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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.

>> Thank you all for coming. I am very pleased to introduce Prof. Raja GuhaThakurta. He's

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宇宙の中の私たちの場所 (Our Place in the Cosmos)

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    van に公開 2021 年 01 月 14 日
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