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Would string theory research papers have value if string theory is physically wrong? 
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#1
Jul2510, 08:49 PM

P: 716

Thus far Tevatron and possibly LHC has found no evidence of SUSY, and DM searches thus far null and void. Steinhardt had a paper showing that inflation is incompatible with higher dimensions. There are no experimental evidence for higher dimensions. Thus far proton decay and magnetic monopoles and cosmic strings have not been observed.
It behooves us to ask whether 2 pillars of string theory, higher dimensions and SUSY are not be physical. Perhaps physical reality is really 4D with no SUSY. If string/Mtheory is physically wrong (for example, neither higher dimensions nor SUSY nor dbranes are realized in nature), would Witten and other string theorists be remembered 20 years from now? if Dbranes and SUSY are unphysical, are string theories' derivation of BH entropy and its conclusions about black hole information paradox valid? How many key results of string theory require SUSY and higher dimensions to be fundamental to nature, and what aspects of string theory can be useful to inform future physics research if the world is, in fact, 4D nonSUSY? for examples, KKLT and Ads/CFT have value? It's Smatrix and calculations of graviton scattering amplitudes? Topology changes? Application to heavy ion collisions? holography? Tduality and mirror symmetry? What would be salvageable for future physics if future physics is just 4D with noSUSY, if string theory and its components like SUSY and extra dimensions are unrealized in nature? Has Witten, Suskind, Greene, Randall, etc string theory papers have value or dead end? Would there be a reason to continue string theory research if SUSY and extra dimensions are unphysical? Would it be scientifically responsible for Briane Greene and Michio Kaku to continue to promote string theory in the popular press to a lay audience if it has been shown that SUSY and extra dimensions are unphysical? Note: I'm not implying LQG (CDT, twistors, NCG etc) is correct, only that higher dimensions and SUSY (maybe GUT's) are unphysical. 


#2
Jul2510, 09:20 PM

Astronomy
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PF Gold
P: 23,230

Stuff you might associate with string research comes up in nonstring contexts. Here are some LQG guys:
http://arxiv.org/abs/1001.2748 Twisted geometries: A geometric parametrisation of SU(2) phase space Laurent Freidel, Simone Speziale 28 pages (Submitted on 15 Jan 2010) "A cornerstone of the loop quantum gravity program is the fact that the phase space of general relativity on a fixed graph can be described by a product of SU(2) cotangent bundles per edge. In this paper we show how to parametrize this phase space in terms of quantities describing the intrinsic and extrinsic geometry of the triangulation dual to the graph. These are defined by the assignment to each triangle of its area, the two unit normals as seen from the two polyhedra sharing it, and an additional angle related to the extrinsic curvature. These quantities do not define a Regge geometry, since they include extrinsic data, but a looser notion of discrete geometry which is twisted in the sense that it is locally welldefined, but the local patches lack a consistent gluing among each other. We give the Poisson brackets among the new variables, and exhibit a symplectomorphism which maps them into the Poisson brackets of loop gravity. The new parametrization has the advantage of a simple description of the gaugeinvariant reduced phase space, which is given by a product of phase spaces associated to edges and vertices, and it also provides an abelianisation of the SU(2) connection. The results are relevant for the construction of coherent states, and as a byproduct, contribute to clarify the connection between loop gravity and its subset corresponding to Regge geometries." http://arxiv.org/abs/1006.0199 From twistors to twisted geometries Laurent Freidel, Simone Speziale 9 pages (Submitted on 1 Jun 2010) "In a previous paper we showed that the phase space of loop quantum gravity on a fixed graph can be parametrized in terms of twisted geometries, quantities describing the intrinsic and extrinsic discrete geometry of a cellular decomposition dual to the graph. Here we unravel the origin of the phase space from a geometric interpretation of twistors." http://arxiv.org/abs/0804.0632 Reconstructing AdS/CFT Laurent Freidel 34 pages (Submitted on 4 Apr 2008) "In this note we clarify the dictionary between pure quantum gravity on the bulk in the presence of a cosmological constant and a CFT on the boundary. We show for instance that there is a general correspondence between quantum gravity 'radial states' and a pair of CFT's. Restricting to one CFT is argued to correspond to states possessing an asymptotic infinity. This point of view allows us to address the problem of reconstructing the bulk from the boundary. And in the second part of this paper we present an explicit formula which gives, from the partition function of any 2 dimensional conformal field theory, a wave functional solution to the 3dimensional WheelerDeWitt equation. This establishes at the quantum level a precise dictionary between 2d CFT and pure gravity." Don't get me wrong. I am not saying that AdS/CFT or twistors are part of superstring theory! Holographic concepts are used entirely outside the superstring context. I am just suggesting that a lot of stuff that you might mentally associate with string is apparently valid and useful mathematics. 


#3
Jul2510, 09:26 PM

P: 716

I've wondered what LQG's answer to holographic principle and AdS/CFT. Lubos Motl's criticism is that LQG simply assumes BH entropy is proportional to area. What about LQG and Tduality and mirror symmetry and topology changes BH information paradox? 


#4
Jul2610, 12:36 AM

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P: 5,451

Would string theory research papers have value if string theory is physically wrong?
I can't see how LQG "simply assumes BH entropy is proportional to area". There is a construction n LQG showing that entropy defined on a arbitrary surface will depend on the area; the details are derived, not assumed.
There is no Tduality; and there is no need for it. There is no mirror symmetry as the structures investigated in string theory simply do not exist. 


#5
Jul2610, 12:59 AM

P: 716

Lubos' criticism is that there's no account that LQG BH entropy is volume extensive, and whether the enclosed region is a BH in LQG. What about string theories research on topology changes in a hypothetical world of 4D no SUSY? 


#6
Jul2610, 01:16 AM

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P: 5,451

Mirror symmetry is very intersting in pure mathematics. There are other mathematical theorems derived (partially proved) in or motivated by physical contexts. Think about SeibergWitten for example. These theorems stay valid w/o SUSY and/or strings realized physically.
I am not sure what the main problem of Lubosz Motl is. I have never seen fair statements regarding LQG from him, so I can't say that one should take this seriously. It is true that somehow LQG doesn't care about the dynamics of the black hole when analyzing the area spectrum. That could be a weak point. On the other hand string theory doesn't care about realistic BHs either. Perhaps the fact that LQG allowes one to define a twodim. ChernSimons theory on any "surface" is a strength, not a weakness. I could very well interpret holography in the sense that any closed surface defines a boundary Hilbert space of the enclosed system. The areadependence of entropy is certainly not derived in a dynamical context; it's simply counting microstates. So the question remains if this context allowes one to identify statistical entropy and thermodynamical entropy (but this question remains open in string theory as well, afaik) 


#7
Jul2610, 01:23 AM

P: 716

One question I've had about LQG BH calculation is this: what is the calculated entropy of a sphere enclosing the sun, and suppose you take a sphere enclosing a BH the size of the sun and a sphere of the same size enclosing the sun. Using LQG BH what is the ratio of total entropy between the 2 spheres?
I've wondered if string theory's BH extremel entropy is a numerical coincidence since it relies on SUSY which has not been shown to exist in the real world. Does string theory offer predictions of Hawking radiation, in the nearextremel case? If nature proves to be 4D and susy is not a symmetry of nature, it doesn't sound like much of string/Mtheory would be of value ? (I"m not suggesting that LQG automatically gains in this regard) 


#8
Jul2610, 01:25 AM

Sci Advisor
P: 5,451

There is one main difference between LQG and string theory. The latter one includes all microstates, whereas LGQ (and its application to horizons) contains only "gravitational" degrees of freedom.
So it may seem counterintuitive or even wrong that any 3volume contains entropy that is basically defined by its 2surface area (this is certainly wrong to usual qm systems). But keep in mind that this applies only to gravitational degrees of freedom, that means to entropy of spacetime. I do not know how this changes if one incorporates matter degrees of freedom. 


#9
Jul2610, 07:45 AM

P: 716

As for string theory BH, and counting all microstates, suppose you calculate BH for a negatively charged extremel BH. You get the value. In one scenario you add neutral matter to the BH so only the mass slightly increases. The string calculations should be fine. In another, You then add positrons to this BH so it goes from extremel to nearextremel, the BH caclulations should initially hold up. Then continue adding positrons until the BH is electrically neutral. In this case the string calculations may not count all the microstates even though the total mass added is the same as in the earlier one. 


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