How can gravity be so strong that it can move planets yet so weak that a simple refrigerator magnet can resist its pull? The question eats at the core of physics; our best theories donâ€™t come close to explaining why gravity is so much weaker than the other fundamental forces (electro-magnetism, for example). Hard problems, though, often demand unorthodox solutions, and the one Nima Arkani-Hamed and his collaborators came up with is a doozy. Gravity, they hypothesized, is seeping out of our three-dimensional universe and into two exceedingly large extra dimensions that are diluting its force. In other words, our universe has a leak.
One year and three papers later, brand-new fields of research had sprouted up around the idea. Just a year after he got his Ph.D. from the University of California at Berkeley, Arkani-Hamed had become a household name (well, in the households of theoretical and particle physicists). â€œIt was obvious to me that Nima was going to be a star, even as an undergrad,â€ says Harvard University theoretical physicist Howard Georgi, who tried unsuccessfully to woo Arkani-Hamed to New England for grad school. â€œNow he is so far ahead of everyone else in his generation that itâ€™s a little embarrassing.â€
Arkani-Hamed did eventually end up at Harvardâ€”at 30, he was made a full professor of physicsâ€”and itâ€™s there that heâ€™s following his latest hunch. But this time, itâ€™s not extra dimensions heâ€™s betting on. Itâ€™s extra universesâ€”some 10500 of them. He and a growing minority of maverick scientists suspect that our universe is just one of untold billions of universes that exist side by side in a cosmic landscape, each with its own laws of physics and its own constants of nature.
His first piece of evidence, albeit indirect, for this multiverse could be collected as soon as next year, when physicists in Geneva turn on the Large Hadron Collider (LHC), the most powerful particle accelerator in the world. If Arkani-Hamedâ€™s calculations are correct, the LHC will reveal a hidden feature of the universe called split supersymmetry, or split susy (pronounced â€œSOO-seeâ€), a theory that half of all particles in the universe have partner particles that the LHC will be able to see.
(Not incidentally, the LHC may instead turn up Arkani-Hamedâ€™s extra dimensions.) If it works, and the LHC finds these partner particles, â€œit will be a mammoth hint that the multiverse is real,â€ Arkani-Hamed says.
So what does this mean? Remember 500-odd years ago when a heretic named Copernicus broke the news that our little planet Earth was not, in fact, the center of the universe? Well, brace yourself. If Arkani-Hamed and his cohorts are correct, our existence is about to be denigrated again. As he explains, â€œThe significance of our world within the multiverse will be no greater than one atom relative to all the matter in our universe.â€â€”rena Marie Pacella