Integral challenges physics beyond Einstein

[stevebd1]

ESA article

http://www.esa.int/esaCP/SEM5B34TBPG_index_0.html"

30 June 2011

'ESA’s Integral gamma-ray observatory has provided results that will dramatically affect the search for physics beyond Einstein. It has shown that any underlying quantum ‘graininess’ of space must be at much smaller scales than previously predicted.

Einstein’s General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric. Yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach.
One of the great concerns of modern physics is to marry these two concepts into a single theory of quantum gravity.

Now, Integral has placed stringent new limits on the size of these quantum ‘grains’ in space, showing them to be much smaller than some quantum gravity ideas would suggest...'

 

[unusualname]

The puplished paper:

Constraints on Lorentz Invariance Violation using integral/IBIS observations of GRB041219A

was posted a while back on arXiv http://arxiv.org/abs/1106.1068

In the ESA discussion they say 10^-48 m has been demonstrated as an upper limit on the "graininess of space" , but I can't see this clearly derived in the paper.

 

[nicoo]

Thanks for the link stevebd1

Let me quote the interesting part :
"Some theories suggest that the quantum nature of space should manifest itself at the ‘Planck scale’: the minuscule 10-35 of a metre, where a millimetre is 10-3 m.

However, Integral’s observations are about 10 000 times more accurate than any previous and show that any quantum graininess must be at a level of 10-48 m or smaller."

If I am right, in literature LQG defines minimal length to be 10-33cm (planck length). So if it is confirmed, that may be the first experimental result against LQG..

I have no idea if ST predicts any minimal length for space. Can anybody tell me ?

 

[Prathyush]

isnt it odd that the scale of space time grainess is smaller than the plank scale

 

[unusualname]

I think there is some confusion here, that the ESA article doesn't help to clarify.

Even String Theory has discrete "grains" in Matrix theory versions. However Matrix theory is not Lorentz Violating.

I think what the result shows is, if your model has explicit lorentz violation then that violation must occur below 10^48m (although this length is only mentioned directly in the esa article).

So naive lattice models of space would have to have a finer graininess to be consistent with this result.

Most discrete models don't specify a scale at which lorentz violation would occur,so not sure if the result is that useful.

 

[bcrowell]

Sounds to me like this might relate to claims by Smolin and others a while back that LQG made definite predictions about the dispersion of the vacuum...? I don't think LQG practitioners believe these days that there is any such prediction.

 

[unusualname]

user vela has kindly explained the derivation of the 10^-48m limit

https://www.physicsforums.com/showpost.php?p=3386196&postcount=11

and in the same thread, marcus has pointed out that LQG has a lorentz invariant formulation http://arxiv.org/abs/1012.1739.

So, the Integral result doesn't affect Matrix String Theory or LQG, so which major discrete theories does it apply to?

 

[erkokite]

Horava Gravity would likely be affected by this. And maybe CDT (apparently equiv to Horava gravity anyway).

 

[tom.stoer]

Unfortunately we have two threads regarding the same topic; so I'll post my comment here as well:

I think the statement

It has shown that any underlying quantum 'graininess' of space must be at much smaller scales than previously predicted

is missleading b/c it suggests that the "grains" themselves must be much smaller - which is not necessarily the case. Instead the effects of these grains need to be much smaller. So if there is a theory which is compatible with Planck-space grains but w/o any violation or deformation of Lorentz invariance at all (like LQG) then this theory remains to be a perfectly valid candidate theory for quantum gravity.