String theorists at UCLA gather Wednesday mornings to talk about
the world as they see it, a place so bizarre it tears common
intuition to shreds.
There are 11 dimensions ““ one of time and 10 of space
““ instead of the conventional four.
The smallest particles that make up matter, like electrons and
the quarks that constitute protons and neutrons in atoms, are not
points, as previously thought. Instead, each elementary particle is
a tiny, tense loop of string, like a one-dimensional rubber band,
whose length is usually 10-33 centimeters.
The strings’ vibrations at varying energies give
elementary particles their characteristics, which include their
spins and masses. A similar concept explains how string instruments
work: The note a guitar string produces depends on how hard a
musician plucks it.
So it goes according to string theory and the researchers at
UCLA and around the world who study it.
But unlike past theories built with evidence from experiments, a
major challenge plagues the world of strings.
“There’s no direct justification,” said Eric
D’Hoker, a string theorist at UCLA. If they exist, strings
are too small to observe using modern technology, he said.
While scientists have thought of ways to infer the presence of
strings without actually having to “see” them, no
experiment as of yet has laid the ground for proving the
theory.
This means research consists of paper and pen and computers, and
complex calculations that can go on for hundreds of pages, said Per
Kraus, a professor and string theorist.
Physics in conflict
String theory solves a problem in physics that has roots in
Albert Einstein’s theory of general relativity, published in
1916.
Physicists use general relativity, which describes how gravity
works, to examine how objects interact over long distances. Quantum
mechanics, another theory, explains how the world works on a
microscopic level.
When equations for the two theories are combined, they generate
answers of infinity, which means the two theories are fundamentally
at odds with one another, D’Hoker said.
But believing one set of laws applies to the entire universe, on
large or small scales, physicists have sought to unify quantum
mechanics and gravity.
And with string theory, the infinities seem to disappear,
D’Hoker said.
On a less technical level, the conflict between general
relativity and quantum theory manifests itself in the way each
treats a black hole, Kraus said. According to general relativity,
“you just toss things in a black hole. They just
disappear,” he said.
“It really underscores the fundamental difference in
quantum mechanics and gravity. Quantum mechanics says that you can
never lose information.”
It was while studying black holes that Kraus became interested
in string theory. Besides eliminating the infinities, the theory
gives physicists a way to describe the internal workings and
structure of a black hole, Kraus said.
What lies at the heart of string theory’s attraction is
its ability to unify the four forces that govern the world ““
gravity being one of them ““ under the same mathematical
framework.
The electromagnetic force and strong and weak forces (which keep
an atom’s nucleus together and control radioactive decay,
respectively) can all be described using a branch of physics called
quantum field theory; gravity stands alone, unable to fit under
that umbrella.
Physicists don’t know exactly what string theory will say
about the world, Kraus said. But by accounting for all forces under
one mathematical roof, string theory, if correct, is the unifying
theory ““ the theory of everything.
Strings around the world
D’Hoker and Kraus’ offices sit side by side on the
fourth floor of the new Physics and Astronomy Building. They are
two of 10 people working on string theory at UCLA, Kraus said.
Talking about the advancement of strings in physics, Kraus
speaks always exclusively in terms of “we.”
String theorists worldwide communicate constantly, whether
through e-mail or through the more intimate meetings held here
Wednesdays.
Jay Hauser, a professor of physics, says string theory
hasn’t always been popular. Periods of “relative
boredom” follow excitement after discoveries that occur once
every five or six years.
While Hauser’s specialty isn’t in string theory, his
research could impact that area. He will head to Switzerland in the
next couple years to work with other scientists, conducting
experiments with a giant accelerator that slams elementary
particles into one another.
He said the group expects to begin taking data in 2007.
If particles appear on only one side of the experiment, this
could indirectly support string theory. Particles in this scenario
may have “disappeared” by entering another one of the
dimensions predicted by calculations central to string theory.
Kraus said theorists are hoping the Switzerland project reveals
something deeper ““ they don’t know what ““ about
the universe.
“Something unexpected,” Kraus said.
Why should we care?
In coming up with the theory of relativity, Einstein began with
a principle: The laws of physics are the same for everyone,
regardless of their motion. The math came later.
At 37 years old, string theory doesn’t have a principle
yet, D’Hoker says.
But theorists studying it believe they are chasing after
something grand.
D’Hoker’s fascination with strings began around
1981, when he was finishing graduate school.
“I tried to read the papers that were coming out and it
was absolutely unreadable,” said D’Hoker, who for a
long time kept on his desk a pile of research published on string
theory.
“It was written in a language that was so unfamiliar to
me.”
While he and other theorists know more now, much work remains,
D’Hoker said.
“Practically at this point, the effects … are
minute,” he said. “You could perfectly well continue to
use your laptop, look at the stars, go driving, without knowing the
basics of string theory.”
But people woke, slept, worked and lived before relativity, too.
What Einstein did was to change the way they thought about space
and time.
Kraus believes string theory’s principle, whatever it
might be, will deepen understanding of our world by unlocking
knowledge about the universe as Einstein did a century before.
“In 1985, (string theorists) felt within a year,
they’ll know everything,” Kraus said. “Well, that
was 20 years ago.
“It’s very peculiar. It’s a very strange
situation. You’re sort of chasing little bits of this theory.
When it will be revealed, it will be very beautiful.”