微软亚洲研究院演讲系列：量子力学的奇妙故事.doc

Kim Ricketts: My name is Kim Ricketts, and Im here to introduce and welcome James Kakalios, who is visiting us as part of the Microsoft Research visitor research series. James is here today to discuss his new book, The Amazing Story of Quantum Mechanics. Science has met more demands of science fiction than most people realize, thanks to quantum mechanics. Though we dont see the world of the Jetsons with flying cars, people getting to work by jet pack or Star Treks teleporters, yet, we do have smart phones, pocketsize computers and hybrid vehicles. Because of quantum mechanics, we may also see many more science fiction technologies become a reality. James is a professor in the School of Physics and Astronomy at the University of Minnesota. He served as a consultant for the film Watchmen and won a regional Emmy Award for his role in the Science of Watchmen. He is the author of the critically acclaimed The Physics of Superheroes. So please join me in welcoming James Kakalios to Microsoft. applause. James Kakalios: Thank you very much. Thank you for the introduction. Thank you all very much for inviting me and welcoming me. I must say the working title of my new book originally was the World Of Tomorrow and so its kind of a pleasure to come here, see the guys responsible for that. Actually Microsoft seems to be following me. Two weeks ago I was in New York for some media events and walking around Times Square at night seeing these huge throngs of people lined up. And what impose are concert are they going to? No, theyre waiting for the Connect to go on sale at midnight. So I assume that you just like give one out to the speakers, but laughter. So I want to talk about the The Amazing Story of Quantum Mechanics, my new book. First let me give you a little bit of background. How did a mildmannered physics professor get associated with comic book superheroes, SpiderMan, Superman in my day job Im a condensed matter experimentalist though I do basically solid state physics. Ive been doing this for over 20 years. Doing research on amorphous semiconductors, you know, this is amorphous silicon used in solar cells or flat panel displays. Done film transistors. Ive done a lot of work on studying electronic noise in these materials. For about ten years I studied sand piles. Sand was quite hot in physics there for a while. We call it granular media when we talk to the funding agencies. laughter. And most recently collaborating with professors in neurosciences using techniques that developed a semielectronic noise into sorted semiconductors and applying them to voltage fluctuations in the brain. But thats not why Im here. Im here because back in 2001 I created a freshman seminar class at that time University of Minnesota called everything I know about science I learned from reading comic books. Which my colleagues said explained a lot. laughter. This is a really physics class that covers everything from Isaac Newton to the transistor, but theres not an incline plane or pulley in sight. All the examples come from superhero comic books and as much as possible those cases where the superheroes get their physics right. Now, obviously, you know, the super powers themselves are impossible, but once you grant a one time miracle exemption from the laws of nature, what theyre showing doing with their powers is scientifically correct. I showed this cover here because this is actually a comic that I bought as a kid, even though I wasnt a big fan of Superman at the time because Superman is here visiting a college campus and I was just fascinated to find out what life in college was going to be like. Even as a kid, back in the60s I knew that this part wasnt too accurate. But there are things here on the cover that, you know, as you all know turn out to be correct, namely all professors at all times always wear caps and gowns. laughter. And all professors are 800 year old white men. But from this class then in May of 2002, I wrote an op ed that was published in the Minneapolis Star Tribune pointing out how a key scene in a classic SpiderMan comic book turns out to be a textbook illustration of Newtons laws of motion. I thought, well, the SpiderMan movie is about to open, the first one. And so this might be a good opportunity to get some science into the newspaper. The University of Minnesota put out a little press release saying, well, SpiderMans on the big screen but if you want to know about the science of superheroes, the person to ask is Jim Kakalios, he teaches this freshman seminar, blah, blah, blah. I should point out that theyve sent out press releases about me before, about my work on amorphous semiconductors or one over F noise. Result? Zero. You write one story about SpiderMan, however, and the movie opened on Friday, the on end appeared on Friday. By money was getting calls from the BBC, the London times, CNN Headline News, the Associated Press came to my office where I just happened to have these lecture demonstration tools on hand. laughter. That was a lucky break. At this stage of my life, Ive reconciled myself to the fact that I can win three mobile prizes and I know what photo theyre using in my obituary. My colleagues say win three mobile prices like how, on eBay? This article actually went across the nation. This is a clipping from the Chicago Sun Times. It actually went around the world. I think I know what theyre saying about me here. In a Turkish clipping. And then I started showing up in places that physicists dont usually appear. So if youre ever playing Trivial Pursuit and youre playing volume six and you get card 291, Ill tell you right the science question, the answer is Kryptons. The question is what planets gravity did science professor Jim Kakalios estimate by calculating the force needed to leap over an earth building in a single bound? Now, I didnt even know about this. One of the graduate students came to me one day and showed me this card, brought this to my attention. I borrowed the card, brought it downstairs, showed it to my department chairman. And I said, Alan, who is the most famous scientist you know? laughter. And he looked at the card and he looked at me and he said Steven Hawking. laughter. Who is not a genius. Oh, well then its you. And so in 2005, one of the nice things about all this attention was the receiving hundreds and hundreds of emails from students and teachers and people long out of college who liked this idea of teaching science using comic books, asking if I had a book, which eventually led to my writing a book, which is now out in a second edition. And that has led me to the current talk and the current book talking about the The Amazing Story of Quantum Mechanics that I want to talk about today. Because there is also a comic book connection to this. You know, reading comic books, they all predicted what life was going to be like in the future. Heres heres an old adventure comics where Superboy visits goes 1,000 years in the future and meets these other super power teenagers, the legion of superheroes. And this was a very popular feature and he constantly by being able to break the time barrier would go a thousand years into the future and have adventures with the legion of superheroes. And in the future it was promised that we would be in a better place. And the reason we would be in a better place is thanks to science. In a thousand years from now, if you got in trouble, you wouldnt call for the police, you called for the science police. Here in another comic, one of the legionaires is falsely accused of betraying the legion and so they lock him up. And hes got this computerized device that provides the three necessities of life, food, water, books. laughter. But really, this goes back even further. Heres from 1928, if first appearance of Buck Rogers in the science fiction pulp magazine Amazing Stories. And they promised us that in the future wed have jet packs, flying cars, robot domestic assistants, underwater cities. What we got instead why cell phones, laptop computers, DVDs, Magnetic Resonance Imaging. So some guys are reluctant to give up on the jet pack. laughter. But we do have jet packs. And you can take a jet pack to work provided you live just a couple of blocks from where you work. Because the problem is it they the writers of the science fiction pulps and kind of books thought that we would have a revolution in energy, which is necessary in order to have like flying cars and death rays when what we got instead was a revolution in information. And energy youre pretty much limited to the chemical bonding strengths between atoms and molecules. And, you know, for the physicists its on the order of a few electron volts. Thats the energy scale, visible like red light has an energy of about a little under two electronic volts. So that gives you the sense of the energy. What you very few people in order to have enough energy to take an extended trip or to levitate a car, youd need like nuclear power which produces millions of electron volts per reactive. And but few people are willing to have an unlicensed nuclear power pack on their backs unless youre a member of the Ghost Busters. But there was still it was promised that we might have, you know, nuclear power in our daytoday lives thought back in the 50s. This is the 1957 Ford Nucleon, the prototype of a nuclear car. I like they never built it, but it would have a little nuclear fission reactor with little mini cooling tower here with tail fins longer than the car even. And the idea is that you could go 5,000 miles before you would have to swap out the nuclear core. What you do in the case of a fender bender was never really talked about. But theres actually an interesting convergence between the science fiction future and the real future that we had. Hugo Gernsback first publishes Amazing Stories, the first pulp magazine devoted to science fiction in April 1926. Also publishing in 1926, Erwin Schrodinger, publishing his the Schrodinger equation, which would serve as the foundation for modern quantum theory. Schrodinger and a handful of other scientists developed quantum mechanics because theyre trying to understand how atoms interact with light. A generation later, groups of scientists at Bell Labs, other research laboratories developed the laser and the transistor. You dont accidentally discover a laser, okay, you have to go into the lab and willfully, with malice aforethought go in and build such a device. And you cant do it without an understanding of how atoms and light interact provided by quantum mechanics. A generation later you get CD players, personal computers, laptops, cell phones, everything my teenage children would say without which life is not worth living. None of these are possible without the transistor and or the laser, neither of which are possible without quantum mechanics. This is pure nowadays, we would say that this is curiosity based research. Schrodinger is just trying to understand how the world works. Schrodinger, Heisenberg, Pauli, Born. If you went to him and said, nice equation, Erwin, whats it good for, hes not going to say well if you want to store music in a compact digital format, but really without the insights provided by a handful of people, the world we live in would be profoundly different. For example, you know, wed still have computers, but they would use vacuum tubes. So to have a computer that has the same power as a laptop, it would have to have be about the size of the room. So there would be very few of them. Only corporations and the government would own them. There would be very little reason to link them together in an Internet. There would be no World Wide Web. So theres all sorts of things that the world has changed that we dont really think of. I think I once figured out that in an average hospital theres probably more transistors than there are stars in the Milky Way galaxy. So we dont notice how often this comes about. So this all came about thanks to semiconductor and solidstate physics which was enabled due to quantum mechanics.How many people dont know quantum mechanics here? Great. That will change by the end of the talk. I have like about 40 minutes to teach you all quantum mechanics which leaves me with a problem. What am I going to do with the other 35? laughter. It has a reputation for being weird and incomprehensible. The ideas are certainly weird, but theyre no weirder than saying that we live in a sea of invisible electromagnetic waves, only a small slice we can actually detect. We never think about that unless you cant get five bars or your phone or your laptop. Then you notice that the sea is missing. So lets let me boil it down to understand how quantum mechanics leads to something like a laser. Let me boil it down to three things like in the comic book, three suspensions of disbelief, three things that you would have to buy into. That light has both a wave and particle like property associated with the term photons, matter has both particle and wavelength properties, and of everything, light and matter has an intrinsic spin. These are this is all if you buy that, thats this is not, this has nothing to do with, you know, wave indeterminacy or the measurement problem or Schrodingers cat. This is Im taking what I describe a working mans view of quantum mechanics. This is the stuff that we experimentalists make use of when designing semiconductor devices. So lets look at the first principle. Light has both a wave and particle like property, photon. A manifestation of that is that when you shine light on a metal, if light was just a continuous series of waves like washing up on a beach, the waves might eventually push some pebbles up the slope of the beach. But really what the light is composed of is a series of is a machine gun bullet spray. And by changing the frequency of the light, is the waves would just the frequency would just be the spacing between the crests, and that would just determine the rate at which the pebbles are advanced. But the frequency actually controls the energy of the bullets and so by increasing the frequency we can have bullets that can promote the electrons out of the material. This is called the photoelectric effect. There are of course practical applications to this that we all know, right, that you can get laughter photon in this way. Matter has both partially and wave like properties. One of the most striking examples of this is interference. Thats the hallmark of wave phenomena. You have a wave striking a surface and it gets reflected. But maybe part of it passes through and reflects off the bottom and if these two waves are in phase they would add up coherently, we would get a very strong signal. But if they come in out of phase here, then they would add up destructively and cancel out. And so when you look at an oil slick on a wet driveway, the oil slick floats on the water and create a free floating freestanding film. And if its not too thick, some of the light can be reflected from the top or passed through and come out because the oil slick is not a uniform thickness. Some regions might have a thickness such that some colors add up coherently. Well see the red light out of the white light thats striking the surface whereas the other wavelengths interfere destructively and cancel and then we might get a blue light over here and so on. And this interference pattern is a hallmark of the wave phenomena. If I pass a laser light through a screen, I can get an interference pattern. By choosing the grid of the screen, I can get this nice circular with dot pattern. But if I send electrons on a crystal, electrons have a wavelike nature thats associated with their momentum. We dont notice our wavelike aspect because were made of lots of atoms. So we have even moving very slowly, we have an enormous momentum compared to an electron. The bigger the momentum, the smaller the wavelength. If I walk across the room, the momentum of my matter wave is a trillionth, trillionth smaller than the nucleus of an atom. Its impossible to detect. Theres no way to see such a thing. For electron inside an atom, its wavelength is about the size of the atom. Its impossible to ignore. And thats why this wavelike nature only became evident when studying the properties of atoms in detail. Back in the 1920s. You send you choose the momentum of the electrons correctly and they scatter off the atoms in a crystal and well, if the room were darker you could actually see this a little bit better, but you see the same type of ring pattern with the spots that I saw this is for laser light, and these are for electrons. So you have the same interference pattern for matter or light. And then the last part is that everything light and matter has an intrinsic spin. Of course those who look at the old those old pulp magazines know that every month had an application of spin. But Im actually more talking about the spin say like of a twirling ballerina. Even that is a bit of a misnomer. Its not as if the electron were actually rotating like a top but this is still the phrase thats used. This rotation is also associated with a magnetic field that has both the North and South Pole, and we know the North and South Pole the magnetic fields flow out of the north into the south. And so that means that electrons can have magneti