[Paleopsych] NYT: On Gravity, Oreos and a Theory of Everything

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On Gravity, Oreos and a Theory of Everything
http://www.nytimes.com/2005/11/01/science/01prof.html

[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
    concepts.

    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
    strings.

    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
    kismet.

    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.
    Randall said.

    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
    separate universe.

    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
    accelerator.

    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
    nice."

    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
    in particular."

    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
    real."