In the popular imagination, black holes are voracious monstrosities that devour everything in their vicinity. Because of this, there are occasional concerns that physicists might accidentally or intentionally build one, perhaps in a particle accelerator like the Large Hadron Collider (LHC) at CERN near Geneva. Would such a dark beast devour the earth itself? Not quite. Nobody has ever created a black hole on our planet before. But even if someone did, it probably wouldn’t pose much of a threat.
Black holes in the real world are only scary in the sense that you can’t escape if you get too close to one. But even if someone created a black hole in a laboratory on Earth, the limitations of human technology would prevent us from conjuring up anything particularly dangerous. “It would probably be so low in mass that its gravitational influence would be relatively small,” says Eliot Quataert, a theoretical astrophysicist at Princeton University. “It wouldn’t really gobble up that much matter.”
In fact, the possibility of creating a black hole in a laboratory is a goal that scientists are actively pursuing – one that could allow researchers to answer many fundamental questions about quantum mechanics and the nature of gravity.
A black hole is usually formed when a star much more massive than our sun dies. As the outer layers of such a star explode outward in a spectacular supernova, its core crumbles inward, pressing down on its central point with such force that no known force in the universe can stop it. The result is a subatomic speck of unimaginable mass and density, whose gravity is so strong that even something traveling at the speed of light could not move fast enough to escape its clutches. These types of black holes are common throughout the universe.
Of course, as long as something doesn’t get too close to a black hole, it’s safe. Only within a spherical boundary surrounding the black hole, known as the event horizon, would a person or object be inexorably pulled inward. Giant black holes have large event horizons – millions of kilometers across – while smaller ones have tinier event horizons, just tens of kilometers across. If you could make a black hole in a laboratory that weighed just half a kilogram, it would have an event horizon a trillion times smaller than a proton.
Fears that the LHC could create a black hole stem from the fact that in Einstein’s special theory of relativity the mass (M) and energy (E) are interchangeable – hence the famous equation E = mc2Where “C‘ is the speed of light. As a supercollider hurls protons together at incredible speeds (almost the speed of light) and energies, all sorts of weird and exotic particles can erupt, possibly including a black hole. But creating a black hole with even a microscopic event horizon would require billions of times more energy than the LHC can produce. And even if it could produce such a black hole, that object would quickly lose energy and disintegrate in the blink of an eye.
Before the facility went live in 2008, some researchers had postulated that a black hole could form if the fabric of spacetime had additional dimensions, as suggested by string theory — a possible way to consolidate quantum physics and gravity into a single theory combine. That’s because in our four-dimensional universe (with three space dimensions and one time dimension), gravity is too weak to pound matter into a black hole. However, if other dimensions exist, gravity may not be the weakling it seems to us because some of its power could leak into those other strange dimensions. In such a universe, a black hole appearing in an atom smasher becomes much more feasible, potentially revealing insights into the nature of gravity. This discovery was “among the strangest and most startling physical phenomena to be seen at the LHC,” says Juan Maldacena, a theoretical physicist at the Institute for Advanced Study in Princeton, NJ
The idea was picked up by the media and caused a stir. A German chemist even filed a lawsuit against CERN in the European Court of Human Rights. A special committee of physicists had started looking into the matter as early as 2003, concluding that the possibility seemed unlikely because particles from outer space are slamming into the atmosphere at energies far higher than the supercollider, with no black holes to create. The committee’s report was reviewed and reissued in 2008 with more information to allay public concerns.
To date, no black holes have been sighted at the LHC. Confirming string theory’s predictions “would have been nice,” says Maldacena, “but it didn’t happen.”
Recently, a team announced that they had used a quantum computer to create a simulation of a baby wormhole – a kind of bridge through reality created from two black holes. Although the result was widely covered in the press, it wasn’t exactly the breakthrough that many had envisioned.
“What was created is more like a strange quantum mechanical property of matter that has mathematical properties associated with wormholes,” says Quataert. “It’s more of a conceptual connection than a literal connection.”
Still, the research is promising, says Maldacena, and in the future, more powerful quantum computers may one day create objects that simulate black holes using Albert Einstein’s equations, allowing physicists to study their behavior in detail.
If he had a real black hole in his lab, Quataert would be keen to learn more about the bright flares called accretion disks that these objects produce as they shred nearby material. “I would throw matter at the black hole to create a small accretion disk and observe the gas spiral and create a lot of light,” he says. “It would be great to understand how these accretion disks actually work in a controlled environment.”