You know those black holes the Large Hadron Collider was going to make and kill us all? Well, not only are we still here, but the LHC doesn't seem to be making black holes at all---their decay signature is markedly absent from the data collected so far. While that is good for those of us who want to keep living (we jest---the hypothetical micro black holes posed no danger), it's also helping physicists make up their minds about how many dimensions there are in our universe. The lack of black holes at the LHC nullifies some of the wackier versions of string theory which depend on multiple dimensions.
"In order for the LHC to produce some of these black holes, we really have to go beyond the normal theory of gravity," [CERN theoretical physicist Michelangelo Mangano] said [two years ago]. "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." [CosmicLog]
These extra dimensions, beyond the four that we experience, are needed to rectify the inconsistencies between general relativity (the physics of gravity and space-time) and quantum mechanics (the physics of subatomic particles). Some string theories predict that gravity is stronger in these other dimensions, and that at very small distances (where these dimensions are experienced), it would be strong enough to create a black hole. Since the scientists haven't seen the signals that these black holes would make, it's likely that this particular flavor of string theory isn't correct. The data will be published in Physics Letters, and is currently available on arXiv
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