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Black Holes and Hidden Dimensions
Slackware Geek writes "It is being reported in the Nature Science Update that a new observitory being built in Argentina to study cosmic rays could detect extra hidden dimensions if they exist. 'Cosmic rays could find holes in Standard Model of particle physics ...If the Universe contains invisible, extra dimensions, then cosmic rays that hit the atmosphere will produce tiny black holes. These black holes should be numerous enough for the observatory to detect.'"
Reply to parent: nothing. antimatter is not a very exotic thing, normal matter with reverse charge reverse spin. Once in the blackhole there is no telling whether what fell was matter or antimatter, they all behave the same (increase black hole's mass, that is, and nothing else.)
Gentlemen, you can't fight in here, this is the War Room!
This would be a nice feather in the cap of string theory, which to this point does not have any experimental observations to back it up.
One of the predictions (or you could say requirements) of string theory, is that the universe contains a total of 11 space-time dimensions, 7 of which are "curled-up" and are extremely tiny. Every time you move, you pass through the entire universe in each of these 7 dimensions, although your position in the 3 "enlarged" dimensions hardly changes. The interesting thing is that a guy predicted these extra dimensions way back in the 1910's, and was ignored for about 50 years. Experimental evidence on the side of string theory (or as they're calling it now, M-theory) would go a long way towards convincing the experimental physicists that all these theoretical physicists aren't off their rockers.
---- El diablo esta en mis pantalones! Mire, mire!
>Is this detecting the Hawking radiation from an
>evaporating hole, or is it detecting other effects?
Yes, this is essentially what happens. The decay is actually somewhat more complicated; there is an initial "balding" phase in which the black hole loses its hair, along with a "spin-down" phase... after this, there's a very quick evaporation with high sphericity. Go to http://arxiv.org and search for "black hole production"; some recent papers by Giddings have details. It was believed for a while that the cross-section is geometric, which would lead to a good chance of detecting these in the next generation of colliders if large extra dimension (LED) models are correct. A paper by Voloshin indicates, on the other hand, that the cross-section is really exponentially suppressed by the black hole action. I'm not sure this has quite been settled completely.
The basic idea behind all this, by the way, is that there may be extra dimensions which are large compared to the Planck scale (up to a millimeter in size - that's about as far as gravity has been probed!). Gravity would be a field in "the bulk", that is it propagates in all the dimensions, but the standard model fields are localized on some sort of 4-dimensional "brane." There are actually a couple of different models with large extra dimensions - one is the ADD model (Arkani-Hamed, Dimopolous, Dvali) and another is the Randall-Sundrum or "warped extra dimension" model. Searching on arxiv.org for any of these names should get you links to the papers.
The basic reason for looking into all of this is the hierarchy problem, namely that the gravitational force is far weaker than the other forces. The electroweak scale is on the order of one TeV (= trillion electron volts, where one electron volt is about 1.6*10^-19 Joules). Gravity, on the other hand, is associated with a much higher energy scale. To explain this, the ADD model proposed that maybe the fundamental Planck scale is actually on the order of a TeV, like the electroweak scale. In other words, they solve the hierarchy problem by saying there is no hierarchy. Gravity propagates in more dimensions, so that its effect in our four-dimensional part of the universe looks much weaker. The other fields are localized in such a way that this ratio doesn't take any effect for them, so we see them at the "true" Planck scale on the order of a TeV.
It just so happens that the TeV scale is what we're looking at with current colliders, which is why there's so much interest in this lately. But cosmic rays give an alternate approach. Keep in mind that these ideas are very speculative, but still worth looking into.
Matt Reece