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SHOW 207 TRANSCRIPT
Why Is Quantum Physics Beautiful?

BEAUTY, elegance, charm; flavor, color, vibration; string, symmetry, strangeness. These are the actual words that physicists use to portray the most fundamental natural phenomena. Their field, quantum physics, describes how the world really works, from the minuscule microstructure of atoms to the cosmic macrostructure of the universe. What they envision is breathtaking. Quantum physics may seem like fantasy--or magic--because quanta don't behave like anything you're familiar with. An electron can be in two places at once. Subatomic particles, in fact, cannot really be said to "be" anywhere in particular, unless they are measured--that is, observed--to be there. If you think quantum physics sounds hard to understand, unfortunately it's even worse than that. Quantum physics is, to say the least, counterintuitive, and the Danish physicist Niels Bohr, one of its founders, is supposed to have remarked to his German colleague Werner Heisenberg that if it doesn't make you schwindlig (dizzy), you haven't really understood it. Nobody in his right mind, my friends warned me, would dare do television like this. So there I was, doing it, because quantum physics is real and relevant, and because every literate person can appreciate its profound beauty. We invited five physicists to provide us with their impassioned portrait of this new reality. So tilt your head and it won't be so hard. Stick with us. My bet is that you'll get it and like it. Who knows? It may forever change the way you think about the world around you.
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PARTICIPANTS

Dr. Gregory Benford teaches plasma physics and astrophysics at UCI and is also a leading writer of science fiction. Greg says the world is not as ordinary as it seems, and he uses poems and paintings to illustrate how strange it really is.

Dr. Charles Buchanan, a high-energy experimental physicist, teaches a course at UCLA called "Science and the Human Condition," which brings quantum theory and cosmology down to earth. Chuck notes that quantum theory is fundamental for biology as well as physics.

Dr. Steven Koonin is vice president and provost of Caltech, where he is a professor of theoretical physics known for his work in computational and nuclear physics. Steve gives us examples of quantum physics in action and tells us about Schrödinger's cat.

Dr. Leon Lederman, director emeritus of the Fermi National Accelerator Laboratory, in Batavia, Illinois, was awarded the Nobel Prize in physics in 1988 for his contributions to the body of evidence that revolutionized our understanding of the subatomic world. Leon describes a quantum and its history and explains why it seems spooky.

Dr. Andrei Linde, a Russian professor of physics now at Stanford, is a principal inventor of the "chaotic inflationary" model, which describes the universe as a metauniverse, continually and randomly giving birth to new universes in a series of what he likes to call "Pretty Big Bangs"--a process generated by quantum physics.

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ROBERT: Leon, pretend I'm your grandchild; how would you explain what you do for a living?

LEON: Look, kid, listen closely. I try to solve some of the mysteries--things we don't understand--about the world. We want to understand how the universe works, why things happen the way they do. We work on little pieces at time. Sometimes we have a simple problem, like how did the world begin. Now, Andrei's the expert on that, but there are a lot of things he has to know first. 

ROBERT: I heard you were there at the beginning.

LEON: I was there, that's right. I'm here because I was there. I knew the Dead Sea before it was even sick…. But to answer these questions it's important to have evidence. We do know that the universe began and at the beginning it was all particles, and particles are what we do in our laboratories. I do my research at Fermilab, thirty miles west of Chicago. Everybody's invited, it's an open lab, and scientists from all over the world come to address issues having to do with the most primordial building blocks of matter and energy. A city might be made of bricks and cement, but what are the bricks and what is the cement? A library is composed of books, but the books are composed of letters and the letters, ultimately, are composed of [information] zeros and ones. There are rules by which you put the zeros and ones together to represent the letters, and rules of spelling to make the words, and rules of grammar to make the sentences of all the books in the library. My job is to ask, What are the zeros and ones of our universe?

ROBERT: Steve, your research interests at Caltech are very broad, ranging from nuclear astrophysics to global climate change. What's so special about quantum physics and what are some of its practical applications?

STEVE: There are many incredible things about quantum mechanics, and one of them, at least to me, is that it really works. It's the theory of the universe. It describes what's happening here on earth and what's happening across the whole cosmos. When we think about how those building blocks that Leon just mentioned fit together to make the world around us, we use quantum mechanics to describe [the nature and behavior of] nuclei, atoms, molecules, and light. Because quantum mechanics is the theory of the world, it's not surprising that we see everyday occurrences and applications: for example, the lasers used in compact-disc players, or the MRI images of medicine. The lines of research that lead to developments like these began decades ago with basic quantum science. 

ROBERT: Chuck, your teaching at UCLA is interdisciplinary, and you integrate the physical sciences with the biological and social sciences. How do your undergraduate students from other disciplines deal with fundamental physics?

CHUCK: Well, it's a lot of fun. We take the sorts of things you've been discussing and try to communicate that excitement to a broad group of undergraduates. One course I particularly enjoyed recently was an honors collegium--a seminar entitled "Science and the Human Condition," which I taught with two biology professors, one from molecular biology and one from genetic evolution. The question that framed the course was "Where do we come from and what are we?" We started with the beginning of the universe and proceeded through the formation of the heavy elements in supernovae [exploding stars], the formation of our solar system, the evolution of life on earth, and on up to human beings. It's fascinating how those heavy elements, formed under such extreme conditions, are absolutely essential for life.

ROBERT: Could you relate that to quantum mechanics?

CHUCK: Quantum mechanics is everywhere throughout this whole process.

ROBERT: Andrei, quantum cosmology theorizes about the role of elementary particles in the early universe. How can stuff so unfathomably minuscule have affected something that is now so unfathomably gigantic?

ANDREI: Years ago it would have seemed impossible that quantum mechanics could have any relationship to the universe, because quantum mechanics is supposed to be important for only very, very small particles. Well, over the last twenty years the study of cosmology has changed. To the standard Big Bang theory we are now applying something else, called inflationary theory, which claims that the entirety of the universe began from a tiny spot smaller than an elementary particle and then expanded incredibly fast. In analyzing this expansion, small quantum fluctuations, though initially invisible, become huge and build galaxies--and they are continuing to build different parts of the universe.

ROBERT: So the quantum mechanics of elementary particles, the smallest things there are, is directly responsible for creating the entire universe and its macrostrucure, the largest thing there is.

ANDREI: Yes. Indeed, you can't understand galaxy formation if you don't understand quantum mechanics.

ROBERT: Today, particle physicists look to cosmology almost as a virtual experimental test of quantum mechanics. Greg, you've studied exotic areas of astronomy, like quasars, the extremely distant and incredibly energetic objects thought to be the nuclei of very young galaxies, but you're also a poet. How does the poet, not the physicist, see quantum physics?

GREG: Well, think of quantum mechanics as being like a French impressionist painting--luminous, vibrant--of, say, a cow, but the miracle is that real cows give milk. Painted cows don't. The universe is better than any metaphor we can imagine, even though we trade in them.

STEVE: To quote an old song, "There's nothing like the real thing, baby."

GREG: Right. And you were asking how we can explain the huge universe with tiny quantum mechanics, which acts only on very small scales, but you have to remember that once the universe was extremely small, too. As I said in a poem once, "All that bang and sass/ Beneath an eyelid's underpass." Everything was once ruled by quantum mechanics, not the categories of physics we exaggerated chimpanzees are used to today. Sticks and stones are OK if you're hunting down game on the African savanna a million years ago, which is when our physical ideas began. But they're crude approximations when you go down the scale to where physics does its heavy lifting. So we say that an electron is like a particle--a stick or a stone--and it's also like a wave, which in fact means that it's neither of these. It's something for which we don't have a good category. It's as if quantum mechanics is saying to us, you humans may be great chimpanzees, but you're not ready for prime time as far as our metaphors go.

LEON: I just want to add that particles are studied in large accelerators, which the media calls atom smashers. The Big Bang was an atom-smashing laboratory with a totally unrestricted budget. (That's the budget we'd like….) Out of that lab came the beginning and all subsequent events--oceans roiled, and out of oceans things crawled, and eventually here we are, wondering how the universe began. 

ROBERT: Leon, define a quantum. Remember, I'm still your grandchild.

LEON: Yeah, I know--go clean your room…. Quantum theory characterizes the difference between the subatomic world and the common world we know--the classical world that was clarified by Isaac Newton in the seventeenth century. Quantum mechanics began in the 1920s, and what it showed is that nature prefers discreteness to continuity. Things come in pieces. The word "quantum" arose from a study of electromagnetic radiation. When you heat up a body, it radiates energy, and around 1900 that radiation was discovered not to be smooth--zzzzzzzzzz--but to exist in discrete packets.

ROBERT: ch, ch, ch, ch, ch.

LEON: That's very good--a terrific simulation of quantum theory. There are so many of these packets, these radiating pieces, that collectively they give rise to what looks like a continuum, a smooth beam of light, whether from the sun in our sky or lightbulbs in our living rooms. But when you get down to individual processes within individual atoms, these are discrete events. Envision an atom as a flight of stairs, with nothing in between each step.

ROBERT: You're either on one step or another, never in between. Everything happens in steps or pieces, and each distinct unit of energy is what's called a quantum. 

LEON: That realization utterly changed our view of the world. The quantum world is very different from the world we know. Everything we see is composed of billions and billions and billions and billions of atoms, and this is what makes for the apparent smoothness. If you were to watch from afar someone pouring a stream of fine sand from one bucket to another, the stream of sand would look like a liquid--a continuum--to you; but if you got close enough, maybe with a magnifying glass, you would see tiny, discrete grains. And it's an understanding of the nature and behavior of those grains that has so remarkably changed our view of the microworld.

STEVE: One of the beautiful aspects of quantum theory is how this discreteness, or quantum nature, merges eventually into the classical behavior that we see all around us. It's the so-called "semiclassical regime," where, instead of things just becoming smooth, what actually happens is these discrete units oscillate faster and faster, so that the average of all of them melds into the familiar laws of Newton.


ROBERT: Let's talk a little about probability in quantum physics. You've written papers on what's called Monte Carlo simulations. Are you a gambler?

STEVE: In many senses, scientists are gamblers in their work. But here's the story on Monte Carlo. One of the things that quantum mechanics tells us, beyond the fundamental discreteness of nature, is how particles travel. If I'm a particle, and I want to go from here to there, Newton [and common sense] would advise me to go in a straight line. But what quantum mechanics does is to let the particle explore all possible paths from here to there--[Caltech physicist] Dick Feynman was the first to express it this way. So the particle can go in a straight line, or it can take a big curve, or it can follow zigzag paths, and so on. If you want to model such uncertain routing, it's impossibly hard, even in a computer, since you'd have to count up all those innumerable possible paths, adding this one and that one and on and on--because in quantum mechanics the particle takes all of the paths, and you can't tell which one it actually took unless you measure it. So we choose those paths at random with a computer. First we take this one, then that one, then another one in a very random way. We can't take them all, but if you judiciously choose a few, you can get the total effect. It's like taking a poll of only a few voters to predict the outcome of an election. 

ROBERT: So you have a probabilistic analysis of what happens in the subatomic world, which seems totally different from the apparent certainties of the real world.

STEVE: The subatomic world is the real world. It's just that our everyday experience is an imperfect image of it.

ROBERT: Good point. Leon, why is quantum mechanics spoken of as "spooky"?

LEON: Oh, it's very spooky. First of all, probability by itself is spooky. Let me illustrate how probability enters the system. You walk past a store window and see an image of yourself reflected there--hmmm, you're looking good, for a man of your age. The guy in the store window who's arranging the mannequins sees you at the same moment that you're seeing yourself. What's happening here? A stream of photons from the sun bounces off your face, heads for the window--let's consider a single one of those photons. It has a choice: it can go right through, so that the guy behind the window can see you, or it can be reflected back from the window and into your eye so that you see your own reflection. So some fraction of the innumerable photons are reflected, and some fraction go through. What determines the fate of each particular photon? Countless such examples have taught us that the outcome [for each photon] is random, it's a throw of the dice, and that's what led to Einstein's famous statement that he didn't believe that God plays dice with the universe.1 

{FOOTNOTE}1 Einstein apparently made several references to dice, such as a remark to Niels Bohr: "You believe in the dice-playing god, and I in the perfect rule of law." Alice Calaprice (in "The Quotable Einstein") quotes from an Einstein letter to Cornelius Lanczos, one of his biographers: "It is hard to sneak a look at God's cards. But that He would choose to play dice with the world...is something that I cannot believe for a single moment." And in a letter to Franck: "But that there should be statistical laws with (in)definite solutions, i.e., laws that compel God to throw dice in each individual case, I find highly disagreeable." {/FOOTNOTE}

At every instant, for that single object, for every quantum object, we have probability; we do not have certainty. That gives us an indeterminate world, which in some sense frees us from the old classical world of Newton, where everything is predetermined, everything goes according to forces and positions, so that in principle the entire world could be predicted by some all-knowing mind or super supercomputer. In classical theory, if you knew all the data, you could toss a coin and predict the outcome with certainty. But now we know that's not so. There is a fundamental quantum nature that in some sense frees us from this determinism.


ANDREI: Well, I do not quite agree. The question is about free will. Classical theory says that everything is determined by something that happened in the past, even a million years ago. Quantum theory says that you can never know for sure what will happen in the future. But nothing is determined by anything other than your past. So if your will is not completely determined by things that were before [i.e., because of the uncertainty of quantum mechanics], but it is not determined by anything else, then you can't have free will unless you assume that your will (and your consciousness) is something separate and additional, that it has its own degrees of freedom.
ROBERT: What's fascinating is how quantum mechanics has the broadest applications, from the beginning of the universe to the freedom of the will to the lasers at your supermarket's checkout counters. We're not talking about something esoteric here, but something that affects everything that has to do with human life. Yet it has all these tortuous problems.

LEON: Scientists wrestled with these terrible problems through the 1920s up to 1930. Real data was coming in from the atom; finally they realized that here was something absolutely new and counterintuitive to human experience. Most experimentalists appreciate the fact that it was the experimental data which we had to rub in the faces of these itinerant theoretical scientists like Einstein. At times, some of those theorists would say, "We're going to get out of physics." [The Austrian-born particle physicist] Wolfgang Pauli once said, "I'm going to go and become a stand-up comic, because this business doesn't make any sense." 

ROBERT: And quantum mechanics is one of the most remarkable achievements of human endeavor.

LEON: Absolutely!

STEVE: And very beautiful.

CHUCK: This is where much of the beauty comes from. We were used to a relatively rational, understandable world of Newtonian mechanics, and then quantum mechanics came along. It's down underneath everything else. It's bizarre, it's elegant, it's mysterious, it's surprising. It's all these things and yet it really works.

ROBERT: How do you differentiate between elegance and beauty? 

LEON: I'll take a shot at that. Quantum mechanics is elegant, in that it is a wonderful solution to incredibly difficult experimental data that looked contradictory. As for beauty...hmmm. Well, when you see someone else's theory and you don't like it, you say, "Boy, that's a beauty!"

STEVE: I think elegance is economy of expression. It's being able to write down a short, fundamental equation that can express and predict all these implications that we've been talking about [such as the Schrödinger equation for quantum mechanics]. That's elegance. Beauty is when you work out the implications and it matches what we see in the real world.

CHUCK: Beauty is also mysterious.

STEVE: Right. A different dimension.

LEON: Beauty is in the eye of the beholder. A theorist's theory is beautiful; it's his child, it has to be beautiful.

GREG: Truth is beauty; beauty is truth.

ROBERT: Let's apply some beauty and elegance to what's known as the Standard Model--that is, our current understanding of the elementary particles and the fundamental forces, or interactions, of nature. There are four of these interactions: the strong nuclear force, the weak nuclear force, the electromagnetic force--those two unified as the so-called electroweak force--and gravity. Gravity has not yet been incorporated into the Standard Model. So let's define each of these. Gravity I think people know about--the attraction between masses. Gravity structures the universe, from the shapes of galaxies to the earth's orbit around the sun to keeping our feet planted firmly on the ground. It's the easiest one to describe but the hardest one to explain; in fact, the Standard Model has to pretend that gravity doesn't exist. How about the electroweak force?

CHUCK: The electroweak force combines, in a very elegant theory, the electromagnetic interaction--which is manifested by both electricity and magnetism--with the weak nuclear interaction, which governs the kind of radioactivity known as beta decay [in which a neutron decays into a proton, an electron, and a neutrino]. The weak interaction, which is the hardest one to grasp, describes what happens when a particle decays and it disappears, and in its place two or more new particles appear. The sum of the masses of the new particles is always less than the mass of the original particle.

ROBERT: Research in radioactivity first suggested the existence of the weak interaction.

CHUCK: As for the strong force, this is what binds the quarks together inside nucleons--that is, the protons and neutrons in atomic nuclei--and holds the nucleons themselves together in the nucleus. The theory of the strong force is known as QCD, for quantum chromodynamics. 

ROBERT: Now let's define quarks, which are fundamental components of the Standard Model. 

STEVE: As far as we know, quarks are the most elementary building blocks of protons, neutrons, mesons--the stuff that makes up most of the matter in the universe.2 

{FOOTNOTE}2 A proton consists of two up-quarks and one down-quark; a neutron consists of one up-quark and two down-quarks. The existence of quarks was proposed in the early 1960s, by Murray Gell-Mann, then at Caltech, and independently by George Zweig, then at CERN (the European Center for Nuclear Research, in Geneva). Gell-Mann named them, borrowing the quirky term from a phrase in James Joyce's novel Finnegans Wake,"three quarks for Muster Mark." Quarks are extremely small, occupying a minute fraction--perhaps only a billionth--of the volume of the particles they comprise. No one has ever observed a free quark, because they are inextricably bound inside their protons, neutrons and other particles, but there is strong evidence for their existence.{/FOOTNOTE}

ROBERT: How many kinds of quarks are there and how do they bind together?

STEVE: Six. They come in six flavors, which we've named down, up, strange, charm, bottom, and top--well, "flavors" here simply mean different kinds--and three colors: red, green, and blue. "Color" here doesn't mean real colors, of course; the term is simply an analogy with the way the primary colors mix to make real colors. Quarks have charges of 1/3 or 2/3 that of an electron [which has a negative charge of -1] or a proton [which has a positive charge of +1], and thus quarks can be positive or negative. They have spin; they whirl around like little tops, and the spin is characterized as "up" or "down." The quarks are bound inside the proton or the neutron by quantum chromodynamics. QCD is very interesting, in that we think we understand the theory but we can't make it explain how the strong force attraction between the quarks actually works. Although we use the term gluon to describe what is exchanged to effect this interaction among quarks, we don't quite know how they hold the stuff together.

ROBERT: Now we come to what is called the Theory of Everything, or TOE. What do we have to do to get it?

GREG: Wow, lots! You have to stitch all of this fabric together and somehow make a suit that people want to wear. I don't work in the field, and so I'm sort of an informed skeptic about it. The current hot topic, of course, is string theory.3

{FOOTNOTE}3 String theory is the most viable candidate for a Theory of Everything. Based on complex abstract mathematics, string theory claims to integrate gravity with the Standard Model and general relativity with quantum mechanics. It replaces the numerous pointlike particles with ultra-tiny strings, coils or loops, whose vibrations are manifested as particles--something like the way musical vibrations are perceived as distinct notes. The way these vibrations occur is through compacting or curling up six extra dimensions of spacetime--a state difficult to imagine and impossible to visualize--in addition to the usual four dimensions. The size of the strings would be at the (effectively invisible) scale of quantum gravity, which is about 10-33 centimeters. There are many string theories, each targeted at separate phenomena, and an attempt to combine them all is known in some quarters as M Theory, as in "the Mother of all theories."{/FOOTNOTE}

LEON: Four of the principal string theorists came out of Princeton. They were four great guys, and they're known as the Princeton String Quartet.4 

{FOOTNOTE}4 David Gross, Jeffrey Harvey, Emil Martinec, and Ryan Rohm {/FOOTNOTE} 
GREG: String theory is certainly the most complex physical theory ever advanced. And you can tell, because all these brilliant people are having a visibly difficult time with it--which is encouraging, since a really great theory that tells us everything ought to be really hard; it shouldn't come to one person in a weekend. It's the best clue that we may be on the track of something large. But what we're on the track of is still very mysterious. The idea that particles are not little dots but strings that vibrate sits at the core. Of course, that's another chimpanzee metaphor. But the implications are huge: it goes from Andrei's cosmology to the fundamental way you glue all these particles together.

LEON: The Standard Model is a powerful theory that explains all the data coming out of all the accelerators since Galileo dropped those two students--one fat, one thin--off the Leaning Tower of Pisa. But one of the problems with the Standard Model, as we've touched on, is that gravity has not been incorporated into it gracefully. And the Standard Model itself is ugly. Six quarks, three colors each; six leptons [the electron, the muon, the tauon, and their neutrinos]; the bosons, or force carriers, like the photon and the gluons. The Greeks promised us aesthetic simplicity, a beauty and an elegance that we don't have. We can't even fit all these particles on a T-shirt.

CHUCK: But the Standard Model is incredibly elegant compared to what preceded it in the 1960s, which was a mess.

STEVE: And it's a powerful synthesis of many phenomena and data. 

LEON: We want a T-shirt embroidered with one thing, or group, that does everything.

CHUCK: That's TOE.

STEVE: You know, we've seen this pattern repeat over and over in science. Look at the periodic table. In the nineteenth century, when people were organizing the elements, it was a mess all right. There were ninety or so elements, and you really couldn't understand this, and there was certainly nothing you could put on your T-shirt. And then came the periodic table.

LEON: The Standard Model is the physicists' version of the periodic table. And we know that there's something simpler, some underlying simplicity or unity. We're looking for missing pieces, like the Higgs particle, or the Higgs boson, and we tried to build this humongous machine [the Superconducting Supercollider] in Texas in order to find it--but the Congress didn't let us. Scientists must rededicate themselves to a massive effort at raising the science literacy of the public. Only when citizens have reasonable science savvy will their congressional servants vote correctly. But we'll eventually come to terms with something that must be simpler than the Standard Model. Our belief in simplicity and elegance, which has not disappointed us over the centuries in which we've done good science, tells us there's better to come.

ROBERT: Why should the public fund this search?

LEON: Oh, well, because it's beautiful, because it's elegant, and because we want to know, to understand, something about the world we live in. And because, according to some absolutely closer-to-truth testimony I gave before Congress, quantum mechanics accounts for 37.9 percent of the gross national product, or some number like that.

ROBERT: Thanks for the plug, but how do you get that percentage?

LEON: Well, I made up the number, but it's plausible. You get it by tallying up what we have thanks to our understanding of the quantum theory. Without that understanding, we would never have had transistors and therefore microprocessors, and the whole microelectronics revolution wouldn't have taken place. Our computers wouldn't be what they are. The biotechnology revolution was catalyzed by Watson and Crick's discovery of the structure of DNA in 1953, which was stimulated by a book by [Austrian physicist] Erwin Schrödinger on the quantum theory of large molecules. The core products of twenty-first-century technology--electronics, computers, biotech--all relate directly to an understanding of quantum theory. 

ROBERT: Steve, let's look deeper into the bizarre essence of quantum mechanics. Tell us about "Schrödinger's Cat."

STEVE: There are a lot of bizarre things, and people work hard trying to understand them. One of them is that although we know that subatomic particles exist only in discrete states, they can exist in several of those states at the same time, and only when you look at them--that is, take a measurement--do they collapse into a single state. Schrödinger's Cat is a famous thought experiment [conceived, in a moment of frustration, by Erwin Schrödinger, whose famous equations form the foundation of quantum mechanics]. You put a cat in a box with an capped bottle of poison gas and close the box. You can't see inside it--and you don't peek. There's also an apparatus in the box that will uncap the bottle of poison gas--and thus kill the cat--but only if one particular radioactive atom in the box decays. Quantum theory dictates that this atom must exist simultaneously in two states--that it is both "decayed" and "not decayed" until it is measured. But since you can't do this measuring without opening the box, while the box remains closed, the cat must be both dead and alive at the same time. And you don't know which one it is, not even in principle, until you open the box to check it. 

ROBERT: But is the cat alive or dead?

STEVE: It's neither… and both. While it's in the box it's in some combination of both, and only when you do the measurement--when you open the box up and look, thus collapsing the atom's dual state into one state, "decayed" or "not decayed"--does the cat become alive or dead. The point is that the cat does exist in those two states until you open the box-- and only when you open the box up will probabilities determine whether the cat is actually dead or alive.

ROBERT: Leon, does that make any sense?

LEON: It doesn't make any sense. It's one of the bizarre features that derives from the fact that quantum mechanics denies the possibility of knowing, for example, how a particle moves from point A to point B. If you try to find out by experiment, you spoil the experiment. It's like trying to measure the precise temperature of a small cup of water by taking a big, fat, hot thermometer and thrusting it into the cup, splashing out the water and heating it--you'll never know the original temperature. Denying the possibility of knowing how a particle goes from A to B leads quickly to the notion that it has no path between A and B, and then the mathematics says to try all paths. But fundamentally we can't know, and therefore we deny the reality of the particle's transit from point A to point B--and that's bizarre. Einstein never accepted the fact that we can't know the particle unless we look at it. He asked, "Does the moon disappear if we don't look at it?" Well, the moon is a macroscopic object, as is the cat. In quantum mechanics, we sort of accept the notion that since we can't predict the properties of a particle, we give up the possibility that it has those properties--until we measure them. But requiring the intervention of human consciousness is very upsetting to scientists.

ROBERT: Andrei, if we don't look at the universe, does that mean it doesn't exist?

ANDREI: This is one of our main challenges. With Schrödinger's Cat, the question is whether the cat was really dead or really alive before we opened the box. The answer that quantum mechanics gives you, as Steve [Koonin] said, is that it was neither dead nor alive--at least in the standard Copenhagen [Bohr-Heisenberg] interpretation of quantum mechanics. Now assume that when you open the box you see that the cat is dead, then the most you can say is that everything looks as if the cat was dead before you opened the box; or if it is alive, you can say that everything looks as if the cat was alive before you opened the box. So when you look at the universe, the maximum that you can possibly say is that everything looks as if the universe has existed for some billions of years.

ROBERT: But it may not have?

ANDREI: Oh, it may not have, and that's the main challenge. You think you are describing reality, but then the whole concept of reality becomes dependent on an observer--which brings you to the nature of consciousness, and this is something dangerous.

LEON: The problem gets worse if you say, "I'm not going to look in the box, but I have a camera that takes a picture inside the box." Now what happens to the cat? Say the film isn't developed? Or if the film is developed, it's viewed only by a computer? Quantum mechanics leads to incredible conundrums.5 

{FOOTNOTE}5 In a talk at Caltech, Sidney Coleman of Harvard continued the serious fun. Suppose you look in the box and see that the cat is alive, but you're alone in your lab. You want to tell someone, but as you reach for the phone you have a heart attack and die. Is that cat now back to being alive and dead at the same time? A joke, half a joke, or both a joke and not a joke, depending on whether you were the one looking in? {/FOOTNOTE}

STEVE: So you can see why people got all tangled up when they tried to understand or interpret what was going on.

LEON: We should emphasize that almost all working physicists ignore these questions [and just get on with their calculations, which consistently say that quantum mechanics is right].

ROBERT: Greg, I'm asking the science fiction writer, not the physicist: Why is reality structured this way? 

GREG: Why is the world the way it is? Gee, give me an easy one. We have simple categories, analogies, and metaphors that we make about the world, but the world is more sophisticated than we are--and in fact it's alien, it is truly strange. That's really the essential message of quantum mechanics--that there is a strangeness to the world and it does not respond at every level to our chimpanzee categorizations of it. It's as if you were viewing wonderful French impressionist paintings at a museum, and then you slowly discovered that the paintings changed in response to whether or not you were looking at them. That's how strange quantum mechanics is.

ROBERT: But all this very indeterminate small stuff we study yields all this very ordinary stable stuff we see.

GREG: The world isn't as ordinary as you think. We just get used to it, and we don't inspect the stuff that's really strange.

ANDREI: And also, when you ask this question you are assuming that the world is everywhere the same. But in fact our new theory of inflationary cosmology tells you that our universe must be incomprehensibly huge, and it may be divided into many many regions, all of which may be absolutely different from one another. So there are some regions where the world is absolutely bizarre and you cannot live there, and there are some regions where everything is ordinary and you can live there. That's why you can have science.

ROBERT: And since we can only be conscious where we can be alive, then that's the only kind of universe we can observe.

ANDREI: Right.

LEON: Yes, but once you understand the processes and the confusion and the indeterminacy, understanding leads to control. Everything is made of molecules, and molecules are made of atoms. We can zoom down into atoms and examine their properties. So we learn that electrons in a certain kind of atom can move around in a certain kind of way, and out of this can come the invention of a transistor. And even some of the most bizarre consequences of quantum theory can be used in the frontier work of quantum computing, which [because of the opportunities for parallelism] will be unimaginably more powerful than anything we have today.

STEVE: I think we'll see a quantum computer in the next ten to twenty years. We don't quite know how we'll make it, whether with atoms or with the spins of nuclei, but we will make it.

ROBERT: Won't quantum computers be limited to certain kinds of problems?

STEVE: Well, they'll probably solve all kinds of problems, but they'll be most efficient and effective for a certain class of problems, at least as we understand it. For example, the factoring of large numbers--decomposing 6 into 2 x 3 but amplified to hundreds of digits.

ROBERT: So someone with a quantum computer can eventually steal my credit card?

LEON: My grandson can do that now.

ROBERT: It's not worth stealing. A prediction please. A hundred years from now, will there be a Theory of Everything that will be complete, unassailable, and forever immutable.

LEON: Immutable? Yes.
ANDREI: No, I don't think so.

CHUCK: Yes, I do think so. Look at how far we've come in the last hundred years.

GREG: I believe so, but remember, even a Theory of Everything won't actually tell you everything.

LEON: Not how to avoid a traffic jam in Chicago or cure the common cold. 

ROBERT: Or why you wore that tie.

STEVE: I think we'll have a Theory of Everything to account for what we now observe. But it's likely that we will observe new things that won't quite fit into that theory, and then we'll be back to where we are right now. That's one of the joys of science.

ROBERT: So there'll still be a purpose for this show.

STEVE: Indeed, we'll always be trying to get closer to truth.

ROBERT: CONCLUDING COMMENT

THE great mystery of quantum physics is that it works. Really weird stuff at the subatomic level forms rather ordinary stuff at the human level, so that the uncertainties and probabilities of the quantum world produce the certainties and absolutes of our normal world. The experimental data is now overwhelming in its scope and captivating in its elegance. Quantum physics is simply the way everything had to be, explaining the behavior of the small zoo of subatomic particles that make up the atoms of the hundred or so elements that in turn make up an unlimited multiplicity of molecules. But the Standard Model remains incomplete: gravity must be integrated with the strong nuclear and electroweak forces to yield a Theory of Everything, the Holy Grail of physics. The best current idea drops down a level lower and envisions seemingly mystical, minuscule strings, all wrapped up in ten dimensions, whose vibrations may make the universe sing. It gives a chill to reach so deeply into reality. But quantum physics has made people queasy from its inception. If you're unconvinced of its truth, don't feel bad--you're in good company. Albert Einstein never accepted it either. Which just demonstrates how very difficult it is, sometimes, to get closer to truth.

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