Physicists using Europe's Large Hadron Collider say they haven't seen any microscopic black holes yet — and perhaps they never will. The most they can say right now is that if they exist, the exotic objects would have to have a mass of more than 3.5 trillion electron volts.
Some flavors of string theory have suggested that micro-black holes could be created at the LHC if the universe has "rolled-up" dimensions in addition to the three space dimensions plus time with which we're familiar. In such a universe, the force of gravity might become dramatically stronger at very small distances, and colliding particles occasionally could create an energy density large enough to produce a black hole for just an instant of time.
Two years ago, CERN theoretical physicist Michelangelo Mangano told me that the black-hole scenario was a long shot.
"In order for the LHC to produce some of these black holes, we really have to go beyond the normal theory of gravity," he said at the time. "We have to assume that there are extra dimensions. By the way, there are many theories that have extra dimensions. Not all of them would give rise to black holes at the LHC. It's only highly fine-tuned ones that make this possible."
So it's not correct to say that the lack of black holes suggests string theory is a failure. In fact, string theory covers so many possibilities that another theoretical physicist, Arizona State University's Lawrence Krauss, jokes that it's a "theory of anything" rather than a theory of everything. But the latest findings do eliminate some of the theoretical models, which is a useful exercise.
The current state of things is described in a draft paper submitted to Physics Letters this week by the team analyzing data from the LHC's Compact Muon Solenoid detector, or CMS. It's also summarized in a statement from CERN. The CMS collaboration is due to take much more data next year, and Nature's Geoff Brumfiel quotes CMS spokesperson Guido Tonelli as saying the LHC should be able to exclude the creation of black holes almost entirely by the end of the next run.
For years, the LHC's critics have worried that microscopic black holes would somehow spin out of control, despite physicists' reassurances that such a doomsday scenario runs counter to theory as well as observations. The latest findings demonstrate that it's harder to create a black hole than some theoretical physicists may have thought. But the bottom line remains the same: DON'T PANIC.
More about the LHC and black holes:
- Nightmares and dreams at the LHC
- CERN may extend big-bang research
- Black holes for beginners
- Special report: The Big Bang Machine
- Ars Technica: LHC spots no black holes
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