Read Present at the Future Online
Authors: Ira Flatow
“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:
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.”
Not only would it shift our view of physics but it would also change the way we look at the world.
“It would change the very notion of reality, if you really want to be more precise, because most of us, at least, think about reality as existing in a region of space and taking place through some duration of time. If we learned that those basic ideas, the arena of space and the duration of time, are not concepts that even apply in certain realms, the realm of, say, the very extreme of energy or the very extremes of small size and tiny intervals…if the notions of space and time evaporate, then our whole conception of reality, the whole container of reality, will have evaporated and we’ll have to learn to think about physics in the universe completely differently.”
To my way of thinking, if there were ever a case of fact being stranger than fiction, this would be it. But don’t get carried away, says Smolin.
“It’s not—it’s not as far out as it sounds. Really, it’s not. And seeing space is made up of something—‘atoms’ of something more fundamental—you can go a long way with an image that the air looks smooth, the water looks smooth, and we discover that really it’s made out of atoms.”
And one great consequence of that image, says Smolin, is that it allows us to experiment with the concept, to see if it stands up to scrutiny. We can search for evidence of those “atoms” of space. “And that’s why I keep pushing about experiment so much, because indeed it does seem that if space is made of atoms, there are consequences for how light propagates. And these consequences are checkable by experiments that use observations of light coming from very, very far away to look for very small differences in how light of different colors or different energies propagate.”
It doesn’t matter, he says, that we don’t have a theory that predicts “an absolutely precise prediction for what these experiments
should see. And that’s a source of great frustration to all of us. But we have some general ideas about what the effect should be to look for, and if those effects are seen—and this could be in as little as a year and a half, two years, from this experiment that I was talking about that looks at gamma rays coming from very, very far away—then that will indicate that what Greene is saying is absolutely right. That will be the discovery of the atoms of space in the same way that some of Einstein’s discoveries really cemented the idea that matter is made of atoms.
GETTING READY FOR GLOBAL WARMING
IS EVERY COASTAL CITY A NEW ORLEANS WAITING TO HAPPEN?
The human race is conducting a profound and largely irreversible experiment on world climate. Increasing atmospheric concentrations of carbon dioxide and other greenhouse gases are expected to cause a global warming that could raise the sea several feet in the next century. Should we wait for this experiment to unfold, or prepare now for its possible consequences?