Gamma-ray burst restricts ways to beat Einstein's relativity

Symmetry ^ | Thursday, October 29, 2009 | David Harris

[SunkenCiv]

When the Fermi team did the calculations, using the most conservative estimates for how astrophysics plays into this, they determined that the mass scale must be at least 1.2 times the Planck mass, and by using reasonable but less conservative assumptions, they derived lower limits on the mass scale of up to 100 times the Planck mass. One way to interpret this is to say that there is no variation of the speed of light coming from any quantum gravity effects at less than 1.2 times the Planck mass. And given that some quantum gravity frameworks predict that effects should be showing up at that point, perhaps those models are simply wrong, and there is no changing speed of light.

There are, however, quite a few caveats. The limit on the mass scale is only true if the quantum gravity effects show up in the simplest possible phenomenology where the time difference is proportional to the energy difference scaled by the quantum gravity mass. Some models suggest that the time difference might be proportional to the square of the energy difference scaled by the quantum gravity mass. That would be a much smaller time difference and not observable in this kind of experiment.

Additionally, other quantum gravity models could still have quantized space-time but wouldn't show an energy-dependent speed of light in this form. Instead, speed might depend on the polarization of the light (called birefringence, like the optical property of calcite crystals which create two images when you look through them). There are other options floating around as well.

To be fair to the claim, though, ruling out the simplest dependence of speed on energy at the expected Planck scale is a significant constraint on future theories of quantum gravity.

[SunkenCiv]

[the link behind this image leads to an mp4]

In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect, eliminating some approaches to a new theory of gravity. Click for an animation that shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet

[SunkenCiv]

Here’s the Ars Technica I couldn’t use because of copyright restrictions through the failing Conde’ Nast:

http://arst.ch/9dp

[SunkenCiv]

Quantum gravity site:freerepublic.com

Google

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[Recon Dad]

The limit on the mass scale is only true if the quantum gravity effects show up in the simplest possible phenomenology where the time difference is proportional to the energy difference scaled by the quantum gravity mass.

The above cleared it all up for me.

[The Comedian]

[SunkenCiv]

That should do it...

[OneWingedShark]

LOL

[mikrofon]

Some models suggest that the time difference might be
proportional to the square of the energy difference
scaled by the quantum gravity mass

Anyone with even half a brain knows that....

[SunkenCiv]

[oldbill]

Makes sense to me.

[JoeProBono]

[airborne]

The limit on the mass scale is only true if the quantum gravity effects show up in the simplest possible phenomenology where the time difference is proportional to the energy difference scaled by the quantum gravity mass.

" The above cleared it all up for me."

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The above made my head hurt! :^p

[Kevmo]

Sounds a lot like this thread I posted back in June:

Re-Analysis of the Marinov Light-Speed Anisotropy Experiment
http://www.freerepublic.com/focus/f-bloggers/2270920/posts
06/12/2009 11:25:41 PM PDT · by Kevmo · 27 replies · 1,125+ views
arxiv.org ^ | Reginald T. Cahill

[tlb]

>>>the mass scale must be at least 1.2 times the Planck mass, and by using reasonable but less conservative assumptions, they derived lower limits on the mass scale of up to 100 times the Planck mass.

I was thinking that just the other day. Darn I knew I should have written it down.

[SunkenCiv]

It looked familiar, but the commie search engine turned up nothing. :’)

[SunkenCiv]

:’)