The complexities of contemporary physics are mind-boggling, but explaining "the theory of everything" to a lay audience may be even harder. With a pathbreaking new book, Columbia physicist Brian Greene is strengthening the bonds between advanced research and the general public
Trying to untangle some of the more esoteric concepts of modern physics might tie most people up in knots, but Columbia's Brian Greene has string theory wrapped around his finger. Greene's new book, The Elegant Universe (NY: Norton, 1999), succeeds in explaining string theory in accessible language, visualizing the microscopic world in terms of garden hoses and violins. His patient eloquence brings string theory within range of even the most phobic of math- and physics-phobes.
String theory merges two revolutionary theories of modern physics -- quantum mechanics and general relativity -- into a common framework. Quantum mechanics is very good at explaining what happens when things are very small or light, like molecules, atoms, and subatomic particles. General relativity steps in when things are very large or massive, on the scale of stars, galaxies, and the universe itself. Neither theory has an adequate grasp on the physics of things that are both tiny and massive, like a black hole or the beginning of the universe.
At its most basic, string theory posits that the fundamental ingredients in matter are vibrating loops resembling unimaginably tiny, taut rubber bands. "If you take anything at all, and just keep slicing it into smaller and smaller pieces," says Greene, "the theory suggests that the smallest things that you will ultimately come upon are these strings." Envisioning the fundamental bits of matter as tiny strings rather than point-like particles gives scientists the theoretical framework to probe the physical properties of things like black holes. The theory has begun to sew together our fragmented understanding of the universe.
Theorists first promulgated the idea in the early 1970s. Early predictions were contradicted by accelerator measurements, and the idea lost favor for a while, but conceptual revolutions in the mid-1980s and mid-1990s have shown how powerful the theory is for marrying the physics of the very small and the very large. "For a long time people have had to live with two theories that each work well but are in conflict with each other: general relativity and quantum mechanics," Greene says. "That truly has been a puzzle, leaving physics in a fairly precarious state if you want to have a consistent description of the entire universe. Now we've really taken a step towards resolving that."
The vibration patterns of the strings, like the vibrations of violin strings, give rise to slightly more familiar fundamental particles such as quarks and gluons. These, in turn, are the constituents of protons, neutrons, and electrons, which make up atoms and molecules. "The different patterns in string theory don't correspond to different musical notes the way they do with a violin string," Greene says, "but they correspond to the different particles that make up all of the stuff in the world around us, so there can be a richness that emerges even though the basic ingredient is so simple." String theory's ability to tie together general relativity and quantum mechanics with a common language has led some to call it the "theory of everything."
Popularizing without dumbing downGreene studied physics as an undergraduate at Harvard, but it was as a graduate student at Oxford in 1984 that he first became interested in string theory. "Just by chance, when I was walking down the street, there was a sign for a public lecture on something called the theory of everything. I had no idea what it was at all, but I went to it," he recalls. "And I really got hooked on the ideas and basically jumped in at that moment, as did the rest of the world; that's when string theory made its big splash."
Explaining physics comes naturally to Greene; analogies roll off his tongue with the effortless precision of a Michael Jordan lay-up. "I don't know that everybody realizes that even physicists themselves often do maybe not always explicitly, but implicitly use analogies in the way that they actually think about things," he said. "It really is how you sharpen your intuition by having a good mental image, a good metaphor, that captures the heart of the matter without getting bogged down in the details."
Several years ago, Greene began giving popular-level lectures on string theory to general audiences. The lectures attracted a broad range of people: artists, investment bankers, theologians, homemakers. "People afterwards would always come up to me and say, 'What can I read to learn more about this? It's real interesting stuff,'" he recalled. Greene realized that there was nothing in circulation that both captured the theory's historical development and presented the cutting edge of new ideas comprehensibly.
Reluctant at first when he was approached by a publisher about writing such a book, Greene refused to sign a contract "because if it didn't work, I didn't want anybody to know," he says. "I just wanted to throw it away and forget about the whole thing." Rocketing to No. 1 on the Internet-based Amazon.com sales index shortly after its publication in February, Greene's Elegant Universe still lingers in the top 150 at this writing.
His eminently readable book and his clarity as a lecturer have attracted ample media attention, bringing string theory's abstract mathematical concepts into the mainstream. Among other TV engagements, he appeared on CNN and collaborated with ABC in producing a one-hour special on string theory for "Nightline in Prime Time." Although he feared a negative backlash from his colleagues, Greene says the reception he's gotten has been very positive. "People are very excited that ideas that are close to the heart of many people in the field, that have been locked behind the doors of universities, are now being given a wider stage and a wider, broader audience."
Predicting unknown dimensionsOne of the more startling predictions of string theory is that there are more dimensions in the universe than meet the eye. "For a very long time people have assumed that what you see is what you get when it comes to the number of dimensions in our universe," Greene said. "You look out in the world around you and you see three spatial dimensions -- you know, left-right, back-forth, and up-down -- three dimensions that we all meander through freely all the time without even thinking about it." String theory doesn't assume a particular number for the number of dimensions in the universe; rather, it predicts the number. "And that number is not three; it's more than three," he said. "And that's bizarre at first sight."
String theory suggests that as many as nine or 10 spatial dimensions, plus time, may exist, for a total of 10 or 11 spacetime dimensions. Most of them are tiny and curled up, so small we may never be able to perceive them. It's the complex patterns of vibrations throughout these 10 or 11 dimensions that give rise to the rich family of particles scientists can detect experimentally.
Unfortunately, detecting strings themselves is impossible given our current technology. Right now, string theory is just that: a theory. But scientists hope one day to be able to verify some of the predictions of string theory experimentally. For one thing, string theory predicts that the universe is symmetric, or rather "supersymmetric," meaning that for all the so-called fundamental particles detected so far (electrons, neutrinos, quarks, etc.), there ought to be a "superpartner" -- probably very heavy that hasn't been seen yet. There is hope that the Large Hadron Collider, now being constructed in Geneva, Switzerland, and scheduled to be operational before 2010, may be a powerful enough accelerator to detect some of these hypothetical superheavy superpartners, named selectrons, sneutrinos, squarks, and so forth.
Unfortunately, finding supersymmetry won't necessarily confirm string theory, because supersymmetry could be a property of the universe even if string theory isn't correct. "But supersymmetry really has a very natural home in string theory," Greene says. "That was where it was discovered, as a matter of fact, so many of us feel that if supersymmetry is confirmed, it will really be a very important confirmation of an essential feature of the theory."
On a more abstract note, Greene and others are working on dissecting the essential components of time and space, the same way earlier theorists dissected matter into strings. "You can ask yourself, 'Are space and time themselves made up of something? Are they merely abstract concepts? Or are they really out there and perhaps even built up from something smaller?'" he says.
He isn't just talking about minutes or seconds here. "A second is an abstract idea. It's a unit of time, but it's not the most basic, because we know that there are time periods certainly that are shorter than a second," he says. Now he invokes an analogy."You've got some big, gushy cheese lasagna. When you look at that, it's got interesting structure to it. But as a physicist, we know that that large-scale interesting structure that you immediately see when you look at it is obscuring what's happening at a microscopic level. Down there, there are atoms and subatomic particles, and perhaps ultimately these strings. But those are all in some sense hidden within that larger structure. Could space and time similarly be obscuring something more elementary out of which they are composed?"
Greene acknowledges that this is a conceptual leap for anyone, including himself. He writes in his book, "Like the Stephen Wright one-liner about the photographer who is obsessed with getting a close-up shot of the horizon, we run up against a clash of paradigms when we try to envision a universe that is, but that somehow does not invoke the concepts of space or time." Untangling space and time is not for the faint of heart, but Greene expects that the next conceptual revolution in string theory will come from a more basic understanding of these ideas. And not only will he be contributing to the research, but Greene is also the kind of storyteller who can translate tomorrow's complex ideas into a tale most of the rest of us can understand.
Prof. Greene's research homepage
String theory homepage, UC Santa Barbara
Edward Witten, "Duality, Spacetime, and Quantum Mechanics," RealAudio lecture on competing string theories, Institute for Theoretical Physics, UC Santa Barbara
The Second Superstring Revolution, John H. Schwarz, Caltech
The Particle Adventure, introduction to standard model of fundamental particles and forces, Lawrence Berkeley National Laboratory
Boyce Rensberger, "A Short Course in String Theory (with No Equations)," Washington Post, December 11, 1996
Jennifer Senior, "He's Got the World on a String" (profile of Prof. Greene), New York, Feb. 1, 1999
Assorted quantum mechanics links, Rhett Savage, Reed College
Space and Time since Einstein, a project of Columbia's Center for New Media Teaching and Learning
M.A. Program in the Philosophical Foundations of Physics, Columbia Departments of Philosophy and Physics
DIANA STEELE is a free-lance science writer based in Chicago who specializes in physics and astrophysics. Her most recent work appeared in Astronomy.
Photo Credits String Theory: Photo - Brian Greene / Computer Illo Howard R. Roberts
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