Smolin: Falsifiable Predictions from QG

[marcus]

just out today:

http://arxiv.org/abs/hep-th/0501091


Falsifiable predictions from semiclassical quantum gravity
Lee Smolin
9 pages

"Predictions are derived for the upcoming AUGER and GLAST experiments from a semiclassical approximation to quantum gravity. It is argued that to first order in the Planck length the effect of quantum gravity is to make the low energy effective spacetime metric energy dependent. The diffeomorphism invariance of the semiclassical theory forbids the appearance of a preferred frame of reference, consequently the local symmetry of this energy-dependent effective metric is a non-linear realization of the Lorentz transformations, which renders the Planck energy observer independent. This gives a form of deformed or doubly special relativity (DSR), previously explored with Magueijo, called the rainbow metric. The argument is general, and applies in all dimensions with and without supersymmetry, and is, at least to leading order, universal for all matter couplings. The argument is illustrated in detail in a specific example in loop quantum gravity.
A consequence of DSR realized with an energy dependent effective metric is a helicity independent energy dependence in the speed of light to first order in the Planck length. However, thresholds for Tev photons and GZK protons are unchanged from special relativistic predictions. These predictions of quantum gravity are falsifiable by the upcoming AUGER and GLAST experiments."

 

[selfAdjoint]

I just scanned this paper. He asserts that Planck length physics modifies, but does not truly violate, the Lorentz transforrmations to produce DSR. The difference is a subtle one, and he discusses it carefully. The LTs pick up a nonlinearity.

 

[R0man]

Smolin's paper presents an interesting and potentially groundbreaking approach to quantum gravity. By using a semiclassical approximation, he argues that the effect of quantum gravity is to make the low energy effective spacetime metric energy dependent. This leads to a form of deformed or doubly special relativity (DSR), which he calls the "rainbow metric". This theory is applicable in all dimensions, with or without supersymmetry, and is universal for all matter couplings.

One of the key predictions of this theory is a helicity independent energy dependence in the speed of light to first order in the Planck length. This means that the speed of light would vary with energy, but not with the direction of motion. This prediction is in contrast to traditional theories of relativity, which predict a constant speed of light regardless of energy or direction of motion. Smolin suggests that this prediction can be tested by upcoming experiments such as AUGER and GLAST.

If these experiments do indeed confirm Smolin's predictions, it would be a major step forward in our understanding of quantum gravity. It would also have significant implications for our understanding of the fundamental nature of spacetime and the laws of physics. However, it is important to note that these predictions are based on a semiclassical approximation and may not hold up in a full theory of quantum gravity. Nevertheless, Smolin's paper presents a compelling argument and adds to the ongoing discussion and research on quantum gravity.