# Gamma Rays Photons Slower?(Quantum Foam)

1. Oct 7, 2007

### sanman

I don't know if you've heard the latest news from the MAGIC telescope researchers, but they may possibly have come across evidence of Quantum Foam:

http://www.universetoday.com/2007/10/03/high-energy-gamma-rays-go-slower-than-the-speed-of-light/

Gamma rays were apparently found to have arrived 4 minutes behind other photons that were supposedly emitted at the same time from a Blazar source 500 million light-years away.
This has led to some speculation that the delay may be due to the intervention/interaction of Quantum Foam.

Obviously there are many possibilities for error or alternative conclusions in this measurement.

But if enough credence is given to the results to warrant further investigation, then what other means could be devised to test out this hypothesis? Merely observing other blazars, or could some clever in-laboratory means be used, that would provide much more controlled and known test conditions?

2. Oct 8, 2007

### marcus

we had a thread about that here at PF in August sometime. the MAGIC paper was posted on arxiv around 21 August and there was a lot of reaction in the various physics blogs at that time.
Our PF thread would either be here in "Beyond" forum or in "Cosmology".

Personally I think the result merits further investigation and I think it will get it.
I expect that more AGN flares will be studied to see if there is a similar delay and whether or not it is proportional to distance.

3. Oct 8, 2007

### sanman

Well, 4 minutes is a long time, but why couldn't smaller time lapses be detected inside the smaller confines of a local laboratory experiment?

These days, scientists are able to produce attosecond pulses to measure the briefest of physical phenomena, and synchrotron radiation frequencies can also go quite high. So if frequency is correlated to interaction with quantum foam itself, then I'd wonder why laboratory-generated phenomena couldn't unveil it, under more precisely calibrated conditions.

4. Oct 8, 2007

### marcus

If you do the arithmetic you will easily see that the effect cannot be measured in laboratory.

No existing manmade device can produce TeV gammaray photons. The effect depends on having high energy photons

The ratio between 4 minutes and 0.5 billion years is about 10-14.

that is a TRILLIONTH OF A PERCENT. the delay is a trillionth of a percent of the travel time.

they compared the arrival time of 0.5 TeV with 2.5 TeV photons, something like that. I don't remember exactly.

Let's say in the lab you can make 0.5 MeV and 2.5 MeV photons and compare their arrival times. then according to their model you should expect the ratio to be 10-20.

a million times smaller because the photon energy is a million times smaller and the conjectured effect is proportional to energy.

In the lab, light travel times are on the order of 10-8 seconds (that is 10 nanoseconds)

therefore, if the ratio is 10-20, then the delay time is on the order of
10-28 second.

there is no clock on earth that can meaure a delay of 10-28 second.
and there is no detector on earth with such a fast reaction time that it can detect such a small delay.

Even with unlimited funding I do not see how you could not do such an experiment within the confines of the solar system.

You talk about "attosecond" but that is 10-18 second.
compared with 10-28 second it is still too big by ten orders of magnitude.

So I don't think it makes sense to imagine lab experiments of this.

Besides, the IACT (imaging air cherenkov telescope) is very beautiful. have you seen the photographs of the MAGIC instrument?

5. Oct 8, 2007

### sanman

Hi, sorry, don't get me wrong -- I was not in any way trying to diminish the importance and the value of the MAGIC telescope project. I think it's great, and hopefully it has unveiled to us some new evidence of some new physical phenomenon/effect that we were not previously able to see.

I was just trying to propose some further even more accurate experimental determination of this effect, if possible. Because whatever great discovery MAGIC might have made, it would be necessary to probe/measure/categorize this effect even further, to more accurately understand it.

I've always thought that accelerator scientists boast that they can recreate conditions that existed mere moments after the Big Bang, and that they can accelerate particles to relativistic speeds, and so I assumed that whatever is happening en route from this blazar to Earth can be recreated or reproduced in some experimentally adequate way.

Right now the LHC is supposed to be the most powerful device on the planet -- so how close does it come to being able to generate these energies?

Anyway, perhaps there might be some other indirect way to probe the quantum gravity effect to verify its existence, even without having to resort to such high energies and vast distances. Aren't there "delayed path" experiments which specialize in redirecting light along very long circuitous paths? Maybe the use of some clever optics could help to achieve this?

6. Oct 8, 2007

### sanman

Here's a quick article on LHC that I just surfed to:

http://oscar.virginia.edu/researchnews/x9305.xml

So conceivably, we could get some pretty high-frequency gamma rays out of that device.
And if as you've said, the delay effect is proportional to the energy, we could see an even more pronounced delay ratio (ie. relative to the path travelled)

So if we're measuring those hi-freq gamma rays against some ridiculously low-freq photons (radio waves?) then that would give us maximum contrast.

Then if we want to further bump up the distance of measurement, maybe we could send some ion-propelled space probe out to the Kuiper belt with a gamma-ray detector. Perhaps it could then record any delays in signal received.

And actually, if this hypothetical effect is indeed found to be valid, I'm wondering if it couldn't also become a useful tool for astronomy. After all, if you're detecting incoming gamma rays in conjunction with other photons from a distant source, then you could use any delay to determine the distance of the source. I dunno, just a thought.

So that then provokes another question in me -- if the effect is found to be valid, then what practical uses/applications could be found for it?
Like I said, could we use it for astronomical measurement purposes? Could we use it for anything else?

7. Oct 8, 2007

### marcus

Sanman, your post touches on many points. I will let other people respond, if they wish, to all the points except the original one we were discussing.

Our discussion revolved around whether you could produce TeV photons in earthbased lab.

You seem to think that it might be possible for an earthbased lab like LHC to produce TeV gammaray----so that a dispersion experiment might be performed similar to the astronomy-based one in your original post.

I think this is a good point to be clear about. I want to emphasize that in my unexpert opinion LHC will not produce TeV gammaray photons. I think when two protons or nuclei collide, even with very high energy, their energy gets divided up in a whole lot of different stuff and no way should you expect a source of TeV gammaray. But that is just my own opinion! I'd be delighted to hear more from someone knowledgeable about colliders.

Hopefully, if this issue is not settled in your mind yet, we can focus some attention just on this one issue and get it resolved.

Thanks

8. Oct 8, 2007

### ZapperZ

Staff Emeritus
The LHC will not produce TeV gamma rays. We don't even have a standard way to produce GeV gamma rays for a possible gamma-gamma collider, much less, TeV range. The gamma rays that will be produced at the LHC (and most accelerator facilities) are the Bremsstrahlung radiation, and you don't get that with TeV electrons/protons.

Zz.

9. Oct 8, 2007

### marcus

Thanks Zapper! I am very glad to have that matter resolved.

Now maybe we can look at the question raised in Sanman's original post at the beginning of the thread:

This is actually a very interesting question. One never likes to say anything is impossible because experimentalists (including high-energy expermentalists) are exceedingly clever and inventive.

We are talking about testing a relation like

$$\frac{\Delta c}{c} = - 6 \frac {E}{E_{Planck}}$$

this is roughly what they found empirically, with some factor like 6 which I don't remember exactly, and plenty of errorbar uncertainty. the Planck energy here is the "reduced" version that everybody seems to be using instead of Planck's original version.
In the case they studied both sides of the equation would be about 10-14, assuming the delay was due to a difference in speed (a rather bold hypothesis, much in need of testing )

This is clearly something that CAN be tested in a straightforward way by observing lots of AGN flares of different sizes and at different distances! Indeed one may very well be able to refute it by observing galaxies at different distances and showing that the delays are not proportional to distance! So one potentially has very good control of this question entirely by astrophysical means.

But my suspicion is that it would be virtually impossible---unimaginable even in fantasy---to test such a relation in earthbased lab!
Again, I would like to hear comment from others about this, since it is just my opinion. Maybe someone with a better imagination than mine could think how to do it.

Last edited: Oct 8, 2007
10. Oct 8, 2007

### BDOA

Since an earthbased lab it out of the question, how about space probe,
accelerator combination. Orbit your probe so its, say 2AU away from earth,
and you've got 1000 seconds of speed of light, time delay. Now you an
TeV source near the earth, (firing a proton beam through the autosphere
doesn't seem very safe or accurate), so we're probably need a small but
high energy accelerator in low earth orbit. Wakefield accelerators might just make this cheap enough.

How hight an energy do we need?, Our electronics works at speeds of 10GHz today, so we can maybe measure delays of 100ps. That gives us,
a relative gap of 10^-13. So we're need a 10 TeV acclerator. So we're just out of reach right now. But boost our measurement speed up to 1ps, and put a 100GeV accelerator in LEO or on the moon, and it should be possible.

11. Oct 8, 2007

### sanman

Can't we do some clever interference fringe experiment that would allow us to pick up the delay in a more clever way, a la Michelson-Morley, rather than having to do all this brute-force setup of high energy across vast distance?

Isn't there some clever way to exploit light to measure other light, or something nifty like that? I dunno, just a stab in the dark.

Or what about these oh-so-amazing atom lasers and BECs? Aren't they supposed to have amazing measurement precision?

12. Sep 10, 2009

### Primordial

This statement gave me an Idea, "The LHC will not produce TeV gamma rays. We don't even have a standard way to produce GeV gamma rays for a possible gamma-gamma collider, much less, TeV range. The gamma rays that will be produced at the LHC (and most accelerator facilities) are the Bremsstrahlung radiation, and you don't get that with TeV electrons/protons." , the initial energy of the burst could produce high energy particle bremsstrahlung photons, if the source of the particles were not the initial trigger, but just in the path of the higher frequency gamma photons and close enogh to become the leading edge of the event. Just a guess.

13. Sep 11, 2009

### tom.stoer

Of course you will never see Bremsstrahlung in the same energy range as the beam energy itself, otherwise the accelarator would not be able to accelerate. Bremsstrahlung is the reason for linear electron accelarators. As the LHC uses protons the Bremsstrahlung has much lower energy.

High-energy photons can be produced by free-electron lasers, but as far as I know they are in the Roentgen energy range, no gamma rays.

14. Sep 11, 2009

### sanman

How about these proposed high-energy muon-colliders, which are considered to be the next generation beyond LHC? I've even heard speculation that they could become "Higgs factories", since their collision energy is so high.

Or what about laser-wakefield in combination with muons rather than electrons, to provide a huge acceleration gradient and ultimately a high collision energy? It seems to me that laser-wakefield devices could be made compact enough to be fitted onto a spaceprobe and sent far out (eg. a few AUs, like a previous poster said, for significant travel time)