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_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.
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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.
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[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's
gravity,
even
light,
is sucked in.
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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.
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