Gamma ray burst, LQG and String Theory

[Jimmy84]

I was reading this:
https://www.physicsforums.com/showthread.php?t=181830

On Aug 26, 7:12 am, Rex <relativitexcali...@yahoo.com> wrote:
> On Aug 26, 7:52 pm, Rex <relativitexcali...@yahoo.com> wrote:
> > On Aug 26, 7:07 pm, Jerry <Cephalobus_alie...@comcast.net> wrote:
> > > On Aug 26, 2:48 am, Rex <relativitexcali...@yahoo.com> wrote:
>
> > > >http://blog.sciam.com/index.php?titl...own_of_relativ ...
>
> > > > "Scientific American August 22, 2007 Hints of a breakdown of
> > > > relativity theory? "TheMAGICgamma-raytelescope team has just
> > > > released an eye-popping preprint (following up earlier work)
> > > > describing what might be the first observational hint of
> > > > quantum gravity. What they've seen is that higher-energy
> > > > gammarays appear to travel through space a little bit slower
> > > > than lower-energy ones, contrary to one of the postulates
> > > > underlying Einstein's special theory of relativity -- namely,
> > > > that..."
>
> > > > Did anyone notice the scientific american article above
> > > > has reported findings that is the exact opposite of the
> > > > predictions of loop quantum gravity?? According to LQG,
> > > > each photon occupies a region of lines at each instant as it
> > > > moves through the spin network that is space. The discrete
> > > > nature of space causes higher-energy gamma rays to travel
> > > > slight faster than lower-energy ones. In the above article,
> > > > the result is the opposite to the LQG prediction. If the
> > > > finding is accurate, does this prove Loop Quantum Gravity
> > > > wrong??
>
> > > What is your source for this supposed LQG prediction?
> > > I read -contradictory- reports on what LQG predicts.
>
> > My source is the January 2004 Scientific American issue
> > with the cover "Loop Quantum Gravity" written by
> > Lee Smolin himself.
>
> >http://www.sciamdigital.com/index.cf...ssuePreview&AR...
>
> > So do higher energy photons travel faster or slower relative
> > to lower energy photons??
>
> > rex
>
> Ok. Here's the direct material from the article:
>
> http://www.pbase.com/image/84490660/original
>
> You can see that Lee Smolin put it in illustration and
> state that high energy gamma ray travel faster, not
> slower.
>
> Gee. What is really the case?

I've cross-posted to sci.physics.research, since there is unlikely
to be anybody on the unmoderated groups with the expertise to
answer this question.

So far as my own reading goes, this is what I have so far after a
couple of hours of Googling. Obviously I can't claim to really
understand any of the papers that I've been skimming, so don't you
DARE accept anything I say except with a big grain of salt!

It would seem that LQG predictions of an energy-dependent speed
of light arise out of general heuristic considerations rather than
as a specific, unique prediction of the theory. General bounds can
be set as to the magnitude of the effect, if it exists. However,
not all formulations of LQG predict energy-dependent speed of light,
and not all formulations of LQG which predict energy-dependent speed
of light agree on the sign of the effect.

I will gladly accept corrections from anybody reading this who
genuinely understands the subject rather than has only a passing
understanding. Whoever you may be, thanks in advance!

> > > The following is quoted from an interview with Lee Smolin:
> > > "So Gambini, Pullin, and others calculated how light travels in
> > > a quantum geometry and found that the theory predicts that the
> > > speed of light has a small dependence on energy. Photons of
> > > higher energy travel slightly slower than low-energy photons.
> > > The effect is very small, but it amplifies over time. Two
> > > photons produced by a gamma-ray burst 10 billion years ago, one
> > > redder and one bluer, should arrive on Earth at slightly
> > > different times."
> > > http://www.edge.org/3rd_culture/smol...n03_print.html
>
> > > Some other sources (of perhaps lesser authority) state the
> > > opposite.
>
> > > The situation is rather confusing to those interested amateurs
> > > among us who rely on secondary sources for our knowledge. Is
> > > there a professional out there who could clarify?

Jerry
To be honest Jerry this finding if confirmed would be more of a disaster for
all the rest of modern physics in which the assumption has been that c is
an absolute constant.

LQG's main competitors have not predicted any deviation in the speed of
light at all. Where as theories of space time in which there is a shortest
allowable wavelength and thus a highest allowable energy ( E=hc/\lambda )
generally predict some variance in the speed of light.
--
""I am enough of an artist to draw freely upon my imagination. ..." A.
Einstein
http://www.geocities.com/hontasfx/theory.xhtml

I was wondering if there is any up to day info about the speed of gamma ray burst that could confirm or debunk these claims. Or are LQG and String Theory in troubles?

 

[turbo]

Hi, Jimmy. Quite a few years ago an associate (and former protege, IIR) of Smolin's predicted this frequency-dependent delay in arrival times. Her name is Fotini Markopoulou and she thought that if light interacts with the space through which it propagates, AND if space has a fine structure, then high frequency, high energy EM ought to interact more frequently, and thus be delayed WRT low frequency, low energy EM. She pinned her hopes on data from GLAST, though MAGIC might have scooped GLAST, if the observations and interpretations from last year are reliable. There are a couple of levels of interpretation at interest, here. If Glast observations indicate that there is a frequency-dependent delay in EM arrival times, that would be VERY important, if it could be determined that the delays were (likely) not due to some local mechanism at the GRB. If follow-up observations with similar GRBs show that the magnitude of the delay is proportional to the redshift of the host, we would have to rethink all of cosmology.

The former is posited. The latter is extrapolate from the former, and IMO should be observed. If not, the former observation cannot be said to result from interaction of EM with space along its path of propagation, and is falsified.

 

[friend]

Hi, Jimmy. Quite a few years ago an associate (and former protege, IIR) of Smolin's predicted this frequency-dependent delay in arrival times. Her name is Fotini Markopoulou and she thought that if light interacts with the space through which it propagates, AND if space has a fine structure, then high frequency, high energy EM ought to interact more frequently, and thus be delayed WRT low frequency, low energy EM.

If photons interact with space itself, then don't interactions by definition exchange energy and momentum and so the photon would gradually lose energy as it traveled through space?