation value um, but you might be

(38:56):
able to have places without space or you know, past
the edge of the unit verse where her where the
space ends. But we don't know. That's that part is
really speculative. And maybe there is a part of the
universe that is all water with fish scientists asking that
question where all the podcasts are all wet, and I
think that their their podcasts are called podcasts. And so

(39:25):
to recap near the Earth, we have like a few
million molecules per cubic meter, and then once you get
outside the Solar system, it drops to like between a
million and a hundred molecules per cubic meter. Then between
galaxies it gets down to like one to ten per
cubic meter. But the emptiest place in space is out
there in the voids between the bubbles of superclusters, which

(39:48):
is crazy empty. Well, I guess the question that the
answer to the question can space be empty? Is yes,
sort of, but not all the time, or not an
average or not for long kind of I would say.
I would say most of the space we see is
not empty, and as you get further out, it gets
emptier and emptier and emptier to get pretty empty, but

(40:08):
never totally truly empty, but but not not all the time, right, Like, um,
you could my mic get a cubing meter with nothing,
absolutely nothing in it, no matter, but before long you'll
see matter popping in and out all the time. Yeah,
before long, meaning like ten of the twenty three seconds.
So congratulations in your accomplishments. That's that's what my grandma

(40:33):
would call it. A Panamanian minute. Okay, I don't know
what that means, but it sounds awesome, all right. I
hope that podcast filled your space with interesting knowledge and
ideas to think about. That's right, I hope we blew
your mind and injected some space in there. And remember
that we live in a vast universe filled mostly with nothing, yeah,

(40:53):
except on the in the space around you, So take
some time to appreciate all this stuff around you because
it could be pretty empty out there, all right. Thanks
everyone for listening, and if you have questions, send them
to feedback at Daniel and Jorge dot com. Thanks for listening,
see you next time. If you still have a question

(41:18):
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
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and Jorge Explain the Universe is a production of I
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(41:41):
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