[ Silence ]
>> I want to introduce the-- pretty much I will
say if there is one person that is, you know,
seriously responsible for my being
here, our dean of Sciences, Dave Kotz.
[ Applause ]
>> Thanks Stefan.
It's my great pleasure to be here today
and to attend many of these talks.
It's a fantastic symposium.
Thank you all for attending.
And it is my particular pleasure now to
introduce the next speaker, David Spergel,
who is the Charles Young Professor of Astronomy
at Princeton and also the Chair of the Physics--
of Astrophysical Sciences at Princeton.
And actually, I can relate to this in many ways.
He did his undergraduate degree at Princeton.
I did my undergrad at Dartmouth and then
came back on the faculty of Dartmouth
and so I can understand that appeal.
He got his bachelors at Princeton in 1982 and
then three years later his PhD at Harvard.
His biography goes on quite extensively,
there's a lot of impressive awards
that I won't be able to name all of them.
For example, he had the MacArthur
Fellowship in 2001.
He was elected this year to the
American Academy of Arts and Sciences.
He is part of the new Princeton Center for
Theoretical Science and is a co-founder
of the Institute for Physics and
Mathematics of the Universe in Tokyo.
And he currently chairs the National
Academy of Sciences Committee on Astronomy
and Astrophysics, so he gets around.
His interests range from the search
for planets around nearby stars
to the shape of the universe itself.
And he's working now with
others to develop technologies
that may enable the direct
imaging of earthlike planets.
We have evidence increasingly--
extensive evidence on the existing--
existence of earthlike planets, but
nobody has ever actually seen one.
And so it's pretty cool, I think, that
he's working on ways to actually see them.
So with that, it's my pleasure
to introduce David Spergel.
[Applause]
>> Thank you.
[ Applause ]
I want to begin by thanking all the folks here
at Dartmouth who'd made this
very interesting meeting possible
and by the congratulating Stefan on
starting here as the E.E. Just Professor.
I think it's a very exciting opportunity
and we're all looking forward to coming back
and visiting you here over the years.
[ Inaudible Remark & Laughter ]
And, you know, you mentioned the
American Academy of Arts and Sciences,
one of the neat things is next week I'll
be inducted and that two of the people
who are inducted with me include Mel Brooks
and Clint Eastwood and I'm bringing a chair.
[ Laughter & Applause ]
So I want to start.
There's a lot of students in the audience.
When you give a talk like this sort of looking
at where you field is, it's fun to step back
and say, "Oh, where was this
field when I was a student?"
And when I first took my first cosmology
course, there were a bunch of questions
that we really didn't know the answer to.
How old is the universe?
It could have been 10 billion
years old, 20 billion years old.
We know it was older than the Earth,
but beyond that there was a factor two
uncertainty in the age of the universe.
How much stuff is in there in the universe?
There we had more like a factor 10 uncertainty.
You know, where the galaxies come from?
What's the universe shape?
These are all questions we
didn't know the answer to.
And to sort of summarize in
a sense where we've gone,
these are now questions we can get
pretty detailed quantitative answers to.
The universe is now, we believe, 13.7
billion years old since the Big Bang.
And that's something we know to about a percent.
While we don't know what the dark
matter and the dark energy is,
we do know how much stuff there is there.
And we had a pretty good idea about the
overall geometry or shape of the universe
and a theory for how a galaxy is formed.
And to begin with the conclusion of the
talk, today we have a cosmological model
with five basic parameters-- the
density of atoms, the density of matter,
how old the universe is, how lumpy it is
and how that lumpiness varies with scale.
With those five numbers, each of which I
know to a couple percent, we can describe all
of our observations in cosmology
and in astronomy,
of large scales and properties of the universe.
That's pretty good, right?
That's what you want to do in science, is to
have a simple theory that fits lots of data.
The problem is, while it's
simple, it's really strange.
Atoms make up less than 5
percent of the universe.
And we have given names to the other 95 percent.
But just because we gave them a name
doesn't mean we know what it is.
In fact, I think one of the great
mysteries of physics is trying to figure
out what the dark matter is and
what's going on with the dark energy.
And I'll come to that-- back to
those subjects as we go on the talk.
In order to describe how we got to this picture,
I have to first teach you a few key ideas
in spatial relativity and general relativity.
But don't worry, these are easy.
They'll take less than five minutes.
All right, spatial relativity.
The key idea you need to know for spatial
relativity is light travels at a finite speed.
That means when you look out in
space, you look back in time.
It takes a few nanoseconds for
light to get from Stefan to me.
So I see him as he was a few nanoseconds ago.
I don't see him as he is right now.
Now, Stefan hasn't changed that
much over the last few nanoseconds
so he probably hasn't changed that much since.
[Laughter] The further out we go in
space, the further back we look in time.
So we sit here and, you know, and hand over
and we look out and we look out towards Mars
and it takes like, you know, a finite
time to get to Mars so you can [inaudible]
with the Curiosity rover,
there's a real delay, right?
You send a signal, the time it comes back
and told you you've done that,
it takes like over 20 seconds.
Sorry, over 20 minutes.
20 minutes, sorry.
And that's a big effect.
You actually want to have a lot of autonomy
for the robot because lots-- things can happen.
You know, Martians can come over
and turn the Curiosity upside
down before we have time to respond.
The further out you go in
space, the further back in time.
The nearest stars are about
four light years away.
What does that mean?
That's a unit of distance.
A lot of times in science fiction shows,
it really bugs me when they say oh
that happened four light years ago.
No. Four light years is distance.
It's how far light goes in
a year, is one light year.
So is you're-- we see the nearby
stars as they were four years ago.
The further out you go, the further back.
If you were look-- orbiting one of these planets
that people are discovering now around, say,
a star that was 20 light years away, you'll
be seeing us as we were 20 years ago.
You'd see me with full head of hair.
[Laughter] The further back you go in
space, the further back you go n time.
So you'll hear about the Hubble telescope
discovering, you know, some galaxy that was,
you know, we see it as it
was 13 billion years ago.
We're seeing galaxies so far away
that we're seeing them, you know,
relatively close to the beginning
of the universe.
When we look out-- the further out we
look, the further back we go in time.
All right, so you now know spatial relativity.
Good. Now I want to talk
about the Big Bang Theory.
And when I talk about the Big Bang
theory, I'm not talking about the TV show.
Though, one of my colleagues
likes to claim that its view
of Caltech is not a comedy, it's a documentary.
[ Laughter ]
The Big Bang Theory really rests on two pillars.
One is general relativity,
and general relativity,
as my academic great grandfather Johnny Weiler
[phonetic] taught, consists of two ideas:
matter tells space how to curve,
and the curvature of space tells
matter and light how to move.
So once I specify how matter is distributed,
that tells me about the curvature of space.
And that's all people are
pretty comfortable with.
The thing that I think people struggle with
when they hear about the Big Bang Theory
and the thing that comes out of it which is to
say the universe is expanding actually don't
like the name of The Big Bang Theory.
It was invented by Fred Hoyle who was
an opponent to the Big Bang Theory.
He likes to study state cosmology.
I think a better name for it is
the Expanding Universe Theory
because what it tells us is the universe
is expanding, getting less dense with time;
and since it's filled with this hot
radiation, getting cooler with time.
And I think of it as describing the history
of the universe since the first few moments.
That's a very interesting question, Lee raised
some of these issues, Robert raised some
of these issues, and what happens earlier on,
but I think if I-- I like to start with the--
what we see today and run it back in time so if
the universe is expanding going forward in time,
it's contracting going back in time.
When we hear the universe is expanding,
the first question many people ask and some
of you are probably thinking this
now, what is it expanding into?
And that's because you're thinking abut
space as absolute that it's, you know,
it's like a balloon that's
expanding in this room.
It's expanding into the space around it.
What I like to think about relativity is it
says space is not absolute, space is relative.
Space is only defined in the
relationships between objects.
So we're not expanding into anything.
Things are getting just further apart.
Or if you want to think about
it expanding into something,
think about expanding into the future.
And the image I have when I think about
the universe's expansion is I can't think
about four dimensions so I think about three.
I ignore-- and I ignore one dimension of
space so I imagine that we're all living
on the surface of a big ball and we're ants
and all the galaxies are ants in the big ball.
And as the universe expands,
it's expanding into the future.
So that balloon is getting bigger
and the radial direction is time.
The radius of the balloon is time.
So as the universe expands, the ants
on the balloon get further apart
and that's the expansion of the universe,
making ants getting further and further apart.
And as we go further into the future, it
gets-- the ball gets bigger and bigger.
We'd run that back in time, the universe
gets denser and denser, hotter and hotter,
and the moment of the Big Bang is when
I shrink that balloon down to zero.
Okay. So here's history of our universe.
Here we are today looking back in
time at stars and galaxies forming.
Keep in mind, the age of the Earth if
kind of interesting on this, right?
The Earth is about four and a half
billion years old, so the Earth--
the age of the Earth is about a third of the
age of the universe, so we're relatively recent.
But in the grand schema things,
we kind of show--
or when the Earth forms,
shows up in this [inaudible].
Our solar system forms.
Go further back in time, a lot of what I'm going
to talk about today is the microwave background
which is the leftover heat for the Big Bang.
And most of what we see in the microwave
background is what the universe looked
like about 400,000 years after the Big Bang.
And I'll talk about some results from
our space observations with the WMAP
and some measurements we'll
be making from the ground.
So first let me begin by
talking about WMAP that stands
for the Wilkinson Microwave Anisotropy Probe.
Wilkinson's easy, that's my
late colleague Dave Wilkinson
who played a pivotal role
in experimental cosmology.
And after he died, NASA generously
let us name the satellite after him.
Microwave, that's suppose the--
it's the radiation we're looking at.
And it's just like your microwave oven.
It's that wavelength of radiation.
Anisotropy is a word that
many people struggle with.
I know when I get introduced,
people often can't pronounce it.
And it just means how things
vary across the sky.
Isotropic means the same everywhere on the sky.
Anisotropic means it varies from place to place.
So all that says is we're
looking at how thing vary.
And this just shows where
the satellites goes in order
to make better environment that's very clean
to observe the leftover heat from the Big Bang.
We actually go out at a distance about
four times the distance of the moon.
And we're out there or-- we were
out there in space orbiting,
taking pictures of this leftover heat.
So when we look out in space,
we look back in time.
If we look back in time, the
universe gets hotter and hotter.
How hot the universe is relative to today?
It's one way of thinking about redshift.
You hear astronomers talk about redshift.
So when we get to redshift of 1,000, that's when
the universe was 1,000 hotter than it is today.
10,000 when it's 10,000 much hotter.
So that going this way, the
universe is getting hotter and denser
and this plot shows how density
behaves with time.
As the universe gets hotter, it goes from being
made up of neutral hydrogen to ionized hydrogen.
Neutral hydrogen is transparent to radiation.
So light can travel freely
through it, or microwave light.
Ionized hydrogen, electrons and protons,
the radiation interacts with the electrons.
So it acts like a dense cloud.
So over here it's like a--
those of you who are up--
you know, was up running in
the morning, it's all foggy.
Dense fog back here.
We can't see through it.
As we look out in space back in time, we
see back to the moment or the period of time
when the universe made this transition
from being neutral to being ionized.
So our satellite maps what the
universe looked like back then.
So this cosmic background radiation, if we
had eyes that could see in the microwave,
would look more like this orange picture.
It's actually very uniform at a
temperature of about 2.7 degrees.
You have to look with very high
sensitivity and this is the image
from the COBE satellite which
was WMAP's predecessor.
And it's made the first detections of
variations in the microwave background,
variations about 1 part in 100,000.
And our goal was to try to look at that in
more detail to be able to determine things
like what's the shape, what's
the geometry of the universe.
Since you're all general relativist
now, you know that the amount
of matter determines the geometry.
So if you got a lot of matter,
it's going to curve space a lot.
Space will be positively curved closed geometry.
That means when we look at the--
left these fluctuations back then,
we actually know how big
the fluctuation should be.
The characteristic size is how far
light can travel in the 400,000 years.
So nature's is kind of holding up a ruler
for us that's 400,000 light years across.
And if the universe was closed,
those spots would look very big
because like the path light
would take-- would be different.
The density of the universe was
low, the spots should be smaller.
If the density of the universe was jus right, so
that the total energy of the universe is zero,
that the energy in expansion equals the energy
in mutual attraction, which is negative,
then the spots would be about a degree.
So those are the kinds of
things we want to measure
by making a precision measurement to the sky.
So we sent the satellite up.
It was really fun.
We went down to the cape.
Put it on a big delta rocket,
launched it into space,
and I actually did go to
Disney World afterwards.
[ Laughter ]
So here is our satellite.
Oops. There's our satellite.
But I want to see it right, spinning in space.
There you go.
I'm just going to have to hit-- and
it's out there spinning in space.
It's measuring these tiny fluctuations.
And the way we try to make these measurements
to higher precision is we make
a differential measurement.
A very good experimental trick is if you want
to measure something to very high accuracy,
don't make an absolute measurement,
do it differentially.
So if I brought two of you down who were
both, you know, one is 5'8", one is 5'9"
and I want to measure who's taller.
If I take a ruler and try to measure
it with those 12-inch rulers we've got
in elementary school, that's hard.
On the other hand, if I put you back
to back and I put a ruler on your head,
it's easy to see if people
are back to back who's taller.
That's a differential measurement.
And if you make a careful differential
measurement and you do things like we want
to make sure this ruler is not warped so
we're going to flip it around lots of times
and that's what we do with
the spinning satellite.
We have two different points.
We look at it in any given time.
We measure the temperature difference.
We spin around, a minute later,
measure the difference again, reversed.
You can make a very accurate map of the sky.
And that's what the satellite does.
And these are our maps of the sky.
We mapped them at different frequencies.
This is like seeing what the intensity
looks like and how much red light there is
in different parts of the
sky, how much yellow light,
how much green light except
for radial frequency.
So we're seeing how much
energy emission are we getting
at 22 gigahertz, 30 gigahertz, and so on.
And this is a map is like looking
at a globe where you take the sphere
and project in on the plane, right?
I could-- this is showing the sky around us.
And the first thing you'll notice
if you look at this picture is
that big bright red thing across the sky.
That's the galaxy.
That's dust and electrons in
our own galaxy, the Milky Way.
That's not what we're interested at.
That's stuff that's been traveling
towards us for about 10,000 years.
Boring. You know, we're interested in this blue
and yellow stuff on the bottom and the top.
That's the stuff that's been going--
traveling towards us for 13.7 billion years.
So we take data at many different
frequencies, five in our case.
As we go up in frequency, the
galactic emission gets less
and we know how this galactic
emission varies with frequency.
So what we do is we try to make our best
map combining all of the frequencies
and try to remove the contamination from our
own galaxy and from quasars and nearby galaxies
and this is our picture of what the
universe looked like 13.7 billion years ago.
And this is a really handy picture
to have because it can tell us a lot
about the properties of the universe.
We can count up and see what's the
number of spots we see on the sky.
How big they are?
How the fluctuations vary with scale.
So I can ask, you know, how lumpy
is this map at the 1 degree scale,
the five degree scale, the 10 degree scale.
Do I see equal numbers of
hot spots and cold spots?
Lee mentioned the possibility
of looking for non-Gaussianity.
One form of non-Gaussianity would be we have
more really bright hot spots than cold spots.
That would be a non-Gaussian fluctuation.
And that'll be very interesting, had
we seen that, that would have told us
that there's something beyond
our current simplest theory.
As Lee pointed out the interpretation of
that is more difficult, but that's the kind
of thing you can look at that would
tell us something new from this data.
Now, when you look at data like
this, if you look carefully,
you'll start noticing patterns like this.
Notice the letters SH, I first noticed
this-- actually in my colleague, Lyman Page
and I were sitting in a big conference.
Steven Hawking was speaking.
This was at UC Davis in 2003.
Lyman turned to me who did like-- Lyman designed
most of the instrument and said does that--
did they put up the letters SH as a joke?
Is this right?
Because of-- it's what the students
put there and we looked at our data.
No. It's there on the data.
[Laughter] This maybe telling
us something profound.
[Laughter] My own theory is
that the galactic emission
over here to the right is a bit stronger.
Perhaps we'd lost some information
when we removed it.
We're missing the letters I and T.
[ Laughter ]
When the initial conditions were created,
they realized there was a
mistake made and [inaudible].
More likely, I think, this
actually represents evolution.
We've been selected to find patterns and
it's-- those of us whose ancestors, you know,
they'd look in the woods
and nine times out of ten
when they jump was they thought
there was a tiger, they were wrong.
But one time out of ten, they were right.
So it's better to error on
jumping when you see something.
And the people who didn't jump
at all when they saw something
in the woods, they're not our ancestors.
[Laughter] They were ET.
[ Laughter ]
So how do we take-- what do
we do with data like this?
Well, we try to quantify what's
going on with the fluctuations.
We measure how lumpy as a function of scale.
And this plot here shows the points,
the amplitude of the fluctuations
as a function of angle.
And the conventional way we do it, spherical
harmonics for those of you who are more expert.
[Inaudible] the units we
use are 180 over the angle.
So that at ten, we're measuring how lumpy
things are smooth on the 18 degree scale.
The 1 degree scale, at about 200.
The tenth of the degree scale, when
we get out [inaudible] of 2,000.
So just looking at the lumpiness
as a function of scale,
and you'll notice there's a
really regular pattern you see.
And that regular pattern is set
by the fact that we're looking
at are sound waves on the early universe.
And that the amplitude of the signal
depends on how the sound waves behave.
So the spacing between the peaks
depends on what universe is made of.
You have more atoms that changes
the spacing between peaks.
We measure that.
The position of the peaks depends on
the distance from here to the surface.
That's how we know that the
universe is 13.7 billion years old.
If the universe was older, the
peaks would shift to the right.
Younger, they'd shift to the left.
The relative amplitudes of
peaks depends on the composition
of the universe because gravity matters.
The amount of matter in the universe
determines, particularly dark matter,
the amplitude of that third peak in particular.
So by seeing how-- if there was more matter
on the universe, that peak would be higher.
So you can look at this data and it's all
just sound waves in the early universe.
It really is fundamentally, you
know, it's freshman physics.
So it would take one or two fresh lectures
for a freshman class glass to get it.
But we can work all that through and see
what we predict for a simplest model.
And what we find with the simple model with
five parameters, we predict that red curve
and that's a pretty good fit to the data.
And when you look at the
properties of the fluctuations,
the universe turns out to be remarkably simple.
That whole math, I only need
five numbers to describe it,
the fluctuations that we call Gaussian.
So this is the number of hot spots versus
temperature as a smooth on the 4 degree scale,
the 1 degree scale, and the
quarter degree scale.
The black histogram is our data.
The red curve is the Gaussian curve
and it has one parameter, the width.
So once I specify that one parameter,
that red curve is completely predictive.
And you can see it's a very good fit
to that-- those-- that black data.
We don't have more hot spots than cold spots.
They're really basically equal numbers.
The universe turns out to be remarkably simple.
We don't see any evidence of interaction.
We don't see any evidence
that the universe is finite.
We look for these things and
so far it seems very simple.
So we now have the universe's baby picture.
We know what it looks like
400,000 years after the Big Bang.
So we can then evolve it forward in time.
And for that purpose, I've selected
three randomly chosen babies [laughter]
and evolved them forward in time to
about-- this is about eight years ago.
And then that's what the universe would look
like, you know, about when the Earth formed.
And we can then compare them
to our observations then.
And we could then evolve it even further
forward in time-- oops, you don't really care,
but that's a picture of my kids skiing.
[Laughter] And that's further forward in time.
And this is what we do with our models.
We take the initial conditions, we
put them in a big computer simulation,
we evolve that computer simulation forward in
time starting with the initial conditions based
on what we see in the microwave
background to go to, at least talk,
this is sort of classical physics in the sense.
You're specifying things not in the very first
moments, but 400,000 years after the Big Bang.
That sets our initial conditions.
The laws of physics we use
here is general relativity.
You're all relativist, it's
straightforward to do.
And we evolve it forward,
you see structure emerge.
And we then compare the structure we see
how lumpy that is today in the models
or how lumpy it was when you-- at the
time the Earth formed and we compare it
to our observations and see what we see.
And to do that, you need to
see what the galaxies are.
And one of the efforts to do this
is the Sloan Digital Sky Survey.
This is my colleague Jim Gunn who led
the survey and here is some work by one
of my thesis students, Beth Reed, where she
took some of the data that was collected
and measured the lumpiness versus scale.
And black curve is an extrapolation
from our data and those are the points.
In this plot, don't worry about the
axis, but just lumpiness versus scale
and it just shows we can match the properties
of today's universe running it forward in time.
That says that our model
has the right ingredients.
And in fact, as we walk at all the
different ways we can look at the universe.
So, in cosmology, how fast
the universe is expanding?
We do that by measuring the Hubble Constant,
it's one of the things the Hubble telescope did.
The age of the universe, we
can look at how old stars are.
The properties of clusters, and
I'll show some cluster data later.
The abundances of the deuterium and
helium produced in the universe.
How much lensing we see of distant galaxies?
The properties of distant gas
cloud seem toward quasars.
Supernovas, which are these
powerful explosions we see
through the universe and
this is the supernova data.
For example, this platter
is a function of red shift.
Remember, that's how hot the
universe is, how far away we look
versus the brightness of the Supernova.
If there was no dark energy, the
curve will look like the dash line.
At best, what we project from
our data is the solid line.
Those points are the points from the
supernova and you can see our data,
the mile that fits our data
fits that quite well.
In fact, you know, go and-- I've given
versions of this talk in Stockholm.
And it's one of the things that can
help convince the folks in Stockholm
to give the Nobel Prize this past year to Riess,
Schmidt, and Perlmutter, shown here smiling.
And what they all did, and this is the strongest
evidence we really have that the universe--
we have this dark energy, the universe is
accelerating, they looked at distant galaxies.
They then came back a bit later.
Notice when they took data
in those distant galaxies,
these bright arrows appeared [laughter] and the
bright arrows pointed to these exploding stars
that were so powerful that
they're as bright as the galaxy.
We know how bright those
stars are intrinsically,
these explosions called supernova.
We looked at how bright they are.
We looked at that brightness versus
distance, and that's another way
of measuring the basic properties
of the universe.
And all these pieces fit together.
Here's another way of seeing this.
The same sound waves, this is a big Sloan--
recent data from the big more recent
Sloan survey, version of the Sloan survey.
This is actually led by a guy Dan Eisenstein.
Dan took freshmen-- since junior
year took cosmology from me.
And it's kind of cool when
there are people who you--
first taught them as undergraduates are now
leading major projects that are finding evidence
for things like the existence of dark energy.
And you can see at this plot below, those same
sound waves that we saw in the early universe,
that made those fluctuation patterns,
Dan and his colleagues are finding
in a large scale distribution
of galaxies in your body.
We're seeing that same imprint.
And the position and height of those peaks
are bang on what the simple model predicts.
So you take what fits the
data we have from space,
predict what Dan's group should
see and it fits very nice.
Let me just skip through clusters.
This is fun.
There's a list of all the parameters
measuring all the different ways.
That's a real eye test and you should just
see the numbers, all look about the same.
So, how do we push the model further?
You want to test it.
So this is a plot of how
lumpy it is versus scale.
The black points of the data, but our
theory predicts what you should see
on even smaller scales.
So you want to go test that.
So we go and build a small-- even more
sensitive small scale experiment for--
in our case, we went to Chile to the
Atacama Desert which is very cold and dry.
Our colleagues went to the South Pole
and there's a very similar experiment
at the South Pole, also mapping the sky.
And we look at this microwave background
on smaller patches in the whole sky,
but at much higher sensitivity
and higher resolution.
And here's a Goggle Sky image of our telescope.
Because it's inside a ground screen,
we can't see what it looks like
from above, but Goggle can.
Goggle Sky images are pretty
impressive, you can look at your--
I know we can look at our house and I can
count the number of sky lights in my house.
I can just-- Goggle Sky knows there's
a sky light over our bathroom.
[Laughter] You guys know everything.
And so we're zooming in and looking at
these fluctuations on smaller scales.
This is what our data actually look like.
Actually, we turned down
the light just a little bit.
You can actually see-- this is sort of nice
because you see a bit of
the messiness of real data.
You'll see these bright little sources,
that little dot, that's a big radio source.
We have to mask that.
And towards the bottom and
the top, you see stripes.
That stripes, that's the Earth's atmosphere.
We-- those are regions where we have it masked--
mapped often enough because we'd map it more
in the center, and we're left
with noise from the atmosphere,
at least [inaudible] streaky,
we have to filter that out.
You're trying to measure
things that are fluctuations
at level of a few millions of a degree.
The Earth's atmosphere is a lot hotter
than that and you have to deal with that.
And we focus, you know, and we see actually this
whole black spots are clusters casting shadows.
And one of the fun things, I'll show you one
or two images of the clusters we discovered.
But most importantly, we looked at
these smaller-scale fluctuations.
Here's the clusters and we go,
we see these clusters as shadows;
and what's fun is you then go to your optical
telescope, you know where the shadow is,
you discover new clusters of galaxies.
And we've discovered hundreds of new clusters.
And the numbers of clusters we see,
and their properties are again
consistent with our basic cosmology.
And remember I had this prediction
on what the model should look like.
How do we do?
We do remarkably well.
So before, our curve only went out to here.
We saw those first three
peaks in the sound waves.
Now, we see about eight picks and the amplitude
of those sound waves, how they're propagating,
how the universe behaves
when you hit it and bang it
and let it shake a bit, just
cons-- is very consistent.
So this is, you know, kind of
classically how we do science, right?
You have a model, make it fit the
data, predict more sensitive--
make predictions, you go test
it, it's holding up really well.
And these are two independent experiments.
The red points are from measurements
made in the group in the South Pole.
The blue points are our measurements,
completely independent, consistent story.
So, this is great.
The good news is we have a standard model.
All the pieces fit together.
We know what's going on.
Well, it's not quite true.
The glass is either half full or half empty.
Atoms make up only five percent of the universe.
We don't know what that dark matter is,
we don't know what the dark energy is,
we don't really understand where
the fluctuations came from.
We have interesting ideas,
but we don't believe them.
So, let me end by asking three questions.
What's the dark matter?
Is it new particles from supersymmetry?
Those of you who are lucky-- fortunate
enough to hear Jim's talk yesterday,
you heard a bit about supersymmetry.
One of its really neat predictions is it offers
a way of explaining what the dark matter is,
is that the lightest particle predicted
by supersymmetry could be stable,
it could be the dark matter.
And what's very exciting about
that possibility is it's one
that we might know what the answer to soon.
This big Collider in Geneva could see it.
We might see it underground
searches looking for dark matter.
We might see its astrophysical signature.
So we actually might know
that the dark matter is soon.
Or it could be something very different.
It could be black holes.
It could be a new type-- another
type of particle collapsing on--
or maybe something we haven't figured out yet.
[ Pause ]
I mentioned the universe seems
to be accelerating today.
It's actually very strange.
The universe is behaving and that's
what the supernova data is showing,
that's what our data is showing.
As if you threw a ball up instead of gravity
making it fall back down, it kept accelerating--
it started accelerating and
started moving faster.
So this expansion of the universe,
you'd expect to slow down from gravity.
But instead of slowing down, it's accelerating.
It's very weird.
We don't know whether this is due to the fact
that General Relativity, which is we're applying
on these large scales is breaking down.
Or whether it's being driven
by energy associated
with empty space that we call vacuum energy.
Or whether it's being driven
by some new physics entirely.
And, Stefan, I will get to that paper
draft on our ideas on this new physics.
But we'll get-- life is busy,
Too many things to do.
One of the intriguing things we're seeing
is we see this pattern of fluctuations.
And this pattern of fluctuations,
we see it consistent with this idea
of inflation that Robert talked about.
And this inflationary model has
some very attractive features in it.
If you go back and look at this inflationary
model and what are predicted in the 1980's,
it predicted those fluctuation
should be Gaussian.
It predicted the amplitude should
be about the same on all scales.
It predicted that they should be able to call
Adiabatic, which means when I have more atoms,
I have more dark matter, I have more radiation.
And when I have less, I have less of everything.
It predicted the basic properties
of those fluctuations.
It-- you know, it's the--
one of the basis we use
for computing those beautiful
curves that fit the data so nicely.
So observationally, it seems
to be doing really well.
The problem is, as we started thinking
about its theoretical underpinnings,
there's a lot of problems.
We don't understand where the initial
conditions come from in the model.
We don't understand-- or to make inflation
work, you have to tune all these things
in the model very, very accurately.
We don't know why we have to do that.
We know it's a-- we can make
it work by tuning every thing,
but it seems like an artificial
construction in some ways.
There's lots of problems.
The model tends like to run off and it
tends somewhat to predict the universe
that keeps inflating forever, it doesn't stop.
So, my own feeling is this, you
know, we do seem to see evidence
that the universe accelerated in the past.
It's happening now, it probably happened then.
I think our theoretical understanding of it
are-- is that an early stage, perhaps where--
like the theory quantum mechanics where
there was an old quantum mechanics
to explain the hydrogen atom
that Niels Bohr developed
and it was a good start, but
we needed something deeper.
And one of the things that you've got
a taste of and some of the early--
the talks today and you'll hear some more
tomorrow, is different ways we're struggling
with trying to understand
these kinds of questions.
And as you know, alternative
versions we can come out,
and we have to get the final revision done.
And while this is an area where
we're asking very profound questions
that cross the border sometimes
between physics and philosophy,
it's also in area where there are significant--
there are real observations that we can make.
Some we're making now, some we
hope to make in the next few years
that can test some-- a lot of these ideas.
So, one of the things that is
predicted, for example, by law,
these inflationary models is a
pattern of gravitational waves,
ripples and space time itself
that are actually predicted
to leave a distinctive signature
on the microwave background.
And one of the kind of next generation
experiments that we're thinking about
and working on is trying to
detect these gravitational waves.
So we're not, you know, these are models
that make real predictions and will be able
to separate or at least falsify some of
the models by these future observations.
So let me conclude.
And this picture of a turtle and
a hare, I tool in my front yard.
I don't know what it symbolizes, but I was
just so cool to see a turtle and a rabbit lined
up looking like they're about ready to race.
But I thought I had to use it in the talk.
[Laughter] But I tried to convey in my
talk sort of two-halves of the story.
On one hand, we've made significant
progress in understanding--
and one of the properties the universe, it's
composition, it's age, how lumpy it was,
where galaxies come from, and
we have a pretty simple model
in some ways that fits a host of data.
And the data over the past decade has improved
dramatically and will continue to improve.
And as it continues to improve,
well there's two possibilities.
It will either keep fitting this model or it
will point to something beyond that model.
And I think we sort of know there's got to be
more stuff out there that we haven't understood.
We have a model in which atoms make up 4
percent of the universe and-- or 4.5 percent.
We-- and we don't know what the rest is.
We're missing some important things.
You know, and we don't understand
why there's more atom--
more, you know, we heard about matter and
antimatter, why are there more electrons
in the universe than positrons, antielectrons?
We have ideas for this, but we
don't know what the right theory is.
So this question of, you know, why
is there the stuff that makes us up?
We don't understand the atoms that well either.
And while it's very exciting to me that we've
seen what the universe looked like 400,000 years
after the Big Bang and can extrapolate back
to the first moments after the Big Bang,
we're still struggling to understand
what that data is telling us
about the basic properties of the universe.
So, you know, for those of you who are
students thinking about which way to go
and this is an area where those of us working on
the field, we've solved some amazing problems.
And there's some really hard interesting
ones for you to solve and, you know,
you're probably going to
be the ones who'd do it.
So that's a great-- it's a
great and very exciting time.
So let me stop there.
[ Applause ]
>> All right, so the-- we actually have
of time for discussion, 10 minutes.
But people have to-- we then-- we
are going to head over to 104--
>> 105.
>> Sorry.
>> Kemeny.
>> 105 Kemeny.
[Inaudible] to myself.
Working with where we were before.
>> Why not?
>> But I'm serious.
[Inaudible] And the next talk is also
going to be pretty cool and exciting.
No panel discussions and
[inaudible], but-- [inaudible].
[ Inaudible Remark ]
Now, I'm going to put on medical hats on, okay?
>> Bur not yet, I still have 8 minutes.
>> Yes, 8 minutes.
So yes, the question, and wait
for the mic to get to you.
>> I came in late and I wonder
if you'll address-- oh.
I came in late and I wonder-- and did
you, you know, earlier address the issue
of whether there's something drastically
wrong with General Relativity and all this?
>> Well, I'd put that not-- I didn't address it.
I raised it as a question [inaudible] sense.
The fact that we see, in my conclusion,
that universe is accelerating,
perhaps it's telling us that what's going wrong
is the way we're interpreting the observations,
what's going wrong is the
way we're applying General--
is General Relativity is
invalid on those scales.
Now, we can test this in different ways.
General Relativity makes a prediction on
how distance should behave with red shift,
so we can look at the supernova
observations and see how they-- what--
whether the supernova data fits the model
for how distance behaves with red shift.
Then we could look at how structure
grows, you saw that computer simulation
of how the universe got lumpier with time.
So we compare the lumpiness we see with
time versus the theoretical prediction
and see if structure is growing
the way we think it grows.
There are modifications of General
Relativity that people have come up with
that make different predictions for the
relationship between distance and red shift
and structure growth and red shift.
So far what we see is consistent
with General Relativity,
but one of the things we're interested in doing
is improving our data and seeing if we can test
that the universe is behaving as
the theory predicts on those scales.
And, you know, we don't have-- you know, people
have many alternative theories of gravity
that replace General Relativity to
explain the cosmic acceleration.
I think the theories at this point,
I think of them as baby aardvarks.
They're beautiful to their parents, [laughter]
but no one else finds them
theoretically compelling.
With that said, some of the most interesting
ones have the advantage of, you know,
not requiring dark energy
and making new predictions.
And one of the things we do is we
try to make ever better measurements
and measure the microwave
background fluctuations,
the properties of galaxies
in-- with better-- more detail.
And here we're helped by,
basically, our engineering colleagues
who build more sensitive detectors, bigger
cameras, developed the technology to do that
and then we can make more precise
measurements and test the theories.
I mean an interesting kind of philosophical
discussion is does science drive engineering,
or do advances in technology drive science.
And my own view is yes.
[Laughter] Yeah?
[ Pause ]
>> I have a very elementary question
and it's about the observational method.
So, this notion of the background radiation
and that it would be comprised if microwaves
and those are the things that you would measure
with-- when you got to out to outer space,
where did those notions come from, why would
select microwaves as the primary signatures
of the supposed origin of the universe.
>> So we stumbled on to it,
that's the history of it.
So, Arnold Penzias and Bob Wilson
are two astronomers at Bell Labs.
The '60s, Bell Labs was supporting a
lot of fundamental research and Bell--
but stuff that was useful for the
company and one of the things they wanted
to do is a maybe we'll use
microwaves for phone communication.
We should study what the universe-- what things
looked like in microwaves and map the sky.
So Penzias and Wilson built a really sensitive
microwave experiment, and they went out
and they looked and they worked, you know, for
the company, you know, I'm sure when they went
and did the presentation for their company Vice
President they said, "We're doing this so--
when AT&T uses microwaves, we'll be ready."
And-- but as a scientist they
want to see what was there.
And they saw our galaxy coming
up and down that pattern--
remember that pattern, you
saw a red, they found that.
And then they saw this uniform
stuff everywhere they looked.
And one of the things that made them
such great scientist was they didn't
ignore something they didn't understand.
And they had this leftover signal
and they worked for a year trying
to find the source of that leftover noise.
They replaced detectors, they, you know,
famous story there was a pigeon boosting
in their telescope and they all thought
that maybe it was heat from the pigeon crap.
So they went, you know, well sometimes
part of science is going in there
and clearing out the pigeon shit.
And you go out, you clear that
out, sometimes it's metaphorical
and sometimes it's real pigeon shit.
And they did that and result stayed.
And at the same time, some
of my colleagues, Bob Dickey,
John Pebbles were actually independently
rediscovering some work done in the '50s
by Alpher and Herman and Gamow,
realized that if you start
out with the hot Big Bang you could explain
the abundance of helium in the universe
and predict this leftover radiation,
and the temperature would turn
out to be such, that'll be in the microwave.
So that's how we found out
there was a hot Big Bang.
And then once you saw this uniform radiation,
the next step was trying
to find the fluctuations.
And that led to a series of
experiments of increasing sensitivity,
is people looked for the leftover fluctuations.
And, you know, initially the models predicted
the fluctuation should be much brighter
because the models were based on the
universe made of atoms and radiation
and electrons, you know, and protons.
It didn't assume any dark manner and
said that the fluctuation should be
about ten times brighter than they should be.
And in fact, you know, I remember as a student,
people hadn't discover those fluctuations yet
and it was-- you know, I go talk about subject,
they were boring because they're just limits
on what you saw and, you
know, we slowly move forward
until the Colbert Result came
out I only saw the fluctuations.
And then, you know, the ideas here have
come at-- if you look at their history,
they kind of made different ways.
So the notion of dark matter
goes back to work from Zwicky.
When he looked at these clusters of galaxies,
he noticed the galaxies themself were moving
around so rapidly that there had
to be more stuff holding it there.
So he said there had to be extra
matter and he posted that in the '30s
and there was work done looking
at the Andromeda galaxy
in the early '30s that showed that it had it.
And it was really only in the '70s when
that idea got revived as people trying
to understand galaxy properties
realizing you need a dark matter.
And this idea of a cosmological cause
or a vacuum energy, well the mathematics
of it goes back to Einstein and
Einstein put the [inaudible] term in.
Einstein actually cleared in
for the completely wrong reason.
Einstein looked at his theory
of General Relativity,
realized it predicted the universe
must be expanding or protracted.
As far as Einstein knew,
the universe was static.
He didn't know about the
work that Hubble was doing.
And so he added a term to
make the universe static,
it's something he called his greatest mistake,
that this theory actually predicted the
expanding universe, but then he screwed up
and he took-- you know, then he learned
about Hubble, then he threw the term away.
But that term kept coming back.
So in the '50s, there were some deviations.
People postulated and then by the '90s,
there was kind of growing theoret--
observational evidence that would be
better understood by adding a constant--
constant logical constant and the theory
it made that fits the data better.
But it was the supernova data in the late '90s
that was really the turning point and it was,
yeah, it wasn't that it was a surprise,
that data, but it was strong enough evidence
that really swung the pendulum
of intellectual opinion.
And it's the point where it really--
the case became strong for dark energy.
Yeah, [inaudible] right about there?
[Inaudible] do you want to
just pass the mic up or?
>> Thank you.
I sort of had a question that might be
a little bit of a philosophical question
but in the last talk by Dr. Smolen [phonetic],
we were discussing the possibility that the laws
of the nature might have evolved overtime
because they can't be completely extrinsic
to the system that they're part of.
And so, if the standard mile that
you're presenting can predict accurately
and stay consistent with, you know,
the cosmic microwave background
and it's also relevant today, does
that sort of preclude the possibility
that the laws of nature evolved over time or?
>> No. And in fact, the question where the laws
of nature could evolve with time is one we try
to ask experimentally or
observationally extent we can.
So, you know, what we can do is we can ask
400,000 years after the Big Bang to the point
of which were observed in
the microwave background,
was the mass of the electron
same as it is today.
Was the strength of the attraction between
electrons and protons the same as it is today?
And we make an estimate of what will do.
And it turns out what we can say is the laws of
physics, those laws, haven't changed to a part
in the 10 to 4 over that period of time.
Now, then the maj-- the basic properties
of the universe over that period of time,
the universe since then has
been relatively well behaved
and it's been conditions like
we see in the laboratory.
You know, I think the kind of things
that Lee thinks about when he's thinking
about the law is changing, he
is imagining happening earlier.
He's imagining happening in the Big
Bang itself and before and before.
So you're looking at, you know-- so yeah,
we do ask, but you can imagine the theory
where it's changing then might
predict some later changes,
but doesn't have to, so we look for it.
And if we saw evidence for it,
that would be for the interesting.
And we hope to, you know, one of
the things we will do, you know,
and motivated by just these kinds of
questions, is go and look and say,
"All right as our data improves, would we see--
do we see evidence for the laws
of nature changing in time?"
So, one of the things I find so exciting about
being a cosmologist is you can take a lot
of these questions that are, you
know, really very philosophical
and about our beginnings and things.
And some of them you can work them to a point
where there are predictions that you can test
with data and go out and
measure it, see what's there.
Yeah? Okay.
[ Inaudible Remark ]
Or, right or most immediately
as we walk over you could--
I will be walking after I answer these question
and happy to answer them as I walk and talk.
I can do both at the same time.
>> I just wanted to pick
at your data a little bit.
>> Okay.
>> The power spectrum data that you had with
the really high multiple moments up the 3,000?
>> Yup.
>> So it looked like the Antarctic data,
the red dots were slightly
higher than your other comma--
>> Yeah.
>> -- points.
Is there a reason behind that?
>> Yeah. There's a reason behind it
and a bit of a story I didn't get into,
which is when you look at the data, you
have-- in addition to the fluctuations we saw,
you have this radial sources,
you have those bright spots
and they're producing additional
fluctuations on small scales.
Now the brightest ones, we just removed.
But there's always dimmer ones that
we can't see with our telescope.
And those dimmer objects
contribute fluctuations.
They don't have the same-- they actually have
nothing to do with the microwave background.
But with our data we can't distinguish
between a few radial sources and--
>> So would you say that you're
data is clearer than the--
>> No, it's just the aversion of the data.
Their data is very high quality.
So, what we can do-- oh.
[Inaudible Remark] So, what I
didn't show-- I have it here.
I can show you a more complete
version of the data.
That might be here.
[ Pause ]
Well, this is the version
of this talk with equations.
[Laughter] If I find a better version,
a more complete version of data.
Ah, no [inaudible].
All right, I'll just graph
what our data looks like.
Amplitude of fluctuations versus--
equal L, so it's 180 degrees over angle
and our data looks like-- or at
least our theory looks like that.
And the database simply follows that.
You'll have a really high L, you get a
contribution that looks like that from sources.
And to make life easy, I stop the graph there,
but we actually have data going up here.
And we spend a lot of time trying to figure
out for what we measure here
what the contamination is here.
And another thing we do, so I showed
on frequency, we measured that the sky
at two frequencies, the experiment in
South Pole measures at three frequencies.
How does the amplitude depends on frequency?
We're taking data with European
satellite called Herschel.
We'll look at the same region, we're looking
at that data, we're looking at some data.
The same dusty galaxies,
they're kind of interesting in--
you know, in science, one man's annoying
source is another woman's object of study.
These dusty galaxies or where most--
the galaxy formation or star information
in the universe are taking place,
so they're really pretty
interesting in and of themselves.
So they become kind of really interesting
objects to study and we try to characterize that
and understand that and then
see what's going on here.
[ Applause ]
