On 12/12/2013 5:12 PM, LizR wrote:
On 13 December 2013 14:04, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    The result was lack of frequency dispersion for gamma rays.  So it was 
assuming some
    interaction between photons and the discrete units of spacetime.  That 
seems pretty

Assuming the interpretation is correct, at least. Do you know the theory of why that was supposed to happen, and how the quantisation was reduced so far below the Planck length? If so I'd be interested in an explanation, assuming I can understand it.

Bounds on Spectral Dispersion from Fermi-detected Gamma Ray Bursts
Robert J. Nemiroff,1 Ryan Connolly,1 Justin Holmes,1 and Alexander B. Kostinski1
1Dept. of Physics, Michigan Technological University, 1400 Townsend Dr., Houghton MI, 49931, USA
Data from four Fermi-detected gamma-ray bursts (GRBs) is used to set limits on 
spectral dis-
persion of electromagnetic radiation across the universe. The analysis focuses on photons recorded
above 1 GeV for Fermi detected GRB 080916C, GRB 090510A, GRB 090902B, and GRB 
because these high-energy photons yield the tightest bounds on light dispersion. It is shown that significant photon bunches in GRB 090510A, possibly classic GRB pulses, are remarkably brief, an order of magnitude shorter in duration than any previously claimed temporal feature in this energy range. Although conceivably a > 3 fluctuation, when taken at face value, these pulses lead to an order of magnitude tightening of prior limits on photon dispersion. Bound of c/c < 6.94 x 10-21 is thus obtained. Given generic dispersion relations where the time delay is proportional to the photon energy to the first or second power, the most stringent limits on the dispersion strengths
were k1 < 1.61 x 10-5 sec Gpc-1 GeV-1 and k2 < 3.57 x 10-7 sec Gpc-1 GeV-2 
respectively. Such
limits constrain dispersive effects created, for example, by the spacetime foam of quantum gravity.
In the context of quantum gravity, our bounds set M1c2 greater than 525 times 
the Planck mass,
suggesting that spacetime is smooth at energies near and slightly above the 
Planck mass.


(Presumably if correct this result also screws up things like calculations of black hole entropy, which seem to rely on the Planck length being a "unit" in some sense - at least according to the "science for dummies" books I've read.)

Does quantum mechanics tell an atomistic spacetime?
Hans-Thomas Elze
Dipartimento di Fisica "Enrico Fermi", Largo Pontecorvo 3, I-56127 Pisa, Italia
E-mail: e...@df.unipi.it
Abstract. The canonical answer to the question posed is "Yes." -- tacitly 
assuming that
quantum theory and the concept of spacetime are to be unified by 'quantizing' a 
theory of
gravitation. Yet, instead, one may ponder: Could quantum mechanics arise as a 
reflection of the atomistic nature of spacetime? -- We speculate that this may 
indeed be the
case. We recall the similarity between evolution of classical and quantum mechanical ensembles,
according to Liouville and vonNeumann equation, respectively. The classical and 
mechanical equations are indistinguishable for objects which are free or 
subject to spatially
constant but possibly time dependent, or harmonic forces, if represented 
appropriately. This
result suggests a way to incorporate anharmonic interactions, including 
fluctuations which are
tentatively related to the underlying discreteness of spacetime. Being linear 
and local at the
quantum mechanical level, the model offers a decoherence and natural 
localization mechanism.
However, the relation to primordial deterministic degrees of freedom is 



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