Superstring theory, Brian Greene's web site explains, "purports to give us our first sensible theory of quantum gravity as well as a unified theory of all forces and all matter."
In The Fabric of the Cosmos, Greene takes readers into a world where time doesn't flow and the three dimensions we recognize exist among more than twice as many that we don't. Where does such a world exist? All around you, if string theory proves to be true.
To catch up: In 1905 and 1915, Albert Einstein published two relativity theories that revolutionized our understanding of the universe: space and time were not independent and absolute, as Newton had asserted; in fact, space and time are inextricably connected. Almost a century later, string theorists believe Einstein only scratched the surface. If experiments at the Large Hadron Collider under construction in Geneva confirm their calculations, as Brian Greene and many others hope, "space and time will dissolve away into more fundamental ideas."
What does all this mean? Ask Greene, cutting-edge physics' main interface with the public. A New York native, the Columbia University professor of physics and mathematics has lectured in dozens of countries to general and technical audiences alike. In 1999, he published the Pulitzer Prize finalist The Elegant Universe, and last year he reached an ever larger audience by hosting a television documentary of the same name.
"Greene [has an] unparalleled ability to translate higher mathematics into everyday language and images," Publishers Weekly raved in a starred review. "He not only makes concepts clear, but explains why they matter."
Brian Greene: There are two parts to the answer. The first is that, indeed, while writing The Elegant Universe I found that I had to exercise a great deal of restraint to not allow two supporting characters to take over the entire discussion. Those supporting characters were space and time, themselves. There are so many wonderful features about space and time that we've learned in the last few decades, but they would have been a diversion from the story The Elegant Universe was trying to tell—namely, the search for the unified theory. It became clear to me that there was another book I needed to write in which space and time would become the main focus.
But I guess the second part of the answer, which I would emphasize, is that you don't need to read The Elegant Universe to read The Fabric of the Cosmos. It's not a follow-up in the sense of a sequel. In many ways, I would suggest reading The Fabric of the Cosmos first because I think the level of difficulty is more constant, whereas The Elegant Universe gets steeper as you go along.
Dave: I wondered about that. Readers approach your books with a wide range of physics and math backgrounds—from extensive backgrounds to none at all. As you're writing, then, you have to reiterate a lot of the basic principles, albeit in a different way for each book. You can't just drop readers into the middle of the story.
Greene: One review of The Elegant Universe, I think it was by George Johnson, said that people who write popular physics books are constantly encumbered by the fact that they have to cover certain essential basics in every book to make them self-contained. It was as if, he said, in every book about baseball you had to lay out the rules of the game in the first hundred pages.
It is a challenge from that point of view. You do want the book to be completely self-contained, and that does mean that similar ground rules need to be set up in order to explore the new ideas that book is dedicated to. In this book, my task was made easier because questions like "What is space? Is it real?" and "What is time? Is it just something the human mind imposes on reality?"—these questions allowed me to cover the basics of relativity and quantum mechanics in a very different way than I covered them in The Elegant Universe. From that point of view, I think the discussions are complementary.
Dave: String theory supposes that the world has eleven dimensions— not three or even four, but eleven. That concept is extremely hard to grasp on any intuitive level. Do we have to reconsider our entire idea of what a dimension might be in order to begin to understand?
Greene: I don't think you need to consider what a dimension is, but you do need to think it through very carefully because everyday experience can make you feel pretty blasé about ideas that prove critical in developing these theories.
By dimension, we simply mean an independent direction in which, in principle, you can move; in which motion can take place. In an everyday world, we have left-right as one dimension; we have back-forth as a second one; and we have up-down as a third. Any direction in which you walk is some combination of motion in those three dimensions. Now, string theory comes along and says there literally are more. And I don't mean something that's in between left-right and up-down; I'm talking about a direction that is not encompassed by the three that we just mentioned.
I agree with you: it is very hard to picture. I cannot picture it in my mind. I can use equations to describe it and I can use analogies, as in the book, to try to get a feel for it, but if you ask me, literally, can I picture eleven dimensions? No, I can't.
Dave: Six of these dimensions are ultramicroscopic Calabi-Yau shapes or spaces. You describe these extra dimensions as being "tacked on to every point in the usual three dimensions." How can one dimension—or six, in this case—exist within every part of the other, more familiar dimensions?
Greene: The best way to explain is to work by analogy. Consider a very long drinking straw. The straw's surface has two dimensions. If you were a little ant on the surface, you could move left-right along the length—that's one direction—or you can move clockwise-counterclockwise around. Those are the two dimensions on the surface of the straw.
If you think about it, the straw itself can be described as though it has one long direction, the left-right one that we were just talking about. Now, at every point along its extent there's a little circular direction tacked on, the circular girth, the circular part of the straw itself. That's an example where you have one big direction with a tiny circular direction tacked on at every point.
We want to generalize that to imagine that we have three big dimensions in the world around us; they're like the length of the straw. But at every point in our three dimensions there are these six extra ones that are tacked on, much like that circular part of the straw is tacked on at every point along its length.
It's totally elusive, but if you consider the everyday example of the straw, with the long part and the circular part tacked on at every location, that really is what we're talking about. It's just harder to picture.
Dave: Physicists have never been able to prove that time actually flows. That it's moving.
Greene: In fact we seem to come to quite the opposite conclusion.
Dave: Toward the end of The Fabric of the Cosmos, you mention a theory in which time is cycling around and around.
Greene: That's a possibility, too. Again, I think the spatial analogy is a good one. If you are walking in a circle, you repeatedly come back to your starting point over and over again. That's a circle in space. Now imagine a circle in time, where time elapses and at the end of the temporal period you find yourself back at the moment of time from which you initiated your journey.
Again, it is thoroughly unfamiliar, and that's why it is so hard to wrap your mind around this kind of idea. We don't even know if it's right, but it is one of the ways in which time may behave in the context of these cutting edge theories.
Dave: A few months ago, in an Op-ed piece for the New York Times, you wrote that it was inevitable that "time and space would be rendered secondary, derivative features."
Dave: How long has that concept been floating around?
Greene: It's really gained some prominence in the last decade, the last ten years.
Dave: Specifically due to string theory?
Greene: I think string theory initiated that way of thinking. There's another approach to that discussion at the very end of the book called "loop quantum gravity." It's a competitor of string theory, but it comes to the same conclusion: that it's likely space and time will dissolve away into more fundamental ideas.
Dave: Given that it is extremely expensive, and therefore restrictive, to test these theories through experiment, whereas physicists can play with math under any conditions, is there a point where theory will run so far ahead of experiment that these concepts will be more like philosophy than science?
Greene: I don't think so. Very much, string theory is simply a work in progress. What we are inching toward every day are predictions that within the realm of current technology we hope to test. It's not like we're working on a theory that is permanently beyond experiment. That would be philosophy. We are working on a theory that through every step of progress is coming closer to being tested, and in fact there are proposed tests today that could be carried out in the next decade, if we're lucky.
It takes a certain amount of optimism about parts of string theory that we haven't yet figured out, but there's actually a chance that these ideas will be tested in the next decade. I can assure you that no string theorist would be interested in working on string theory if it were somehow permanently beyond testability. That would no longer be doing science.
Dave: What about funding. I know they're building the collider in Switzerland, but clearly this is not happening in every back yard. What is the funding situation like in America today?
Greene: Fermilab in Batavia, Illinois, is basically our flagship accelerator today, and it has just been upgraded. There's a chance—a small chance —that it may be able to assist in the search to test string theory. It's not as strong as the accelerator that's being built in Geneva, therefore it will within the next few years be completely superseded. Whether we are competitive again with an experiment machine does depend on funding, and right now the funding is not there.
Dave: What role do the books you're writing and the NOVA program [The Elegant Universe] —the popularization of these theories and ideas, in other words—what role does this type of outreach play in the development? Not in the lab so much, but in terms of funding and the general perspective society brings to these efforts?
Greene: I don't know about the funding question. Maybe it helps. I haven't looked into it too closely, but I do think that having the general public understand your work is the first step toward having the general public behind your work.
When people learn about the wonder of these ideas, they get excited. They get fired up. And look, we should be funding things that people are excited about in science, right? It's American tax dollars, so certainly we should be funding things that the American people have some access to and that they find interesting and exciting. I think that the work we're doing fits both of those characteristics.
Dave: In the new book, many of your analogies allude to The Simpsons, The X Files, and other television shows. Did you find that those popular references suited the subject more this time around?
Greene: The material seemed to lend itself to it. To tell you the truth, when I first started writing Fabric of the Cosmos I anticipated not having any characters at all; I'd sort of used that approach in The Elegant Universe. But, as I was writing, it seemed there were moments in my text that were ripe for irreverent, unexpected moments where, say, Bart would come on the scene. It just organically emerged in the writing process, so I went with it.
Dave: I also noticed a nod to The Simpsons in the NOVA program. Are you a long-time fan?
Greene: I like The Simpsons quite a lot. I love the irreverent character of the whole show. It's great.
Dave: In Fabric of the Cosmos, you describe a game you played with your father as a boy, a game about perspective. I was wondering if you could talk about that a bit. In retrospect, it seems very much a foreshadowing of the physicist-to-be opening his mind to scientific inquiry.
Greene: Without a doubt. My dad was a composer and a musician, but he never finished high school. His formal education was rather minimal from the standards of today's college graduates and Ph.D.'s, but he had a deep interest in questions of science and questions of the universe. One thing that was very important to him was to have your mind open to a variety of points of view so you didn't get stale in your thinking.
The game that you're referring to jumped off from that goal. We'd walk down the streets of Manhattan, and one of us would refer to something that was happening in the world around us. The examples I give in the book are a coin falling to the ground or a bird in flight, something like that. Rather than describe what we see, the game amounted to us describing what we would be seeing if we were the coin falling to earth or what we would be seeing if we were the bird flying. We'd give the other person that description, and the challenge was for the other person to figure out the perspective of the description they were hearing.
It really forced you to not make your point of view, your perspective, the only one or the dominant one, but to have the flexibility of thought to put your mind into the point of view of something very unfamiliar.
Dave: You're operating as a professional physicist and mathematician; you've been schooled for this career. Have you been trained as a writer? Were you a big reader when you were young?
Greene: No, in fact I wasn't really a big reader growing up. I would read some things, but I wasn't one of those kids with a flashlight and a book late at night. For me, it was much more about playing with math, playing with numbers—that was the obsession, if you will. But I found that when I would lecture on this material, be it on a general or a technical level, that I was very comfortable articulating abstract ideas in a way that would be accessible to people who might not be expert in what I was talking about. I decided to try to take that comfort and see whether I could transfer it to the written word.
Basically, in the first book I sat down and started to write in the manner that I would speak when I was lecturing. I think that helped to give it a loose, conversational feel without straying too far from the scientific ideas, but I didn't know if it was going to work at all when I started. In fact, I didn't tell anybody that I was writing The Elegant Universe because if it didn't work out I just wanted to put it in a drawer and lock it up or just throw it away. But I found that it did seem to flow, and I decided to go with it. It worked out pretty well.
Dave: Does writing complement your research? How does it relate? You're still a physicist.
Greene: It both hurts and helps. It hurts because certainly it takes time away from just doing the pure research, although I do make an effort in the majority of the writing days to work in the evenings so I can do my research during the day. Though, you know, near the deadline it's hard to stay with that schedule.
The way that it helps is that it forces you to take a step back from the details of the science and really have a global perspective on the questions that have been answered and the questions that still need to be addressed. And to tell you the truth, The Elegant Universe showed me that issues of cosmology were pretty critical to string theory, and since the publication of that book my own research has shifted to cosmology. I think partly that shift did come from writing The Elegant Universe. In that way, it really helped give a sense of what the important issues are.
Dave: Do you have plans for another book?
Greene: Not now. I have vague thoughts about things that would be interesting or appreciated, but I certainly won't be writing again for a while.
Dave: On the other side, then, is there a particular focus of research that's on your mind?
Greene: Definitely. It's two things—actually, some of the stuff I wrote about in The Fabric of the Cosmos. I'm working hard to find out whether astronomical data, as opposed to atom smasher data, might give us insight into whether string theory is correct, the hope being that the strings could have left tiny imprints on the universe near the Big Bang, then through billions of years of cosmic expansion that imprint would be stretched out across the sky and all we need to do is figure out how to read the data appropriately.
So that's one thing that I'm working on research-wise. The other is to figure out what the basic entities that make up space and time actually are. The atoms, if you will, of space and time; researching to find those ingredients. It's my belief, and many others agree, that when we can delineate the elementary makeup of space and time themselves, that will be the moment of the next revolution in physics. That's what we're heading toward.
Dave: A famous analogy about novel writing compares the role of the author to a person driving a car: the novelist looks ahead at the unwritten story, always seeing just a short ways ahead, like a driver can only see as far into the dark as the headlights reach. In both cases, the farther forward you progress, the more that's revealed.
Science seems to work on similar terms. It's as if science keeps driving forward, seeing farther and farther into the dark. How far can you see at this point? What do you think people will be working on in a couple generations time?
Greene: It's tough to say. I do think that space and time will be the key enigmas for years, if not decades, to come, but once that is cracked I think people may be able to answer questions like How did the universe really begin? Where did it all come from? We still don't know. The ability to address these questions quantitatively, which I believe we'll be able to do in the next few decades, will be another major moment in human thought. We will perhaps have come to an explanation and understanding of how there is anything at all, why there is something rather than nothing—the great philosophical question. To make headway on that would be a major achievement.
Dave: And that goes back to the whole notion of time and space being secondary, derivative features. The question that immediately arises is, If time and space only exist in the aftermath of something like the Big Bang, what else is there?
Greene: I agree, and we don't know, but that kind of question is where we're heading. How amazing would it be to have an answer?
Dave: One of our programmers, Chris, wants me to ask how a particle, like a gluon or a graviton, exchanged between two other particles can impart an attractive force.
Greene: The issue Chris probably has is that when you throw a baseball back and forth it exerts a repulsive force; you catch the baseball and it kind of pushes you away from the person that threw it. But there's a problem with that image: it's not exactly what happens at the level of subatomic particles.
When a particle is exchanged between two objects or two other particles, it doesn't push the particle that receives it; rather, it communicates a message of how that particle is meant to move after receiving this message from the messenger particle, as we call it. If the message is "move away," it will exert a repulsive force; if the message is "come back together," there will be an attractive force. So rather than just use the analogy of a baseball thrown back and forth, perhaps also imagine that the two people playing catch are connected by rubber bands. One object, the baseball, can push them apart, but the rubber bands can pull them back together. Elementary particles can play both the role of the baseball and the rubber band in this context.
Dave: Are there particular questions that mysteriously don't get asked as you're conducting interviews or readings? Or do some points keep coming up again and again that weren't necessarily as obvious to you, maybe that you didn't anticipate when you wrote the book?
Greene: As for the first question, it seems that every possible question gets asked, stuff that relates to everything in the book. Is there one kind of question that comes up that I wouldn't have anticipated? I don't really think so. People seem to be reading it very thoroughly, and different people get excited or caught up in different aspects, be it entanglement or the arrow of time or the flow of time and so on. I don't feel that there's a stone unturned, nor do I feel that there are questions asked that make me stop and think, Whoa, where did that come from? In a sense, the questions are all what I might have anticipated.
Dave: Physicists often do their best work when they're young. Why might that be?
Greene: I think it's not that the brain is younger or more facile. I think it's really that people get stale. They work on the same thing for many, many years, and they lose the ability to look at it in a fresh way. That, for me, is for instance why I've recently shifted from working on the mathematical aspects of string theory, which I did for ten or fifteen years, to these cosmological aspects now. It's not a major shift, but it entails new material and new methods, which I think is how you stay fresh.
Dave: And in terms of presenting the material, you're teaching and you're writing and you've done some television now, too. What kind of challenges does TV present that weren't necessarily obvious from writing and teaching?
Greene: The main challenge that television presents is that I have a tendency to say things with a great deal of precision and accuracy. Often a description of that sort, which will work in a book because people can read it slowly—they can turn the pages back and so on—doesn't really work on TV because it interrupts the flow of the moving image. Although TV is fantastically useful in some ways, you do have to cut back on a certain level of detail.
On the other hand, there are things that would take me fifteen pages to write in words, whereas the right animation, the right visual, can communicate the idea in fifteen seconds. So it really goes both ways. It's just a different medium, that's the lesson.
Dave: I have another note here from Chris that I'll read to you. He says: "I'd never heard relativistic time dilation stated as a motion-through-time vector decreasing as a motion-through-space vector increased. That made the concept much easier for me to grasp. Thanks."
Greene: I appreciate it. That's one of my favorite little mnemonics for describing relativity. I think it really does capture it pretty well, so thank you.
This interview is dedicated to Mr. Oliphant, who introduced us to physics at Framingham (Massachusetts) North High School. We liked Mr. Oliphant so much we invited him to our end of the school year pool party, though regretfully, he could not attend.
Brian Greene visited Powell's City of Books on March 10, 2004.
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Books mentioned in this post
Dave is the author of Out of the Book, Volume 3: State by State