Only about 5% of the
universe is made up of stuff
that we're familiar with.
Protons, neutrons,
electrons, quarks,
and all the other matter
that make up our bodies,
the planets, the stars,
everything we've ever seen,
is only a tiny fraction of what
makes up our entire universe.
85% of the universe's
mass is made up
of something called dark matter.
And we don't even
know what it is.
PADDY FOX: So why is
it called dark matter?
So it's called matter
because it gravitates
in the same way you and I do.
And it's called dark because
we've not seen it very well.
CRAIG BENZINE: This is Paddy
Fox, theoretical physicist
at Fermilab, which is
home to the world's
second-largest
particle accelerator,
and where lots of cool
science stuff happens.
PADDY FOX: Basically,
it doesn't reflect light
and it doesn't emit light.
But it also doesn't
interact in any other way,
as far as we can tell,
very, very strongly.
So it interacts very,
very, very, very weakly.
That basically means it can fly
through stuff with impunity.
And that's why it's
so hard to measure.
But we know it's out there.
How do you know that?
PADDY FOX: That's
a good question.
So we know that from the way
it interacts gravitationally.
So basically, all matter
pulls stuff towards it.
You and I are being pulled
towards each other right now,
very, very weakly by gravity.
And although we don't know
what makes up dark matter,
we know how it interacts
in terms of gravity.
And we've seen its
effects gravitationally
on the cosmos at large.
Invisible matter was first
postulated in 1932 by Jan Oort.
But it wasn't until a year
later that Fritz Zwicky,
while measuring the
gravitational mass of the Coma
Cluster of galaxies,
noticed something odd.
By measuring the velocity
of the orbiting galaxies,
Zwicky was able to calculate
the mass of the cluster.
However, the mass
he calculated was
far greater than the observable
stars in the galaxies.
His results seemed to suggest
that there's more matter
out there than could be seen.
He called this Dunkle Materie
or dun-clay materie-ay
or something, which
translates to dark matter.
However, for the time
being, his results
were largely ignored.
CRAIG BENZINE: In the
'60s and '70s scientist
Vera Rubin noticed a
difference between the angular
motion of the
galaxies she predicted
and the motion she observed.
This was a huge problem.
Basically, Rubin found
the galaxies were spinning
too fast-- so
fast, in fact, they
should be flinging all their
stars out into outer space.
But they weren't, obviously.
MATT WEBER: This came to be
known as the Galaxy Rotation
Problem.
To solve this problem,
Rubin calculated
that there had to
be a bunch of matter
that they couldn't see keeping
the stars gravitationally bound
to their galaxies-- as much
as 10 times as much matter.
CRAIG BENZINE: While at
first met with skepticism,
her work was
eventually verified.
And it became the
strongest evidence
we had for the existence
of dark matter.
And since then, we've
seen more and more evidence
of dark matter.
Although we've never directly
seen dark matter itself,
we can infer its presence by
how it affects regular matter.
CRAIG BENZINE: And its
effects are pretty noticeable.
We can see it in the way
it affects the microwave
background radiation left
over from the big bang,
and how it has shaped
the large-scale structure
of the universe itself.
Galaxies wouldn't
even exist if it
weren't for the extra
pull of dark matter.
So
PADDY FOX: We've inferred
the existence of dark matter
indirectly from those effects.
But we've never really got our
hands on the stuff in the lab
in a very direct way yet.
If we believe this dark matter
stuff is basically everywhere--
it pervades the
galaxy we live in,
that in fact our galaxy
sits inside a cloud
of this dark matter stuff.
And so we'd like to see
if they are particles,
whether they come
in and interact
with anything in the lab.
The problem, though,
with detecting dark matter
is that it's pretty
much undetectable.
The hypothetical particles
that make up dark matter
are called WIMPs.
WIMPs stands for Weakly
Interacting Massive Particles.
And since they only weakly
interact with ordinary matter,
we have a hard time knowing
that they are there.
They go straight
through anything,
including our detectors.
MATT WEBER: Regular
matter, on the other hand--
the matter we're made
up of-- does a fantastic
job of interacting with itself.
Isn't that right, Craig?
CRAIG BENZINE: Ho,
ho, hey, ho, ha.
Yeah, just having
a little fun with--
CRAIG BENZINE:
Interacting matter.
PADDY FOX: I mean, I can't
put my hand through this wall,
because I interact too strongly.
CRAIG BENZINE: It's good to know
that you're not dark matter.
PADDY FOX: Yeah, right.
Exactly.
But since ordinary matter
interacts with itself so much,
it can act as noise,
triggering sensitive detectors,
mucking up results, and
basically drowning out
any dark matter particles
that might be coming through.
So you have to stop all the
ordinary stuff from interacting
with your experiment.
And that includes
high-energy particles
like cosmic rays that
are raining down on Earth
all the time.
And the best way to
do this is the put
as much earth between
your experiment
and all the cosmic rays
raining down on the planet.
In other words,
put your experiment
as far underground as possible.
Little shaky.
I'm not claustrophobic or
anything, though, so I'm OK.
You guys, anybody
here claustrophobic?
Uh-oh.
How do you do, man?
ROBERTO VEGA-MORALES:
I try to pretend
I don't know where I am.
CRAIG BENZINE: So what is this?
BILL LEE: So this is
the DM-Ice experiment.
This is a dark
matter experiment.
What they've done is they
put a sodium iodide crystal
inside this lead coffin.
CRAIG BENZINE: And
it's poisonous.
BILL LEE: Lead is poisonous.
CRAIG BENZINE: That's true.
It's a good point.
It's like they just
had a little extra room
under the stairway
and they-- oh, let's
experiment with dark matter.
BILL LEE: We put
experiments wherever we can.
The real experiment
is at the South Pole,
where they have put it in
with the IceCube experiment,
about two miles
under the ice there.
The Ice Cube he's
talking about is not
the star of "XXX, the
State of the Union"
or "Are We There Yet?"
It's the IceCube
Neutrino Observatory,
which is a gigantic telescope
designed to detect neutrinos
which are made of ordinary
matter, but like dark matter,
are notoriously hard to capture.
And instead of being
buried underground,
the IceCube's
neutrino detector is
buried under two kilometers
of ice, just like Ice Cube.
The IceCube hopes to
get indirect evidence
of dark matter through the
detection of excess neutrinos.
Theoretically, since dark
matter particles have mass,
they should be gravitationally
attracted to the sun.
Enough dark-matter particles
should be trapped by the sun
and collect in its core to
annihilate with each other,
giving off neutrinos.
The IceCube should be able
to infer this dark matter's
existence by detecting
occasional unexplained neutrino
collisions and tracing
them back to the source.
There are also experiments
measuring the release of gamma
rays at the center
of the galaxy,
and looking for any
excess that might suggest
the presence of dark matter.
But they've never directly
detected a dark matter
particle.
The Cryogenic Dark
Matter Search,
which is located deep in a
mine in northern Minnesota,
has picked up several
interesting signals since 2007
that might be evidence
of dark matter.
But it could be nothing at all.
CRAIG BENZINE: Now
these are always--
these can go either way.
I mean, this could be
the tip of an iceberg,
or it could just
be the background--
just a fluke, an accident.
MATT WEBER: So it's hard
to detect dark matter,
because it hardly ever
interacts with regular matter.
But another problem is
that we don't know exactly
where all the dark matter is.
CRAIG BENZINE: If you want to
have the best chance of finding
dark matter, it's best
to point your detector
where all the dark
matter is hiding.
And I'm very good
at hide and seek.
I know these things.
So we're pretty sure our
galaxy sits in a spherical halo
of dark matter.
Most of the dark
matter is in this halo.
And a surprisingly little
amount of dark matter
inhabits the disk where we live.
So looking for dark
matter within our vicinity
might be very difficult.
MATT WEBER: But we'd expect
an increase in dark matter
toward the core the
galaxy since the density
of matter increases.
CRAIG BENZINE: Of
course, just because we
know where dark matter
might be doesn't mean
we have any more of a clue
of what it actually is.
The main theory is that dark
matter is a new particle--
one that's not currently
part of our standard model.
But there are other
theories as well.
It's been theorized that dark
matter isn't a particle at all,
but that gravity might not
work like we think it does.
On large scales, like
the scale of galaxies
and the universe
at large, gravity
might display
different properties.
And the excess mass we
see all over the universe
might just be a side effect
of this modified gravity.
But once you start
messing with gravity,
you start messing
with relativity.
And everybody knows that
Einstein doesn't go away
without a fight.
MATT WEBER: So maybe
it would better
if dark matter wasn't some
new, unheard of kind of matter,
but regular matter,
just in an exotic form,
like a primordial black
hole, or something even more
undetectable than a neutrino.
CRAIG BENZINE: But
that seems unlikely.
If it was ordinary matter and
as common as it seems to be,
it would start clumping up
into visible objects like stars
and galaxies.
MATT WEBER: Or
maybe it's some kind
of super fluid, which goes
through different phases, which
makes it hard to detect, and
gives it unexpected behaviors.
CRAIG BENZINE: But the
new particle theory
is definitely the
most widely accepted,
and the strongest candidate for
dark matter's secret identity.
MATT WEBER: And if it's one
thing for sure, whatever
dark matter's
secret identity is,
its discovery will revolutionize
physics as we know it.
CRAIG BENZINE: And
by revolutionize, we
mean really screw up how we
thought the universe works.
We have no idea what's going on.
MATT WEBER: Yeah,
totally clueless.
RYAN: It seems like if there is
another particle that makes up
dark matter, it screws up this
nice, neat, standard model
that you have.
Is that, like, how
you feel about that?
PADDY FOX: It would be awesome.
CRAIG BENZINE: Yeah,
it would be awesome.
PADDY FOX: Yeah, the one
thing every theorist, and I
believe every
experimentalist craves for
and hopes for on
a daily basis is
something comes along that
screws up the standard model.
The standard model
is a wonderful theory
that explains
everything we've seen
so far about subatomic
physics, or subnuclear physics.
But we don't think
it's the final story.
We don't think it is the
final answer for the way
Nature works.
So we believe there's
more out there.
So to see some
phenomena that isn't
explained by the standard
model would be fantastic.
And it could well be.
I mean, there's five
times as much dark matter
as there is regular matter.
So it's unlikely that the dark
sector, as we like to call it,
is simply just one new particle.
There's probably a whole lot
of new phenomena in there
that we just aren't privy to
yet because it is hard for us
to measure it.
But we need to find ways that
will allow us to measure it.
And it will be a whole
new realm of physics
for us to investigate.
So what do you
think dark matter is?
Is it a new particle, or is
it gravity behaving weirdly?
Or maybe it's a wholly
unknown form of physics
that we're only
beginning to understand.
And most importantly,
will we ever
be able to harness it as fuel
for an interstellar delivery
spaceship?
LEELA: It's dark matter.
BENDER: So this guy just
unloaded a steaming pile
of starship fuel?
Let us know in the comments.
I wanted to say that.
Let us know in the comments.
Go ahead, there you go.
I want to let you know
about another series here
on the internets that everyone
on this show has worked on.
It's called--
Platoon of Power Squadron.
That's right.
It's about superheroes.
Well, no, they're
not superheroes.
They're normal people
with superpowers.
Thats' right.
And there's a star on
that show who's awesome.
Yeah, Jake Jarvi.
No, Craig Benzine, me.
I'm in it as well.
Oh, you're in that show?
I am.
What part do you play?
Are you just like an
extra or something?
Extra good.
If you've never heard
of it, I'm going
to put a link right up
here on Matt's head that
gives a great description
of the first nine episodes.
And there's an
Indie-Go-Go fundraiser
linked in the du-be-du
for the 10th episode.
After six years, the final
episode is being made.
You guys should check it out.
It has nothing to do this show.
But we're all
really proud of it,
and we think you'll like it.
OK last week we talked
about Henry Darger.
And you guys had a
lot of things to say.
And we got a lot of
things to say as well.
We do.
Bert Paulson, among
others, pointed out
that we didn't mention that some
of the girls that Darger drew
had penises.
This wasn't oversight.
And we did have some
discussions about
whether we should
mention it or not.
But it seemed too distracting
from the bigger picture.
And in the end, there's
no explanation for it.
There's a lot of
theories, though.
Some have mentioned that
the penises represent
Darger's issues of gender.
He might have been gay or
experienced gender dysmorphia.
Or maybe he didn't
understand the difference
between girls or boys, or that
the penises on the Vivian girls
represented
masculinity and power.
Whatever the
reason, Darger isn't
around to explain it to us.
So we will never know.
A few of you thought
Darger's depictions
of naked and tortured children
represented a fetish, or maybe
latent pedophilia.
And that's why he didn't
want anybody to see his art.
We'll never know for sure
what it all meant to Darger,
but there doesn't seem
to be much evidence
that he was a pedophile.
He didn't sexualize
the children.
And all the stories
are from the point
of view of the Vivian
girls and the children.
So it seems like we're supposed
to sympathize with them,
and not the evil men
that are torturing them.
There's much more
evidence that Darger had
a troubled childhood himself.
And the violence and the
torture we see in his art
is probably a way of him
processing and dealing
with his own child abuse.
And there's always
the possibility
that it means nothing at all.
He did it for no reason.
But we'll never know for sure.
I would also argue that
there's a lot weirder and more
disturbing art out
there right now.
But we don't accuse
the artists of being
deranged, because they're
still around to explain it.
The fact that we don't
know much about Darger
makes him kind of
a blank canvas.
And we can make him whatever
kind of person we want.
It's really up to you.
A lot of you had some great
answers for what art is.
High-Waisted Pantaloon
says "The Art Assignment"--
a fellow PBS digital show--
taught me that art has no
single definition.
Art is everything.
Art is anything
that makes you feel.
Verdatum said
something similar.
He basically said, anything that
evokes an emotional reaction
could be considered art.
Sure.
LynneSkysong said that art
doesn't need an audience.
Art just is.
I like that one.
I like the way you think.
Thanks for all your
wonderful comments.
Next week is our final episode
in the secrets playlist.
It's all about hackers.
Good hackers.
Yeah, good hackers.
Like Angelina Jolie
and the other person.
In "Hackers"?
Yeah.
Would they be technically
considered good hackers?
Yeah, they're the
good guys, right?
In the movie.
I've never seen that movie.
Yeah, but they
do break the law.
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