Speed of Light not Constant?

[bystander]

New Window on the High-Energy Universe
ScienceNews - 2008 Dec 09

New telescope finds that the high-energy share of gamma-ray bursts arrive at Earth significantly later than the low-energy portion.

In the article, it mentions the time delay between the onset of low and high energy emissions of up to 16.5 seconds from the source GRB 080916C. Visible light afterglow of the event suggest a source in a galaxy some 12.2 billion light years away. I realize that very small differences in velocity will have a significant impact on time when distances are measured in billions of light-years, but isn't the speed of light constant. This article seems to be implying that high-energy photons are slower than low-energy photons (that seems counter-intuitive in itself - higher energy, less speed??) What am I missing? Somebody please explain.

[neufer]

New Window on the High-Energy Universe
ScienceNews - 2008 Dec 09

New telescope finds that the high-energy share of gamma-ray bursts arrive at Earth significantly later than the low-energy portion.

In the article, it mentions the time delay between the onset of low and high energy emissions of up to 16.5 seconds from the source GRB 080916C. Visible light afterglow of the event suggest a source in a galaxy some 12.2 billion light years away. I realize that very small differences in velocity will have a significant impact on time when distances are measured in billions of light-years, but isn't the speed of light constant. This article seems to be implying that high-energy photons are slower than low-energy photons (that seems counter-intuitive in itself - higher energy, less speed??) What am I missing? Somebody please explain.

Perhaps the (as yet poorly understood) physical process that generates these gamma rays takes a full 16.5 seconds in order to build to a crescendo of high-energy gamma-rays.
-----------------------------------------------
http://en.wikipedia.org/wiki/Gamma_ray_burst

<<Most observed GRBs appear to be collimated emissions caused by the collapse of the core of a rapidly rotating, high-mass star into a black hole. A subclass of GRBs (the "short" bursts) appear to originate from a different process, the leading theory being the collision of neutron stars orbiting in a binary system. The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2007 there is still no generally accepted model for how this process occurs.[36] A successful model of GRBs must explain not only the energy source, but also the physical process for generating an emission of gamma rays which matches the durations, light spectra, and other characteristics observed. The nature of the longer-wavelength (X-ray through radio) afterglow emission that follows gamma-ray bursts has been modeled much more successfully as synchrotron emission from a relativistic shock wave propagating through interstellar space, but this model has had difficulty explaining the observed features of some observed GRB afterglows (particularly at early times and in the X-ray band), and may be incomplete, or in some cases even inaccurate.>>
---------------------------------------------

[Chris Peterson]

In the article, it mentions the time delay between the onset of low and high energy emissions of up to 16.5 seconds from the source GRB 080916C. Visible light afterglow of the event suggest a source in a galaxy some 12.2 billion light years away. I realize that very small differences in velocity will have a significant impact on time when distances are measured in billions of light-years, but isn't the speed of light constant. This article seems to be implying that high-energy photons are slower than low-energy photons (that seems counter-intuitive in itself - higher energy, less speed??) What am I missing? Somebody please explain.

To be clear, the article first suggests a very plausible explanation for why the different energy particles arrive at different times, based simply on different times of production. It makes it very clear that the quantum gravity explanation remains highly speculative.

That said, it may not be a good idea to think of the speed of light as a constant. The actual constant is c, which isn't the same as the speed of light. We consider the speed of light in a vacuum to be equal to c, but under quantum gravity theories the idea of a "vacuum" becomes very complicated. So even if the speculative theory turns out to be correct, it doesn't mean that c isn't a true constant.

I was thinking about another possibility not discussed. I don't know if it's already been analyzed and found false, not considered, or simply not mentioned in the article. The speed of light in any medium is less than c, and the actual amount it is less depends on wavelength (energy). So for photons traveling through a medium, you would expect particles with different energies to arrive at different times. Space isn't a perfect vacuum; I can imagine that over billions of light years there's enough material that photons pass through to produce a measurable separation in particles as a function of energy.

[bystander]

Perhaps the (as yet poorly understood) physical process that generates these gamma rays takes a full 16.5 seconds in order to build to a crescendo of high-energy gamma-rays.

To be clear, the article first suggests a very plausible explanation for why the different energy particles arrive at different times, based simply on different times of production. It makes it very clear that the quantum gravity explanation remains highly speculative.

That said, it may not be a good idea to think of the speed of light as a constant. The actual constant is c, which isn't the same as the speed of light. We consider the speed of light in a vacuum to be equal to c, but under quantum gravity theories the idea of a "vacuum" becomes very complicated. So even if the speculative theory turns out to be correct, it doesn't mean that c isn't a true constant.

I was thinking about another possibility not discussed. I don't know if it's already been analyzed and found false, not considered, or simply not mentioned in the article. The speed of light in any medium is less than c, and the actual amount it is less depends on wavelength (energy). So for photons traveling through a medium, you would expect particles with different energies to arrive at different times. Space isn't a perfect vacuum; I can imagine that over billions of light years there's enough material that photons pass through to produce a measurable separation in particles as a function of energy.

Thanks Art and Chris. I had read the first explanation and was ok with that. It was the second explanation I had trouble wrapping my feeble mind around.

First I have to rid myself of classical physics where more energetic particles are faster, and I understand that light speed in any medium is less than c. So we are left with more energetic means more massive in a medium that is something other than a vacuum. I guess I can see (imagine) how more massive photons would be infuenced (slowed) more by quantum gravitation than the less energetic photons.

How does the quantum gravity solution compare to your explanation, Chris? Would more energetic photons (more massive, shorter wavelength) be slowed more than less energetic photons in a medium with positive refractive index?

[Chris Peterson]

How does the quantum gravity solution compare to your explanation, Chris? Would more energetic photons (more massive, shorter wavelength) be slowed more than less energetic photons in a medium with positive refractive index?

This isn't my explanation, just something that seems superficially reasonable to me, and which I therefore wonder if it has been addressed. It has no relationship to the quantum gravity explanation, but is purely classical. Normally, index of refraction in a medium increases with frequency. In other words, higher energy photons travel slower than those with lower energy. So again, this seems reasonable given the observation. I don't know if this conventional relationship between wavelength and index holds for the extremely high energy particles under discussion here, or if the density of the interstellar medium is high enough to introduce significant dispersion, or even if the interstellar medium behaves as a normal refractive material (I suppose it could even behave like a metamaterial, with a negative index and who-knows-what sort of dispersion properties).

[neufer]

I was thinking about another possibility not discussed. I don't know if it's already been analyzed and found false, not considered, or simply not mentioned in the article. The speed of light in any medium is less than c, and the actual amount it is less depends on wavelength (energy). So for photons traveling through a medium, you would expect particles with different energies to arrive at different times. Space isn't a perfect vacuum; I can imagine that over billions of light years there's enough material that photons pass through to produce a measurable separation in particles as a function of energy.

The usual Maxwellian concept of light propagating "in a (dielectric?) medium" involves a homogeneous medium of particles whose average separation is much smaller than the wavelength of the light itself. This is certainly rather an alien concept as regards most EM radiation (especially gamma-rays) interacting with rare space matter particles.

I suppose that doubly Compton scattered photons might find their way into the observing telescope but it would be scattered photons of lower energy which would show up late.

[Chris Peterson]

The usual Maxwellian concept of light propagating "in a (dielectric?) medium" involves a homogeneous medium of particles whose average separation is much smaller than the wavelength of the light itself. This is certainly rather an alien concept as regards most EM radiation (especially gamma-rays) interacting with rare space matter particles.

That's certainly true. But the behavior of the propagation is continuous- that is, while it varies with the separation between the particles, there is no value of that spacing (say, the wavelength of the radiation) where the behavior changes radically, or where a medium ceases to be refractive. So while I'd absolutely expect any dispersive effect of a highly rarefied medium on extremely short wavelength particles to be exceedingly small, I have no gut feeling for how that smallness weighs against the vast distances involved.

(I like best the explanation that the particles were produced at different times.)

[neufer]

The usual Maxwellian concept of light propagating "in a (dielectric?) medium" involves a homogeneous medium of particles whose average separation is much smaller than the wavelength of the light itself. This is certainly rather an alien concept as regards most EM radiation (especially gamma-rays) interacting with rare space matter particles.

That's certainly true. But the behavior of the propagation is continuous- that is, while it varies with the separation between the particles, there is no value of that spacing (say, the wavelength of the radiation) where the behavior changes radically, or where a medium ceases to be refractive. So while I'd absolutely expect any dispersive effect of a highly rarefied medium on extremely short wavelength particles to be exceedingly small, I have no gut feeling for how that smallness weighs against the vast distances involved.

(I like best the explanation that the particles were produced at different times.)

So do I....but your concept of Intergalactic EM dispersion is worth examining:

1) Sodium D line refractive index of Hydrogen gas at STP = 1.000132

2) Hence, 35 light hours of Hydrogen gas at STP is required to produce a 16.5 second delay.
(a full passage through VY Canis Majoris perhaps [ignoring absorption]?)

3) Intergalactic Hydrogen gas is ~10^19 less dense than Hydrogen gas at STP; ergo:
About 4 10^16 light years of intergalactic Hydrogen gas is required to produce a 16.5 second delay.

4) This is ~30,000,000 times more Hydrogen gas than there is across the galaxy.

5) Expected EM delay times across the galaxy should be less than 1 microsecond.

The effect of the real part of the refractive index causing time delays is usually always
much less than that of the imaginary part of the refractive index causing absorption;
if you can observe through it at all (e.g., a kilometer of pure water)
then the time delays are generally no more than microseconds.

[Chris Peterson]

1) Sodium D line refractive index of Hydrogen gas at STP = 1.000132

2) Hence, 35 light hours of Hydrogen gas at STP is required to produce a 16.5 second delay.
(a full passage through VY Canis Majoris perhaps [ignoring absorption]?)

3) Intergalactic Hydrogen gas is ~10^19 less dense than Hydrogen gas at STP; ergo:
About 4 10^16 light years of intergalactic Hydrogen gas is required to produce a 16.5 second delay.

4) This is ~30,000,000 times more Hydrogen gas than there is across the galaxy.

5) Expected EM delay times across the galaxy should be less than 1 microsecond.

An interesting analysis, but I don't find the logic behind linearizing the problem this way very convincing.

The effect of the real part of the refractive index causing time delays is usually always
much less than that of the imaginary part of the refractive index causing absorption;
if you can observe through it at all (e.g., a kilometer of pure water)
then the time delays are generally no more than microseconds.

I like that argument much better.

Still, we're talking about a delay (delta t / t) that amounts to about one part in 10^16. I could believe any number of effects might be responsible for that.

[neufer]

The effect of the real part of the refractive index causing time delays is usually always
much less than that of the imaginary part of the refractive index causing absorption;
if you can observe through it at all (e.g., a kilometer of pure water)
then the time delays are generally no more than microseconds.

I like that argument much better.

Good.

So we both probably would agree that the 16.5 second delay of high energy gamma-rays is more likely a consequence of a slow devolving "Salome dance of the veils" absorption process at the burst source, itself, rather than any sort of "easily understood" EM dispersion process. (Assuming, that is, that the fundamental burst process is more or less simultaneous at all frequencies to begin with.)

("Light echoes" are also a possible consideration but it is hard to imagine that the gamma ray burst lies IN FRONT OF any violent particle burst such that the delayed echo would get a Compton scattering boost of energy.)

Still, we're talking about a delay (delta t / t) that amounts to about one part in 10^16. I could believe any number of effects might be responsible for that.

Who knows what lies in the heart of dark matter/energy?

[harry]

G'day from the land of ozzzzzzzz

This paper may be of interest on varying speed of light.

http://arxiv.org/abs/astro-ph/0305457
New varying speed of light theories

Authors: Joao Magueijo
(Submitted on 23 May 2003 (v1), last revised 15 Oct 2003 (this version, v3))

Abstract: We review recent work on the possibility of a varying speed of light (VSL). We start by discussing the physical meaning of a varying $c$, dispelling the myth that the constancy of $c$ is a matter of logical consistency. We then summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz invariance; bimetric theories (where the speeds of gravity and light are not the same); locally Lorentz invariant VSL theories; theories exhibiting a color dependent speed of light; varying $c$ induced by extra dimensions (e.g. in the brane-world scenario); and field theories where VSL results from vacuum polarization or CPT violation. We show how VSL scenarios may solve the cosmological problems usually tackled by inflation, and also how they may produce a scale-invariant spectrum of Gaussian fluctuations, capable of explaining the WMAP data. We then review the connection between VSL and theories of quantum gravity, showing how ``doubly special'' relativity has emerged as a VSL effective model of quantum space-time, with observational implications for ultra high energy cosmic rays and gamma ray bursts. Some recent work on the physics of ``black'' holes and other compact objects in VSL theories is also described, highlighting phenomena associated with spatial (as opposed to temporal) variations in $c$. Finally we describe the observational status of the theory. The evidence is currently slim -- redshift dependence in the atomic fine structure, anomalies with ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data. The constraints (e.g. those arising from nucleosynthesis or geological bounds) are tight, but not insurmountable. We conclude with the observational predictions of the theory, and the prospects for its refutation or vindication.

[Martin]

It seems to me that observing GRB's in greater detail would eventually lead to more evidence for or against Dark Matter.

[Chris Peterson]

It seems to me that observing GRB's in greater detail would eventually lead to more evidence for or against Dark Matter.

Why? Dark matter is dark because it doesn't interact with electromagnetic radiation, or with particles of normal matter except through gravitation. But our observations of GRBs are carried out only by observing such radiation and particles. So I don't see what GRB observations are likely to tell us about dark matter.

[Martin]

I was thinking along the lines that GRB's are the most luminous electromagnetic events occurring in the universe.....

The search continues for that perfect lens, with many multiply-imaged arcs. Gravitational lens, Wikipedia

Perhaps I am confusing this process in my mind though. The light source is not the lens but rather the curvature of space is? So what would a perfect lens be?

[Chris Peterson]

Perhaps I am confusing this process in my mind though. The light source is not the lens but rather the curvature of space is? So what would a perfect lens be?

The more complex the lensed image, the more detail that can be extracted. A better lens will have more mass, and will yield a complex image of the background. A lensed GRB would potentially be a great light source, because it has a fast, time-varying spectrum that would allow the different optical paths to be deciphered. But we're a long way from being able to do that: Since GRBs are non-repeating, you have only a few seconds or minutes to collect a high resolution, spectral image of the source- and the odds of one occurring behind a large intervening mass are very small to begin with. First we'd need to build some rather esoteric space-based gamma ray telescopes, and then we'd have to get very lucky.

[Martin]

I think we are currently detecting about four GRB's per month? Chris, your reply appears to indicate that my original statement could be accurate?

[Chris Peterson]

I think we are currently detecting about four GRB's per month? Chris, your reply appears to indicate that my original statement could be accurate?

In principle, but not I think in practice. We don't have any gamma ray telescopes with sufficient resolution, GRBs are statistically unlikely to be located such that there's a gravitational lens between us and them, and even if we got lucky with position and had launched a high resolution gamma ray telescope, GRBs don't typically last long enough to actually image the lensed result.

[Martin]

I understand Chris. Thank you for your reversal and partial agreement. However, most scientific adventures are difficult and dependant upon luck. Some were near impossible with major odds stacked against them. But the quest for knowledge must prevail.

[mopedtothemoon]

Yes .. speed of light .. what is speed but in relation to time .. what is time in relation to gravity. Think about it. gravity effects time. Time is variable. Speed is therefore variable. If speed is variable then certainly speed of light is variable. Simplicity itself.

[Chris Peterson]

Yes .. speed of light .. what is speed but in relation to time .. what is time in relation to gravity. Think about it. gravity effects time. Time is variable. Speed is therefore variable. If speed is variable then certainly speed of light is variable. Simplicity itself.

It isn't simple at all. Time and space are different aspects of the same thing. Mass affects both, which isn't the same as saying "speed is variable". As closely as we can measure (and our ability is currently very good), c is a constant. Note that c is not the speed of light; rather, light in a vacuum is observed to have a speed equal to c.

Very few scientists think that c is variable at any given time, but it is a respected area of study to consider the possibility that c, and other fundamental physical constants as well, might not be constant as a function of time. One way (but by no means a necessary way) of explaining the observed evolution of the Universe is by allowing certain constants to either change with time, or to have had different values early in the Universe.

[IPRider]

Yes .. speed of light .. what is speed but in relation to time .. what is time in relation to gravity. Think about it. gravity effects time. Time is variable. Speed is therefore variable. If speed is variable then certainly speed of light is variable. Simplicity itself.

It isn't simple at all. Time and space are different aspects of the same thing. Mass affects both, which isn't the same as saying "speed is variable". As closely as we can measure (and our ability is currently very good), c is a constant. Note that c is not the speed of light; rather, light in a vacuum is observed to have a speed equal to c.

Very few scientists think that c is variable at any given time, but it is a respected area of study to consider the possibility that c, and other fundamental physical constants as well, might not be constant as a function of time. One way (but by no means a necessary way) of explaining the observed evolution of the Universe is by allowing certain constants to either change with time, or to have had different values early in the Universe.

It's so simple you can't even begin to grasp it, Chris .. you're blinded by what you think you know, you're trapped in your forms of understanding without reaching for free thought .. your supposed knowledge makes you who you think you are .. new knowledge will shake your identity so badly you can't consider lowering your shields to allow new information into your sphere .. but you're just typical of Science .. almost every new discovery is met with derision .. even Einstein couldn't accept what his theories meant in reality and condemed the scientists who could understand. I have been reading Chris .. you pulled the wool over my eyes a few times but I know what's going on in this forum .. 'yes' people saying yes to 'yes' people .. and if you say 'No that's not right" you get accused of attacking people and banned .. tough .. ban those with real insight because it's the scientific way .. scientific history proves it time after time after time after time after time. I'm banned from this forum? What an honour. What a loss to your minds. Read some books, Chris.

[IPRider]

Chris .. did you even know that Gravity affects time? I have my doubts. Did you know that the phases of the sun afects length of radioactive decay? That means the sun affects the best timepieces man has developed. Such a lot of revelations to be had to those who explore. Start to explore, Chris.

[IPRider]

New Window on the High-Energy Universe
ScienceNews - 2008 Dec 09

New telescope finds that the high-energy share of gamma-ray bursts arrive at Earth significantly later than the low-energy portion.

In the article, it mentions the time delay between the onset of low and high energy emissions of up to 16.5 seconds from the source GRB 080916C. Visible light afterglow of the event suggest a source in a galaxy some 12.2 billion light years away. I realize that very small differences in velocity will have a significant impact on time when distances are measured in billions of light-years, but isn't the speed of light constant. This article seems to be implying that high-energy photons are slower than low-energy photons (that seems counter-intuitive in itself - higher energy, less speed??) What am I missing? Somebody please explain.

Perhaps the (as yet poorly understood) physical process that generates these gamma rays takes a full 16.5 seconds in order to build to a crescendo of high-energy gamma-rays.
-----------------------------------------------
http://en.wikipedia.org/wiki/Gamma_ray_burst

<<Most observed GRBs appear to be collimated emissions caused by the collapse of the core of a rapidly rotating, high-mass star into a black hole. A subclass of GRBs (the "short" bursts) appear to originate from a different process, the leading theory being the collision of neutron stars orbiting in a binary system. The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2007 there is still no generally accepted model for how this process occurs.[36] A successful model of GRBs must explain not only the energy source, but also the physical process for generating an emission of gamma rays which matches the durations, light spectra, and other characteristics observed. The nature of the longer-wavelength (X-ray through radio) afterglow emission that follows gamma-ray bursts has been modeled much more successfully as synchrotron emission from a relativistic shock wave propagating through interstellar space, but this model has had difficulty explaining the observed features of some observed GRB afterglows (particularly at early times and in the X-ray band), and may be incomplete, or in some cases even inaccurate.>>
---------------------------------------------

Explain? Gravity affects time. Speed of light is based on time per second. Gravity affects the length of a second. Time for an astronaut is different than time at sea level. This has to be taken into account for satellite transmissions, time signals, GPSs. So the speed of light is definitely NOT constant. Time runs differently at mountain top and at sea level .. this had been measured .. on vast distances how variable is time .. what is speed in the total absence of gravity when gravity affects time. This is all so amusing. As well, the sun's phases affect the times of radioactive decay .. this has been measured .. Cesium clocks are affected .. so time speeds up and slows down according to fluctuations in the sun. We are just beginning to understand what we think we have long understood. The tips of our fingers only have touched the light of knowledge.

[astrolabe]

Hello IPRider,

Gravity affecting time is not by any means something new. It is not a new idea, a left-of-center concept or a new revelation of any sort. Nor is the variations in the speed of light. Oh, it may take a little longer for light to reach us (observers) because of a gravity well, or not at all because of the event horizon of a black hole or two, but it'll get here eventually. So it's nothing innovative nor previously unthought of; did you think it a point somehow completely missed or rejected out hand?

[aristarchusinexile]

Hello IPRider,

Gravity affecting time is not by any means something new. It is not a new idea, a left-of-center concept or a new revelation of any sort. Nor is the variations in the speed of light. Oh, it may take a little longer for light to reach us (observers) because of a gravity well, or not at all because of the event horizon of a black hole or two, but it'll get here eventually. So it's nothing innovative nor previously unthought of; did you think it a point somehow completely missed or rejected out hand?

Hi Astro. Who's this IP? Related to Jake Ip? I did meet a couple guys here in Peterborough .. a 'Sputnick' was one of them, wearing an aluminum and copper hat with wires of all kinds hanging off in weird springy ways, a little tuning fork on top. He rambled on, with alittle tear in his eye, that the Peterborough Public Library computers are banned from APOD .. mentioned being in court in Australia with the kangeroos .. a nice guy despite his eccentricities .. very fond of the APOD folks. He says he has no internet at home and uses public computers, same as me, like the one I'm on now at an Employment Service, and it's a shame they get disconnected from APOD. Have you heard split personality syndrome is on the rise?

As far as the 'time' thing, no, I did not think it's a new idea .. just not taken into account nearly enough to assist in understanding the universe's machinery nearly enough because, I suspect, it's thought of as a measurement instead of as an entity, not a living entity of course, not a being, but a thing, an entity in that meaning, with its own powers affecting other entities.