New theory of quantum gravity.

[michaelmozina]

http://www.spacedaily.com/reports/Rewri ... y_999.html

This is an interesting article about a new theory of quantum gravity that looks promising.

 

[origin]

http://www.spacedaily.com/reports/Rewriting_General_Relativity_999.html

This is an interesting article about a new theory of quantum gravity that looks promising.

The article was a little short on details, but we shall see...

 

[michaelmozina]

I agree it's a little sparse on specifics. It does seem inevitable to me that GR will eventually be replaced with a quantum explanation of gravity. That may not happen in this specific case, but it seems likely to me that it will eventually happen.

 

[ramparts]

Well, Hořava's theory is an interesting bit of work, but as this article says, a lot has yet to be done on it. Incidentally, from what I can tell this new paper (which has gotten mentioned in a couple of threads here in the last few days) doesn't have any shocking new results, it just shows some of the limitations of Hořava gravity and points some directions for the future.

It's a very new theory and a lot of work has yet to be done on it. The violation of Lorentz invariance doesn't help (it might be true but that's a knock on any theory, let's be honest), and it needs a bit of fine-tuning to make it match reality. Also, bear in mind that this isn't actually a theory of quantum gravity, just a modification to general relativity that might be a useful stepping stone to quantum gravity. Hořava gravity, to the best of my knowledge, is purely a theory of gravity, and incorporating it into a full quantum theory of particle interactions will be difficult, to say the least.

That said, it is a theory of gravity that plays a lot more nicely with quantum mechanics, and that's certainly something to be looked at.

Here's a somewhat technical (but also more detailed) view on the same article: http://physics.aps.org/articles/v2/71

 

[harrycostas]

G'day from the land of ozzzzz

Michael said

http://www.spacedaily.com/reports/Rewri ... y_999.html

This is an interesting article about a new theory of quantum gravity that looks promising.

and the link it refers to is

http://arxiv.org/abs/0904.1595
Solutions to Horava Gravity

Authors: H. Lu, Jianwei Mei, C.N. Pope
(Submitted on 10 Apr 2009 (v1), last revised 31 Jul 2009 (this version, v4))

Abstract: Recently Horava proposed a non-relativistic renormalisable theory of gravitation, which reduces to Einstein's general relativity at large distances, and that may provide a candidate for a UV completion of Einstein's theory. In this paper, we derive the full set of equations of motion, and then we obtain spherically symmetric solutions and discuss their properties. We also obtain solutions for the Friedman-Lemaitre-Robertson-Walker cosmological metric.

 

[michaelmozina]

Thank you ramparts and harry for those links. I appreciate it.

 

[harrycostas]

G'day Michael

Please do not think that I'm trying to be smart by posting these links. In my search to understand the Quantum crytical points at various phases and their properties, I came across reading these links. Understanding them is not the issue, the issue is putting the puzzel together in trying to understand the varous forms of solitons and their importance to astrophysics.
It looks like I have a few more years of reading.

I thought you may find this link interesting. I'm still reading through it.
Where there is a blank the name lifshitz goes. For some reason it went blank.

http://arxiv.org/abs/0907.5201
Cuscuton and low energy limit of Horava-Lifshitz gravity

Authors: Niayesh Afshordi (Perimeter Institute)
(Submitted on 30 Jul 2009 (v1), last revised 7 Aug 2009 (this version, v2))

Abstract: A proposal for a power-counting renormalizable theory of quantum gravity at a Lifshitz point was recently put forth by Horava (arXiv:0901.3775), and has been since dubbed as Horava-Lifshitz gravity. The theory explicitly breaks Lorentz invariance, which introduces an apparent extra scalar degree of freedom. In this note, we show that the low energy limit of (non-projectible) Horava-Lifshitz gravity is uniquely given by the quadratic cuscuton model: a covariant scalar field theory with an infinite speed of sound and a quadratic potential, which is minimally coupled to Einstein gravity. This implies that the extra scalar is non-dynamical to all orders in perturbation theory. Using current cosmological constraints on the quadratic cuscuton model, we can constrain the low energy Lorentz breaking parameter of Horava-Lifshitz theory (which leads to a running of Planck mass on the Hubble scale) to |lambda-1| < 0.014 (at 95% confidence level). We also point out that, with reasonable boundary conditions, the spatial hypersurfaces in this theory are constant mean curvature (CMC) or uniform expansion surfaces at low energies, and introduce geometrical symmetries that can protect the non-dynamical nature of these theories from quantum corrections. We also notice that the theory with lambda < 1 might suffer from a non-perturbative UV instability.