October 16, 2018 • 24 mins
How dark matter was discovered, and what it might be
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Speaker 1 (00:05):
Pretty much all the stuff that we're made out of.
Me and you and cats are made out of quarks
and electronics. We cats are made out of something strange though, right, Yeah,
some people sinspect cats come from another dimension. We made
little weird particles, and that would explain a lot um.
But so far, everything that we've ever interacted with, all
(00:27):
the history of science, everything we've been studying for hundreds
of years, um is only studied stuff that's made out
of quarks and electrons. And so for a long time
we thought, well, maybe everything's made out of cork and electrons. Right,
We've never seen anything else. Hi, I'm Daniel and I
(00:56):
and this is Daniel and Jorge Explain the universe. Today
we're going to talk about dark matter. What is dark
matter anyway? How dark is it? Does it really matter?
I mean, who cares? Right, Well, hopefully they care because
they clicked on the podcast. Well, dark matter certainly matters
to us, and so today we'll be talking about all
(01:17):
the interesting things about dark matter, all the mysteries and
amazing facts that we've know and don't know about dark matter.
So what do you think dark matter is? We went
out in the street and we asked people what they thought.
Here's what they had to say. Ah, I don't remember.
It's like black holes, right and stuff like that. Lava,
(01:37):
I don't know. I'm thinking it's like this dark mass
that I have no idea what's in it, but it's
just a dark mass. Cool. Wow. People have some pretty
interesting ideas about what dark matter is and what dark
matter isn't so I think it's pretty good that we're
going through this to explain all the details of dark matter. Yeah,
and it's interesting that most people seem to have heard
of it, but people sort of don't quite have a
(01:58):
good grasp of it. Well. I think there's also a
lot of abuse of the phrase dark matter you see
in science fiction. It's the title of several albums and
bands that have nothing to do with dark matter. So
it sort of entered like the pops popular lexicon without
carrying along with the possibles. I would like a dark
matter popsicle. Um, it's under the popular lexicon without sort
(02:21):
of carrying along with it what it actually means. So
this phrase which exists in the language, and it's been
stripped of scientific meeting and lots of content. I know
that I've read a lot of science fiction novels that
talk about dark matter title dark matter and have nothing
to do with dark matter. Right, So it's just two
words that are tailor made for like science fiction, right,
dark and like matter. You know, like that's a great triumph.
(02:44):
It's a great triumph of marketing. Right, it's an awesome
sounding theory. Yeah. Yeah, secured those jobs for those physicists,
that's right, that's how we get paid. Yeah, coming up
with cool names for theories. Well, we came up with
the list of the four things you should know about
dark matter, and the first thing you should know about
dark matter is that it's a different kind of matter
(03:05):
than what you and me and Daniel are made out of. So, Daniel,
what does that mean that it's a different kind of matter.
That's a great question. Well, to answer that, we really
have to think for a moment about what we're made
out of. Right, I'm made out of particles. You're made
out of particles. This chair I'm sitting on his mating
(03:26):
out of particles. Everything we know pretty much is made
out of particles. Particles like atoms. Yeah, particles inside atoms.
So you have the molecules your body is made out of,
and those are made out of atoms like hydrogen and
lithium and that kind of crazy stuff. And inside those
are smaller particles protons and neutrons and electrons, and inside those,
(03:48):
generally down even further are quarks. Everything in the universe, um,
everything out there that we've seen is made out of
these things quarks, electric right, that's right, it's the stuff
we can see, and and we what can we see
where we can see stuff that sends us light like stars.
We can see stuff that reflects light, like gas and
(04:09):
dust and and stuff like that that reflects light from
other stars, like the moon. Right, the moon doesn't give
off its own light, it's not doesn't shine, but we
see it in the sky because it reflects the light
from the sun. So it's something that we can see.
It's a kind of matter. We know, we understand it.
I can think about everything's made out of these three things.
But dark matter is something different, right, dark matter is
(04:32):
something else. It's a different kind of matter. It's not
made out of quirks and electrons. And there are even
other weird kind of quirks that we discovered, like by
smashing particles together. And we know dark matter is not
made out of any of those, something of any kind
of quirks or even weird kind of electrons. It's something else,
something different, something new that we don't know what that is.
(04:53):
We don't know what that is at all. We don't
know if it's another kind of particle. We don't know,
if it's a weird new kind of matter, this not
made out of particles. We don't know, if it's something
we haven't even imagined yet. That's my personal fantasy is
I hope that when we do figure out what dark
matter is, it totally blows our minds and turns out
to be something that even science fiction writers that never
(05:14):
thought of. That would be my my favorite scenario. So
it's something that's made out of something entirely different than us.
But there's a lot of it. And that's the second
thing you should know about that we wrote down we
should you should know about dark matter, which is that
there's a ton of it in the universe and it's
all around us. That's right. Dark matter is everywhere. So
(05:34):
people talk about dark matter like, oh, it's it's weird
stuff out in space, or these other galaxies have dark matter,
But dark matter is all around us. It's there's a
huge blob of it in the center of our galaxy,
and then there's a big diffuse cloud of it that's
that envelops the entire galaxy and pretty much every galaxy
out there. Dark matter is matter. It's stuff, right, And
when we say it's matter, we mean that it feels gravity.
(05:57):
And that's actually how we figured out that it's there.
After all, matter something that feels gravity. But wait back
up a second. So it's it's like there's blobs of
it floating out in space. Is that is that kind
of what we know about dark matter, Like it floats
and blobs. Dark matter definitely forms blobs because it feels gravity,
and like anything else, things that feel gravity are going
(06:18):
to slowly accumulate and pull themselves together. So just like
normal matter, you know, the gas and the dust pulled
themselves together to form stars and galaxies, dark matter also
pulls itself together and form these big blobs. So those
blobs aren't like out there in space, they're on top
of us. They're here with us. If you lift up
your hand right now and wave it all around, you're
(06:40):
passing through a huge blob of dark matter that's there
in your living room or kitchen or car or wherever
you happen to be. It's like in the air around us, Um,
what does that mean? Like, it's like it's in the
space between regular particles. It's here with us, and there's
a lot of space between particles. Right, particles are super
duper super tiny, and if you don't feel a force
(07:04):
that the particles are pushing back on you with, then
you can't even tell that they're there. There's lots of
examples of that. For example, there's a lot of neutrinos
that pass right through your body all the time. There's
a hundred billion neutrinos passed through your fingernail every second.
You can't feel them, um, And they just zip right
through and don't even notice you. And the reason is
that they don't have any way to talk to you.
(07:25):
So if you can't communicate with them, you can't. There's
no way for you to push them or pull them,
or for them to push your pull you. You can't
even tell them they're You just walk right through them
the way you walk through an empty room. So you're saying,
we're sort of swimming in dark matter. Absolutely, we're almost
drowning in it, because there's more dark matter than normal matter.
(07:45):
So there's your room that you're sitting in has five
times as much dark matter as it has air in it.
For example, it's five of all the energy in the
universe is normal stuff, and then something like is dark matter.
So it's like, you know, one sixth of all the
stuff that's in the universe, of all the matter that's
in the universe, is what we used to call normal matter,
(08:07):
and the rest of it is dark matter. And that's
mind blowing to discover that what you thought was typical,
we thought was normal, what you thought you know was
the basic unit of the universe turns out to be
a little extra bit. You know. It's like we've been
eating the frosting and ignoring the cake, right, or we've
been like focusing on the tail and ignoring the whole elephant.
I have so many questions for you, but before we
(08:29):
dive in, let's take a short break. So dark matter
doesn't feel electromagnetism. And we know that because we know
it's there, but we don't see it. Right, that's what
we mean by see it and feel it. So that's
(08:51):
what it's called dark right, It's you can't see it
exactly that's just what we mean by dark that awesome
marketing campaign of dark matter. That's the concept behind dark.
Dark meaning we don't see it or feel it is
right by it doesn't care. That's right. Yeah, But then
you might wonder, like, well, if we can't interact with
(09:12):
it at all, how could we possibly know it's there? Right?
If you can't feel it or see it in any way,
is it not just some fantasy some speculations, and like
why should we care, Like if we can't see it
or touch it, why why is it important to the universe?
That's right? And so there is one way we can
interact with dark matter, and that's through gravity. Dark matter
(09:34):
is and that's the matter part of it, right, dark
meaning we can't see it. Matter meaning it has stuff
to it has gravity, and we know that it's a matter.
We know it's made of something and it does have gravity.
That's what matters is kind of defined as stuff that
feels gravity and has mass. Yeah, exactly. That's what makes
matter matter, is that it has some stuff to it,
(09:56):
some mass to it, and anything that has mass to
it is going to feel gravity. Okay, it's true that
we can't feel or see dark matter because it doesn't
have any electromagnetism, but it does have gravity, and so
we can detect it. But because gravity is so weak,
it takes enormous amounts of dark matter for us to notice.
So kind of actually that there's so much dark Like
(10:18):
even if there's a blob of dark matter right in
front of me, I know I can't see it or
touch it because it doesn't feel like your mignety forces. Um,
but I know that you're telling me that I have
like a gravity relationship with this blob, right, But it's
super right. It's I don't even feel the gravity from
this blob. There's definitely gravity between you and that room
(10:39):
full of dark matter. Okay, And depending on what your
math is, we don't have to say on that head. Yeah,
even if you're a super massive guy who never left
the house or massively cool, right or just massively funny
and that's how weird, right, Like, um, like I have
a gravity relationship with the error around me, have a
gravity relationship with the like the microphone in front of me,
(11:02):
with the table in front of me, with the car
when I'm driving, But you just don't really feel that
gravity relationship, right, That's right, You can't tell. It's drowned
out by everything else in your life, and so you
don't even notice. So you know, you can act like
there's no gravitational force between you and the chair in
front of you, because it's almost true. It's only like
(11:23):
with the entire Earth that I feel that gravity relationship. Right,
that's the one that pulls me down, That's right. And
it takes a huge blob of stuff the size of
the Earth for you to even notice. Okay, so dark
matter is a different kind of matter. There's a ton
of it in the years. It's all around this. We
can't see it because it doesn't feel electromagnetic forces. We
(11:45):
can't touch it also because of that um, but it
does feel gravity. So how do we know that it
was there? Like, how do we can't see or touch it?
How do we how do we figure that? Yeah, it
took people a while before they really accepted the dark
matter was the thing. And it's a fun story because
it's started with just a discrepancy. What they were doing
was they were checking to see if they understood how
(12:07):
galaxies spin. So our galaxy, you know, we are in
a solar system, and a solar system is part of
a big group of stars called the galaxy that all
spins around. And our galaxy is called the Milky Way.
And there's lots of galaxies in the universe, trillions more
even more than that, probably, And we can look out
into the sky and you can see other galaxies also spinning.
(12:29):
And you can think of a galaxy sort of the
way you think about like a America round. If you
have a merriga round and you put a bunch of
pink pong balls on it, you spin it, what's going
to happen? The pink pun balls will fly off? Yeah,
they'll shootout and hit your sister in the face. And
then you get a diferent And those are some dark matters,
(12:52):
and um, so what happens with the galaxy? Well, in
the case of a galaxy, it's got a bunch of
stars in it, and the galaxy is spinning. So why
don't the ours get thrown out into intergalactic space all
the time the way the ping pong balls might from
Amerry around? Right, So galaxies are spinning their stars in it,
why don't the stars just like spill out? That's right,
I wanted they get tossed out? And the answer is gravity.
(13:14):
The galaxy is a lot of gravity from all those
stars in the black hole in the center and all
that stuff, and that gravity holds the stars in place,
like keeps everything in orbit. That's right, Yeah, it pulls
it together and keeps stuff from getting thrown out. So
some grad student went out to check this and they
got a crazy result. And the result is that these
(13:34):
galaxies are spinning way, way, way too fast. There's no
way that the amount of stuff that we see in
those galaxies is providing enough gravity to hold the galaxies together. Okay,
something else had to be there, right, that's right, because
the stars are not getting thrown into space, right, the
galaxies are getting held together. So, as you know, first time,
(13:54):
you have a crazy result. And there's a lot of
explanations people come up with, and so the simplest explanation
in some sense is, well, there's some kind of gravity
that that's from something we can't see. So let's invent
a new kind of stuff. It has to be dark
because we can't see it. It has to be matter
because it's giving us gravity. So we'll come up with
a cool name for this new thing, called it dark matter.
(14:17):
And that sounds like a simple explanation. But on the
other hand, is not because there's not a tiny amount
of stuff you have to add to these galaxies. Right,
they're spending way too fast. And that's how we know
that there's a ton of dark matter, because to get
enough gravity to hold these galaxies together, you have to
multiply the amount of stuff you can see by a
(14:39):
factor of five. Tells you that, yeah, it tells you
that what you see of the galaxy is not most
of the galaxy. You know, you're looking at the galactic tonails,
or you know they're just the galactic fingertips or something.
Most of the galaxy is something else, right, right, the
milky toes of these and and so for a long
(15:00):
time people didn't accept that, and there were other ideas.
People thought, well, that's crazy because you can't just say, oh,
my experiment didn't work. Maybe the universe is filled with
there's a new kind of stuff that nobody's ever seen before,
and there's a huge amount of it and it's everywhere. Right,
it's sort of a convenient and crazy explanations. Remever, in science,
(15:20):
we like simple explanations, right. We want the simplest set
of ideas to explain everything. We see so that was yeah,
so that was that was that was the mindset, right.
I was like, Okay, we know, we think we know
the universe. Let's check to see if the galaxies are
spinning as they should. But they found out they're spinning
too fast. And the only explanation someone could come up
(15:41):
with was like, may there's invisible gravity stuff in these
galaxies that's like five times eavery than all of those stars.
That's right, That was the idea of dark matter. There
actually were other explanations that lived for a little while,
and recently they died because they they were ruled up
by other experiments. Since then, we're pretty sure that dark
(16:04):
matter is a thing. And one way that we were
able to figure out that dark matter is there and
it's not just a misunderstanding of the way gravity works,
is that we found a few other ways to spot it.
So they're all they're almost all gravitational, but there are
other ways to spot it to tell us that would
give different results if it was actually dark matter or
(16:25):
this other weird kind of theory about gravity. And I
want to talk about that some more, but first let's
take a quick break. So one way, it's called gravitational lensing,
and that's when dark matter in the sky bends the
(16:47):
light and gives these crazy optical effects. And that's one
way we can tell where dark matter is. It's in
a blob here, it's in a blob there makes these
cool distortions in the sky because it has gravity, and
it's like not just pulls the stars and planets around it,
but it also bends light around it, because we know
that's what gravity does, right, Yeah, because that's what matter does. Matter,
(17:07):
All matter has gravity, and dark matter can bend the
space because it has gravity, so it acts like a
cosmic lens in the sky. It's totally mind blowing and
everybody out there should google gravitational lensing and see those
those images because they're gorgeous. And then the other way
that we know that it's definitely there through gravity is um, what,
(17:29):
what's the other thing? Yeah? The other thing was this
amazing event that happened very far away, a long long
time ago when two clusters of galaxies smashed into each other.
And what every every cluster of God sees has both
normal matter like me and you and gas and stuff
and dust and also dark matter. So when they smash
into each other, the normal matter smashes and creates explosions
(17:51):
and gives off light, and we can see that. But
the dark matter passed right through to the other side,
so you can and we can see the dark matter
there because of the gravitational lensing, so that dark matter
got separated from some of the normal matter, and we
can see its gravitational effects on its own And that
was the key to knowing that dark matter really is
its own thing with its own gravity. It's not just
(18:12):
the misunderstanding of the way gravity works, right, because if
that were the case, you wouldn't be able to separate
this new new gravity from the old gravity. But because
you can, because you can say, oh, here's this dark
matter separated from all that gas in the dust. We
can see it has its own gravity. It must be
its own thing. So that tells us there's a lot
of dark matter. It's out there. We can see it
(18:34):
kind of through gravity, even not directly, but doesn't really
tell us that much more about dark matter. Why if
is this care about dark matter? Like, why is it?
Why is it important? Why is it cool? And interesting? What?
We want to make awesome sunglasses? That's the number one goal.
How would you make dark matters sunglasses, that would be
pretty pretty easy. Yeah, well matter for sure. No, it
(19:02):
just comes out of a desire to understand. You know,
we look at the world around us. We want to
know how does this all put together? You know, what
is the principle that organizes this um And part of
it is a desire to build new kinds of stuff.
I mean, if you understand the world around you, then
you know how to manipulate it and use it and
build transistors and all sorts of cool stuff. So there's
thousands of applications as soon as you understand how matter works.
(19:24):
But there's also just that core curiosity. We're like, you know,
five dots away from being able to connect dark matter
with anything specifically that's useful. But every time we found
something new about the universe, some surprise, something crazy, something new,
it's always led to, you know, economic revolutions, or technological revolutions,
or even just intellectual revolutions. I mean, if you find
(19:46):
out that the universe works in a way different from
what you expected, it changes the way you think about
your life and the whole human experience. I mean it's
not just a little bit. It's like we're we're the
minority in the universe, you know, not been We're not
even the center of gravity of the universe by any means, right,
that's right. If there was an election, we would definitely
(20:06):
not any representatives. But yeah, that's that that's wild to know, right, Like,
we're not the most kind of stuff in the universe.
And so that's that's why dark matter is important. It's like,
that's that's the bigger chunk of the universe, and so
it kind of affects the way we know how things happen. Yeah,
and it's responsible for the basic structure of the universe.
(20:27):
We've done simulations. For example, we say, what would the
universe look like if there hadn't been any dark matter? Right,
run those stimulations forward and fourteen billion years in, you
don't have any galaxies really, And the reason is that, yeah,
you don't have dark matter pulling together normal matter and
compressing it. No, we wouldn't be here at all. The
universe would be much more diffuse and boring. We wouldn't
(20:48):
have any podcasts at all. That's not to say like
dark matter is the reason for creation or is more
important than us. I mean, we don't really know what
it is at all. It could be totally boring and
sterile and just a bunch of little particles that are
kind of aloof and ignore us, all right. It could
be something more interesting though, So dark matter it's a
different kind of of stuff of matter than us. We're
(21:10):
made out of quarks and electrons um. Dark matters maybe
made it out of something different that um. It's not
quite the same thing as we were made out of, right,
And it could be particles. It could not be particles.
It could be um stuff. It could be some new
kind of stuff how other stuff works. So it's different
(21:30):
than us. There's a ton of it in the universe.
There's five times more dark matter than regular matter. And
it's all around us. It's like it's it's almost on
top of us, you know, we're in it, and it's
inside us. It's everywhere and passing through us. And you're
waving your arms through right now. I feel that dark matter, Yeah,
I feel it. It's it's inside of you. It's been
(21:52):
inside of you all along. Well that sounds a little
in appropriate. No, it's like a like courage, you know,
it's like cark ridge or or wisdom, summon the dark
matter within you sort of thing. Yeah, Okay, it could
be like complex stuff, right, dark matter could be interesting
and complex and have different kinds of properties to it. Right,
(22:15):
that's right, because there could be other checkboxes we talked about,
you know, the strong and the weak force, and electromagnetism
and gravity. Those are the four forces we know, but
there could be a fifth force that only dark matter feels.
And it feels it with itself. It's easy to say, well,
the simplest idea is dark matter is all just one particle.
And that's simple idea, and we like to start with
simple ideas to mapically work versus just like a weird
(22:36):
homogenous blog. Yeah, but you know, look at the five
percent in the universe we've studied. It's not just one
kind of particle. It's a bunch of different kind of particles,
and it's complicated and interesting. So there's no real reason
to expect that dark matter is different. It could be
even more complicated. And that's and that's assuming Remember that
dark matter is a particle. We have actually no evidence
(22:56):
whatsoever proving that dark matter is a particle. Of the
normal matter we've ever seen is made out of particles,
And that's the assumption we're using to say, well, probably
dark matters also made out of particles. That's like saying
I've only ever seen the tail of the elephants, so
the rest of the elephant must also be tails, right card,
It's all tales all the way down. It sort of
(23:18):
falls apart, and it's a good way to start, you know.
But I'm hoping that we discover the dark matter is
something else, insing, weird, some different kind of matters just
sort of expands our minds out of our current way
of thinking into some new direction where we consider possibilities
we hadn't even considered before. Do you have a question
(23:39):
you wish we would cover, Send it to us. We'd
love to hear from you. You can find us on Facebook, Twitter,
and Instagram at Daniel and Jorge one Word, or email
us to feedback at Daniel and Jorge dot com. N
Pretty much all the stuff that we're made out of.
Me and you and cats are made out of quarks
and electronics. We cats are made out of something strange though, right, Yeah,
some people sinspect cats come from another dimension. We made
little weird particles, and that would explain a lot um.
But so far, everything that we've ever interacted with, all
(00:27):
the history of science, everything we've been studying for hundreds
of years, um is only studied stuff that's made out
of quarks and electrons. And so for a long time
we thought, well, maybe everything's made out of cork and electrons. Right,
We've never seen anything else. Hi, I'm Daniel and I
(00:56):
and this is Daniel and Jorge Explain the universe. Today
we're going to talk about dark matter. What is dark
matter anyway? How dark is it? Does it really matter?
I mean, who cares? Right, Well, hopefully they care because
they clicked on the podcast. Well, dark matter certainly matters
to us, and so today we'll be talking about all
(01:17):
the interesting things about dark matter, all the mysteries and
amazing facts that we've know and don't know about dark matter.
So what do you think dark matter is? We went
out in the street and we asked people what they thought.
Here's what they had to say. Ah, I don't remember.
It's like black holes, right and stuff like that. Lava,
(01:37):
I don't know. I'm thinking it's like this dark mass
that I have no idea what's in it, but it's
just a dark mass. Cool. Wow. People have some pretty
interesting ideas about what dark matter is and what dark
matter isn't so I think it's pretty good that we're
going through this to explain all the details of dark matter. Yeah,
and it's interesting that most people seem to have heard
of it, but people sort of don't quite have a
(01:58):
good grasp of it. Well. I think there's also a
lot of abuse of the phrase dark matter you see
in science fiction. It's the title of several albums and
bands that have nothing to do with dark matter. So
it sort of entered like the pops popular lexicon without
carrying along with the possibles. I would like a dark
matter popsicle. Um, it's under the popular lexicon without sort
(02:21):
of carrying along with it what it actually means. So
this phrase which exists in the language, and it's been
stripped of scientific meeting and lots of content. I know
that I've read a lot of science fiction novels that
talk about dark matter title dark matter and have nothing
to do with dark matter. Right, So it's just two
words that are tailor made for like science fiction, right,
dark and like matter. You know, like that's a great triumph.
(02:44):
It's a great triumph of marketing. Right, it's an awesome
sounding theory. Yeah. Yeah, secured those jobs for those physicists,
that's right, that's how we get paid. Yeah, coming up
with cool names for theories. Well, we came up with
the list of the four things you should know about
dark matter, and the first thing you should know about
dark matter is that it's a different kind of matter
(03:05):
than what you and me and Daniel are made out of. So, Daniel,
what does that mean that it's a different kind of matter.
That's a great question. Well, to answer that, we really
have to think for a moment about what we're made
out of. Right, I'm made out of particles. You're made
out of particles. This chair I'm sitting on his mating
(03:26):
out of particles. Everything we know pretty much is made
out of particles. Particles like atoms. Yeah, particles inside atoms.
So you have the molecules your body is made out of,
and those are made out of atoms like hydrogen and
lithium and that kind of crazy stuff. And inside those
are smaller particles protons and neutrons and electrons, and inside those,
(03:48):
generally down even further are quarks. Everything in the universe, um,
everything out there that we've seen is made out of
these things quarks, electric right, that's right, it's the stuff
we can see, and and we what can we see
where we can see stuff that sends us light like stars.
We can see stuff that reflects light, like gas and
(04:09):
dust and and stuff like that that reflects light from
other stars, like the moon. Right, the moon doesn't give
off its own light, it's not doesn't shine, but we
see it in the sky because it reflects the light
from the sun. So it's something that we can see.
It's a kind of matter. We know, we understand it.
I can think about everything's made out of these three things.
But dark matter is something different, right, dark matter is
(04:32):
something else. It's a different kind of matter. It's not
made out of quirks and electrons. And there are even
other weird kind of quirks that we discovered, like by
smashing particles together. And we know dark matter is not
made out of any of those, something of any kind
of quirks or even weird kind of electrons. It's something else,
something different, something new that we don't know what that is.
(04:53):
We don't know what that is at all. We don't
know if it's another kind of particle. We don't know,
if it's a weird new kind of matter, this not
made out of particles. We don't know, if it's something
we haven't even imagined yet. That's my personal fantasy is
I hope that when we do figure out what dark
matter is, it totally blows our minds and turns out
to be something that even science fiction writers that never
(05:14):
thought of. That would be my my favorite scenario. So
it's something that's made out of something entirely different than us.
But there's a lot of it. And that's the second
thing you should know about that we wrote down we
should you should know about dark matter, which is that
there's a ton of it in the universe and it's
all around us. That's right. Dark matter is everywhere. So
(05:34):
people talk about dark matter like, oh, it's it's weird
stuff out in space, or these other galaxies have dark matter,
But dark matter is all around us. It's there's a
huge blob of it in the center of our galaxy,
and then there's a big diffuse cloud of it that's
that envelops the entire galaxy and pretty much every galaxy
out there. Dark matter is matter. It's stuff, right, And
when we say it's matter, we mean that it feels gravity.
(05:57):
And that's actually how we figured out that it's there.
After all, matter something that feels gravity. But wait back
up a second. So it's it's like there's blobs of
it floating out in space. Is that is that kind
of what we know about dark matter, Like it floats
and blobs. Dark matter definitely forms blobs because it feels gravity,
and like anything else, things that feel gravity are going
(06:18):
to slowly accumulate and pull themselves together. So just like
normal matter, you know, the gas and the dust pulled
themselves together to form stars and galaxies, dark matter also
pulls itself together and form these big blobs. So those
blobs aren't like out there in space, they're on top
of us. They're here with us. If you lift up
your hand right now and wave it all around, you're
(06:40):
passing through a huge blob of dark matter that's there
in your living room or kitchen or car or wherever
you happen to be. It's like in the air around us, Um,
what does that mean? Like, it's like it's in the
space between regular particles. It's here with us, and there's
a lot of space between particles. Right, particles are super
duper super tiny, and if you don't feel a force
(07:04):
that the particles are pushing back on you with, then
you can't even tell that they're there. There's lots of
examples of that. For example, there's a lot of neutrinos
that pass right through your body all the time. There's
a hundred billion neutrinos passed through your fingernail every second.
You can't feel them, um, And they just zip right
through and don't even notice you. And the reason is
that they don't have any way to talk to you.
(07:25):
So if you can't communicate with them, you can't. There's
no way for you to push them or pull them,
or for them to push your pull you. You can't
even tell them they're You just walk right through them
the way you walk through an empty room. So you're saying,
we're sort of swimming in dark matter. Absolutely, we're almost
drowning in it, because there's more dark matter than normal matter.
(07:45):
So there's your room that you're sitting in has five
times as much dark matter as it has air in it.
For example, it's five of all the energy in the
universe is normal stuff, and then something like is dark matter.
So it's like, you know, one sixth of all the
stuff that's in the universe, of all the matter that's
in the universe, is what we used to call normal matter,
(08:07):
and the rest of it is dark matter. And that's
mind blowing to discover that what you thought was typical,
we thought was normal, what you thought you know was
the basic unit of the universe turns out to be
a little extra bit. You know. It's like we've been
eating the frosting and ignoring the cake, right, or we've
been like focusing on the tail and ignoring the whole elephant.
I have so many questions for you, but before we
(08:29):
dive in, let's take a short break. So dark matter
doesn't feel electromagnetism. And we know that because we know
it's there, but we don't see it. Right, that's what
we mean by see it and feel it. So that's
(08:51):
what it's called dark right, It's you can't see it
exactly that's just what we mean by dark that awesome
marketing campaign of dark matter. That's the concept behind dark.
Dark meaning we don't see it or feel it is
right by it doesn't care. That's right. Yeah, But then
you might wonder, like, well, if we can't interact with
(09:12):
it at all, how could we possibly know it's there? Right?
If you can't feel it or see it in any way,
is it not just some fantasy some speculations, and like
why should we care, Like if we can't see it
or touch it, why why is it important to the universe?
That's right? And so there is one way we can
interact with dark matter, and that's through gravity. Dark matter
(09:34):
is and that's the matter part of it, right, dark
meaning we can't see it. Matter meaning it has stuff
to it has gravity, and we know that it's a matter.
We know it's made of something and it does have gravity.
That's what matters is kind of defined as stuff that
feels gravity and has mass. Yeah, exactly. That's what makes
matter matter, is that it has some stuff to it,
(09:56):
some mass to it, and anything that has mass to
it is going to feel gravity. Okay, it's true that
we can't feel or see dark matter because it doesn't
have any electromagnetism, but it does have gravity, and so
we can detect it. But because gravity is so weak,
it takes enormous amounts of dark matter for us to notice.
So kind of actually that there's so much dark Like
(10:18):
even if there's a blob of dark matter right in
front of me, I know I can't see it or
touch it because it doesn't feel like your mignety forces. Um,
but I know that you're telling me that I have
like a gravity relationship with this blob, right, But it's
super right. It's I don't even feel the gravity from
this blob. There's definitely gravity between you and that room
(10:39):
full of dark matter. Okay, And depending on what your
math is, we don't have to say on that head. Yeah,
even if you're a super massive guy who never left
the house or massively cool, right or just massively funny
and that's how weird, right, Like, um, like I have
a gravity relationship with the error around me, have a
gravity relationship with the like the microphone in front of me,
(11:02):
with the table in front of me, with the car
when I'm driving, But you just don't really feel that
gravity relationship, right, That's right, You can't tell. It's drowned
out by everything else in your life, and so you
don't even notice. So you know, you can act like
there's no gravitational force between you and the chair in
front of you, because it's almost true. It's only like
(11:23):
with the entire Earth that I feel that gravity relationship. Right,
that's the one that pulls me down, That's right. And
it takes a huge blob of stuff the size of
the Earth for you to even notice. Okay, so dark
matter is a different kind of matter. There's a ton
of it in the years. It's all around this. We
can't see it because it doesn't feel electromagnetic forces. We
(11:45):
can't touch it also because of that um, but it
does feel gravity. So how do we know that it
was there? Like, how do we can't see or touch it?
How do we how do we figure that? Yeah, it
took people a while before they really accepted the dark
matter was the thing. And it's a fun story because
it's started with just a discrepancy. What they were doing
was they were checking to see if they understood how
(12:07):
galaxies spin. So our galaxy, you know, we are in
a solar system, and a solar system is part of
a big group of stars called the galaxy that all
spins around. And our galaxy is called the Milky Way.
And there's lots of galaxies in the universe, trillions more
even more than that, probably, And we can look out
into the sky and you can see other galaxies also spinning.
(12:29):
And you can think of a galaxy sort of the
way you think about like a America round. If you
have a merriga round and you put a bunch of
pink pong balls on it, you spin it, what's going
to happen? The pink pun balls will fly off? Yeah,
they'll shootout and hit your sister in the face. And
then you get a diferent And those are some dark matters,
(12:52):
and um, so what happens with the galaxy? Well, in
the case of a galaxy, it's got a bunch of
stars in it, and the galaxy is spinning. So why
don't the ours get thrown out into intergalactic space all
the time the way the ping pong balls might from
Amerry around? Right, So galaxies are spinning their stars in it,
why don't the stars just like spill out? That's right,
I wanted they get tossed out? And the answer is gravity.
(13:14):
The galaxy is a lot of gravity from all those
stars in the black hole in the center and all
that stuff, and that gravity holds the stars in place,
like keeps everything in orbit. That's right, Yeah, it pulls
it together and keeps stuff from getting thrown out. So
some grad student went out to check this and they
got a crazy result. And the result is that these
(13:34):
galaxies are spinning way, way, way too fast. There's no
way that the amount of stuff that we see in
those galaxies is providing enough gravity to hold the galaxies together. Okay,
something else had to be there, right, that's right, because
the stars are not getting thrown into space, right, the
galaxies are getting held together. So, as you know, first time,
(13:54):
you have a crazy result. And there's a lot of
explanations people come up with, and so the simplest explanation
in some sense is, well, there's some kind of gravity
that that's from something we can't see. So let's invent
a new kind of stuff. It has to be dark
because we can't see it. It has to be matter
because it's giving us gravity. So we'll come up with
a cool name for this new thing, called it dark matter.
(14:17):
And that sounds like a simple explanation. But on the
other hand, is not because there's not a tiny amount
of stuff you have to add to these galaxies. Right,
they're spending way too fast. And that's how we know
that there's a ton of dark matter, because to get
enough gravity to hold these galaxies together, you have to
multiply the amount of stuff you can see by a
(14:39):
factor of five. Tells you that, yeah, it tells you
that what you see of the galaxy is not most
of the galaxy. You know, you're looking at the galactic tonails,
or you know they're just the galactic fingertips or something.
Most of the galaxy is something else, right, right, the
milky toes of these and and so for a long
(15:00):
time people didn't accept that, and there were other ideas.
People thought, well, that's crazy because you can't just say, oh,
my experiment didn't work. Maybe the universe is filled with
there's a new kind of stuff that nobody's ever seen before,
and there's a huge amount of it and it's everywhere. Right,
it's sort of a convenient and crazy explanations. Remever, in science,
(15:20):
we like simple explanations, right. We want the simplest set
of ideas to explain everything. We see so that was yeah,
so that was that was that was the mindset, right.
I was like, Okay, we know, we think we know
the universe. Let's check to see if the galaxies are
spinning as they should. But they found out they're spinning
too fast. And the only explanation someone could come up
(15:41):
with was like, may there's invisible gravity stuff in these
galaxies that's like five times eavery than all of those stars.
That's right, That was the idea of dark matter. There
actually were other explanations that lived for a little while,
and recently they died because they they were ruled up
by other experiments. Since then, we're pretty sure that dark
(16:04):
matter is a thing. And one way that we were
able to figure out that dark matter is there and
it's not just a misunderstanding of the way gravity works,
is that we found a few other ways to spot it.
So they're all they're almost all gravitational, but there are
other ways to spot it to tell us that would
give different results if it was actually dark matter or
(16:25):
this other weird kind of theory about gravity. And I
want to talk about that some more, but first let's
take a quick break. So one way, it's called gravitational lensing,
and that's when dark matter in the sky bends the
(16:47):
light and gives these crazy optical effects. And that's one
way we can tell where dark matter is. It's in
a blob here, it's in a blob there makes these
cool distortions in the sky because it has gravity, and
it's like not just pulls the stars and planets around it,
but it also bends light around it, because we know
that's what gravity does, right, Yeah, because that's what matter does. Matter,
(17:07):
All matter has gravity, and dark matter can bend the
space because it has gravity, so it acts like a
cosmic lens in the sky. It's totally mind blowing and
everybody out there should google gravitational lensing and see those
those images because they're gorgeous. And then the other way
that we know that it's definitely there through gravity is um, what,
(17:29):
what's the other thing? Yeah? The other thing was this
amazing event that happened very far away, a long long
time ago when two clusters of galaxies smashed into each other.
And what every every cluster of God sees has both
normal matter like me and you and gas and stuff
and dust and also dark matter. So when they smash
into each other, the normal matter smashes and creates explosions
(17:51):
and gives off light, and we can see that. But
the dark matter passed right through to the other side,
so you can and we can see the dark matter
there because of the gravitational lensing, so that dark matter
got separated from some of the normal matter, and we
can see its gravitational effects on its own And that
was the key to knowing that dark matter really is
its own thing with its own gravity. It's not just
(18:12):
the misunderstanding of the way gravity works, right, because if
that were the case, you wouldn't be able to separate
this new new gravity from the old gravity. But because
you can, because you can say, oh, here's this dark
matter separated from all that gas in the dust. We
can see it has its own gravity. It must be
its own thing. So that tells us there's a lot
of dark matter. It's out there. We can see it
(18:34):
kind of through gravity, even not directly, but doesn't really
tell us that much more about dark matter. Why if
is this care about dark matter? Like, why is it?
Why is it important? Why is it cool? And interesting? What?
We want to make awesome sunglasses? That's the number one goal.
How would you make dark matters sunglasses, that would be
pretty pretty easy. Yeah, well matter for sure. No, it
(19:02):
just comes out of a desire to understand. You know,
we look at the world around us. We want to
know how does this all put together? You know, what
is the principle that organizes this um And part of
it is a desire to build new kinds of stuff.
I mean, if you understand the world around you, then
you know how to manipulate it and use it and
build transistors and all sorts of cool stuff. So there's
thousands of applications as soon as you understand how matter works.
(19:24):
But there's also just that core curiosity. We're like, you know,
five dots away from being able to connect dark matter
with anything specifically that's useful. But every time we found
something new about the universe, some surprise, something crazy, something new,
it's always led to, you know, economic revolutions, or technological revolutions,
or even just intellectual revolutions. I mean, if you find
(19:46):
out that the universe works in a way different from
what you expected, it changes the way you think about
your life and the whole human experience. I mean it's
not just a little bit. It's like we're we're the
minority in the universe, you know, not been We're not
even the center of gravity of the universe by any means, right,
that's right. If there was an election, we would definitely
(20:06):
not any representatives. But yeah, that's that that's wild to know, right, Like,
we're not the most kind of stuff in the universe.
And so that's that's why dark matter is important. It's like,
that's that's the bigger chunk of the universe, and so
it kind of affects the way we know how things happen. Yeah,
and it's responsible for the basic structure of the universe.
(20:27):
We've done simulations. For example, we say, what would the
universe look like if there hadn't been any dark matter? Right,
run those stimulations forward and fourteen billion years in, you
don't have any galaxies really, And the reason is that, yeah,
you don't have dark matter pulling together normal matter and
compressing it. No, we wouldn't be here at all. The
universe would be much more diffuse and boring. We wouldn't
(20:48):
have any podcasts at all. That's not to say like
dark matter is the reason for creation or is more
important than us. I mean, we don't really know what
it is at all. It could be totally boring and
sterile and just a bunch of little particles that are
kind of aloof and ignore us, all right. It could
be something more interesting though, So dark matter it's a
different kind of of stuff of matter than us. We're
(21:10):
made out of quarks and electrons um. Dark matters maybe
made it out of something different that um. It's not
quite the same thing as we were made out of, right,
And it could be particles. It could not be particles.
It could be um stuff. It could be some new
kind of stuff how other stuff works. So it's different
(21:30):
than us. There's a ton of it in the universe.
There's five times more dark matter than regular matter. And
it's all around us. It's like it's it's almost on
top of us, you know, we're in it, and it's
inside us. It's everywhere and passing through us. And you're
waving your arms through right now. I feel that dark matter, Yeah,
I feel it. It's it's inside of you. It's been
(21:52):
inside of you all along. Well that sounds a little
in appropriate. No, it's like a like courage, you know,
it's like cark ridge or or wisdom, summon the dark
matter within you sort of thing. Yeah, Okay, it could
be like complex stuff, right, dark matter could be interesting
and complex and have different kinds of properties to it. Right,
(22:15):
that's right, because there could be other checkboxes we talked about,
you know, the strong and the weak force, and electromagnetism
and gravity. Those are the four forces we know, but
there could be a fifth force that only dark matter feels.
And it feels it with itself. It's easy to say, well,
the simplest idea is dark matter is all just one particle.
And that's simple idea, and we like to start with
simple ideas to mapically work versus just like a weird
(22:36):
homogenous blog. Yeah, but you know, look at the five
percent in the universe we've studied. It's not just one
kind of particle. It's a bunch of different kind of particles,
and it's complicated and interesting. So there's no real reason
to expect that dark matter is different. It could be
even more complicated. And that's and that's assuming Remember that
dark matter is a particle. We have actually no evidence
(22:56):
whatsoever proving that dark matter is a particle. Of the
normal matter we've ever seen is made out of particles,
And that's the assumption we're using to say, well, probably
dark matters also made out of particles. That's like saying
I've only ever seen the tail of the elephants, so
the rest of the elephant must also be tails, right card,
It's all tales all the way down. It sort of
(23:18):
falls apart, and it's a good way to start, you know.
But I'm hoping that we discover the dark matter is
something else, insing, weird, some different kind of matters just
sort of expands our minds out of our current way
of thinking into some new direction where we consider possibilities
we hadn't even considered before. Do you have a question
(23:39):
you wish we would cover, Send it to us. We'd
love to hear from you. You can find us on Facebook, Twitter,
and Instagram at Daniel and Jorge one Word, or email
us to feedback at Daniel and Jorge dot com. N
Hosts And Creators
Daniel Whiteson
Jorge Cham
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