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Into the fifth dimension

Nima Arkani-Hamed hasn't seen the fifth dimension. But he's pretty sure it's there, somewhere.

In his spare Harvard office, with its elegant wood desk and floor-to-ceiling blackboard, the long-haired tenured theoretical physicist sucks down espressos at a rapid clip as he ponders the nature of, well, everything.

"The universe," he says, "is much more interesting than we realize."

Questions about the universe come naturally to this son of Iranian-born physicists. As a boy, he puzzled: How long does it take a lake to freeze? Where do rainbows appear? How do stones skip across a lake? But even more enthralling to Arkani-Hamed was that the simple physics equations he learned in school, like force = mass x acceleration, provided the answers.

"You could explain the world around you," he says.

Arkani-Hamed, 32, studied math and physics at the University of Toronto, then received a doctorate in physics at the University of California at Berkeley. By this time, he had moved on from rainbows to the laws of nature.

Four basic forces govern everything. There are the weak and strong forces, which bind together and regulate the movement of subatomic particles, like the protons and neutrons in the nucleus of every atom. There's the electromagnetic force, which regulates everything containing electric charges, making possible all the high-tech gadgetry that drives the world.

And then there's the problem child, good old-fashioned, apple-plunking-down gravity. Physicists believe that, on a fundamental level, the first three forces are essentially the same. But gravity is inexplicably weak. Consider: Even the gravity emanating from the massive moon can barely hold humans to the ground.

However physicists tweak the equations, they can't seem to fit gravity in with the other forces. It's just too weak. This is a problem. The basic quest in physics for the last 50 years has been to unify everything, reduce the universe to its simple essence. But gravity simply hasn't complied.

Arkani-Hamed began pondering this quandary as a Stanford University researcher and continued at Harvard. He stumbled onto the idea of extra dimensions. Imagine a piece of paper floating in space. The space is the fifth dimension. Our world, everything we can perceive, is confined to that paper. But what if there is interaction between the paper and the surrounding space?

Perhaps gravity bleeds into this fifth dimension, Arkani-Hamed theorized, or even more dimensions. But, given our four-dimensional reality, we're able to experience only the gravity left over. In other words, gravity is much stronger than we realize. Perhaps, Arkani-Hamed speculated, at super high energy levels, of an intensity never seen by humans, such as the split second after the Big Bang, gravity is like the other forces, before leaking into the fifth dimension.

Describing this conceptual breakthrough, which he backed mathematically, thus rocking modern physics, Arkani-Hamed says: "At the time, I was just in the mood for thinking about something different." As speculative as his ideas might sound, experimental verification is on the way. In three years, a massive particle accelerator in Switzerland comes on line, giving scientists a means to create super-high energy levels that will enable them to measure nature at the most fundamental scale ever. This should provide evidence confirming -- or refuting -- Arkani-Hamed's theory.

"Until then, the next two years are just a fun period of irresponsibility," he says, laughing.

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