It's been 10 years now since physicists first raised the possibility that particle accelerators on Earth could produce microscopic black holes. This phenomenon initially seemed hugely exciting since it hinted at a way scientists could test their ideas about quantum gravity, the theory that reconciles quantum mechanics with general relativity. .
Since then, much of the excitement has died down. It turns out that the energy required to create these objects vastly exceeds what is possible in the world's most powerful accelerators and, indeed, is far more than found in the most powerful cosmic ray ever recorded.
There are various loopholes that allow micro-black holes to form at lower energies, however. The most widely discussed is the possibility that the universe has extra dimensions on microscopic scales that significantly weaken gravity at this level. These dimensions would need to operate at a scale greater than 10^-19 metres to allow microscopic black holes to form more easily.
But here again, the evidence is constraining this idea. The world's most powerful accelerator, the Large Hadron Collider, has been running for a year or so and so far failed to produce black holes with masses up to 4.5 TeV. That means any extra dimensions must be smaller than 10^-12 metres in size.
Nevertheless, black holes could still be produced at the LHC at a rate of perhaps 100 per year. But how to spot them?
Today, Marcus Bleicher at the Frankfurt Institute for Advanced Studies in Germany and a few pals outline some of the open problems concerning black hole production and detection at the LHC, assuming it takes place at all.
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