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Illustration by Christoph Neimann

THE PAPER: A Rotating Black Ring Solution in Five Dimensions

THE JOURNAL: Physical Review Letters, March 11, 2002

THE AUTHORS: Roberto Emparan and Harvey S. Reall

THE GIST: If you know anything about black holes, you probably think their shape can only be spherical. But they might also be shaped like tiny doughnuts. And if that’s true, we might be living in a five-dimensional universe.

Physicists like to say that black holes have no hair. What they mean is, if we were able to see them, each one would look exactly the same: dark as can be, and shaped like perfect spheres. This we know because it was mathematically proven back in the early 1970s by the not-yet-famous Stephen Hawking and his colleagues. In fact, they actually called it their “no-hair theorem.”

But according to CERN’s Roberto Emparan and Harvey Reall at Queen Mary College in England, black holes may turn out to be a little furrier than previously thought. These scientists say that, within a few years, it might be possible to create miniscule doughnut-shaped black holes, proving that these dense tangles of matter, which have so fired scientific imagination about the nature of time and space, are even more profound than we knew. Indeed, if scientists could create such a black hole, the clear implication would be that we live in a universe with more than four dimensions.

Of course, creating such a hole will not be a simple task. Unlike the massive black holes that already exist, insatiably gobbling gas and dust far away in the cosmos, black hole doughnuts made by humans would be not much bigger than the nucleus of a single atom (black holes in space can be as massive as 100 million suns). Physicists would have to generate them inside huge particle accelerators–tubular machines built literally miles long, whose job is to send tiny bits of matter smashing into each other at fantastic energies. The most powerful particle accelerator in the world–CERN in Geneva, Switzerland–is undergoing an upgrade that’s scheduled to be complete by 2006. When it’s finished, it just might have enough power to create these infinitesimal black holes.

Now, here’s the rub: Without at least one dimension beyond the four we know about, physicists have mathematically proven that it is impossible to create black hole doughnuts. There are four known dimensions: three of space–left-and-right, up-and-down, front-and-back–and one of time. A fifth dimension would be another direction in space, though it’s unclear exactly what direction that could be. But obviously, this dimension would have to be extremely small–certainly less than a millimeter–because if it were any larger, we would have already found it by now.

Of course, if we do one day discover that there are more than four dimensions to our world, the discovery could hold many surprises far beyond hairy black holes. For starters, string theory–the notion that everything in the universe is made from tiny vibrating strings– depends on the existence of 10 dimensions. The tiny doughnut would give this theory a tremendous boost: After all, if there are five dimensions, why couldn’t there be five more?