okay so we've talked about space a
couple of times on this series how cool
it is and all the different kinds of
amazing work that Livermore scientists
are doing in space I mean it's big out
there there's a lot going on but at the
same time we know so little about space
you guys we don't even know what most of
the universe is so dark matter and makes
up 85% of the mass in the universe that
means stuff like you me this table here
it's only 15% of the rest of the mass
everything and all the complexities that
we know in our daily life is a small
fraction of the total mass in the
universe I mean what that's right folks
today we are tackling dark matter
so this is how little we know about dark
matter all right we don't know if dark
matter is one of the lightest particles
in existence or if it's thousand solar
mass black holes or anything in between
this is we're in a bit of a predicament
here but how do we know that all of this
unknown stuff is dark matter or that
it's even there in the first place
well that is a small history lesson
right there in the 1930s a Swiss
astronomer named Fritz Zwicky was
working at Caltech and he noticed that
galaxies were moving around their galaxy
clusters way too fast for all of their
stuff to be held in place by just
gravity okay like if the galaxy is a kid
riding a merry-go-round then the galaxy
cluster is going around and around way
too fast for the kids or the galaxies to
be held in place by just their gravity
alone there's got to be something else
holding them in place too and Zwicky
called that thing dark matter it does
have a very cool name I'll give him that
and so ever since astronomers have been
asking themselves okay so does this mean
we need a new theory of gravity like
does gravity not work the way we thought
it did or is this due to some kind of
unknown particle and while we're pretty
sure that our existing theory of gravity
continues to hold up we're still trying
to figure out the rest but just one
quick question how do you look for
something that you can't see and haven't
figured out how to detect yet seems like
a big challenge so again because we have
no idea and we're covering many orders
of magnitude you've got astronomers like
me we're using the cosmos in different
observables in the universe to try to
constrain the properties of dark matter
but you have other people like there are
people at the lab who are using solar
observing telescopes to look for
accion's you also have others who are
doing more laboratory experiments where
they are staring at tons of liquid xenon
which interacts very little with the
rest of the universe and every once a
while looking for a dark matter
particles coming in
scattering off one of these liquid
Xenon's and creating a free flash of
light which you can measure but then you
have others who are at colliders so
particle accelerators trying to actually
generate Dark Matter assuming that it's
some supersymmetric particle like a wimp
which is a weakly interacting massive
all and then you have others that are
using telescopes and gamma-ray
observatories on the off-chance the Dark
Matter decays and annihilates into other
energetic particles and so we're really
trying to approach it from as many
different angles as we can
what's all this about black holes okay
sure so this is a remote observing room
and so this enables us to connect the
telescope that's down in Chile which is
a four meter telescope so pretty large
telescope that we use to survey the
center of our own galaxy the center of
the Milky Way and the large and small
Magellanic Clouds our nearest largest
neighbors okay but how do you look for a
black hole I'm so glad you asked because
you know a black hole swallows all of
the light that gets close to it so how
can you measure any of it
notoriously greedy and difficult
cosmological bodies black holes the way
that Will and his colleagues are doing
it is using something called
gravitational lensing which relies on
Einstein's theory of general relativity
black holes are so dense and so full of
the stuff that they suck up that they
actually distort space-time they cause
curvatures in the fabric of the universe
and so the black hole actually acts as a
gravitational lens so almost like a
magnifying glass that causes a star to
brighten as it passes behind the black
hole and it shines it's light on its way
to you and so focus is that light it
gets brighter with time and then
eventually it will turn back to its
regular brightness now the chances of a
star passing right behind a black hole
are near in decimal so what we have to
do is we have to study billions we stare
at millions of stars just on the off
chance that every once a while a few of
those stars will pass right behind a
black hole and give us that telltale
signature that there was a black hole
there then that that enables us with
other methods to measure the mass of
that black hole and so we can both count
the number of black holes in their mass
add all that up and see if it's enough
to make up dark matter Wow
I mean uncovering the identity of the
rest of the 85% of the mass of the
universe that we don't understand yet
would be huge and that's one part of me
but the other part of me is also a
little bit like
why exactly do we care well we have
strong evidence that Dark Matter exists
but dark matter also doesn't fit into
the existing models of the universe that
we've come up with so if we could
somehow peel back the curtain on dark
matter it could totally upend our
understanding of what our universe
actually is and also if dark matter does
end up being these primordial black
holes that we'll studies and black holes
are thought to be the first objects to
have formed in the universe then we get
ever closer to understanding those
crucial moments at the beginning of well
everything it's kind of like we are
currently seeing our universe and
everything in it with 10-20 vision and
understanding more about dark matter
would be a pair of prescription glasses
like a heck of a lot would come into
focus and it's all pretty mind-boggling
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address something max leave all of that
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case you missed any as always thank you
so much for watching and I will see you
next time I will say though that that
whenever I was in my graduate career and
I was studying merging galaxy clusters
and we were getting tantalizing evidence
that Dark Matter might be interacting
with itself I was like okay within five
years we're gonna have Dark Matter
nailed down this is gonna be amazing
it's been more than five years now and
we haven't quite done it so I'm not
giving up but I wouldn't be surprised if
dark matter ends up being something that
we haven't even thought of yet
you
