For physics, I think this news is of fundamental significance. This is a huge step towards describing the real world in terms of string theory. The backstory is that almost 40 years ago, Bekenstein and Hawking came up with a formula for black hole entropy, but it was based on macroscopic behavior (like the Hawking temperature) and not on a counting of microscopic states. In the mid-90s you had the first microscopic derivation of black hole entropy in string theory, but it was for supersymmetric black holes in five dimensions. Last year that research reached the point of describing an ordinary black hole spinning at maximum velocity, and now it’s made contact with the rest of the real-world black holes.
The other important fact is that this is all done using the “AdS/CFT correspondence”, which is the “holographic principle” applied to string theory. The holographic principle is the proposition that quantum gravity should be equal to a quantum theory without gravity and with one less spatial dimension. The inspiration is again the Bekenstein-Hawking entropy of a black hole, which depends on the surface area. This places an upper bound on the entropy (as a function of energy and volume), and therefore on the number of states, in any field theory containing gravity; if the theory contains more states, it can’t describe black holes. In string theory, the first implementation of the holographic principle was achieved in an “AdS” (anti de Sitter) space, which is a type of spacetime with a boundary of one less dimension. String theory on AdS spaces appears to be equivalent to a certain field theory on their boundaries.
AdS is not the geometry of the real world—that appears to be de Sitter space. However, the geometry near a real-world rotating black hole is a product of an AdS geometry and a circle, and that permits a form of AdS/CFT to be used. The other feature of the real world remaining to be described is, well, ordinary matter outside black holes, and for that “AdS/QCD” should be relevant, though I don’t yet see how to combine the two applications of the correspondence at once.
My excuse for posting this is that I see here and there the assumption that string theory is a dead end irrelevant to reality. This is wrong, the other unification frameworks you hear mentioned are just nothing by comparison. But because a proper understanding of string theory has been years in the making, in recent years the media celebration of string theory has turned into media skepticism. Don’t be fooled; string theory is where the real progress is taking place.
Actually, it’s even better than I realized when I posted that comment. I hadn’t yet grasped the “F-theory” model building program in string theory, which is about two years old. I’ve been studying that lately, and it was mentally apocalyptic to realize how all the details of the standard model could be expressed as a configuration of branes in hyperspace. The morning after, life went on, and I still have heaps to learn, but there’s no turning back after an experience like that.
String theory derives entropy for astrophysical black holes. Some references here.
For physics, I think this news is of fundamental significance. This is a huge step towards describing the real world in terms of string theory. The backstory is that almost 40 years ago, Bekenstein and Hawking came up with a formula for black hole entropy, but it was based on macroscopic behavior (like the Hawking temperature) and not on a counting of microscopic states. In the mid-90s you had the first microscopic derivation of black hole entropy in string theory, but it was for supersymmetric black holes in five dimensions. Last year that research reached the point of describing an ordinary black hole spinning at maximum velocity, and now it’s made contact with the rest of the real-world black holes.
The other important fact is that this is all done using the “AdS/CFT correspondence”, which is the “holographic principle” applied to string theory. The holographic principle is the proposition that quantum gravity should be equal to a quantum theory without gravity and with one less spatial dimension. The inspiration is again the Bekenstein-Hawking entropy of a black hole, which depends on the surface area. This places an upper bound on the entropy (as a function of energy and volume), and therefore on the number of states, in any field theory containing gravity; if the theory contains more states, it can’t describe black holes. In string theory, the first implementation of the holographic principle was achieved in an “AdS” (anti de Sitter) space, which is a type of spacetime with a boundary of one less dimension. String theory on AdS spaces appears to be equivalent to a certain field theory on their boundaries.
AdS is not the geometry of the real world—that appears to be de Sitter space. However, the geometry near a real-world rotating black hole is a product of an AdS geometry and a circle, and that permits a form of AdS/CFT to be used. The other feature of the real world remaining to be described is, well, ordinary matter outside black holes, and for that “AdS/QCD” should be relevant, though I don’t yet see how to combine the two applications of the correspondence at once.
My excuse for posting this is that I see here and there the assumption that string theory is a dead end irrelevant to reality. This is wrong, the other unification frameworks you hear mentioned are just nothing by comparison. But because a proper understanding of string theory has been years in the making, in recent years the media celebration of string theory has turned into media skepticism. Don’t be fooled; string theory is where the real progress is taking place.
That is excellent news!
Actually, it’s even better than I realized when I posted that comment. I hadn’t yet grasped the “F-theory” model building program in string theory, which is about two years old. I’ve been studying that lately, and it was mentally apocalyptic to realize how all the details of the standard model could be expressed as a configuration of branes in hyperspace. The morning after, life went on, and I still have heaps to learn, but there’s no turning back after an experience like that.