Fermi event

The Fermi experiment detected a 31 GeV photon emitted by a short gamma-ray burst and "this photon sets limits on a possible linear energy dependence of the propagation speed of photons (Lorentz-invariance violation) requiring for the first time a quantum-gravity mass scale significantly above the Planck mass".

In other words, the observed event suggests that Lorentz invariance holds up to (and in fact above) the Planck scale and thus provides an empirical argument to rule out several proposals for quantum gravity. As far as I know, this is the first time direct empirical evidence about the Planck scale was obtained!

Via Lubos.

So what does this tell us about string theory?


Lumo said...

It doesn't tell us anything about string theory we didn't know: it just tells us we knew it correctly because the exact Lorentz invariance in the UV is a universal feature of all stringy vacua, Wolfgang.

wolfgang said...

So I have to conclude that the authors of the five papers I linked to express this universal feature in a *very* obscure way 8-)

PS: By the way, congratulations!
The result certainly supports your point of view, which you advocated and argued consistently.
Now, if they could just get the LHC to work and find some sparticles ...