_The Baltimore Sun_
Baltimore Sun Co. Jan 9, 1998
Universe's blueprint doesn't come easily;
Physics: A Baltimore-born star of the field says obstacles remain on the road to a long-sought "Theory of Everything."
By Douglas M. Birch
Edward Witten was back in his home town of Baltimore this week, gently fretting over the lack of recent progress in his effort to draw a basic blueprint of the universe.
No one seems to be better suited for this task than the 46-year-old physicist, considered by some of his colleagues to be the smartest of them all. And no one has generated more brilliant insights into what he calls "the foundation of everything that's known."
Not only is his work cited by other physicists more often than anyone else's, he has already won a Fields Medal, the mathematics world's equivalent of a Nobel prize. Now based at the Institute forAdvanced Study at Princeton, Witten was in Baltimore Wednesday for the American Mathematical Society's annual meeting, and delivered the 71st annual Gibbs lecture. He is one of a few non-mathematicians to be so honored.Another was Albert Einstein, who delivered the 11th Gibbs lecture in 1934.
The current lull in discoveries in Witten's field follows three years of conceptual leap-frogging. So perhaps it is understandablet hat Witten, during an interview at the Renaissance Harborplace Hotel, seemed preoccupied...
"There are some signs that the field is starting to get stuck again, progress is slowing down," he lamented, speaking in his soft, almost childlike voice. "We might be entering a period like the late '80s and early '90s, where you start filling in more details."
Witten is the leading proponent of string theory, more formally known as superstring theory, which holds that while molecules are made of atoms and atoms are made of tinier objects called quarks, quarks are constructed of even smaller bits called strings.
[mitch] This is not necessarily so - I think people would normally suppose that a quark was an individual string in a particular state.
Strings, which are billions of times smaller than the atom, have been described as mathematical curves, tiny threads of energy or rips in the fabric of space-time. These objects, far too small to be seen by even the most powerful microscopes, are thought to be either open-ended, like lengths of rope, or looped, like rubber bands.
As they fly around the subatomic world, these strands vibrate like violin strings. But instead of producing musical sounds, their complex harmonics create the whole wild and woolly menagerie of fundamental particles -- from electrons and protons to positrons and neutrinos -- that are the construction materials for the universe, from sunbeams to silly putty.
When they were first dreamed up in the late 1960s, strings quickly became popular. They instantly solved a nagging problem. They reconciled the two theories that dominate modern physics.
One is Einstein's theory of general relativity, the notion that gravity results from the way matter bends space. The other is quantum mechanics, which accurately predicts the behavior of matter at very tiny scales.
[mitch] This history is slightly wrong. String theory was first advanced as a theory of nuclear particles. In the early '70s some of the string theorists suggested that, since the theory contained a graviton-like particle, that it might be a unified theory instead. But this new use for the theory didn't become popular until 1984, when Green and Schwarz made a major discovery.
The main problem, Witten said, is that quantum mechanics is not compatible with general relativity. Specifically, quantum theory makes gravity impossible, while relativity makes it inevitable.
String theory bridges this gap, allowing the quantum world to produce gravity.
Superstrings seemed like a candidate for the long-sought "Theory of Everything," a small number of equations that would vastly simplify human understanding of the physical world. Witten was smitten. Butt here were several big problems.
Early on, it was clear that superstrings only exist in 10 dimensions, six more than the four dimensions we humans experience -- up anddown, left and right, forward and back and the fourth dimension, time. And there seemed to be an infinite number of potential string theories, which, to say the least, complicated the search for the one true theory.
String theorists quickly disposed of the surplus dimensions. They were, they said, probably rolled up tightly like little sleeping bags and stowed in the sub-quark realm. In the human-scale world we live in, they remain invisible.
But the hunt for a consistent string theory among all the possible ones proceeded slowly, and fueled the skepticism of many anti-string physicists, who rebelled at the notion of curled-up dimensions.
"It was difficult to show that there were consistent quantum string theories," Witten said. "A huge amount of work went into that in the 1970s and early 1980s." Finally, by the mid-1980s, five rugged and equally plausible theories emerged. Interest in string theory revived.
Five theories is fewer than an infinity, but it's still troubling.
"If one of them describes our world," Witten asked, "who lives in the other worlds?"
So Witten and others began searching for links between these theories. Then, in 1995, Witten made a breakthrough. He realized that, by changing the superstring picture, all five of the theories could be viewedas instances of a single, more fundamental theory.
Witten calls this deeper understanding of strings "M theory," with M standing, he says wryly, for "mystery, magic or matrix, my three favorite words."
Before, string theorists envisioned strings and loops. Now, those strings and loops are anchored to sheets and bubbles. Hence the term matrix: Mystery and magic are self-explanatory.
[mitch] Actually, the "matrix" in M theory refers to ordinary mathematical matrices.
The leading proposal for the specific form of M theory uses matrices.
Physicists call these sheets and bubbles "d-branes," but most people know them better by another name. They're called black holes.
Traditional black holes, of course, are stellar objects, never directly observed but thought to be created when an ultra-massive star collapses. The gravity is so intense, the whole star crunches into a dimensionless point.
Everything that falls within the long arm of the object'sgravity, even light, is sucked in.
Physicists long speculated on the existence of black holes the size of fundamental particles. M theory yielded the first consistent descriptions of these exotic objects.
And so Witten's picture of the sub-quark world is now one of a bubbling stew of strings that begin and end in black holes. But the progress of discovery has slowed. Roadblocks remain. Witten is especially concerned about one long-standing problem of string theory that M theory did not banish: the speed of the expansion of the universe.
Current M theory equations, Witten said, predict that sometime in the future the universe is likely to expand catastrophically, just as it may have done soon after the primordial Big Bang.
While this second round of expansion, called inflation,would confirm string theory, it would also likely wipe out all life forms everywhere. No one thinks this is really going to happen. Neither does Wittenthink the tools are available yet to fix the problem with the theory.
It's frustrating, but string theory has always been difficult. Partly, that's because it's a product of reverse engineering.
"Usually if there's a theory you're studying, pretty much by definition you at least know what its basic equations are," Witten said.
"Here, at the foundations, we don't know what the basic equations are."
The long-term goal, Witten said, is to find those equations. It could take another 30 years. Still, the physicist is not daunted.
"We've definitely penetrated now to a deeper level than we were a decade ago," he said.
And he is closer than ever, he said, to "what's really important . . . the foundation of everything that's known."
[mitch] The part about M theory predicting a second stage of inflation is especially interesting - I suspect it would be associated with the expansion of some of the compact dimensions, which would be a disaster for life as we know it, since particle interactions would change and matter would become unstable. It would require Tipler-scale cosmic engineering to survive such an event.