Greene did not invent string theory. But in 1999, he published “The Elegant Universe” (Norton), a popular presentation of string theory that became a major best seller and Pulitzer Prize finalist. Last fall he hosted a “Nova” television series based on that book. Now he’s back with “The Fabric of the Cosmos: Space, Time, and the Texture of Reality” (Knopf) published last month. Once again, assuming an audience of lay readers, Greene explains some of the more mind-melting features of today’s cutting-edge physics in a language that is easy to understand. For example, one feature of string theory–also known as superstring theory–is that it suggests the universe has more than three, and possibly up to 11, spatial dimensions. Reality as we perceive it may in fact just be an approximation of the universe we inhabit. Time, which is relative to space, may not allow us to ever visit the past, but jumping into the future is possible within the laws of physics.
Greene recently spoke with NEWSWEEK’s Brian Braiker, who is–under this theory–just a vibrating mass of tiny string, about the ideas he explores in the new book. Excerpts:
NEWSWEEK: Why is going from the concept that everything is made up of little tiny atoms and subatoms to the concept that it’s all fundamentally squiggly, vibrating lines such a revolutionary idea?
Brian Greene: At first sight it wouldn’t be. But when you study it in detail, you find that it is for a number of reasons. The first is that we believe that it gives a uniform description of all matter and radiation and all the forces of nature in one unified language. Prior to string theory, when you spoke about the elementary constituents of matter, you had to talk about electrons, you had to talk about protons and neutrons, you had to talk about the quarks that make them up. When string theory comes on the scene, everything simplifies because you have one entity: the string. And like any other string that you’re more familiar with, like on a violin or a cello, the string in string theory can vibrate in different patterns. When a string on a violin vibrates differently, it produces different musical notes. Here when the little strings vibrate, they produce different particles.
So you and I are just piles of vibrations? What is it that’s vibrating?
What is the string made of? We don’t know for certain. One answer is that this may be the one time when that question fails to make sense. When you look at anything around you–the mug on your desk or the tabletop that you’re working on–you can say, “What’s it made of?” You can ask what the atoms that you hypothesize and prove by experiment make up the entity are themselves made of. You can ask what the nucleus of an atom is made of and get to the neutrons and protons. And you can ask what they’re made of: quarks. But when you get down to strings, it may be that that’s where the story ends. It may be that they are the fundamental entity.
You keep saying “may,” which means none of this is certain at all.
Oh, string theory is definitely a work in progress. It’s definitely a theory; it has yet to be experimentally confirmed. [But] if string theory is right–and again, I always emphasize the “if”–it is a unified theory. I think the important thing to bear in mind is that general relativity has been tested up the wazoo to incredible accuracy. Quantum mechanics has been tested; it works with fantastic precision. String theory simply puts them together in the first consistent framework.
General relativity basically being an explanation of the macro-scale universe and quantum mechanics at the micro level?
Exactly. General relativity is a theory of gravity. Gravity becomes most relevant when things are big–the earth’s gravity, the sun’s gravity–but rarely do we talk about the gravity of a coffee cup because it’s too small. Quantum theory is most relevant on the opposite end of the spectrum; it comes into play when you are talking about atoms and subatomic particles. But we have come upon realms where you need both theories at the same time, such as black holes and the big bang–two examples where you have a lot of materials crushed to a very small size. Therefore you can’t live your life keeping general relativity and quantum mechanics permanently separate. That’s not how the world works, so you need a theory that can put them together in a consistent manner. String theory is the first theory to do that.
In your new book you talk about the possibility of there being up to 11 possible dimensions, where are they? What do they look like?
I think this is the most stunning and surprising element of this theory. One approach, which is one that I’ve actually worked on for maybe 15 years now, is that they’re all around us, they’re just tightly curled up. If you imagine a garden hose that’s unfurled long and horizontal stretched out, but it’s far in the distance, it’ll look like a straight line because you won’t be able to see the thickness. You’ll think that it only has a left-right dimension along its horizontal extent and nothing else. But then you take a pair of binoculars and zoom in, you know that there’s more to the surface than just left-right. It also has clockwise and counterclockwise, the circular girth of the hose, which is a curled-up circular dimension you don’t see without binoculars. We think the same may be true of the universe, namely there may be big easy-to-see dimensions–the horizontal extent of the hose–but there might also be tiny, curled-up dimensions all around us–like the circular part of the hose–but so tiny that we don’t have the magnifying equipment like binoculars adequate to reveal the existence of these extra dimensions.
What’s another way of envisioning the possibility of other dimensions?
The idea is that the extra dimensions that we don’t see might be big like the ones we know about, but we don’t see them because we see with light. It might be that light is trapped in our three dimensions and it can’t escape into the other dimensions and that’s why they remain invisible to us. Imagine a universe as a big loaf of bread and what we’ve always thought to be the universe is merely one slice of bread in this huge cosmic loaf. Light in this picture will be trapped in our slice of bread; it can’t travel to the other slices. The only force that wouldn’t be trapped, it turns out, is gravity. So it might be possible one day to detect these extra dimensions through gravity. Experiments are actually underway today in an attempt to do that.
But we still wouldn’t be able to see them.
We wouldn’t see them with light. But we would see them indirectly with gravity. The experiment is so simple: at the Large Hadron Collider, which is an atom-smasher being built [at the particle-physics laboratory] CERN in Switzerland, they’re going to take protons and send them circling around a huge tunnel in opposite directions right near the speed of light. Every so often they’ll use magnets to direct the beams of protons to smash into each other in head-on collisions. The idea is that in the collision, a certain amount of gravity will be produced. It might be that some of that gravity can leak off our dimensions, off of our slice of bread, and disappear into the other dimensions. If that happens, the amount of energy before the collisions will be a little bit bigger than the amount of energy after the collision because some of it will have seeped away. So the scientists are going to look for missing energy. If it’s missing in just the right pattern, it could be very strong evidence that the extra dimensions are real, that it has gone into other dimensions.
Why is time forward moving when everything else seems to tend toward randomness?
It’s a real big puzzle as to why time seems to be different. You stand in space and can move at will–left or right, back or forth, up or down, no constraint–but with time we seem to be relentlessly dragged forward. Why is that? We think that the answer, surprisingly, is to be found in the big bang itself. The big bang started the universe off in an incredibly ordered state and things tend to become more disordered over time. For that disorder to happen, you’ve got to begin highly ordered. There are sequences of events that we only see happen in one order–eggs splatter, they never unsplatter; glasses shatter, they never unshatter. I think it’s a wonderful idea–every time you drop an egg and it splatters, it’s actually telling you something very deep about the big bang itself.
So time travel may never be possible?
I firmly believe that one day we will rule out the possibility of time travel to the past. On the same point, it’s worth emphasizing that time travel to the future is a completely different ballgame. That is within the laws of physics as we understand them. Einstein himself showed us how to accomplish time travel to the future. If you want to see what the earth is like ten or 100 or a million years into the future we know in principle how to do it: You build a spaceship; you travel out into space at near the speed of light; you turn around and come back. Perhaps a year may elapse for you, but because time slows down when moving at high speeds, 1,000 or a million years may have elapsed when you return to earth. That means you have jumped into earth’s future. We can’t build such ships yet, but these are technological issues. But physics definitely shows that this kind of leapfrog into the future is within the laws of physics.
When you really think about this–that we’re just made up of vibrating strings, that we fail to perceive everything that constitutes reality–is it hard not to feel a little despair?
When we recognize that the same laws that govern us are the laws that govern the molecules and atoms in interstellar space, the processes in the sun and the countless other stars in the heavens; when we learn, for instance, that the very atoms that make up our body were produced in stars and spewed out into space through supernova explosions, I think it makes us feel more connected to the cosmos. We may not be anything particularly special, but we’re definitely part of the grand scheme. I think that can be very uplifting.
