Gamma rays travel slower than low-energy photons?

[bascule]

According to recent observations, yes:

 

http://www.news.ucdavis.edu/search/news_detail.lasso?id=8364

 

Different frequencies of photons travel at different speeds? Speeds other than c?

[Severian]

It seems a little unhelpful that they say "Ferenc cautioned that... a simpler explanation had not been ruled out", and not tell us what it is.

[Mr Skeptic]

The simpler explanation is probably that the photons were emitted at different times. The solution is to look at photon sources of similar nature at different distances and see if the high and low energy photons arrive proportionately more or less separated.

[Martin]

Bascule, good find!

 

 

I read the original paper back in August when it came out and they considered the possibility that the higher-energy part of the flare was emitted some 4 minutes later because of some not-yet-known mechanism. But they could not specify what that might be.

 

I got the impression (which may be obvous to everybody in this thread) that the thing to do is observe lots of flares, coming from AGN (active galactic nuclei) at all different distances.

 

If the delay is due to something that happens during travel, then it will be proportional to the travel time.

 

If the delay is due to something at the source (releasing the higher-energy photons later) then it won't be proportional----it might, say, always be 4 minutes regardless of how near or far the AGN is! Or it might depend on the size of the AGN rather than how far it is, and so on.

 

Finally, if repeated observation sees NO DELAY then theirs must have involved some fluke or error.

 

So my impression was that this is a preliminary finding and that all it shows is that they consider their IACT technology (imaging air cherenkov telescope) sensitive enough to detect energy-dependent delay in gammaray flares.

And all this pioneering result means is that it should be repeated with other flares from different AGN

 

The technology is the interesting thing to me. They can tell the difference between a 2 TeV photon and a 0.5 TeV photon by how much of a shower it causes.

 

The photon buzzes in from some direction and in a layer of atmosphere from 10 - 20 km it makes a shower of millions of electron-positron pairs all going more or less in the same direction and going faster than the speed of light in air. Going faster than the speed of light in the medium makes Cherekov-----the eerie blue glow in the water around reactors, that you see in pictures.

 

So a single photon makes this PLUME coming down thru the atmosphere. It shows up as blue and UV Cherenkov which the IACT telescope can see.

It has UV-sensitive detectors and it constructs an optical IMAGE of the plume. It is like the phosphorescent wake of a ship, in a way.

One TeV is an enormous amount of energy for one photon to carry.

 

The telescope can see an individual photon track, and image it, and tell the direction it came from, and even judge its energy by the size of the glowing track (plume, shower whatever you want to call it)

 

At the website and in their papers they have pictures, including an image of one of these showers.

 

It is a 17 meter mirror dish. The largest optical dish in the world. There are larger radio antenna dishes of course. But this is bright mirror. Very beautiful. They have pictures at the site of that too. It looks lovely in the sunset.

 

It is made very light material----carbon fiber, composites, so that it can wheel around quickly when it gets the message from a satellite that a gammaray flare is coming in. flares only last a short while so the whole 17 meter wide dish has to have small weight and inertia for fast positioning.

 

Technically the thing is stunning. It is a new kind of telescope. mankind has grown a new kind of eye.

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

 

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 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."

 

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

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

 

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

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

 

The delay of 4 minutes was 10^-14 of the travel time, of half a billion years.

If that delay were due to difference in speed of travel, proportional to energy (just one hypothesis, one possibility) then we would be looking at something like

 

delta c/c = 10^-14 = one trillionth of one percent

 

and as a first order approximation that might be proportional to the difference in energy which was on the order of a TeV

And the energy difference (of around a TeV) is on the order of a trillionth of a percent of the Planck energy!

That is probably what got them so excited. Otherwise they might have waited and only published when they had observed several similar flares.

 

As I recall there was an unexplained factor of 6. But the rough arithmetic was that you use the reduced Planck energy of 2.4 10^-15 TeV and roughly it looks like

 

[math]\frac{\Delta c}{c} = -6 \frac{ E}{Planck}[/math]

 

that is, low energy photons go at the limit and the more energetic ones are slowed down somehow.

The fraction by which he is slowed down is given simply by his energy divided by Planck energy (times this factor of six).

So the more energetic he is, the more he is slowed.

But the Planck energy is so stupendously large that ANY photon's energy (that we are likely ever to observe) is such a small fraction of it, that this fractional slowing down is normally too small to observe.

 

You would only observe it (assuming the hypothesis that it exists) in photons of very high energy which have been traveling for a very long time (on the order of a billion years)

 

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

It seems a little unhelpful that they say "Ferenc cautioned that... a simpler explanation had not been ruled out", and not tell us what it is.

 

the reporter is paraphrasing. the guy may have said "It has not been ruled out that there is some simpler explanation." (unspecified)

 

I got the impression that they did not have any alternative explanation for the delay, if it occurred at the source---just some unknown mechanism that might cause the more energetic photons to be emitted later. Maybe in time someone will think of one.

[pioneer]

Maybe the affect is similar to sound waves. Sound will travel faster in a solid, than in a liquid and then in a gas. The longer wavelengths are seeing a favorable transmission medium for rapid transmission. The Gamma is seeing a less favorable medium for its slower transmission. This could be simply due to gamma interacting more with matter and losing time between absorption-release, until it finally leaves the medium.

 

Say we have a steel plate. We shoot a strong laser beam at one side, to burn a hole through the plate. This takes 2 min. Before we ever see the laser light, on the other side, we will see IR, then visable energy, as the metal plate begins to glow. Finally after two minutes the laser light exists. All the energy left the lazer beam at exactly the same time. If we were 5 light minutes away from this metal plate, we would see the IR coming first, after the switch was thrown and two minutes later the laser.

 

What that observation seems to indicates is the blackhole can also throw out very dense matter that can act as a barrier to gamma, but is able to conduct weaker energy quite easily. I am not sure what this implies in terms of materials. A blackhole is a giant intergalactic trash compactor so it should be fusing before final compaction. Some of this material may get ejected. A blackhole may be good for space dust, but feed it a good size object; squeak!!

[Klaynos]

pioneer, so what you're saying is that the photons are passing through a medium with a wavelength dependent refractive index. Which is highly possible, but 4 mins is quite a bit, and I'd hope they'd have thought of that and looked for clues...

[bascule]

pioneer, so what you're saying is that the photons are passing through a medium with a wavelength dependent refractive index. Which is highly possible, but 4 mins is quite a bit, and I'd hope they'd have thought of that and looked for clues...

 

Didn't the Michaelson-Morely experiment effectively rule out any sort of medium in which light travels?

[Klaynos]

Didn't the Michaelson-Morely experiment effectively rule out any sort of medium in which light travels?

 

I meant something like glass... not ether...

 

Or more likely in space a gas cloud...

[Severian]

Maybe the affect is similar to sound waves. Sound will travel faster in a solid, than in a liquid and then in a gas. The longer wavelengths are seeing a favorable transmission medium for rapid transmission. The Gamma is seeing a less favorable medium for its slower transmission. This could be simply due to gamma interacting more with matter and losing time between absorption-release, until it finally leaves the medium.

 

That was actually one of their main proposals. We have known that light slows down when passing through various materials (that is how a lens works) and that is due to interaction with the particles in the medium. One normally presumes the vacuum of space to be empty, so they are instead suggesting that there is an interaction with the 'quantum foam' which is a hypothesised breaking up of space-time on very small distance scales.

 

This seems a little exotic to me. I would have thought you would get a larger effect just from hitting the odd particle in the 'vacuum' in deep space. Every vacuum has some sort of particles. There would even be a possibility of self-scatter, having light scatter off itself; for a very small fraction of time during light by light scattering, the photon is converted to a fermion-antifermion pair which have mass and don't travel at c.

 

I presume they have thought about all these things though. Also, I suspect that most of these would conflict with the very tight mass bounds we have on the photon from other experiments.

 

As a side point, it is something similar that it thought to cause the masses of ordinary particles. The vacuum is not empty but filled with the Higgs field. The particles interact with this background field and are slowed down, giving them an effective mass. (The photon doesn't couple to the Higgs boson, so remains massless.)

[pioneer]

One of the biases of blackholes, is that matter can not excape. This has never been proven. Maybe this observation proves that blackholes are not perfect when we feed it too much. I look at a black hole this way. Say the blackhole formed from a huge star. The gravity summation is limited to the mass in that star. When matter is pulled in, it has to be compressed to extreme densities, but the blackhole gravity is sort of finite, until full compaction in its very center. It does the best it can at the perimeter, but a large asteroid made of iron, for example, is going to put up a fight and resist be compacted its finite perimeter gravity. The trash compactor temporarily ejects excess material so it can chew easier. But it still has this matter in its gravity scope, and will collect it on the next pass. This material is opague to gamma but radiates heat/light with weak energy first. But the gamma burns through, so we see it later.

 

I remember a summer job in a corrigator plant (box cardboard with the sinewave between layers of paper). I was utility and one assignment was to clean up a bales of recycled board that had split. I had to pickfork it into this vaccum uptake, that could pull the pitchfork out of your hand. Luckily, the intake had a curve so the pitch fork couldn't take the corner. The material was being sucked up onto huge silo. I was in good shape and fed the material so fast, that I made beast choke. If the blackhole eats too much, it can also choke and has to hurl chunks. If it did not, the compression heat in the undigested matter could cause it to fluff up. It goes out of business for a while, until it is able to get back on line. Pulsars without any apparent history of a major local nova, could be a choke. It hurls chunks, until it can get the upper hand and then reforms again.

[uncool]

Pioneer - do you have any mathematical or physical reason, any reason at all, to believe that? I'm sorry, but if you cannot back up what you're thinking, then no one is going to believe you.

 

However, there is reason to believe you are wrong - the only currently known reason (that I know) for things to get out of a black hole is Hawking radiation. Nothing can get out of a black hole - because that is the definition of a black hole. Light cannot escape, by definition. If light cannot escape - that is, if light does not have enough energy to escape - then nothing can have enough energy. Things can, however, fall in and eliminate mass - like photons/etc.

=Uncool-

[bascule]

One of the biases of blackholes, is that matter can not excape. This has never been proven.

 

If matter can't reach the speed of light, and even light can't travel fast enough to escape from beyond the event horizon, how could matter possibly be traveling fast enough to escape?

 

Furthermore, that isn't really one of the "biases of blackholes" (whatever that means)... virtual particles can be boosted up to the level of the event horizon, where they are emitted as Hawking radiation.

[elas]

Didn't the Michaelson-Morely experiment effectively rule out any sort of medium in which light travels?

 

They thought they did but, one can question the premises on which they based there reasoning. A different solution is possible if one considers that the speed of light is determined by the rate at which photons are passed from particle to particle. This rate is determined by particle densities, not by the speed of the host particles. Thus photons arriving at planet Earth’s gravitational field from any direction will always travel at the same speed within that field, regardless of the relative velocities of the originating and receiving bodies (because photon speed is determined by the rate it passes from graviton to graviton; which in turn is determined by the graviton density). It also follows that any variation in the density of photons will also result in a difference in speed. There should be a gradual decrease in photon speed relative to the reduction in wavelength; which is the same as saying an increase in energy.

[pioneer]

Refraction demonstrates how light can appear to slow down. It is like light bending in water, increasing its travel distance, then it exits out the other side, and then resumes. Energy's electric field causes charges, within the refracting medium, to try to follow and align with photons electric field. But there is a time delay. Although the overall frequency stays the same, the waves coming from the charge occilation are out of phase with the incoming radiation and add to form a composite that is longer. I am not sure what type of materials gamma needs to cause a phase change that increases its path, like light in water.

 

What came to my mind was a gamma jet being refracted. The cooler energy appearing first implies it is not chemical but more nuclear, since there is much less phase delay at the level of the chemical state. The foam may work but this is speculation and can't be demonstrated. One might be able to set up a nuke medium that will refract gamma. Common sense is not always important to physics, exotic is always better.

[foodchain]

Refraction demonstrates how light can appear to slow down. It is like light bending in water, increasing its travel distance, then it exits out the other side, and then resumes. Energy's electric field causes charges, within the refracting medium, to try to follow and align with photons electric field. But there is a time delay. Although the overall frequency stays the same, the waves coming from the charge occilation are out of phase with the incoming radiation and add to form a composite that is longer. I am not sure what type of materials gamma needs to cause a phase change that increases its path, like light in water.

 

What came to my mind was a gamma jet being refracted. The cooler energy appearing first implies it is not chemical but more nuclear, since there is much less phase delay at the level of the chemical state. The foam may work but this is speculation and can't be demonstrated. One might be able to set up a nuke medium that will refract gamma. Common sense is not always important to physics, exotic is always better.

 

 

As waves move through matter in the earth say from an earthquake I think velocity of such waves are based on density of medium they happen to be traveling through which is basically refraction. Such also has an impact in regards to path of what is observed. That’s the earth though which I am sure will express differently then the topic at hand.

[pioneer]

That is true. Light works the same way as it passes through different materials. Light will bend more in the denser diamond and less in the less dense alcohol. The type of refraction possible with gamma should tells us the nature of the medium. One might try different things in the lab to see if anything on earth could cause the same level of refraction. This may not prove anything, but it could give us a feel for what is needed. If no material on the earth can do this, then exotic things could be needed.

[bascule]

Can someone please prune the pioneer pseudoscientific bullshit into the pseudoscience forum where it belongs?

[Martin]

Sorry, I for one was distracted elsewhere---will give more attention to subsequent posts.

[Martin]

Pioneer,

please do not post further on this thread claims that stuff "escapes from blackholes".

 

Once stuff falls in thru a BH event horizon it does not come bursting out along the axis of rotation.

 

The jets which have been observed are made of stuff which clearly did not fall in yet.

 

you got a mistaken impression from some popular journalism and so you keep trying to say that science needs to be reformed to allow for stuff bursting out of black holes.

 

I have moved several posts to a new thread

http://www.scienceforums.net/forum/showthread.php?t=28969

Please do not copy removed material back into this thread.

If you question my judgment that your revolutionary ideas are speculative, please open a thread in the Feedback forum.

[bascule]

I have moved several posts to a new thread

http://www.scienceforums.net/forum/showthread.php?t=28969

Please do not copy removed material back into this thread.

 

Thank you

[Martin]

Bascule, I am a bit concerned that we have not heard anything more from the MAGIC telescope team about energy-dependence in the speed of high energy gamma photons.

 

In a way that is good news because it could mean that the first observation was a fluke and that the standard picture is NOT going to be challenged.

 

Maybe the speed of light will turn out to be constant out in empty space all across the board---regardless of photon energy. maybe standard Lorentz invariance will hold.

 

MAGIC has published dozens of papers since that one, but always about other stuff. It is a great telescope of a totally new kind and there is a huge amount of new discoveries for them to make. The team is about 130 people and they have a bunch of different interests. So that all makes sense.

 

But I would kind of like them to observe another flare like Makarian 501 and do the same analysis and either say yes or no. Either we did see a comparable delay of the higher energy ones, or we did not see.

 

It would like them to get us out of the suspense, and resolve the thing, either way.

 

If there is a delay proportional to travel time (and energy) as they suggested in the first paper then that is new physics. bigtime. A lot of new theoretical work would spring up. An approach by Martin Reuter that I like very much would prosper.

(But the cagey Reuter has been very quiet all this time. Based on just one observation he will not jump up and say "I can explain it!" only to be proven a fool when new observations don't see the effect.)

 

We should continue to follow this, and maybe keep this thread alive, just in case it is confirmed.

[bascule]

We should continue to follow this, and maybe keep this thread alive, just in case it is confirmed.

 

Yeah, speaking of which, I should bump another thread I'm interested in