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
tight.
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
090926A
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.
arXiv:1109.5191v2
(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
coarse-grained
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
quantum
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
nonlocal.
arXiv:0906.1101v1
Brent
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