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>> 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.