Planck Scale Fluctuations

In a recent paper by Ragazzoni et al.,

[[Mod. note -- I believe the poster is referring to
http://www.arxiv.org/abs/astro-ph/0303043

Title: Lack of observational evidence for quantum structure
of space-time at Plank scales
Authors: R. Ragazzoni, M. Turatto, W. Gaessler
Comments: 12 pages, 3 figures, accepter for ApJL
Journal-ref: Astrophys.J. 587 (2003) L1-L4

It has been noted (Lieu & Hillmann, 2002) that the cumulative affect
of Planck-scale phenomenology, or the structure of space-time
at extremely small scales, can be lead to the loss of phase of
radiation emitted at large distances from the observer. We elaborate
on such an approach and demonstrate that such an effect would lead
to an apparent blurring of distant point-sources. Evidence of the
diffraction pattern from the HST observations of SN 1994D and the
unresolved appearance of a Hubble Deep Field galaxy at z=5.34 lead us
to put stringent limits on the effects of Planck-scale phenomenology.

-- jt]]

the author describes an
experiment known as PSP or Planck-scale Phenomenology. PSP
apparently leads to an angular broadening of a light source (say
distant quasar) placed at a distance L, as seen from a telescope
of diameter D. If lp is the Planck length and lambda the wavelength,
the apparent angular broadening is given by

theta = a0*(L/D)(lp/lambda)^alpha

where alpha and a0 are model dependent parameters (alpha=1 for
linearized theory.

The fuzziness (foamlike) structure of spacetime on scales of the
Planck length evidently affects a photon making a long journey
through this spacetime. The PSP has an effect on the random phase
variation by depending on the ratio of the photon's wavelength
to the Planck length.

My question is this. Does this hypothesis assume a universe with
3 spatial dimensions? Would the presence of 7 more spatial
dimenisons have an effect on the Planck length itself, thereby
altering the effect of the PSP (10 total spatial dimensions)?
Since the Planck length is given by

lp=[(G x h-bar)/c^3]^1/2

would G be altered when extending the experiment into 10 spatial
dimensions (gravity field being diluted due to these extra
spatial dimensions -- maybe explains why the gravitational force
is so weak compared to the other fundamental forces)?

Perhaps the PSP experiment could be used to test for the presence
of extra spatial dimensions!



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| R. Mark Elowitz |
| American Astronomical Society Member |
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