Present at the Future

by Ira Flatow

  —RICHARD FEYNMAN

  Sometimes you hear something so often that you think it must be true. You wish it were true because it would solve a lot of problems (does “weapons of mass destruction” sound familiar?). That’s not supposed to happen in science. Ideas and theories are put to the test, to find out if they can stand up to scrutiny. If they do, they become an accepted part of the way we look at the world, until something better comes along. Relativity theory is one such idea. It expanded on a really nifty theory of gravity put out by a guy named Newton, hundreds of years before it. Reality itself has been under scrutiny and test for more than a hundred years, since a pretty good physicist named Einstein published the first of his many papers about relativity in 1905.

  Isaac Newton was the rock star of science in his time. And relativity theory—more accurately, Albert Einstein—was the darling of the media immediately after a famous eclipse of 1919 proved true his revolutionary theory that gravity curved space. The modern equivalent would be string theory. Countless books, papers, articles, and TV shows have sought to explain it to us; it has made media stars out of scientists, such as Brian Greene, professor of physics and mathematics at Columbia University in New York. He’s also the author of several books, including The Elegant Universe and The Fabric of the Cosmos.

  STRING THEORY IN A NUTSHELL

  According to Greene, “We have two main pillars of understanding in physics that were developed in the twentieth century. One is the general theory of relativity, Einstein’s theory that describes gravity. And gravity is a force that’s relevant mostly when things are big—stars and galaxies and so forth.

  “The other major development is quantum mechanics, a theory that describes the other end of the spectrum, the small things—the molecules and the atoms and so forth.

  “Now for a long time, we’ve recognized that these two theories have to talk to each other in a sensible way. There are realms, extreme realms, where things are both heavy and small, like black holes or the beginning of the universe. And because those realms exist, you need to use gravity, general relativity, and quantum mechanics all at the same time.

  “The problem is that for many decades, any attempt to put the two theories together, to unify them, didn’t work. It gave wrong, nonsensical answers. String theory is an attempt to fix that, to give us a theory that won’t give nonsensical answers, that will give answers that make sense when you put gravity and quantum mechanics together.”

  QUANTUM RELATIVITY

  In a nutshell, string theory says that instead of tiny little subatomic particles being at the root of all matter and energy, tiny little strings exist instead. And when plucked just the right way, they vibrate to produce the building blocks for everything we see around us. And most importantly for cosmology, string theory, theoretically speaking, can unite the disparate worlds of gravity and quantum mechanics.

  Sounds great so far, doesn’t it? But as with anything else in life, string theory comes with a little bit of extra baggage. A few big problems. Because while string theory may look sweet, mathematically speaking, it requires that our world be composed not of the 3 or 4 dimensions familiar to all of us but instead 10 or 11 dimensions, most of which remain hidden from view. “Whether there really are extra dimensions or not, I think, remains to be seen,” says Dr. Lawrence Krauss.

  Even Einstein found no way to unite gravity and quantum mechanics. And that’s where some scientists see the problem: String theory is aging, and not elegantly. It has been around long enough to be tested, and we should have found experimental evidence to prove that it works. And because it hasn’t been tested, scientists, in a rapid sequence of speeches, articles, and books, are beginning to openly question its usefulness in physics. They say that it is not living up to its promise, that it’s more hype than science.

  Take Lee Smolin, faculty member at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. Smolin, of The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, says he is trying to understand why string theory, which he has worked on himself, is so problematic. “Why the ideas which seemed at first so beautiful, so natural, were not getting us where we expected to get twenty years ago.”

  Smolin points out that just about every 25 to 30 years, new ideas in physics come along to replace the old ones. If you look back over the last 200, he says, it’s very unusual for three decades to pass without a scientific revolution. For example, he writes that “from 1830–1855 Michael Faraday introduced the notion that forces are conveyed by fields, an idea he used to greatly further our understanding of electricity and magnetism.”

  In the 25 years that followed, James Clerk Maxwell expanded those ideas into “our modern theory of electromagnetism.” He explained how light was also like radio waves and unlocked other secrets of our natural world. Then came the next dramatic period, 1880 to 1905, in which electrons and X-rays were discovered. In that 25-year period, Smolin continues, Max Planck’s work would “spark the quantum revolution.” Einstein’s era would arrive in 1905, and understanding the impact of relativity would occupy the next two and a half decades. By Einstein’s death in 1955, we would know all about a whole new world of subatomic particles and organize the forces of nature into a family of four.

  The next 25 years and the 25 after that would see the creation of a “standard model” of the elementary particles in the universe, and on a larger scale, we’d see Stephen Hawking and other luminaries enlighten our understanding of black holes, the big bang, and dark energy and matter.

  But since the 1980s, says Smolin, we have been stymied. String theory is now more than 20 years old and doesn’t seem to be yielding the answers that have been expected of it. “History seems to show that when there’s a good idea about unifying different parts of physics, it works fast if it’s going to work.” Scientists should be able to conduct experiments that either bolster or bat down that new idea. But the problem with string theory is that so far, there are no experiments that can solidify it. Or, as Smolin puts it, “string theory is not making experimental predictions. There are certainly very beautiful things about it,” but a theory that can’t be tested is nothing more than a theory. In science, you can’t hang on to an idea too long; if it can’t be tested and proven, it’s on to the next big thing.

  Krauss agrees. He says string theory has been a failure. “There isn’t a shred of empirical evidence, not only for extra dimensions but essentially also for string theory. They [scientists] haven’t made any predictions that have been tested. And moreover, in fact, to some extent, we’re still just learning what the theories are.”

  Greene agrees that the evidence, so far, has been lacking. But as one of string theory’s greatest proponents, he says we have to give the experimentalists a bit more time to find the evidence.

  “How long will it take for those experiments to happen? I don’t know. We could get lucky. It could be that the Large Hadron Collider, which will turn on in 2007 or 2008,” will show some evidence for string theory. “We might see some of the fingerprints of string theories through something called supersymmetry, certain particles that the theories suggest should be there but nobody has yet seen.”

  Astronomers, looking into space, might also find evidence of string theory. “That’s what I spend my time on these days, trying to see where these strings might leave some imprint in the microwave background radiation, the heat left over from the big bang. All of these are long shots. But we’re doing exactly what Lee is saying one should do in science—namely, work toward experimental verification. How long? I can’t predict. Nobody can predict.”

  Greene says it could be years, even decades, before experiments can determine the validity of string theory. And should that happen, interest in the theory would drop off “because the people who work on string theory are physicists, and physicists want to make contact with physical reality.” But what has happened since the 1980s is that the theory has gone through “what we call
revolutions in our thinking time and time again, which has given a surge of energy, a surge of interest in the theory, which has kept us going even though we’ve yet to make that desired contact with experiment. Our understanding of the underlying theory, our understanding of the equations, our understanding of the fundamental ideas and how they relate to one another—we’ve made great strides.

  “We have an international meeting every year, a string theory conference that has something like fifty talks. And these talks are generally amazing. They’re generally showing how people are making great progress in spite of not having the guide of experiment. So if it turns out, as Lee is saying, that some of the experiments he’s describing or the experiments of the Large Hadron Collider, if in the next couple of years these experiments bear fruit and begin to show us some of the features of the theories that we’ve been working on for a long time, things will definitely take a major leap forward.

  “So it’s a very exciting time, waiting to see the results of those experiments. And in no way would one want to say that the theory is moving slowly. It perhaps is moving slowly toward these experiments, which are coming online. But the theory itself is developing rapidly. In fact, it’s hard to keep up. The theory is able to embrace all of the major developments in physics having to do with the elementary particles in quantum mechanics that were discovered before string theory in the middle of the twentieth century, leading up to the end of the twentieth century. They all naturally find a home within string theory. And that’s very compelling to us because usually a revolution doesn’t actually erase the past. It embraces the past but goes further. And that’s what string theory seems to be doing.

  “The other side of it is that even without the experimental confirmation, string theory has a very intricate mathematical structure that holds together with a kind of tight, logical cohesion. There are checks and rechecks in the calculations, enormous number of consistency checks, and they’ve all passed. The theory comes through with flying colors every step of the way. And that again keeps us going, keeps us thinking that this theory is at least heading in the right direction.”

  To hear Krauss talk about string theory, it sounds more like a solution in search of a problem.

  “It still amazes me, when you think about it, that string theory arose in the 1970s when people were trying to understand all this host of new elementary particles that were being discovered in accelerators and they couldn’t make sense of it. This theory came along that looked like it might help you make sense of it, but, by the way, it required twenty-two extra dimensions. And I’m amazed in some sense that physicists were willing to automatically assume that maybe all those extra dimensions exist just to solve that problem. It turned out it wasn’t the solution to that problem. But then a decade later, physicists realized maybe it was the solution of another problem involving gravity. And physicists, many of them, are convinced those extra dimensions are out there.

  “And to the credit of the physics community, there are some people who are actually trying to think of experiments that might actually be able to test this, so it isn’t just metaphysics.”

  IS NEW SCIENCE SUFFERING?

  Smolin says that he would never tell Greene or anyone else working on string theory to drop what they are doing and head into something else. “Certainly time will be the judge. If somebody feels that string theory or anything else is the most promising thing they know about, certainly they should work on it.

  “But there is another level, and that’s the level where we think about science as a very risky activity. And if it is a very risky activity, something like development of a new technology, the question arises: Do we support only one direction? Do we put all of our apples or whatever it is in one basket? Or do we hedge our bets? Do we support all the people who are excited about the good ideas that they have?”

  And this is in large part an issue that concerns Smolin. “It’s not a question of what one individual scientist does. One individual scientist should do what he or she deeply believes in.” But it is a question of science as a community, where so many scientists are working only in one direction: string theory. That kind of community does not encourage scientists to strike out in other directions, on their own, where historically new ideas arise. “The analogs of the great physicists of the past who always struck out on their own, people like Galileo and Einstein, those people didn’t have an easy time because of the way that universities are very averse to risks. They’re very averse to hiring people who are working on their own ideas as opposed to ideas that large communities of people have been working on for decades. We should try to find ways to help and support those people who have new ideas and have the courage to work on their own ideas.”

  As a community, “we can take attitudes where we encourage people to strike out on their own, to leave behind old ideas, even if [there are] still things about them we love, and to encourage the young people, especially the young people, to forget what people of our older generations have done and strike out for new directions.”

  On this point, there is no disagreement. “On this other issue of encouraging young students to strike out on their own and pursue their own ideas, I couldn’t agree more,” says Greene. “I, for instance, in the last couple of years have had students that don’t work on string theory. I’ve had students that have worked on relatively fringe ideas, according to the mainstream point of view. I’ve had students working on more bread-and-butter particle physics. So absolutely, we need to encourage diversity of thought. We need to encourage the young students to express their creativity. Who would ever say otherwise?”

  THINKING OUTSIDE THE BOX

  And just what kinds of “diversity of thought” might one find? What is occupying some of the best young minds? Smolin points to a few mind-numbing approaches:

  Deformed special relativity: It’s the idea “that quantum gravity alters the basic equations of special relativity in ways that are testable by experiments” to be performed in the near future.

  Dynamical triangulation: “One of several ideas on the basis of which space is made of discrete elements. One tries to find effects that come from the hypothesis that space is discrete,” as opposed to being the continuous, smooth place we experience it to be.

  Loop quantum gravity: Smolin’s own area of research, “something that is a successful unification, at least at the level of the equations, of general relativity and quantum theory. It has led to a very particular picture of space being made out of discrete elements. And there are consequences of that which people are exploring.” This theory says that the big bang was not the beginning of time, so that time continues into the past.

  What should we expect once we can unite quantum mechanics with Einstein’s concept of space? Some very interesting results because of the difference in the ways the two act. Quanta like to “leap” in discrete jumps, and quantum particles can appear in many places at the same time—even tunnel through things. But our concept of space is one of smoothness. Objects travel through space in smooth lines, sailing on a continuous, uninterrupted trajectory from the Earth to the moon, for example.

  So uniting the two worlds would lead to some ideas that seem to come right out of science fiction. You get sort of a hybrid of the two. “The notion of space should disappear,” says Smolin, “just like the notion that the trajectory of a particle disappears in quantum mechanics.” Instead, you get the spooky world of a quantum state, where “a particle is either a wave or a particle, depending on what questions we ask about it. The idea that we’re living in this three-dimensional, fixed geometry goes away.”

  REVOLUTION IN PHYSICS

  Where is all this leading to? Smolin is unequivocal. “I think we do need a new physics. We need to complete a revolution. Einstein started this. Einstein started the revolution in the early 1900s when he was the first person to declare that we needed a quantum theory to break with the physics that went before. And he also brought us relativity theory. And that was the launch
of the revolution. And we’re still engaged in that same revolution. It won’t be over until this problem of putting together relativity and quantum theory is solved, and not just solved in principle on a pad of paper but solved in such a way that it leads to new experiments and new predictions for experiments.”

  Greene goes even further. “I full well believe that when we do complete this revolution that Lee’s referring to, we will have a completely different view of the universe.”

  But there’s more. “I totally agree with Lee that everything that we know points to space and time not even being fundamental entities.” Now that is revolutionary. Space and time no longer the basic building blocks, yet we think they are? Greene shows why he is such a good explainer.

  “The way I like to think about it is to take the concept of temperature. We all know what it means for something to be hot or to be cold. We can experience it. But scientists taught us that there’s an underlying physics to temperature which has to do with how fast particles, molecules, are moving. Molecules move fast, it appears hot. It feels hot. Molecules move slowly, it will feel cold. So the idea of temperature rests on a foundation of more fundamental ideas, motion of molecules.

  “We think that space and time are like temperature in the sense that they rely upon more fundamental ideas as well. Now what those more fundamental entities are—the so-called atoms, if you will, that make up space and time—we don’t know yet. String theory has some vague suggestions. Loop quantum gravity has some vague suggestions. We’re not there yet.

  “But when we get there, I think we will learn that space and time are not what we thought they are. They are going to morph into something completely unfamiliar. And we’ll find that in certain circumstances space and time appear the way we humans interpret those concepts, but fundamentally the universe is not built out of these familiar notions of space and time that we experience.”