How can we see Dark Matter?

We know it exists but what is it and how can we see it?

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Episode Transcript

Speaker 1 (00:08):
Wouldn't it be cool to have, um, like the power
to see invisible things, like if you had anti invisibility glasses. Yeah,
there's so much of our universe around us that we
can't see things that are going on all the time
that are invisible to us. It'd be awesome to invent
some new technology to reveal that, to peel back that
layer of reality and show us all the crazy stuff

(00:29):
that's happening. No. Yeah, I would definitely love to see that.
Do you have a million dollars to invent invest in
my startup? I have a million dollars, but um, maybe
not to invest in you, Dadia. Oh, somebody already got
to you with that idea, didn't they. Somebody already pitched
you Maybe maybe, But yeah, no, I like this idea
that there are invisible things out there in the universe

(00:51):
that are really important and are maybe determining my fate
and the fate of our planets in our solar system
and our galaxy. Hi, am Ory, I'm a cartoonist and

(01:17):
the creator of PhD comics. Hi I'm Daniel. I'm a
particle physicist. I've never created a web comic, but I
did co write a book with a web comic. It's
called We Have No Idea and it's all about the
unknowns in the universe. Oh man, that sounds amazing. I
would love to read that. You should, It's fantastic. I
did actually read it a couple of times as I

(01:38):
helped write it. Did you read your name on the cover?
For example? But welcome to our podcast Daniel and Jorge
Explain the Universe, a production of I Heart Radio in
which we zoom all around the universe and find cool
and fascinating and bizarre stuff to blow your mind. But
we don't want to explode your mind. We actually want
to take that stuff and insert it into your brain.

(01:58):
We want to break it down and make it acessible
and reassemble it inside your mind. That's right, when it
stuff in your mind with as much stuff as we
can't without exploding it critical mental density. That's where we're
going for in today's show. But yeah, all the cool stuff,
all the amazing stuff, all the dark stuff in the universe,
all the invisible stuff, all they have visible stuff and
everything in between, because there are invisible things out there

(02:20):
in the universe, right there are invisible forces and objects
and maybe even matter. There definitely is there's a huge
amount of stuff going on in the universe that is
not directly observable to us, and it's only recently that
we've been gone peeling back those layers of invisibility, figuring
out ways to subtly detect what's out there that we
haven't even noticed, right, And we also try to talk

(02:42):
about how scientists are trying to discover these things, how
they're trying to peel back that layer and understand what's
going on in the invisible universe. That's right. Sometimes I
think about it like scientists are are out there inventing
new senses, right, Like your senses are your ways of
interacting with the world. Old you can see, you can smell,
you can touch, all these things help you build up

(03:03):
a model of what's outside your body. Right. Well, scientists
were like trying to create new contraptions that are basically
new senses, things machines that can see things that we
our bodies cannot see, and they can translate what they
see into something that we can understand. That would be
cool if you can build me like a like a
radar helmet, like a radar chip, I can implant in

(03:25):
my brain and have like bad like abilities or dare
devil like abilities exactly. Well, um, if you have a
million bucks, you can put that towards the startup I'm
going to start after this show inventing the radar helmet.
That sounds like an awesome idea. Man, you're really hungering
for some hankering for someone for a million bucks here, Daniel.
But you know, we we do this kind of thing
a lot, right, We extend the power of our senses, right,

(03:47):
Think about like what X rays are, right. X rays
are these little invisible rays. You can't see them, but
we can use them to see inside of stuff, right,
to give us to translate what we couldn't see before
into what we can see now. Wow, Yeah, you're right,
physicists did invent X ray vision. That's right. We literally
happen literally right, Yeah, yeah, absolutely, And we do this

(04:11):
kind of thing all the time. You know. That's basically
what experimental physics is. It's like try to develop a
new technology that can discover things that nobody's seen before.
Like you know, we've talked on this podcast before about neutrinos.
Neutrinos are these weird little particles that are everywhere and
they're you know, part of the table of matter as
we understand them. But they're very very hard to see
because they mostly just fly through stuff. But physicists figured

(04:34):
out a way to spot them. It takes billions of
neutrinos to fly through your detector before you see one,
but we can see them in that way. We discovered
that they're there, that the air is full of them.
And so today we're going to talk about what scientists
are doing to see to actually maybe even touch a
very important part of the universe, very big part of
the universe, maybe even the biggest part of the universe

(04:56):
that's invisible to us. That's right. It makes up most
of the matter of the universe, like of the stuff
in the universe. It's literally the biggest mystery in the universe.
And so today on the program, we'll be talking about
how can we see dark matter, how can we interact

(05:19):
with it, how can we finally sort of see it
up close, touch it maybe and to understand what it is,
because right now we have no idea what it is,
right Daniel, that's right. We know that it's there, we
know that it's stuff. We know it's some kind of
matter because it creates gravity. But we don't know what
it's made out of. We don't know if it's made
out of particles, made at one particle, two particles, seventeen particles,

(05:41):
something else that's not a particle. You know, we only
have very indirect evidence, very solid, but indirect evidence. It's
sort of like you're solving a murder mystery and you
have a bunch of circumstantial evidence. You know that Joe
Schmo is the guilty party, but you don't have that
smoking gun, you don't have the bloody knife or something.
You're not going to rest until you really find all

(06:02):
the details that really conclusively demonstrate to you what happened
on that fateful night. And that's sort of the situation
in the case of dark matter. I mean, it could
turn out to be that I was a physicist in
the cloak room with the wrench, right, I mean, that's
what dark matter could be. It could be unicorns, it
could be it could have been the engineer in the

(06:22):
library right with the bag of dark matter, that's right,
trying trying to make things work. Engineers always have altruistic
motives in your mind, right, whereas scientists are out there
like trying to take over the world. Right, Well, you know,
I like to think engineers actually know what they're doing
and they're not toying with things they don't understand. You're

(06:48):
not trying to create black holes here on Earth, you know, Hey, hey,
there's nothing wrong with trying to create black holes on here.
And they're tiny, little, cute, very safe black holes. Okay,
right right, ped black holes, cozy little black holes, and
we got to rebrand them. You know, they sound so dangerous,
you know, unicorn black holes. Exactly do you feel like

(07:10):
they have a PR problem? Yeah? Exactly, black holes have
a PR problem exactly. And for those of you hearing
that we are trying to create black holes at the
Large Adrian Collider and worrying about it, we have a
whole episode dedicated to that, you are in no danger whatsoever. Wait.
I just thought of a really nerdy joke. Mm hmmm,

(07:31):
Actually black holes have an e PR problem. That's that's
a pretty nerdy joke. I agree. Impressive. Thank you. When
you have to laugh at your own joke and then
rib the other person into into acknowledging it, then that's
how you know it was a good joke. Those are
Those are the best jokes. Those are the dad jokes. Right,

(07:54):
you just made a combination scientist dad joke. It's a
whole new subgenre of humor, a dad scientist joke. Well
you fortunately, you are as bad scientists, so that hasn't
been right. They hit you right in the center. That's right.
I am your demographic h Well, that's that's all. Who's
listening to this podcast? Right? That's right. Hey, give me

(08:14):
a million bucks and I'll do a startup company with
dad's scientists jokes. Alright, but only if you pay your
podcast partner all of the million dollars. Done and done.
All right, we did some business today, all right. So yeah,
dark matter, we don't know what it is, and so
today we're going to talk a little bit about how
we might be able to see it and what scientists

(08:35):
are doing to actually see what dark matter is. That's right,
and to tease it a little bit. There are three
ways that we're looking for dark matter. You can either
shake it, break it, or make it. That's also a
recipe for cooking a delicious dark matter soufle I feel
like that's an informercial all now, and you will receive

(08:57):
our special offer for a shake it, break it, and
make it and that clever line about shake it, make it,
or break it is not something that I came up with.
I think the first person to say that was Jonathan
Fan He's a dark matter expert at You See Irvine.
All right, well let's see how we can shake, break,
or make dark matter. But first we were wondering how
many people out there think that we could ever see

(09:20):
dark matter? Or if we can see dark matter? That's right.
So I walked around the campus I You See Irvine
and asked folks, hey, do you think we could ever
see dark matter? And didn't explain to them what dark
matter was or give them much background, and just pop
this question on them. And so think about it for
a second. If somebody asked you randomly on the street, like, hey,
do you think we can ever see dark matter? Think
about for a second, how would you answer this question?

(09:42):
And would you give that guy a million bucks for
his dark matter startup? No? Well, anyways, here's what people
had to say. Have you heard of dark matter? Yes,
but I don't know what it is? Okay, give any idea?
How much see dark matter? Like? How dope? We just
discover it. It's like energy electrons. Maybe I'm not really sure,

(10:03):
all right, thanks very much. Have you heard of dark matter? Yes?
Do you have any idea how we could see or
discover dark matter? No? Because it isn't it just a theory?
Have you heard of dark matter? Do you know how
how might we see dark matter? I don't know if
dark I've heard of it, but I can't confidently see

(10:23):
about it. Do you know if it's something we could
ever see? Like? Can we see or detect dark matter?
One day? Probably? I mean I'm not sure now, but
I'm confident that one day we'll all find out what
it is and discover many things. Okay, I've heard of
the term. I'm not exactly sure. I know it's related
to like physics in space. Do you know if dark

(10:46):
matter something we can ever see? I can we ever
be able to see it or detect it? The name
implies that we can't, but I'm sure there are methods too,
I mean through like radiation, probably can detect if it's there,
but I don't know. Pre too visible to see. All right,
a little bit of optimism. Some people have never heard

(11:08):
of it, Yeah, some people were a little skeptical. I
like the well, it's just a theory, like I could
have gotten into a whole discussion there about what is
a scientific theory, evolution is a theory, what does theory mean?
But I just world have nodded and moved on. There
was one interesting answer here, uh that said that, UM,
that the answer is no because the name of it

(11:29):
implies that we can't see it. That's kind of a
pretty metaphysical answer, right, like, if we can't see it
one day, do we need to change the name of it? Oh?
I see, Well, I think that's a little bit more
thought than this person I had given it. Um. I
think they were not sure what dark matter was and
just trying to sort of grasping for clues about how
to answer this question based on the limited information in

(11:51):
the question. And uh, I think that's where they were going.
But I like, I like the idea that if we
see dark matter, we can't call it dark anymore. We
have to rename it. And probably you're angling to be
on that committee to rename it, because I know you
have opinions about how physicists have named things. It's not
that I'm angling, I just I just feel like anyone
could do a better job. Put that on your application

(12:13):
to be on the committee. Man, you guys are terrible.
Anybody could do a better job than you. Yeah, for sure,
they should put kids in charge of naming things. You know,
then we'd be called squishy rainbow matter. Yeah, there you go.
It would make a lot more sense and be harder
to write grand proposal saying please give us money to
see squishy rainbow particles. Right, unless it's also children reviewing

(12:35):
the proposals. Sometimes I think it is children reviewing the
proposals based on the referee reports. So Dan, it remind
us what dark matter is, right, So we don't know
what dark matter is, but we know that there's something
out there. We know that there's a bunch more stuff
in the universe than we can see. And we know
this in a few ways, but all of them just

(12:56):
use gravity. Gravity is our clue that tells us that
there's something us out there that has mass, because remember
mass is what creates gravity, a mass and energy. And
we have a few clues, like we looked at galaxies
and we see that galaxies are spinning really really fast,
and there doesn't seem to be enough gravity inside those
galaxies just from the stuff we can see, the stars

(13:18):
and the dust and stuff to hold those galaxies together.
So based on how fast they're spinning, the galaxies should
be tearing themselves apart, the stars should be thrown off
into interstellar space, but they're not. So people suggested this idea.
Maybe there's some invisible matter in there that's creating this
gravity to hold the galaxies together. And that's the key.
It's invisible. We can't see it, hence the name dark,

(13:40):
but it creates the missing gravity. We need to explain
how these galaxies are spinning. So they called it matter
because it gives gravity. So it's like we we can
feel it, but we just can't see it. Like we
can see it affecting the orbits of things around it,
and we can see it affecting how light moves around
it and through it, but we can actually see something

(14:01):
there or detect something there through light. That's right. We
can't use light to detective because it doesn't seem to
interact with light at all. It's invisible, you know, the way,
like the air is. You can tell the air is
there because it pushes against you, but you can't see it. Right,
you'd love to be able to see the air. Imagine
you had like glasses that you could see different air
currents and stuff like that. The world would look like
a crazy place. But we can see it only through gravity.

(14:25):
You can tell that it's there through gravity. And the
reason that's the problem. It's pull. Yes, we can feel
it's pull. And you might think, isn't that enough, Like,
I mean, you're getting greedy, Like you can already tell
the dark matter is there, why do you need to
see it? The thing is that gravity is really really weak.
It's the weakest force by huge amount, by millions and
millions and millions, and so we can only use gravity

(14:47):
to see dark matter when there's a huge amount of it,
like galaxy sized blobs of it. So that tells us
that it's there, but it doesn't really tell us what's
going on where the dark matter is, to see any
detail in it, to see this isn't made out of
particles or is it made out of something else? Really weird.
It's like it's enough to know that it's there and
roughly where it is, but nothing else about it. And

(15:08):
that's tantalizing, you know, because we want to know what
this is made out of and how it works and
does it interact and is there complicated stuff going on?
But we can't. Right, we're blind because gravity is so weak, right,
And and so it doesn't reflect light, like if I
shine a light into it, the light it is going
to go through, and it doesn't emit any light, Like,
it doesn't glow or it doesn't give off its own

(15:29):
energy that we can see. And so that's what makes
it invisible. That's right. Stars give off lights so we
can see them. Planets reflect lights so we can see them.
Dark matter doesn't either. It doesn't glow and it doesn't
reflect light. Yeah, it's totally invisible to loost. It's like
a ghosts ghost, Yeah, exactly. I like how sometimes you
say that it should have just been called invisible matter,

(15:51):
not dark matter. Yeah. I think probably there was a
meeting some somewhere somebody said let's call it invisible matter,
and then no, dark matter sounds cooler, and I think
dark matter does sound cooler. Honestly, dark implies something mysterious,
write something maybe a little sinister. One of my favorite
questions I get when we give public lectures is somebody
invariably asks, is dark matter like bad matter? Like is

(16:13):
it dangerous? You know, because it's an error of like
you know, sinisterns or what's the word cynicism sinisterism? Do
just call it evil matters? Well, I mean, who wouldn't
fund that project? Yeah, it's it's like the dark side
of the force, right, you know, it's just there, you go,

(16:34):
there's my million bucks boom, just like, Hey, there's evil
matter out there. We need to track it down. That's
something the current administration would probably go for you. Yeah, alright,
So that's what that's what dark matter is. Uh, it's
some stuff out there in the universe. There's a lot
of it. There's a there's like five times more of

(16:54):
it than regular matter. But we can't see it through
light or touch it because how we touch things is
the through electromagnetic forces, right, that's right. If you want
to push on the wall that's next to you, for example,
why doesn't your hand go through the wall. It's because
your hand is a bunch of molecules, and those molecules
are tied together with chemical bonds, which are mostly bonds

(17:15):
from electrons, and so though that uses electromagnetism. So your
hand is like a like a chain link fence, and
the walls like a chain link fence, and those links
press against each other. So electromagnetism is the dominant force
and how you see things and how you feel things
in dark matter just doesn't feel it at all. So
it seems kind of unlikely that will ever be able

(17:35):
to touch it or see it or know what it
is with any kind of resolution. And so let's get
into this idea of shaking it, breaking it, and making it.
But first let's take a quick break, Okay, Daniels. So

(17:59):
dark matter, it doesn't give off light or reflect light,
or it doesn't even care about light, and just light
just goes through it or magnets. Hey, you don't know that.
Maybe it's like feeling left out. It's like, hey, this
is this LFE part of the universe and all this
fun stuff is happening, and we're stuck over here in
the dark corner. Maybe we should call it sad matter
then depressed matter exactly. But yeah, so but you know,

(18:23):
and generally you can't touch up with light, you can't
touch it with a magnet, you can't touch it with
your finger. Um, but we know it's there because we
feel it's gravitational pool. So you're saying that that that
gravitational poll is not enough to really study it, to
really kind of kind of like run it through your
fingers and study what it is and what it's made
out of. That's right. The goal is to get a

(18:45):
finer grain sense of where it is, like where on
Earth is the dark matter? Is it just a big
diffuse blob. Is it clumped up somewhere? Is it all
gathered in the sun. You know, we'd like to be
able to see it much more, a much finer grain resolution,
which requires interacting with it more powerfully than gravity can do. Um,
that's one thing. And the other thing is we'd like
to know what it's made out of, right, like is

(19:07):
it made out of particles, it made multiple particles or
something else totally different, And that definitely requires seeing it
more up close and interacting with it. And so currently
the only thing we can do is gravity. And you know,
let's start off pessimistically. It might be that dark matter
only feels gravity and that's the only force that ever
will feel, and that seeing it or touching it or

(19:27):
whatever is totally hopeless. But we have no concrete evidence
that it has to feel another force. We have some
indirect clues from the way things happened in the early universe,
but nothing really solid. Well, here's a question then, I mean,
we know that dark matter doesn't feel light or electromagnetic forces,
and we know it doesn't feel weak forces or strong forces.

(19:51):
I know it's because I listened to our podcast episode
about dark matter. Um, but um, how do we know
it doesn't feel maybe some other forces, some other year
to undiscovered forces in the universe. Yes, in fact, we
are hoping that it does, right, We are arresting the
entire This entire field of searching for dark matter rests
on the hope that there is some new kind of force,

(20:11):
some way that dark matter interacts with itself and with
our kind of matter. So if it only interacts with
via gravity, then we're kind of sunk. All we can
never do is do observational astronomy and see galaxy sized blobs.
But if there is some new force we haven't discovered yet,
then maybe it can mediate the interactions between normal particles
like electrons and corks and these dark matter particles. So

(20:34):
that would be awesome because you could make two discoveries
at once. You discover some new force which is huge,
and you discover that that new force interacts with dark
matter particles, so you discover a new force and a
new particle and the same day, like two discoveries for
the price of one. Is that possible though? Is it
possible that there is another force that we haven't noticed? Oh? Absolutely, absolutely,

(20:56):
it's possible. Yeah. I mean we've only studied a tiny
fraction of the universe and the interactions between those particles,
So it's certainly possible that there are other kinds of
interactions that we haven't noticed because the particles were familiar
with don't interact that way. Oh I see so, but
so then we wouldn't be able to measure this force then,
exactly so. But it could also be that this force

(21:18):
is just very very weak, that it's not very powerful,
and so it's hard to detect. But if you have
enough clever physicists, they can build a device to suss
it out and to notice those tiny little hints that
give us the clues that it's there, just like we
found neutrinos. Neutrinos are very very difficult to interact with.
They only feel the weak nuclear force, but we were
able to build detectors that can spot them, so we

(21:40):
know that they are there. In the same way, if
there's another force that dark matter feels where we're gonna
talk about in a minute. Are all the ways that
we're trying to reveal dark matters interaction with normal matter
through that new force. But if it only feels gravity,
don't we have some amazing gravitational wave detectors now, couldn't
that may be help us. We do have amazing gravitational

(22:02):
wave detectors, but as far as I understand, they don't
give us much insight into where the dark matter is
because gravitational waves come from like huge accelerating masses like
black holes and neutron stars circling each other and eating
each other. Dark matter, as far as we know, doesn't
do that, and so it doesn't create gravitational waves as
far as I know. But you know, there could be

(22:23):
black holes made of dark matter. I guess that are
doing that, but it wouldn't necessarily give us insight into
the dark matter itself. But wait, would those be dark
black holes or black dark holes? I don't know. Um,
that's your responsibility since you're being nominated to the Physics
Naming Committee, But I'm pretty sure that every black hole
has to have some dark matter in it, because remember,

(22:44):
eight of the matter in the universe is dark matter.
So if you're a black hole, you're just indiscriminately sucking
up matter and you're definitely gonna hoover up some dark matter.
So it seems like a pretty hard problem. And so
break it down for us den. What are some of
the different options for studying dark matter? Alright? So number

(23:05):
one is shake it. And the idea here is, let's
build a really big tank a very quiet liquid. By quiet,
we mean liquid that doesn't interact very much, mostly just
sits there. And we put this tank really far underground,
so the cosmic rays and other particles from space don't
interact with it very much. And then you just wait.
You wait for one of those particles to shake. The

(23:28):
idea is that maybe a dark matter particle, which should
have no trouble penetrating through the ground and getting all
the way underground into your your vat of liquid, will
bump using this new force, will bump into one of
these molecules and shake it a little bit. And when
you spot that, you can say, ah, maybe that was
dark matter. Oh I see, so you're not shaking the
dark matter. You're just waiting for dark matter to shake

(23:49):
something else. That's right. We're hoping that dark matter flies
down and then occasionally bumps into one of these it's
usually liquid xenon atoms, and then we can see that
atom shaking, so we you know that that's where the
force comes in. Gravity isn't enough for that to happen.
But if dark matter has this new force, it could
give a little bump to one of these xenon atoms,

(24:10):
and by seeing them get bumped, then we could deduce
that maybe it's dark matter. So the theory is that
maybe dark matter feels does feel more than just gravity,
like maybe it feels us some kind of other force.
But it's so weak that you really would have to
isolate everything else just to maybe every once in a
while feel that force from dark matter. It's like you're

(24:32):
listening for the tiniest little whisper. Right, you don't want
to do that in a crowded stadium or in a bar.
You want to go to a place where there's nothing
going on, so you can really crank up they gain
on your on your microphone and listen for that little whisper.
So we go deep, deep underground to look for these
little particle whispers because they're probably drowned out. I mean,

(24:52):
if dark matter is around, then it may be interacting
with us all the time, right, giving little shakes, But
you can't tell because there's particles everywhere giving shakes, but
deep down underground, most of those particles are filtered out.
And you put a really quiet liquid there, and then
you hope that dark matter hits it, and you know,
you might be thinking, well, how can you tell it
was dark matter not something else? Right? What they've come

(25:14):
up with really clever ways to distinguish between dark matter
hitting it and like a gamma ray hitting it or
nuclear radioactive decay hitting it, because dark matter is probably
heavier than like electrons, and and because different kind of
recoil than a gamma ray. So they have all these
really clever details about ways to see it, and that

(25:35):
make it more likely to tell if it's dark matter
or not. But you can never be for sure. You
can never be sure that one of these wiggles is
exactly dark matter. Okay, so that's pretty good. Is that
an actual like physics position, like particle whisperer, But it
should be. It should be again, when you're on the
naming committee, you can rename these titles anything you like.
You know, throw a professor and come in with particle whisper.

(25:59):
But the key is the key is that I don't
think anybody would really conclusively accept the discovery of dark
matter just from that kind of experiment. And that's why
we have three prongs of this search. We have um,
shake it, break it, and make it, because if dark
matter does exist and it does feel this new force,
we would expect to see it in all three prongs,
and that would really be more conclusive. Why don't you

(26:20):
think people would not believe it? It's a hard experiment
to do, and the kind of signal we're looking for
is like one or two shakes over a year of running.
And then you have to really have a lot of
confidence that these folks know what other kind of things
might shake those molecules at the same level, Um, that
they've really done everything carefully. You know, it's not as

(26:43):
like direct as you'd like. You'd like to like hold
the dark matter particle and say here it is, everybody,
come and look at it. We found it, right, But
instead you're you're noticing it bumps somebody, and that's still
a bit indirect. I mean, it's more direct than gravity
because you're talking about the interaction with a particle, but
you're not left with it. You haven't to create intergator
been able to study it. Well, I remember our conversation

(27:03):
about the sky being blue. That you know, things have
to be kind of around the same size or the
same frequency for them to interact. Is it possible that
maybe dark matter is just like at a different frequency
or wavelength. It's certainly is possible, right, It's possible that
dark matter fields forces and those forces don't interact with
our matter at all. Right, it's certainly possible. Um. And

(27:25):
these detectors are sensitive to dark matter of certain masses, right,
usually between like a few giga electron volts and a
hundred giga electron bolts. And they're sensitive to those masses
because those are the masses that are going to make
the particles shake the way they're expecting. If the masses
are much much smaller or much much heavier than the
shake is going to be different and they might not
spot it. So yeah, these have windows where they can

(27:48):
see it. And again that's why we have different approaches,
so we can try to cover all the blind spots. Okay,
so that's option number one in our infomercial offering is
listening to dark matter whispers at the dark whispers that's right,
And see if it maybe bumps a particle in a really,
really really quiet environment. But that one is a little
suspicious because it's so hard, and but you're saying there's

(28:10):
a second option, which is to break it, break dark matter.
That's right. Um, if you imagine this the interaction we
talked about a moment ago shaking it, that's one dark
matter particle comes in and a normal matter particle comes in,
like xenon, and then both those come out. Xenon comes
out and dark batter comes out. Can sort of rotate
that ninety degrees in your head and say, well, if
that can happen, then maybe it's possible for two dark

(28:33):
matter particles to bump into each other, annihilate using the
same force, and turn into normal matter particles quarks for example,
which is what makes a zenon. And so it's the
same interaction, right, it's dark matter interacting with quarks um,
but instead of dark matter bouncing off of corks, it's
dark matter annihilates itself and turns into corks. Oh, because

(28:58):
dark matter, if it's in our universe, it's stuff. And
if it's stuff, then it can turn into energy, which
can then turn into other things. That's right, And only
if there's this particular force, this force that can that
can touch normal matter and can touch dark matter, then
dark matter can annihilate. It turns into the particle that

(29:21):
mediates this new force, and that particle that mediates this
new force can also touch normal matter, right, and so
we can turn into normal matter. That's the idea. It
would have to be a new kind of force, or
it could like the weak force or one of these
forces do that. We thought for a while the weak
force might be able to do that, and maybe dark
matter felt the weak force like neutrinos, but we pretty
much ruled that out because if that had happened, we

(29:43):
would have seen it already. Our detectors are powerful enough
to see dark matter interacting via the weak force, and
it hasn't. So it have to be a new force.
But you're saying, but we don't really know what dark
matter is, So how can we be so confident that
we haven't seen it this way? We don't know what
dark matter is, and so we are not confident in
basically anything. But all we can do is what we

(30:03):
can do, and we can say, well, what if dark
matter is a particle, and what if it interacts with
normal matter? What would that look like. Okay, let's go
look for that and if we find it, awesome. If
we don't find it, then there's a lot of things
that we might wonder about, like, well, maybe it's not
a particle, or maybe it doesn't interact with via this
new force, or maybe we built this thing wrong. Right,

(30:23):
So negative results are less powerful than positive results, for sure,
But you can only do what you can do right.
And in science we do this a lot. We say,
we don't know how to solve this problem. Let's start
simple and see if that works. Let's imagine it's a
unicorn and see if we see any rainbows. That's right.
And so you might be wondering like, well, how do
you make dark matter collide into other dark matter? And
the way you do it is that you just look

(30:44):
for places where there's a lot of dark matter. And
we think that dark matters clumped at the center of
the galaxy, like close to that black hole that's the
biggest blob of dark matter. So what we do is
we point our space telescopes at the center of the
galaxy and we wait and we hope to see like
a flash of light from the center of the galaxy

(31:04):
that's of a particular energy that would tell us that
dark matter collided and created normal matter. It's a really
hard thing to do. Yeah, it seems like a really
wishful thinking, or you know, like you're reaching a little bit.
It is, but you know, there was a moment when
we thought we saw a signal a few years ago.
We had the data from this telescope. And if dark

(31:25):
matter exists and it can do this and it happens,
then you would expect that all the particles that come
from the center of the galaxy would have a particular energy,
and that energy would tell you what the mass of
the particle was. So you'll be looking for like a
peak over a spectrum. And there was a guy in
the Germany who looked at the data and he saw
this big peak in the spectrum and every thought, oh
my gosh, maybe he discovered dark matter. Then it turned

(31:48):
out no, really, so um it would it would happen
in a big flash that's brightened us for us to see.
It's not one big flash. It's a slow accumulu lation
of data. It's like great build up years and years
of information and then maybe you see a bunch of
of um. You see a bunch of these things all

(32:09):
the same energy, and that tells you that maybe there's
something else going on here, some process that's happening in
the center of the galaxy that's producing these particles at
all the same energy, and that gives you a clue
as to what the dark matter is. And again, on
its own, not that convincing. But if you see that
and you see something in these underground detectors and the
two are consistent, you're like, oh, look, maybe these two

(32:30):
things are telling us the same story from a different
point of view. Then you start to build up a
credible story. All right. But then and now there's even
um a third option to study dark matter, right, that's right,
And this is my favorite because of the one that
I personally work on, and that's making dark matter. I
feel like, if we're going to believe the dark matters
of particle, we got to be able to create it.

(32:51):
We've got to be able to like make it in
the lab and play with it and study it. So
that's what we're trying to do at the large hair
Dum Collier. You laugh, You think that's ridiculous. Wow. We
just talked a little bit earlier about scientists making things
and playing with things that they don't fully understand. Yeah, exactly,
that's how we understand them. Right, you know, what is

(33:11):
this thing? I don't know? Let's make a pile of
it and poke it and see what happens. That's not
a grand plan to take over the world. It's not
like here, I'm going to become the dictator of the
Earth by making dark matter. Right, dark matter is not dangerous.
It's like it's even difficulty to spot, to to interact with. Right,
it's not going to hurt anybody. We just like want
to create some of us so we can see what
it's like. Is that so wrong? Uh? Well, I'll let

(33:38):
you know, of you guys the story of the Earth.
I'll let you know if that was a good idea
or not. Drop me a line. But then on my tombstone?
Was that so wrong? In your tombstone? Inside the dark
matter black hole? Okay, that sounds good. Dark matter black holes.
There's a start of idea. One million bucks. Please, Well,
this is a perfect point to take a break. You're

(34:11):
saying another way to study dark matter is to make
it to like created out of nothing. Yes, not out
of nothing. So imagine think about the process we just
talked about in the Galactic Center. We're talking about dark
matter annihilating it to some particle and that particle turning
into quarks. Well, if that can happen, then the reverse
can happen. That is, quarks should be able to annihilate

(34:33):
turn into some new force particle, and that new force
particles should be able to turn into dark matter. So
we should be able to smash corks together and create
dark matter. And that's coincidentally exactly what we're doing at
the Large Hadron Collider. We smash quarks in the form
of bags that we call protons together it's super high speeds,
and try to create new kinds of matter. But again,

(34:54):
that assumes that you have this magical force that helps
you go between the two worlds kind of right, Yes, exactly,
we have to assume that it's it's there to look
for it, right. It's like you're saying, like, well, you
went hunting for unicorns in the forest, and you're assuming
the unicorns exist, Well, you know, we're out there looking
for them, like we'll see. Right. It is that kind

(35:16):
of similar, right, Like yeah, yeah, sure. But you know,
if you go out looking for unicorns and you find
something else crazy instead, you still call it a success. Right,
But you have to have something to look for, and
this in particular, like you know, we believe dark matter
is there. Of all the crazy things we look for
at the Large Header and Collider, most of them we
have no clue that exists. Supersymmetry and large extra dimensions

(35:38):
and all this other crazy stuff. We have no real
clue that it's even real. Dark matter, we know is
a thing. It's out there. It's part of the universe. Man,
It's like it's an important element in the matter pie.
So at the Large Hadron Collider and we smash particles together,
we make everything that can be made. So if dark
matter exists and it can be made, then eventually we'll

(35:59):
make it, and we to be able to find it
in the remnants of some of those collisions. Right. And
the interesting thing is that it's not like you make
it and then you hold it in your hand and say,
hey see I made it. It's more like you made it.
That is my particular fantasy. But you're right, well, technically
you do have some dark matter in your hand already. Right,
that's right. But you can't hold it because it passes
through you, because it doesn't interact with you. But you're right,

(36:21):
go ahead. You can't just make it and hold it. Yeah, yeah,
I think the the idea is that you make it
and you um, and you know that you made it
because some energy disappeared and you can't account for it. Exactly.
The problem with making dark matter is that we can't
and then see the dark matter. It's like, hey, look,
I here's my Science Fair project. I made an invisible man.
You can't touch. Where is he? I don't know. Um,

(36:44):
it's not that convinced. I made your lasagna, but it
disappeared after I made it. But hey, the effort is
what counts, right, honey, here's your invisible Mother's Day present. Um, exactly,
I didn't forget. It's just invisible. It's extra impressive. Um.
That's exactly the problem. But as you say, we can
do the presence of invisible things because we know some
things about how these collisions work, and in particular, we

(37:06):
know that momentum is conserved, meaning you have momentum coming
into the collision. All that same momentum has to come
out of the collision. So if you add up all
the stuff that you saw come out of the collision,
and we're pretty good at capturing things, and something is missing,
it doesn't add up. Then you know something disappeared, something invisible.
So we can tell them when we make invisible stuff
at the colliders, and in fact we do this all

(37:27):
the time. We can't see neutrinos either, and all the
time we do this interaction where quarks annihilate and then
they turn into a pair of neutrinos, which just basically
look invisible. So we we can do this, We've measured this,
we can see it's happening. The question is is it
also making dark matter? So that's what we're doing. We're
trying to tell like is it just making neutrinos or
is it making neutrinos and dark matter? All right, So

(37:55):
those are the three ways in which we might see
dark batter um again just to recab. One of them
is to listen for it really really quietly. The other
one is to see try to look for places where
it's crashing into itself. And the other one is to
try to make it here on Earth. That's right, with

(38:15):
a million dollars, that's right, exactly so we have those
three ways, and you know, we've been doing this for
a while, and at first we were sort of just
playing around with like could we even see dark matter
and the collider, could you look at the center of
the galaxy. And people spend a lot of time refining
these techniques and making them more and more powerful, and
at the same time, we have predictions. We have like
clues from the early universe, that's say, dark matter is

(38:36):
definitely there, and and these clues from the early universe
tell us that probably dark matter came into equilibrium with
normal matter, and that means that it's like the energy
has sort of like smoothed out, and for that to happen,
it has to be able to interact. So we suspect
that there's some way for dark matter to interact with
normal matter, but it's very indirect clue, and we just
don't know how what that is. So we're hoping that

(38:59):
we'll be able to see it in one of these experiments,
and that india clue suggests that the experiments that we're
doing now in the next few years should be able
to see dark matter interact with interacting with normal matter
at the level necessary to explain that equilibrium. So it's
an exciting moment in the search for dark matter. Can
you explain what that a clear remans? So you're saying
that that you have some sort of feeling that it

(39:22):
does feel a special force that we haven't discovered yet
because because there's evidence that it has interacted with matter
in this way. That's right. We can sort of trace
back the history of the universe and the very beginning
of the universe just after the Big Bang there was
a bunch of matter created, some matter, some some normal
matter or some dark matter, right, and then the universe

(39:44):
expanded and cooled. Right at some point, the universe cools
enough that certain kind of interactions can't happen anymore. So
that's what we call that freeze out because it's not
hot enough to like make certain things happen anymore. Since
the freeze out moment is less interaction between normal matter
are in dark matter, we think, right, So we think
that before that they were sort of mixing and playing
along and interacting, and then the universe cooled down and

(40:07):
is less interaction. And we can do those calculations and
we could say if there was interaction and things were
you know, getting into equilibrium and bouncing off each other.
That changes how much dark matter is left in the universe.
So we call this a relic density. So the amount
of dark matter in the universe now depends on how
much it was interacting with normal matter in the early universe,

(40:28):
because that changes like how much is made when when
normal matter turns into dark matter, or how much disappears
when dark matter interacts with itself and turns into normal matter.
And so the amount of dark matter we see in
the universe now tells us that there was very likely
interactions in the early universe. I think what you're saying
is that, um, you know, the universe right now only

(40:51):
makes sense from what we know of it. If there
is some sort of interaction between dark matter and regular matter. Yes, yes, exactly, Okay,
But if it turns out that there isn't this special
magical unicorn force, then we're sort of toast right like
there's then there's really no way for us to really
study dark matter. It would be much much harder, and
all we can do in that case is lean on gravity,

(41:13):
and we're pressing that pretty hard. You know. We're looking
at galaxies and how they rotate, but we're also looking
at gravitational lensing, we're looking at collisions. We're doing everything
we can to try to use the gravitational information, but
it's pretty limited. Gravity is a weak force and it
doesn't capture a lot of information. So it would be
a bit of a tragedy if dark matter doesn't feel
anything but gravity, it would make it really hard to

(41:35):
ever discover. Is it made of particles, is it made
it something else? Is it made of the unic horns?
You know, it would be it would be a sad
day if we discovered that. So that's that's amazing. It
could be that will never ever in the history of
humanity until the end of the universe know what this
thing is. You sort of sound like you're rooting for
that outcome, not either outcome. Are you playing that playing

(41:57):
on the tragic arc here? I'm not taking sides between
the dark side on the light side. I'm just saying
that that that is a distinct possibility, and it's interesting
to think about, isn't it to know that maybe there
are mysteries will never know the answer to. I'm sure
there are mysteries we never know the answer to, and
probably the greatest mysteries we don't even know to ask, right,
we're that clueless when it comes to the nature of

(42:17):
the universe. This is a mystery that we've recently stumbled on,
that we've discovered that this huge parts of the universe
we don't understand. In fact, most of it the biggest
slice of the pie. So we should even be grateful
that we know it exists. And now we're getting greedy.
We don't want to know everything about it, right, But
you're right, it could be that we never know anything
more than that it's there and that it has gravity
and it plays a role in how things clump. All right.

(42:39):
So that's the answer to the question can we ever
see dark matter? And the answer is stay tuned, right,
Maybe we'll see it, maybe we won't. The answer is
keep funding particle physics. The answer is San Daniel a
million dollars. That's the answer to every question, isn't it sure? Yeah?
What did you have for breakfast? I don't know. I

(43:00):
sent Daniel million bucks and I'm still waiting for my eggs, Benedict, Hey,
startups don't offer a quick return, okay, right? Right? Or
breakfast or breakfast not usually? All right? Well, thanks for
joining us. I hope you enjoyed that discussion, and next
time you look out there into the universe, I know
that they're you are bathing in dark matter, but that

(43:22):
we may never or possibly soon be able to see it.
That's right, Mysteries the Universe potentially revealed tomorrow on our
net next podcast. Stay tuned, all right, see you next time.
Thanks for tuning in. If you still have a question

(43:48):
after listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge That's
one word, or email us at back at Daniel and
Jorge dot com. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of I
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(44:11):
the I Heart Radio app, Apple Podcasts, or wherever you
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