Energy dependence in speed of light may have been observed

[Martin]

here is website for the "magic" collaboration, showing one of their dishes. they have an observatory in the Canary Isles.

http://magic.mppmu.mpg.de/

recent news

http://magic.mppmu.mpg.de/physics/recent/index.htm

 

they observed gammaray flares from an AGN (active galactic nucleus) some half-billion LY away

and found that the higher energy bunch was coming in with about a 4 minute delay, pointing to a fractional decrease in the speed the photons were traveling of 10^-14. That is "ten quadrillionths". It means some of the photons in the flare were moving ten quadrillionths slower than the rest.

 

http://arxiv.org/abs/0708.2889

Probing Quantum Gravity using Photons from a Mkn 501 Flare Observed by MAGIC

J. Albert, et al., for the MAGIC Collaboration, John Ellis, N.E. Mavromatos, D.V. Nanopoulos, A.S. Sakharov, E.K.G. Sarkisyan

5 pages, 3 figures, submitted to Phys. Rev. Lett

(Submitted on 21 Aug 2007)

 

"We use the timing of photons observed by the MAGIC gamma-ray telescope during a flare of the active galaxy Markarian 501 to probe a vacuum refractive index ~ 1-(E/M_QGn)^n, n = 1,2, that might be induced by quantum gravity. The peaking of the flare is found to maximize for quantum-gravity mass scales M_QG1 ~ 0.4x10^18 GeV or M_QG2 ~ 0.6x10^11 GeV, and we establish lower limits M_QG1 > 0.26x10^18 GeV or M_QG2 > 0.39x10^11 GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect."

 

one of their findings is about the fractional change in the photons speed, with energy. the fractional change in speed is written delta c/c

 

they found that if the dependence is LINEAR on energy then there is a coefficient which is one sixth the Planck energy and the equation is:

delta c/c = - (E/ 1/6 Planck)

 

this is the reduced Planck energy 2.43 x 10^18 GeV

which you can see defined here

http://en.wikipedia.org/wiki/Planck_energy

 

There are of course many reasons to be very skeptical and cautious about this. Also the result is just plain unexpected.

 

But regardless of reservations, it is something to know about. If it is right it means that what we call the speed of light is really the speed of LOW ENERGY light and as you get up into the gammaray range of a TeV (trillion electron volts) where one photon carries a TeV of energy, then you can see a very slight energy dependence of the speed. Like the photon might be going ONE QUADRILLIONTH slower than is normal for light.

 

Some of the authors of the paper are well-known highly respected. Like John Ellis is a senior guy at CERN. the paper carries some weight despite seeming a bit out there on the edge.

[alan2here]

light is a wave so it wouldn't make much sense for it to be moving in space slowly and more than a wave on a lake of water so move slowly?

 

Can you simply some of the rest of that post please.

[BhavinB]

Question: How do they know that the delay is not caused by dispersion of any material in the path of the light?

[Martin]

A growing chorus of voices is saying that the authors over interpreted their data.

 

It could become like "cold fusion".

 

Other groups observing AGN flares might try to replicate, with flares at different distances so that one would expect different dispersion (if the effect happens during travel and not at the source).

 

And if other groups can't find the effect then the excitement just dies down.

 

Bee Hossenfelder's blog "Backreaction" has this comment:

http://backreaction.blogspot.com/2007/08/magics-observation-of-gamma-ray-bursts.html

 

"This is the summary, status Sunday evening. In case I loose one or the other reader here, let me give you my opinion up front: there is no experimental evidence for quantum gravity, and none of the present theories can be tested with currently available data. If you're looking for sensations, you're on the wrong blog. I suggest you try one of those mentioned above instead."

 

=====================

UPDATE. Since I can still edit I'll answer BhavinB's post here

Are all flares expected to provide similar delays regardless of the source strength?...

 

Bhavin, I don't think there is agreement about what to expect. More flares need to be observed. So far we just have a sample of one, basically.

Observing more flares at different distances can (if the effect persists) be used to exclude the possibility that the delay happened at the source and to confirm

that it is something that occurs during the travel time.

 

So far, the relation they claim to see evidence for is that THE DELAY AS A FRACTION OF TRAVEL TIME should be equal to E/M

where E is the energy of the photon and M is a constant about 1/6 of the reduced planck energy.

if that relation between photon energy and delay time can be established it would seem to me to require new physics to explain by whatever means.

[Klaynos]

Question: How do they know that the delay is not caused by dispersion of any material in the path of the light?

 

I was wondering something similar.

[BhavinB]

A growing chorus of voices is saying that the authors over interpreted their data.

 

It could become like "cold fusion".

 

Other groups observing AGN flares might try to replicate, with flares at different distances so that one would expect different dispersion (if the effect happens during travel and not at the source).

 

And if other groups can't find the effect then the excitement just dies down.

 

Bee Hossenfelder's blog "Backreaction" has this comment:

http://backreaction.blogspot.com/2007/08/magics-observation-of-gamma-ray-bursts.html

 

"This is the summary, status Sunday evening. In case I loose one or the other reader here, let me give you my opinion up front: there is no experimental evidence for quantum gravity, and none of the present theories can be tested with currently available data. If you're looking for sensations, you're on the wrong blog. I suggest you try one of those mentioned above instead."

 

Are all flares expected to provide similar delays regardless of the source strength? If not, then you can't say whether a different shift is caused by dispersion or a variation in the speed of light.

Unless the source strength can be inferred from the spectral width...I guess.