Three dimensions from strings, or may be seven...
First we thought that strings live in 26 dimensions. Then it turned out that it is 10. Now string theory says that we should either be in a 3 or a 7 dimensional brane. That's what Karch and Randall's analysis claim in hep-th/0506053. You can also read the recent AIP news article here.
The argument is that if the universe (of course the 10D one) is initially filled with branes of all dimensions and sizes, eventually only 3 and 7 dimensional ones will survive and dominate the universe. So the dimension of our world is not chosen by landscape or some fundamental principle, but by the cosmological dynamics. I can't go into the details here, but it is interesting that branes with dimensions have different reasons to dilute away.
I am certainly not an expert, but the arguments here seems to be very basic. If they survive it might be a major milestone in string theory. All we need is an anthropic principle to choose 3D ones ;) Actually these things are already in the market. Structures will not be stable in universes with 7 space and 1 time dimensions. But Karch and Randall suggest that if the expansion of the universe is dominated by something other than branes, there is quite a good chance that 3D ones dominate 7D ones anyway.
It looks interesting, I'll keep an eye on these.
The argument is that if the universe (of course the 10D one) is initially filled with branes of all dimensions and sizes, eventually only 3 and 7 dimensional ones will survive and dominate the universe. So the dimension of our world is not chosen by landscape or some fundamental principle, but by the cosmological dynamics. I can't go into the details here, but it is interesting that branes with dimensions have different reasons to dilute away.
I am certainly not an expert, but the arguments here seems to be very basic. If they survive it might be a major milestone in string theory. All we need is an anthropic principle to choose 3D ones ;) Actually these things are already in the market. Structures will not be stable in universes with 7 space and 1 time dimensions. But Karch and Randall suggest that if the expansion of the universe is dominated by something other than branes, there is quite a good chance that 3D ones dominate 7D ones anyway.
It looks interesting, I'll keep an eye on these.
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