JIM ALEXANDER: Good evening, everybody. Good evening, and welcome to the 48th Bethe Lecture. My name is Jim Alexander, and I'm going to tell you a little bit about the life and times of Hans Bethe, and then introduce our distinguished speaker tonight.
So Hans Bethe, as you know, was one of the great physicists of the 20th century. And he entered physics at a very propitious time, in 1926. And he quickly mastered the new ideas of Schrodinger's quantum mechanics. And he began applying them to a very wide range of condensed matter physics. And by the time he was 25, he had already published 10 papers, of which four of them remain today as enduring classics.
And by the way, by the age of 27 he had written two book-length reviews, one on the physics of one- and two-electron atoms, and one on the behavior of electrons in metals. And both of these two became classics, and educated a generation of physicists. In 1933, he began immersing himself in the new field of nuclear physics, and he soon wrote a landmark paper on the structure of the deuteron, and rapidly became acknowledged as the world expert on all matters of nuclear physics.
He came to Cornell in 1935, and in his first two years here, he wrote the three-volume review of everything that was known at that time about nuclear physics, the work we typically call Bethe's Bible today. And in 1938, he turned his attention to the problem of energy generation in stars, and he quickly discovered the complex cycle of reactions that power the sun and affect stars of all sizes, for which he later won the Nobel Prize in 1967.
At the outbreak of World War II, he plunged into work on military problems. And when the Manhattan Project was formed, he was appointed head of the theoretical division at Los Alamos National Laboratory. And following the war, he returned to Cornell, and he brought with him various luminaries from the Manhattan Project, including Richard Feynman and Robert Wilson.
And in the '50s and '60s, he worked extensively on nuclear arms control, and became a regular advisor of presidents Eisenhower, Kennedy and Johnson. And at that same time he was shaping the physics department at Cornell, leaving the imprint we see today in its structure and its open and collegial atmosphere.
In the later stages of his career he took up new scientific issues, including the study of supernova mechanisms, and as an octogenarian he solved the long-standing solar neutrino problem that had stymied a generation of younger colleagues for 20 years. He retired in 1975, but you could still see him in his office after the turn of the millennium. And the Bethe Lecture series was established at the time of his retirement, and began in 1977, to honor this man and his many contributions to the department. And over the years it's brought dozens of brilliant physicists for both technical and public lectures.
Now, I want to introduce our speaker. But first, let me note that after the talk there will be a little reception up in PSB 401. So please come. So, it's my pleasure to introduce our distinguished Hans Bethe lecturer, Professor Hitoshi Murayama. Professor Murayama is the McAdams professor of physics at Berkeley, and also the founder and director of the Kavli Institute of Physics and Mathematics of the Universe at the University of Tokyo.
He did his PhD at the University of Tokyo and post-doctoral work first at [? Tohoku, ?] and then at Lawrence Berkeley Lab. He is the recipient of many honors and awards, including the Yukawa Prize for Theoretical Physics. He is a fellow of the American Physical Society and a member of the American Academy of Arts and Sciences. His advice and opinions are sought out by almost everyone in the world of particle physics.
And he is a current or recent member of the Science Council of Japan, which advises the Japanese government on science policy; the High Energy Physics Advisory Panel that advises the US government on matters of particle physics; and the CERN scientific policy committee, which advises the CERN laboratory on the research priorities, and in fact, all aspects of science that affect the laboratory. And several others, including one we were on a few years ago.
His research covers a remarkably wide range of topics from particle phenomenology to cosmology, including dark matter and dark energy, and even includes work in condensed matter physics, and leadership roles in experimental collaborations. He is widely sought out for talks, and we are very pleased to have him here this week as our Bethe lecturer. So please join me in welcoming Professor Hitoshi Murayama.
HITOSHI MURAYAMA: Well, thank you, Jim, for kind introduction. I sounded much better than I actually am, anyway. And so it's a really great honor to be invited as a Bethe lecturer to give a talk at Cornell. You can't imagine, if you're not a physicist, how great a person Hans Bethe was. For baseball players, like Babe Ruth. Or Joe Montana for a football player. Or Jimi Hendrix for a rock guitarist. You know, it's an incredible honor to be invited as a Bethe lecturer.
So today, I'd like to actually give a talk with the title "The Quantum Universe," which is meant to be an oxymoron, because the quantum physics, which Bethe really worked very hard on, is about tiny, tiny things smaller than the size of an atom. But that also has to do something with the universe, which is really an oxymoron. How can these small things and the biggest thing we can observe connect to each other? But that's the idea I'd like to convey today in my lecture today.
But before getting into that, I have to actually do a little, make a remark, that the physicists are often misunderstood. Most people in the world think that physicists are supposed to look like that, right? But even people who know me, they always ridicule me. So when I became this-- I accepted a job of being the director of the new institute called the Kavli Institute for the Physics and Mathematics of the Universe, my friends in Berkeley said, OK, wow, that's a long title. I can't remember that. So let's shorten it, taking the beginning and the end of the title, and make it that one. That sounds like a lot of responsibility. And it turned out that back home, even this title is not high enough authority, because somebody else who claims she is the voice of God. You can't compete with that.
But anyway, so what do physicists do then? Well, what physicist do is to ask really simple and profound questions, like any little kid might ask. Looking up at the night sky. And if you look at the beautiful night sky, there are galaxies and stars out there. Then you get caught up with all these profound questions. I'm sure you've had that experience. You know, how did this big universe begin? What is its fate? Where are we going from here? What is it made of? What are its fundamental laws? How do things work? And where do we come from? I'm sure you have grappled with these really profound questions when you are looking at the stars or whatever.
So let's get started, for example, a question like this one, where do we come from? And this kind of question [? of ?] [? course ?] has been the [? realm ?] of religions for millennia. Also in philosophy. And much more recently, probably starting with Darwin or someone, we start to talk about where we come from in the context of evolution of biology. And of course, I'm not really sure if human beings evolve in the right way these days, looking at how we look like. But anyway, so it became a scientific question in a way.
And really, in order to answer this question, where do we come from? What we would love to have is a time machine. It turns out we do have time machines. Well, sort of. So the kind of machines we use to study this question are two kinds. One of them is giant telescopes. For example, people are trying to now build a telescope whose mirror is as big as 30 meters, 100 feet tall and wide. So we are trying to build these things.
And another things is called giant particle accelerators. For example, I will talk about the accelerator called LHC later on. This thing is 17 miles all around. And these giant machines, in some sense, are time machine for us. And I'll tell you why.
So if you use one of these giant telescopes, it's so big, you can collect so much light, you can look very far-- look at really, really dim things. For example, this is a picture we took using a new camera we bought for a telescope. It's a picture of Andromeda. Andromeda is 2.3 million light years away from us. So what that means is that if there's somebody who is living in Andromeda who happens to be looking at a planet Earth now, then what would he would see is the way the planet Earth was 2.3 million years ago. So what they're going to see is really that. That's how far away Andromeda is.
These days, using these giant telescopes, you can study galaxies billions of light years away. So if somebody is out there looking at the planet Earth, then they're going to see us as single-cell organisms. Then, this is the Guinness record, how far we've managed to look so far. If you look at this image taken by Hubble Space Telescope, you cut this piece out, you zoom in. You cut this piece out, zoom in.
Then you see this little red speck. It's actually a galaxy. This is the farthest ever galaxy we have ever seen, which happens to be 13.3 billion light years away from us. So if anybody is out there looking at the planet Earth, what would they see? Nothing. Our solar system hadn't been born back then. So that's how we can look back into the past using these giant telescopes. So that's how we can study where we come from.
But very unfortunately, there is a limit to that. If you look really, really far away, well, maybe you have this idea that the universe started with a big bang, and it happened 13.8 billion years ago. So if you look at [? a dedicated ?] telescope, and try to look 13.8 billion light years away from us, you can see the big bang. Now, you can really see it. You look with the telescope and say, ah, there's the big bang! The universe's heart. You can really see it.
And that's this picture here. This is a picture of the big bang. As we speak, we can see big bang happening in front of your eyes. But there's a little catch to this. Anything has a catch, right? So if you look at the big bang, it's sort of like looking at the sun. I don't recommend you to do it, because it would burn your eyes. But if you are protective enough, let's say you imagine looking at the sun.
All you can see, either with naked eyes, or best telescopes, whatever, what you can see is the surface of the sun. Because the sun is such a hot, dense ball of gas, light can't get through it. It's like trying to look through the fog. You can't see through it. You can't see the inside of the sun. All you can see is the surface. Big bang is the same way. Long time ago, universe was so much smaller, so much hotter, so much denser, the light can't go through it. All you can see is the surface of the big bang, and that's this picture.
It turns out that this picture, what we can see, is about 380,000 years after the big bang, not quite the big bang itself. That's the best we can ever see with best telescope you can ever imagine. So it's a wall. And you don't see beyond that unfortunately. You can see the big bang itself with no matter what great telescopes you ever built. But then of course you wonder, OK, we really would like to understand where we come from. How can we go beyond that wall? Is there anything we can do about it?
And that's where this particle accelerator I briefly mentioned at the beginning actually comes in. So here's is the big bang, 13.8 billion years ago. This is you, sitting in the auditorium thinking about where you came from. And using this telescope, you can look this far back into the beginning of the universe when it was only 300,000 years ago. This is really a baby universe. If you think of this big bang to now as sort of a year, then this is when the universe was only 15 minutes old. You can really go back to the baby age of the universe using telescopes, but we would like to go farther than that.
And that's where, as I said, something called particle accelerators come in. And the idea is very simple. If you can't look at it, why don't we do it? Let's do the big bang. Well, you know, you can't really do the big bang. You can't recreate the universe. But you can do a little bang. You smash things against each other. Create the conditions where it's so dense and hot that you can sort of tell what was going on at the very beginning of the universe.
And one of the things we have done is this. We can mimic the situation when the universe was only three minutes old. What do you do, is that, you know when the universe was that young it was a very thick soup made of small particles called electrons, photons, protons, and neutrons. And you can mimic what was going on in that hot, dense soup, like throwing neutrons and protons against each other. And then once in a while, you can see in the laboratory, that they stick with each other.
Then what you can tell is that, well, out of these neutrons and protons, you managed to make helium, which you would use in the birthday balloons. So by doing these kind of experiments, you know how much of this helium had been made in the big bang. So it turns out that you get a ratio of hydrogen to helium about three to one. And when you go out there and look at the sky and try to see how much helium there is in the universe today versus hydrogen, that also turns out to be about three to one. So they agree.
What that means is that what we can see in the telescope today is really what came out from the big bang. You know you're really studying the way the universe was very early on. So that's great. This is the way we can move forward. We want to get closer and closer to the very beginning of the universe to understand where we come from. So that's the idea.
We like to study the universe by doing experiments in the laboratory, by looking at smaller and smaller things. Because when the universe was very small, it was the small things that mattered, and decided the way the universe evolved, and also its fate eventually. So that's the idea of my title, "The Quantum Universe."
But now I have to come back to this issue, where do you come from? I told you where helium comes from, but your body doesn't have any helium. You've got hydrogen. There you go, that's good. But you also need carbon, calcium, potassium, iron, all these other chemical elements. But as far as we can tell by doing these accelerator experiments, big bang didn't make those. Then where do we come from? Where is your calcium coming from? Otherwise you wouldn't have your bones. Were does iron come from? Otherwise you wouldn't have your blood. We need to somehow find a way to make them in the universe.
So where do we come from? Well, this is a picture of my daughter on a bad-mood day. She's made of atoms. Atoms are made of atomic nuclei, which Bethe studied a lot of. It's made of protons and neutrons. Now we know they are also made of even smaller things called quarks. But somehow, we need to get started with these tiny things, build neutrons and protons, and build up these bigger nuclei, like iron, calcium, and so on. Where do they come from?
It's really Hans Bethe who figured this out. They are made in stars. So he grappled with this question, millennium-old questions. Why does the sun shine? It's an interesting question. And surprisingly, we didn't know the answer to this question until early 20th century. It's an age-long question, actually. And one of the breakthrough was Einstein, who came up with this famous equation, E equals mc squared. And what does he mean?
OK. So according to what people figured out, Hans Bethe did a lot of work on this. What's going on in the core of the sun is this. You start with [? four ?] hydrogen atoms or protons. And inside the sun, there is so much gravity, they get crushed against each other. And once in a while, they fuse together to form helium, just like in the big bang. But this process also spits out two other particles called positron, which is a form of anti-matter. I come back and talk about anti-matter later on. And another form of particle called neutrinos, which you may not have heard of, a very shy, tiny, tiny particles, and with some energy left.
The way it works is this. I try to put them on a scale, OK? And here are four protons, that's kind of heavy. And this is what you end up with, that's kind of light. So the mass has been lost. And that sounds really crazy, right? If you think of a collision of two cars, two cars come in the opposite direction, they collide against each other, there is so much debris on the street. But if the policeman comes, you collect everything on the street, get everything out, and measure everything he could collect on the road, then it should weigh exactly the same amount as the two cars originally combined.
We learn in high school, there is a conservation law of mass. But it's not true. The mass you start out with, the mass you end up with, it's different. The mass is lost. And that's where Einstein comes in. E equals mc squared. What that means is that m, mass, is the same thing as energy with some constant multiplying it. So when you lose mass, you can convert that mass into energy. And that's how the sun shines. So that's the idea.
So as we speak, actually, our sun is getting lighter by 4 million tons every second. It's converting this much mass into energy. That's why the sun is so bright, giving us abundant light and heat, so that we can happily live on this planet Earth. So we've got to be really grateful to her. But I'm always jealous about this. If I can shed some of my mass and turn that into energy, that would be really wonderful, isn't it? But I don't know how to do that.
Anyway, this is what Hans Bethe eventually figured out for us. But how do we know this is true? Well, there's something I mentioned earlier, neutrinos. They are so shy that they just get out of the sun without any trouble. It doesn't see anything in the way. The entire sun is kind of transparent to them. It doesn't interact very much. It's incredibly shy. So if you manage to see these neutrinos, because it just comes out straight out of the center of the sun, we can look back into the center of the sun and see if this is really happening at the core of the sun.
And there's so many of them. As a matter of fact, there are 100 trillion neutrinos going through your body every second. Well, you might think, oh this guy's crazy. It's the middle of the night. The sun is on the other side of the Earth. But it's true. The neutrino is so shy they can just pass through the entire planet without any problems. Even if in a bed at night, 100 trillion neutrinos are going through your body every second. It's a huge wind of neutrinos coming from the sun.
Does any refute this wind of neutrinos coming from the sun? No? Whenever I ask this question in Berkeley, always some couple of people raising their hands. I guess Ithaca is a more civilized place than Berkeley, I guess. Anyway, so if you do manage to see these neutrinos coming from the sun, then you can see actually the center of the sun. And that would be wonderful.
And the one experiment that managed to do this is actually this huge water tank. The idea is very simple. There are so many neutrinos coming from the sun anyway. All you have to do is build a big enough target that there is some chance that they might actually cause some reactions in it. So let's build just a huge target. It's a water tank, because water is cheap. That's the idea. And this is a big water tank, that's about like a 15-story building, 40 meters high, 40 meters wide.
And what you see here is a bunch of eyes, that's mechanical eyes that can detect just a tiny flash of light. It's called photomultiplier tubes. And this one thing is actually this big. So it's actually humongous construction. You might spot two poor graduate students working here on a rubber [? raft. ?] And this rubber raft is actually very important. They're on a mission. So what they do have to do is the following.
Because the neutrinos are so shy, they don't do very much. Most of the time, you have to worry about the noise in this experiment. To avoid noise, they have to keep this humongous water tank incredibly clean. So they are on a mission to actually take an alcohol, a swab of cloth, and then wipe these mechanical eyes. One, two, three-- you remember, it's 40 meters wide. You go all the way around, and then come back. And then what they do is to pour more water in. But you go one step up, wipe, wipe, wipe-- again, all the way around. And then one step up.
And they spend like four months doing it. Because, you know, you can appreciate how big this water tank is. Let me move this picture. It's that big. And using this huge target, they did manage to capture these neutrinos coming from the sun. And despite this big size, they see only like 10 a day. But they manage to do that. So this will be a proof that this reaction is really happening.
At the center of the sun, you can never, ever see with any telescopes, but you can see through it using neutrinos. And, if you get 10 neutrinos a day, and if you are patient enough, it's sort of like if you're taking a picture of a distant star, you need to keep the exposure camera open for a while, right? If you can get a decent picture out of it. They kept the exposure open for five years to get a decent number of neutrinos, and managed to get a picture of the sun like this.
This is one kilometer underground, 3,000 feet underground, in pitch darkness. No light comes in, but you can still see neutrinos coming from the sun. This is the picture of the sun taken with neutrinos. Not just a picture of the sun, this is a picture of the center of the sun. That's how you know Hans Bethe was right. The sun shines because of this process of building up bigger and bigger atomic nuclei. That's really happening. The stars are actually the factory of building bigger atomic nuclei.
OK, that sounds good. But is it really where we are coming from? Calcium, potassium iron-- is that really true? Well, it's not quite true. But now we know where it's coming from. Once in a while you'll see this incredible explosion of stars. The stars also have an age. They will eventually die. But when some heavy stars die, they're going to have a humongous explosion, so that one star becomes brighter than an entire galaxy. It can become that bright. And when this happens, then it's at the end process of being a factory building bigger atomic nuclei. And that also releases a huge amount of neutrinos.
So one earlier experiment, which is also a big water tank, managed to see these neutrinos from exploding star actually 160,000 light years away. And as I said, most of the time, the only thing you see is noise. So what this experiment has seen, is that you can see, most of the time, this is noise. But at one instance, within 10 seconds or so, there was a burst-- boom, boom, boom, boom, boom! Well, it's only 11 neutrinos, but anyway, it was a big, big burst here.
So that suggests that something explosive must have happened. And after the fact, astronomers looked at the sky and found, OK, here's an exploding star. So this is the way we know what's going on in distant stars, 160,000 light years away. Based on this discovery, Masatoshi Koshiba got Nobel Prize in 2002. And this is really incredible. Because for this to make happen, you need to make sure that noise is low enough, right? If the noise level is that far up, then even dispersed will be buried, and you wouldn't have been able to tell.
They had to work incredibly hard to bring this noise level down. Actually, only a month before this discovery, they managed to bring the noise level down. So they got just ready a month before the discovery. Also at the same time, a month after this, Professor Koshiba was subject to mandatory retirement. There was only two-month window. And exactly 160,000 years before this two-month window, the star exploded. And that's how he got a Nobel Prize for it. So this is a message to young people in the audience. You know, you should really aim for tremendous luck to succeed.
But any case, this is how we learn that these distant stars. Probably we can never get there and study it directly, but we know they are the big factories of building bigger and bigger atomic nuclei. And that's where the heavy elements had been made.
So this is what we now know. So universe in big bang made hydrogen and helium, but that's it. And initial stars were made of helium and hydrogen only. But as the star burns, they make bigger and bigger atomic nuclei. And at the end of its life, it explodes. And that releases all these synthesized heavy elements back into empty space in a form of dust.
Then eventually, this dust gets collected again and forms the second generation star. That's the children of the first stars. Then eventually they make more and more heavy elements, and they also explode, releasing so much dust into empty space. And you collect them again, and they form the third generation of stars, that's the grandchildren.
And from what we know, our sun is a third-generation star. That's why it has so much heavier chemical elements like iron, silicon, potassium, calcium. So when the solar system was made, there was this cloud that eventually became this little rock called the planet Earth, that really had so much heavier chemical elements so that we could be born out of that.
So out of these exploding supernovae, how they are called, everything we are made of came. That also made the Nobel Prize. So one take-home message today is that you are stardust. Literally, you came from stars. One little bit of advice is that when you see a stranger, and when they ask you where you come from, don't tell them that you came from a star. That will get you into trouble. But it's true. You are stardust. All of you came from stars.
One thing that means, though, is that our sun will also eventually die. And will probably last for another four and a half billion years or so, but it will eventually run out of its fuel. Sun will also encounter an energy crisis. It can't produce energy any more, then it can't sustain its own weight. Everything collapses to the bottom, and everything else bounces back.
So sun would become very big. It doesn't quite explode, but it becomes very big. So big to the extent that Earth, that's revolving around the sun, gets swallowed up. As we know it, this is the end of the planet Earth. So I really encourage students among you at Cornell to work very hard to come up with some escape plan in four and a half billion years. I'm counting on you guys, OK?
But it doesn't solve the entire puzzle about where do we come from. So far it tells you where these atomic nuclei come from. But to build your body, you need atoms. Atoms need these tiny particles called electrons moving about the atomic nuclei. So without those electrons, again, we can't live. We wouldn't have been born.
But it turns out, to make electrons move about, go around atomic nuclei, we've got to solve another puzzle. And that puzzle has to do with something you might have heard before, called the Higgs boson. Higgs boson is a new particle we didn't know before that existed before 2012. It was made, literally, by these particle accelerator experiments, LHC, which stands for Large Hadron Collider.
It's a humongous experiment. This dotted line is the border between Switzerland and France. So if you get on an aircraft, you'll see this dotted line. You know that. And this is the airport of Geneva. And this circle here is actually an underground tunnel you don't see from an aircraft. It's just painted on an aerial photograph. This is like 17 miles long.
And this incredible big tunnel is instrumented with these very high-tech devices all the way around. It's a huge tunnel. So even though it's a circle, if you just casually look at it, it's hard to tell that it's actually round, right? It almost looks totally straight. So this is how big the tunnel is.
And all these, the tubes that are lining up in this tunnel, is high-tech devices-- superconducting dipole magnets, RF cavities-- they come with these funny names. But it's a really high-tech experiment, which is as big as 17 miles. And using this humongous instrument, you accelerate tiny particles called protons to an incredible speed and energy. You smash them against each other to redo the big bang. Or little bang, I told you that.
And using this experiment, they discovered this new particle. This is also part of the question, why, where do we come from? Discovery happened on July 4 in 2012. There was a huge celebration going on at this laboratory CERN in Europe. And it was a long time in the making. That when people came up this idea of this funny particle called the Higgs boson, that was like 50 years ago. When people start to think about building this experiment to test that idea, that was like 30 years ago. And when they start building this humongous thing, that was like 15 years ago.
And it took this many years to get to this stage that was really a historic moment in the history of physics. So all of us were ecstatic at this announcement. I was home in Berkeley late at night, watching this webcast from CERN, and so that was a really, really amazing moment. I even wept seeing this discovery. And then went back to bed, woke up in the morning, and all of us were so excited, especially given it was on July 4. All of us celebrated Higgsdependence Day. And it was covered all over in the media.
And people at Cornell made a big contribution to these experiments. This is one of the experiments called CMS. That stands for compact meuron detector. Compact, in this case, means 20 meters long, 50 meters high. That's compact. Because their competitor, called ATLAS experiment, is even bigger-- 40 meters long. And that this is a video of the ATLAS experiment they actually made before the construction for outreach. They've been very active about that. So let me just run it for you.
So this is the way the protons come together, smashed against each other, mimic the condition of the big bang. Put in so many different things. Now we can start to tell what movie they had in mind when they made it. And they are damn serious about this. Just keep watching for a while. Isn't that great?
And because these instruments, they are just humongous, but in some sense, they have a sense of beauty. This is the picture of this ATLAS experiment in the middle of construction. So it's actually empty inside. It's now completely filled up with high-tech equipment. You see a guy standing here? You can sort of tell how big this whole thing is. But you know, there's some sense of beauty. The [INAUDIBLE] I mentioned looks like a cathedral. This also looks like some kind of elaborate construction.
So this kind of thing, and this beautiful image, make not only an impact on science, but also in the world of art. There was once an opera in Valencia, Spain, by Berlioz. And their stage was like this. See? It's a big impact on art. I'm not sure if this is the right way of doing the opera. It looks really avant-garde. But anyway, so it has some influence in art, as well.
And so what the CMS experiment the people here have worked on has done is to bring the protons against each other. Then you see this spray of particles coming out from this little bang. And in the end, you see these two specks of yellow deposits of energy. So when you can manage to make the Higgs boson, it actually disintegrates right away. What you're looking for is its fragments. But as long as you can capture those fragments, you can tell that you managed to make this Higgs boson.
So in this case, the Higgs boson disintegrated into two particles of light called photons. So this particle really exists. And that's part of the reason why you are here, where you come from. And so the idea is the following.
When universe was really hot, small, and dense-- you know, anything hot, like vapor coming out from volcano, means-- and anything hot has these tiny particles zooming about incredibly fast. This is what it means to be hot. Everything is sort of chaotic, random. But when things cool down-- one, if you cool down vapor, it eventually becomes water, and eventually ice. And ice means all these tiny molecules are lined up very neatly. That's why ice looks transparent and clean and beautiful.
So what happened here is go from chaos, what we call disorder, to neatly arranged structure, what we call order. So you go from disorder to order. And that is what happened in the universe. So Higgs boson, that was zooming about in this very tiny universe, got so neatly ordered today, Higgs boson got frozen into empty universe. And we are actually swimming in the ocean of the Higgs boson today.
So how cold was it? So this Higgs boson froze into empty space when the universe got as cold as 4 quadrillion degrees. That sounds pretty cold. So this is what happened. Higgs boson is frozen into empty space. Where will you go in the universe? It's right here. Right out there. Everywhere is filled with this Higgs boson. And that's the trick.
When electron comes close to these atomic nuclei, electron actually wants to go with speed of light. That's what it wants to do. But it's moving in this ocean of the Higgs boson. It bumps on it and gets slowed down. So he doesn't go the speed of light anymore. And that's how the electron happens to happily move about atomic nucleus, and how the atoms were born.
So if for some reason Higgs boson that's frozen in empty space just vaporized, then you would also vaporize in a nanosecond. Because all the electrons and atoms inside your body would start moving at the speed of light, and it takes only a nanosecond for them to disappear. So Higgs boson is really keeping you together. That's why you are here. That's where you come from.
So after this major discovery, I actually got to a major news show on TV in Japan. And this is the newscaster on a prime time TV show in Japan. And so she listened to my explanations and she said, OK, Professor Murayama, that kind of makes sense. But if it is true that everywhere is so filled with the Higgs boson, why didn't we notice that before? That's a very good question. Why didn't we notice that before? I had to think a little bit.
And then this is the way I answered this question. You know, Higgs boson is really everywhere. But we don't notice it, because it's just like the air. How do you know air is here? You are living inside the air. How do you know that? You can't touch it, you can't smell it, you can't see it, you can't taste it. How do you know? I think about myself, I'm sure my parents or teachers told me that, here is the air. But, now, how do we know that?
Well, Asian people actually didn't know that, that we live in the air. But once in a while, you sort of sense it if there's some motion. In this case, the motion of air is the wind. If wind hits your face, you can say, oh, something's here. But some Asian cultures said there's something called wind. Wind exists, not the air. So it's very difficult to tell if something is there. All the time you take it for granted, and it's very difficult to tell that something is actually there.
So Higgs boson is sort of like this. But of course, if you can make some motion in Higgs boson, you should be able to tell. But how do we do that? Well, that's very difficult. Because the Higgs boson is frozen so rigidly into empty space, there is no way you can just push and move this entirety of the Higgs boson. You can't do it.
So the only thing we managed to do is this. Take a piece of hammer, and bring it up, and whack the empty space. And if you can put enough energy into it, Higgs boson, that was already there, just pops up. And of course, it disintegrates right away, but you can see its fragment of it.
That's exactly what this Large Hadron Collider did. Smashing protons against each other, it's a big hammer. You are smacking, with this big hammer, empty space. You think there is nothing there, but it turned out, Higgs boson was already there. You let it pop up, and you manage to actually see its fragments.
So this is something that actually pleased the newscaster. She said, OK, that makes sense. That's why we didn't notice it before. Now comes the challenge to you. How do we explain the whole thing to average viewers of the show? I again, had to think a bit about this. And this is what I requested. Um, can you please bring in a bunch of kids to the studio? And let them just run around like crazy.
So this is kindergarten. And let all the kindergartners run around crazy. And that's what they do. That's why my kids used to do. And you know, it's a chaos. It's very difficult to stop them and calm them down. But one point, there comes this magician called the Higgs boson. He casts a spell on these kids. And due to some reason, all the kids slow down, calm down, get back into the room, and sit at their own desks. The desk is the nuclei. Kids are electrons. And there go the atoms.
And so this is what they actually did for me. So that's the way the TV show was put together. This is the way universe change from disorder to order. So the Higgs boson did this incredible thing of bringing order to the universe. It's a very important particle.
But then I'd like to know, OK, how does he look like? Who is he? Well, as far as we can tell, the Higgs boson is faceless. It's really spooky. We still haven't understood, what exactly is this thing? Is it alone? Does it have siblings? Why did you get frozen into empty space? And it's very, very strange.
Because this is one of a kind. Higgs boson is a kind of particle we have never seen before. And what I mean by this is that every small particle we have seen today is like a top, eternal top. It's spinning all the time. All the elementary particles we know are spinning forever. Electrons, photons, quarks, and we have heard of [? names ?] like this. But only the Higgs boson we discovered just three years ago, it doesn't spin.
And that's really strange. If something is spinning like this, depending on how you look at it, they look different to you, right? In some sense it's got a face. It's pointing to something. But the Higgs boson is not spinning. So it looks like it's a complete bland, boring object. No matter how you look at it, it looks exactly the same to you. It's a very strange, faceless, spooky particle. That's why I put up this picture of Jason.
So I really just couldn't believe such a thing could exist. And when I was back in grad school, I had to read a textbook that explains this idea that the universe is filled with these faceless particles. That didn't make sense. You know, why do we think about a faceless particle? Nobody has seen before to do this most important job in the theory of the universe. It just sounds too artificial to me. Just way too convenient. It must be a big cheat.
So after I got my PhD degree, I started to work with a bunch of great people, including Csaba Csáki, sitting here in this audience here, when he was a postdoc in Berkeley. So, you know, we've got to do something about this. So we in the end proposed what is called the Higgsless theories. We were very happy about that for a while. But now it's discovered. Hmm.
So recently, whenever I go to some international conferences, wow, OK, I'm sorry, pretending I'm a proper Japanese, I have to apologize like this. But it still begs this important question. We discovered this particle, but what exactly is it? Who is he? Is it only one that's faceless? Maybe he has siblings and relatives. Maybe this is the first guy in this new tribe, faceless tribe.
Or maybe, that's another idea Csaba Csáki and I came up with here, maybe Higgs boson is secretly spinning. But it's spinning in extra-dimensional space we don't get to see beyond the three dimensions we do observe. Maybe that's why we think it's not spinning, but it's actually secretly spinning.
Maybe it's not an elementary particle. And after all these questions, we should still ask the question, why does this particular particle freeze into the empty space? We still don't know the answer to that. So we've got to study this particle in much greater detail. And of course, we got this Large Hadron Collider. It's a very powerful tool.
But whenever you do this collision of protons against each other, what you get is a picture like this. It's a huge mess. And the reason is very simple. What you are colliding against each other is the proton against proton. Proton is a bag of quarks bound together with another particle called gluons. So what it means is that this experiment is sort of like smashing a cherry pie against cherry pie.
Cherry pies are kind of easy to throw. It looks pretty easy to make them meet with each other. But when they meet, you've got this huge splash, right? But what you are really looking for is when a cherry pit inside the pie and a cherry pit in another pie would meet with each other, and see if anything can happen out of it. And that's a very difficult thing to pick out from this huge goo coming out from cherry pies.
If you manage to throw cherry pits against cherry pits, then it's much cleaner. But as you can easily imagine, throwing tiny things are more difficult. And making sure that these tiny things can meet against each other is even more difficult. So technologically, indeed, doing an experiment like that is far more difficult.
But now, a lot of people at Cornell also work very hard to try to come up with this technology. And now we think that we can. So in principle, we can do an experiment like this one, where you can throw cherry pits against cherry pits. And cherry pit, in this case, is the elementary particle. That's electron inside your body meeting against its anti-matter counterpart, positron, I mentioned, that's produced in the sun.
And what we have to do is again, build a big, big accelerator. You keep accelerating these electrons over about 15 kilometers or so. You can do so in what is called the cavity, that was developed here. And what you do is put a powerful radio wave into it. It's a wave. So you can be like a surfer sitting on the wave, and the wave just keeps pushing you farther and farther away.
All these particles get accelerated at incredible speed, very close to the speed of light. Eventually, you actually focus them down to a very tiny size, make sure they will meet each other. And then you can create very clean collisions like this one. So using this, we hope to understand this mysterious particle called the Higgs boson a lot better sometime in the future.
OK? Then is that the end of the problem? No. So I told you, atoms were made thanks to stars, and also the Higgs boson. But then you have the question, OK, how were the stars born? Where do they come from? How were the stars made? And once you get to this stage, again, there are a lot of mysteries. Because, as far as we know, stars got built because of something even more mysterious called dark matter.
What is dark matter? Well, if you look at the sky and take pictures of faraway galaxies, sometimes you find something-- this. Doesn't that look kind of cute? You know, you see two eyes, nose, mouth, the frame of a face. This is a real picture taken with telescope. But that looks really strange, right? You know, what is this very much stretched out object? It doesn't look like a galaxy. It's not a star. What is it?
But anyway, this system looks so cute it was actually given a name. Its name is Cheshire Cat like in Alice in Wonderland. And you see many of these things. This is an even bigger picture of a cluster of galaxies. So each yellow blob is a galaxy that has like 100 billion stars in it. About 100 galaxies are living together in a little village. And then, again, you see this really, really stretched out object. Here, there, here, here again, also here, there, here. You know, what are these things?
Well, they are actually galaxies. They are ordinary, round galaxies. But they look different. They look really, really stretched out. What's going on, it turned out, is this mysterious dark matter playing tricks on you. This is the way it goes.
So a cluster of galaxies here is a big collection of dark matter. And it has a very strong gravity, because it is very heavy. It has a tremendous amount of mass. And there was the galaxy behind it. So this is where you are, this is the galaxy behind it. The light coming from the galaxy gets pulled by the gravity, and light falls. It bends. So the collection of dark matter here looks like a gigantic magnifying glass. Light bends, and images get distorted.
So this is the collection of dark matter in this galaxy. It's a faraway galaxy, light ray bends. And this is the computer simulation of how it happens. Just imagine that you have this collection of dark matter in front, and all the faraway galaxies are moving behind it. And this is the way it's supposed to look like. This is where dark matter is. And when all these faraway galaxies go behind it, they look really, really stretched out.
But nothing really happened to them, because once they pass behind it they go back to ordinary shapes. Nothing really happened to them, it's just a trick played by dark matter in front of them. But this is great. You know, dark matter is still mysterious. We don't know what it is yet. But we can at least tell where it is. Because if they are playing tricks on you, you know where the tricksters are. So this is the way you can actually take a map of dark matter.
So this is the picture you can take with some of the giant telescopes. And forget about this, that looks like crosses in front-- they are nearby stars. What we care about is these little dots. And they are mostly galaxies billions of light years away from us. But if you look very closely at them, you can tell that their images are also distorted because of the tricks played by dark matter. Now you're in business. You can tell where the tricksters are. So even though you don't see dark matter at all in this picture, you can make a map of dark matter, and you know where they are.
So this is what we can do these days. And one of my colleagues in Japan is working on this, together with his assistant. And this is the way we know more than 80% of matter in the universe is not what you are made of. It's not atoms, but something totally different, that's dark matter. That's as much as we know.
And also we have learned that dark matter is also very shy, sort of like neutrinos. And we know that from this picture. While this looks like a very beautiful picture, this is a cluster of galaxies 4 billion light years away from us. And where it's painted pink is hot gas. It's so hot, it's radiating with x-ray. What's painted in blue is where dark matter is. We figured this out using this distortion of images of the background galaxies.
So you have one place where dark matter is, but this is where the hot gas is. Another dark matter, and another hot gas. And somehow, they are separated from each other, which looks kind of odd. Because dark matter provides this strong gravity, everything is supposed to be pulled by it. So the hot gas is supposed to be with dark matter, but it's separated. Hot gas is supposed to be with dark matter, but they are separated. So what's going on here?
It turns out that this is a beautiful place, but it was a really, really ugly place that you should be happy you are not there. This was in the aftermath of the collision of one cluster of galaxies in another cluster of galaxies at the whopping speed of 4,500 kilometers per second. And we can see what happens when that happens using the computer simulation.
So both cluster of galaxies are basically just a big blob of dark matter with the ordinary gas just sprinkled in there. But when they collide, ordinary gas made of ordinary atoms would scatter against each other, they get heated up, there's friction, they slow down. But dark matter just keeps moving as if nothing has happened. And that's how the ordinary gas got dragged down, and then being pulled by the gravitational pull of the dark matter. That's how you can understand this picture.
So dark matter is definitely not one of us. It doesn't interact with us. It doesn't interact with itself. Maybe at some level it does, but very little. So we know dark matter is something very, very special. And this picture is actually called a bullet cluster, for an obvious reason. But anyway, so dark matter also looks kind of spooky.
But this is also very important for us. It's again, part of the question, where we come from. It turns out that dark matter is our mom. You saw the picture of the big bang before. And that picture had the contrast incredibly enhanced. But if you look at the real picture, everywhere you look looks completely the same. It's very bland and boring place. That's the way big bang was.
But starting from a very boring place, there are parts that have a little bit more dark matter, parts that have a little less of dark matter. And if they have more dark matter, there's a stronger gravity that pulls more dark matter in. It becomes more dense, pulls more stuff in, becomes even more dense, and so on.
Eventually you see a big contrast between dense spots and empty spots. And in those dense spots, because of so much gravity of dark matter, it puts the ordinary atoms in. And they interact with each other as in the previous slide. And then eventually they lose light, lose energy, they collapse down, form stars and galaxies, and that's how you were born.
But in hypothetical wrong universe, without dark matter, universe starts company bland, but there's nothing that can collect more stuff. So 13.8 billion years later, nothing. No contrast, no stars, no galaxies, no you. So that's what I mean that dark matter is our mom. She made us, but we don't know who she is. So she got separated from us at birth. We've got to find her and thank her, and that's what we'd like to do.
A Nobel laureate colleague of mine in Berkeley, after he got Nobel Prize by taking this picture of the big bang, he actually got called by the university administration and was asked to do something interesting for them for fund raising. Obviously, right? We have to raise funds. And so he decided to reenact the big bang with the Cal marching band. Cal is the nickname for the football team at the University of California, Berkeley.
So let me run this for you.
- I really admire the band. And so when they said we wanted to reenact the big bang with the guys from your lab, I said, no way. I want the band. OK. So now I've got to tell you what the big bang is so that you get to do this before the sun goes down.
OK. So the idea is everything in the early universe was packed together very densely. We're not infinite. We don't have infinite people, so we just have the people we've got. And everything stretched, right? Everything got bigger. And the further away you are, the faster you go. So we're gonna want to start in the beginning with everybody packed dense and jostling around and playing high-tempo, rapid--
HITOSHI MURAYAMA: So here's the big bang. And they are running very fast.
- The people on the outside moving faster than the people on the inside. And there's a little bit of the--
HITOSHI MURAYAMA: Regular motion.
- [INAUDIBLE] I'm going to make you do this, right? And then what happens is, you're going to form-- you're going to coalesce together in groups of six. All right? So you have to find six buddies. And half of you are going to form spiral galaxies. Three people facing one way, three the other. And you rotate slowly as you move out. And the other half will form elliptical galaxies, which are--
HITOSHI MURAYAMA: galaxies. Spiral galaxies.
- Now, there's a brass section out there with those tubas. They'd make a really spectacular spiral galaxies. A really big one. Like our own galaxy, or like Andromeda. So you guys get to be near the middle. And you're going to make a really cool-- you don't have to run out so fast. But you get to make-- you get to [INAUDIBLE]. Half is facing the other way. And you get to rotate with a sort of twist [INAUDIBLE]. And you're like the centerpiece of this whole thing. Go tubas.
HITOSHI MURAYAMA: Really good, huh? This is where we came from. But 80% of the people here is dark matter. You don't get to see them. And George Smoot, my colleague at the center of the Milky Way galaxy, he is a super-massive black hole, as heavy as 4 million times our sun. You don't get to see most of the things in the universe.
So OK, how do we solve this puzzle? Who is dark matter? Who is our mom? Well again, the idea is that they are tiny, tiny particles. They are very shy. They pass through the entire planet Earth very easily. But they must have been born in the big bang itself. Some of them are still out there, and that's how they managed to build stars and galaxies eventually.
But we have learned this before, right? We managed to capture neutrinos coming from the sun by going deep underground. Maybe we can do that again. I used to work underground myself. Underground is a pretty dark place. I brought my family over there.
And there's another laboratory in the United States, in a Homestake mine in South Dakota, where people do underground experiments. And some people, again, built a humongous device, big target, hoping that once in a while dark matter might cause some reaction in it. And this is the big celebration when one of these experiments had been completed. You know, physicists don't dance very often. But anyway, so they were very happy, clearly.
So maybe we can see dark matter eventually. Well, I told you, we manage to see 10 neutrinos a day. But in the case of dark matter, no matter how big an instrument you build, maybe you get to see two dark matter a year. You've got to be really, really patient for this.
Another way we might know what dark matter is is by making them in a laboratory. If big bang managed to make them, maybe we can. Again, smash particles against each other at incredible speed and incredible energy, maybe they pop out dark matter particles, too. Maybe we can see them in something like this. So here you see a spray of particles going that way. You don't see anything down there, but that is kind of wrong. Everything needs to balance out. So if you see something up here, there must be something down here, too. But you don't see them.
And what it means is that you have managed to make some invisible particles in this particle accelerator. So this is the way we hope eventually to understand what dark matter is, who our mom is. And once we do, we get back all the way, back to the point when universe was a tenth of a billionth of a second old. Higgs boson may go even farther away, a trillionth of a second old, closer to the big bang. And this is the way we hope we can understand the question, where we come from.
And I skip just one subject, and then I'll go to the very beginning of the universe as much as I can in the remaining five minutes or so. And that's an idea called inflation. So this is really the question, how exactly the universe got started. What was the big bang?
And from what we can tell in the telescope today-- this is actually based on real data. You know, all these galaxies in this video have been measured using a telescope. We know where it is, which direction it is, what is the shape, what is color. You put them in a computer, then you can pretend you are flying through them.
Well, you know, if you really would like to do this, then you have to fly at a speed about 10 trillion times faster than the speed of light. So don't try this at home. But the basic message out of this video is that no matter how far you go, universe looks pretty much the same. You know, it doesn't seem to change. But what we know is that there are some dense spots and empty spots.
This is the map of galaxies in the universe. It's 2 billion light years across. It's a huge map. In this huge map, OK, there are some spots that are dense, some spots that are empty. But more or less, it goes on like nothing happens. Tiny wrinkles on them, but more or less the same everywhere. So how do we understand that?
And this is where things get really, really crazy. Maybe you have heard of this idea called uncertainty principle. If you actually squeezed the universe to an incredibly small size-- that's the way the universe was at the very beginning-- empty space becomes very active. This is a simulation of empty space. When you're looking at a tiny, tiny universe, it's filled with a lot of activities. It's alive. Empty space isn't empty. It's borrowing and lending energy all the time.
And this is what is based on something called uncertainty principle. You can never exactly tell where energy is, because it's moving about all the time. And the idea is that this active vacuum is ultimately where we came from. So the idea is the following. Universe was born incredibly tiny. The entire invisible universe today, 13.8 billion light years across, was much smaller than the size of an atomic nucleus, like this. And that tiny universe got stretched out to this huge universe today.
And when the universe was this tiny-- and this quantum physics, uncertainty principle, plays such an important role-- was bubbling with activity. And so much lending and borrowing energy was going on. And when you borrow energy, like borrowing money, you're supposed to give it back, right?
Suppose you borrowed money. But if the universe is getting stretched at an incredible speed. That's what happened. Inflation would stretch out the size of bacterium, a moment later become the size of a galaxy-- incredible stretching. So if you borrowed money from your friend, but if the entire universe is getting stretched like this this quickly, then before you try to give money back to your friend-- ooh! Where are you? You can't give it back any more, so you are stuck with the money you borrowed.
And that's how you end up with these small changes in densities and temperature of the big bang. And that's small density change got magnified by dark matter, who is our mom, and that eventually became galaxies and stars today. That is the serious theory we are talking about.
How do we know this is true? Well, we are not entirely sure yet. But we try to prove that by doing a better measurement. If the universe was getting stretched like crazy, if everything is bubbling like crazy, space and time itself must have been bubbling like crazy. And that eventually leaves some imprint on the light coming from the big bang in the form of something called a polarization of light.
So what my friends are trying to do, and many people working on this, is to send out a new satellite into space, watch this light coming from the big bang much more carefully than we have done so far. And maybe we can really tell that the space and time itself is bubbling, because it was once incredibly tiny, and empty space was very much alive. And that's where we came from.
If we manage to do that, well, we get back to this. When the universe itself was 0.0000-- 33 zeros all the way-- one second old, to understand where you all came from. So we physicists, most of us belong to this society called the Division of Particles and Fields in the American Physical Society, what we want to understand is really simple questions. How did the universe begin? Where are we going? What is it made of? What are it's laws? How does it work? Where do we come from? That's what we talked about today. And we are slowly but finally getting there, I think. We are learning a lot. And this is the way we scientists really would like to solve the mysteries of the universe. Thank you for your attention. [APPLAUSE]
JIM ALEXANDER: We have time for a few questions.
HITOSHI MURAYAMA: Don't be shy. You are not neutrinos.
JIM ALEXANDER: Back there.
AUDIENCE: [INAUDIBLE] neutrino [INAUDIBLE] How do they know that [INAUDIBLE]
HITOSHI MURAYAMA: It's very simple. So when neutrinos come from the sun, they come pretty fast. And what they do is knock out electrons are living inside the water tank. So because when neutrino comes pretty hard on electrons, electrons get knocked out pretty much along the direction neutrinos came from. They just point back to the sun. Very simple.
AUDIENCE: So when you collide particles to knock out the Higgs boson and get its remnant, does it immediately get replaced by another one in that space, or where does it go?
HITOSHI MURAYAMA: As far as we know, that's the case. It sort of repairs itself. And so, that is still kind of a mystery that, as you know, for example, the universe is getting bigger. But does the Higgs boson thin out? Apparently not. It sort of produces itself all the time to maintain the constant density of the Higgs boson in empty space. It's really weird. And that's another big puzzle called, what is the energy in the universe today? I didn't get to talk about it today, but that's also a very big question we haven't understood yet. Over there.
AUDIENCE: So you said that we cannot see beyond 3,000 years because of the cosmic microwave background wall?
HITOSHI MURAYAMA: That's right.
AUDIENCE: And beyond that, you said you should [INAUDIBLE]. But is there something that [INAUDIBLE] that is beyond that border, and how far can it go?
HITOSHI MURAYAMA: Excellent. So the last thing I talked about, how we might be able to prove that the universe, space and time itself, is bubbling and wobbling, is actually based on this idea called gravitational waves. The gravitational wave is this idea of wobbling space and time. So inflation made it. It was wobbling all the time, and then we can see through this wall of cosmic microwave background-- that's [? the surface ?] of the big bang-- and hopefully detect that.
So there are some things that can pass through this wall. In the same way that we are using neutrinos that past through the surface of the sun and look inside, if we can capture neutrinos coming from the big bang, we can look back to the point where the universe was one second old. If you capture dark matter coming from the big bang, we can look back at the universe when it was a tenth of a billionth of a second old. And using gravitational waves, we may be able to go all the way back to the point of this inflation. So you're completely right. Because we're using light, this is a limit. But if you can use other things, we can look farther back. That's exactly the idea I tried to mention today.
AUDIENCE: What is the significance of whether the Higgs spins or not?
HITOSHI MURAYAMA: I couldn't hear, I'm sorry.
AUDIENCE: What is the significance of whether the Higgs spins or not? You mentioned some research--
HITOSHI MURAYAMA: Right, right. Yeah. So the Higgs doesn't seem to spin, as far as we can tell. And as I said, we have never, ever seen an elementary particle that doesn't spin so far. So it's definitely a new breed. We're sure about it. And also, the spinless particles are very difficult to control. So if you jiggle it a little bit, what we think is the Higgs boson all of a sudden becomes incredibly heavy, or go all the way down the other direction. It's very unstable.
So it is sort of like, in trying to bring-- a screwdriver like this one is meant to be sort of round. And you try very hard to keep it straight up, make sure it doesn't fall when you release your hand. I can't do that. The Higgs boson spinless particle feels that way. It's very unstable. [? Spinful ?] particles-- electrons, photons-- they are very stable. Once you get their mass, it stays that way. But not with spinless particles. So it looks very, very strange that Higgs boson is the way it is. It's frozen into empty space, it's doing a very important job, but so unstable. So that's why we still feel unhappy.
AUDIENCE: Since the universe used to be smaller than the size of an atom, wouldn't there theoretically be multiple places where things could be exactly the same? Because in quantum mechanics things can be in two places at once.
HITOSHI MURAYAMA: Yeah. So that's a very profound question. So universe looks, as I said, very much the same everywhere you go. And even beyond the place we can see, there probably space just keeps continuing on maybe forever. But how come the different parts of the universe look very similar to each other? Actually, inflation was meant to be partly a solution to this puzzle.
So if you look at the big bang that way, light took 13.8 billion years to reach us. And there was not enough time for that light to reach the other end of the universe. So they haven't talked to each other. But how come they have almost exactly the same density and temperature?
And somebody actually gave me this analogy. It's like if you are a world traveler, and you discover two remote islands in different parts of the globe. But once you get there, you discover that the people in this island, people in that island on the other side of the Earth, speak the same language. And I'm not an anthropologist, but then I surely would come up with a theory that they came from the same place, right? They must have interacted in the past.
So that's the idea of inflation. That part of the universe and that part of the universe looks like they have never talked to each other, but they must really have been together at some point, and they got separated so that they look far away from each other now. But they must have been together so that they can talk to each other, make sure their temperatures are the same. But to make that happen, you need this period where a tiny universe gets stretched like crazy.
They look separated from each other now, but they were together before. And that's how this idea of inflation initially came about. Was really about trying to answer your question. And we still don't know if that's true, but we are trying to come up with some evidence for that.
AUDIENCE: You mentioned that the universe is expanding. Do you have any ideas about what exactly it's expanding into?
HITOSHI MURAYAMA: Yeah, that's an interesting question. So there are several ways to think about it. So the universe may be like what Asian people used to think of the planet Earth. People thought Earth is flat. And there is the cliff at the end of the day, and then you might fall down. But what we have now understood is that the surface of the Earth is actually round. If you just keep going that way, then you come back from the other end.
So maybe the universe is like that, too. If your just keep going that way, you might find yourself coming back from the other side. We now know based on data that the universe is pretty big, at least like trillion light years big. So it would take a long time to get back. But it might be like that. So if that's true, the universe is only expanding in itself. There's no end to it.
Well, other people think the universe might have an end. Or other people think that we might be able to get out of the universe. People talk about extra dimensions, I mentioned. People also talk about multiverse. There are many, many universes. We live in one little island, but there could be other universes. Maybe we may be attracted to it. So there are all kinds of speculations, but right now we don't have any evidence for any of this. So we still got to keep walking.
AUDIENCE: What does it mean that the entropy of the universe was [? so low ?] at the big bang?
HITOSHI MURAYAMA: That's also a very good question. So right now, the current theory is that when inflation happened, everything got so much stretched that the universe would become pretty much completely empty. But even though there was nothing inside, there was at least the energy that expanded the universe so much, and that energy that caused inflation can turn into matter and energy of something we are familiar with.
So that's when what you call entropy had been created. That's the process called reheating. Again, we don't really know if that's true, but all evidences so far, sort of circumstantial evidences, suggests that that is indeed what happened. So by the kind of doing measurement I talked about at the very end of my talk, we hope to prove it. But we're not there.
AUDIENCE: So you said a moment ago that the universe is trillions of light years out. How could we know that if the universe is only 13.8 billion years old?
HITOSHI MURAYAMA: An excellent question. And the way we know it is by drawing a triangle. So what we learn in, I think, elementary school math, is that if you add up angles of a triangle, they have to sum up to 180 degrees. And you know that's wrong, right? If you draw a big triangle on the surface of the Earth, because Earth is round, They don't add up to 180 degrees. It's bigger than that-- 200 degrees, 240 degrees.
So what you can do is draw a big triangle in space and try to measure the sum of angles. If the space is curved, so that you can come back all the way from that direction to that direction, then they should add up to a number bigger than 180 degrees. Well, you know, any measurement has some errors. Right now the answer turns out to be 180 degrees plus or minus one degree.
It could be exactly flat. It may be a little bit round. So that's how we know, if it is round at all, it should be bigger than something. And that's where the number comes from. Very good question. So you mentioned that we are now able to look at objects which are farther beyond the time when the solar system was born and our galaxy was born. So when you look at an object which is, say, some light years away, we are looking at the image of that object so many years ago, right?
HITOSHI MURAYAMA: That's right.
AUDIENCE: So imagine we are-- imagine someone is at an object which is older than the age of the solar system and looking at us, what would they see?
HITOSHI MURAYAMA: Can you say that last sentence again?
AUDIENCE: So imagine that there is a star which is farther away from us in terms of years than the age of the solar system, or the age of the Milky Way galaxy. And if they have a telescope there and they are looking at us, what would they see?
HITOSHI MURAYAMA: Empty space. There's no star yet, there's no solar system yet, they don't see anything. What we do know, though, is that our Milky Way galaxy was assembled. It wasn't born on one day. Just like Rome, I guess. The universe made tiny stars, and then tiny galaxies. They looked kind of irregular. And they sort of smashed against each other, they collided, they merged, and they grew and matured.
And the way the galaxies are today, is they are slowly dying. Most of the stars in the universe today were made billions of years ago. Most galaxies we see today are slowly dying. There's aging going on. And eventually it becomes a very boring place to be. But when the galaxies actually collide against each other, undergo a merger, they all of a sudden would get rejuvenated. New stars are born, and it becomes sort of alive again.
So our Milky Way system has been doing that all the time apparently. We don't know exactly, but apparently. So those far away people might see sort of the initial ingredients of the Milky Way. Not the whole Milky Way, but these little parts. Back there? I guess the last one I was told.
AUDIENCE: Does the Higgs know why some particles are more massive than the others?
HITOSHI MURAYAMA: That's an interesting question, too. It doesn't. So the only way we sort of think about it is that electron bumps on the Higgs boson, slows down, and they happily go about inside of atom, I said. Some other, heavier particles-- electron has its cousin called muon, which looks very much the same, but it's 200 times heavier. So this particle should bump into Higgs boson 200 times more often. Even heavier particles might bump on Higgs boson a million times more often.
But who decides that? That's another big question we haven't understood yet. So we know this is the way it should work, but how different particles end up with different masses, different bumping on the Higgs boson, why they are different from each other, that's also a big puzzle people are trying to understand. Now, we have some ideas, but we are very far from really understanding it. So that's where you come in.
JIM ALEXANDER: Let's thank Professor Murayama again.
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The universe was once much smaller than the size of an atom. Small things mattered in this small universe, where quantum physics dominated the scene. To understand how the universe works today, we have to solve remaining major quantum puzzles.
Theoretical particle physicist Hitoshi Murayama discusses these puzzles -- the recently-discovered Higgs boson and mysterious dark matter -- in his Bethe Lecture Oct. 21, 2015. Murayama is a professor of physics at the University of California, Berkeley and the founding director of the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo.