>> Thank you all for coming.
I am very pleased to introduce Prof. Raja
GuhaThakurta.
He's a professor of astronomy at UC Santa
Cruz and he's an expert on galaxy formation
and Andromeda.
And he's going to give us a talk about our
place in the cosmos today.
He's also started a innovated program for
high school students to do research at UC
Santa Cruz this summer and he's going to talk
a little bit about that towards the end of
the talk.
So I'm trilled to introduce Raja.
>> GUHATHAKURTA: Thank a lot Jeff and thanks
Boris.
Can you hear me okay at the back there?
Okay, great.
And thank you both for setting this up.
In fact, the high school program that Jeff
mentioned is the exact reason for my connection
to Jeff.
His daughter is in this program.
So, I'm going to talk about that at the very
end.
And I see a bunch of high school student,
I see a bunch of middle school students here,
right?
Middle or elementary?
>> Elementary.
>> GUHATHAKURTA: Elementary.
Even better.
Good to start early.
So, I'm going to talk about galaxies today
but I want to explain why it's important to
talk about galaxies.
I'm going to explain why I study galaxies.
And, so the title of today's talk is, "Our
Place in the Cosmos."
And what I want to do is explain why, you
know, why galaxies have any connection at
all to you and me.
By way of, you know, giving credit where it's
due, these--many of the slides you'll see
today, most of the narrative you'll see today,
was put together with the help of one of my
colleagues at the UC Santa Cruz Astronomy
Department.
Her name is Sandra Faber.
Sandy has been studying galaxies for 30 years,
she's one of the world's experts in study
of galaxy formation and evolutions.
I've had the privilege of working with her.
We've worked together to keep this narrative
current.
As the years have gone by, we've adapted our
story to new findings.
We've adapted the images and animations to
new findings.
So, I hope to give you a little bit of a tiny
flavor of the kind of galaxy research that
goes on at Santa Cruz and around the world.
So, I wanted to put in a little bit of a disclaimer
also, that astronomy and cosmology are often
confused with astrology, gastronomy, and cosmetology.
And I just want to set those three topics
aside.
They actually rear their ugly head more often
than I care in my studies especially when
people find out I'm from India and I study
astronomy, I always get asked about palmistry
and telling the future.
I know absolutely nothing about astrology.
I know a little bit about gastronomy, it keeps
me alive.
And I know very, as you can tell looking at
me, I know nothing about cosmetology at all.
So, but I'll--where they do rear their ugly
head, I'll mention them but I, you know, this
is a good example of cosmetology rearing its
ugly head, no pun intended.
So, let me--let me actually give you a little
bit of a road map of where we're going to
go with this--with this narrative today.
So, I'll start with our place in the universe,
in the cosmos.
And, it turns out our place in the cosmos
is directly linked to a concept that's best
thought of as recycling.
Recycling of chemicals, recycling of the elements
in the periodic table but done by the cosmos.
Not done by West Valley Recycling, it's done
by--on a much larger scale in the cosmos.
And it's done inside galaxies.
Galaxies are the cosmos' recycling plants.
Now, galaxies do a whole bunch of thing in
addition to cosmic recycling.
They are also cannibals, they like to eat
their own.
They like to eat their children in particular.
So, nothing to be scared about, you kids.
Your parents are not at all like that.
But galaxies, in fact, do this all the time.
And I'll talk about how cannibalism plays
an important role in galaxies.
So you can see, gastronomy is already rearing
its ugly head here.
The formation of galaxies involves cannibalism
but only in the late stages of galaxy evolution.
Today, there's a lot of cannibalism going
on in the Milky Way, in Andromeda.
But in the early stages, you don't have cannibalism
because there's nothing to cannibalize.
You need to have galaxies in place for them
to cannibalize one another.
So, the early stages of galaxy formation actually
involve other processes, and I'll talk a little
bit about that.
The early formation of galaxies involves ripples
in the fabric of the cosmos.
I'll talk a little bit about the processes
that give rise to those ripple.
It has to do with quantum mechanics.
It has to do with a phenomenon called inflation,
not the economic kind but the kind the universe
does.
And it has to do with gravity.
So, I'll talk about those things.
And at the--at, you know, the end of the science
part of the presentation, what I want to emphasize
is that astronomy is a physical science.
So like everything in the--in the sciences,
it's evidence-based.
So if I tell you a story, I have to also tell
you the basis behind the story.
Why, you know, why do we believe the story,
why do we believe what we believe, not just
what we believe.
So I'll tell you a little bit about this evidence
and that really has to do with using telescopes
as time machines to test theoretical predictions.
Okay, so I'll start with Our Place in the
Cosmos.
And if I could have the lights down a little
bit in the front of the room if possible because
many of my slides have a dark background.
I don't know--if that's easy to do.
If not, it's--things are pretty visible on
this--on this screen anyway.
I just realized that many of my--you know,
the night sky is dark.
So when I take pictures of the night sky,
the background is dark.
It's not my fault.
It really is that way.
But Jeff, this is already helping a lot.
>> [INDISTINCT]
>> GUHATHAKURTA: Yes.
This is--this is good.
So, oh, this is even better.
>> [INDISTINCT]
>> GUHATHAKURTA: Yes.
Thank you.
Thank you.
So when I think of our place in the cosmos,
I think of my, you know, my favorite people
up there, you might think of your favorite
people up there.
So I am going to put up an example of who
I think of when I think of our place in the
cosmos.
You know, on the right is my--is my daughter,
she was seven years old at that time.
And on the left is my newly adopted son at
that time.
Okay.
He was--he hadn't been groomed in a while,
so I apologize for his appearance there.
But what is common to those two entities,
you know, it's a form of K9 life and human
life, is our protein molecules.
So my biochemist friends tell me that protein
molecule are the basic building blocks of
life.
Now if I were being absolutely precise with
my language, I should say protein molecules
are the basic building blocks of life as we
know it.
Now, we know of many forms of life here on
earth, from the simplest viruses, they're
made of RNA, to the most complex mammals.
DNA and RNA are examples of protein molecules.
Enzymes, hormones, these are all neurotransmitters.
These are all important aspects of life and
it's fair to say protein molecules are the
basic building blocks of life as we know it.
Protein molecules are very complex as this
picture shows, but if we would extend our
definition of life a little bit, another way
to write that phrase would be to say complex
molecules are almost certainly the basic building
blocks of any kind of interesting life.
So if there is life outside the solar system,
and you know there might be, we haven't discovered
it, we can only speculate about it at this
point.
But if there's life beyond the solar system,
the kinds of life we'd be most interested
in better be rich, better be diverse, like
the kinds of life we see here on earth.
Those are the kinds we'd be interested in.
And to have any kind of rich and diverse life,
you can bet they would have to have at its--at
its basis some kind of complex molecule.
Because complex molecules have lots of chemical
bonds, they are capable of--they have many
degrees of freedom, they are capable of taking
on many forms.
Those are the kinds of life forms that we'd
be interested in.
Now, so to form protein molecules or to form
complex molecules of any kind, you need atoms
with lots of electrons and protons in them.
You need things that are not right at the
beginning of the periodic table but somewhat
into the periodic table.
In the case of protein molecule, those atoms--I
am highlighting carbon, nitrogen and oxygen,
I'm leaving out hydrogen deliberately.
Hydrogen is actually formed in copious quantities
early in the universe's history.
Electrons and protons are initially moving
around too rapidly for them to be bound by
each others electrostatic forces.
Because the universe is very hot in its earthly
phases.
Hot means high temperature, high temperature
means rapid motion.
When electron and protons have too high an
energy, they can't bind stably because, you
know, their collisions are too energetic for
them to be--to remain bound.
So when the universe cools down to a certain
point, about 300,000 years after the Big Bang,
the first hydrogen atoms formed, and hydrogen
protons and electrons mate for life.
They stay together for 14,000,000,000 years.
Now, it's a little more difficult to produce
more complex elements like carbon, nitrogen,
oxygen.
Actually hydrogen, helium, traces of lithium
and beryllium, form early in the universe's
history just through this natural collisions
of particles.
But carbon, nitrogen and oxygen don't form
that easily.
They are actually cooked inside stars.
They are cooked, when I say cooked I mean
through nuclear fusion reactions, they are
produced inside stars.
So, you might look at this and say, "Okay,
all is well."
You know, we know where the carbon and nitrogen
and oxygen came from because we live around
such a star.
We live around the star that's undergoing
fusion reactions [INDISTINCT] that's what
you see on the right there.
It turns out the sun's atmosphere contains
carbon, nitrogen and oxygen.
You know very well that the earth certainly
contains C, N and O. You know, if you've been
to a barbeque recently or if you're wearing
a diamond ring or if you are breathing, which
you certainly are, you are taking in nitrogen
and oxygen.
So these elements are present in abundance
on the earth, in the oceans, on the earth's
crust.
These elements are present in abundance.
But there is a little bit of a mystery here.
The sun, even though it contains carbon, nitrogen
and oxygen actually has no business to contain
them because the sun has not yet produce these
elements through nuclear fusion reactions.
The sun is merely converting hydrogen to helium
in its core.
That what gives the sun, you know, the--that's
what gives helium its name.
Helium comes from the Greek word for Helios.
The sun is merely converting hydrogen to helium,
near the end of its life, about 5,000,000
years from now, 5,000,000,000 years from now,
the sun is going to cook helium into lithium,
beryllium, boron, it will get up to carbon,
nitrogen and oxygen and then die.
Die in the sense it will stop nuclear fusion
reactions.
So about 5,000,000,000 years from now, the
sun will have some legitimate claim to some
carbon, nitrogen and oxygen because it would
have cooked it within its interior.
So what business does it have containing,
you know, having some of these elements today?
Well, its business is, it is descendant of
other stars.
And what I mean by that is there are other
stars--this is a picture of a star field--there
are other stars that lived and died before
the sun came into being.
And I--what I mean by died is these stars
rapidly cooked these elements, nuclear--they
went through nuclear fusion reactions.
They cooked all the elements up to iron in
fact within their interiors, through nuclear
fusion reactions.
It turns out iron has the--is the most stable
of the elements in terms of binding energy
per nucleon.
So fusion is favorable energetically as long
as you go up to iron.
Beyond that, you don't produce elements through
fusion.
You actually produce them in stellar explosions
through neutron bombardment in supernova explosions.
So, but the point is the sun is not a first
generation star.
The sun was born well after some of its ancestors
rapidly cooked these elements in their interiors,
carbon, nitrogen and oxygen, and indeed, many
other elements.
And these ancestral stars, their ancestors
in the same way we have ancestors, these stars
died before the sun was born.
They were very efficient cooks.
They cooked all these elements within their
interior, but they were also very generous
cooks.
They die in a spectacular way.
These stars explode when they died.
And you--what you are seeing here is a real
picture of an exploded star as it looks a
thousand years after the explosions, so about
a thousand year old explosion that you see
over there.
So the stuff that was once inside the star,
was once cooked inside the star, gets generously
dispersed into surrounding space.
So the sun was born out of the dust, the stardust,
the exploded ashes of many, many, many stars.
So, in the words of Crosby, Stills, Nash & Young,
"We are stardust."
You know, and for the young ones among you,
you don't know who Crosby, Stills, Nash & Young
are, they are not a law firm.
They are a rock group.
And they must have known some astronomy because
they knew exactly what they were talking about
when they said, "We are stardust."
So indeed, if you look around you, your neighbor,
the chair you are sitting on, the stuff that
makes up this beautiful building, all of these
was once cooked inside a star.
Not the sun but some other star, that enriched
the cloud of gas and dust from which the sun
and earth, and the other planets formed.
So that's a remarkable--that is actually a
remarkable thing to think that our origins
are spatially quite large.
That is our--the elements that make up our
bodies come from a large region within our
collection of stars.
Now, a collection of stars is what we had
to be part of.
And a collection of stars is what we call
a galaxy.
Because if we weren't part of a collection
of stars, if the sun were alone, the nebula
from which the sun formed were alone with
no other stars around it, there's a pretty
good bet that we would be made of hydrogen
and helium today.
Not any of these other elements.
And believe me, a speaker who is made of only
hydrogen and helium is far less interesting
than, you know, than I hope to be.
Okay, and indeed, an audience made of hydrogen
and helium is far less interesting than you
are.
So this particular picture is a picture of
a galaxy.
But some of you have already guessed that
this is not a picture of the Milky Way Galaxy
because we live inside the Milky Way Galaxy.
We can't take pictures like this of the Milky
Way Galaxy.
What we do instead is we take pictures of
our siblings.
This is our sister galaxy, she's our older
sister.
Well, at least, a biggest sister, I don't
know about older.
But this is the Andromeda Galaxy.
This is my favorite galaxy in the whole world,
as Jeff mentioned, and I'll talk about it
in some more detail.
Now, it's worth pausing here for a little
bit to reflect on what we are doing here.
We live in a world without mirrors.
We can't see ourselves.
You know, we can't see our Milky Way Galaxy.
Imagine if you lived in a--imagine, you kids,
living in a world without mirrors.
It will take you much less time in the morning
to get ready and go to school.
That would be a benefit.
But the downside is you wouldn't know what
you looked like.
You would have no idea.
You would have to look at your siblings, you
would have to look at your neighbors to figure
out what you look like form the outside.
That's what we do here.
Another analogy might be living in a house
that you can never leave.
You wouldn't know what buildings look like
until you looked out your window and looked
at your neighbor's buildings.
And that's what we're doing here.
This is our neighbor, the Andromeda Galaxy.
And to give you a sense of scale, light would
take a hundred thousand years to get across
this rectangle, a hundred thousand years.
Light takes one second to get to the moon,
eight minutes to get to the sun, four hours
to get to Pluto, four years to get to the
nearest star, but we're talking about a hundred
thousand years to get across this picture.
Now, we live in a very average part of the
Milky Way Galaxy.
In fact, astronomy is a very humbling subject
because it tells you over and over and over
again that you're completely mediocre.
You know, our planet is completely mediocre,
our star is completely mediocre, our galaxy
is mediocre.
And people speculate our universe may even
be mediocre because people talk about multiverses,
not uni but multiverses.
Ours may be one of many.
So mediocrity is the theme of astronomy but
it's a good kind of mediocrity in this case,
okay?
So we live in an average part of the galaxy.
We don't live on Castro Street in downtown
Mountain View where there are lots of, you
know, lots of people, lots of stars close
together.
We don't live often in the Hills of Los Altos.
We live in somewhere near the Google campus
perhaps.
You know, it's the--pretty representative
part of--part of town.
We're about 25,000 light-years from the center
of the Milky Way Galaxy.
Now, one of the things our group has discovered,
our research group has discovered over the
years is the Andromeda Galaxy is five times
bigger than this picture would suggest.
You know, when we started our work, conventional
wisdom was the Andromeda Galaxy went out about
as far as you see in this picture.
But we've been studying stars far away from
this--from the center of this picture literally,
five times further out than this picture shows
and we've been continuing to find stars that
are plausibly associated with the Andromeda
Galaxy in the sense that they're the right
kind of stars, they have the right chemical
mix, they have the right velocities, they're
moving with the rest of the Andromeda Galaxy,
and so on.
Okay.
So, let me talk a little bit about that.
I love this picture.
This is a Robert Gendler photograph of Andromeda
and I was talking about how it's eating its
children.
Well, here is one of its children, M32.
Those are snacks only, those two, those are
breakfast and lunch up there.
Lunch is at noon, you know, 12 o'clock.
Right above it.
And if you look closely, you'd see there's
a bridge of stars that--this--that's been
stretched out from that galaxy that's immediately
above Andromeda.
The process is very simple.
If, you know, if I were the Andromeda Galaxy
and you guys were a satellite, or vise versa,
what happens is gravity is an inverse-square
law force.
Gravity pulls hardest on something that's,
you know, closest to you.
So I would pull very hard on the front row,
I would pull less hard on the back row, and
the, you know, people sitting in between would
feel a force that's somewhat intermediate
between these two extremes.
What that would do is it would stretch out
this galaxy by virtue of this differential
gravitational force.
That's what Andromeda is doing to that galaxy
up there.
It really is a--this effect is called tidal
effect, this is exactly what we experience
here on Earth.
The--when the moon pulls on the near side
of the Earth, it pulls harder than the far
side.
So the Earth tries to stretch out into a cigar
shape.
The Earth is made of rocks, it can't do that.
But the oceans, the water on the Earth that
can respond, stretches out into a cigar shape.
So you--we have high tides at two ends and
you have low tides everywhere else.
Okay, so, tidal forces are very common in
nature.
So, I started the Andromeda Galaxy and one
of the benefits is not only is it our neighbor,
it's close enough that we can see individuals
within our neighbor's house.
We can see individual stars within Andromeda
and I will show you some examples of that
in just a minute.
To see individual stars in Andromeda you need
powerful telescopes, so we used the Hubble
Space Telescope a lot, but we also use the
Keck Telescopes that Jeff and I visited in
August.
Here's a picture of the Keck Telescopes, there
you go, these are--there are two Keck Telescopes.
They are the world's biggest optical telescope.
If you would have put the mirror of the Keck
Telescope in this room, it would occupy about
the space occupied by the seats here.
It's about 10 meters across, 10 big steps
across in diameter.
So they are very expensive and of course we've
done the right thing and we've put them right
on top of a volcano, in Mauna Kea.
And we've--keeping our fingers crossed that
the volcano is dormant for a long time or
hopefully even extinct.
So, I use one of these two telescopes a lot
to study the Andromeda Galaxy.
And I'm going to show you some more details
of these telescopes.
It's a little difficult to get a sense of
the scale of these telescopes just looking
at these pictures because the top of Mauna
Kea looks like--it has a lunar landscape.
There are no trees, there are no rocks.
I mean--oh, there are--there are rocks but
there is no sense of how big those rocks are.
So, just to give you a sense of scale, somebody
has conveniently parked an SUV right there.
That's an SUV.
That is a bigger than average car.
That building, my guess is it's about 15 stories
high.
That's how--but it just looks like a tiny
little--it looks like a little football helmet
that somebody has placed on the field, but
it's really large.
Let us look inside it and I will show you
a couple of views.
In this particular view, you see the telescope
which is sort of pointed horizontally in this
view, the telescope--the piece of glass is
actually made up of 36 segments.
The segments are hexagonal in shape, you can
probably make out these hexagonal shape.
Each hexagonal element is about six feet tall,
1.8 meters in diameter, the size of a human
being, a good sized human being.
So, again, nothing to reference anything by,
so it's very difficult to get that sense.
In this picture you do get a sense of scale.
These are not plastic models, these are real
human beings.
They are standing next the silver cylinder
which is the camera portion of the telescope,
the DEIMOS spectrograph that I use a lot,
was built in Santa Cruz.
I've walked inside the spectrograph, or you
can walk inside this camera because as telescopes
scale up so have--the instruments got to scale
up proportionately.
In the same way that we now have tiny little
cameras that are embedded within cell phones.
Technology has also, obviously, pushed in
this direction, the size of making things
bigger.
So with this spectrograph you can take spectra
of individual stars in the Andromeda Galaxy.
That's what this is.
This is a raw spectrogram.
It's a very unusual view of the Andromeda
Galaxy.
It's one that spectroscopists used to, but
this is--the Keck Telescopes are used for
this, one of the two Keck Telescopes.
DEIMOS is the name of a spectrograph.
It stands for Deep Extragalactic Imaging Multi-Object
Spectrograph.
It's probably the most powerful spectrograph
in the world.
It was built at Santa Cruz by Sandra Faber.
And we could get a spectra of something like
250 to 300 stars at once.
So, I'm going to zoom in a couple of times
and you zoom in to--you know, you can now
see that there are vertical bands running
through this picture there, there are about
250 vertical bands across the whole thing.
But you see a subset of them here.
So the first thing you learn is textbooks
are wrong.
Textbooks always show a spectra running horizontally,
well in the DEIMOS spectrograph they run vertically.
This is a real spectrograph.
In my mind, spectra now run vertically.
So, each band is a spectrum taken through
a cut in a piece of metal called a slit.
We cut a slit at the right location of a piece
of metal, so when you point your telescope
right there is a star shining through it.
In fact, if you look closely, every one of
these bands has a streak going vertically
through it.
That's the light of an individual star in
the Andromeda Galaxy.
I'm not kidding you, that's what that is.
What is even more prominent than that--those
vertical streaks are these horizontal lines
here.
They look like barcodes.
In fact, you can see this code over here,
you see the code repeated here.
You see it shifted a little bit and repeated
there.
You see it shifted even further up there.
In this one, it shifted way up.
In these two, it shifted way up there.
In this one, it may be shifted off the--off
the screen.
This barcode, this repeating barcode is a
signature of the Earth's atmosphere.
So the Earth's atmosphere, even at the darkest
sight, Mauna Kea is a very dark sight, but
if you--if you go to a dark--even to a very
dark sight, the Earth's atmosphere actually
glows.
There's oxygen and OH in the Earth's atmosphere.
It glows.
It puts out things called emission lines,
light of very specific wavelengths or frequencies.
Those create this pattern.
Since all of these slits are looking at the
Earth's atmosphere, even the stars beyond
the atmosphere, it can't help but get light
from the atmosphere, since all of them are
looking at the same atmosphere, they all have
exactly the same barcode.
The shift from one slit to another is--has
to do with the physical placement of the slit
within the focal plane, because different
stars--the stars are not aligned in a convenient
line.
Like that's--they're in different parts of
the--for our field of view.
So because the slits are positioned according
to the location of stars, the barcode shifts
up or down accordingly.
So, this is in fact--the Earth's glow is in
fact the reason why you cut a slit to look
at a star.
A star looks like a blob, why not cut a circle
in a piece of metal?
The difficulty with cutting a circle is the
light that would come in through the circle
would be the light of the star and the light
from the earth's atmosphere, and you would
have no way of telling those two apart.
So by cutting a slit, you can look on the
star and off the star, and you can use the
part that's off the star to subtract off the
effect of the earth's atmosphere.
This is a process called sky subtraction.
You subtract the sky.
I don't mean the sky--the blue sky above you.
You don't--you never subtract that.
But you see--you subtract the glow of the
night sky in this way, the signature of the
night sky.
So with the help of spectra like this, we
can measures how fast each star is moving.
We can measure its velocity.
We can measure what chemical composition it
has.
You know, that's important--you know, vis
a vis the discussion we've just had earlier
about chemical evolution.
And in fact, one of the lines--I study [INDISTINCT]
three absorptions lines in stars quite a lot,
and they are produce by calcium ions in the
atmospheres of these stars.
So it's quite remarkable to me that you can
take a galaxy that's--you know, Andromeda
is about 2.3 million light-years away.
You can take individual stars in that galaxy
and you can figure out just by understanding
the properties of light, you can figure out
what its chemical composition is, how fast
it's moving.
And how fast it's moving actually tells you
about what gravitational field these stars
are experiencing, which in turn tells you
how much dark matter is contained within the
Andromeda Galaxy.
So, this is remote sensing at its best.
Astronomy is mostly about remote sensing because
you are only getting light from a distance,
that's all you get.
All right.
So, I've talked about the Andromeda Galaxy
a fair bit and it's a good sibling of the
Milky Way Galaxy.
But galaxies come in many shapes and sizes,
some strange and some not.
This one has this lovely little twist going
through the-going through this hula hoop that's
around this central ball of stars.
This is a view of another galaxy, probably
similar to the last one, but happens to be
viewed from a [INDISTINCT] so, you're looking
at it from top down or bottom up as you like,
and these colors actually mean something.
So these pictures were taken with real telescope,
these colors mean something.
When you see yellowish white at the center
you're seeing old stars, sun-like stars.
When you see bluish white, as you do in the
ring, you're seeing young stars, massive stars
typically.
Those are the ones that are capable of rapid
nuclear fusion reaction, those are the ones
that produce many of the elements that are--you
see in the sun and Earth today.
You see really bad looking galaxies, this
one's having a terrible day and you know these
blemishes that you see, these so called blemishes
that you see, are extremely important.
And I'll talk about those.
Those--these dark clouds that you see against
the face of the galaxy are actually birthplaces
of new stars.
So, they're dark not because there are no
stars there.
They're dark because they're blocking the
light of stars in the galaxy in the same way
that a cloud on a cloudy day can block the
light of the sun.
That's what these clouds are doing.
These are giant clouds.
They're much bigger than clouds in the--in
our atmosphere.
Here are two galaxies that are going through
some kind of collision.
I just want to give you a flavor of different
kinds of galaxies.
Here's another one where you can see a collection
of these clouds of gas and dust.
This is actually the near end or near edge
of the frisbee.
The frisbee is oriented like this and these
clouds of gas and dust are blocking, you can
see them in silhouette.
Here's another one that is against [INDISTINCT]
angle.
You were worried about circles looking oval.
Well, this is what I meant by--most of my
pictures are already oval.
Just to give you a quick--just a very quick
primer on why galaxy look the way they do.
So this is a spiral galaxy.
You can see why it's called a spiral galaxy
right away.
It has these spiral arms.
Galaxies spin on a very unusual way.
When you think of a frisbee spinning, every
part of the frisbee completes the--a circle
in the same amount of time.
That's not how galaxies spins.
Galaxy, by contrast, most stars move at the
same speed, they move at the same speed.
If, you know, if you're running in a circular
track and you're all moving in the same speed,
the person in the inside track has an advantage.
So, stars in this part of the galaxy have
an advantage.
They can complete many circles in the time
that a star in the outer part completes one
circle.
So, this is what gives galaxies their sort
of twisted up appearance like this.
And the best analogy I can think of is if
you take dark coffee and spin your cup of
dark coffee, the coffee that's against the
walls of the mug, because of friction, that
coffee is not spinning very rapidly.
The part in the center is spinning rapidly.
Coffee exhibits differential rotation like
galaxies.
If you put a little bit of cream into that,
it gets an appearance like this.
The cream in the case of galaxies is the birth
of new stars.
When new stars are born, the bright patch
gets shared out into the spiral pattern by
the differential rotation of galaxies.
There's actually a well developed theory,
Spiral Density Wave Theory, that explains
the appearance of spiral galaxy.
Here's a spiral galaxy, that same one that
you saw in the last picture, a different one
from the previous picture naturally.
We can't take different prospective images
of the same galaxy, that's our--that's one
of the banes of astronomy.
We're stuck with the perspective we have,
you know, for the foreseeable future.
And here's another one.
Here's another galaxy that we happened to
see perfectly along its edge.
People have taken this galaxy and they have
said, "This one is just like the Milky Way."
In fact, our view of this galaxy, if you look
at this rectangle, our view of this galaxy--you
know, we are not at the center, we are not
right at the edge, we're some way here.
So our view of the galaxy is sort of like
the view of this--our view of this galaxy.
So, you don't need to take my word for it.
Here's a picture of the Milky Way taken from
the southern hemisphere.
This is with a telescope in Chile.
A fisheye lens looking at a large patch of
the sky.
The horizon looks curved like this because
of the distortion in the camera.
But you could see the Milky Way beautifully
going across the sky.
It's a milky way, it's a band of light.
And if I go back and forth between this picture
and this one, you can see the similarity.
Now just a pause here to talk about the word
galaxy.
The word galaxy actually comes from the Greeks.
You know, astronomy is a very, very old science.
Astronomy has been around as long as civilizations
have been around.
This is one of the beautiful things about
astronomy.
It's also a very new science because it's
technology driven.
And every time there's new telescope, new
detectors, we make advances.
So, the ancient Greeks--well, maybe not all
of the ancient Greeks, but the ancient geeks
among the ancient Greeks, decided that this
looked like a band of milk across the sky
and the word galacto and the word lactose
have--you know, are all rooted in the word
of milk.
So, what we've done is we've taken the appearance
of our own galaxy and we've called every galaxy
the same thing.
We call galaxy a band of milk.
So that's what the word galaxy means.
So, it's pictures like this that gives us
confidence that we live in a spiral galaxy
and we live among these clouds of gas and
dust that you see cutting a dark band across
the Milky Way.
What I'm going to do in the next few slides
is focused on the--these particular clouds
of gas and dust.
I said they were important because they're
birthplaces.
Well, here's a detailed view of one of these.
Astronomers have lovely romantic names for
these thing.
This one is called NGC 6357.
This is a picture taken with the Hubble Telescope
and the colors are something that's worth
paying attention to because this is what the
eye would see if it were sensitive enough.
So the red hue is actually the glow of hydrogen-alpha.
This is electrons cascading down from level
three in the hydrogen atom to level two, produces
this intense red color.
You see a piece of a cloud of gas and dust,
you see a young star that's been born.
It has carved out a little cavity, it's created
a little cave for itself.
It's peering out.
It's--in time, it will actually blow away
the material that it was formed from.
Stars commit fratricide.
They, once they're born, they prevent others
stars from being born around them.
You can see that they're also born in groups.
There's a litter of stars.
Just like puppies, they're born in--they're
born in groups.
Okay, so do you see a group of stars in the
upper part of this picture?
Those stars are freshly formed stars from
this cloud but they've eaten away at the cloud
they were--in their--in their immediate vicinity.
The intense radiation actually exerts a pressure,
ionizes and blows away the cloud around it.
So, let's look at this process in a bit more
detail.
This is the Orion Constellation.
You might recognize the shoulders, the belt,
the sword of Orion.
It turns out, the sword of Orion, the bright
spot there is not a single star but it's a
nebula.
In fact, this is a wonderful picture taken
with the Hubble Space Telescope of the Orion
Nebula.
And we'll zoom in a few times.
Hubble has amazing detail and with pictures
like this, Hubble also has this great benefit.
That when you take pictures, they come with
circles marking interesting things.
No, just kidding.
That doesn't happen.
Someone has gone in there and marked these
circles to mark interesting objects here.
And what are these interesting objects?
Let's zoom in a little more.
So the interesting objects here, these four
objects, are young stars that are in the process
of being born.
So, every one of these four is a star.
You can see the star quite clearly but it's
got a plume of gas and dust around it.
This one, the star is actually hidden from
view.
You see a sort of silhouette of a dust cloud.
And in the other two, they're--these stars
are trying to make their presence felt.
They're trying to brake free from the--a little
piece of cloud they formed from.
These four, on the other hand, have more or
less broken free.
You can now see through to the stars.
But they have a little band of, you know,
a dark band around them.
They're actually surrounded by a disk of material,
these stars.
Now these are real stars.
These are--they're called protostars.
They're on their way to becoming real stars.
They haven't quite started their fusion reactions
yet.
Here's one that--particularly advantageous
view.
This is one that's seen along it's edge and
you can see the star peeking out from the
top but you can see this edge of--this edge
on view of a dust disk.
It's 17 times the size of Pluto's orbit, so
only slightly bigger than our solar system.
And these are called proplyds.
They're in Orion.
Pro stands for proto, so they're protostars.
Well they're protoplanetary disk.
Protoplanetary disk.
These are disk of material that will give
rise to planets.
So they're protoplanetary disk.
And in--so far I've been showing you pictures
taken with telescope.
I'm going to give you an artist's view of
a simulation of what these dust disk might
look like if you had enough detail, if we
had enough detail.
We don't have this kind of detail yet.
But this is a little movie showing how these
debris disk of dusts and rocks might evolve.
You can see a channel opening up here, probably
because there's a planet forming there sweeping
things in.
Sweeping--accreting material.
So planets grow at--by sweeping up this dust
and gas.
And over time, the giant planets clear out--sorry--clear
out everything in the--in this dust disk and
you're just left with these coagulated elements
which are the planets, okay?
So this is an artist's view, I say, but--with--based
on some pretty detailed physics calculations,
formation of a systems of planets.
All right, so, just to wrap up this cosmic
evolution idea, this cosmic chemical evolution
idea, chemical recycling idea, here's a picture
of a galaxy with a spot in it.
Now this picture of a galaxy comes from a
really boring project.
There's a group in Berkley that does an extremely
boring project.
They go to the telescope every night and they
take pictures of the same galaxies, night
after night after night.
They have a list of galaxies and they just
take pictures of the same darn things every
night.
But once in a while, they get lucky, and they
see a spot in the galaxy where there wasn't
one the night before, or there wasn't one
the week before.
That's an example of one such thing.
That spot that you see, marked supernova,
wasn't there the previous night or two nights
back, whenever the previous picture was taken.
That's an example of a star that's in the
process of exploding and it's probably a young
massive star that's exploding.
You can see it's relatively close to this
disk of dust and gas.
At its brightest, a supernova stellar explosion
can outshine the rest of the galaxy.
Depending on the size of the galaxy, a single
star can outshine the rest of the galaxy.
This is not too far from it.
In fact, it's hard to see.
The star's light is saturated in that spot
there, but there's a lot of light in that
spot.
If you give it a thousand years, it expands
into--ejector, the stuff ejected from the
explosions spreads out, and enriches surrounding
clouds of gas and dust, interstellar gas and
dust.
Out of which young stars are formed or new
stars are formed, which then go through their
own fusion reaction.
So this is the--this is the cosmic chemical
cycling we've been talking about.
Now, Sandy found this amazing picture taken
by a astrophotographer, I wanted to show this.
And Sandy and I saw some really poetry in
this picture.
Wally Pacholka may have seen the same poetry
in the picture when he took it.
This is an astrophotographer's photograph
of a cave in the Southwestern United States,
okay?
This is looking out of a cave, I believe in
New Mexico, he was looking out.
You see a bunch of rocks here.
You see an arrangement of these rocks or--suggesting
that this was a family's home, perhaps even
a community's home in the ancient time.
But if you think about these rocks, these
rocks are made of iron, silicon, magnesium,
oxygen, it's made up of a bunch of elements
in the periodic table.
These elements in the periodic table wouldn't
exist if it hadn't been for the fact that
our planet and our solar system and our sun
are part of a family that's, you know, part
of a grander home and you're seeing that grander
home through the opening of this cave.
So this immediate home belong to some family
or community is embedded within a much larger
home and that's what gives--gave these rocks
their existence.
So there's a--there's a beautiful symmetry
to this picture.
All right.
So we've been talking about galaxies and why
galaxies are important and I hope I've convinced
you galaxies are important.
But I haven't quiet told you where galaxies
come from and--so I want to spend the next
few minutes talking about that.
I'm taking you sort of further back in time.
In fact, taking you back to some of the earliest
imaginable moments in the universe's history.
So to do this I want to give you a sense of
what our environment looks like.
So I'm going to play this movie and I'll talk
while this movie is being played.
This is a movie where you can see the Orion
Constellation.
But very quickly, you'll see the Orion Constellation
break up into sort of funny shapes because
this movie has realistic distances attach
to everything.
So this is really a series of astronomical
pictures that have been stitched together
in a clever way by Brent Tully, one of the
astronomers who studies the structure of the
Milky Way and things in it.
And we're flying at an unrealistic speed here,
just to be sure.
You know, don't--kids, don't expect to be
actually able to take this journey.
This is a virtual tour of most of the solar--most
of the solar system, most of the galactic
system, and in fact, we'll go beyond the galaxy
in a bit.
And this is a very unusual journey.
This cosmic pilot has this real sense of bravado.
He takes us to the most dangerous parts of
our galaxies.
We just went through an exploded star.
But what is remarkable about this picture
is it's really--it is based of actual astronomical
images.
I like to think of it as a documentary because
it's a series of real images that have just
been stitched together in a meaningful way.
There is a small bit here though, where it
goes from being a documentary to a docudrama,
in Hollywood terms.
So Brent goes Hollywood for just a little
bit and it's not by choice.
He has to go Hollywood in this segment because
we've never taken pictures like this of the
Milky Way from the outside.
So in this case, there's an actor playing
the role of the Milky Way.
There's a different galaxy that's being used
to portray the Milky Way just for this segment.
And then we go back to documentary mode because
these are two real pictures of satellites
of the Milky Way, the large and small Magellanic
Clouds.
You'll see the Andromeda Galaxy coming in
from the--from the upper right with its companions.
There she is.
Okay.
Andromeda with one of its companions and here
is another one of Andromeda's companions.
And you'll see as we fly through that galaxy,
that's M33 over here, this galaxy we're about
to fly through, that has exploded stars within
it.
We're going to fly through one of those.
And, you know, what you see, very quickly,
each of these galaxies is, you know, tens
to hundreds of thousands of light-years across.
They look--they look like tiny blobs, but
each of these things is a galaxy.
Some the size of the Milky Way, some bigger,
some smaller, and in fact there's this lovely
concentration of galaxies over here.
This is called the Virgo Cluster, it's in
the constellation of Virgo.
There's a lovely cluster of galaxies in Virgo
that--it's our nearest big concentration.
But it gives you a sense that we are not alone.
You know, we are not alone as planets in the
solar system, we are not alone as stars in
the Milky Way.
You know, the sun is one of a hundred billion
stars in the Milky Way.
And indeed the Milky Way Galaxy isn't alone.
It's part of a family, we're part of a group
of galaxies called the Local Group but we're
not too far away from an even bigger collection
of galaxies called the Virgo Cluster.
In fact, the biggest galaxy in the Virgo Cluster,
M87, this one, has a super massive black hole
at its center.
We now know that every galaxy worth its salt
has a black hole at it's center.
So, in true--true to her form, we're going
to--this pilot is going to crash land us right
at the center of this black hole, the center
of M87.
Okay, so the idea behind this movie is to
give you a sense of where we live, you know,
our neighborhood, our galactic neighborhood.
And you might have noticed that galaxies are
not distributed uniformly, they're distributed
in clusters, in clumps.
And one of the great advances of the last
decade has been high powered computer simulations.
In fact, the first of this was published in
2000.
It was called The Millennium Simulation.
We've made a lot of progress since then.
And you--I'm going to show you the results
of The Millennium Simulation where you start
out with a universe that's more or less smooth
but over time, gravity takes over and takes
tiny little ripple that you saw early on,
polarizes them, makes their amplitude greater.
If it's a tiny trough, if it was slightly
less dense than average, than that region
complete empties out and you'll see the formation
over time.
You see time counting up in the upper right.
Gigayears is the unit, billions of years.
So we are at a quarter or a third of a billion
years there.
But it's going to go all the way to 14,000,000,000
years.
But given enough time, gravity can act and
it can turn even tiny ripples in the fabric
of the cosmos into these amazing structures.
This particular structure, you are all familiar
with the World Wide Web, this particular structure
is called the cosmic web and it's somewhat
larger than the World Wide Web.
This is, you know, just to give you a sense,
Milky Way Galaxy might be something like that
blob moving up there.
So the Milky Way Galaxy is really very, very
ordinary in this--in this--yes, please?
>> Is the rotation from the...
>> GUHATHAKURTA: This...
>> [INDISTINCT] or is there initial...
>> GUHATHAKURTA: The--this shoot--this video
is a bit confusing because our perspective
is changing.
This is not real rotation, it's merely perspective
that's changing.
So we're both moving and it's collapsing under
its gravity.
That's a good question.
We don't expect nearly this much rotation.
We expect some rotation in systems and you
will--you will occasionally see that.
But most of this--most of this swirling motion
that you see here is real, because that's
going on but our perspective is changing.
We're also zooming in somewhat because you
can see this bar was much smaller before.
A kiloparsecs, by the way, is about 3,000
light-years, so this is 500 kiloparsecs.
So, a much bigger scale than individual galaxies.
I should emphasis also, this picture is a
picture--is a map of how the dark matter in
the universe would evolve.
Not stars, but how dark matter would evolve.
So, it's a detail calculation of the gravity
that every particle feels relative to every
other particle.
And I just want to explain this very, very
simply.
If you have a sea of particles, it's a perfectly
uniformed sea of particles, you--a particle
in that uniformed sea would feel an equal
pull in all directions.
So there'd be no net motion, there'd just
be the expansions of the universe.
There'd be no net motion relative to other
particles and the patterns would stay fixed.
If, on the other hand, you live right next
to a slightly dense region, you've got particles
pulling you in all possible directions but
you've got a slightly extra number of particles,
a slightly high number of particles pulling
you in one possible direction, where that
ripple is, where the--where the over densities
is, so you tend to migrate towards that.
So, something that's slightly richer than
average gets even richer overtime.
The rich get richer, the poor get poorer thanks
to gravity.
Gravity is a great polarizing agent in that
sense.
Okay.
So this was a dark matter simulation.
You see it stopped at about 13 point some
billion years.
That's how old we believe our universe to
be.
That's how much time we think has elapsed
since the Big Bang.
This next simulation is a zoom in on one of
these filaments in the cosmic web.
And this time not only is dark matter's gravity
being modeled properly, but dark matter isn't
even being shown here.
It's hidden in the simulation.
Its gravity is being modeled properly.
Well, what is being shown is the response
of gas and dust to the gravity of dark matter.
And now you'll see things forming that look
more like galaxies, they don't look like blobs.
The dark matter is much more blobby.
Gas and dust tends to form along these filaments,
tends to congeal along these filaments.
You can see these two galaxies about to collide.
And, you know, while this cosmic wreck is
going on, you'll see that other galaxies,
you know, like these two galaxies are in the
process of colliding.
You see some rubberneckers going by on the
cosmic freeway.
But these two galaxies are colliding and,
you know, you'd--you might look at this and
say, "These don't really look like galaxies.
They look like complete--they look like a
complete mess."
In fact, galaxies, we think, look like complete
messes early on.
Over time, as the cannibalism has occurs--the
cannibalism is actually a very strange kind
of cannibalism.
It's more like a corporate merger.
When stars--when galaxies smash into each
other, stars don't smash into each other,
they merely switch loyalties.
When we have two galaxies, you've got two
centers of loyalty.
You've got a bunch of stars going around one
center, you've got another--a set of stars
going around another center.
When they collide, they're going around a
common center.
And now you can begin to see that this entity
that looked like a complete mess before, starting
to look like some of the images you've seen
of spiral galaxies.
So, these simulations, these sort of computer
simulations that show the cosmic web--and
now we're changing our perspective, nothing
is happening to the simulation.
We are just moving from the lower part to
the upper part of the simulation.
You can see, there's a swarm of stars in the
center, the spiral arms.
I think this represents one of the triumphs
of modern day computing as it pertains to
astronomy and cosmology.
You can--you produce realistic looking galaxies.
This particular one was done in Japan.
All right.
So, so far, sort of going on with the story,
we need--we think galaxies form because of
gravity.
But gravity needs something to latch onto.
You need these ripples to be present in the
fabric of the universe.
So you have to ask the natural question, "Why
didn't the universe start out perfectly smooth?
Why were there these little bumps and wiggles
in the universe?"
And the answer to that--there are two words
to answer that.
That's quantum mechanics.
Quantum mechanics is the reason why the universe
didn't start out perfectly smooth.
Now, instead of trying to explain quantum
mechanics, I want to put up a little cartoon
here where there are two quantum physicists.
One says to the other, "Oh, Alice, you're
the one for me."
And Alice being a really smart quantum physicist
says to Bob, "In a quantum world, how can
we be sure?"
There's no--there's a lot of uncertainty that
quantum mechanics teaches us about.
Okay.
So, I can't resist this.
You know, Professor Heisenberg is the person
who is responsible for coming up with the
uncertainty principle.
There was a lot of opposition to quantum mechanics
when it was first proposed.
Einstein was one of the great opponents of
quantum mechanics.
He said, "How can something as beautiful as
the universe be governed by chance."
Einstein had a famous quote, he said, "God
does not play dice."
That was his famous objection to quantum mechanics.
Einstein was wrong as it turns out because
he came around later to try and to incorporate
quantum mechanics into his theories.
But, Einstein was scolded appropriately in
those times by Niels Bohr.
Niels Bohr is someone who was a quantum physicist.
He studied the structure of atoms.
When Einstein said, "God does not play dice."
Niels Bohr said to Einstein, "How dare you
tell God what to do."
You know, this was--this was a very, you know,
very deep debate going on, about a hundreds
years ago.
And quantum mechanics, it's fair to say even
today, is not very well understood.
You know, the joke goes about Heisenberg,
you know, they--you know, momentum and position
can be predicted absolutely precisely.
So if you can measure X, you know, the position,
there's a certain uncertainty that delta X
momentum P delta P, the product of those two
is finite, it can't be zero.
So, if you know your position, you don't know
your momentum very well.
If you know your momentum precisely, you don't
know your position very well as well.
Heisenberg is driving along the autobahn one
day, he's speeding as usual.
The cop pulls him over.
The German cop does the same thing that cops
all over the world do.
They ask you this question, "Do you know how
fast you were going?"
And Heisenberg, you know, quips, "No, but
I know exactly where I was."
Because, you know, the uncertainty, momentum
and position, if you--if you don't know your
speed, you know your position very well.
Okay, jokes aside, another way of stating
the uncertainty principle is to say that delta
E times delta T, delta energy times delta
time, is a constant.
So, you know, dimensionally in terms of units,
the--if you take the units of position and
momentum and multiply them together, they're
the same as the units of energy and time multiplied
together.
So, if you can--if you know exactly which
instant you're talking about in the universe's
history, then, you can predict the energy
of that parcel of the universe with arbitrary
position.
So, quantum mechanics imposes on us these
fluctuations just because of the uncertainty
principle.
So, delta E, delta T being--the product of
those two being constant means in early times,
where you have to know the time precisely,
there were fluctuations at the level of one
part in a hundred thousand.
So, the power--at the level of ten to the
minus five, there were fluctuations.
Now, normally you'll think, "Okay, these are
fluctuations in the quantum domain, are microscopic,
they don't really affect us."
But the--it turns out they do affect us.
And the person who convinced us that the--that
quantum fluctuations affect us is Schrödinger.
Schrödinger came up with this experiment
called the Schrödinger's Cat experiment.
And--in which he said let's device an experiment,
a gedankenexperiment, a thought experiment.
He didn't actually carry this out.
No animals were harmed in the making of this
experiment, okay, as they say in the movies.
So, you start out with a radioactive particle
and--or a group of radioactive particles.
And you put them in a box.
You close the box.
You come back after an hour.
There's a 50% chance that the radioactive
particle would have decayed to produce an
alpha particle, that's a helium nucleus, two
protons and two neutrons.
The alpha particle has a certain probability
of existing an hour after you've started the
experiment, a certain probability.
So let's say a 50% probability it exist, 50%
probability it hasn't--this hasn't decayed
in which case the alpha particle doesn't exist.
If the alpha particle was created, then, there's
a Geiger counter.
Normal Geiger counters beep.
So, since this is a gedankenexperiment, Schrödinger
says, "Lets set up our Geiger counter so that
it doesn't beep but instead has a hammer fall
and you'd get the sound of breaking glass
as that hammer falls on a bottle, on a glass
bottle that contains poison, that stuff is
lethal to cats."
So that's why there are two states of this
cat.
The cat can either come out like this, all
happy, or like that where it is unhappy and
you're unhappy if you're its owner.
So, those are the two possible states of the
cat in the Schrödinger's Cat experiment.
Fifty percent chance it comes out in upper
state, fifty percent chance it comes out in
the lowest state.
Now, Schrödinger didn't carry out this experiment,
but there's an uncertainty in this experiment.
If you set up a thousands of these boxes,
you can't predict beforehand which of these
cats is going to end up in the upper state,
which one is going to end up in the lowest
state.
That's the uncertainty.
You cannot predict the fate of an individual
entity in this--in this scenario.
Schrödinger didn't carry out this experiment,
but the universe went ahead and did it.
The universe went ahead and did its version
of the Schrödinger's Cat experiment.
This is a timeline in the universe where you
have the Big Bang on the left, the present
day on the right, you know, 14,000,000,000
years after the Big Bang.
You've got, shortly after the Big Bang, there
were quantum fluctuations.
And just like the Geiger counter takes these
tiny microscopic phenomena, moves them into
the microscopic domain, in this case, inflation,
this very rapid expansion in the universe's
history, there's a very rapid phase of expansion
in the universe's history.
It last for 10 to the minus 23 seconds and
the universe expands by a factor of--not by
two or four or ten, it expands by a factor
of 10 to the power of 50 during that time.
Inflation is here to stay.
It's--even though it sounds crazy, it's here
to stay.
It's something that explains a lot of things
in the observed universe and it is the thing
that takes these quantum fluctuations, blows
them up, freezes them into the fabric of the
universe.
So, in a real sense, if something was slightly
lower than less than average, it becomes a
void.
If something was higher than average, it becomes
a galaxy.
A galaxy is a live cat in the Schrödinger's
Cat experiment.
A void between galaxies is a dead cat in the
Schrödinger's Cat experiment, in the universe's
version of the Schrödinger's Cat experiment.
Okay, finally, three predictions.
Galaxy collision should be common.
Galaxy collisions unfortunately take a long
time.
They take a billion years to unfold and no
astronomer has had that kind of time to watch
them, so we have a computer simulation instead.
And what we're going to do is watch what happens
to these two galaxies as they get closer together.
We're going to stop the simulation and you'll
see two pictures of real galaxies that are
about to collide.
Then we'll go back to the computer simulation,
let gravity do its thing over time and you
could stop to see the distortions happen in
this galaxy as the near end is being pulled
harder than the far end.
Again we'll stop and rotate our--change our
perspective so you can see a pair of real
galaxies that are going through this process.
Here are two real galaxies that are in early
phases of their collision.
Now, we wait a little bit longer.
You can start to see the distortion very clearly
now in these two galaxies.
They're stretching each other out.
And let's stop, but here are two real galaxies
going to this process.
So galaxy collisions are very common around
us.
They last a long time.
But the advantage is we have many of these
so we can see snap shots of different phases
of a galaxy collision.
Infant galaxies should look ragged.
You know, you saw in those simulations, early
galaxies look terrible.
They don't look like, you know, nice symmetric
things.
So here's a picture taken with the Hubble
Telescope that lets us look at infant galaxies.
The way you look at infant galaxies is very
simple.
When you're studying infants in--on earth
you just have to gather up kids and you can
see, you know, children, adults, very easy
to do that.
In the universe, it's just as easy.
All you have to is look around us and you're
going to see near us things that have been
around for a long time.
Far away from us are things that haven't been
around for a very long time.
The reason is simple.
Let's zoom in, I'll explain what I mean.
If you look at a galaxy like this, this is
3,000,000,000 light-years away from us.
The universe is 14,000,000,000 years old.
If that galaxy is 3,000,000,000 light-years
away, light has taken 3,000,000,000 years
to travel from that galaxy to us.
So the universe was 11,000,000,000 years old
when light left that galaxy.
The information is always backdated and it's
backdated by an amount that depends on how
long that information's been transmitting,
how long that light has been traveling.
So here's another galaxy that's 7,000,000,000
light-years away.
It left the universe when the universe was
middle aged.
When the universe was 7,000,000,000 years
old it's been traveling for--light has been
traveling for 7,000,000,000 years.
And you can see that that galaxy is not nearly
as symmetric and organizes as this one.
And in fact, if you looked 10,000,000,000
light-years away at yet another galaxy, you
can see that this is like a teenaged galaxy.
It's still troubled, it's trying to find itself,
it's trying to get itself together.
You can see that the different pieces of the
galaxy are in the process of organizing.
Now these sorts of pictures were taken with
the Hubble Telescope but there's a lovely
technique that astronomers have adopted from
SDI, from Strategic Defense Initiative, Star
Wars, those of you who remember Star Wars
from the Reagan years.
We have these satellites looking down at the
Russian missile silos and we couldn't get
detailed pictures of them because the earth
has an atmosphere, it's moving around, so
get distorted images.
It's like looking down into a swimming pool
and trying to read some writing at the bottom
of the pool.
You can't because the water is moving around.
So if you have an adaptive system that corrects
in real time for the distortion then you can
fix this.
And astronomers, of course, use this technique
but they look in the other direction through
the atmosphere.
They look from the bottom up.
And as you see these light waves come in,
you'll see that when light comes in they should
come in as plain waves but they don't and
that's why stars twinkle.
So you'll see these waves coming in.
They look like potato chips.
They don't look--they don't look flat.
In fact they don't even look like--they look
like--they don't look like Pringles potato
chips.
Pringles potato chips, all of them look--have
the same shape.
Here, you see the shape is changing all the
time.
So that mirror dances equal and opposite to
the changing shape and that causes the star
to stop twinkling.
So this is a technique called adaptive optics
and it is--a simple way to remember it is,
"Untwinkle, untwinkle little star," is a good
way to remember adaptive optics.
So it's an amazing technique used to take
sharp pictures.
Now this is just to reinforce the idea of
looking back in time.
If you look close to us, you'll see old things.
If you look a little bit further away, you'll
see slightly less old things.
And, you look even further away you'll see
things that are halfway through.
You'll see younger entities.
And one of the amazing things about astronomy
is you can see unborn entities.
You can see unborn galaxies.
Astronomers love doctors.
You know, they keep us alive but they also--medicine
makes astronomy look like an exact science.
I don't know how this doctor decided that
that was a foot but we'll go with it.
And, you know, what you--what it's pointing
to over there are the ripples that give rise
to galaxies.
So I want to talk about that next.
The last of these predictions--I said I'll
talk a little bit about these predictions
of the story, is you can actually see the
ripples in the cosmic ocean that give rise
to galaxies.
Here's a picture taken with radio telescopes
of the sky all around us that is projected
onto a globe--oops.
It's projected onto a globe.
Let me see if I can play this movie here.
What you are seeing is the afterglow from
the Big Bang.
The Big Bang was a very hot phase in the universe's
history.
You know, just like you can turn off your
barbecue oven but it takes a long time for
the embers to cool.
The embers of the universe are still cooling
but you can see that the afterglow from the
Big Bang was not perfectly uniform.
It has ripples at the level of one part in
a hundred thousand.
These are the tiny fluctuations that gave
rise to galaxies.
Okay.
So, I hope I've convinced you that biologically
and chemically our history links us to galaxies,
to Milky Way and Andromeda.
Galaxies grow through cannibalism.
They grow from tiny seeds in the universe's
fabric.
So really our true ancestors are quantum mechanics
blown up by inflation and then gravity amplifies
them over time.
So you start out with these ripples in the
cosmic ocean.
You take a little hotspot there and that grows
into an infant galaxy where the pieces come
together to form a nice symmetric galaxy in
which stars undergo chemical fusion reactions,
enrich the space around them through explosions.
Out of that--out of this material our planet
and star were formed, complex molecules and
wonderful entities like this.
Okay, so that's the end of our cycle and I
thought I would spend just one slide talking
about the Science Internship Program that
Jeff referred to early on.
We have high school students doing research
at Santa Cruz and in fact they--we have freshmen
coming in, high school freshmen coming in,
high school seniors.
And I want to emphasize that these are real
research projects they're doing.
They're not just doing something where, you
know, they're given a problem where the answer
lies on a certain page in the book.
No.
These are problems for which nobody knows
the answer, not the person assigning them
the problem and certainly not the student
who's doing the problem.
They're real research projects.
They'll--that's how project are in the real
world.
They're not--they don't have answers written
somewhere.
If they were, there wouldn't be problems anymore.
And the topics in which these students are
doing research include astronomy, physics,
chemistry, biomedical engineering, marine
biology.
I think we're going to add computer science.
We're going to add a few other topics this
coming summer.
It's been going on for three years.
The high school students' projects are part
of bigger projects that are being worked on
by PhD students, postdocs, faculty, undergraduates,
so they're part of the community.
They get to see how science actually works;
the process, not just the results.
And the students have been amazingly successful
in national science competitions.
So it's been an extremely, extremely rewarding
experience for me.
My work gets amplified tenfold every summer.
The productivity of my research group gets
amplified every summer.
And in fact so much so that we're continuing
this project during the school year in their--in
their spare time, between, you know, the school
work duties, the students are continuing their
projects.
So that's where I'll stop.
Thank you for your--thank you for your attention.
>> How do you square inflation with the speed
of light?
>> GUHATHAKURTA: That's a very good question.
So the question is, "How do you square inflation
with the speed of light?"
So, yes, if you're going to expand by a factor
10 to the 50 in 10 to the minus 23 seconds,
it means particles move apart from each other
faster than the speed of light.
This is one of these well hidden secrets in
relativity.
Special relativity tells us that nothing can
travel faster than the speed of light.
General relativity happily allows that, allows
that if the gravitational fields are strong
enough.
If there's--if spacetime is curved not flat
in topology terms, in general relativity terms,
then it does allow travel faster than the
speed of light.
Inflation was designed to satisfy Einstein's
field equations of general relativity.
So yes it does [INDISTINCT] travel faster
than the speed of light and yes relativity
allows it, general relativity allows it.
>> I think they're not really moving away
from each.
The space between them is expanding.
It's not the same thing as [INDISTINCT] look
at the [INDISTINCT]
>> [INDISTINCT] waves.
>> GUHATHAKURTA: Well...
>> ...where particles [INDISTINCT] with [INDISTINCT]
>> GUHATHAKURTA: But if you take any given
pair of particles...
>> Yes.
[INDISTINCT]
>> GUHATHAKURTA: ...their relative speed is--their
relative speed is faster than the speed of
light and that is allowed, that is allowed
in curved spacetime.
>> In what manifold?
>> GUHATHAKURTA: Sorry?
>> In what manifold?
>> GUHATHAKURTA: In what manifold?
Well, in this particular case we're talking
about a four-dimensional spacetime.
We're talking about three-dimensional space
one dimension at time so nothing exotic in
this particular case.
I have to take this question, please.
>> Is there such as a thing as neutral matter?
>> GUHATHAKURTA: There is such a thing as
neutral matter, of course, there is.
Electrons and protons are negatively and positively
charged respectively.
But there's a particle called a neutron, for
example, that is--that has no charge at all.
And you may have heard, there are also particles
called neutrinos.
There's been a lot [INDISTINCT] simply about
some people think neutrinos might be traveling
faster than the speed of light and that hasn't
been confirmed yet.
There's a joke about this that's going around
that says, "The bartender says, 'We don't
serve neutrinos here,' a neutrino walks into
a bar, because, you know, causality is reversed."
Okay.
Yes, go ahead, please.
Yes.
>> My question--you know, what I meant is
like neutral matters that--it's not dark matter
or is it any matter that we know of.
>> GUHATHAKURTA: Well, if we don't know of
it I wouldn't be able to talk about it, right?
So, I think--I think I understand what you're
asking.
I think what you're--the way--you know, when
people talk about dark matter, "Why even talk
about it if it's dark?"
You know, what might be your question.
Dark matter is known to exist, I want to emphasize
that.
Dark matter is known to exist because even
though we don't see any light from it, we
can sense its gravity.
So, the reason people talk about dark matter
is because galaxies are spinning much faster
than they should.
Galaxies are spinning much faster than they
should if the only gravity they were feeling
were the gravity of all the stars in the galaxy.
This--the speeds are way too high by a factor
of 10, way too high compared to how--to the
gravity the stars should be feeling if stars
were the only thing present in the galaxy.
So that's we know dark matter is present,
is through--we can sense it's presence through
its gravity even though we can't see its light.
I don't know if that--if that answers your
question at all.
Yes, please.
>> Is there any evidence that other universe
exist--other universes exists?
>> GUHATHAKURTA: That is a tremendously good
question.
The question is, "Is there any evidence that
other universes exists?"
People speculate about it.
They think about it, they make theories about
it.
I think it's unlikely that we'll ever be able
to confirm whether other universes exists,
because by definition our universe is everything
we can sense, everything that can send us
signal.
When we're talking about another universe,
it means we can't make any measurements of
it.
We can speculate about it.
And in fact, it's nice to speculate about
it, to say that, you know, our universe is
ordinary, it's not a universe, it's part of
a multiverse.
We can speculate about it and it's nice philosophically.
But when it comes to the language of physics,
of getting hard evidence, I think it's going
to be very hard to prove, one way or the other.
Okay.
Let me take those two questions and I'll come
back to you.
Okay, let's start with you.
>> If there is possibly a multiverse, like,
galaxies wouldn't they collide?
And we wouldn't know about the multiverse?
>> GUHATHAKURTA: That's a very good question.
"Would we know about a multiverse?"
By definition, if we're talking about another
universe, not ours, at least as I understand
it, as physics portrays it today, it would
have to be a piece that we're not able to
communicate with at all.
We're not able to see, we're not able to get
any information from.
So, it doesn't necessarily mean that galaxies
would collide because of that.
Galaxies collide anyway, galaxies collide
because gravity makes them collide.
Even though the universe is expanding, that
universe has stopped expanding in certain
parts, let's say between us and Andromeda,
the universe is not expanding.
There are certain pockets of space where gravity
has stopped the expansion and, in fact, things
have reversed and things are colliding.
Okay?
>> What if--what if [INDISTINCT] the universe
is colliding, what [INDISTINCT]
>> GUHATHAKURTA: Yes.
So it's not clear.
When people talk about multiple universes,
it's not clear that those are going to collide,
it's not clear what separates them, you know,
they talk--there's talk of domain wall that
separates them.
They don't necessarily communicate with each
other, no.
There wouldn't be collisions between galaxies
and parallel universes.
That would defeat calling them parallel universes
because they really have to be out of communication
with each other.
I saw--I saw a hand up here.
Yes, please.
>> Could you comment more on dark matter?
Because it's used to--it's invoked to explain
the rate of rotation of galaxies.
Also you--invoked to explain the rate of expansion
of the universe...
>> GUHATHAKURTA: That's correct.
>> ...which I think [INDISTINCT]
>> GUHATHAKURTA: Right.
No, so, there are two different things here.
One is called dark matter, one is called dark
energy.
>> All right.
>> GUHATHAKURTA: So, they are both dark in
the sense we're in the dark about them.
So there are some Nobel Prizes to be won there
in the future.
But, so we don't know the exact composition
of dark matter.
We know its demographics though.
We know how much is present in galaxies.
And dark matter actually even plays a role
in this expansion.
People thought early on that if there's dark
matter present then the expansion rate of
the universe should be slowing down over time.
And, in fact, if you look back at the history
of the universe's expansion just by looking
out in space, you can look back in time.
The universe, in fact, was expanding faster
then started slowing down.
But one of the remarkable discoveries in the
last, you know, five or ten years is that
that's been speeding up again.
So that requires something--exactly as you
said, has to behave opposite to dark matter,
has to have a pushing out, a pressure.
And that we're equally ignorant about and
we call that dark energy.
And I used to joke to say that gravity sucks
but dark energy is truly repulsive.
But both of those things are here to stay.
I mean, the evidence is very clear that--and
in fact there's a recent Nobel Prize given
out for the discovery of dark energy.
Okay.
Let me take a question over there then I'll
come back to you.
>> Mine is a very simple question.
So, all these pictures of galaxies, are they
optical pictures?
>> GUHATHAKURTA: Many of them are optical
pictures but one can take pictures in radio
waves, in gamma rays.
Such pictures do exists.
In fact, slipped in among my pictures, there
were some x-ray pictures, there were some
infrared pictures, there was--many of them
are optical or ultraviolet pictures.
>> If that is the case, you said they were
like thousands of light-years away.
It means the pictures that you have, is it
as old that we don't know that they even exist
now.
>> GUHATHAKURTA: Absolutely right.
We don't know if they exist now.
In fact we have no choice but to look into
the past.
In fact, when you--when you're seeing me and
I'm seeing you, I'm seeing you in the past.
It's just--it so happens that that past is
only a fraction of a second in the past which
is a small fraction of human lifetime.
In this case the distances are big enough
that it's much larger than human lifetime,
much larger than our civilization's lifetime.
So, looking into the past is nothing new and
that's imposed on us by the finite speed of
light.
There is no--there is no such thing as the
present in some sense, you can only sense
the past.
And how far in the past, depends on how far
away.
So those two things are a couple, space and
time are a couple along something called a
light cone.
So as you look out in space, you're looking
back in time proportionate to the distance
you're looking out to.
Okay.
Yes, I haven't heard a question from you,
please.
>> So, if you said, like, if it was a pattern
that it slows, like, if it speeds up and then
it goes down, would it--would it be like the
same thing or would the pattern change?
>> What is the question?
>> GUHATHAKURTA: So the question is, "As the
universe expands--" you said, "The pattern
expands and then shrinks and then expands
again?"
It doesn't shrink.
The rate of expansion slows down a little
bit.
It's still expanding but just not as rapidly
as before and now it's speeding up again.
Yes, to answer your question, you asked, "Does
the pattern of galaxy stay the same?"
On large scales, yes it does.
On very large scales it does.
On small scales, it doesn't.
Galaxies--there are pockets of the universe
where the expansion has stopped.
Gravity has taken over, there's reorganization
going on there.
Those patterns are indeed changing.
So on very large scales the overall distribution
pattern of galaxies are staying the same.
I...
>> Just one or two more questions.
>> GUHATHAKURTA: One or two, okay.
Way at the back there then I'll come back
to you, okay?
>> Two questions.
One is that, do you think the universe is
like finite or infinite?
>> GUHATHAKURTA: So, I--if you had asked me
this question a few years ago, whether the
universe is finite or infinite, I would have
said infinite.
But now there's talk of multiverses so that
automatically means there has to be some limit
to our universe.
So you might ask, "How far away is that limit?
How far away is the nearest domain wall?"
I can only give you a guess at that.
We can see out to 14,000,000,000 light-years.
You multiply that by 10 to the power of 50.
That might give us a rough sense of where
the nearest domain wall is.
So, yes there are--if there are domain walls,
they're very far away, very likely.
And your second question?
>> The second question is, if you use, like,
mass and energy together and conserve [INDISTINCT]
energy [INDISTINCT]
>> GUHATHAKURTA: Yes?
>> You think that it's zero or non-zero?
>> GUHATHAKURTA: That is very good question.
The question is, "Is there conservation of
mass and energy or is the sum zero or non-zero?"
The sum is most certainly non-zero.
The--you know, in fact if the universe is
infinite, that sum is infinite.
But how dark energy behaves as the universe
expands, the so called equation of state of
dark energy--we know how an ideal gas behaves
as you expand or contract it--how dark energy
behaves as we expand, as the universe expands,
is one of those big burning questions, about
trying to characterize dark energy.
It's something called the equation of state
of dark energy, and there's a--there's a so
called quintessence theory of dark energy
that tries to address this question.
But it has some variables that one can try
to pin down.
I see, absolutely burning questions and I'm...
>> We should close now.
>> Yes.
Yes.
>> GUHATHAKURTA: Okay.
All right.
If we can carry on this discussion over lunch,
if people are coming to lunch, that would
be great.
>> All right.
So, let's thank our speaker.
Thank you very much Raja.
