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Gravity on the Brane
March 6, 2010  |  by Michael Anft

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SUNDRUM’S OFFICE LOOKS LIKE HE just moved in, even though he’s held down a spot in the Bloomberg Physics building since 2000. There’s a blackboard for drawing crude-but-useful explanatory pictures for students and other inquiring (if not quite as developed) minds, along with a computer and a desk that doesn’t look all that busy. He’s a big one for holding a lot of stuff in his head, so the lack of clutter or personal effects makes sense. (Not that Sundrum, a confident, pleasant fellow, doesn’t have a bit of the absent-minded professor in him. On the outside of his right hand is scrawled HOME WATER, a reminder from his wife to turn off the patio hose before that night’s early-winter freeze.) Newly hatched ideas—even ones with a 1 percent probability of being right—need big room to play in. And mucking around in theoretical space is where Sundrum, a rangy, energetic sort, gains a sense of comfort.

It took him a while to carve it out. As a teen growing up in Australia, Sundrum thought he’d follow in the footsteps of his forebears and get into medicine. But the field lacked the profundity he intuited was part of his nature, a need for solemn, if spirited rumination that led him to mull over the concepts of free will and artificial intelligence, or to develop algorithms he tried out on his homely and primitive PC. “I’d worry about things like, what makes a machine think?” he recalls. “My psychology at the time was to see things and say, ‘Man, that’s really deep,’ whereas other things might seem interesting or important but not necessarily as deep. When I was making plans as to what I wanted to do with my life, something popped into my head at the last minute: Don’t go to medical school!”

Raman Sundrum: “I’m  1 percent sure I’m right, which is better than thinking I’m .0001 percent right.” Photo: Mike Ciesieski

Raman Sundrum: “I’m 1 percent sure I’m right, which is better than thinking I’m .0001 percent right.” Photo: Mike Ciesieski

Sundrum was a math prodigy, but claims he was never good at math. (He might be exercising some modesty: He twice won top honors in Australia for his talent with numbers.) “I always wanted to be good at math because I thought I’d be more popular—and yes, I know that’s a ridiculous thing to say,” he says. “But I wasn’t one of those people who loved math. I wanted something with some creativity to it. At the tail end of high school, I decided to go into the deep end. I was succumbing to my romance with Newton and Einstein.”

As an undergrad in Australia, the profundity of Newton and Einstein became difficult—Sundrum flailed in the deep end. “I really felt like a complete mediocrity. I was good at the math, but I struggled with the physics. In physics, someone says something in plain English—like, ‘gravity is surprisingly weak’—and you’re supposed to come up with a question from that, figure out what is relevant, and then form a mathematical equation to solve it. That’s incredibly hard. Most people aren’t born with that gift,” he says.

What helped turn him around was an essay assignment he received as an upperclassman. An instructor asked each member of his class to write a report on an article in Scientific American magazine about physics. Sundrum uncovered one about fiber bundles, a branch of geometric space that was curved, similar to that posited by the theory of relativity. “I thought the definition of them in mathematical terms was fascinating,” says Sundrum. “It was just a beautiful subject. What blew me away was that there was a branch of physics where fiber bundles mattered. I thought, ‘Wow!’ Here I was doing electro charges on plates, about which I could not care less, and yet here is this whole other branch of physics that deals with this.”

A professor told him this was called particle physics. In it, he found his niche, earning a PhD from Yale after leaving home for the United States. Thus began a long exile in the academic wilderness. Unable to snag a teaching job and too reluctant to publish because he had fragments of ideas and no definitive, Einstein-correcting answers, he spent nearly a decade doing postdoctoral jobs, traveling from the University of California at Berkeley to Harvard to Boston University to Stanford. He stoked his curiosity, taking on some of the big issues in physics, studying some of the forces, including strong nuclear interactions, as well as emerging ideas about extra dimensions and dark energy, the force that causes the universe to expand at an ever-faster clip. But he couldn’t find a tenure-track post. “I was kind of oblivious to the fact that you had to make a career,” Sundrum says. “I turned down a couple of invitations to apply for jobs, then regretted it. The question became: What else could I do?”

He got a shot at a position with McKinsey & Co., the business-consulting outfit—like many financially oriented companies, McKinsey covets sharp formula guys from the world of physics—acing the first pair of interviews in 1998. “I was told that the third round would be plain sailing, but I didn’t make it,” he recalls. “I didn’t take it as seriously as I should have.” It seems that during his plane trip to the interview, he thought about nothing but physics. “I wasn’t in the right mindset.”

Around the same time, he had made a breakthrough or two on the “career” that hadn’t yet taken flight. After reading a paper on the possibility of extra dimensions written by three of the world’s most prominent particle physicists, Sundrum was inspired to jot down some of his own observations on the topic. He had been using the concept of extra dimensions to deepen his explorations of dark energy, how the universe expands, and whether Einstein’s thinking on the subject—a concept called the cosmological constant—was correct, when the paper in question crossed his desk. The authors “made perfectly reasonable statements about extra dimensions and things that had nothing to do with the cosmological constant,” he says, his voice rising as he remembers the surprise the paper evoked in him. For him, such a paper, to be truly significant, needed to discuss the constant. “I realized that people publish with a much lower threshold than I had led myself to believe was necessary—they publish when they don’t have all the answers. I was being too pure.”

Those who know Sundrum and his style agree that the paper in question emboldened him. “He was worried that those theorists had solved the cosmological constant—’Oh, my God, they’ve done it!’—then read the paper and figured out they hadn’t solved anything,” says David Kaplan, an associate professor of physics and astronomy at Johns Hopkins, and a favorite sounding board of Sundrum’s. “He realized at that moment you could have much lower standards in what you actually put into print. It liberated him.”

Sundrum quickly published two papers on extra dimensions. Besides breaking a logjam of long-repressed deep thought, the publications caught the eye of Lisa Randall, like Sundrum a former math prodigy who had decided to take on the universe’s biggest questions. Then hovering between appointments at MIT and Princeton, Randall rang up Sundrum, then at Boston U., to discuss how his vision of extra dimensions might fit in with her leading-edge theories on supersymmetry. The two brought similar appetites 
for calculus, coffee, and long speculative talks.

But they came at questions from totally different places—something that made the partnership particularly effective, Randall, now at Harvard, says. “Raman was the type who would go off and do his own thing, but he had thought about branes and extra dimensions before I had. Our styles are different, but we agree on what things are important enough to look into. If you have a good idea in science, you have to be both exuberant and skeptical about it. We both had that,” she says.

Sundrum thought that extra dimensions could lead him to an explanation for what makes up dark energy, which accounts for as much as 70 percent of the universe and is causing its expansion to accelerate. But his research needed tweaking. He worried that “a sign mistake” would create a “catastrophic instability” in his adaptations of the higher-dimensional Einstein equations he was using. He and Randall worked it out during one of several 90-minute sessions spent amid the bustle of an ice cream shop.

“We would gossip, tell jokes, work on ideas—it was all mixed in there,” Sundrum says. “The brain has to be loose—you can’t come up with ideas if it’s all tensed up. We shared this playfulness, this willingness to make guesses and see where they’d lead us.” To test their estimations, they’d travel to Sundrum’s office nearby, or stalk down the halls of MIT in search of an empty, darkened classroom with a blackboard. There, the concepts would be turned into the language of numbers.

After talking about extra dimensions for several sessions, the two began to work out the math. “We found some kind of magic,” Sundrum recalls. “We worked out this problem of an infinite extra dimension in the presence of supersymmetry. It kind of fell into our laps. As we continued mapping out this formula, we thought we’d be proven wrong in five minutes. But the longer we kept at it, the better it looked.” The discovery was part inspiration and part happenstance: “We found that my love affair with dark energy and extra dimensions wasn’t going to pan out, but other things would.”

Randall and Sundrum would actually produce four papers together in 1998 and 1999, but the ones involving RS models are those most read by other theoretical physicists. So far, they’ve stood the test of time—people still cite them because they remain theoretically viable and, some physicists say, downright vibrant, even to those who refuse to buy into the whole idea. The math adds up.

As physics gained a new way to look at an old problem, Sundrum’s exile from the academy was about to end. Johns Hopkins hired him as an associate professor in 2000 and named him a full professor a year later. A shaky decade of daring thinking on a variety of Big Questions—and a measure of self-doubt—had come to a fruitful end. “Running into Lisa Randall, who has a killer instinct and who likes to work on only big things, helped Raman,” says Kaplan. “It actually woke him up.”

TO TALK ABOUT EXPERIMENTS AT the Large Hadron Collider, one must use the language of Carl Sagan. And not just words like quarks and leptons and bosons, but others that hint at the immense quantities of things—billions and billions of this, trillions of that—responsible for outfitting the world’s poshest techno-pit 50 stories below the French-Swiss Alps. The place is a surreal complex of cosmic numbers. Thousands of scientists from 77 countries have devised experiments that will play out amid the $10 billion or so it took to hammer together a machine that sends as much as 7 trillion electric volts through trillions of protons. That level of energy gets the particles up to speeds that cause them to tear through a 17-mile-long loop and smash into each other.

The idea is to re-create the conditions of the Big Bang, or at least one-millionth of a billionth of a billionth of a second after it, so scientists can come to some common understanding as to why elementary particles are perceived as being so light, or why gravity refuses to play by the rules associated with the other three forces of nature. Some secrets of dark matter, the shadowy stuff that makes up 25 percent of the universe, might be gleaned as well.

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