The MAGIC gammaray flare result, if true, favors Spinfoam LQG

[marcus]

Energy dependent speed of gammaray photons may have been observed, by the MAGIC collaboration at its Canary Islands observatory.

Lee Smolin has been making the point for several years now that if an energy dependent speed of gammarays is ever observed it will be an enormous stimulus to LQG.

AFAIK it has never been proven that any full 3+1D LQG-related theory NEEDS the slight bending of special relativity involved here-----"deformed special relativity" (DSR).
But DSR is very "Loop-friendly" and if some deformation of special relativity---with, for instance, a slight energydependent speed of light---were confirmed that would facilitate several research lines in the Loop community.

By itself, this doesn't PROVE anything. It strikes me as something analogous to the relation of the string community to SUPERSYMMETRY. Observing SUSY at LHC would be a big shot in the arm for stringfolks. But they aren't predicting it. Or maybe a better analogy would be detectable extra dimensions. They'd like it but they aren't betting serious money or professional honor on it.

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

But I just want to remind whoever's around that Laurent Freidel et al DID PROVE THAT deformed relativity WAS NECESSARY IN SPINFOAM in the 2+1D case.
This is an important result and it was reported in a Physical Review Letters piece by Freidel and Livine last year.

IF A SIMILAR RESULT happens to be proved for the next higher dimension case then that Spinfoam model will be falsifiable and if the MAGIC result is confirmed it will have passed a test. It is always possible that such a result for the 3+1D case will be proved.
They may even be working on it. So we should check out the Freidel Livine paper.

http://arxiv.org/abs/hep-th/0512113
3D Quantum Gravity and Effective Non-Commutative Quantum Field Theory
Laurent Freidel, Etera R. Livine
Phys.Rev.Lett. 96 (2006) 221301
4 pages
(Submitted on 9 Dec 2005 (v1), last revised 17 May 2006 (this version, v2))

"We show that the effective dynamics of matter fields coupled to 3d quantum gravity is described after integration over the gravitational degrees of freedom by a braided non-commutative quantum field theory symmetric under a kappa-deformation of the Poincare group."

===========
the idea is if you take a spinfoam picture of gravity, and couple matter to it so that you now have a combined quantum spacetime-and-matter picture, and then if you TURN OFF GRAVITY then you get back a certain quantum field theory, of the matter, on a spacetime that is now FLAT because you turned off gravity. And the symmetry of that quantum field theory turns out to be a deformed special relativity.

There are some people around who are more familiar with this work and can interpret it better. I hope they correct me if I've made any major blunders here.

What I'm saying is that IF by good fortune Freidel and or some others should happen to extend this result to the full 4D, then it would be an example of a spinfoam QG theory that MUST have deformed relativity in the flat case.
And that is very nearly tantamount to saying that it should have energydependent speed of gamma, in the flat case of little or no gravity.
And that flatness is what prevails most of the way between the sources of those gammaray flares and where we are observing them.
Then there would be a really falsifiable QG that would be shot down if the MAGIC observation is not confirmed. and would survive if it was confirmed.

 

[turbo]

Got links to the data, Marcus? Fotini has been hanging her hat on this energy-dependent c for a while, and I would love to see her idea supported or negated, since either outcome would represent a net increase in our understanding of the nature of the vacuum.

 

[marcus]

Hi Turbo,
I don't have their data. here was some earlier comment on the MAGIC gammaray flare news
https://www.physicsforums.com/showthread.php?t=181415

I will summarize here, without wasting so much space.

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)

The thing is at redshift z = 0.034 meaning light travel time of 0.46 billion years
and there was a delay of 4 minutes
between two batches or "bins" of photons, a high-energy bunch 1.2-10 TeV and a lower-energy bunch 0.25-0.6 TeV

the rough order of magnitude is that the higher-energy ones traveled about 16 quadrillionths slower

the flare-up at the AGN (active galactic nucleus) only lasts a few minutes*, so the size of the delay is about the same as the length of the flare.

it is the sort of thing that BEGS to be replicated with other galaxies and at greater distances.

they put a linear model to it and they estimated that there was a coefficient which I would write as 1/6 of the reduced Planck energy (the Planck energy with 8 pi G instead of G is about 2.43 E18 GeV)

in their linear model the fractional reduction in speed, for a photon with energy E, was E/M where M is 1/6 Planck energy.

Of course at that rate if the linear model was accurate to much higher energy then if you made a photon with 1/6 Planck energy then it would just sit there and have speed zero.

speed (E) = 1 - E/M

but we are talking about linear approximation in the regime where E/M is about 10^-14

*they say doubling time about 2 minutes---gives idea of attack and decay timescale

 

[turbo]

I don't have their data. here was some earlier comment on the MAGIC gammaray flare news
https://www.physicsforums.com/showthread.php?t=181415

I will summarize here, without wasting so much space.

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)

The thing is at redshift z = 0.034 meaning light travel time of 0.46 billion years
and there was a delay of 4 minutes

Thanks, Marcus. Thanks to Google I was able to find:

http://arxiv.org/abs/0708.2889

as well. The results fit with the idea that more energetic (higher-frequency) EM must interact more frequently with the propagating medium (space) than lower frequencies, resulting in a lower speed of propagation through the same medium. If this effect can be confirmed, it will open up inquiries into the fine structure of the vacuum, and eventually into the proposition that the fundamental properties of the vacuum can be conditioned by the mass embedded in it - a key concept in Einstein's view of space as a refractive medium.

Nice catch.

 

[hellfire]

To my knowledge one can also heuristically derive modified dispersion relations in string theory. So does this MAGIC result really give any hint to any special research direction?

 

[ZapperZ]

Aren't we being a bit premature in jumping all over this?

I mean, besides the fact that it has to be (i) published first, (ii) verified by other observations, etc., even the authors are cautioning that there could be other factors involved here that could explain their results. I've seen string theorists grasping even the smallest hint of "experimental evidence" out of desperation, but I didn't t know it applies to LQG theorists as well!

Zz.

 

[francesca]

AFAIK it has never been proven that any full 3+1D LQG-related theory NEEDS the slight bending of special relativity involved here-----"deformed special relativity" (DSR). But DSR is very "Loop-friendly" and if some deformation of special relativity---with, for instance, a slight energydependent speed of light---were confirmed that would facilitate several research lines in the Loop community.

I hope so, even if, as you said Marcus, by itself, this doesn't PROVE anything.:uhh:
Well, QG people are arguing so far about LI breaking, but I was told that this would be a secondary question if you conder that the whole theory needs to reach a more complete structure. I'm aware of more predictions about it from the stringy side that from the QG side... isn't it so? http://www.sissa.it/app/QGconference/program.htm(slides available)

the idea (of Freidel and Livine) is if you take a spinfoam picture of gravity, and couple matter to it so that you now have a combined quantum spacetime-and-matter picture, and then if you TURN OFF GRAVITY then you get back a certain quantum field theory, of the matter, on a spacetime that is now FLAT because you turned off gravity. And the symmetry of that quantum field theory turns out to be a deformed special relativity.

I hope that Etera would like to say something about...

Actually the conprension of the astrophysical process of the flare is worth. I think that in the analysis they assume that tha flare is almost istantaneus.
"We cannot exclude the possibility that the delay we find,which is significant beyond the 95% C.L., may be due to some energy-dependent effect at the source."
The way to have a better knowledge about it is first to study more sources applying the same analysis.
"This pioneering study demonstrates clearly the potential scientific value of such an analysis."
That's to say: always more work for esperimentalists...:grumpy:

 

[ccdantas]

I did not read the paper. But of course there is a caveat. One should know exactly what is happening at the source. High energy and "low" energy photons must have been emitted simultaneously. There is a lot of astrophysical stuff to be learned and cleaned up before making any firm conclusions about possible quantum gravity effects. I hope all this can be improved more and more in the years to come...

 

[turbo]

I did not read the paper. But of course there is a caveat. One should know exactly what is happening at the source. High energy and "low" energy photons must have been emitted simultaneously. There is a lot of astrophysical stuff to be learned and cleaned up before making any firm conclusions about possible quantum gravity effects. I hope all this can be improved more and more in the years to come...

Certainly, the importance of an observed delay rests on the assumption that a burst emits all frequencies simultaneously, and that there is no evolution in the energy of the photons populating the burst with time. We don't know that is the case. If the effect is real, the magnitude of any delay should be proportional to the distance that the EM from the burst traveled, too. More observations are needed. GLAST is scheduled for launch in Feb 2008 and its observations may help clarify some of this.

 

[marcus]

As several people have indicated already, nothing is proven so far.
Fortunately gammaray flares and gammaray bursts (GRB) happen often so the key idea will be to replicate.

An additional instrument that is expected is GLAST (gammaray large area space telescope)
the latest date given for its launch is here:
http://www.nasa.gov/missions/highlights/schedule.html

when I checked the schedule it had been updated 23 August and the date for GLAST was 5 February 2008 (but it was not a firm launch date, just a "no earlier than")

To my mind until they replicate by timing other flares it is not even clear that there is a delay. Once it is established that there is a regular delay, if that happens, then people can try to pin down the cause. Obviously the cause could be an unknown effect at the source as well as QG dispersion.

The main people in this case are the 130+ experimentalists called the MAGIC collaboration. The paper is very short, 5 pages, because it is written for Physical Review Letters.

The idea of publishing in PRL is when one has an important result of wide interest, that one wants to get out to other physicists quickly. So they have submitted this as a letter to PRL and they will doubtless be bringing out a LONGER paper that gives more details and data, to submit for publication elsewhere.

The over a hundred people in the MAGIC collaboration (very similar to what one sees in accelerator research ) are concerned with the instruments, the data collection, the statistical analysis etc. I would say that the collaboration is the principle author. It is not a theoretical paper but primarily a practical one, which
the paper comparatively easy to read. They want to tell you how they binned the data and about their 1000 Monte Carlo computer simulations with artificial data that they used to check their analysis, so as to make sure they were not being fooled.

Also they have ideas about effects at the SOURCE which might interest you.
they estimate the source plasma diameter to be about 10⁹ kilometers (see the bottom of page 4). Which is about 50 light minutes. The delay they found was about 4 light minutes. One would think that just going thru the plasma could introduce some delay which might be energy dependent. They did some analysis of this. In other words they have been trying to exclude source effects. But the main way to exclude source effects is to replicate with AGN at different distances (redshifts)---because the hypothesized QG dispersion delay depends directly on the distance the light travels.

 

[marcus]

Blog reaction.
SciAm blog by George Musser one of the editors of Scientific American
http://blog.sciam.com/index.php?title=hints_of_a_breakdown_of_relativity_theor&more=1&c=1&tb=1&pb=1

exerpt from George Musser's post:
"this is one of those "extraordinary claims require extraordinary evidence" situations. But if the high-energy gammas really did lose the cosmic race, we're talking Big Discovery. It could be a way to constrain string theory, loop quantum gravity, and other bleeding-edge theories.

The basic picture is that high energies might cause small-scale fluctuations in the shape of spacetime, which would act as subatomic lenses. The higher the photon energy, the more it might induce such lensing and the slower it would cover large distances. Four minutes isn't much of a delay over a half-billion-year journey, but then again, you don't expect much. From the lag, you can deduce where quantum gravity kicks in."

Ars Technica blog by Chris Lee
http://arstechnica.com/journals/sci...obing-quantum-gravity-with-gamma-ray-bursters

 

[jal]

"if true, favors Spinfoam LQG"
heheheh
The string people are already getting their public relation/publicity working into high gear to get there first with their claims.
Spinfoam LQG better hurry up if they do not want to face an uphill battle.
Reuters paper would be a good place to start from.
jal

 

[quantum123]

Hints of a breakdown of relativity theory?

The MAGIC gamma-ray telescope team has just released an eye-popping preprint (following up earlier work) describing a search for an observational hint of quantum gravity. What they've seen is that higher-energy gamma rays from an extragalactic flare arrive later than lower-energy ones. Is this because they travel through space a little bit slower, contrary to one of the postulates underlying Einstein's special theory of relativity -- namely, that radiation travels through the vacuum at the same speed no matter what?

 

[SpitfireAce]

maybe the gamma rays passed through a nebula or something and the low energy rays were absorbed and reemitted slowing their effective velocity while the high energy rays passed right on through, or maybe differences in deflection... in any case, it would take a lot more than this to cause a breakdown in relativity, even if this is a valid exception, if it can't be explained away it will probably just be chalked up to "technical difficulties"

 

[marcus]

Peter Woit has a post about reactions to the MAGIC paper
http://www.math.columbia.edu/~woit/wordpress/?p=591

Among other things he quotes a calming wait-and-see comment from J.L. Kelley an avowed astrophysicist

What they are saying is that there are still details we don’t understand about AGN [active galactic nuclei] like Markarian 501. So, while this effect could be a first sign of quantum gravity (*not* string theory in particular, as others have pointed out), it could also simply be something going on in the intrinsic spectrum of the flares themselves. I’d personally consider the second explanation more likely at this stage.

As they also point out, one approach to sort out the ambiguity would be to observe other flary AGN at different redshifts (distances). One could then, for example, see if the delay gets shorter or longer as the distance changes, as one would expect with a quantum gravity effect due to propagation to Earth.

here's the link to J. Kelley's comment
http://science.slashdot.org/comments.pl?sid=279505&cid=20351213

 

[turbo]

The MAGIC gamma-ray telescope team has just released an eye-popping preprint (following up earlier work) describing a search for an observational hint of quantum gravity. What they've seen is that higher-energy gamma rays from an extragalactic flare arrive later than lower-energy ones. Is this because they travel through space a little bit slower, contrary to one of the postulates underlying Einstein's special theory of relativity -- namely, that radiation travels through the vacuum at the same speed no matter what?

Einstein stated here:

http://www.bartleby.com/173/22.html

that the speed of light through a vacuum must be variable to permit the deflection of light expected from gravitational effects. He explained that the constancy of the speed of light in a vacuum is a concept that is peculiar to special theory of relativity and not to the general theory of relativity. Until the end of his life Einstein tried to determine what properties of space were modified by the presence of embedded matter. I think that he would have been quite excited about some aspects of LQG, including the premise that the vacuum is not smooth and monolithic, but has a fine-scale structure.

The person quoted on Peter Woit's blog has exactly the right mind-set on follow-up.

As they also point out, one approach to sort out the ambiguity would be to observe other flary AGN at different redshifts (distances). One could then, for example, see if the delay gets shorter or longer as the distance changes, as one would expect with a quantum gravity effect due to propagation to Earth.

It would also be valuable to compare the observations to those of other programs - GLAST in particular. Could be exciting times.

 

[marcus]

... GLAST in particular. Could be exciting times.

YES! Either way, up or down, it's going to be good.

This was the attitude expressed in Smolin's book (p. 237)

It would be wonderful to get a real prediction out of a quantum theory of gravity and then have it shown to be false by an unambiguous observation. The only thing better would be if experiment confirmed the prediction. Either way we would be doing real science.

It looks as if gammaray astronomy is going to be able to test quantum gravity. and that's the main thing---to have theories confronted by observation. It matters much less whether this or that particular theory is falsified or not falsified.

=============================
It is interesting to read about how the IACT (imaging air cherenkov telescope) type of telescope works
Here is a general page from the MAGIC observatory site
http://magic.mppmu.mpg.de/introduction/index.html
here is a special page on how IACT works
http://magic.mppmu.mpg.de/introduction/iact.html

they can actually photograph the electron-positron SHOWER that a single TeV gamma photon makes in the atmosphere (10-20 km altitude)
by the brief Cherenkov glow that the shower makes
and from that they can tell the direction the original gamma photon came from and also the energy of the original photon.

this is what that 17 meter diameter optical mirror dish is doing
==============================

TURBO, you asked about a link to their data.
http://arxiv.org/abs/astro-ph/0702008

this is a 51 page paper they posted earlier about the same observations, where they did not offer a quantum gravity explanation (very little attempt at explanation of any sort)
in this paper they give a lot of data, plotting it various ways. It may be the kind of thing you were interested in seeing.

 

[marcus]

Bee's blog on MAGIC

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

Bee usually has something sensible to say. Figuring out how theories could be tested is her specialty. She has a long informative discussion but
here is the essential conclusion:
"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."

 

[turbo]

TURBO, you asked about a link to their data.
http://arxiv.org/abs/astro-ph/0702008

this is a 51 page paper they posted earlier about the same observations, where they did not offer a quantum gravity explanation (very little attempt at explanation of any sort)
in this paper they give a lot of data, plotting it various ways. It may be the kind of thing you were interested in seeing.

Yes, that's what I wanted to see. Thanks for the link.

 

[ccdantas]

Hi Marcus,

I agree 100% with Sabine on those matters. As I have pointed out elsewhere and perhaps a couple of times, there is a lot of astrophysics to be learned before having a solid basis to move on to other territories. This is not excessive prudence, but simply the usual scientific method. This does not mean, however, that one should not be open to new ideas and possibilities. These should always be put into perspective.

 

[marcus]

Hi Marcus,

I agree 100% with Sabine on those matters. As I have pointed out elsewhere and perhaps a couple of times, there is a lot of astrophysics to be learned before having a solid basis to move on to other territories. This is not excessive prudence, but simply the usual scientific method. This does not mean, however, that one should not be open to new ideas and possibilities. These should always be put into perspective.

Hi Christine,
I am not sure what your post means!
The MAGIC team consists of about 130 observational astrophysicists.
They have a new type of telescope which works like a giant particle detector by visually imaging the TRAILS left by TeV photons in a 10 kilometer layer of atmosphere.

Are you saying that MAGIC team should not have done the research they did?

Did those 130 astro folks "move on to other territories" prematurely before they had learned a "lot of astrophysics"?

Are you saying, as I think Sabine does, that they overhyped their result?

You don't seem to be saying this, from your comment, but maybe that is what you mean.

I would agree about the salesmanship. I think they put some extra hype on it (by taking theorists Ellis and Mavromatos on board) to get attention.

Maybe that is a lapse in style, a failure to have proper scientific form. A matter of propriety.
=======================

However I think that it is one of the roles of experimentalists to give guidance to theorists and this work is excellent and important from that standpoint because as a pioneer study it tends to show that if there is any dispersion at all it is probably NOT in the direction of increased speed.

Being sure about this would make the theorists' work only HALF AS DIFFICULT because the mathematics is different when you do speed decrease Lorentz deformation as compared with speed increase Lorentz deformation.

So I am very happy with MAGIC result. I see it as very helpful and according to how science should be done at least some of the time

It should be replicated over and over at different redshifts to eliminate source effects and if they can confirm that at least there is NO SPEED INCREASE with energy (by showing either no effect or else some speed decrease) that will be a big help to theorists.

One should keep an open mind about Lorentz invariance----it might be deformed some way or violated. We really do not know. If confirmed this kind of observational result can be a helpful guidance to theorists who want to work out different Lorentz-bending models

 

[ccdantas]

Are you saying that MAGIC team should not have done the research they did?

Did those 130 astro folks "move on to other territories" prematurely before they had learned a "lot of astrophysics"?

Argh! No, of course I'm not saying that! How strange it is to realize that what I write can be completely misunderstood! It must be a language problem or you are being unkind to me, Marcus?? (or both...) How I am to say those 130 researchers should not have done that work?

What I am trying to say is as plain as possible: there is a lot of astrophysics to be learned. I am certain those astrophysicists know this better than I do. Concerning what I mean by "other territories": yes, I do think it is too early to make any claims on possible quantum gravity effects, that is what I mean, and that is all, that's no big deal, what I am saying is obvious. I'm not saying people should not be looking for those problems. I'd like to be looking for those problems myself! I'm not sure they are making big claims, but perhaps they could have written some more details on the problems involved. Their new analysis method sounds interesting, and I would like to learn about it if I find some time. These are my opinions, I hope they are clear enough.

Bee did a very nice job on her post, I recommend it.

 

[marcus]

If you don't object to the research that the MAGIC group did, then perhaps you are criticizing their presentation for its attention-getting excesses. I didn't get that message explicitly from your post, but I was asking if that is what you meant:

Are you saying, as I think Sabine does, that they overhyped their result?

You don't seem to be saying this, from your comment, but maybe that is what you mean.

I would agree about the salesmanship. I think they put some extra hype on it (by taking theorists Ellis and Mavromatos on board) to get attention.

Maybe that is a lapse in style, a failure to have proper scientific form. A matter of propriety.

If the issue is hype or salesmanship, let's make it clear that we are not critisizing their science. I agree with Sabine about the hype (she says it is like "strawberry" yoghurt with no strawberries in it, only artificial color and flavor.)

They didnt have to invite Nick Mavromatos and John Ellis on board. They could simply have published results of a pioneer study with new telescope technology which found tentative evidence of Lorentz bending! Then let Ellis et al write their own paper.
That was the artificial flavor and coloring.

But I think Sabine was out of line in being TOO DISAPPROVING of them. She was really annoyed and sour in her tone.
This is a team of 130 Germans, Italians, and Spaniards who have built a really interesting new kind of telescope and who have done a really interesting piece of work with it on Makarian 501. And it is good science regardless of how they hyped it, and they should be getting credit for that.

What I am wondering about is WHY Sabine, who is usually not so severe, is being so tough with them in this case? Are German astrophysicists supposed to live up to some higher standards of decorum than, say Americans? Maybe that is not it. Maybe it is that energydependent speed is a really really sensitive topic.

Or maybe it is timing. GLAST is supposed to launch February 2008 and everybody thought they had a few months breathing time, to get their ducks in a row and their house in order before having possibly to face dispersion news from GLAST. (Up or down either way it is measuring something about the universe and has to be stressful.)
and so maybe people are reacting this way because they were STARTLED that information came at them from an unexpected direction and about 6 months or a year early.

Anyway let's be clear what we are criticizing these MAGIC people for, if we are criticizing. And if it is important observational research, let's say so. I think it's great!

 

[ccdantas]

But I think Sabine was out of line in being TOO DISAPPROVING of them. She was really annoyed and sour in her tone.

(...)

What I am wondering about is WHY Sabine, who is usually not so severe, is being so tough with them in this case?

Well, perhaps she was in a bad day; you have to ask her... I think she was just having her dose of scientific skepticism, which is the positive aspect that I saw in her post, regardless of the subjective tone... Perhaps the comment section of that post will be interesting to follow.

 

[pervect]

My $.02. The Magic people seem to be doing OK with their reporting, but one can see a lot less caution on the part of the journalists, who are a bit on the sensational side for my taste.