You know black holes, right? Those fearsome cosmic quicksand pits that swallow everything, even light?

They're the unhappy consequence of exhausted stars that collapse in on themselves. The resulting maw seethes with gravity so powerful it can, as astronomer Neil deGrasse Tyson writes in Death by Black Hole, rip apart anything that strays too close, "atom by atom."

Given such a nasty disposition, why would scientists want to try to create black holes here on Earth? And not just one, but lots of them -- miniature black holes belched out as often as once per second like exploding popcorn kernels by the just-activated Large Hadron Collider, an underground machine so colossal it straddles two countries, Switzerland and France?

Because of the remarkable things they would reveal about the universe, physicists say.

"It's the biggest experiment in human history," said Nima Arkani-Hamed of the Institute for Advanced Study in Princeton, N.J., whose theories helped lay the groundwork for the black hole hunt.

If the LHC succeeds in a long-shot effort to make so-called micro black holes -- which experts contend would vanish harmlessly in less than a trillion-trillionth of a second -- that would provide powerful evidence of extra dimensions.

It would illuminate astounding new properties of gravity, and perhaps aid physicists' search for a "Theory of Everything" knitting together all of nature's particles and forces in one seamless explanation.

Many news accounts of the LHC's September start-up (an electrical failure has since idled the collider until next spring) focused on the doomsday scenario, portraying black holes as the offspring of an experiment run amok, an unintended byproduct of smashing protons into protons.

But physicists like Glenn Starkman of Case Western Reserve University have been methodically planning (and hoping) for their production.

Starkman is a kind of black hole profiler, anticipating what properties a stealthy micro black hole should have and how to spy it among the blizzard of exotic particles the LHC will produce. He has co-written a computer program called Black Max that mimics a micro black hole's behavior as it pops into and out of existence.

In a concrete catacomb deep underground at the LHC, the hulking 7-story-tall ATLAS detector encircles the particle racetrack where protons whiz around at nearly the speed of light. The detector will watch for proton smashups like a highway traffic camera. ATLAS' operators are using Black Max to train the detector to spot micro black holes in the collision aftermath.

"We know there are signatures," said Starkman. "We haven't nailed them down precisely. We know ATLAS will be able to detect these objects even if they aren't the simple objects that were [first] proposed."

The quest to make micro black holes at the $8 billion LHC springs from physicists' attempt to solve a profound mystery.

Of nature's four fundamental forces, three operate at roughly the same strength: the strong force, which binds the restless bunches of quarks in an atomic nucleus together; the weak force, which enables nuclear decay; and electromagnetism, which keeps electrons locked in their frenzied orbits.

But the fourth force, gravity, is the weakling of the family. It might seem powerful when you're trying to get off the couch, but it pales compared to the abilities of the other forces.

"If you hit something," said Starkman, rapping his knuckle on the side of his coffee mug, "what's stopping you from putting your hand through it is electromagnetism. That's much stronger than the force pulling it down to the ground," he said, lifting the mug to show how easily gravity is overcome.

Physicists call this vexing disparity the gauge hierarchy problem, and it's a major speed-bump on the road to a Theory of Everything. In 1998, a trio of physicists -- Arkani-Hamed, Gia Dvali and Savas Dimoupolos -- proposed a radical explanation for gravity's apparent wimpy-ness.

Maybe gravity is weak, they reasoned, because it's diluted. Maybe, unlike the other forces, it extends into extra dimensions beyond the three we inhabit. If our 3-D universe is the top of a stack of pancakes, gravity is the syrup that dribbles over the flapjack's edge, down the sides and onto the plate below.

"If there are extra dimensions, you almost can't stop gravity from spreading out into them," Starkman said. "You imagine that gravity spreads out for a while, then stops. It could stop spreading if space wasn't infinite in those extra dimensions."

Physicists have worked out different scenarios in which extra dimensions vary by size, number and even shape. One large extra dimension, or several smaller ones, could account for gravity's diluted strength in our own universe, in roughly the same way that one large paper towel or several smaller ones can sop up an equal amount of spilled milk.

If, if, if. How could anyone test for the existence of extra dimensions and leaking gravity? Black holes and the formidable particle-slamming power of the LHC suggested a way.

The black holes we've come to know from planetarium shows and sci-fi movies are spawned by the runaway implosion of giant stars whose fuel is spent. However, there's no reason any object -- the Earth, a pumpkin seed, a proton -- couldn't be coerced to form a black hole.

All it would take is enough energy to squeeze the object's mass down to a point so small that gravity can overpower the nuclear forces keeping its atoms pumped up. If the Earth could be compacted to fit on the period at the end of this sentence, it would cascade into a black hole.

No machine could ever squash something as big as a planet. Compressing tiny protons might seem easier, but calculations show that even a device as powerful as the LHC shouldn't be able to smash the particles together hard enough to trigger a gravitational avalanche -- unless there really are extra dimensions, with "extra" gravity inside ready to be unleashed.

Assuming that's the case, the boost the LHC gets by tapping those reservoirs of extra-dimensional gravity should tip the balance and pop out short-lived micro black holes.

"Gravity's hoodwinked us for a long time into thinking that it took a lot of energy" to forge black holes, Starkman said. "If this idea is right, it's not true."

But if even the tiniest and shortest-lived black holes swallow light, how would you know they're there? Fortunately, black holes aren't completely black.

The renowned physicist Stephen Hawking figured out that, by a complicated quirk of quantum mechanics, some particles at the black hole's perimeter should escape. Cosmic black holes, the kind created by collapsed stars, should glow with what's come to be called Hawking radiation. If that escaping mass isn't replenished, a black hole should starve and eventually disappear in a final high-energy puff of Hawking radiation.

But because of their unique properties, man-made micro black holes at the LHC may disappear with more of a whimper than a bang.

They will likely spew lots of gravitons when they go, according to recent research by Starkman and colleagues. Since those wispy gravity particles don't show up in any detector, a micro black hole's signature may be missing energy, rather than an abundance of it -- like breaking a dish and only finding half the pieces.

"The main thing is they may not have as much energy as you thought they would," Starkman said. "You could get fooled into thinking there are no black holes if you're not looking for the right thing."