Why does Stephen Hawking omit all mention Loop Gravity?

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  • #51
MTd2
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Various recent papers have shown that unphysical degrees of freedom do not decouple, as had been anticipated by many.
But it seems several of these articles also argue that these unphysical degrees are in fact dark matter.

I think it is ok to study non stringy theories, because when SUSY is ruled out, we will have more options.
 
  • #52
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But it seems several of these articles also argue that these unphysical degrees are in fact dark matter.

I think it is ok to study non stringy theories, because when SUSY is ruled out, we will have more options.
If SUSY is never detected, and is not detected at LHC nor any astrophysical observation, and is thus not an explanation for stabilization of the electroweak scale and the higgs field, (something else explains Higgs field or electro-weak breaking) is there any reason for popular writers like Hawking, Greene, Kaku, Weinberg etc. to continue to promote strings as the only game in town?
 
  • #53
atyy
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If SUSY is never detected, and is not detected at LHC nor any astrophysical observation, and is thus not an explanation for stabilization of the electroweak scale and the higgs field, (something else explains Higgs field or electro-weak breaking) is there any reason for popular writers like Hawking, Greene, Kaku, Weinberg etc. to continue to promote strings as the only game in town?
It's probably a caricature to say that Hawking, Greene etc "promote strings as the only game in town". However, string theory is the only known consistent quantum theory of gravity at the moment - asymptotic safety is undemonstrated, and condensed matter approaches including Horava gravity have difficulties such as giving the graviton a mass or the wrong dispersion relation. Furthermore, string theory has invigorated QFT because of AdS/CFT. Weinberg, 't Hooft, Wilczek, Hawking have all mentioned non-string approaches, and that string theory may not be ultimately correct, but they have all also acknowledged the importance of string theory.
 
  • #54
tom.stoer
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If you are really interested why Hawking does not mention LQG you should ask him :-)
 
  • #55
atyy
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But it seems several of these articles also argue that these unphysical degrees are in fact dark matter.
Could you post some links? I looked through Marcus's thread, but there are too many for me to find them.
 
  • #56
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[...]
Thanks for the good laugh. I hope you realize you are trying to convince me than you know myself better than I do... Also, I have enough ego not to consider you as an "opponent". I do appreciate your disagreements, at least they are honestly frank. I do not pay attention to your claims of my ignorance, but do pay attention to your scientific comments.
 
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  • #57
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I am still waiting for you to retract or justfy your statement about (the supposed existence of) gauge/gravity dualities in 5 dimensions.
I mentioned the existence of MODELS inspired from Maldacena conjecture entirely restricted to 5 dimensions. It is very different. For instance
Light-Front Holography: A First Approximation to QCD
Phys. Rev. Lett. 102, 081601 (2009)
Guy F. de Téramond and Stanley J. Brodsky
 
  • #58
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string theory unambiguously predicts SUSY
How about misaligned SUSY ? I thought it provides an opportunity for SUSY on the worldsheet but not necessarily on the target space. I guess that does not count as "mainstream"...
 
  • #59
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No way, lorentz symmetry is one of the main constraints in string theory.
Another "non-mainstream" approach
Branes on Charged Dilatonic Backgrounds: Self-Tuning, Lorentz Violations and Cosmology
JHEP 0108 (2001) 005
DAMTP-2001-45, LBNL-48377
C. Grojean, F. Quevedo, G. Tasinato, I. Zavala
We construct an n+q+2 dimensional background that has dilatonic q-brane singularities and that is charged under an antisymmetric tensor field, the background spacetime being maximally symmetric in n-dimensions with constant curvature k=0,+1,-1. For k=1 the bulk solutions correspond to black q-branes. For k=0,-1 the geometry resembles the `white hole' region of the Reissner-N"ordstrom solution with a past Cauchy horizon. The metric between the (timelike) singularity and the horizon is static whereas beyond the horizon it is cosmological. In the particular case of q=0, we study the motion of a codimension one n-brane in these charged dilatonic backgrounds that interpolate between the original scalar self-tuning and the black hole geometry and provide a way to avoid the naked singularity problem and/or the need of having exotic matter on the brane. These backgrounds are asymmetrically warped and so break 4D Lorentz symmetry in a way that is safe for particle physics but may lead to faster than light propagation in the gravitational sector.
 
  • #60
MTd2
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Could you post some links? I looked through Marcus's thread, but there are too many for me to find them.
In fact, Marcus just post a tiny part of what is posted about Horava gravity. I guess this article is not there, so, here it goes:

http://arxiv.org/abs/0905.3563 and its citations.

This one is more recent, from the same author, and make a nice job of reinterpreting Horava Gravity bugs as nice features:

http://arxiv.org/abs/0906.5069

If you want some heavy criticism, this one is the best, uploaded last week:

http://arxiv.org/abs/0907.1636

It hits the theory at its most fundamental base, that is, about the existence of a fixed point. But these authors make a constructive criticism, since they point out possible solutions to solve them. I personaly think that the nature of said solutions will lead to a convergence to the assymtotic safety situation similar to that of einstein quantum gravity.
 
  • #61
atyy
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In fact, Marcus just post a tiny part of what is posted about Horava gravity. I guess this article is not there, so, here it goes:

http://arxiv.org/abs/0905.3563 and its citations.

This one is more recent, from the same author, and make a nice job of reinterpreting Horava Gravity bugs as nice features:

http://arxiv.org/abs/0906.5069

If you want some heavy criticism, this one is the best, uploaded last week:

http://arxiv.org/abs/0907.1636

It hits the theory at its most fundamental base, that is, about the existence of a fixed point. But these authors make a constructive criticism, since they point out possible solutions to solve them. I personaly think that the nature of said solutions will lead to a convergence to the assymtotic safety situation similar to that of einstein quantum gravity.
Thanks! Also for pointing out the latest Wen paper on Marcus's thread! He'd indicated the results at the end of this talk http://pirsa.org/08110003/, so I was hoping for the details to be out soon.
 
  • #62
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Hum, I have seen that you repeatelysay "SUSY/SUGRA is not renormalizable".

I am not sure why civilzed or others didn't mention it, but nowadays the general belief is that SUGRA (D=4, N=8 at least) is very probably renormalizable: See for example: http://arxiv.org/abs/0903.4630
 

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