On the theoretical side, an outgrowth of inflationary theory called eternal inflation is demanding that the world be a megaverse full of pocket universes that have bubbled up out of inflating space like bubbles in an uncorked bottle of Champagne. At the same time, string theory, our best hope for a unified theory, is producing a landscape of enormous proportions. The best estimates of theorists are that 10500 distinct kinds of environments are possible.
Very recent astronomical discoveries exactly parallel the theoretical advances. The newest astronomical data about the size and shape of the universe convincingly confirm that inflation is the right theory of the early universe. There is very little doubt that our universe is embedded in a vastly bigger megaverse.
But the biggest news is that in our pocket the notorious cosmological constant is not quite zero, as it was thought to be. This is a cataclysm and the only way that we know how to make any sense of it is through the reviled and despised anthropic principle.
I don’t know what strange and unimaginable twists our view of the universe will undergo while exploring the vastness of the landscape. But I would bet that at the turn of the 22nd century, philosophers and physicists will look back nostalgically at the present and recall a golden age in which the narrow provincial 20th century concept of the universe gave way to a bigger better megaverse, populating a landscape of mind-boggling proportions.
Below is a wide-ranging Edge conversation with Lenny in December 2003 on the anthropic principle and on the early history of string theory:
The Landscape
What I mostly think about is how the world got to be the way it is. There are a lot of puzzles in physics. Some of them are very, very deep, some of them are very, very strange, and I want to understand them. I want to understand what makes the world tick. Einstein said he wanted to know what was on God’s mind when he made the world. I don’t think he was a religious man, but I know what he means.
The thing right now that I want to understand is why the universe was made in such a way as to be just right for people to live in it. This is a very strange story. The question is why certain quantities that go into our physical laws of nature are exactly what they are, and if this is just an accident. Is it an accident that they are finely tuned, precisely, sometimes on a knife’s edge, just so that the world could accommodate us?
For example, there’s a constant in nature called the cosmological constant, and it’s a certain number. If that number differed by the tiniest amount from what it really is, the universe could not have been born with galaxies, stars, planets, and so forth. Is it an accident that the number was exactly right to be able to form the universe as we see it? Or is it some feature of the way the universe works that makes it necessarily create life? It sounds crazy and most physicists think such thoughts are hogwash, but I’ll give you an example.
Suppose we lived on a planet and we couldn’t see out because there was too much fog and too many clouds. Suppose we wanted to know why the temperature on this planet is precisely right for us to be able to live without getting cooked and without getting frozen. Is it an accident, or is there a design involved? Most people, knowing the answer, would say that if you look out far away into the cosmos, you see all kinds of planets, stars, empty regions and so forth. Some of them are much too hot to live on, some of them are much too cold to live on, and some of them are in between but don’t have water. There are all kinds of planets are out there.
The answer is that we simply live on the planet that we can live on because the conditions are exactly right. It’s an environmental fact that conditions are exactly right, so it’s no accident that we happen to find ourselves in an environment which is finely tuned, and which is precisely made so that we can live in it. It’s not that there’s any law of nature that says that every planet has to be livable, it’s just that there are so many different things out there—roughly 1022 planets in the known universe, which is a huge number—and surely among them there will be a small number which will be at the right temperature, the right pressure, and will have enough water, and so forth. And that’s where we live. We can’t live anywhere else.
The question is whether our environment in a bigger sense—in terms of the laws of nature that we have, the elementary particles, the forces between them, and all those kinds of things—are environmental things which are contingent in our particular region of the universe or are exactly the same throughout the whole universe. If they’re contingent, that means they may vary from place to place, or they may vary from one thing to another thing to another thing. If that were the case, then we would answer some subset of the questions we’re interested in by saying things are the way they are because if they were any other way we couldn’t live here. The environment has to be right for us to exist.
On the other hand, if everything is the same, all across the universe from beginning to end, then we don’t understand why things are tuned in the way that allows us, with knife-edge precision, to be in an environment that supports life. This is a big controversy that’s beginning to brew in physics: whether the laws of nature as we know them are simply derivable from some mathematical theory and could not be any other way or if they might vary from place to place. This is the question I would like to know the answer to.
In the United States, the cosmologists don’t like the idea of the anthropic principle at all. In England they love it. I was very surprised to find out, when I started talking about this, that the physicists like myself, people who are interested in theoretical, mathematical questions in physics, are rather open to it in the United States, but the cosmologists are not. This [anthropic] idea originated to a large extent among British cosmologists—Martin Rees being one of them, John Barrow being another one. There’s also Andrei Linde, who is a Russian but of course lives in the United States, who was one of them, as was Alexander Vilenkin. But that’s not the crowd I’m addressing my remarks to.
The crowd I’m addressing are the high-energy physicists, the string theorists, and includes the Brian Greenes, the Ed Wittens, the David Grosses, and so forth. The reason is because over the last couple of years we’ve begun to find that string theory permits this incredible diversity of environments. It’s a theory that simply has solutions which are so diverse that it’s hard to imagine what picked one of them in the universe. More likely, the string theory universe is one with many different little patches of space that Alan Guth has called pocket universes. Of course they’re big, but there are little patches of space with one environment, little patches of space with another environment, etc.
Mostly physicists have hated the idea of the anthropic principle; they all hoped that the constants of nature could be derived from the beautiful symmetry of some mathematical theory. And now what people like Joe Polchinski and me are telling them is that it’s contingent on the environment. It’s different over there, it’s different over there, and you will never derive the fact that there’s an electron, a proton, a neutron, whatever, with exactly the right properties. You will never derive it, because it’s not true in other parts of the universe.
Physicists always wanted to believe that the answer was unique. Somehow there was something very special about the answer, but the myth of uniqueness is one that I think is a fool’s errand. That is, some believe there is some very fundamental, powerful, simple theory which, when you understand it and solve its equations, will uniquely determine what the electron mass is, what the proton mass is, and what all the constants of nature are. If that were to be true, then every place would have to have exactly the same constants of nature. If there were some fundamental equation which, when you solved it, said that the world is exactly the way we see it, then it would be the same everywhere.
On the other hand, you could have a theory which permitted many different environments, and a theory which permitted many different environments would be one in which you would expect that it would vary from place to place. What we’ve discovered in the last several years is that string the
ory has an incredible diversity—a tremendous number of solutions—and allows different kinds of environments. A lot of the practitioners of this kind of mathematical theory have been in a state of denial about it. They didn’t want to recognize it. They want to believe the universe is an elegant universe—and it’s not so elegant. It’s different over here. It’s that over here. It’s a Rube Goldberg machine over here. And this has created a sort of sense of denial about the facts about the theory. The theory is going to win, and physicists who are trying to deny what’s going on are going to lose.
These people are all very serious people. David Gross, for example, is very harshly against this kind of view of diversity. He wants the world to be unique, and he wants string theorists to calculate everything and find out that the world is very special with unique properties that are all derivable from equations. David considers this anthropic idea to be giving up the hope for uniqueness, and he quotes Winston Churchill when he’s with young people, and he says, “Nevah, nevah, nevah, nevah give up.”
Ed Witten dislikes this idea intensely, but I’m told he’s very nervous that it might be right. He’s not happy about it, but I think he knows that things are going in that direction. Joe Polchinski, who is one of the really great physicists in the world, was one of the people who started this idea. In the context of string theory, he was one of the first to realize that all this diversity was there, and he’s fully on board. Everybody at Stanford is going in this direction. I think Brian Greene is thinking about it. Brian moved to some extent from hardcore string theory into thinking about cosmology. He’s a very good physicist. There were some ideas out there that Brian investigated and found that they didn’t work. They were other kinds of ideas, not this diversity idea, and they didn’t work. I don’t know what he’s up to now. I haven’t spoken to him for all of a month. Paul Steinhardt hates the idea. Alan Guth is certainly very susceptible; he’s the one who coined the term “pocket universes.”
The reason there is so much diversity in string theory is because the theory has an enormous number of what I call moving parts, things you can tinker with. When you build yourself an example of string theory, as in Brian’s book, it involves the geometry of these internal compact spaces that Brian became famous for studying. There are a lot of variables in fixing one of them, and a lot of variables to tinker around with. There are so many variables that this creates an enormous amount of diversity.
String theory started out, a long time ago, not as the theory of everything, the theory of quantum gravity, or the theory of gravitation. It started out as an attempt to understand hadrons. Hadrons are protons, neutrons, and mesons—mesons are the particles that fly back and forth between protons to make forces between them—just rather ordinary particles that are found in the laboratory that were being experimented on at that time.
There was a group of mathematically minded physicists who constructed a formula. It’s a formula for something known as a scattering amplitude, which governs the probability for various things to happen when two particles collide. Physicists study particles in a rather stupid way; somebody described it as saying that if you want to find out what’s inside a watch, you hit it as hard as you can with a hammer and see what comes flying out. That’s what physicists do to see what’s inside elementary particles. But you have to have some idea of how a certain structure of particles might manifest itself in the things that come flying out. And so in 1968 Gabrielli Veneziano, who was a very young physicist, concocted this mathematical formula that describes the likelihood for different things to come out in different directions when two particles collide. It was a mathematical formula that was just based on mathematical properties, with no physical picture, no idea of what this thing might be describing. It was just pure mathematical formula.
At that time, I was a very young professor in New York, and I was not an elementary-particle physicist. I tended to work on things like quantum optics and other things, just whatever I happened to be interested in. A fellow by the name of Hector Rubinstein came to visit me and my friend, Yakir Aharonov, and he was wildly excited. He said, “The whole thing is done! We’ve figured out everything!”
I said, “What are you talking about, Hector?”
And jumping up and down like a maniac, he finally wrote this formula on the blackboard. I looked at the formula and I said, “Gee, this thing is not so complicated. If that’s all there is to it, I can figure out what this is. I don’t have to worry about all the particle physics that everybody had ever done in the past. I can just say what this formula is in nice, little, simple mathematics.”
I worked on it for a long time, fiddled around with it, and began to realize that it was describing what happens when two little loops of string come together, join, oscillate a little bit, and then go flying off. That’s a physics problem that you can solve. You can solve exactly for the probabilities for different things to happen, and they exactly match what Veneziano had written down. This was incredibly exciting.
I felt, here I was, unique in the world, the only person to know this in the whole wide world! Of course, that lasted for two days. I then found that Yoichiro Nambu, a physicist at Chicago, had exactly the same idea, and that we had more or less by accident come on exactly the same idea on practically the same day. There was no string theory at that time. In fact, I didn’t call them strings—I called them rubber bands.
I was just incredibly excited. I figured, “OK, here I am. I’m going to be a famous physicist. I’m going to be Einstein, I’m going to be Bohr, and everybody’s going to pay great attention to me,” so I wrote up the manuscript.
In those days we didn’t have computers and we didn’t have email, so you hand-wrote your manuscript and gave it to a secretary. A secretary typed it, and then you went through the equations that the secretary had mauled and corrected them, and this would take two weeks to get a paper ready, even after all the research had been done and all you had to do was write it up. Then you put it in an envelope and you mailed it by snail mail to the editor of the Physical Review Letters. Now, the Physical Review Letters was a very pompous journal. They said they would only publish the very, very best. What usually happens when people start getting that kind of way is they wind up publishing the very worst, because when standards get very, very high like that, nobody wants to bother with them, so they just send it to someplace where it’s easy to publish.
I sent it to the Physical Review Letters, and you understand, weeks had gone by in which I was preparing it and having it typed, and I was getting more and more nervous, thinking somebody was going to find out about it. I was telling my friends about it, and finally I sent the manuscript off. In those days it went to the journal, and the journal would have to mail it, again by snail mail, to referees. The referees might sit on it for a period and then send it back. All of this could take months—and it did take months.
And how did it came back? Well, they said, “This paper is not terribly important, and it doesn’t predict any new experimental results, and I don’t think it’s publishable in the Physical Review.”
Boom! I felt like I had gotten hit over the head with a trashcan, and I was very, very deeply upset. The story I told Brian Greene for his television program was correct: I went home; I was very nervous and very upset. My wife had tranquilizers around the house for some reason, and she said, “Take one of these and go to sleep.” So I took one and I went to sleep, and then I woke up and a couple of friends came over and we had a couple of drinks, and this did not mix. I not only got drunk but I passed out, and one of my physicist friends had to pick me up off the floor and take me to bed. That was tough. It was not a nice experience.
Of course I wasn’t going to leave it at rest that way; I sent it back to them and said, “Get another referee.” They sent it back to me and said, “We don’t get more referees.” I sent it back saying, “You have to get more referees. This is important.” They sent it back, saying “No we don’t,” and finally I sent it to another journal, whi
ch accepted it instantly. It was Physical Review, which is different from Physical Review Letters.
The discovery of string theory is usually credited to myself and Nambu. There was another version of it that was a little bit different, but the guy had the right idea, although it was a little bit less developed. His name was Holger Nielsen. He was a Dane at the Niels Bohr Institute, and he was very familiar with these kinds of ideas. A little bit later, he sent me a letter explaining his view of how it all worked, and it was a very similar idea.
After the paper came out, it was not accepted. People are very conservative about thinking pictorially like that, building models of things. They just wanted equations. They didn’t like the idea that there was a physical system that you could picture behind the whole thing. It was a little bit alien to the way people were thinking at that time. This was five years before the standard model came along in ’74 or ’75.
The first thing that happened is that I immediately realized that this could not be a theory of hadrons. I understood why, but I also knew that the mathematics of it was too extraordinary not to mean something. It did turn out that it was not exactly the right theory of hadrons, although it’s very closely related to the right theory. The idea was around for two or three years, during which it was thought that it was the theory of hadrons, exactly in that form. I knew better, but I wasn’t about to go tell people, because I had my fish to fry, and I was thinking about things. I was not taken seriously at all. I was a real outsider, not embraced by the community at all.
I’ll tell you the story about how I first got some credit for these things.
The already legendary Murray Gell-Mann gave a talk in Coral Gables at a big conference and I was there. His talk had nothing to do with these things. After his talk, we both went back to the motel, which had several stories to it. We got on the elevator, and sure enough the elevator got stuck with only me and Murray on it.
The Universe_Leading Scientists Explore the Origin, Mysteries, and Future of the Cosmos Page 16
