BOSTON, MASS. -- "Reality is merely an illusion, albeit a persistent
one," according to the late Albert Einstein. But, "if everything is
an illusion and nothing exists," humorist Woody Allen has observed,
"I definitely overpaid for my carpet."
Hang onto your carpet receipts:
Our understanding of reality -- that is, a world where events happen
over time within a three-dimensional space -- may be turned on its
head by the year 2005, scientist Maria Spiropulu said today during
the American Association for the Advancement of Science (AAAS) Annual
"The way we think about things is about to change completely," said
Spiropulu. "This is truly a revolution in the way we understand our
Spiropulu, a 32-year-old scientist with the Enrico Fermi Institute at
the University of Chicago, is hot on the trail of extra dimensions.
She's using new methods to prove, experimentally, whether our reality
is more complicated than we previously assumed.
"We are very close" to a new reality, she said. "Right now, we imagine
space and time as a static question, and we solve equations as a
function of space and time. But, what we're learning is that, at the
very large scale or the very small scale, space and time are dynamic.
What is happening at those scales, we cannot explain. So we have to
wonder, do these scales hold some extra dimensions?"
Traditionally, physicists have mathematically explained all that
happens in the world by using a "standard model." In this system,
all matter is made of lightweight "leptons" (such as electrons and
neutrinos) and quarks. Three forces manipulate these particles:
electromagnetism, and strong and weak nuclear reactions.
But, this traditional approach doesn't explain gravity, the fourth
force. The conventional rules of quantum mechanics have been
successfully married with Einstein's Theory of Special Relativity,
which explains the behavior of very fast objects -- but not with his
Theory of General Relativity, the guidebook to gravitational force.
Mathematical gobbledygook usually results from trying to combine
quantum mechanics and general relativity. Consequently, we still
don't know, for example, what happens to particles sucked into a
In an effort to uniformly explain all events, physicist Gunnar
Nordstrom (1881-1923) first introduced the notion of an extra
dimension at the beginning of the 20th century. Perhaps, he thought,
gravity happens in a realm we don't understand and can't
mathematically define. Some 10 years later, Theodor Kaluza
(1885-1954) and Oskar Klein (1894-1977) took Nordstrom's ideas
another step forward: An extra dimension may be curled up like an
unimaginably small ball, they said, on the order of the Planck
scale -- the smallest unit of length in the universe (10 to the
minus 33 centimeters).
The idea of an extra dimension was resurrected yet again in the late
1990s, as scientists began to ask whether Newton's Law of Universal
Gravitation reliably predicts gravity's behavior below the
centimeter scale, Spiropulu explained. Physicists were energized in
1997 by the discovery of possible links between the standard model
and "superstring theory" -- the notion that a series of extremely
tiny, vibrating strings may lurk beneath the level of quarks and
Researchers Nima Arkani-Hamed, Savas Dimopoulos, and Gia Dvali then
caused further excitement, by suggesting that at least one of these
tiny dimensions might, in fact, be large enough to measure. Still,
no one has produced undeniable proof of superstrings, and many
Since then, Spiropulu reported to AAAS attendees, experiments have
shown that Newton's Law is valid down to the 200-micron level. That
is, gravity "follows the rules" at that scale. But, the physical
reality below this level remains a mystery. Somewhere within the
Planck scale, or at extreme energy levels, an incredibly small
extra dimension may finally combine gravity and electromagnetism,
"We're very close into the energies where we can see effects of a
very low-energy Planck scale," she said. "If an extra dimension
is mirroring the Planck Scale, that means that gravity and the
electromagnetic theory is going to be unified tomorrow."
Gravity, Spiropulu said, may soon be unified in an "unexplainable
hierarchy of scale."
Various scenarios or "frameworks" are emerging to describe a
mysterious sister world where, as Alice in Wonderland once remarked,
"nothing would be what it is, because everything would be what it
Our three-dimensional world includes the coordinates X, Y, and Z,
extending infinitely throughout the universe. But, some researchers
have proposed that extra dimensions may be finite, and compacted
around a sphere, pole, or other geometrical shape. Others have said
that quarks, the standard-model particles, may have "technicolor"
cousins in another realm. Or, quarks and neutrinos may exist in a
mirror-world, as "squarks" and "sneutrinos."
To learn more about what's happening at the very small scale,
Spiropulu and her colleagues are staging high-energy particle
collisions. Extra dimensions, she explained, would leave behind a
"signature," and she hopes to detect it. The classic signature might
be a graviton -- the carrier of gravity -- capable, perhaps, of
trickling to another dimension. In her experiments, protons (the
hydrogen nucleus is a proton) going at almost the speed of light
smash head-on into anti-protons. "What comes out," she said, "is a
graviton, escaping into an extra dimension, and leaving a viable
signature in your detector."
In particle collisions, the conservation of energy and momentum can
be measured, so that what goes into the initial experiment must jive
with what's left over, post crash-test. "If it doesn't add up and
you have significant imbalance," she explained, "that is a viable
signal that there is an extra dimension where, if these theories are
valid, gravity may become very strong, and other weird properties
might kick in. The idea is that there may be a form of super-gravity
in the extra dimension."
Spiropulu shared the latest experimental findings at the AAAS
meeting, including a completely new -- and what she described as
"totally innovative strategy" -- worked out by Harvard's Nima
Arkani-Hamed and others for "dynamically generating an extra
dimension and then testing it," rather than the opposite, more
conventional strategy: Searching for proof of an assumed extra
"We're looking at some really neat, new ideas," she concluded. "We
hope by 2005 to have great results on this topic."
American Association for the Advancement of Science
Monica Amarelo, firstname.lastname@example.org, 617-236-1550
16 Feb 2002
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