
English: 
[rock music]
 [upbeat music]
>> NASA's Jet Propulsion
Laboratory presents
the von Karman Lecture,
a series of talks
 by scientists and engineers
  who are exploring our
  planet, our solar system,
  and all that lies beyond.
 [audience applauding]
  >> Hey, everybody.
Well, welcome to our
monthly public talk here
 at NASA's Jet
 Propulsion Laboratory.
  My name is Preston Dyches.
 Well, it's October,
 and Halloween is just
  >> Ooh.
  >> a couple of weeks away.

English: 
 This is the time of year
 when we become acutely aware
 that there are things
 out there in the dark.
 [audience laughing]
things beyond our understanding.
So in the spirit of the season,
 we've prepared a talk for you
 about two of the most
 terrifying, I mean fascinating
[audience laughing]
mysteries of the cosmos.
 These are the enigmatic
 dark matter and dark energy.
We'll have a single talk tonight
  in which our two speakers
  will share the stage,
 and then we'll take
 your questions.
  And if you're watching the
  live webcast on YouTube,
 we'll work in a few
 of your questions
from the chat, as well.
 So now to introduce
 our speakers.
Our speakers this month
are a unique pairing.
Alina Kiessling and Jason Rhodes
are both astrophysicists at JPL,
 where they are
 involved in a variety
of exciting astronomy projects.
 Both have a history
 of using a technique
 called gravitational lensing
 to study dark matter
 and dark energy.
 She's worked on simulating it,
  while he's worked
  on measuring it.
  But what's really special

English: 
 NASAS JET
PROPULSION LABORATORY PRESENTS
THE VON KARMAN LECTURE, A SERIES
OF TALKS BY SCIENTISTS AND
ENGINEERS EXPLORING OUR PLANET,
OUR SOLEAR SYSTEM AND ALL THAT
LIES BEYOND.

English: 
  is that these two
  gifted researchers
were pulled together by,
 let's call it a mutual
 force of attraction.
 [audience laughing]
 You see, they just happen
 to be married to each other.
 [audience laughing]
  So we think you'll
  enjoy their take
  on the dark and
  mysterious forces at work
  in the universe around us,
  so please welcome
  Jason and Alina.
 [audience applauding]
 >> Thank you so much, Preston.
  Jason and I are so excited
  to be here tonight,
 and wow, look at this crowd.
 It is so big.
 [audience laughing]
 It's very exciting.
  And as science-interested
  people,
  I'm sure that you
  can all also agree
that the universe is really big.
But sometimes it's hard to think
about really, really big things,
 so let's try to put it into
 context a little bit for you.

English: 
>> HEY, EVERYBODY.
WELCOME TO OUR MONTHLY PUBLIC
TALK HERE.
MY NAME IS PRESTON DYCHES.
WELL, IT'S OCTOBER.
AND HALLOWEEN IS JUST A COUPLE
OF WEEKS AWAY.
THIS IS A TIME OF YEAR WHEN WE
BECOME ACUTELYWARE THAT THERE
ARE THINGS OUT THERE IN THE
DARK, THINGS BEYOND OUR
UNDERSTANDING.
SO WHEN THE SPIRIT OF THE
SEASON, WE PREPARED A TALK FOR
YOU ABOUT TWO OF THE MOST
TERRIFYING, I MEAN FASCINATING
MYSTERIES OF THE COSMOS.
THOSE ARE THE ENIGMATIC DARK
WE'LL HAVE A SINGLE TALK IN
WHICH OUR TWO SPEAKERS WILL
SHARE THE STAGE AND THEN TAKE
YOUR QUESTIONS.
IF YOU'RE WATCHING THE LIVE
WEBCAST ON YOU TUBE, WE'LL WORK
IN A FEW QUESTIONS FROM YOU, AS

English: 
  Let's talk about some big
  numbers to start with,
  numbers like a million, a
  billion, and a trillion.
  There was a study
  done that found
  that 35% of people
  thought that these numbers
 were equally spaced
 on a number line.
 I can tell you that
 this is not correct.
  So if you had zero at one
  end of the number line
 that's 10 centimeters long,
and you had one billion
at the other end
  of that same number line,
  one million would be
  just one human hair width
away from zero.
So one million is almost
nothing compared to one billion.
 And we can put this a
 little bit more into context
with some things that
we're all familiar with.
So let's take a dime, 10 cents.
 I'm walking along the street,
 I see a dime on the ground,
  but I've got a bit
  of a sore back.
  I'm just, I'm not
  gonna pick it up.
A dime compared to $100,

English: 
WELL.
OUR SPEAKERS THIS MONTH ARE A
UNIQUE PAIRING.
ALINA KIESSLING AND JASON RHODES
ARE BOTH ASTRO PHYSICISTS WHERE
THEY ARE INVOLVED IN A VARIETY
OF PROJECTS.
BOTH HAVE A HISTORY OF USING A
TECHNIQUE, GRAVITATIONAL LENSING
TO STUDY DARK MATTER AND DARK
ENERGY.
SHE WORKED AND STIMULATING IT,
HE WORKED ON MEASURING IT.
WHAT IS SPECIAL IS THESE TWO
GIFTED RESEARCHERS WERE PULLED
TOGETHER BY LETS CALL IT A
MUTUAL FORCE OF ATTRACTION.
THEY JUST HAPPEN TO BE MARRIED
TO EACH OTHER.
SO WE THINK YOU'LL ENJOY THEIR
TAKE ON DARK AND MYSTERIOUS
FORCES AT WORK IN THE UNIVERSE
AROUND US.
SO PLEASE WELCOME JASON AN
ALINA.
[ APPLAUSE ]
>> THANK YOU SO MUCH, PRESTON.
JASON AND I ARE SO EXCITED TO BE
HERE TONIGHT AND WOW, LOOK AT

English: 
 which is a nice dinner
 out in Los Angeles
for Jason and I,
 so 10 cents is almost nothing
 compared to that $100.
 And that's the same
 as the difference
 between one million
 and one billion.
  Now, let's look at
  a larger number,
 so we've got $100
 compared to $100,000,
which is the equivalent
of a down payment
on a house here in Los Angeles.
 So the $100 is almost nothing
 compared to the $100,000,
 and this is the equivalent of
 one billion to one trillion.
So these numbers really
are very, very different
 to each other.
 The 10 cents is
 really insignificant
  compared to the $100,000,
 just like one million
 is very insignificant
  compared to one trillion.
  So now that we've
  got some context
 on the relative
 sizes of the numbers,
  we can put it into
  context with the universe.
 So when I was a kid,

English: 
 I thought the earth
 was really big.
 And my parents
 used to take me out
 into the desert of Australia
 and we were looking for opals.
And one day, I found an
opalized dinosaur bone.
This was really exciting for me,
and it started me on my
career in astrophysics.
 And I wanted to learn
 how the earth began
 and evolved over time,
 but then I realized
 that I wasn't really
 thinking big enough.
Did you know that about
one million earths
  would fit inside
  the sun, our sun?
 And our sun is a star.
  And there are around 100
  billion stars in a galaxy,
 and there's around 100 billion
 galaxies in the universe.
 So that's 100 billion galaxies
times 100 billion stars,
 or 10 billion trillion
 stars in the universe.

English: 
THIS CROWD.
IT'S SO BIG!
VERY EXCITING.
AND AS SCIENCE INTERESTED
PEOPLE, I'M SURE THAT YOU CAN
ALL ALSO AGREE THAT THE UNIVERSE
IS REALLY BIG.
BUT SOMETIMES, IT'S HARD TO
THINK ABOUT REALLY, REALLY BIG
THINGS, SO LET'S TRY TO PUT IT
INTO CONTEXT A LITTLE BIT FOR
YOU.
LET'S TALK ABOUT SOME BIG
NUMBERS TO START WITH, NUMBERS
LIKE A MILLION, A BILLION AND A
TRILLION.
THERE WAS A STUDY DONE THAT
FOUND THAT 35% OF PEOPLE THOUGHT
THAT THESE NUMBERS WERE EQUALLY
SPACED ON A NUMBER LINE.
I CAN TELL YOU THAT THIS IS NOT
CORRECT.
IF YOU HAD ZERO AT ONE END OF A
NUMBER LINE, THAT'S
10 CENTIMETERS LONG AND YOU HAD
1 BILLION AT THE OTHER END OF
THAT SAME NUMBER LINE, 1 MILLION
WOULD BE JUST ONE HUMAN HAIR
WIDTH AWAY FROM ZERO.

English: 
1 MILLION IS ALMOST NOTHING
COMPARED TO 1 BILLION.
WE CAN PUT THIS A LITTLE BIT
MORE INTO CONTEXT WITH THINGS
WE'RE ALL FAMILIAR WITH.
SO, LET'S TAKE A DIME, 10 CENTS
AND WALKING ALONG THE STREET, I
SEE A DIME ON THE GROUND, BUT
I'VE GOT A BIT OF A SORE BACK,
I'M NOT GOING TO PICK IT UP.
A DIME COMPARED TO $100, WHICH
IS A NICE DINNER OUT IN LOS
ANGELES FOR JASON AND I.
SO 10 CENTS IS ALMOST NOTHING
COMPARED TO THAT $100, AND
THAT'S THE SAME AS THE
DIFFERENCE BETWEEN 1 MILLION AND
1 BILLION.
NOW LET'S LOOK AT A LARGER
NUMBER, SO WE'VE GOT $100
COMPARED TO $100,000, WHICH IS
THE EQUIVALENT OF A DOWN PAYMENT
ON A HOUSE HERE IN LOS ANGELES.
SO THE $100 IS ALMOST NOTHING
COMPARED TO THE $100,000, AND
THIS IS THE EQUIVALENT OF
1 BILLION TO 1 TRILLION.

English: 
Now that is an enormous number.
I started to get an idea
  of just how big
  the universe was,
 and I knew that I
 needed to understand
 how the universe began
 and evolved over time.
  That's how I got
  into astrophysics.
 But as Jason's going
 to tell you next,
this 10 billion trillion
stars in the universe
 is really just a tiny fraction
 of everything there is.
 >> So Alina and are
 are cosmologists.
Those are scientists that study
 the contents of the universe.
 And when a cosmologist
 starts to talk,
he or she usually
starts with this chart,
 The Universe as a Pie Chart,
 and it's a pie
 because it's round.
And this is the contents
[audience laughing]
of the universe,
and you can see that the
contents of the universe
 are divided up into
 very uneven pieces,
 probably very unfair
 pieces for those kids
  that want the big
  piece of the pie,
 but maybe their brother or
 sister gets the bigger piece.
  But the universe is not
  given to very even pieces.

English: 
SO THESE NUMBERS REALLY ARE
VERY, VERY DIFFERENT TO EACH
OTHER.
THE 10 CENTS IS REALLY
INSIGNIFICANT COMPARED TO THE
$100,000, JUST LIKE 1 MILLION IS
VERY INSIGNIFICANT COMPARED TO
1 TRILLION.
SO NOW THAT WE'VE GOT SOME
CONTEXT ON THE RELATIVE SIZES OF
THE NUMBERS, WE CAN PUT IT INTO
CONTEXT WITH THE UNIVERSE.
SO WHEN I WAS A KID, I THOUGHT
THE EARTH WAS REALLY BIG, AND MY
PARENTS USED TO TAKE ME OUT INTO
THE DESERT OF AUSTRALIA AND WE
WERE LOOKING FOR OPEN PAMS.
ONE DAY I FOUND AN OPENNALLIZED
DINOSAUR BONE.
THIS WAS EXCITING FOR ME AND
STARTED ME ON MY CAREER IN
ASTROPHYSICS.
I WANTED TO LEARN HOW THE EARTH
BEGAN AND EVOLVED OVER TIME BUT
THEN I REALIZED THAT I WASN'T
REALLY THINKING BIG ENOUGH.
DID YOU KNOW THAT ABOUT
1 MILLION EARTHS WOULD FIT
INSIDE THE SUN, OUR SUN, AND OUR

English: 
 The pieces that Alina was
 talking about, the stars here,
 only make up about
 1% of the universe.
  There's a lot more gas in
  the universe than that.
 That's a few percent.
 And one of the things
 that we've found
 in the past few years
  is that almost every star,
  we think, has a planet.
  So we think that those
  10 billion trillion stars
 that Alina was talking
 about in the universe
 probably each have
 at least one planet.
 But those planets are such a
 small part of the universe,
 they don't even show
 up on this pie chart.
The other piece of what we call
normal matter is neutrinos.
 Neutrinos are small,
 ghostly particles,
  billions of which pass
  through you every second,
  but you can't feel them,
  but we know they're there.
  But all the stuff
  I've talked about
 is what we call normal matter,
 it's the stuff we can
 see in the universe,
 it's the stuff we can detect,
 it's the stuff that we see
 with telescopes and our eyes.
It's you and me.

English: 
SUN IS A STAR.
THERE ARE AROUND 100 BILLION
STARS IN A GALAXY AND THERE'S
AROUND 100 BILLION GALAXYION IN
THE UNIVERSE, SO THAT
100 BILLION GALAXIES TIMES
100 BILLION STARS OR
10 SEXTILLION STARS IN THE
UNIVERSE.
NOW THAT IS AN ENORMOUS NUMBER.
I STARTED TO GET AN IDEA OF JUST
HOW BIG THE UNIVERSE WAS AND I
KNEW THAT I NEEDED TOPPED HOW
THE UNIVERSE BEGAN AND EVOLVED
OVER TIME.
THAT'S HOW I GOT INTO ASTRO
PHYSICS.
AS JASON'S GOING TO TELL YOU
NEXT, THIS 10 SEXTILLION STARS
IN THE UNIVERSE IS REALLY JUST A
TINY FRACTION OF EVERYTHING
THERE IS.
>> SO ALINA AND I ARE CROSS
MOLESTINGISTS, THE SCIENTISTS
THAT STUDY THE UNIVERSE.

English: 
That only makes up about
5% of the universe.
 And we've known for the
 better part of a century now
 that most of the matter in
 the universe is dark matter.
 It's a ghostly form of matter
 that's not giving off light,
  it's not absorbing light,
 and that's why we
 call it dark matter.
 And when I went
 into graduate school
 in the 1990s after college,
 I wanted, like Alina,
  to understand the
  contents of the universe.
 So I went to graduate
 school thinking
  I'm gonna figure out
  what this dark matter is.
But a funny thing happened
while I was in graduate school.
 Some of my colleagues
 doing some work
that we'll tell you
about later in this talk
 realized that the dark matter
  isn't even the biggest
  component of the universe.
  There's a bigger
  component of the universe
  that we call dark energy.
So when I finished
graduate school in 1999,
  like Alina, I realized the
  universe was much bigger
than I thought, and I
needed to think bigger.
 And so now, I'm
 trying to figure out

English: 
what the dark matter
and the dark energy are.
 So we don't know what
 these things are.
 Let's talk about what we
 do know about them tonight.
And we're gonna start
by talking a little bit
  about dark matter.
 >> Before we move on, I wanna
 share a little story with you.
 So let's take a look at what
 Jason's wearing here tonight.
 [audience laughing]
 I came across Jason
 earlier with his tie
measuring with a ruler,
  I thought, Jason, what
  are you doing, seriously?
 And he said, "Well,
 Halloween theme,
 "so I'm gonna dress
 up as the universe."
[audience laughing]
And I'm just making sure
 that my tie is about
 5% of my surface area.
 [audience laughing]
 [audience applauding]

English: 
WHEN WE TALK, WE USUALLY START
WITH THIS CHART, THE UNIVERSE IS
A PIECHART AROUND IT'S A PIE
BECAUSE IT'S ROUND.
THIS IS THE CONTENTS OF THE
UNIVERSE.
YOU CAN SEE THAT THE CONTENTS OF
THE UNIVERSE ARE DIVIDED UP INTO
VERY UNEVEN PIECES, PROBABLY
UNFAIR PIECES FOR THOSE KIDS
THAT WANT THE BIG PIECE OF THE
PIE BUT MAYBE THEIR BLOWER OR
SISTERS GETS THE BIGGER PIECE.
THE UNIVERSE IS NOT GIVEN TO
VERY EVEN PIECES.
THE PIECES THAT ALINA WAS TALK
ABOUT, THE STARS HERE ONLY MAKE
UP ABOUT 1% OF THE UNIVERSE.
THERE'S A LOT MORE GAS IN THE
UNIVERSE THAN THAT.
THAT'S A FEW PERCENT.
ONE OF THINGS THAT WE FOUND IN
THE PAST FEW YEARS IS THAT
ALMOST EVERY STAR, WE THINK, HAS
A PLANET SO WE THINK THAT THOSE
10 SEXTILLION STARS THAT ALINA
WAS TALKS ABOUT IN THE UNIVERSE
PROBABLY EACH HAVE ONE PLANET,
BUT THEY ARE SUCH A SMALL PART
OF THE UNIVERSE, THEY DON'T EVEN
SHOW UP ON THIS PIECHART.

English: 
 That's what it's like being
 married to a cosmologist.
 [audience laughing]
So let's talk about dark matter.
Back in the 1930s here in
Pasadena, California at Caltech,
 a scientist named Fritz Zwicky
 was looking at
 galaxies in the sky,
and he was trying to
understand how they move
relative to each other.
  And while he was
  observing their movements,
he realized that there had to be
something unseen in the universe
 to be causing those
 galaxies to be moving
the way that they were.
  And he called this
  unseen, unknown component
 of the universe dark matter.
 Fast forward to the 1960s,
 and the scientist Vera Rubin.
 She was looking at
 individual galaxies
and trying to understand
how their stars rotate.
 So if we look at
 our galaxy up here,
 we've got lots more
 stars in the center
 than we do at the outskirts,

English: 
THE OTHER PIECE OF WHAT WE CALL
NORMAL MATTER IS NUTRINOS, SMALL
GHOSTLY PARTICLES BILLIONS OF
WHICH PASS THROUGH YOU EVERY
SECOND BUT YOU CAN'T FEEL THEM,
BUT WE KNOW THEY'RE THERE.
ALL THE STUFF I TALKED IS WHAT
WE CALL NORMAL MATTER, THE STUFF
WE CAN SEE IN THE UNIVERSE, THE
STUFF WE CAN DETECT.
IT'S THE STUFF THAT WE SEE WITH
TELESCOPES IN OUR EYES, IT'S YOU
OR ME.
THAT ONLY MAKES UP ABOUT 5% OF
THE UNIVERSE AND WE'VE KNOWN FOR
THE BETTER PART OF A CENTURY NOW
THAT MOST OF THE MATTER IN THE
UNIVERSE IS DARK MATTER.
IT'S A GHOSTLY FORM OF MATTER
THAT'S NOT GIVING OFF LIGHT,
IT'S NOT ABSORBING LIGHT AND
THAT'S WHY WE CALL IT DARK
MATTER.
WHEN I WENT INTO GRADUATE SCHOOL
IN THE 1990'S, AFTER COLLEGE, I
WANTED LIKE ALINA TO UNDERSTAND
THE CONTENTS OF THE UNIVERSE, SO
I WENT TO GRADUATE SCHOOL
THINKING I'M GOING TO FIGURE OUT
WHAT THIS DARK MATTER IS.
BUT A FUNNY THING HAPPENED WHILE
I WAS IN GRADUATE SCHOOL.

English: 
SOME OF MY COLLEAGUES DOING SOME
WORK THAT WE'LL TELL YOU ABOUT
LATER IN THIS TALK REALIZED THAT
THE DARK MATTER ISN'T EVEN THE
BIGGEST COMPONENT OF THE
UNIVERSE.
THERE'S A BIGGER COMPONENT OF
THE UNIVERSE THAT WE CALL DARK
ENERGY.
SO WHEN I FINISHED GRADUATE
SCHOOL IN 1999, LIKE ALINA, I
REALIZED THE UNIVERSE WAS MUCH
BIGGER THAN I THOUGHT AND I
NEEDED TO THINK BIGGER SO NOW
I'M TRYING TO FIGURE OUT WHAT
THE DARK MATTER AND THE DARK
ENERGY ARE, SO WE DON'T KNOW
WHAT THESE THINGS ARE.
LET'S TALK ABOUT WHAT WE DO KNOW
ABOUT THEM TONIGHT, AND WE'RE
GOING TO START BY TALKING A
LITTLE BIT ABOUT DARK MATTER.
>> BEFORE WE MOVE ON, I WANT TO
SHARE A LITTLE STORY WITH YOU.
LET'S TAKE A LOOK AT WHAT
JASON'S WEARING HERE TONIGHT.
I CAME ACROSS JASON EARLIER WITH
HIS TIE MEASURING WITH A RULER.

English: 
  and Vera Rubin was looking
at how fast those stars
were rotating around.
 In my figure here, we're
 showing increasing velocity
  as we go up for the stars,
 and as we go to the right,
 we've got increasing distance
 from the center of the galaxy.
What scientists expected to see
when they first started
looking at these stars
  was that the stars
  at the outskirts
 would be moving slower than
 the stars at the interior.
 And that's shown
 with this blue curve.
 But when Vera Rubin measured
 the velocities of the star,
 she found that they
 were actually moving
 at the same velocity,
  no matter how far
  out she looked.
 And the only
 explanation for this
  is that there's some form
  of unseen dark matter
 holding that galaxy together
 because without that matter
 to hold the galaxy together,

English: 
 those stars rotating
 that quickly
 would be flung out
 away from the galaxy.
And this is considered
the first real evidence
of dark matter in our universe.
  >> So fast forward
  a few more decades
  after Vera Rubin's
  incredibly important work,
  and we have a lot more
  evidence for dark matter.
I'm showing here a baby
picture of the universe.
 This is the universe when it
 was only 300,000 years old,
 after the Big Bang, which
 happened 13 billion years ago.
 This is a map of the
 temperature of the universe.
And in this map, you
see hot and cold spots,
 red and blue spots.
  And in fact, those
  hot and cold spots
are almost the same temperature.
 The difference between
 the hot and cold spots
  is only about one
  part in 10,000.
 So we had an almost
 uniform early universe
with tiny fluctuations,

English: 
I'M LIKE JASON, WHAT ARE YOU
DOING, SERIOUSLY.
AND HE SAID WELL, HALLOWEEN
THEME, SO I'M GOING TO DRESS UP
AS THE UNIVERSE.
I'M JUST MAKING SURE THAT MY TIE
IS ABOUT 5% OF MY SURFACE AREA.
[ APPLAUSE ]
>> THAT'S WHAT IT'S LIKE BEING
MARRIED TO A CROSS MOL GIST.
LET'S TALK ABOUT DARK MATTER AT
CAL TECH, A SCIENTIST NAMED
FRITZ WAS LOOKING AT GALAXYION
IN THE SKY AND TRYING TO
UNDERSTAND HOW THEY MOVE
RELATIVE TO EACH OTHER.
WHILE HE WAS OBSERVING THEIR
MOVEMENTS, HE REALIZED THAT
THERE HAD TO BE SOMETHING UNSEEN
IN THE UNIVERSE TO BE CAUSING
THOSE GALAXIES TO BE MOVING THE
WAY THAT THEY WERE, AND HE

English: 
  and those fluctuations
  corresponded to over-dense
 and under-dense parts
 of the universe,
 that is, parts of the universe
 where there was more stuff,
 and parts of the universe
 where there was less stuff.
 And a part where
 there's more stuff,
 there's more gravity,
 there's more mass,
 there's more gravity.
 And those parts grew
  through what we call
  gravitational instability.
 They accreted stuff
 from around them,
 and they eventually
 became the galaxies
and clusters of galaxies
that we see today.
 So from a very early universe
 that was extremely uniform,
we have a very
clustered universe today
 with galaxies and
 clusters of galaxies
  like the ones I'm showing
  in this picture here.
 This picture is one
 of the deepest images
we've ever taken of the cosmos,
and this is a picture taken
with the Hubble Space Telescope
 called the Ultra Deep Field.
 This picture is a very,
 very small piece of the sky.
  If I managed to
  pick up that dime
 that Alina was
 talking about earlier
 and I held that dime
 at arm's length,

English: 
CALLED THIS UNSEEN UNKNOWN
COMPONENT OF THE UNIVERSE DARK
MATTER.
FAST FORWARD TO THE 1960'S, AND
THE SCIENTISTS VERA REUBEN
LOOKING AT INDIVIDUAL GALAXIES
AND TRYING TO UNDERSTAND HOW
THEIR STARS ROTATE.
IF WE LOOK AT OUR GALAXY UP
HERE, WE'VE GOT LOTS MORE STARS
IN THE CENTER THAN WE DO AT THE
OUTSKIRTS AND VERA WAS LOOKING
AT HOW FAST THOSE STARS WERE
ROTATING AROUND.
IN THE FIGURE HERE, WE'RE
SHOWING INCREASING VELOCITY AS
WE GO UP FOR THE STARS AND AS WE
GO TO THE RIGHT, WE'VE GOT
INCREASING DISTANCE FROM THE
CENTER OF THE GALAXY.
WHAT SCIENTISTS EXPECTED TO SEE
WHEN THEY FIRST STARTED LOOKING
AT THESE STARS WAS THAT THE
STARS AT OUTSKIRTS WOULD BE
MOVING SLOWER THAN THE STARS AT
THE INTERIOR AND THAT'S SHOWN
WITH THIS BLUE CURVE.

English: 
 Roosevelt's eye would cover
 about the same area of the sky
 as this picture here.
  But in this picture, we're
  seeing 5,000 galaxies.
 Each of those small
 smudges of light there
  is a galaxy, much like
  our own Milky Way Galaxy,
  which, as Alina told you,
  has 100 billion stars.
 So there's many, many
 galaxies in the sky.
  And what we now realize is
  without the dark matter,
 we never would have
 had enough stuff
 for this very early
 uniform universe
  to become the very clumpy
  universe we see today.
  But keep in mind with this
  picture we're seeing here,
 we're only seeing the
 tip of the iceberg.
We're seeing the visible matter.
  We're not seeing the
  invisible underpart there
of the iceberg.
 That's the dark matter
 holding everything together.
 So now I'm gonna
 digress a little bit,
  and I'm gonna talk
  about the growth
  of a different structure.
 This is the earliest
 known picture

English: 
BUT WHEN CERVA MEASURED THE VERY
WELL CITIES OF THE STAR, SHE
FOUND THAT THEY WERE ACTUALLY
MOVING AT THE SAME VELOCITY, NO
MATTER HOWEVER OUT SHE LOOKED.
AND THE ONLY EXPLANATION FOR
THIS IS THAT THERE'S SOME FORM
OF UNSEEN DARK MATTER HOLDING
THAT GALAXY TOGETHER, BECAUSE
WITHOUT THAT MATTER TO HOLD THE
GALAXY TOGETHER, THOSE STARS
ROTATING THAT QUICKLY WOULD BE
FLUNG OUT AWAY FROM THE GALAXY,
AND THIS IS CONSIDERED THE FIRST
REAL EVIDENCE OF DARK MATTER IN
OUR UNIVERSE.
>> SO FAST FORWARD A FEW MORE
DECADES AFTER VERA REUBEN'S
INCREDIBLY IMPORTANT WORK AND WE
HAVE A LOT MORE EVIDENCE FOR
DARK MATTER.
I'M SHOWING HERE A BABY PICTURE
OF THE UNIVERSE.
THIS IS THE UNIVERSE WHEN IT WAS
ONLY 300,000 YEARS OLD AFTER THE
BIG BANG WHICH HAPPENED
13 BILLION YEARS AGO.
THIS IS A MAP OF THE TEMPERATURE

English: 
 of Jason and Alina.
 [audience laughing]
 [audience applauding]
It was taken about 10 years ago
 at a conference in Scotland
 where Alina was
 living at the time,
  and at this conference, we
  were studying dark matter
 and how to measure it.
 And I don't know, but it
 looks to me a little bit like
 Alina's even ignoring
 me in this picture.
 [audience laughing]
But like in the early universe,
 there was a small attraction,
 [audience laughing]
 I'm sure.
 And that attraction
 grew over time,
 and eventually, Alina
 moved here to JPL,
and we ended up with the
structure we see today.
 [audience laughing]
 >> Wow.
 >> So I'm gonna now switch,
 you're here to
 hear about science,
 so I'm gonna switch back and
 talk about science again.
 So I'm gonna tell you about
 how we measure dark matter
 since it's invisible.
 What I have here is a cartoon

English: 
OF THE UNIVERSE, AND IN THIS
MAP, YOU SEE HOT AND COLD SPOTS,
RED AND BLUE SPOTS, AND IN FACT,
THOSE HOT AND COLD SPOTS ARE
ALMOST THE SAME TEMPERATURE.
AND COLD SPOTS IS ONLY ABOUT ONE
PART IN 10,000.
SO WE HAD AN ALMOST UNIFORM
EARLY UNIVERSE WITH TINY
FLUCTUATIONS, AND THOSE
FLUCTUATIONS CORRESPONDED TO
OVER DENSE AND UNDER DENSE PARTS
OF THE UNIVERSE, THAT IS PARTS
OF THE UNIVERSE WHERE THERE WAS
MORE STUFF AND PARTS OF THE
UNIVERSE WHERE THERE WAS LESS
STUFF.
AND A PART WHERE THERE'S MORE
STUFF, THERE'S MORE GRAVITY,
THERE'S MORE MASS, THERE'S MORE
GRAVITY AND THEY GREW THROUGH
GRAVITATIONAL INSTABILITY.
THEY SECRETED STUFF FROM STUFF
AROUND THEM AND BECAME THE
GALAXIES AND CLUSTERS OF
GALAXIES THAT WE SEE TODAY.
FROM A VERY EARLY UNIVERSE THAT
WAS EXTREMELY UNIFORM WE HAVE A
VERY CLUSTERED UNIVERSE TODAY
WITH GALAXIES AND CLUSTERS OF

English: 
 of how we measure dark matter.
In cosmology, we measure
distances with a unit called z.
  So we're here at z of
  zero, we're the observer.
 We're zero distance
 from ourselves,
  and here's our telescope.
 And we look at distant
 galaxies out in the universe,
these distant galaxies
that are of z about one,
 and that might sound
 like a small distance,
 but how we do it in cosmology
 is a distance of one
 is actually about
 halfway to the edge
of the visible universe.
  So this is a very
  distant galaxy.
 In the absence of anything
 between us and that galaxy,
 the light from this
 galaxy would take
 a straight path to us.
 But we know from the work
 that Vera Rubin and others did
 that there's all this
 dark matter out there
in the universe,
 and we're particularly
 sensitive with this technique
 to dark matter
 that's about halfway
 between us and the distant
 galaxy [hiccups], excuse me.
One of the consequences of
Einstein's theory of relativity

English: 
GALAXIES LIKE THE ONES I'M
SHOWING IN THIS PICTURE HERE.
THIS PICTURE IS ONE OF THE
DEEPEST IMAGES WE'VE EVER TAKEN
OF THE COSMOS AND THIS IS A
PICTURE TAKEN WITH THE HUBBLE
SPACE TELESCOPE CALLED THE ULTRA
DEEP FIELD.
THIS PICTURE IS A VERY, VERY
SMALL PEELS OF THE SKY.
IF I MANAGED TO PICK UP THAT
DIME THAT ALINA WAS TALKING
ABOUT EARLIER AROUND HELD THAT
DIME AT ARM'S LENGTH, ROOSEVELT
SAID EYE WOULD COVER ABOUT THE
SAME AREA OF THE SKY AT THIS
PICTURE HERE, BUT IN THIS
PICTURE, WE'RE SEEING 5,000
GALAXIES.
EACH OF THOSE SMALL SMUDGES OF
LIGHT THERE IS A GALAXY, MUCH
LIKE OUR OWN MILKY WAY GALAXY
WHICH HAS 100 BILLION STARS.
THERE'S MANY, MANY GALAXIES IN
THE SKY.
WHAT WE NOW REALIZE IS WITHOUT
THE DARK MATTER, WE NEVER WOULD
HAVE HAD ENOUGH STUFF FOR THIS
VERY EARLY UNIFORM UNIVERSE TO
BECOME THE VERY CLUMPY UNIVERSE
WE SEE TODAY.

English: 
or theory of gravity is
that mass bends space.
So what this means is the light,
  when it gets near
  this dark matter,
 won't take a
 straight path to us.
  That light is gonna take a
  distorted and curved path.
And I'm showing a very,
very exaggerated version
 of that here so
 it's easier to see.
The consequence of this is
that we will not see the galaxy
  as it actually is.
 We'll see a distorted
 version of the galaxy.
  So the dark matter between
  us which we can't see
has distorted our image
of this distant galaxy,
 and in doing so, it's
 telling us something
 about the dark matter.
Now, these distortions
are usually quite small,
 but sometimes, they
 can be quite large.
And we call this strong
gravitational lensing.
 What I'm showing here is a
 picture of a galaxy cluster.
  All the bright spots
  here are nearby galaxies,

English: 
BUT KEEP IN MIND WITH THIS
PICTURE WE'RE SEEING HERE, WE'RE
ONLY SEEING THE TIP OF THE
ICEBERG.
WE'RE SEEING THE VISIBLE MATTER.
WE'RE NOT SEEING THE INVISIBLE
UNDERPART OF THE ICEBERG.
THAT'S THE DARK MATTER HOLDING
EVERYTHING TOGETHER.
SO NOW I'M GOING TO DIGRESS AND
TALK ABOUT THE GROWTH OF A
DIFFERENT STRUCTURE.
THIS IS THE EARLIEST KNOWN
PICTURE OF JASON AND ALINA.
IT WAS TAKEN ABOUT 10 YEARS AGO
AT A CONFERENCE IN SCOTLAND
WHERE ALINA WAS LIVING AT THE
TIME.
AT THIS CONFERENCE WE WERE
STUDYING DARK MATTER AND HOW TO
MEASURE IT.
I DON'T KNOW, BUT IT LOOKS TO ME
A LITTLE BIT LIKE ALINA'S EVEN
IGNORING ME IN THIS PICTURE BUT
LIKE IN THE EARLY UNIVERSE,
THERE WAS A SMALL ATTRACTION,
I'M SURE, AND THAT ATTRACTION

English: 
 and they're part of a
 cluster of galaxies.
  And that cluster has a
  lot of dark matter in it.
  It's very massive.
 And the consequence is that
 galaxies behind that cluster
 have their images
 magnified and changed
 by this gravitational
 lensing technique.
 So these giant arcs
 you see, like that,
this pointer's a little tricky,
like that, and all around,
 these giant arcs are actually
 very distant galaxies
 that would be only
 tiny smudges on here
 if it wasn't for the
 gravitational lensing
  caused by the dark matter
  in these galaxy clusters.
  So this is great
  evidence for dark matter.
Again, we can't see it,
  but we can see its effect
  on these distant galaxies.
 And seeing the effect of dark
 matter on distant galaxies
 makes us as scientists
 really happy.
 [audience laughing]
 And I have to clarify here,
 this is not an image
 that we created
 on our computer for this talk.

English: 
GREW OVER TIME AND EVENTUALLY
ALINA MOVED HERE TO JPL AND WE
ENDED UP WITH THE STRUCTURE WE
SEE TODAY.
SO I'M GOING TO NOW SWITCH YOU
HERE TO HEAR ABOUT SCIENCE, SO
I'M GOING TO SWITCH BACK AND
TALK ABOUT SCIENCE AGAIN.
SO I'M GOING TO TELL YOU ABOUT
HOW WE MEASURE DARK MATTER,
SINCE IT'S INVISIBLE.
WHAT I HAVE HERE IS A CARTOON OF
HOW WE MEASURE DARK MATTER.
IN CROSS MOL GEE WE MEASURE
DISTANCES ABOUT Z.
WE'RE HERE AT Z OF ZERO, HERE'S
OUR TELESCOPE.
WE LOOK AT DISTANCE UNIVERSE.
Z OF ABOUT ONE, THAT SOUNDS LIKE
A SMALL DISTANCE, BUT A DISTANCE
OF ONE IS ABOUT HALFWAY TO THE
EDGE OF THE VISIBLE UNIVERSE, SO
THERE IS A VERY DISTANT GALAXY.
IN THE ABSENCE OF ANYTHING
BETWEEN US AND THAT GALAXY, THE

English: 
 This is an actual image taken
with the Hubble Space Telescope
of strong gravitational lensing,
 and I think it's the
 universe telling us
we should be happy about
the clues it's giving us
 about dark matter.
 [audience laughing]
>> So I'm gonna tell you
with one more analogy,
  I'm gonna use another
  analogy for how we measure
 >> That's interesting.
 >> dark matter.
  This is a penny in a pool,
  that's the analogy here,
 and full disclosure,
 Alina and I don't
 actually have a pool,
 so you're looking at a
 penny in our bathtub,
 [audience laughing]
 but penny in the pool
 sounds better.
 So in this analogy, the penny
 is like the distant galaxy,
 and the water in our bathtub
 or the water in a pool
is like the dark matter.
 You don't see the water here,
but you know it's there
  because you see the effect
  on the image of the penny.
  So what's happening is
  the light is coming to us
from the penny,
 and it's taking
 some distorted path
  that changes our perceived
  shape of the penny

English: 
LIGHT FROM THIS GALAXY WOULD
TAKE A STRAIGHT PATH TO US, BUT
WE KNOW FROM THE WORK THAT VERA
REUBEN AND OTHERS DID THAT
THERE'S ALL THIS DARK MATTER OUT
THERE IN THE UNIVERSE, AND WE'RE
PARTICULARLY SENSITIVE WITH THIS
TECHNIQUE TO DARK MATTER THAT'S
ABOUT HALFWAY BETWEEN US AND THE
DISTANT GALAXY.
ONE OF THE CONSEQUENCES OF
EINSTEIN'S THEORY OF RELATIVITY
OR THEORY OF GRAVITY IS THAT
MASS BENDS SPACE.
WHAT THIS MEANS IS THE LIGHT,
WHEN IT GETS NEAR THIS DARK
MATTER WON'T TAKE A STRAIGHT
PATH TO US.
THAT LIGHT IS GOING TO TAKE A
DISTORTED AND CURVED PATH.
I'M SHOWING A VERY, VERY
EXAGGERATED VERSE OF THAT HERE,
SO IT'S EASIER TO SEE.
THE CONSEQUENCE OF THIS IS THAT
WE WILL NOT SEE THE GALAXY AS IT
ACTUALLY IS.
WE'LL SEE A DISTORTED VERSION OF
THE GALAXY, SO THE DARK MATTER
BETWEEN US, WHICH WE CAN'T SEE
HAS DISTORTED OUR IMAGE OF THIS

English: 
 so that we know
 the water is there,
 in much the same way as the
 light from a distant galaxy
 comes to us, takes a distorted
 path through the dark matter,
 and we see a distorted
 image of that galaxy.
But we don't see
the dark matter,
we don't see the water.
  Now, you can imagine that
  I can't tell very much
  about the water in my tub
  from just looking
  at this one penny.
But if I had a big pool
 and I threw thousands or
 perhaps billions of pennies
  at the bottom of the pool,
I could tell a lot about
the water in that pool
by looking at how the
shapes of those pennies
appeared to me.
 I could tell the
 density of the water
 and how much water there was,
  and in the same
  way, in the 2020s,
we're gonna launch some
telescopes into space,
and we're gonna use some
telescopes on the ground
  that are gonna measure
  billions of galaxy shapes
 across the universe,
 and that's gonna tell us a lot

English: 
DISTANT GALAXY, AND IN DOING SO,
IT'S TELLING US SOMETHING ABOUT
THE DARK MATTER.
NOW THESE DISTORTIONS ARE
USUALLY QUITE SMALL, BUT
SOMETIMES THEY CAN BE QUITE
LARGE, AND WE CALL THIS STRONG
GRAVITATIONAL LENSING.
WHAT I'M SHOWING HERE IS A
PICTURE OF A GALAXY CLUSTER, ALL
THE BRIGHT SPOTS HERE ARE NEARBY
GALAXIES, AND THEY'RE PART OF A
CLUSTER OF GALAXIES, AND THAT
CLUSTER HAS A LOT OF DARK MATTER
IN IT.
IT'S VERY MASSIVE.
THE CONSEQUENCE IS THAT GALAXIES
BEHIND THAT CLUSTER HAVE THEIR
IMAGES MAGNIFIED AND CHANGED BY
THIS GRAVITATIONAL LENSING
TECHNIQUE, SO THESE GIANT ARCS
YOU SEE LIKE THAT, THIS
POINTER'S A LITTLE TRICKY, LIKE
THAT AND ALL AROUND, THESE GIANT
ARCS ARE ACTUALLY VERY DISTANT
GALAXIES THAT WOULD BE ONLY TINY
SMUDGES ON HERE IF IT WASN'T FOR
THE GRAVITATIONAL LENSING CAUSED

English: 
BY THE DARK MATTER IN THESE
GALAXY CLUSTERS, SO THIS IS GRAY
EVIDENCE FOR DARK MATTER.
WE CAN'T SEE IT BUT WE CAN SEE
ITS EFFECT ON THE DISTANT
GALAXIES.
SEEING THE EFFECT OF DARK MATTER
ON DISTANT GALAXIES MAKES YOU
GUESS AS SCIENTISTS REALLY
HAPPY.
I HAVE TO CLARIFY HERE, THIS IS
NOT AN IMAGE THAT WE CREATED ON
OUR COMPUTER FOR THIS TALK.
THIS IS AN ACTUAL IMAGE TAKEN
WITH THE HUBBLE SPACE TELESCOPE
OF STRONG GRAVITATIONAL LENSING
AND I THINK IT'S THE UNIVERSE
TELLING YOU ALSO WE SHOULD BE
HAPPY ABOUT THE CLUES IT'S
GIVING US ABOUT DARK MATTER.
SO I'M GOING TO TELL YOU WITH
ONE MORE ANALOGY, I'M GOING TO
USE ANOTHER ANALOGY FOR HOW WE
MEASURE DARK MATTER.
THIS IS A PENNY IN A POOL.
THAT'S THE ANALOGY HERE AND FULL
DISCLOSURE, ALINA AND I DON'T
ACTUALLY HAVE A POOL, SO YOU'RE
LOOKING AT A PENNY IN OUR
BATHTUB BUT PENNY IN THE POOL

English: 
 about the properties
 of dark matter.
  That's how we're learning
  about dark matter now,
  and that's how we're gonna
  learn about dark matter
 in the future.
So we've talked a little
bit about dark matter,
  but that's not the biggest
  component of the universe,
as I found out when I
was in graduate school,
 and as my colleagues found out
 when I was in graduate school.
 So we have to think bigger.
So let's talk about dark energy.
 >> All right, so
 what's dark energy?
 It's Halloween, so I have to
 scare you all a little bit
  with the equation.
 But I don't wanna
 scare you too much,
 so this is the only
 equation in our talk today,
 and I can reassure you
 it isn't actually
 all that difficult.
  This is Einstein's
  field equation,
and it explains everything
that's going on in the universe,
  just in this one,
  simple equation.
 On the left here, this term,
 we've got gravity,
 which curves space.

English: 
SOUNDS BETTER.
IN THIS ANALOGY, THE PENNY IS
LIKE THE DISTANT GALAXY A THE
WATER IN OUR BATHTUB OR THE
WATER IN A POOL IS LIKE THE DARK
MATTER.
YOU DON'T SEE THE WATER HERE,
BUT YOU KNOW IT'S THERE, BECAUSE
YOU SEE THE EFFECT ON THE IMAGE
OF THE PENNY.
WHAT'S HAPPENING IS THE LIGHT IS
COMING TO US FROM THE PENNY AND
IT'S TAKING SOME DISTORTED PATH
THAT CHANGES OUR PERCEIVED SHAPE
OF THE PENNY SO THAT WE KNOW THE
WATER IS THERE.
IN MUCH THE SAME WAY AS THE
LIGHT FROM A DISTANT GALAXY
COMES TO US TAKES A DISTORTED
PATH THROUGH THE DARK MATTER AND
WE SEE A DISTORTED IMAGE OF THAT
GALAXY, BUT WE DON'T SEE THE
DARK MATTER.
WE DON'T SEE THE WATER.
NOW YOU CAN IMAGINE THAT I CAN'T
TELL VERY MUCH ABOUT THE WATER
IN MY TUB FROM JUST LOOKING AT
THIS $1 PENNY, BUT IF I HAD A
BIG POOL, AND I THREW THOUSANDS
OR PERHAPS BILLIONS OF PENNIES
AT THE BOTTOM OF THE POOL, I
COULD TELL A LOT ABOUT THE WATER

English: 
  On the right, we have all
  the stuff in the universe,
  the matter and the energy.
  Now, keep in mind,
  this is at a time
 when Einstein was
 coming up with this,
 that they knew
 about normal matter
and they knew about dark matter.
 So that's the kind of stuff
  that Einstein was
  thinking about.
 And around that time, Einstein
 and his colleagues thought
 that the universe
 was static, that is,
it wasn't collapsing
and it wasn't expanding.
  And so in order to
  keep the universe
 from collapsing in on
 itself under gravity
  because of all of
  this stuff in it,
 Einstein introduced
 what he called
  the cosmological constant,
and this was supposed
to hold the universe up
against collapsing in on itself.
  Fast forward a few years,
 and we've got
 Hubble, Edwin Hubble.

English: 
  He's here in Los Angeles,
and he's working at the
Mount Wilson telescope,
which is in Los Angeles.
Hubble was interested at looking
at galaxies in our universe
 and determining what velocity
 that they were moving.
So on this figure here,
 we have distance increasing
 away from us as we go right,
and velocity
increasing as we go up.
And what Hubble was able to see
 when he was looking
 at these galaxies
 is that no matter what
 direction he looked,
 the further away a galaxy was,
 the faster it was
 moving away from us.
 And the only
 explanation for this
is if the universe is expanding.
 Totally blew everyone's mind.
 [audience laughing]
  So after this amazing work
  that Edwin Hubble did,
scientists launched a telescope

English: 
IN THAT POOL BY LOOKING AT HOW
THE SHAPES OF THOSE PENNIES
APPEARED TO ME.
I COULD TELL THE DENSITY OF THE
WATER, AND HOW MUCH WATER THERE
WAS, AND IN THE SAME WAY IN THE
2020'S WE'RE GOING TO LAUNCH
TELESCOPES INTO SPACE AND USE
TELESCOPES ON THE GROUND THAT
ARE GOING TO MEASURE BILLIONS OF
GALAXY SHAPES ACROSS THE
UNIVERSE AND THAT'S GOING TO
TELL US A LOT ABOUT THE
PROPERTIES OF DARK MATTER.
THAT'S HOW WE'RE LEARNING ABOUT
DARK MATTER NOW AND THAT'S HOW
WE'RE GOING TO LEARN ABOUT DARK
MATTER IN THE FUTURE.
WE'VE TALKED A LITTLE BIT ABOUT
DARK MATTER, BUT THAT'S NOT THE
BIGGEST COMPONENT OF THE
UNIVERSE AS I FOUND OUT WHEN I
WAS IN GRADUATE SCHOOL AND MY
COLLEAGUES FOUND OUT WHEN I WAS
IN GRADUATE SCHOOL.
WE HAVE TO THINK BIGGER.
LET'S TALK ABOUT DARK ENERGY.
>> ALL RIGHT.
SO WHAT'S DARK ENERG
IT'S HALLOWEEN, SO I HAVE TO
SCARE YOU ALL A LITTLE BIT WITH

English: 
THE EQUATION, BUT I DON'T WANT
TO SCARE YOU TOO MUCH, SO THIS
IS THE ONLY EQUATION I'LL TALK
ABOUT TODAY AND I CAN REASSURE
YOU IT ISN'T ACTUALLY ALL THAT
DIFFICULT.
THIS IS EINSTEINS FIELD EQUATION
AND IT EXPLAINS EVERYTHING
THAT'S GOING ON IN THE UNIVERSE,
JUST IN THIS ONE SIMPLE
EQUATION.
ON THE LEFT HERE, WE'VE GOT
GRAVITY WHICH CURVES SPACE.
ON THE RIGHT, WE HAVE ALL THE
STUFF IN THE UNIVERSE, THE
MATTER AND THE ENERGY.
NOW KEEP IN MIND, THIS IS AT A
TIME WHEN EINSTEIN WAS COMING UP
WITH THIS THAT THEY KNEW ABOUT
NORMAL MATTER AND THEY KNEW
ABOUT DARK MATTER, SO THAT'S THE
KIND OF STUFF THAT EINSTEIN WAS
THINKING ABOUT.
AND AROUND THAT TIME, HIS
EINSTEIN AND HIS COLLEAGUES
THOUGHT THAT THE UNIVERSE WAS
STATIC, THAT IS IT WASN'T
COLLAPSING AND IT WASN'T
EXPANDING, AND SO IN ORDER TO
KEEP THE UNIVERSE FROM

English: 
 and named it in honor of him,
 the Hubble Space Telescope,
  and I'm absolutely certain
  that everybody here
  has heard of this
  amazing telescope.
 One of the projects
 that the Hubble Space
 Telescope continued
was exactly what Hubble started.
 It looked at distant galaxies,
 and it determined how
 fast they were moving.
 And the data in this figure
 that I'm showing
 here is encompassed,
  Hubble's data is just
  that first tiny little bit
of this figure.
 So the Hubble Space
 Telescope has shown
 that further and further away,
 it is still true that the
 galaxies are moving further,
 faster away from us.
So the only explanation for this
 is that the universe
 is expanding.
And so in an expanding universe,
  [audience laughing]
  you no longer have to hold

English: 
  the universe up from
  collapsing under gravity,
 and we don't need a
 cosmological constant.
 Einstein called this the
 biggest blunder of his career.
 He struck it from the record.
 He's looking pretty sad there,
 poor Einstein [laughing].
  >> Well, there's two ways
  that an expanding universe
could behave over time.
On the left, I'm showing
an expanding universe
  that expands for some time
  after the Big Bang
  here in the past,
 and eventually
 collapses in on itself
under its own gravity at
some time in the future.
And we call that the Big Crunch.
  So that's one possibility
 if there's enough
 stuff in the universe
that the universe would
eventually collapse in on itself
 because of gravity.
 Another possibility is
 an expanding universe
 that keeps expanding forever,

English: 
COLLAPSING IN ON ITSELF UNDER
GRAVITY BECAUSE OF ALL OF THE
STUFF IN IT, EINSTEIN INTRODUCED
WHAT HE CALLED THE CROSS
MOLLICAL CONSTANT, KEEPING THE
UNIVERSE UP AGAINST COLLAPSING
IN ON ITSELF.
FAST FORWARD A FEW YEARS AND
WE'VE GOT HUBBLE.
EDWIN HUBBLE.
HE'S HERE IN LOS ANGELES AND
HE'S WORKING AT THE MOUNT WILSON
TELESCOPE, WHICH IS IN LOS
ANGELES.
HUBBLE WAS INTERESTED AT LOOKING
AT GALAXIES IN OUR UNIVERSE AND
DETERMINING WHAT VELOCITY THAT
THEY WERE MOVING, SO ON THIS
FIGURE HERE, WE HAVE DISTANCE
INCREASING AWAY FROM US AS WE GO
RIGHT AND VELOCITY INCREASING AS
WE GO UP.
WHAT HUBBLE WAS ABLE TO SEE WHEN
HE WAS LOOKING AT THESE GALAXIES
IS THAT NO MATTER WHAT DIRECTION

English: 
HE LOOKED, THE FURTHER AWAY A
GALAXY WAS, THE FASTER IT WAS
MOVING AWAY FROM US, AND THE
ONLY EXPLANATION FOR THIS IS IF
THE UNIVERSE IS EXPANDING.
TOTALLY BLEW EVERYONE'S MINDS.
SO AFTER THIS AMAZING WORK THAT
EDWIN HUBBLE DID, SCIENTISTS
LAUNCH ADD TELESCOPE AND NAMED
IT IN HONOR OF HIM, THE HUBBLE
SPACE TELESCOPE AND I'M CERTAIN
EVERYBODY HAS HEARD OF THIS
AMAZING TELESCOPE.
ONE OF THE PROJECTS IT CONTINUED
WAS EXACTLY WHAT HUBBLE STARTED.
IT LOOKED AT DISTANT GALAXIES
AND IT DETERMINED HOW WAS THEY
WERE MOVING,ND THE DATA IN
THIS FIGURE THAT I'M SHOWING
HERE IS ENCOMPASSED, HUBBLE'S
DATA IS JUST THAT FIRST TINY
LITTLE BIT OF THIS FIGURE, SO

English: 
 but expands slower and slower.
 That is a universe that starts
 out expanding quite quickly
 after the Big Bang,
 but gravity tends to slow the
 universe's expansion down.
An analogy I wanna use for that
  is our very own
  Voyager over here.
  This was launched
  some 40 years ago,
 not this one, this is
 a model, of course,
 [audience laughing]
 by JPL, and it left
 the earth's gravity,
 and it eventually left the
 solar system a few years ago.
So the Voyager, like
this expanding universe,
 is gonna keep moving
 away from us forever,
 but it's always slowing down,
 and it's always slowing down
 'cause the sun is always
 tugging on it a little bit.
 So in this expanding
 universe here,
 we have an expansion
 that's slowing down
 under the force of gravity.
 So I'm gonna use
 another analogy here,
 and I swear this was
 full before the show.

English: 
THE HUBBLE SPACE TELESCOPE HAS
SHOWN THAT FURTHER AND FURTHER
AWAY, IT IS STILL TRUE THAT THE
GALAXIES ARE MOVING FASTER AWAY
FROM US, SO THE ONLY EXPLANATION
FOR THIS IS THAT THE UNIVERSE IS
EXPANDING.
IN AN EXPANDING UNIVERSE YOU NO
LONGER HAVE TO HOLD THE UNIVERSE
UP FROM COLLAPSING UNDER
GRAVITY.
EINSTEIN CALLED THIS THE BIGGEST
BLUNDER OF HIS CAREER.
HE STRUCK IT FROM THE RECORD.
HE'S LOOKING PRETTY SAD THERE.
POOR EINSTEIN.
>> THERE'S NO WAYS THAT AN
EXPANDING UNIVERSE COULD BEHAVE
OVER TIME.
ON THE LEFT, I'M SHOWING AN
EXPANDING UNIVERSE THAT EXPANDS
FOR SOMETIME AFTER THE BIG BANG

English: 
  But the expanding universe
 that eventually
 collapses in on itself
  is like this, you throw
  it up, and it comes down.
  That's how we know gravity
  works in our daily lives.
 So that's this character here.
 This is the expanding universe
 that collapses in on
 itself under gravity.
 The second fellow or woman
 here that's throwing a ball
 is throwing the ball that's
 gonna keep going away
 but slower and slower.
 That's the other
 expanding universe,
 an expanding universe
 that expands forever,
 but is slowing down
 the whole time.
 So in the 1990s,
 there were two groups
 at the same time in the world
 trying to understand which of
 these scenarios was correct,
 and how fast the
 universe was expanding
 and how fast it had
 expanded in the past.
And both of those
groups found an answer.
 And that answer was a universe
 that looked like this,

English: 
HERE IN THE PAST AND EVENTUALLY
COLLAPSES IN ON ITSELF UNDER ITS
OWN GRAVITY AT SOME TIME IN THE
FUTURE, AND WE CALL THAT THE BIG
CRUNCH.
SO THAT'S ONE POSSIBILITY IF
THERE'S ENOUGH STUFF IN THE
UNIVERSE THAT THE UNIVERSE WOULD
EVENTUALLY COLLAPSE IN ON ITSELF
BECAUSE OF GRAVITY.
ANOTHER POSSIBILITY IS AN
EXPANDING UNIVERSE THAT KEEPS
EXPANDING FOREVER BUT EXPANDS
SLOWER AND SLOWER.
THAT IS THE UNIVERSE THAT STARTS
OUT EXPANDING QUITE QUICKLY
AFTER THE BIG BANG BUT GRAVITY
TENDS TO SLOW THE UNIVERSE'S
EXPANSION DOWN.
ANNAL GEE I WANT TO USE FOR THAT
IS OUR VERY OWN VOYAGER OVER
HERE.
THIS WAS LAUNCHED SOME FORTH
YEARS AGO, NOT THIS ONE, THIS IS
THE MODEL, OF COURSE, BY JPL,
AND IT LEFT THE EARTH'S GRAVITY
AND IT EVENTUALLY LEFT THE SOLAR
SYSTEM A FEW YEARS AGO, SO THE
VOYAGER LIKE THI EXPANDING
UNIVERSE IS GOING TO KEEP MOVING

English: 
 a universe that was expanding,
 but faster and faster.
  Much like Hubble's
  mind was blown,
cosmologists' minds
were blown in the 1990s
  when they realized
  that the universe
  did not have an expansion
  that was slowing down
due to gravity.
 It had an expansion
 that was speeding up
 due to something else.
 And so we have to
 have a third diagram,
and this is the diagram
that we think represents
what's really happening
in our universe.
  That's a universe that
  started out at a Big Bang,
it started out expanding
somewhat slowly,
and as time has gone on,
 it's expanded faster
 and faster and faster,
 and it looks like it's
 gonna keep expanding
faster and faster in the future.
 So we don't know why that is,
 and we gave the name
of whatever's causing
 that dark energy.
So another way to put it is,
dark energy is the name we gave
 to our ignorance of
 whatever is causing
 this ever-increasing rate of
 expansion of the universe.

English: 
AWAY FROM US FOREVER, BUT IT'S
ALWAYS THROWING -- SLOWING DOWN,
BECAUSE THE SUN IS ALWAYS
TUGGING ON IT A LITTLE BIT.
SO IN THIS EXPANDING UNIVERSE
HERE, WE HAVE AN EXPANSION
THAT'S SLOWING DOWN UNDER THE
FORCE OF GRAVITY.
I'M GOING TO USE ANOTHER ANALOGY
HERE AND I SWEAR THIS WAS FULL
BEFORE THE SHOW BUT THE
EXPANDING UNIVERSE THAT
EVENTUALLY COLLAPSES IN ON
ITSELF IS LIKENESS.
YOU THROW IT UP AND IT COMES
DOWN.
THAT'S HOW WE KNOW GRAVITY WORKS
IN OUR DAILY LIVES.
SO THAT'S THIS CHARACTER HERE.
THIS IS THE EXPANDING UNIVERSE
THAT COLLAPSE INS ON ITSELF
UNDER GRAVITY.
THE SECOND FELLA OR WOMAN HERE
THAT'S THROWING A BALL IS
THROWING THE BALL THAT'S GOING
TO KEEP GOING AWAY BUT SLOWER
AND SLOWER.
THAT'S THE OTHER EXPANDING
UNIVERSE.
AN EXPANDING UNIVERSE THAT
EXPANDS FOREVER, BUT IS SLOWING

English: 
 >> So now we have a universe
 that is not only expanding
 but it's accelerating
 in its expansion.
 So something needs to happen
 to Einstein's field equation
 in order to accommodate
 this accelerating expansion.
  And it turns out that
  this can be accounted for
in the form of Einstein's
original cosmological constant.
 [audience laughing]
 And scientists were
 able to add this back
 into Einstein's field equation
 in the form of dark energy.
 [audience laughing]
 [audience applauding]
  >> Audience Member: What?
 >> Einstein's biggest
 blunder went on
to win a Nobel Prize in Physics
in 2011 for dark energy.
  So what a triumph!
 And as you'll notice up here,
 I have said that the
 cosmological constant
 may not be a constant.
  So scientists still don't
  really know very much

English: 
DOWN THE WHOLE TIME.
IN THE 1990'S, THERE WERE TWO
GROUPS AT THE SAME TIME IN THE
WORLD TRYING TO UNDERSTAND WHICH
OF THESE SCENARIOS WAS CORRECT
AND HOW FAST THE UNIVERSE WAS
EXPANDING AND HOW WAS IT HAD
EXPANDED IN THE PAST, AND BOTH
OF THOSE GROUPS FOUND AN ANSWER.
AND THAT ANSWER WAS A UNIVERSE
THAT LOOKED LIKE THIS.
A UNIVERSE THAT WAS EXPANDING
BUT FASTER AND FASTER, MUCH LIKE
HUBBEL'S MIND WAS BLOWN,
COSMOLOGYISTS MINDS WERE BLOWN
WHEN THEY REALIZED THE UNIVERSE
DID NOT HAVE AN EXPANSE SLOWING
DOWN, IT HAD AN EXPANSION THAT
WAS SPEEDING U DUE TO SOMETHING
ELSE.
WE HAVE TO HAVE A THIRD DIAGRAM,
AND THIS IS THE DIAGRAM THAT WE
THINK REPRESENTS WHAT'S REALLY
HAPPENING IN OUR UNIVERSE.
THAT'S A UNIVERSE THAT STARTED
OUT AS A BIG BANG, STARTED OUT
EXPANDING SOMEWHAT SLOWLY AND AS

English: 
  about dark energy at all.
And theorists are coming
up with different ideas
all the time about what
dark energy might be.
  And there's no
  evidence that says
that it does or does not
have to be a constant.
  It could change over time.
And so it's really
important for scientists
 to investigate dark
 energy in the future
  to try and understand more
  about what's going on.
So we've talked a little
bit about dark energy
and dark matter,
  but how do they work
  together in the universe?
 On the one hand,
 we've got dark energy,
  and it's this kind
  of repulsive force
 that's pushing things apart,
 while dark matter is
 an attractive force,
 it's bringing things together.
 Dark energy affects the speed
 at which the universe expands,
and we now know that the
universe is accelerating

English: 
  in its expansion,
  while dark matter affects
  how clustered objects
  like galaxies are.
Dark energy causes
everything to move away
 from everything else,
while dark matter causes
objects like galaxies
 to want to move
 toward one another.
 So there's this real
 push and pull going on
 between dark matter and
 dark energy in the universe.
  And so scientists need to
  investigate the universe
 over time in order to
 see what's going on
 with the clustering
 and the expansion
  of the universe over time
  to try and understand more
 about both dark matter
 and dark energy.
 >> So how are we gonna measure
 dark energy in the future?
Well, it turns out that
gravitational lensing technique
 that we talked about earlier
 is one of the primary ways
we're gonna measure dark
energy in the future.

English: 
TIME HAS GONE ON, IT'S EXPANDED
FASTER AND FASTER AND FASTER
AROUND IT LOOKS LIKE IT'S GOING
TO KEEP EXPANDI FASTER AND
FASTER IN THE FUTURE.
SO WE DON'T KNOW WHY THAT IS,
AND WE GAVE THE NAME OF
WHATEVER'S CAUSING THAT DARK
ENERGY.
ANOTHER WAY TO PUT IT IS DARK
ENERGY IS THE NAME WE GAVE TO
OUR IGNORANCE OF WHATEVER IS
CAUSING THIS EVER INCREASING
RATE OF EXPANSION OF THE
UNIVERSE
>> NOW WE HAVE A UNIVERSE THAT
IS NOT ONLY EXPANDING BUT
ACCELERATING IN ITS EXPANSION SO
SOMETHING NEEDS TO HAPPEN TO
EINSTEIN'S FIELD EQUATION IN
ORDER TO ACCOMMODATE THIS
ACCELERATING EXPANSION.
IT TURNS OUT THAT THIS CAN BE
ACCOUNTED FOR IN THE FORM OF
EINSTEIN'S ORIGINAL COSMO
LOGICAL CONSTANT AND SCIENTISTS
WERE ABLE TO ADD THIS BACK INTO
EINSTEIN'S FIELD EQUATION IN THE

English: 
FORM OF DARK ENERGY.
EINSTEIN'S BIGGEST BLUNDER WENT
ON TO WIN A NOBEL PRIZE IN
PHYSICS IN 2011 FOR DARK ENERGY.
SO WHAT A TRIUMPH.
AS YOU'LL NOTICE UP HERE, I SAID
THAT THE COSMO LOGICAL
CONSTANTLY MAY NOT BE A CONSTANT
 THEY'RE WRISTS ARE
COMING UP ALL THE TIME ABOUT
WHAT DARK ENERGY MIGHT BE.
THERE IS NO EVIDENCE THAT SAYS
IT DOES OR DOES NOT HAVE TO BE A
CONSTANT, IT CAN CHANGE OVER
TIME SO IT'S REALLY IMPORTANT
FOR SCIENTISTS TO INVESTIGATE
DARK ENERGY IN THE FUTURE TO TRY
AND UNDERSTAND MORE ABOUT WHAT'S
GOING ON.
WE'VE TALKED ABOUT DARK ENERGY,
AND DARK MATTER, BUT HOW DO THEY

English: 
And so on the left here,
I'm showing a very stylized view
  of how this gravitational
  lensing works.
  We've got these
  distant galaxies,
and you can sort of see
the ghostly dark matter.
 And as the light from those
 distant galaxies comes to us
  through that dark matter,
 the shapes of those
 galaxies are changed.
  And again, this is
  an exaggeration.
  We don't usually see
  shape changes this strong,
 and the shape changes occur
  over very, very
  long time periods,
 so we wouldn't see it
 changing like this.
This is just to give you an idea
 of how we're measuring
 that dark matter.
And what we do is we
look at the dark matter
  at different times in the
  history of the universe,
  and this tells us how the
  dark matter is evolving.
  So one of the things that
  we did about 10 years ago,
 some of our colleagues and I,
 is we used the Hubble
 Space Telescope
  to make the map
  of the dark matter
in a very tiny area of the sky.
 And we looked very far away,
 and we were able to
 make a dark matter map
 of the dark matter in
 that area of the sky

English: 
 as it appeared about six and
 a half billion years ago.
 And then we looked
 a little bit closer,
 and the way we do that
 is distant galaxies,
 the light takes some
 time to reach us,
and so the further out we look,
the further back in the
universe we're looking.
 So we looked at
 the dark matter map
 about five billion years ago,
 and then we looked at
 the dark matter map
 about three and a half
 billion years ago.
And in doing so,
 we created a three-dimensional
 map of the dark matter
 in this tiny area of the sky.
 And when I say a
 tiny area of the sky,
it was about two square
degrees on the sky.
  Well, what does that mean?
 The whole sky is about
 40,000 square degrees,
 so we looked at about one two
 thousandth or less than about,
 less than 1/20th of
 a percent of the sky,
a very small amount of the sky,
with the Hubble Space Telescope.
 And what we were able to show
 is that the clustering
 of this dark matter
  changed over time,
  and it changed over a
  time in a way that's given

English: 
WORK TOGETHER IN THE UNIVERS?
ON THE ONE HAND, WE'VE GOT DARK
ENERGY AND IT'S THIS KIND OF
REPULSIVE FORCE THAT'S PUSHING
THINGS APART, WHILE DARK MATTER
IS AN ATTRACTIVE FORCE, IT'S
BRINGING THINGS TOGETHER.
DARK ENERGY AFFECTS THE SPEED AT
WHICH THE UNIVERSE EXPANDS, AND
WE NOW KNOW THAT THE UNIVERSE IS
SELL RATING IN ITS EXPANSION.
WHILE DARK MATTER AFFECTS HOW
CLUSTERED THINGS LIKE GALAXIES
ARE, DARK ENERGY CAUSES
EVERYTHING TO MOVE AWAY FROM
EVERYTHING ELSE.
WHILE DARK MATTER CAUSES
GALAXIES TO WANT TO MOVE TOWARD
ONE ANOTHER.
THERE'S THIS PUSH AND PULL GOING
ON BETWEEN DARK MATTER AND DARK
ENERGY IN THE UNIVERSE, SO
SCIENTISTS NEED TO INVESTIGATE
THE UNIVERSE OVER TIME IN ORDER
TO SEE WHAT'S GOING ON WITH THE

English: 
  by the attractive
  force of gravity
 wanting to pull the
 dark matter together
and the repulsive nature
of the dark energy
 wanting to push things apart.
 So by using this gravitational
 lensing technique,
 we can study both the dark
 matter and the dark energy.
  And that's what we're
  going to do in the 2020s.
There's three primary telescopes
that we're gonna
use in the 2020s
to do this gravitational
lensing technique
 to study dark matter
 and dark energy.
  The first is the Large
  Synoptic Survey Telescope.
This is an eight-meter
ground-based telescope.
 Eight meters is the length,
 or the diameter of the mirror.
 And keep in mind
 that for a telescope,
  the diameter of the mirror
 is driving the power
 of the telescope
 because it determines
 how many photons,
 how much light that
 telescope can collect.
 And there's about 24
 international contributors,
 24 countries helping the U.S.
 build and eventually operate

English: 
CLUSTERING AND THE EXPANSION OF
THE UNIVERSE OVER TIME TO TRY
AND UNDERSTAND MORE ABOUT BOTH
DARK MATTER AND DARK ENERGY.
>> SO HOW ARE WE GOING TO
MEASURE DARK ENERGY IN THE
FUTURE?
WELL, IT TURNS OUT THAT GRAVE
TAKESSAL LENSING TECHNIQUE THAT
WE TALKED ABOUT EARLIER IS ONEHG
TO MEASURE DARK ENERGY IN THE
FUTURE.
SO ON THE LEFT HERE, I'M SHOWING
A VERY STYLIZED VIEW OF HOW THIS
GRAVITATIONAL LENSING WORKS.
WE'VE GOT THESE DISTANT GALAXIES
AND YOU CAN SEE THE GHOSTLY DARK
MATTER AS THE LIGHT FROM THOSE
DISTANT GALAXIES COMES TO US
THROUGH THAT DARK MATTER, THE
SHAPES OF THOSE GALAXIES ARE
CHANGED.
AGAIN, THIS IS AN EXAGGERATION.
WE DON'T USUALLY SEE SHAPE
CHANGES THIS STRONG AND THE
SHAPE CHANGES OCCUR OVER VERY,
VERY LONG TIME PERIODS SO WE
WOULDN'T SEE IT CHANGING LIKE
THIS.
THIS IS TO GIVE YOU AN IDEA OF
HOW WE'RE MEASURING THAT DARK
MATTER.
AND WHAT WE DO IS WE LOOK AT THE

English: 
DARK MATTER AT DIFFERENT TIMES
IN THE HISTORY OF THE UNIVERSE,
AND THIS TELLS US HOW THE DARK
MATTER IS EVOLVING, SO ONE OF
THE THINGS THAT WE DID ABOUT 10
YEARS AGO, SOME OF MY COLLEAGUES
AND I IS WE USE THE HUBBEL SPACE
TELESCOPE TO MAKE THE MAP OF THE
DARK MATTER IN A VERY TINY AREA
OF THE SKY, AND WE LOOKED VERY
FAR AWAY AND WE WERE ABLE TO
MAKE A DARK MATTER MAP OF THE
DARK MATTER IN THAT AREA OF THE
SKY AS IT APPEARED ABOUT SIX AND
A HALF BILLION YEARS AGO.
THEN WE LOOKED A LITTLE BIT
CLOSER AND THE WAY WE DO THAT IS
DISTANT GALAXIES, THE LIGHT
TAKES SOME TIME TO EACH US SO
THE FURTHER OUT WE LOOK, THE
FURTHER BACK IN THE UNIVERSE
WE'RE LOOKING.
SO WE LOOKED AT THE DARK MATTER
MAP ABOUT 5 BILLION YEARS AGO,
AND THEN WE LOOKED AT THE DARK
MATTER MAP ABOUT THREE AND A
HALF BILLION YEARS AGO.
IN DOING SO, WE CREATED A THREE
DIMENSIONAL MAP OF THE DARK
MATTER IN THIS TINY AREA OF THE
SKY, AND WHEN I SAY A TINY AREA
OF THE SKY, IT WAS ABOUT TWO
SQUARE DEGREES ON THE SKY.

English: 
 this Large Synoptic
 Survey Telescope.
  There's about 900
  people worldwide
 working on the dark
 energy planning,
 planning for the dark energy
 survey with this LSST.
  A second mission
  is a space mission
from the European Space
Agency called Euclid.
  Now, when we measure the
  expansion of the universe,
 scientists say we're
 measuring the geometry
  or shape of the universe.
 And you might remember, Euclid
 is the father of geometry.
  So that's how this Euclid
  mission got its name.
 We plan to launch this Euclid
 mission into space in 2022,
and there's about 1500
people working on Euclid
 around the world
 to do a dark matter
 and dark energy experiment.
 And the final experiment we're
 going to talk about tonight
  is WFIRST, the Wide Field
  Infrared Survey Telescope.
This is a NASA telescope that's
gonna be launched in 2025,
and it's gonna do
investigations into dark energy

English: 
WHAT DOES THAT MEAN?
THE TOTAL SKY IS ABOUT 40,000
SQUARE DEGREES SO WE LOOKED AT
ONE 2,000TH, A VERY SMALL AMOUNT
OF THE SKY.
WHAT THEY WERE ABLE TO SHOW IS
THAT THE CLUSTERING OF THIS DARK
MATTER CHANGED OVER TIME AND IT
CHANGED OVER A TIME IN A WAY
THAT'S GIVEN BY THE ATTRACTIVE
FORCE OF GRAVITY WANTING TO PULL
THE DARK MATTER TOGETHER AND THE
REPULSIVE NATURE OF THE DARK
ENERGY WANTING TO PUSH THINGS
APART, SO BY USING THIS
GRAVITATIONAL LENSING TECHNIQUE,
WE COULD STUDY BOTH THE DARK
MATTER AND THE DARK ENERGY AND
THAT'S WHAT WE'RE GOING TO DO IN
THE 2020'S.
THERE'S THREE PRIMARY TELESCOPES
WE'RE GOING TO USE TO DO THIS
GAVE TAKESSAL LENSING TECHNIQUE
TO STUDY DARK MATTER AND DARK
ENERGY.

English: 
 and dark matter, and it's also
 gonna look for exoplanets.
  These are planets outside
  of our solar system,
 and I mentioned those earlier,
 that there might be more than
 10 billion trillion planets
in the universe,
 and we wanna find some
 of those with WFIRST.
 >> That's you.
 >> Oh, okay, still me.
 >> Still him.
 >> So I'm gonna talk a
 bit more about WFIRST.
So WFIRST is a telescope
 that's gonna be
 launched into space.
It's got a mirror that's
2.4 meters across,
 so for those of you that
 know your space telescopes,
  that's the same
  size as the mirror
 on the Hubble Space Telescope,
 which is the one that we used
 to do this dark matter study
  on a very tiny area of the
  sky about 10 years ago.
 So you might ask, why
 didn't we just use
 the Hubble Space Telescope
 to look at more of the sky?
  And the reason is it
  takes too long to do this
with the Hubble Space Telescope.
 And the reason we can do it
 with WFIRST in the future

English: 
THE FIRST IS IS THE LARGE
SYNOPSIS TELESCOPE.
THE DIAMETE OF THE MIRROR AND
KEEP IN MIND THAT FOR A
TELESCOPE, THE DIAMETER OF THE
MIRROR IS WHAT IS DRIVING THE
POWER OF THE TELESCOPE BECAUSE
IT DETERMINES HOW MANY FOE TONS,
HOW MUCH LIGHT THAT TELESCOPE
CAN COLLECT.
THERE'S 24 COUNTRIES HELPING THE
U.S. BUILD AND OPERATE THIS
LARGE 16 NO PARTICULAR
TELESCOPE.
A SECOND MISSION IS A SPACE
MISSION FROM THE EUROPEAN SPACE
AGENCY CALLED EUCLID.
SCIENTISTS SAY WE'RE MEASURING
THE GEOMETRY OR SHAPE OF THE
UNIVERSE.
YOU MIGHT REMEMBER, EUCLID IS
THE FATHER OF GEOMETRY.
THAT'S HOW THIS EUCLID MISSION
GOT IT'S NAME.
WE PLAN TO LAUNCH THIS EUCLID
MISSION INTO SPACE IN 2022 AND

English: 
is because of WFIRST's
really powerful camera.
 I'm showing here the
 Andromeda Galaxy,
  that's the galaxy nearest
  our own Milky Way.
  It's about two and a half
  million light years away.
 And this is a picture
 taken from the ground.
  And a few years ago, one
  of our colleagues decided
 she wanted to study
 the individual stars
in the Andromeda Galaxy.
 And to do that, she used
 the Hubble Space Telescope.
 And she pointed the
 Hubble Space Telescope
 at this galaxy about 400 times
 to cover about half the galaxy
  because the Hubble
  Space Telescope
  has a pretty small camera.
 So it took 400 pointings of
 the Hubble Space Telescope
to look at this galaxy.
 Takes two with WFIRST.
 [audience chattering]
So we're gonna do the same
types of studies of dark matter
 that were possible with
 the Hubble Space Telescope,
 but hundreds or even thousands
 of times faster with WFIRST.
  And that's the power that
  WFIRST is gonna unleash.
 It's a Hubble Space
 Telescope-quality instrument,

English: 
THERE'S 1500 PEOPLE WORKING ON
EUCLID AROUND THE WORLD TO DO A
DARK MATTER AND DARK ENERGY
EXPERIMENT.
THE FINAL EXPERIMENT, WE'RE
GOING TO TALK ABOUT TONIGHT IS W
FIRST, THE Y FIELD INFRARED
TELESCOPE.
THIS IS A NASA TELESCOPE GOING
TO LAUNCH IN 2025 AND DO
INVESTIGATIONS INTO DARK ENERGY
AND DARK MATTER AND IT'S ALSO
GOING TO LOOK FOR EXO PLANETS.
THERE MIGHT BE MORE THAN
10 SEXTILLION PLANETS IN THE
UNIVERSE AND WE WANTED TO FINDS
THOSE WITH W FIRST.
W IS A TELESCOPE THAT'S GOING TO
BE LAUNCHED INTO SPACE.
IT'S GOT A MIRROR 2.4 METERS
ACROSS.
THOSE OF YOU THAT KNOW YOUR
SPACE TELESCOPES, THAT'S THE

English: 
 but with a much bigger camera
 due to advances in creating
 detectors and pixels.
>> So Jason's talked
about the WFIRST camera,
 and let's compare the
 WFIRST camera to the camera
 on the Large Synoptic
 Survey Telescope.
 But first to give you
 some context again,
 the camera on your cell phone
 is maybe about eight million
 pixels, or eight megapixels.
The camera on WFIRST is
around 300 megapixels.
 And the camera on the Large
 Synoptic Survey Telescope
 is around 3,000 megapixels,
 or three gigapixels.
  So this is just enormous.
 And what scientists are
 going to use this camera for
 is every five nights,
 they will take a picture
 of the entire southern sky,

English: 
  and they will do
  this for 10 years.
  So this is going
  to give scientists
 an incredibly deep
 image of the universe,
 but it's also going to
 be like taking a movie
 of how the sky is
 changing over time.
 This is going to be incredible
 data for the scientists
to investigate dark
matter and dark energy.
 And Jason mentioned earlier
that it takes a lot of
scientists to try to understand
this unknown 95%
of the universe.
And the Euclid Space Telescope,
 some of the scientists
 got together
 earlier this year in summer
 in Helsinki in Finland,
 and we were working together
getting ready for the
Euclid Space Telescope,
  which will be the
  first telescope
  entirely dedicated to
  investigating dark matter
and dark energy.

English: 
SAME SIZE AS THE MIRROR ON THE
HUBBEL SPACE TELESCOPE WHICH IS
THE ONE WE USE TO DO THIS DARK
MATTER STUDY ON A VERY TINY AREA
OF THE SKY, ABOUT 10 YEARS AGO.
SO YOU MIGHT ASK WHY DIDN'T WE
JUST USE THE HUBBEL TELESCOPE TO
LOOK AT MORE OF THE SKY AND THE
REASON IS IT TAKES TOO LONG TO
DO THIS WITH THE HUBBEL SPACE
TELESCOPE.
THE REASON WE CAN DO IT WITH W
FIRST IN THE FUTURE IS BECAUSE
OF W FIRST REALLY POWERFUL
CAMERA.
I'M SHOWING HERE THE AN FROM DA
GALAXY, NEAREST OUR OWN MILKY
WAY, ABOUT TWO AND A HALF
MILLION LIGHT YEARS AWAY.
THIS IS A PICTURE TAKEN FROM THE
GROUND AND A FEW YEARS AGO, ONE
OF OUR COLLEAGUES DECIDED SHE
WANTED TO STUDY THE INDIVIDUAL
STARS IN THE AN FROM DA GALAXY.
TO DO THAT, SHE USED THE HUBBEL
SPACE TELESCOPE AND SHE POINTED
THE HUBBEL SPACE TELESCOPE AT
THIS GALAXY ABOUT 400 TIMES TO
COVER ABOUT HALF THE GALAXY,
BECAUSE THE HUBBEL SPACE
TELESCOPE HAS A PRETTY SMALL
CAMERA, SO IT TOOK 400-POINTINGS

English: 
OF THE HUBBEL SPACE TELESCOPE TO
LOOK AT THIS GALAXY.
IT TAKES TWO WITH W FIRST.
WE'RE GOING TOLD THE SAME TYPES
OF STUDIES WITH DARK MATTER THAT
WERE POSSIBLE WITH THE HUBBEL
SPACE TELESCOPE BUT HUNDREDS OR
EVEN THOUSANDS OF TIMES FASTER
WITH W FIRST AND THAT'S THE
POWER THAT W FIRST IS GOING TO
UNLEER.
IT'S A HUBBEL SPACE TELESCOPE
QUALITY INSTRUMENT BUT
MUCH BIGGER CAMERA DUE TO
ADVANCES IN CREATING DETECTORS
AND PIXELS.
>> SO, JASON'S TALKED ABOUT THE
W FIRST CAMERA, AND LET'S
THE CAMERA ON THE LARGE SYNOPTIC
SURVEY TELESCOPE BUT FIRST GIVE
YOU A CONTEXT AGAIN.
THE CAMERA ON YOUR CELL PHONE IS
MAYBE ABOUT 8 MILLION PIXELS OR
EIGHT MEGAPIXELS.

English: 
And we took a photo of ourselves
  to commemorate the moment,
and here is Jason and I.
 [audience laughing]
And notice Jason is not
looking at the camera
because he's looking at
his phone, doing emails.
 [audience laughing]
 This is also what it's like
being married to a cosmologist.
  So I looked at this photo
 and I realized
 something interesting.
These are the
scientists from Pasadena
  who attended this meeting,
  and I worked out that the
  scientists from Pasadena
 make up the 5% normal portion
 [audience laughing]
 of the scientists in Euclid.
 So maybe you're asking
 why are we doing
 three different experiments
to investigate the same
thing in the 2020s?
  And it's a good question,
  and we get asked it a lot.

English: 
 So dark energy, I
 think I've told you,
we really don't know what it is.
Scientists have no idea.
 I think you now know as much
 as I do about dark energy.
 You can pick up your
 PhD at the door.
 [audience laughing]
  And so in order to try to
  understand what's going on
  with this really
  difficult concept,
  it takes a lot of
  different investigations.
  And so it's really useful
to be able to cross check
between the
different experiments
 to understand what's going on.
 And each of the experiments
  that Jason and I have
  talked about this evening
 have their own special skills,
 and they're highly
 complimentary with each other.
 So the Euclid Space Telescope
 is going to be in space,
which means it's above
the earth's atmosphere.
  And Jason told you that we
  want to measure the shapes

English: 
THE CAMERA ON W FIRST IS AROUND
300 MEGAPIXELS.
THE CAMERA ON THE LARGE SYNOPTIC
SURVEY TELESCOPE IS AROUND 3,000
MEGAPIXELS OR THREE GIGA PIXELS,
SO THIS IS JUST ENORMOUS AND
WHAT SCIENTISTS ARE GOING TO USE
THIS CAMERA FOR IS EVERY FIVE
NIGHTS, THEY WILL TAKE A PICTURE
OF THE ENTIRE SOUTHERN SKY, AND
THEY WILL DO THIS FOR 10 YEARS.
SO THIS IS GOING TO GIVE
SCIENTISTS AN INCREDIBLY DEEP
IMAGE OF THE UNIVERSE, BUT IT'S
ALSO GOING TO BE LIKE TAKING A
MOVIE OF HOW THE SKY IS CHANGING
OVER TIME.
THIS IS GOING TO BE INCREDIBLE
DATA FOR THE SCIENTISTS TO
INVESTIGATE DARK MATTER AND DARK
ENERGY.
JASON MENTIED EARLIER THAT IT
TAKES A LOT OF SCIENTISTS TO TRY

English: 
TO UNDERSTAND THIS UNKNOWN 95%
OF THE UNIVERSE, AND THE EUCLID
SPACE TELESCOPE, SOME OF THE
SCIENTISTS GOT TOGETHER EARLIER
IN FINLAND WORKING TOGETHER TOI
GET READY FOR THE EUCLID SPACE
TELESCOPE WHICH WILL BE THE
FIRST TELESCOPE ENTIRELY
DEDICATED TO VETTING DARK MATTER
AND DARK ENERGY, AND WE TOOK A
PHOTO OF OURSELVES TO
COMMEMORATE THE MOMENT.
AND HERE IS JASON AND I.
AND NOTICE JASON IS NOT LOOKING
AT THE CAMERA, BECAUSE HE'S
LOOKING AT HIS PHONE, DOING
EMAILS.
THIS IS ALSO WHAT IT'S LIKE
BEING MARRIED TO A CROSS
EMOTIONALIST.
SO I LOOKED AT THIS PHOTO AND
REALIZED SOME INTERESTING THESE
ARE THE SCIENTISTS THAT ATTENDED

English: 
of the distant galaxies.
 I'm sure you've all
 heard about the song
"Twinkle, Twinkle Little Star."
On earth, stars twinkle because
the light from those stars
is traveling through the
atmosphere of the earth,
  and that's causing
  them to twinkle.
 But if you get outside
 of the atmosphere,
  then those stars
  are very precise.
 And so getting outside
 of the atmosphere
 enables scientists to measure
the shapes of these
galaxies very precisely.
 And Euclid is going to do
 this over a very wide area,
 20,000 square degrees.
  The Large Synoptic Survey
  Telescope, however,
  is on the ground,
 so they have to deal
 with the atmosphere
 when they're trying to
 measure these shapes.
However, LSST is going to
measure the entire southern sky
every five nights for 10 years,

English: 
 which will enable incredibly
 deep images of the universe.
  We'll be looking much,
  much further back in time.
 And so we're getting the
 evolution of what's going on
with the dark matter and
dark energy over time.
  And finally, WFIRST, which
  we'll launch in 2025,
has been designed to be
the most precise camera.
 It's going to take
 the sharpest images,
and it will take the
deepest images, as well.
 So by combining and comparing
 these three experiments,
scientists are going
to be able to make sure
  that we really understand
  what's going on
 and confirm any new,
 exciting discoveries.
>> So we've told you a bit about
 how we're going to
 measure dark energy
 and dark matter in the 2020s,
 and you still might wonder,
 well, why do we
 wanna measure that?
Well, I think, honestly,
for Alina and I
 and a lot of our colleagues
 is we're curious,
we wanna understand
how the universe works.
  But for everybody, I think
  you probably wanna know

English: 
THE MEETING.
THEY MAKE UP THE 5% NORMAL
PORTION OF THE SCIENTISTS IN
EUCLID.
SO MAYBE YOU'RE ASKING WHY ARE
WE DOING THREE DIFFERENT
EXPERIMENTS TO INVESTIGATE THE
SA THING IN THE 2020'S.
AND IT'S A GOOD QUESTION, AND WE
GET ASKED IT A LOT.
SO DARK ENERGY, I THINK I'VE
TOLD YOU, WE REALLY DON'T KNOW
WHAT IT IS.
SCIENTISTS HAVE NO IDEA.
I THINK YOU NOW KNOW AS MUCH AS
I DO ABOUT DARK ENERGY.
YOU CAN PICK UP YOUR PHD AT THE
DOOR.
AND SO IN ORDER TO TRY TO
UNDERSTAND WHAT'S GOING ON WITH
THIS REALLY DIFFICULT CONCEPT,
IT TAKES A LOT OF DIFFERENT
INVESTIGATIONS, AND SO IT'S
REALLY USEFUL TO BE ABLE TO
CROSS-CHECK BETWEEN THE
DIFFERENT EERIMENTS TO

English: 
  what's gonna happen in the
  universe in the future?
 And really, the future
 of the universe,
  how the universe
  evolves over time
 in the coming tens
 of billions of years
 is gonna be determined by the
 properties of dark energy,
 and we just don't know
 those properties very well.
 We think that there's
 probably two scenarios
  that might play out, and
  that's what we think now.
  And we're not sure which
  one of those two scenarios
 will play out,
 and we want to study the dark
 matter and the dark energy
 to find out which one of
 those scenarios will play out.
We're gonna tell
you a little bit
about those two
possible scenarios now.
 >> So if dark energy
 isn't too strong,
 galaxies will continue
 moving away from each other
 like Edwin Hubble discovered,
 and they're going to continue
 moving away from each other
  faster and faster
  until, eventually,
they'll be so far apart

English: 
UNDERSTAND WHAT'S GOING ON, AND
EACH OF THE EXPERIMENTS THAT
JASON AND I HAVE TALKED ABOUT
THIS EVENING HAVE THEIR OWN
SPECIAL SKILLS, AND THEY'RE
HIGHLY COMPLIMENTARY WITH EACH
OTHER.
THE EUCLID SPACE TELESCOPE IS
GOING TO BE IN SPACE, WHICH
MEANS IT'S ABOVE THE EARTH'S
ATMOSPHERE AND JASON TOLD YOU
THAT WE WANT TO MEASURE THE
SHAPES OF THE DISTANT GALAXIES.
I'M SURE YOU'VE ALL HEARD ABOUT
THE SONG TWINKLE TWINKLE LITTLE
STAR.
ON EARTH, STARS TWINKLE BECAUSE
THE LIGHT FROM THOSE STARS IS
TRAVELING THROUGH THE ATMOSPHERE
OF THE EARTH AND THAT'S CAUSING
THEM TO TWINKLE.
BUT IF YOU GET OUTSIDE OF THE
ATMOSPHERE, THEN THOSE STARS ARE
VERY PRECISE, AND SO GETTING
OUTSIDE OF THE ATMOSPHERE
ENABLES SCIENTISTS TO MEASURE
THE SHAPES OF THESE GALAXIES
VERY PRECISELY AND EUCLID IS
GOING TO DO THIS OVER A VERY
WIDE AREA, 20,000 SQUARE

English: 
that they won't be
able to see each other,
 and the universe will become
 an incredibly lonely place,
 and our galaxy will be alone.
Jason, where did you go?
I can't see you!
 [audience laughing]
  >> Don't worry, I'm here.
 [Alina laughing]
 [audience laughing]
 So that's what the universe
 is gonna end up looking like.
  We'll have a universe
  where we're in our galaxy,
  and we can't see those
  distant galaxies anymore.
 They've moved too far away.
 And so sometimes, I've tried
 in the past to use this.
In my funding proposals
to NASA, I say,
 "You've really gotta fund this
 dark energy study right now
 "because eventually,
 I'm not gonna be able
 "to see these distant galaxies
  "if you don't send
  me the money."
 [audience laughing]
 And it doesn't work anymore
 'cause I think my colleagues
 at NASA Headquarters
have realized that this happens
 many, many tens of
 billions of years from now,
 [audience laughing]
 so they think I have

English: 
DEGREES.
THE LARGE SYNOPTIC SURVEY
TELESCOPE HOWEVER IS ON THE
GROUND, SO THEY HAVE TO DEAL
WITH THE ATMOSPHERE WHEN THEY'RE
TRYING TO MEASURE THESE SHAPES.
HOWEVER, LSST IS GOING TO
MEASURE THE ENTIRE SOUTHERN SKY
EVERY FIVE NIGHTS FOR 10 YEARS,
WHICH WILL ENABLE IN CREDIBLY
DE.
WE WILL BE LOOKING BACK MUCH,
MUCH FURTHER INTO TIME GETTING
THE EVOLUTION OF WHAT'S GOING ON
WITH THE DARK MATTER AND ENERGY
OVER TIME.
AND FINALLY, W FIRST, WHICH WILL
LAUNCH IN 2025 HAS BEEN DESIGNED
TO BE THE MOST PRECISE CAMERA.
IT'S GOING TO TAKE THE SHARPEST
IMAGES AND IT WILAKE THE
DEEPEST IMAGES, AS WELL, SO BY
COMBINING AND COMPARING THESE
THREE EXPERMENTS, SCIENTISTS ARE
GOING TO BE ABLE TO MAKE SURE
THAT WE REALLY UNDERSTAND WHAT'S

English: 
GOING ON, AND CONFIRM ANY NEW
EXCITING DISCOVERIES.
>> SO WE'VE TOLD YOU A BIT ABOUT
HOW WE'RE GNG TO MEASURE DARK
ENERGY AND DARK MATTER IN THE
2020 SAID AND YOU STILL MAY
WONDER WHY DO WE WANT TO MEASURE
THAT.
HONESTLY FOR ALINA AND I AND OUR
COLLEAGUES, WE'RE CURIOUS, WE
WANT TO UNDERSTAND HOW THE
UNIVERSE WORKS BUT FOR
EVERYBODY, YOU PROBABLY WANT TO
KNOW WHAT'S GOING TO HAPPEN IN
THE UNIVERSE IN THE FUTURE.
REALLY THE FUTURE OF THE
UNIVERSE, HOW THE UNIVERSE
EVOLVES OR TIME IN THE COMING
TENS OF BILLIONS OF YEARS IS
GOING TO BE DETERMINED BY THE
PROPERTIES OF DARK ENERGY AND WE
JUST DON'T KNOW THOSE PROPERTIES
VERY WELL.
WE THINK THAT THERE'S PROBABLY
TWO SCENARIOS THAT MIGHT PLAY
OUT, AND THAT'S WHAT WE THINK
NOW AND WE'RE NOT SURE WHICH ONE
OF THOSE TWO SCENARIOS WILL PLAY
OUT AND WE WANT TO STUDY THE
DARK MATTER AND THE DARK ENERGY
TO FIND OUT WHICH ONE OF THOSE
SCENARIOS WILL PLAY OUT.
WE'RE GOING TO TELL YOU A LITTLE
BIT ABOUT THOSE TWO POSSIBLE

English: 
  plenty of time to measure
  before this happens.
 And so we've told you
 about a lonely end,
  a possible lonely end,
  kind of a sad end, maybe,
to the universe.
 But it's not the scariest
 possible end to the universe.
>> Audience Member: Oh, come on.
  >> So Alina and I,
  full disclosure,
  we do not have a pool,
  we told you that earlier,
  but we do have a fire pit.
  So in honor of Halloween,
 we want you to all come sit
 with us around the campfire.
  We're gonna tell
  you a scary story
about another possible
future of the universe.
 >> So if dark energy
 is a bit stronger
  than scientists
  currently believe,
 then the universe
 will eventually end.
At around 60 million years
before the end of the universe,
 galaxies will
 begin to rip apart.
So unlike the scenario
we talked about earlier

English: 
SCENARIOS NOW.
>> SO IF DARK ENERGY ISN'T TOO
STRONG, GALAXIES WILL CONTINUE
MOVING AWAY FROM EACH OTHER LIKE
EDWIN HUBBEL DISCOVERED AND
THEY'RE GOING TO CONTINUE MOVING
AWAY FROM EACH OTHER FASTER AND
FASTER UNTIL EVENTUALLY, THEY'LL
BE SO FAR APART THAT THEY WON'T
BE ABLE TO SEE EACH OTHER, AND
THE UNIVERSE WILL BECOME AN
INCREDIBLY LONELY PLACE.
AND OUR GALAXY WILL BE ALONE.
JASON.
WHERE DID YOU GO?
I CAN'T SEE YOU.
>> DON'T WORRY, I'M HERE.
SO THAT'S WHAT THE UNIVERSE IS
GOING TO END UP LOOKING LIKE.
WE'LL HAVE A UNIVERSE WHERE
WE'RE IN OUR GALAXY, AND WE
CAN'T SEE THOSE DISTANT GALAXIES
ANYMORE.
THEY'VE MOVED TOO FAR AWAY.
AND SO SOMETIMES, I'VE TRIED IN

English: 
  where the galaxy
  remained together,
in this scenario, dark
energy becomes so strong
 that it starts to fling the
 stars away inside galaxies.
 >> At about three months
 before the end of the universe
  in this scenario,
 [audience laughing]
even solar systems are
gonna get ripped apart.
 That is, planets are gonna
 be shot away from their stars
 because of the ever-increasing
 expansion of the universe.
 Now, it's not quite as scary
 as you might think for us
 because long before
 that happens,
 our sun will turn
 into a red giant star
and gobble up the earth,
 so I hope I've made
 you feel a lot better
 about this end of the
 universe scenario.
 [audience laughing]
  >> At a few minutes before
  the end of the universe,
 even stars and planets will
 begin to get ripped apart
 by how strong the
 dark energy has become
and stretching out the universe.

English: 
>> In the final moments
of the universe,
 even atoms are gonna
 be ripped apart.
 That is, electrons are gonna
 be ripped from the nucleus,
  and protons and neutrons
  are gonna be ripped apart.
And in fact, we think
the very fabric of space
  will start to rip apart
  in what we call a big rip.
 [audience laughing]
 So these are,
yeah, scientists are very, very
clever with our naming, huh?
  Everything's big or dark.
 [Alina laughing]
 [audience laughing]
  These are the two
  possible scenarios
 that scientists think might
 happen with dark energy,
  and I don't find either of
  them particularly happy,
 a very lonely end or the
 universe being ripped apart.
 Fortunately, this
 is not gonna happen
  for many, many
  billions of years,
 and we've got a lot of time
 to study the dark matter
  and study the dark energy
 and find out which
 scenario might happen.

English: 
THE PAST TO USE THIS IN MY
FUNDING PROPOSE ALLEGES TO NASA,
I SAY YOU'VE GOT TO FUND THIS
DARK ENERGY STUDY RIGHT NOW
BECAUSE EVENTUALLY I'M NOT GOING
TO BE ABLE TO SEE THESE DISTANT
GALAXIES IF YOU DON'T SEND ME
THE MONEY AND IT DOESN'T WORK
ANYMORE BECAUSE I THINK MY
COLLEAGUES AT NASA HEADQUARTERS
HAVE REALIZED THAT THIS HAPPENS
MANY, MANY TENS OF BILLIONS OF
YEARS FROM NOW, SO THEY THINK I
HAVE PLENTY OF TIME TO MEASURE
BEFORE THIS HAPPENS.
SO WE'VE TOLD YOU ABOUT A LONELY
END, A POSSIBLE LONELY END, KIND
OF A SAD END MAYBE TO THE
UNIVERSE, BUT IT'S NOT THE
SCARIEST POSSIBLE END TOHE
UNIVERSE.
SO ALINA AND I FULL DECIDES
CLOSURE, WE DO NOT HAVE A POOL,
WE TOLD YOU THAT EARLIER, BUT WE
DO HAVE A FIRE PIT, SO IN HONOR
OF HALLOWEEN, WE WANT YOU TO ALL
COME SIT WITH US AROUND THE
CAMPFIRE AND WE'RE GOING TO TELL

English: 
 And of course, humans
 are pretty ingenious,
and maybe in the coming
billions of years,
we can use that
ingenuity to figure out
how to harness the dark
matter and dark energy
  and control the universe
  maybe for a happier fate.
 [audience laughing]
  >> So Jason and I really
  want to thank you so much
for being here with us tonight.
  It has been an incredible
  privilege for us
 to talk to you about
 the dark universe,
 and we would be delighted to
 take some of your questions.
 Thank you all.
 [audience applauding]
 >> Preston: Thank
 you, it was wonderful.
 >> Thank you.
  [Preston laughing]
  >> That's right.
 >> Thank you.
 >> And we wanna thank Preston
  who put this all together.
  >> No, I helped out,
 I did a few things.
 You guys can go ahead and
 head toward center stage here,
  and we'll get set
  up for our Q&A.
 So yeah, you guys can
 wander on over there.
 That was a really great talk,
  and because I think a lot
  of us find these topics
  really mysterious,

English: 
YOU A SCARY STORY ABOUT ANOTHER
POSSIBLE FUTURE OF THE UNIVERSE.
>> SO IF DARK ENERGY IS A BIT
STRONGER THAN SCIENTISTS
CURRENTLY BELIEVE, THEN THE
UNIVERSE WILL EVENTUALLY END AT
AROUND 6 MILLION YEARS BEFORE
THE END OF THE UNIVERSE,
GALAXIES WILL BEGIN TO RIP
APART.
UNLIKE THE SCENARIO WE TALKED
ABOUT EARLIER WHERE THE GALAXY
REMAINS TOGETHER, IN THIS
SCENARIO, DARK ENERGY BECOMES SO
STRONG THAT IT STARTS TO FLING
THE STARS AWAY INSIDE GALAXIES.
>> AT ABOUT THREE MONTHS BEFORE
THE END OF THE UNIVERSE IN THIS
SCENARIO, EVEN SOLAR SYSTEMS ARE
GOING TO GET RIPPED APART.
THAT IS, PLANETS ARE GOING TO BE
SHOT AWAY FROM THEIR STARS
BECAUSE OF THE EVER-INCREASING
EXPANSION OF THE UNIVERSE.
NOW, IT'S NOT QUITE AS SCARY AS
YOU MIGHT THINK FOR US, BECAUSE

English: 
LONG BEFORE THAT HAPPENS, OUR
SUN WILL TURN INTO A RED GIANT
STAR AND GOBBLE UP THE EARTHLY,
SO I HOPE I MADE YOU FEEL A LOT
BETTER ABOUT THIS END OF THE
UNIVERSE SCENARIO.
>> AT A FEW MINUTES BEFORE THE
END OF THE UNIVERSE, EVEN STARS
AND PLANETS WILL BEGIN TO GET
RIPPED APART BY HOW STRONG THE
DARK ENERGY HAS BECOME AND
STRETCHING OUT OF THE UNIVERSE.
>> THAT IN THE FINAL MOMENTS OF
THE UNIVERSE, EVEN ATOMS ARE
GOING TO BE RIPPED APART,
ELECTRONS ARE GOING TO BE RIPPED
FROM THE NUCLEUS AND PRO TONS
AND NEW TRANSRIPPED APART.
IN FACT, WE THINK THE VERY
FABRIC OF SPACE WILL START TO
RIP APART IN WHAT WE CALL A BIG
RIP.
SO THESE A, SCIENTISTS A
VERY, VERY CLEVER WITH OUR
NAMING, HUH?

English: 
and we don't even, we
need that kind of primer
 to help us get just
 our basic bearings
 on something so mysterious.
 >> Thank you.
 >> Well, now it's time
 for your questions.
If you have one, please
come to the microphone.
I see some folks lining
up in the center there,
so if you submitted one
on the YouTube chat,
 we'll get to a couple
 of those, as well.
 So we're all set now.
  Go ahead with your
  question, thanks.
  >> If all mass has gravity
  and all matter has mass,
  do you know any
  way to figure out
how much mass and
gravity dark matter has?
 >> Alina: Yeah, okay.
  >> Jason: So we're
  asked, do we know any way
 to figure out how
 much mass and gravity
dark matter has?
 And the answer is yes,
 we know only one way
 to figure out how much
 mass dark matter has,
and that's through this
gravitational lensing technique
 that I talked about tonight.
  That's our only way of
  measuring the dark matter
  because it doesn't
  give off light,
 and it doesn't absorb light,

English: 
  so we have to look
  at it indirectly
through its effect on
these distant galaxies.
So that's the technique
we use to figure out
 how much mass dark matter has.
  >> Audience Member: Okay.
 >> All right, so I actually
 have two questions.
 One, do you take
 interns [laughing]?
 [audience laughing]
 >> Yes, we do.
 >> Yes, we do?
  >> Yes, we absolutely do.
  >> Okay, and--
>> Starting in December,
contact one of us.
 >> All right, and number two,
 how does the heat death theory
 factor into all of this?
 >> I don't know
 the answer to that,
 so I'm gonna give it
 to Jason [laughing].
>> So heat death theory
 says that stars will
 eventually burn out,
 they'll burn their fuel up,
and the, eventually will become,
 universe will become colder
 and colder and colder,
  and more diffuse
  and more diffuse.
 And that's the future
 of the universe
 that we thought might happen
 before we discovered
 the dark energy.
  So that's a future
  of the universe

English: 
EVERYTHING'S BIG OR DARK.
THESE ARE THE TWO SCENARIOS AND
I DON'T FIND EITHER OF THEM
PARTICULARLY HAPPY, A LONELY END
OR THE UNIVERSITY BEING RIPPED
APART.
FORTUNATELY THIS IS NOT GOING TO
HAPPEN FOR MANY, MANY BILLIONS
OF YEARS, AND WE'VE GOT A LOT OF
TIME TO STUDY THE DARK MATTER
AND STUDY THE DARK ENERGY AND
FIND OUT WHICH SCENARIO MIGHT
HAPPEN AND OF COURSE, HUMANS ARE
PRETTY INGENIOUS AND MAYBE IN
THE COMING BILLIONS OF YEARS, WE
CAN USE THAT INGENUITY TO FIGURE
OUT HOW TO HARNESS THE DARK
MATTER AND DARK ENERGY AND
CONTROL THE UNIVERSE MAYBE FOR A
HAPPIER FATE.
>> SO JASON, I REALLY WANT TO
THANK YOU ALL SO MUCH FOR BEING
HERE WITH US TONIGHT.
IT HAS BEEN AN INCREDIBLE
PRIVILEGE FOR US TO TALK TO YOU
ABOUT THE DARK UNIVERSE AND WE
WOULD BE DELIGHTED TO TAKE SOME
OF YOUR QUESTIONS.

English: 
that this
ever-expanding universe
  that was expanding slower
  and slower and slower,
just kind of peter out.
  But with the dark energy,
we think there's likely
different scenarios
for the future of the universe.
>> All right, thank you.
>> Mm-hmm.
  >> And yeah, if you wanna
  look at internships,
 go to the JPL website.
You can find information there.
 We do take interns.
 >> Oh, yeah.
 >> So if we're looking
 at the universe
  and the universe
  is looking at us,
 what's the probability
 of the universe
 just staying the same?
 >> So the question is, we're
 looking at the universe,
  and the universe
  is looking at us,
 and what is the probability
 of it staying the same?
 So scientists,
as they're looking at
the universe right now,
 we're watching it
 change all the time
  because light has
  a finite velocity,
 so we are looking
 further back in time
 as we look out into
 the distant universe,
 and so the probability of
 it staying the same is zero.
 We're watching it
 change all the time.

English: 
THANK YOU ALL.
[ APPLAUSE ]
>> WE WANT TO THANK PRESTON.
HE PUT THIS ALL TOGETHER.
>> I HELPED OUT.
I DID A FEW THINGS.
YOU CAN HEAD TOWARD CENTER STAGE
AND WE'LL GET SET UP FOR OUR G
AND A.
>> YEAH, YOU GUYS CAN WONDER
OVER THERE.
THAT WAS A REALLY GREAT TALK AND
BECAUSE I THINK A LOT OF US FIND
THESE TOPICS REALLY MYSTERIOUS
AND NEED THAT PRIMER TO GET
BASIC BEARINGS ON SOMETHING SO
MYSTERIOUS, WELL, NOW IT'S TIME
FOR YOUR QUESTIONS.
IF YOU HAVE ONE, PLEASE COME TO
THE MICROPHONE.
I SEE SOME FOLKS LINING UP IN
THE CENTER THERE.
IF YOU SUBMITTED ONE ON THE YOU
TUBE CHAT, WE'LL GET TO A COUPLE
OF THOSE, AS WELL.
WE'RE ALL SET NOW.
GO AHEAD WITH YOUR QUESTION,
THANKS.
>> IF ALL MASS THAT GAVE IF I
AND ALL MATTER HAS MASS, DO YOU
KNOW ANY WAY TO FIGURE OUT HOW
MUCH MASS AND GRAVITY DARK
MATTER HAS?

English: 
SO WE'RE ASKED DO WE KNOW ANY
WAY TO FIGURE OUT HOW MUCH MASS
AND GRAVITY DARK MATTER HAS.
AND THE ANSWER IS YES, WE KNOW
ONLY ONE WAY TO FIGURE OUT HOW
MUCH MASS DARK MATTER HAS, AND
THAT'S THROUGH THIS
GRAVITATIONAL LENSING TECHNIQUE
THAT I TALKED ABOUT TONIGHT.
THAT'S OUR ONLY WAY OF MEASURING
THE DARK MATTER, BECAUSE IT
DON'T GIVE OFF LIGHT AND IT
DOESN'T ABSORB LIGHT SO WE HAVE
TO LOOK AT IT INDIRECTLY THROUGH
ITS EFFECT ON THESE DISTANT
GALAXIES.
THAT'S THE TECHNIQUE WE USE TO
FIGURE OUT HOW MUCH MASS DARK
MATTER THIS HAS.
>> OK.
>> ALL RIGHT, SO ACTUALLY I HAVE
TWO QUESTIONS, ONE, DO YOU TAKE
INTERNS?
>> YES, WE DO.
>> YES, WE DO.
>> OK, AND.
>> STARTING IN DECEMBER, CONTACT
ONE OF US.
>> ALL RIGHT.
AND NUMBER TWO, HOW DOES THE
HEAT DEPTH THEORY FACTOR INTO
ALL OF THIS?
>> I DON'T KNOW THE ANSWER TO
THAT, SO I'M GOING TO GIVE IT TO
JASON.
>> HEAT DEPTH THEORY SAYS THAT

English: 
 >> Okay, thank you.
 >> Thank you.
 >> So I was wondering
 if you could clarify
 the effects of
 gravitational lensing.
I've heard different
effects attributed to it
  such as magnifying
  stars or galaxies
 far beyond the amount
 that we could get
 through our telescopes
 if it wasn't aided by
 gravitational lensing.
I've also seen in the
slides you've shown here
 some types of
 spherical aberration
which highly distorts the image.
And then I've even
seen, a few decades ago,
  examples where there were
  literally mirror images
of galaxies in formations,
like reflected upon each other.
 I don't really understand
 how all those things happen.
 Perhaps you could tie
 it together for us.
  >> Sure, so the
  question is about
 what we scientists call
 strong gravitational lensing,
where light from
a distant galaxy
is traveling towards us,

English: 
 and it is being distorted by
 a huge amount of dark matter.
 And that light is
 traveling quite close
 to the large amount
 of dark matter,
 which is causing a
 large lensing effect.
In physics, we can look
at how light deflects
  as it goes through
  this dark matter,
  and these are quite simple
  equations to understand,
 but we expect to see a
 number of different galaxies
 in this strong
 gravitational lensing.
So multiple images is
one of the consequences
 of this strong
 gravitational lensing,
  and you can sometimes even
  do this with a wine glass
and some water.
 It's the same kind of effect
 of the light traveling through
 when you're looking
 at the reflections
  of the light going
  through the glass.
And so all of the things
that you mentioned,
 the giant arcs, the multiple
 images, the magnification,

English: 
STARS WILL EVENTUALLY BURN OUT.
THEY'LL BURN THEIR FUEL UP, AND
THE EVENTUALLY WILL BECOME THE
UNIVERSE WILL BECOME COLDER AND
COLDER AND COLDER AND MORE
DIFFUSE AND MORE DIFFUSE AND
THAT'S THE FUTURE OF THE
UNIVERSE THAT WE THOUGHT MIGHT
HAPPEN BEFORE WE DISCOVERED THE
DARK ENERGY, SOB THAT'S A FUTURE
OF THE UNIVERSE THAT THIS EVER
EXPANDING UNIVERSE THAT WAS
EXPANDING SLOWER AND SLOWER AND
SLOWER JUST KIND OF PETER OUT,
BUT WITH THE DARK ENERGY, WE
THINK THERE'S LIKELY DIFFERENT
SCENARIOS FOR THE FUTURE OF THE
UNIVERSE.
>> ALL RIGHT, THANK YOU.
>> AND IF YOU WANT TO LOOK INTO
INTERNSHIPS, GO TO THE JPL
WEBSITE.
YOU CAN FIND INFORMATION THERE.
WE DO TAKE INTERNS.
>> SO IF WE'RE LOOKING AT THE
UNIVERSEND THE UNIVERSE IS
LOOKING AT US, WHAT'S THE
PROBABILITY OF THE UNIVERSE JUST
STAYING THE SAME?
>> SO THE QUESTION IS WE'RE
LOOKING AT THE UNIVERSE AND THE
UNIVERSE IS LOOKING AT US AND
WHAT IS THE PROBABILITY OF IT

English: 
 they're consequences of
 strong gravitational lensing.
 Do you wanna?
  >> Yeah, you had
  mentioned multiple images
 of the same galaxy,
 and a way to think of that is
  if you have a very
  strong lens here,
a lot of dark matter and
the galaxy back here,
 some of the light is
 gonna come this way,
 it's gonna come to your eye.
  Some of the light is gonna
  come that way to your eye,
 and what your eye is gonna see
 is an image of that distant
 galaxy here and here.
 So we can get multiple
 images of the distant galaxy
from this gravitational
lensing effect,
 and that was one of
 the surprising things
that people started to discover
when we started to have
the quality of images
that we get from the
Hubble Space Telescope.
 >> So then the effect
 depends on the line of sight
  and the relative position
  of the dark energy, or?
>> That's exactly right.
>> That's exactly right.
  >> It depends on
  the line of sight
  and the relative positions
  of the dark matter
and the distant galaxy.
 >> So we know something about

English: 
STAYING THE SAME.
SO SCIENTISTS AS THEY'RE LOOKING
AT THE UNIVERSE RIGHT NOW WE'RE
WATCHING IT CHANGE ALL THE TIME,
BECAUSE LIGHT HAS FINITE
VELOCITY, SO WE ARE LOOKING
FURTHER BACK IN TIME AS WE LOOK
OUT INTO THE DISTANT UNIVERSE,
AND SO THE PROBABILITY OF IT
STAYING THE SAME IS ZERO.
WE'RE WATCHING IT CHANGE ALL THE
TIME.
>> OK.
THANK YOU.
>> THANK YOU.
>> SO I WAS WONDERING IF YOU
COULD CLARIFY THE EFFECTS OF
GRAVITATIONAL LENSING.
I'VE HEARD IT DIFFERENT EFFECTS
AT ATTRIBUTED TO IT, SUCH AS
MAGNIFYING STARS OR GALAXIES FAR
BEYOND THE AMOUNT WE COULD GET
THROUGH OUR TELESCOPES IF IT
WASN'T AIDED BY GRAVITATIONAL
LENSING.
I'VE SEEN THE SLIDES
SPHERICAL ABERRATION WHICH
HIGHLY DISTORTS THE IMAGE AND
I'VE EVEN SEEN A FEW DECADES AGO

English: 
 where the dark
 matter is in clumps
  relative to the
  totality of space?
 >> We do know where
 the dark matter is
  because we can back that
  out using these equations
 when we see these
 gravitational lenses.
 So it's using these
 gravitational lenses,
that's how we measure
where the dark matter is
 and how much there is.
  >> Does it correlate with
  any other visible objects
 in the known universe?
  >> The position of the
  dark matter, it turns out,
 it correlates quite
 well, usually,
 with the position of
 the luminous matter,
  the normal matter,
  the stuff we see.
 And that's because the dark
 matter forms sort of a well
where the normal
matter collects.
It's like a gravitational well.
  The normal matter collects
 where there's a
 lot of dark matter.
 >> Okay, we're gonna move on--
 >> Thank you.
>> to one of our
questions from YouTube,
  thanks very much.
 SSR98 has a good one
 for cosmologists.
 "If the universe is expanding,
 "what is it expanding into?"

English: 
EXAMPLES WHERE THERE WERE
LITERALLY MIRROR IMAGES OF
GALAXIES AND FORMATIONS
REFLECTED UPON EACH OTHER.
I DON'T UNDERSTAND HOW ALL THOSE
THINGS HAPPEN.
PERHAPS YOU COULD TIE IT
TOGETHER FOR US.
>> SURE.
SO THE QUESTION IS ABOUT WHAT WE
SCIENTISTS CALL STRONG
GRAVITATIONAL LENSING, WHERE
LIGHT FROM A DISTANT GALAXY IS
TRAVELING TOWARDS US AND IT IS
BEING DYSPORTED BY A HUGE AMOUNT
OF DARK MATTER, AND THAT LIGHT
IS TRAVELING QUITE CLOSE TO THE
LARGE AMOUNT OF DARK MATTER,
WHICH IS CAUSING A LARGE LENSING
EFFECT.
AND IN PHYSICS, WE CAN LOOK AT
HOW LIGHT DEFLECTS AS IT GOES
THROUGH THIS DARK MATTER AND
THESE ARE QUITE SIMPLE EQUATIONS
TO UNDERSTAND, BUT WE EXPECT TO
SEE A NUMBER OF DIFFERENT
GALAXIES IN THIS STRONG
GRAVITATIONAL LENSING, SO

English: 
  That's a classic.
 [audience laughing]
>> It's a real classic question.
 >> It's not very--
 >> So if the universe
 is expanding, what
 is it expanding into?
 And the very
 unsatisfying answer is
 that the universe is
 really everything.
 So it is, there's
 nothing outside it,
  it's just getting bigger.
 [audience laughing]
 Sorry, do you have a better
 way of saying it? [laughing]
 >> We're just getting
 more universe.
 [audience laughing]
 Yeah.
 >> It's something
 that's very difficult
 for our minds to get around
 because we can only think in
 the three dimensions we see.
 But the universe is expanding,
 it's getting bigger,
and there's more universe today
  than there was yesterday,
 and tomorrow, it's
 gonna be even bigger.
>> So you heard it here.
[audience laughing]
You're getting more
Big Bang for your buck.
 [Alina laughing]
 [audience laughing]
 Next question.
>> It's actually what my
question was gonna be.

English: 
MULTIPLE IMAGES IS ONE OF THE
CONSEQUENCES OF THIS STRONG
GRAVITATIONAL LENSING AND YOU
CAN SOMETIMES EVEN DO THIS WITH
A WINE GLASS AND SOME WATER.
IT'S THE SAME KIND OF EFFECT OF
THE LIGHT TRAVELING THROUGH WHEN
YOU'RE LOOKING AT THE
REFLECTIONS OF THE LIGHT GOING
THROUGH THE GLASS AND SO ALL OF
THE THINGS THAT YOU MENTIONED,
THE GIANT ARCS, THE MULTIPLE
IMAGES, THE MAGNIFICATION,
THEY'RE CONSEQUENCES OF STRONGER
GRAVITATIONAL LENSING.
DO YOU WANT TO?
>> YEAH, YOU HAD MENTIONED
MULTIPLE IMAGES OF THE SAME
GALAXY, AND A WAY TO THINK OF
THAT IS IF YOU HAVE A VERY
STRONG LENS HERE, A LOT OF DARK
MATTER AND THE GALAXY BACK HERE,
SOME OF THE LIGHT IS GOING TO
COME THIS WAY.
IT'S GOING TO COME TO YOUR EYE.
SOME OF THE LIGHT IS GOING TO
COME THAT WAY TO YOUR EYE.
YOUR EYES GOING TO SEE AN IMAGE
OF A DISTANT GALAXY HERE AND
HERE SO WE CAN GET MULTIPLE
IMAGES OF THE DISTANT GALAXY
FROM THIS GRAVITATIONAL LENDING
EFFECT.
AT WAS ONE OF THE SURPRISING

English: 
 But you don't consider
 it the Big Void
  or some infinite haze that
  this is all expanding into
 that's not part of your study,
not part of your consideration?
>> So it's not in the following
sense, is that we think,
 if we look at how the
 universe has evolved,
  we can watch that
  sort of backwards
  as a movie in reverse, and
  eventually, we get back
  to an infinitely dense
  and infinitely small point
 in the past,
about 13-some billion years ago,
 and after that,
 there was a Big Bang,
  and it started to expand.
 And so it doesn't
 mean that that point
 was sitting in space.
 All of space was at an
 infinitesimally small point,
 and we're just
 getting more space.
 It's something that,
 as cosmologists,
 we learn to understand
 in the equations,
 and the equations
 fit our observations,
but as humans, it's pretty hard
to get our mind around that
 because it's not something
 we can visualize very easily.
 >> Or multiple
 dimensions, I suppose?

English: 
THINGS THAT PEOPLE STARTED TO
DISCOVER WHEN WE STARTED TO HAVE
THE QUALITY OF IMAGES THAT WE
GET FROM THE HUBBEL SPACE
TELESCOPE.
>> SO THEN THE EFFECT
DEPENDENCIES ON THE LINE OF
SIGHT AND THE RELATIVE POSITION
OF THE DARK ENERGY?
>> THAT'S EXACTLY RIGHT.
IT DEPENDS ON THE LINE OF SIGHT
AND THE RELATIVE POSITIONS OF
THE DARK MATTER, AND THE DISTANT
GALAXY.
>> SO WE KNOW SOMETHING ABOUT
WHERE THE DARK MATTER IS IN
CLUMPS, RELATIVE TO THE TOTALITY
OF SPACE?
>> WE DO KNOW WHERE THE DARK
MATTER IS, BECAUSE WE CAN BACK
THAT OUT USING THESE EQUATIONS
WHEN WE SEE THESE GRAVITATIONAL
LENS SAYS, SO IT'S USING THESE
GRAVITATIONAL LENSES, THAT'S HOW
WE MEASURE WHERE THE DARK MATTER
IS AND HOW MUCH THERE IS.
>> DOES IT CORRELATE WITH ANY
OTHER VISIBLE OBJECTS IN THE
KNOWN UNIVERSE?
>> THE POSITION OF THE DARK
MATTER TURNS OUT IT CORRELATES
QUITE WELL USUALLY WITH THE

English: 
 >> That's another
 possible explanation,
 but for me, I can't think in
 multiple dimensions, either.
 [audience laughing]
 Just the math.
I can only see the math.
 >> [laughing], thanks a lot.
 [audience laughing]
 >> Audience Member: Hi there.
 >> Hi.
  >> So by the way,
  what would happen
 if the universe keeps on with
 this accelerating expansion?
Would it one day expand
faster than light speed?
 >> You can take it.
 >> So yes, the universe
 will eventually be expanding
faster than light speed,
 so nothing in the
 universe can, itself,
 no piece of matter,
 no piece of light
 can move faster than light.
 But space can expand faster
 than the speed of light.
  >> Right, so what
  space between each
of the individual matter
molecules and stuff
of that star's expanding
faster than light?
Does that mean that no molecule
  will be able to
  touch each other,
  like, no particle will be
  able to touch each other
 because nothing could really
 move faster than light?

English: 
POSITION OF THE LUMINES MATTER,
THE NORMAL MATTER, THE STUFF WE
SEE BECAUSE THE DARK MATTER
FORMS A WELL WHERE THE NORMAL
MATTER COLLECTS.
IT'S LIKE A GRAVITATIONAL WELL.
THE NORMAL MATTER COLLECTS WHERE
THERE IS DARK MATTER.
>> WE ARE GOING TO MOVE ON TO A
QUESTION FROM YOU TUBE.
WE HAVE A GOOD ONE FOR
COSMOLOGISTS.
IF THE UNIVERSE IS EXPANDING,
WHAT IS IT EXPANDING INTO.
IT'S A CLASSIC.
>> IT'S A REAL CLASSIC QUESTION.
SO IF THE UNIVERSE IS EXPANDING,
WHAT IS IT EXPANDING INTO, AND
THE VERY UNSATISFYING ANSWER IS
THAT THE UNIVERSE IS REALLY
EVERYTHING, SO IT IS -- THERE'S
NOTHING OUTSIDE IT, IT'S JUST
GETTING BIGGER.
SORRY, DO YOU HAVE A BETTER WAY
OF SAYING IT?
>> WE'RE JUST GETTING MORE
UNIVERSE.
IT'S SOMETHING THAT'S VERY
DIFFICULT FOR OUR MINDS TO GET

English: 
 >> That's one of the
 possible scenarios
that we talked about at the end,
that we can't see anything else
 'cause it's all moved faster
 than light away from us.
>> And is there a
chance that dark matter,
dark energy phenomenons
that we're observing
  is possibly just curvature
  of spacetime itself,
 but instead of being curved
 by the stuff that we can see,
it's curved by something
that we don't know
 or it's just curved
 to begin with?
 >> So the question was, is the
 dark matter and dark energy
 just a curvature of spacetime?
 >> Right.
 >> Well, we describe gravity
 as the curvature of spacetime.
That's how we describe gravity,
 with our gravity equations
 that Alina was talking about
 in the talk.
 And in fact, it's equivalent
 to what you described.
 So it might be that we don't
 understand gravity very well.
 We think we do, but if we
 don't, that could explain some
 of the things we see.
 >> I mean, right now,
 we have trouble
 even putting gravity
 into particle physics.

English: 
AROUND, BECAUSE WE CAN ONLY
THINK IN THE THREE DIMENSIONS WE
SEE.
BUT THE UNIVERSE IS EXPANDING.
IT'S GETTING BIGGER AND THERE'S
MORE UNIVERSE TODAY THAN THERE
WAS YESTERDAY, AND TOMORROW,
IT'S GOING TO BE EVEN BIGGER.
>> YOU HEARD IT HERE.
YOU'RE GETTING MORE BIG BANG FOR
YOUR BUCK.
NEXT QUESTION.
>> THAT'S ACTUALLY WHAT MY
QUESTION WAS GOING TO BE, BUT
YOU DON'T CONSIDER IT THE BIG
VOID OR SOMETHING IN FINITE HAZE
THAT THIS IS ALL EXPANDING INTO,
THAT'S NOT PART OF YOUR STUDY,
NOT PART OF YOUR CONSIDERATION?
>> SO IT'S NOT IN THE FOLLOWING
SENSE, IS THAT WE THINK IF WE
LOOK AT HOW THE UNIVERSE HAS
EVOLVED, WE CAN WATCH THAT SORT
OF BACKWARDS AS A MOVIE IN
REVERSE AND EVENTUALLY WE GET
BACK TO AN INIFY IN ILI DENSE
AND SMALL POINT IN THE PAST
ABOUT SOME 13 BILLION YEARS AGO
AND AFTER THAT, THERE WAS A BIG
BANG BE AND IT STARTED TO
EXPAND.

English: 
SO IT DOESN'T MEAN AT THAT POINT
WAS SITTING IN SPACE, ALL OF
SPACE WAS AT IN IN FINITE TESS
MALI SMALL POINT AND WE'RE JUST
GETTING MORE SPACE.
IT'S SOMETHING AS COSMOLOGISTS
WE LEARN TO UNDERSTAND IN THE
EQUATIONS AND THE EQUATIONS FIT
OUR OBSERVATIONS BUT AS HUMANS
IT'S PRETTY HARD TO GET OUR MIND
AROUND THAT BECAUSE IT'S NOT
SOMETHING WE CAN VISUALIZE
EASILY.
>> OR MULTIPLE DIMENSIONS, I
SUPPOSE.
>> THAT'S ANOTHER POSSIBLE
EXPLANATION BUT FOR ME, I CAN'T
THINK IN MULTIPLE DIMENSIONS
EITHER.
JUST THE MATH.
I CAN ONLY SEE THE MATH.
>> THANKS SO MUCH.
>> SO BY THE WAY, WHAT WOULD
HAPPEN IF THE UNIVERSE KEEPS ON
WITH THIS ACCELERATING
EXPANSION, WOULD IT ONE DAY
EXPAND FASTER IN LIGHT SPEED?
>> SO YES, THE UNIVERSE WILL
EVENTUALLY BE EXPANDING FASTER
THAN LIGHT SPEED, SO NOTHING IN

English: 
>> That's true.
>> Mm-hmm.
 >> We don't have a complete
 model of particle physics
 that includes gravity.
 >> All right, on to another
 question from YouTube.
 Jane wants to know
 if ordinary particles
can become dark matter.
 >> So can ordinary particles
 become dark matter,
 and I would say that
 the answer to that,
  that scientists
  currently believe, is no.
 We have normal matter
 that we understand,
 and it reflects
 electromagnetic light,
and it emits radiation,
 but I don't think that
 we think it can turn
  into dark matter.
But that doesn't mean that
something couldn't be discovered
 in the future
'cause we don't know
all that much about it.
>> Hey.
 >> I am clearly the
 dumbest person in this room
 [audience laughing]
 as this question will prove.
 I wanna follow you,
 and I'm mostly there.
 But if I understand
 what you're saying,
 there's a distortion
 that we're seeing,

English: 
THE UNIVERSE CAN ITSELF, NO
PIECE OF MATTER CAN MOVE FASTER
THAN LIGHT BUT SPACE CAN EXPAND
FASTER THAN THE SPEED OF LIGHT.
>> WAS SPACE BETWEEN EACH OF THE
INDIVIDUAL MOLECULES AND STUFF
ALL THAT STARTS EXPANDING FASTER
THAN LIGHT, DOES THAT MEAN NO
PARTICLE WOULD BE ABLE TO TOUCH
EACH OTHER BECAUSE NOTHING COULD
REALLY MOVE FASTER THAN LIGHT.
>> THAT'S ONE OF THE POSSIBLE
SCENARIOS THAT WE TALKED ABOUT
AT THE END, THAT WE CAN'T SEE
ANYTHING ELSE, BECAUSE IT'S ALL
MOVED FASTER THAN LIGHT AWAY
FROM US.
>> AND IS THERE A CHANCE THAT'S
THE DARK MATTER, DARK ENERGY
PHENOMENON THAT WE'RE OBSERVING
IS POSSIBLY JUST CURVATURE OF
SPACE TIME ITSELF, BUT INSTEAD
OF BEING CURVED BY THE STUFF
THAT WE CAN'T SEE, IT'S CURVED
BY SOMETHING THAT WE DON'T KNOW
OR IT'S JUST CURVED TO BEGIN
WITH?
>> SO THE QUESTION WAS IS THE
DARK MATTER AND DARK ENERGY JUST

English: 
 and so we're assuming
 it's dark matter?
 Is there any other theories,
or does the math just
say, "Nope, that's it."
 >> So we're seeing these
gravitational
 lensing distortions,
 and the question
 is, are we assuming
  that this is dark matter,
 or are there other theories
 that could explain it.
  And for a long time, there
  were lots of scientists
 that wanted to come up with
 a modified theory of gravity
 that didn't need an
 unseen form of matter.
And over time, there
were lots of experiments
  that scientists
  were undertaking,
 and they were able to rule out
 all of these other theories
 that did not
 include dark matter.
 And so at the moment,
 the only theories
 that work are the ones
  that include dark matter.
>> But there's no way to
actually detect it or prove it.
 It's just--
 >> Yes.
 >> Yeah, okay.
 >> Yes.
 [Alina laughing]
 [audience laughing]
  >> Preston: They're
  workin' on it [laughing].
 [audience chattering]
  >> Hi, I have a question.

English: 
A CURVATURE OF SPACE TIME.
WE DESCRIBED GRAVITY AS THE
CURVATURE OF STAYS TIME WITH OUR
GRAVITY EQUATIONS THAT ALINA WAS
TALKING ABOUT IN THE TALK.
IT'S EQUIVALENT TO WHAT YOU
DESCRIBED.
IT MIGHT BE THAT WE DON'T
UNDERSTAND GRAVITY VERY WELL.
WE THINK WE DO BUT WITH IF WE
DON'T, THAT COULD EXPLAIN NO OF
THE THINGS WE SEE WE DON'T HAVE
A COMPLETE MODEL OF PARTICLE
PHYSICS THAT INCLUDES GRAVITY.
>> ON TO ANOTHER QUESTION FROM
YOU TUBE.
CAN ORDINARY PARTICLES BECOME
DARK MATTER.
>> SO, CAN ORDINARY PARTICLES
BECOME DARK MATTER, AND I WOULD
SAY THAT THE ANSWER TO THAT THAT
SCIENTISTS CURRENTLY BELIEVE IS
NO.
WE HAVE NORMAL MATTER THAT WE
UNDERSTAND AND IT REFLECTS HE
ELECTROMAGNETIC LIGHT AND EMITS
RADIATION, BUT I DON'T THINK
THAT WE THINK IT CAN TURN INTO

English: 
If, after the Big Bang,
all of this matter,
which was essentially particles,
 gradually accreted
 into planets and suns
and galaxies and
galaxy clusters,
and if dark matter is
really little particles
  that we can't see,
 shouldn't it have
 done the same thing,
and shouldn't it be concentrated
 in all the galaxies and stars?
>> So the question--
>> Why is it in between
 the galaxies and
 not in the galaxies?
>> The question is about
how the dark matter
is distributed
throughout the universe.
 And I can let you know
 that the dark matter
 is actually clustered
at the centers of the galaxies.
 And scientists believe that
 the density of the dark matter
 at the center of the
 galaxy is much higher
than the density at the
outskirts of the galaxy.
 When we do simulations of
 dark matter with a computer,
 we get these beautiful
 clustering of the dark matter
  in what we call
  a big cosmic web.
And where we would
expect to see a galaxy,
there's this high
density of dark matter.

English: 
DARK MATTER, BUT THAT DOESN'T
MEAN THAT SOMETHING COULDN'T BE
DISCOVERED IN THE FUTURE,
BECAUSE WE DON'T KNOW ALL THAT
MUCH ABOUT IT.
>> I AM CLEARLY THE DUMB EFFORT
PERSON IN THIS ROOM, AS THIS
QUESTION WILL PROOF.
I WANT TO FOLLOW YOU AND I'M
MOSTLY THERE BUT IF I UNDERSTAND
WHAT YOU'RE SAYING, THERE'S A
DISTORTION THAT WE ARE SEEING
AND SO WE'RE ASSUMING IT'S DARK
MATTER?
IS THERE ANY OTHER THEORIES OR
DOES THE MATH JUST SAY NOPE,
THAT'S IT.
>> SO WE'RE SEEING THESE
GRAVITATIONAL LENSING
DISTORTIONS AND THE QUESTION IS
ARE WE ASSUMING THAT THIS IS
DARK MATTER OR ARE THERE OTHER
THEORIES THAT COULD EXPLAIN IT.
FOR A LONG TIME, THERE WERE LOTS
OF SCIENTISTS THAT WANTED TO
COME UP WITH A MODIFIED THEORY
OF GRAVITY THAT DIDN'T NEED AN
UNSEEN FORM OF MATTER, AND OVER
TIME, THERE WERE LOTS OF
EXPERIMENTS THAT SCIENTISTS WERE
UNDERTAKING AND THEY WERE ABLE
TO RULE OUT ALL OF THESE OTHER

English: 
  And you can trace it along
where you expect to see
the luminous matter.
So really, the luminous
matter is falling
into the center of these
dense dark matter areas.
 >> Okay, thank you.
 And one other little anecdote.
 Is it true that
 when they discovered
  that the Hubble
  Constant was wrong
  and the universe
  was accelerating,
 that there was a
 headline that said,
 "Hubble Double,
 Universe in Trouble?"
 [audience laughing]
 >> [laughing] There
 should have been.
 [Alina laughing]
 [audience laughing]
  Okay, so Derek on YouTube
  asks if dark matter
  has an electrical charge.
 Do we know enough
 about it to say that?
  >> We do, so an
  electrical charge
 comes from the
 electromagnetic interaction.
  And so right now, our
  best guess for dark matter
 is that it does
 not interact at all
 through the electromagnetic
 interaction.
 So it has no electric charge.
  In fact, we think
  that dark matter
only interacts gravitationally.
 It doesn't interact
 in any other way.

English: 
THEY ARE REQUIRES THAT DID NOT
INCLUDE DARK MATTER, AND SO AT
THE MOMENT, THE ONLY THEORIES
THAT WORK ARE THE ONES THAT
INCLUDE DARK MATTER.
>> BUT THERE'S NO WAY TO
ACTUALLY DETECT IT OFF PROVE IT.
>> YES.
>> OK.
>> THEY'RE WORKING ON IT.
>> HI.
I HAVE A QUESTION.
IF AFTER THE BIG BANG ALL OF
THIS MATTER WHICH WAS
ESSENTIALLY PARTICLES GRADUALLY
CREATED INTO MAN R. PLANETS AND
SUNS AND GALAXIE AND GALAXY
CLUSTERS AND IF DARK MATTER IS
PARTICLES WE CAN'T SEE SHOULDN'T
IT HAVE DONE THE SAME THING AND
BE CONCENTRATED IN ALL THE
GALAXIES AND STARS.
WHY IS IT IN BETWEEN THE
GALAXIES AND NOT IN THE
GALAXYION.
>>> THE QUESTION IS ABOUT HOW
THE DARK MATTER IS DISTRIBUTED
THROUGHOUT THE UNIVERSE, AND I
CAN LET YOU KNOW THAT THE DARK
MATTER IS ACTUALLY CLUSTERED AT
THE CENTERS OF THE GALAXIES AND
SCIENTISTS BELIEVE THAT THE
DENSITY OF THE DARK MATTER AT

English: 
That's what we think right now.
So no magnetic charge, no
electrical charge, just gravity.
>> And was that question, sorry,
  about dark matter
  or dark energy?
 >> It was about dark matter,
 >> Yeah, okay.
 >> whether the dark
 matter has a charge.
  >> Alina: Perfect.
 >> Hi.
 >> Hi.
 >> So my question's
 about the Big Rip.
 If everything is, oh, my God.
If everything is ripping apart,
and the atoms get ripped apart,
 wouldn't that create
 energy that would then
 bring it all together,
  and we would have,
  like, a big suck
  and then another big bang,
  [audience laughing]
 and then just start
 all over again?
  >> You can take that one.
>> Oh, you can take it.
 >> So the question is,
wouldn't a big rip create energy
  that might start
  everything all over again?
  And earlier, I said, well,
 I can't visualize an expanding
 universe into something,
it's just the equations.

English: 
THE CENTER OF THE GALAXY IS MUCH
HIGHER THAN THE DENSITY AT THE
OUTSKIRTS OF THE GALAXY.
WHEN WE DO SIMULATIONS OF DARK
MATTER, WITH A COMPUTER, WE GET
THESE BEAUTIFUL CLUSTERING OF
THE DARK MATTER IN WHAT WE CALL
A BIG COMPANIES MICK WEB AND
WHERE WE WOULD EXPECT TO SEE A
GALAXY IS THIS HIGH DENSITY OF
DARK MATTER, AND YOU CAN TRACE
IT ALONG WHERE YOU EXPECT TO SEE
THE LUMINES MATTER, SO REALLY,
THE LOOM NECESSARY MATTER IS
FALLING INTO THE CENTER OF THESE
DENSE DARK MATTER AREAS.
>> OK, THANK YOU.
ONE OTHER LITTL ANECDOTE, IS IT
TRUE WHEN THEY DISCOVERED THAT
THE HUBBEL CONSTANT WAS WRONG
AND THE UNIVERSE WAS
ACCELERATING THAT THERE WAS A
HEADLINE THAT SAID HUBBEL
DOUBLE, UNIVERSE IN TROUBLE?
>> THERE SHOULD HAVE BEEN.
[ LAUGHTER ]
>> OK, SO DERRICK ON YOU TUBE
ASKS IF DARK MATTER HAS AN
ELECTRIC CHARGE.
>> WE KW ENOUGH ABOUT IT TO
SAY THAT?

English: 
 I can tell you that
 the problem there
 is that once we get
 to this Big Rip,
our equations don't
work very well anymore.
 So I don't have an
 intuition from the equations
that tell me what's
gonna happen after that.
 So I don't know, yeah,
what happens after the Big Rip.
>> He was trying to get
me to say I don't know.
 >> Yeah [laughing].
 [Alina laughing]
  [Preston laughing]
  We don't know, how's that?
 [Alina laughing]
 [audience laughing]
 >> And it's that way at the
 beginning of the universe
  as well as the end, right?
We don't--
>> That's right,
 at the time of the Big Bang,
 our equations don't
 work very well,
and it's only after the Big Bang
  that the equations
  start to work.
 So there's still
 work we have to do,
 and don't forget, we
 did start this talk
  by saying that 95%
  of the universe,
cosmologists, people
who study the universe,
  don't understand.
So we stood in front of several
hundred people and said,
  "We don't understand 95%
  of what we do in our job."
 [audience laughing]
 >> And they're okay with that.
 >> Yeah.

English: 
>> WE DO.
AN ELECTRICAL CHARGE COMES FROM
THE ELECTROMAGNETIC INTERACTION,
AND SO RIGHT NOW, OUR BEST GUESS
FOR DARK MATTER IS THAT IT DOES
NOT INTERACT AT ALL THROUGH THE
ELECTROMAGNETIC INTERACTION, SO
IT HAS NO ELECTRIC CHARGE.
IN FACT, WE THINK THE DARK
MATTER ONLY INTERACTS
GRAVITATIONALLY.
IT DOESN'T INTERACT IN ANY OTHER
WAY.
THAT'S WHAT WE THINK RIGHT NOW.
SO NO MAGNETIC CHARGE, NO
ELECTRICAL CHARGE, JUST GRAVITY.
>> AND WAS THAT QUESTION ABOUT
DARK MATTER OR DARK ENERGY.
>> IT WAS ABOUT DARK MATTER,
WHETHER DARK MATTER HAS A
CHARGE.
>> PERFECT.
>> HI.
MY QUESTION IS ABOUT THE BIG
RIP.
IF EVERYTHING IS RIPPING APART
AND THE ATOMS GET RIPPED APART,
WOULDN'T THAT CREATE ENERGY THAT
WOULD THEN BRING IT ALL TOGETHER

English: 
  >> Time for a couple
  more questions, go ahead.
>> Just had a question.
>> Woo!
 >> I just had a
 question on axions.
 What, in your view, is like
 the hypothetical particle
 that dark matter, dark
 energy consists of,
  like neutralinos,
  WIMPs, or what,
 if you could expand
 on that, thanks.
 >> You're a plant from
 Caltech, aren't you?
[Alina laughing]
>> No.
 >> I'm just kidding.
 >> Yeah.
>> So you asked what do
we think dark matter is?
  And right now, the
  theorists on this
  are somewhat
  unconstrained by the data.
 And what I mean by that is,
 [audience laughing]
 >> Preston: Oh, that's
 a good one [laughing].
 >> Do I have any dark matter
 theorists here who are gonna?
 [audience laughing]
  So what it means is
  there's a lot of theories,
and you mentioned a few.
 There's axions, there's WIMPs.
 We're pretty clever
 at naming things.
  There's another
  one called MACHOs.
 [audience laughing]
I'm more partial to that
than the WIMPs, I guess.

English: 
  But these are all
  different theories
 of what the dark
 matter particle is.
 And in fact, the one that's
 been pretty well ruled out
 is the MACHOs, unfortunately.
 [audience laughing]
 But what we're doing
 with the gravitational
 lensing experiments
 is we're starting to rule out
what I'd call different
classes of models,
and because they behave
somewhat differently,
 and when we get better
 and better data,
 we can rule out
 different classes
of dark matter particles.
But there's still a lot
of possibilities left,
and that's why we need
to do these experiments
 like LSST, Euclid, and
 WFIRST in the future.
 >> All right,
 future NASA intern,
you get to have our last
question of the night.
  >> Okay, so I had
  another question.
 You said that, while answering
 your previous question,
 you said that dark
 matter concentrates
 at the centers of galaxies.
Would that have any
relation to black holes
 because black holes
 are theorized,

English: 
AND WE WOULD HAVE LIKE A BIG
SUCK AND THEN ANOTHER BIG BANG?
AND THEN JUST START ALL OVER
AGAIN?
>> SO THE QUESTION IS WOULDN'T A
BIG RIP CREATE ENERGY THAT MIGHT
START EVERYTHING ALL OVER AGAIN.
AND EARLIER, I SAID WELL, I
CAN'T VISUALIZE AN EXPANDING
UNIVERSE INTO SOMETHING, IT'S
JUST THE EQUATIONS.
I CAN TELL YOU THAT THE PROBLEM
THERE IS THAT ONCE WE GET TO
THIS BIG RIP, OUR EQUATIONS
DON'T WORK VERY WELL ANYMORE.
I DON'T HAVE AN INTUITION FROM
THE EQUATIONS THAT TELL ME
WHAT'S GOING TO HAPPEN AFTER
THAT, SO I DON'T KNOW WHAT
HAPPENS AFTER THE BIG RIP.
>> HE WAS TRYING TO GET ME TO
SAY I DON'T KNOW.
>> WE DON'T KNOW.
HOW'S THAT?
>> AND IT'S THAT WAY AT THE
BEGINNING OF THE UNIVERSE AS
WELL AS THE END, RIGHT?
>> THAT'S RIGHT.
AT THE TIME OF THE BIG BANG, OUR
EQUATIONS DON'T WORK VERY WELL
AND IT'S ONLY AFTER THE BIG BANG

English: 
 from what I'd heard,
 to have infinite mass.
 >> Audience Member: No, they
 don't have infinite mass.
 They have finite mass,
 but infinite density.
  >> All right.
  [Preston laughing]
 [audience laughing]
 >> Now we have two interns.
  >> Yeah, we've got plenty.
  [audience laughing]
 [audience applauding]
 Come on down.
 >> So the question
 was is the dark matter
  at the center of galaxies
  related to the black holes
  at the center of galaxies?
And so black holes are
something very different
to dark matter.
Black holes are what come about
when stars, very massive stars,
 reach the end of their lives.
  And then there's some
  coalescing of black holes
  at the center of galaxies
  to make these
  super-massive black holes.
 And we can measure the mass of
 these black holes, actually,
 and as was very
 helpfully mentioned,
they have a finite mass,
but an infinite sort of density.

English: 
THAT THE EQUATIONS START TO
WORK, SO THERE'S STILL WORK WE
HAVE TO DO, AND DON'T FORGET, WE
DID START THIS TALK BY SAYING
THAT 95% OF THE UNIVERSE
COSMOLOGISTS, PEOPLE WHO STUDY
THE UNIVERSE DON'T UNDERSTAND.
WE STOOD IN FRONT OF SEVERAL
HUNDRED PEOPLE AND SAID WE DON'T
UNDERSTAND 95% OF WHAT WE DO IN
OUR JOB.
>> AND THEY'RE OK WITH THAT.
>> TIME FOR A COUPLE MORE
QUESTIONS.
GO AHEAD.
>> JUST HAD A QUESTION ON
AXEONS.
WHAT IN YOUR VIEW IS LIKE THE
HYPOTHETICAL PARTICLE THAT DARK
MATTER, DARK ENERGY CONSISTS OF
LIKE NEWT ROW LEAN KNOWS, WIMPS
OR IF YOU COULD EXPAND ON THAT.
>> YOU'RE A PLANT FROM CAL TECH,
AREN'T YOU?
>> SO YOU ASKED WHAT DO WE THINK
DARK MATTER IS.

English: 
 And so the light can't
 escape from that mass.
And so they're unrelated
to the dark matter
in the center of those galaxies.
 >> Audience Member:
 All right, thank you.
  >> So they're dark matter,
 but they're not dark
 matter, all right.
  >> Sure.
  [Preston laughing]
  >> All right, well, that's
  all the time we have.
 >> I'd like to ask--
 >> for this.
 >> one more question.
 >> And we can have
 some discussion
 >> We'll be here for a while.
>> right after the show,
  and come on up, and we can
  continue this discussion.
 But for our audience at
 home, thanks for joining us.
  Thanks to everyone
  for being here.
  Thank you, again,
  to our speakers.
[audience applauding]
>> Thank you, thank you.
>> Okay, please join us,
  please join us next month
for our show all
about how we use
the International Space Station
[audience chattering]
to study our home planet
 from above, we'll see
 you next time, thanks.

English: 
RIGHT NOW, THE THEORY ITS ON
THIS ARE SOMEWHAT UNCONSTRAINED
BY THE DATA.
DO I HAVE ANY DARK MATTER
THEORISTS HERE?
WHAT IT MEANS IS THERE IS A LOT
OF THEORIES APPROXIMATE UP
THERE'S AXEONS, THERE'S WIMPS,
WE'RE PRETTY CLEVER AT NAMING
THINGS.
THERE'S ANOTHER CALLED MACHOS.
I'M MORE PARTIAL TO THAT THAN
THE WIMPS, I GUESS, BUT THESE
ARE ALL DIFFERENT THEORIES OF
WHAT THE DARK MATTER PARTICLE IS
AND THE FACT ONE THAT'S BEEN
PRETTY WELL RULED OUT IS THE
MACHOS, UNFORTUNATELY.
WHAT WE'RE GOING TO THE
GRAVITATIONAL LENS EXPERIMENTS
IS WE'RE STARTING TO RULE OUT
WHAT I CALL DIFFERENT CLASSES OF
MODELS AND BECAUSE THEY BEHAVE
SOMEWHAT DIFFERENTLY, AND WHEN
WE GET BETTER AND BETTER DATA,
WE CAN RULE OUT DIFFERENT
CLASSES OF DARK MATTER
PARTICLES, BUT THERE'S STILL A
LOT OF POSSIBILITIES LEFT, AND

English: 
THAT'S WHY WE NEED TO DO THESE
EXPERIMENTS LIKE LSST, EUCLID
AND W IN THE FUTURE.
>> FUTURE NASA INTERN, YOU GET
TO HAVE OUR LAST QUESTION OF THE
NIGHT.
>> OK.
SO I HAD ANOTHER QUESTION.
YOU SAID THAT ANSWERING YOUR
PREVIOUS QUESTION, YOU SAID THAT
DARK MATTER CONCENTRAS AT THE
CENTER OF GALAXIES.
WOULD THAT HAVE ANY RELATION TO
BLACK HOLES, BECAUSE BLACK HOLES
ARE THEORIZED FROM WHAT I'VE
HEARD EVER IN FINITE MASS?
>> NO, THEY HAVE FINITE MASS.
>> NOW WE HAVE TWO INTERNS.
>> COME ON DOWN.
>> SO THE QUESTION WAS IS THE
DARK MATTER AT THE CENTER OF
GALAXIES RELATED TO THE BLACK
HOLES AT THE CENTER OF GALAXIES,
AND SO BLACK HOLES ARE SOMETHING
VERY DIFFERENT TO DARK MATTER.
BLACK HOLES ARE WHAT COME ABOUT

English: 
WHEN STARS, VERY MASSIVE STARS
REACH THE END OF THEIR LIVES AND
THEN THERE'S SOME COALESCEING OF
BRACK HOLES AT THE CENTER OF
GALAXIES TO MAKE THESE SUPER
MASSIVE BLACK HOLES AND WE CAN
MEASURE THE MASS OF THESE BLACK
HOLES, ACTUALLY.
AND AS WAS VERY HELPFULLY
MENTIONED, THEY HAVE A FINITE
MASS BUT INFINITE DENSITY AND SO
THE LIGHT CAN'T ESCAPE FROM THAT
MASS, SO THEY'RE UNRELATED TO
THE DARK MATTER IN THE CENTER OF
THOSE GALAXIES.
>> ALL RIGHT, THANK YOU.
>> SO THEY'RE DARK MATTER, BUT
THEY'RE NOT DARK MATTER.
>> SURE.
>> ALL RIGHT, WELL THAT'S ALL
THE TIME WE HAVE FOR THIS, AND
WE CAN HAVE SOME DISCUSSION
RIGHT AFTER THE SHOW AND COME ON
UP AND WE CAN CONTINUE THIS
DISCUSSION BUT FOR OUR AUDIENCE
AT HOME, THANKS FOR JOINING US.
THANKS TO EVERYONE FOR BEING
HERE, THANKS AGAIN TO OUR
SPEAKERS.

English: 
[ APPLAUSE ]
>> PLEASE JOIN US NEXT MONTH FOR
OUR SHOW ALL AUT HOW WE USE
THE INTERNATIONAL SPACE STATION
TO STUDY OUR HOME PLANET FROM
ABOVE.
WE'LL SEE YOU NEXT TIME, THANKS.
