Quantum gravity physics based on facts, giving checkable predictions

Wednesday, September 21, 2005

Black holes (mass) as the 5-D spacetime fabric are gravitational gauge bosons (gravitons) on the 4-D hologram we observe; hence gravity is caused by radiation which has an associated mass

The abstract of a paper by Ruth Gregory http://www.iop.org/EJ/article/0264-9381/17/18/103/Q018l3.html states: 'We show how to extend the usual black string instability of vacuum or charged black p-branes to the anti-de Sitter background. The string fragments in an analogous fashion to the ^ = 0 case, the main difference being that instead of a periodic array of black holes forming, an accumulation of "mini" black holes occurs towards the AdS horizon.'

The paper begins begins: 'It has been known for some time that the extended event horizon of a black string or p-brane in higher-dimensional gravity is unstable to fragmentation into black holes [1], and that this instability extends to a much broader range of charged black holes in string theory--the only exception being extremal solutions [2]. '

I don't remember much about anti-de Sitter (AdS) spacetime, and looking at the material available I can see why. Science which begins by taking a hypothetical spacetime and then investigates its properties, is to me back-to-front science. At least some of the major developments in string theory have been driven by the need to conform to facts, such as the development of superstring theory to incorporate supersymmetry (SUSY) to make the Standard Model unify the fundamental forces (apart from gravity).

For more on 'the holographic principle and M-theory (10/11 Witten spacetime): http://www.damtp.cam.ac.uk/user/gr/public/holo/. After paying homage to Plato and his student t'Hooft, that page states:

'At the heart of many of these exciting ideas is a version of the Holographic Principle known as the adS/CFT correspondence.

'Are YOU a Hologram? M-theory and the adS/CFT correspondence

'The adS/CFT correspondence is a type of duality, which states that two apparently distinct physical theories are actually equivalent. On one side of this duality is the physics of gravity in a spacetime known as anti-de Sitter space (adS). Five-dimensional anti-de Sitter space has a boundary which is four-dimensional, and in a certain limit looks like flat spacetime with one time and three space directions. The adS/CFT correspondence states that the physics of gravity in five-dimensional anti-de Sitter space, is equivalent to a certain supersymmetric Yang-Mills theory which is defined on the boundary of adS. This Yang-Mills theory is thus a "hologram" of the physics which is happening in five dimensions. The Yang-Mills theory has gauge group SU(N), where N is very large, and it is said to be "supersymmetric" because it has a symmetry which allows you to exchange bosons and fermions. The hope is that this theory will eventually teach us something about QCD (quantum chromodynamics), which is a gauge theory with gauge group SU(3). QCD describes interactions between quarks. However, QCD has much less symmetry than the theory defined on the boundary of adS; for example, QCD has no supersymmetry. Furthermore, we still don't know how to incorporate a crucial property of QCD, known as asymptotic freedom.

'Here in DAMTP, we have been working to see if the adS/CFT correspondence can be generalized. Working with collaborators in such far-flung places as the United States, Canada, and Durham, we have managed to show that the duality is still true even when you replace adS with more complicated five-dimensional spacetimes. In particular, we have calculated what happens when you put electric charge in adS, or rotation in adS, or even what happens when you put a certain exotic charge known as "NUT-charge" into adS.'

Nigel said...
Dear Lumos,In a previous post you wrote:"The ratio of shear viscosity to the volume density of entropy seems to be always greater than a fixed constant "1/4.pi" (times hbar over Boltzmann's constant). The inequality is saturated for a large class of strongly coupled interacting quantum field theories - corresponding to a kind of ideal fluids - and one can explain it by the fact that they are the holographic dual of a gas of black holes in some kind of anti de Sitter space."In the new post you write: "The relevant calculation involves a graviton propagator in the background of a large (greater than the AdS curvature radius) AdS Schwarzschild black hole; such a black hole is generically dual to the lowest-viscosity environment. It's a rather tedious calculation but you may get the result including the numerical pre-factor. A simpler but less rigorous calculation involves the quasinormal modes."Are you saying that in field theories you can have viscosity present due to the field in space? If that is what you saying then there will be a drag force on a particle moving through space which is proportional to the viscosity.If the spacetime fabric is a 'gas of black holes' in 5-D, these appear as radiation on the 4-D hologram if I understand what is suggested. The spacetime fabric as seen in 4-D is radiation without viscosity. However, I'm probably on a different wavelength and shouldn't comment.Best wishes,Nigel
1:45 PM

Nigel said...
Hi Lubos,Found the New Scientist article that started your previous post on this subject:"Exotic black holes spawn new universal law16:24 23 March 2005 NewScientist.com news service Jenny Hogan "Black holes may define the perfect fluid, suggests a study of black holes that only exist in a theoretical 10-dimensional space. The finding may have spawned a new universal law in physics, which puts constraints on the way fluids behave in the real world."Dam Thanh Son from the University of Washington, US, and his colleagues used string theory to model a 10-dimensional black hole as a liquid. String theory tries to explain fundamental properties of the universe by predicting that seven dimensions exist on top of the known three spatial dimensions. While the concept is currently unproven as a cosmological model, the tools of string theory can sometimes provide answers to real quantum problems."That means that while the 'black holes' modelled by Son are not astrophysical black holes, but mathematical objects that exist in string theory, their findings may have relevance to the real world."The fluid has two properties that relate to the black hole's surface area: viscosity, which describes how thick the liquid is, and entropy density, which is a measure of the internal disorder. Son's team found that the ratio of these two properties is a constant which can be expressed as a mixture of fundamental constants from the quantum world."My initial reaction above was inspired by the reference you made to a "holographic dual of a gas of black holes" in space.However, I don't care about the entropy of a black hole. All I'm interested in is whether black holes have relevance to the spacetime fabric. The holographic conjecture seemed to me to imply that for dealing with the space time fabric, it is admissible to treat the gauge bosons which cause gravity as radiation which in 5-D spacetime is equivalent to black holes (ie, mass), so the radiation is associated with an equivalent mass of black holes.Best wishes,Nigel


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