The concept of extra dimensions, dismissed as nonsense
even by one of its earliest proponents nearly nine decades
ago, may soon help solve seemingly unrelated problems in
particle physics, cosmology and gravitational physics,
according to a panel of experts who will assemble from
8:30 a.m. to 11:30 a.m. Feb. 15 (Saturday) at the
American Association for the Advancement of Science
annual meeting in Denver.

“It doesn’t happen often that you get a confluence of
ideas and experiments that come together and it’s
something that obviously would change your whole way of
looking at the universe,” said one of the panelists,
Joseph Lykken, Professor in Physics at the University
of Chicago and a scientist at Fermi National Accelerator
Laboratory.

Even though scientists lack direct evidence of extra
dimensions, “we have a number of hints from experiments
and theoretical ideas that make us think they’re probably
out there. That’s why we’re so excited about looking for
them,” Lykken said.

On the theoretical side, string theory, developed over
the past two decades, requires that space-time has extra
dimensions if it is to include gravity. “It’s just built
into the way that string theory works,” Lykken said.

Experiments, meanwhile, have produced the standard model
of physics to describe the most elementary particles and
the forces that hold them together. Physicists have come
to suspect that something is missing from the standard
model.

“There seems to be more particles and forces than we
really need, and they operate in more complicated ways
than they need to,” Lykken said. But extra dimensions
may ultimately help explain these data complications.

“That standard model itself may be our biggest hint that
there’s this world of extra dimensions,” he said.

New experiments at Fermi National Accelerator Laboratory
are producing data that just don’t fit the standard
model, said Maria Spiropulu an Enrico Fermi Fellow at
the University of Chicago. “We have things in the data
that leave our mouths hanging,” she said.

Whether extra dimensions or some other phenomenon emerges
to clarify these murky data, scientists seem certain
that they stand only a few years away from a scientific
revolution.

“What’s going on right now in particle physics,
gravitational physics and cosmology is like when quantum
mechanics started coming together,” Spiropulu said.
Quantum mechanics, developed in the 1920s, describes the
physics of objects at the atomic level and dominates the
concepts of modern physics.

Spiropulu, who organized the AAAS session on the physics
of extra dimensions, spoke at the session along with
scientists from Fermi National Accelerator Laboratory,
Harvard University and the universities of Chicago and
Washington.

Another panelist, Sean Carroll, Assistant Professor in
Physics at the University of Chicago, said that extra
dimensions could help solve two mysteries in cosmology:
what were the initial conditions of the universe and
what is the mysterious dark energy that is accelerating
the expansion of the universe.

The idea of an inflationary universe, one that expanded
rapidly just moments after the big bang, has gained
wide acceptance among cosmologists to explain how
conditions in the early universe could be unexpectedly
different from what they later came to be. But
inflationary cosmology tells scientists nothing about
the initial conditions of the universe. This is where
extra dimensions come in, even though they might be
microscopically small.

“If you had extra dimensions, then when the universe is
very small at early times, the extra dimensions weren’t
small compared to the rest of the universe,” Carroll
said. “They must have played a big role. What was that
role? Could the role have something to do how we
perceive the initial conditions?”

Extra dimensions may also explain dark energy. Physicists
conjecture that dark energy is governed partly by
occurrences in the familiar four dimensions and partly
by occurrences in the extra dimensions, Carroll explained.

“There is the tantalizing possibility that a complete
change of perspective makes all of the problems collapse
at once,” he said.