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## Einstein makes extra dimensions TOE the line

 Scientists say that Albert Einstein's principle of the constancy of the speed of light holds up under extremely tight scrutiny, a finding that rules out certain theories predicting extra dimensions and a "frothy" fabric of space.
http://www.gsfc.nasa.gov/topstory/20...2einstein.html
 Recognitions: Gold Member Staff Emeritus What I want to know is why are those two black hole particle beams "aimed directly at the Earth"? Coincidence? I think not...[o)]
 Recognitions: Science Advisor That's funny, but maybe you should take a look at this, http://xxx.lanl.gov/abs/astro-ph/0308214 "Some models with large extra dimensions are ruled out by the existence of absorption in the very high energy spectra of nearby BL Lac objects. The fact that more distant brighter sources are not seen can also be taken as indirect evidence of intergalactic absorption by pair production interactions. The constraints based on analysis of the Crab Nebula γ-ray spectrum, discussed in the previous section, imply that the quantum gravity scale is orders of magnitude above the Planck mass scale. This indicates that the class of models considered here with linear Planck scale suppressed terms in the dispersion relations cannot be reflective of physics at the Planck scale. Models such as loop quantum gravity with a preferred inertial frame are ruled out by this line of reasoning. Alternative models to consider might be models with quartic momentum terms with $M_{QG}^2$ supression in the dispersion relations, Lorentz invariant quantum gravity models, or really new Planck scale physics such as string theory, which preserves Lorentz invariance."

Recognitions:
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## Einstein makes extra dimensions TOE the line

 Originally posted by selfAdjoint What I want to know is why are those two black hole particle beams "aimed directly at the Earth"? Coincidence? I think not...[o)]
Ah blazars! They're really no different from other active galactic nuclei (AGNs), just that by chance we're looking straight down the jets. You can use data on the observed blazar sky density to do several consistency checks of AGN models; e.g. if the jets have an opening angle of x radians, then the sky density of AGNs should be $$\frac{4\pi}{x}$$.