[Paleopsych] NYT: On Gravity, Oreos and a Theory of Everything
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Sat Nov 12 17:02:27 UTC 2005
On Gravity, Oreos and a Theory of Everything
[I wonder if there are theories that make time multi-dimensional.]
By DENNIS OVERBYE
The portal to the fifth dimension, sadly, is closed.
There used to be an ice cream parlor in the student center at the
Massachusetts Institute of Technology. And it was there, in the summer
of 1998, that Lisa Randall, now a professor of physics at Harvard and
a bit of a chocoholic, and Raman Sundrum, a professor at Johns
Hopkins, took an imaginary trip right out of this earthly plane into a
science fiction realm of parallel universes, warped space and
otherworldly laws of physics.
They came back with a possible answer to a question that has tormented
scientists for decades, namely why gravity is so weak compared with
the other forces of nature: in effect, we are borrowing it from
another universe. In so doing, Dr. Randall and Dr. Sundrum helped
foment a revolution in the way scientists think about string theory -
the vaunted "theory of everything" - raising a glimmer of hope that
coming experiments may actually test some of its ineffable sounding
Their work undermined well-worn concepts like the idea that we can
even know how many dimensions of space we live in, or the reality of
gravity, space and time.
The work has also made a star and an icon of Dr. Randall. The
attention has been increased by the recent publication to laudatory
reviews of her new book, "Warped Passages, Unraveling the Mysteries of
the Universe's Hidden Dimensions," A debate broke out on the physics
blog Cosmic Variance a few weeks ago about whether it was appropriate,
as a commentator on NPR had said, to say she looked like Jodi Foster.
"How do we know we live in a four-dimensional universe?" she asked a
crowd who filled the Hayden Planetarium on a stormy night last week.
"You think gravity is what you see. We're always just looking at the
tail of things."
Although it is the unanswerable questions that most appeal to her now,
it was the answerable ones that drew her to science, especially math,
as a child, the middle of three daughters of a salesman for an
engineering firm, and a teacher, in Fresh Meadows, Queens. "I really
liked the fact that it had definite answers," Dr. Randall said.
At Stuyvesant High School, where she was in the same class as Brian
Greene, the future Columbia string theorist and best-selling author,
she was the first girl to serve as captain of the school's math team,
and she won the famous Westinghouse Science Talent Search competition
with a project about complex numbers. She went on to Harvard where she
stayed until 1987 when she emerged with a Ph.D. in physics.
Those were heady times in physics. Fired by the dream of a unified
theory of everything, theorists flocked to string theory, which
envisioned the fundamental elements of nature as tiny wriggling
Dr. Randall, however, resisted this siren call, at least for a while.
For one thing, physicists thought it would take a particle accelerator
10 million billion times as powerful as anything on earth to produce
an actual string and test the theory.
String theory also stubbornly requires space-time to have 10
dimensions, not the 4 (3 of space and 1 of time) that we experience.
Preferring to stay closer to testable reality, Dr. Randall was drawn
to a bottom-up approach to theoretical physics, trying to build models
that explain observed phenomena and hoping to discover principles with
wider application. But Dr. Randall and string theory had their own
In the mid-90's, theorists discovered that the theory was even richer
than its founders had thought, describing not just strings but
so-called branes, as in membranes, of all dimensions. Our own universe
could be such a brane, an island of three dimensions floating in a sea
of higher dimension, like a bubble in the sea. But there could be
membranes with five, six, seven or more dimensions coexisting and
mingling like weird cosmic soap bubbles in what theorists sometimes
call the multiverse.
"The stuff we're really famous for was really lucky in a way," Dr.
In the summer of 1998, after postdoctoral stints at Harvard and the
University of California, Berkeley, she was a tenured M.I.T. professor
ready to move to Princeton. She wondered then whether parallel
universes could help solve a vexing problem with a favorite theories
of particle physicists.
That theory, known as supersymmetry, was invented in turn to solve
another problem - the enormous gulf known as the hierarchy problem
between gravity and the other forces. Naïve calculations from first
principles suggest, Dr. Randall said, that gravity should be 10
million billion times as strong as it is. You might find it hard to
imagine gravity as a weak force, but consider, says Dr. Randall, that
a small magnet can hold up a paper clip, even though the entire earth
is pulling down on it.
But there was a hitch with the way the theory worked out in our
universe. It predicted reactions that are not observed.
Dr. Randall wondered if the missing reactions could be explained by
positing that some aspects of the theory were quarantined in a
She called up Dr. Sundrum, who was then a fellow at Boston University
and happy to collaborate, having worked with her before. A lot of
physics is taste, he explained, discerning, for example, what is an
important and a potentially soluble problem. Dr. Randall's biggest
strength, he said, is a kind of "unworldly" instinct. "She has a great
nose," Dr. Sundrum said.
"It's a mystery to those of us - hard to understand, almost to the
point of amusement - how she does it without any clear sign of what
led her to that path," he continued. "She gives no sign of why she
thinks what she thinks."
They began by drawing pictures and making crude estimates over ice
cream and coffee in that ice cream parlor, which is now a taqueria.
What they drew pictures of was a kind of Oreo cookie multiverse, an
architecture similar to one first discovered as a solution of the
string equations by Edward Witten of the Institute for Advanced Study
and Petr Horava, now at Berkeley. Dr. Randall and Dr. Sundrum's model
consisted of a pair of universes, four-dimensional branes, thinly
separated by a five-dimensional space poetically called the bulk.
When they solved the equations for this setup, they discovered that
the space between the branes would be warped. Objects, for example,
would appear to grow larger or smaller and get less massive or more
massive as they moved back and forth between the branes.
Such a situation, they realized to their surprise, could provide a
natural explanation for the hierarchy problem without invoking
supersymmetry. Suppose, they said, that gravity is actually inherently
as strong as the other forces, but because of the warping gravity is
much much stronger on one of the branes than on the other one, where
we happen to live. So we experience gravity as extremely weak.
"You can be only a modest distance away from the gravity brane," Dr.
Randall said, "and gravity will be incredibly weak." A result was a
natural explanation for why atomic forces outgun gravity by 10 million
billion to 1. Could this miracle be true? Crazy as it sounded, they
soon discovered an even more bizarre possibility. The fifth dimension
could actually be infinite and we would not have noticed it.
In this case, there would be only one brane, ours, containing both
gravity as we know it and the rest of nature. But it would warp space
in the same way as in the first model, trapping gravity nearby so that
we would experience space-time as four-dimensional. This new single
brane model did not solve the weak gravity problem, Dr. Randall
admitted, but it was a revelation, that an infinite ocean of space
could be sitting next to us undetected.
"So when we wrote this paper, what we were concentrating on was this
amazing fact that really had been overlooked for 100 years - well,
years, whatever - that you can have this infinite extra dimension,"
she said. "I mean it was quite wild."
This was not the first time that theorists had tinkered with the extra
dimensions of string theory, dimensions that had been presumed to be
coiled out of sight of experiment, into tight loops so small that not
even an electron could enter. In 1998, three theorists - Nima
Arkani-Hamed of Harvard, Gia Divali of New York University and Savas
Dimopoulos of Stanford (a group known in physics as A.D.D.) - had
surprised everybody by suggesting that if one or two of the curled-up
extra dimensions had sizes as big as a tenth of millimeter or so
(gigantic on particle physics scales), gravity would be similarly
diluted and weakened.
When Dr. Randall and Dr. Sundrum published their first paper,
describing the two-brane scheme, in 1999, she said that many
physicists did not recognize it as a new idea and not just an
elaboration on the large extra dimensions of the A.D.D. group. In
fact, she said, the extra dimensions don't have to be very large in
the two-brane theory, less than a millionth of a trillionth of a
trillionth of an inch.
When they published their second paper, about the infinite dimension,
she said, even some of their best friends, reserved judgment.
But by the time a long-planned workshop on strings and particle
physics at the Kavli Institute for Theoretical Physics in Santa
Barbara rolled around that fall, string theorists were excited about
the Randall-Sundrum work and the earlier A.D.D. proposal.
The reason was simple: If they were very lucky and one of these
versions of string theory was the one that nature had adopted, it
could actually be tested in the Large Hadron Collider, the giant
particle accelerator due to go into operation at CERN near Geneva in
2007. Colliding beams of protons with a combined energy of 14 trillion
electron volts, the collider could produce particles like gravitons
going off into the fifth dimension like billiard balls hopping off the
table, black holes or even the illusive strings themselves.
"If this is the way gravity works in high-energy physics, we'll know
about it," Dr. Randall said.
Although physicists agree that these theories are a long shot, the new
work has captured their imaginations and encouraged them to take a
fresh look at the possibilities for the universe and their new
Dr. Greene of Columbia said, "Sometimes it takes an outsider to come
into a field and see what is being missed, or taken for granted." At
first the idea that extra dimensions could be bigger than any of us
had thought was shocking, he said.
Andrew Strominger, a Harvard string theorist, said: "Before A.D.D. we
believed there was no hope of finding evidence for string theory at
the Large Hadron Collider, an assumption that was wrong. It shows how
unimaginative and narrow-minded we are. I see that as cause for
optimism. Science and nature are full of surprises, we never see
what's going to happen next."
It was shortly before a conference that Dr. Randall had organized
during the Kavli workshop that she had her own experience with
gravity: she fell while rock climbing in Yosemite, breaking several
bones. Only a day before, she said, she had completed a climb of Half
Dome and was feeling cocky.
Another symptom of gravity's weakness is that a rope is sufficient to
hold a human body up against earth's pull, but Dr. Randall was still
on the first leg of her climb and hadn't yet attached it to the rock..
She woke up in a helicopter. For a long time, she said, new parts kept
hurting as old ones healed. "I was very much not myself. I didn't even
like chocolate and coffee."
Since she was the conference organizer, her ordeal was more public
than she would have liked. "In some ways you sort of want to do this
in private," Dr. Randall said. "On the other hand people were really
After two years at Princeton, Dr. Randall returned to M.I.T. in 2000,
but then a year later moved to Harvard, by then a powerhouse in string
theory. She was the third woman to get tenure in physics there.
Dr. Randall, 43 and single, prefers not to talk about "the women in
science thing," as she calls it. That subject that gained notoriety
earlier this year when Harvard's President Larry Summers famously
ventured that a relative lack of women in the upper ranks of science
might reflect innate deficiencies, but Dr. Randall said it had been
beaten to death.
Asked if she would rather be a woman in science than talk about women
in science, Dr. Randall said, "I'd rather be a scientist."
She did say that part of the reason she had written her book was to
demonstrate that that there were women out there doing this kind of
science. "I did feel extra pressure to write a good book," she said,
adding that the response in reviews and emails from readers had been
much greater than she had expected.
She was particularly pleased that some of her readers were attentive
and studious enough to catch on to various puns and games she had
inserted in the book, like the frequent references to Alice in
Wonderland, which, she said, is a pun on "one-d-land."
Dr. Randall is intrigued by that fact that her results, as well as
other results from string theory seem to paint a picture of the
universe in which theories with different numbers of dimensions in
them all give the same physics? She and Andreas Karch of the
University of Washington have found, for example, that the fifth
dimension could be so warped that the number of dimensions you see
would depend on where you were. Our own universe might just be a
three-dimensional "sinkhole," she says.
"It's not completely obvious what gravity is, fundamentally, or what
dimensions are, fundamentally," she said over lunch. "One of these
days we'll understand better what we mean, what is the fundamental
thing that's given us space in the first place and dimensions of space
She held out less hope for time, saying, "I just don't understand it.
"Space we can make progress with."
Is time an illusion?
"I wish time were an illusion," she said as she carved up the last of
her chocolate bread pudding, "but unfortunately it seems all too
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