The Fall and Rise of the string theory


String theory was once the hottest thing in physics.

 In the 1980s and ’90s, it promised seemingly

unlimited bounty.

 Arising from the notion that matter and energy are

fundamentally composed of tiny,vibrating strings rather than point like particles, this theory attempted to

unify all the known forces into a single,elegant package. 

Some physicists hailed string theory as the long-sought

“theory of everything.”

Harvard University physicist Andrew Strominger, a leader in string theory for decades, remembers the early enthusiasm. “

At the time of its new popularity,” he says, “there was a

declaration that we had solved all the problems in physics

 and had the final theory in hand.”

Strominger knew, even in the euphoric ’80s, that such assertions

were overblown. And, sure enough, skepticism has seeped in over the years. No one has yet conceived of

an experiment that could definitively verify or refute string theory.

 The backlash may have peaked in 2006,

when several high-profile books and

articles attacked the theory. But while

string theory has receded from the

spotlight, it has not gone away. “The theory is still evolving and getting better — and better understood,”

maintains Juan Maldacena of the Institute for Advanced Study at

Princeton University.


Many of today’s string theorists
have adopted a utilitarian approach,
dwelling less on its all-embracing
potential and more on the here and
now. Some practitioners are applying
string theory techniques to problems in
pure mathematics, while Strominger is
working to secure a deeper conceptual
grasp of black holes. Others still are
relying on string theory for unexpected
help with calculations relating to
particle physics and exotic states of
matter. Emerging from this diverse
work is a new consensus: String
theory may not be the fabled theory of
everything, Strominger says, “but it is
definitely a theory of something.”

HIDDEN DEPTHS


Strominger was never one for the

beaten path. He dropped out of
Harvard twice in the 1970s to live in
communes in New Hampshire and
China before returning to college,
bent on probing the universe through
theoretical physics. As an MIT
graduate student, Strominger was told
to steer clear of risky subjects like
string theory; he ignored the advice.
The gamble paid off. In 1985,
three years after getting his Ph.D.,
Strominger co-authored one of the  field’s seminal papers — part of the so-called “first string revolution.”

A central premise of string
theory is that strings, the most basic
unit of nature, vibrate in a 10- or
11-dimensional universe. The three
familiar dimensions plus time make
four, meaning six or seven “extra”
spatial dimensions must lie hidden,
shrunk down so small we can’t see
them. These minute dimensions have
to be “compactified” in a specific way
to reproduce the physics we observe,
and Strominger and his colleagues
determined what that scrunched-up
shape had to be: a six-dimensional
mathematical object known as a
Calabi-Yau space. A particle’s mass,
the strength of a given force and
other fundamental quantities depend
on the shape, or geometry, of this
convoluted space. String theorists soon made a
remarkable discovery. By rotating a
Calabi-Yau space in a special way, they
could produce a mirror image of sorts,
though one with a very different shape.
The surprise was that these apparently
disparate Calabi-Yau shapes had a
hidden kinship, both giving rise to the
same physics. The theorists dubbed the
phenomenon “mirror symmetry.”
Scientists quickly learned that
this newfound symmetry could
be harnessed to address various
mathematical puzzles. In 1991, the
physicist Philip Candelas and his
colleagues used mirror symmetry to
solve a century-old problem, in effect
counting the number of spheres that
could fit inside a Calabi-Yau space.
                                            Calabi-Yau

Mathematicians jumped into the act,
using mirror symmetry to tackle other
unsolved problems in enumerative
geometry, typically entailing counting
lines and curves on complicated
surfaces and three-dimensional spaces.
Mirror symmetry helped rejuvenate the
field, and this line of research is still
going strong with regular international
math conferences devoted to it.
“During the past few years,
progress has been made toward
encapsulating this idea within one
(albeit complicated) formula,” says
Brandeis University mathematician
Bong Lian. “The geometric, algebraic
and physical pictures of mirror
symmetry are all starting to converge.”



THE END