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Tags astronomy , photons , physics

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Old 22nd March 2008, 02:48 PM   #1
wogoga
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A hypothesis for gamma ray bursts: photon cohesion

The conclusion of incredibly high energies involved in gamma ray bursts depends on the following premises:
  1. The sources are far away.
  2. The released energy becomes continuously distributed on an increasing surface (proportional to the distance square from the source).
Based on the second premise one concludes that one "gamma ray burst" could be detected in a huge region of the universe. Nevertheless, one should not forget that this certainly reasonable assumption is not necessarily valid without exception in all possible situations.

Properties of a detected electromagnetic signal can originate from
  1. the source
  2. the transmission of the signal (transmission effect)
  3. the detecting system (instrumentation effect)
Typical instrumentation effects can result e.g. from "improving" faint signals by means of additional electronics and software. A good example of a transmission effect is a mirage (Fata Morgana, an image produced by very hot air).

The existence of coherent sun light consisting of more than one photon (in the same way as induced emission in general) is strong evidence that also photons are "social" particles, interacting with each other.

Because of cohesion forces between molecules, water molecules are not homogeneously distributed in the atmosphere, but can often be found in groups (droplets). Reasoning from analogy could suggest the hypothesis of small cohesive forces between photons.

Such cohesive forces could explain why gamma rays are not always diluted more and more with increasing distance from the source, but break apart into fragments (which are currently interpreted as being a direct result of bursts somewhere in the universe).

Normally the distance between two objects, emitted at the same time with the same speed in slightly different directions from a point-like source, increases continuously. If the two objects are tied with a string of a given length, then instead of drifting apart further they exchange momentum when their distance has reached the length of the string.

The separating force between two photons side by side depends on the angle between the propagation direction of each photon. If they travel in exactly the same direction, then no force at all is necessary to prevent them from drifting apart. If the angle is small, then the separating force is proportional to the angle.

Take the case of fullerenes. Nobody would have been able to predict their existence from our physical theories. Under certain conditions however, hollow balls consisting of each 60 carbon atoms emerge with ease.

In the same way, certain conditions (e.g. photon densities) may lead to cohesive forces between neighbouring photons. So instead of a continuous increase of the mean distances between photons, continuously increasing strain leads to fissures in the gamma ray field.

Photons of the same fragments have therefore adjusted their directions to each other (by exchanging lateral momentum) so that they continue to constitute a detectable unity, even long after the cohesive forces (having led to fragmentation) have disappeared. Nevertheless, in the end the fragments are lost more and more in the normal gamma background noise.

The hypothesis entails that the occurrence of gamma ray bursts must have a strong statistical component, because it depends on chance whether such gamma-ray fragments originating from far-away sources hit detectors on the earth or not.

Cheers, Wolfgang

(This article is a composition of paragraphs from three posts of mine to sci.astro: post_1, post_2 and post_3)
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Old 22nd March 2008, 03:32 PM   #2
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Originally Posted by wogoga View Post
The existence of coherent sun light consisting of more than one photon (in the same way as induced emission in general) is strong evidence that also photons are "social" particles, interacting with each other.
But sunlight is not coherent. And in order for light to interact directly with itself, that would require electromagnetic fields to be nonlinear. There is no evidence that either occurs.

Quote:
Because of cohesion forces between molecules, water molecules are not homogeneously distributed in the atmosphere, but can often be found in groups (droplets). Reasoning from analogy could suggest the hypothesis of small cohesive forces between photons.
Except that Maxwell's equations for electromagnetism are explicitly linear. They would need to be wrong in order for photons to interact directly. There's no evidence they are. I don't think you really understand what you're proposing.

Quote:
Take the case of fullerenes. Nobody would have been able to predict their existence from our physical theories.
Not so. They are easy to predict: they have the same local bonding structure as graphite. The difficulty was manufacturing and detecting them.
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Old 22nd March 2008, 03:33 PM   #3
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Originally Posted by wogoga View Post
The existence of coherent sun light consisting of more than one photon (in the same way as induced emission in general) is strong evidence that also photons are "social" particles, interacting with each other.

Because of cohesion forces between molecules, water molecules are not homogeneously distributed in the atmosphere, but can often be found in groups (droplets). Reasoning from analogy could suggest the hypothesis of small cohesive forces between photons.
You don't need to reason from analogy. If there is a force between photons, we would be able to measure it. Many, many experiments have searched for this "force" at optical wavelengths, and all have shown that photon-photon interactions are incredibly small. The force was finally observed in a special case (inelastic gamma ray interactions) and it agreed with all theoretical predictions.

Thanks for the hypothesis, Wogoga! Unfortunately it has been falsified by these experiments.
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Old 2nd April 2008, 04:49 PM   #4
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Isn't photon-photon interaction(perhaps with other intermediary particles) what Feynman diagrams are all about? But because of renormalization, you generally find that a straight line is the best model for a photon?
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Old 2nd April 2008, 08:18 PM   #5
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Originally Posted by zosima View Post
Isn't photon-photon interaction(perhaps with other intermediary particles) what Feynman diagrams are all about? But because of renormalization, you generally find that a straight line is the best model for a photon?
That's not quite right, but there is a class of photon-photon interaction diagrams; the dominant has a virtual electron going around a loop and touching all four (two incoming, two outgoing) real photons. This has indeed been measured, for extremely high-energy photons: see http://prola.aps.org/abstract/PRL/v79/i9/p1626_1, which isn't quite the process you are looking for but is related.
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Old 2nd April 2008, 10:38 PM   #6
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I wouldn't say I'm looking for anything.
I was thinking that some of the more complex feynman diagrams were essentially computationally intractable due to their combinatoric complexity. Thus as skeptical as I am of these claims, can we necessarily exclude low energy photon-photon interaction?

Or is it correct to say that if we've worked out all the interactions with a small number of particles we can exclude these sorts of interactions with larger numbers of particles?
Is it something like interactions involving large numbers of particles become vanishingly improbable?

I'm not looking to attract any flame here, I'm just interested in understanding this a little better.
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Old 3rd April 2008, 07:12 AM   #7
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Originally Posted by zosima View Post
I wouldn't say I'm looking for anything.
I was thinking that some of the more complex feynman diagrams were essentially computationally intractable due to their combinatoric complexity. Thus as skeptical as I am of these claims, can we necessarily exclude low energy photon-photon interaction?
This is incorrect; more complex Feynman diagrams represent an infinite series. To evaluate a certain cross section to a certain accuracy, you evaluate the first N "orders" in the series, and you can show that the N+1th and N+2th orders are smaller and can be neglected. (Asking whether the *entire series* converges, if you evaluate all orders, is a messy question, but the answer appears to be "effectively yes for physics purposes") So, to say that "the photon-photon elastic cross section is X" isn't all that different than saying "for small x, sin(x) is x - x^3/3! + x^5/5! plus a very small correction."

In practice, it turns out that the simple electron loop should be hugely more important than the next order, so you'll get photon-photon scattering right within (my guess) about 0.01% by evaluating exactly two diagrams: the simple loop and a "crossed" version of it. You can totally ignore the diagrams with two separate electron loops bridged by a virtual photon, or a muon loop bridged by a photon coupling to a virtual W loop, etc.

The more complex diagrams usually become important at high energies; the approximation of ignoring them becomes more and more accurate, not less accurate, at lower energies.

Of course, it's always good to do the experiment. People have looked for optical photon-photon scattering for hundreds of years, always with null results; there are proposals to mount new searches (which may actually be sensitive to the QED prediction) using giant NIF-class lasers.
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Old 3rd April 2008, 11:16 AM   #8
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Thanks, ben, that was a very clear and illuminating explanation.
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Old 27th August 2014, 01:19 PM   #9
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Originally Posted by wogoga View Post
The existence of coherent sun light consisting of more than one photon (in the same way as induced emission in general) is strong evidence that also photons are "social" particles, interacting with each other.
Originally Posted by Ziggurat View Post
But sunlight is not coherent.

Sunlight should indeed be incoherent, because sunlight emerges from thermal radiation, and thermal radiation is considered spontaneous emission. So the phase of one photon should be independent from all other photons.

However photons, as social particles, tend to emerge and travel in coherent groups. And the longer they travel next to one another, the more they become coherent, by exchanging momentum and energy.

So even if sunlight (in a given direction) should not be coherent on Earth, it certainly will become coherent after having travelled some years, as starlight from our nearest stellar neighbors is highly coherent.

"Light from distant stars, though far from monochromatic, has extremely high spatial coherence." (Source)

"Finally it all makes perfect sense: starlight is ULTIMATELY coherent, that's why Stellar Interferometry works: starlight has coherence length in thousands of km, starlight is far more coherent than any human-made laser light." (Source)

So, in the case of starlight we get:
Huge areas of mutually coherent photons separated by "fissures", i.e. boundaries between photons of different phase shift (and maybe of slightly different frequencies).
If we add the hypothesis of cohesion (i.e. attractive forces), we get as a very reasonable consequence:
The gamma rays break apart along the fissures into fragments, and thereafter distances between such fragments will increase more and more.
Cheers, Wolfgang
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Old 27th August 2014, 02:14 PM   #10
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Originally Posted by wogoga View Post
Sunlight should indeed be incoherent, because sunlight emerges from thermal radiation, and thermal radiation is considered spontaneous emission. So the phase of one photon should be independent from all other photons.
Not "should be". Is.

Quote:
However photons, as social particles, tend to emerge and travel in coherent groups. And the longer they travel next to one another, the more they become coherent, by exchanging momentum and energy.
First off, your source is basically religious, not scientific. Second, you seem to be confusing the coherence effects that lead to lasers with thermal emissions. This is wrong, very wrong. Stimulated emission does lead to coherence, but it can never dominate emissions unless you've got population inversion, and thermal emissions from a star are very much NOT inverted thermal populations. Third, photons interact with each other very little. As ben explains above, the photon-photon interaction is basically non-existent within the optical range.

Quote:
So even if sunlight (in a given direction) should not be coherent on Earth, it certainly will become coherent after having travelled some years, as starlight from our nearest stellar neighbors is highly coherent.
It is spatially coherent at long distances simply because the waves have traveled so far that they're basically all traveling parallel to each other. You can only get spatial decoherence when light arrives at your detector from different directions. This is a purely geometric effect, it involves zero interactions between photons. A distant star subtends so little solid angle from our view that it's about as good a point source as you could hope for.

Quote:
Huge areas of mutually coherent photons separated by "fissures", i.e. boundaries between photons of different phase shift (and maybe of slightly different frequencies).
This makes no sense whatsoever.
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Old 27th August 2014, 02:19 PM   #11
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Have you guys looked at the OP date on this zombie or am I missing something?
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Old 27th August 2014, 03:00 PM   #12
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Originally Posted by Monketey Ghost View Post
Have you guys looked at the OP date on this zombie or am I missing something?
The OP brought back his own thread and is on-topic. Though still horribly wrong.
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Old 27th August 2014, 03:09 PM   #13
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I get it now, and yes he is.
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Old 27th August 2014, 03:19 PM   #14
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Originally Posted by ehcks View Post
The OP brought back his own thread and is on-topic. Though still horribly wrong.
So, now there are four, none of whom is a specialist, published in peer reviewed journals, doing actual experiments applicable to their idea(s), or taking real suggestions seriously.

Color me unimpressed.

And, just to remind all, if you have an idea about why something accepted in the science of your choice is obviously wrong, do not send it here - none of us is going to be able to help you in any functional way except to suggest what I just did in my first sentence.
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Old 27th August 2014, 03:24 PM   #15
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Yes... I have a layman's fascination with GRB's and stellar physics in general, and this kind of thread title attracts my interest... but usually devolves into nonsense a few sentences into the opening post.
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Old 31st August 2014, 02:38 PM   #16
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Originally Posted by wogoga View Post
However photons, as social particles, tend to emerge and travel in coherent groups...
Originally Posted by Ziggurat View Post
... Second, you seem to be confusing the coherence effects that lead to lasers with thermal emissions. This is wrong, very wrong. Stimulated emission does lead to coherence, but it can never dominate emissions unless you've got population inversion, and thermal emissions from a star are very much NOT inverted thermal populations.

Population inversion essentially means that the majority of atoms/ molecules are in an excited state. This concept is not necessarily useful in the case of thermal radiation, where instead of discrete energy states a continuous velocity distribution of the atoms/ molecules is the driving force of photon emission. So you cannot conclude from the inadequacy of population inversion in thermal radiation to non-involvement of stimulated emission. Quote:
In 1917 Albert Einstein published an extraordinary piece of analysis which is generally accepted as the foundation of laser physics. This article [On the Quantum Theory of Radiation] is also notable for first introducing the concept (but not the name) of the photon. In this article Einstein argues that in the interaction of matter and radiation there must be, in addition to the processes of absorption and spontaneous emission, a third process of stimulated emission. If stimulated emission exists then he can derive the Planck distribution for blackbody radiation and without it the same argument implies the empirically invalid Wien distribution.

But, in addition to establishing the existence of the process of stimulated emission, Einstein also asserts that the radiation produced in stimulated emission is identical in all relevant aspects to the incident radiation. This is a truly remarkable result.
That "the radiation produced in stimulated emission is identical in all relevant aspects to the incident Radiation" leads directly to the conclusion that photons tend to emerge and travel in coherent groups.

Cheers, Wolfgang
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Old 31st August 2014, 05:30 PM   #17
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Originally Posted by wogoga View Post
Population inversion essentially means that the majority of atoms/ molecules are in an excited state. This concept is not necessarily useful in the case of thermal radiation, where instead of discrete energy states a continuous velocity distribution of the atoms/ molecules is the driving force of photon emission. So you cannot conclude from the inadequacy of population inversion in thermal radiation to non-involvement of stimulated emission.
Still wrong. Thermal emission applies even to systems with discrete energy levels. It does not produce a blackbody spectrum in such a case, but that's irrelevant.

But no matter. The point, which eludes you, is that stimulated emission (which produces coherence in lasers) is essentially irrelevant for thermal emissions. Thermal emission is always, always, dominated by spontaneous emission, which is why it's always incoherent.
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Old 31st August 2014, 07:33 PM   #18
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Originally Posted by wogoga View Post
Population inversion essentially means that the majority of atoms/ molecules are in an excited state....
That is not exactly what the Wikipedia article states, wogoga:
Quote:
In physics, specifically statistical mechanics, a population inversion occurs when a system (such as a group of atoms or molecules) exists in a state with more members in an excited state than in lower energy states.
That is expanded on later - the major point is that it is the same excited state that the members are in.
For thermal emission from stars it is different excited states. We do not see one spectrum line from a star as in a laser, we see many lines superimposed on a continuum.

Also: Linking to a crank web site as in
Originally Posted by wogoga View Post
does not look good, wogoga.

Photons are in fact "social" but that is because they are bosons and obey Bose–Einstein statistics and have Bose–Einstein correlations, not because some crank thinks they have souls!

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Old 4th September 2014, 04:58 PM   #19
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Originally Posted by Ziggurat in #17 View Post
The point, which eludes you, is that stimulated emission (which produces coherence in lasers) is essentially irrelevant for thermal emissions. Thermal emission is always, always, dominated by spontaneous emission, which is why it's always incoherent.

Without stimulated emission, thermal radiation would result in the Wien distribution law. By adding the hypothesis of stimulated emission, we get the Planck law of black body radiation. We conclude that the effect of stimulated emission is the difference between the Wien and the Planck distribution laws, and this difference becomes substantial in the low frequency range.


Originally Posted by wogoga in #16 View Post
Population inversion essentially means that the majority of atoms/ molecules are in an excited state.
Originally Posted by Reality Check in #18 View Post
... the major point is that it is the same excited state that the members are in. For thermal emission from stars it is different excited states.

This is not the decisive point. The relevant condition for stimulated emission is the existence of "excited" states being able to provide the energy (and recoil), necessary for the emission of photons being coherent with the stimulating photons. In the case of blackbody radiation, the probability of this condition is the higher, the lower the frequency of the emitted photons. The reason is simple: The energy for emitted photons comes from kinetic energy of atoms/ molecules. The lower the needed photon energy, the more atoms/ molecules can provide it.

At the far end of the far-infrared (1 mm wavelength) of blackbody radiation of 5777 K, the proportion between stimulated emission and spontaneous emission is 400*. This means: One photon emerging spontaneously leads on average to around 400 coherent photons.

In the case of green light of 540 nm, only around 1 percent of the photons are due to stimulated emission. But this does not prevent such green photons from later becoming coherent with other photons of (almost) the same wavelength flying in (almost) the same direction.

Cheers, Wolfgang

* I hope my calculation (Planck's distribution formula at wavelength of 1 mm divided by corresponding value of Wien's distribution formula) is correct.
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Old 4th September 2014, 06:59 PM   #20
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Originally Posted by wogoga View Post
Without stimulated emission, thermal radiation would result in the Wien distribution law. By adding the hypothesis of stimulated emission, we get the Planck law of black body radiation. We conclude that the effect of stimulated emission is the difference between the Wien and the Planck distribution laws, and this difference becomes substantial in the low frequency range.
And which part of the spectrum do you suppose gamma ray bursts come from? The low frequency tail of the spectrum?

You have not proven your original hypothesis. You have helped to refute it.
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Old 4th September 2014, 07:53 PM   #21
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Originally Posted by wogoga View Post
This is not the decisive point.
...snipped irrelevant wall of text...
That is the "decisive" point - stars are not lasers, wogoga !
The fairly random excitation of electrons in plasma places them into random excited states so we see a roughly black body spectrum from them.

ETA: What you did not quote from Population inversion
Quote:
Creating a population inversion
As described above, a population inversion is required for laser operation, but cannot be achieved in our theoretical group of atoms with two energy-levels when they are in thermal equilibrium. In fact, any method by which the atoms are directly and continuously excited from the ground state to the excited state (such as optical absorption) will eventually reach equilibrium with the de-exciting processes of spontaneous and stimulated emission. At best, an equal population of the two states, N1 = N2 = N/2, can be achieved, resulting in optical transparency but no net optical gain.
Stars are in thermal equilibrium.

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Old 12th September 2014, 06:21 AM   #22
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Originally Posted by Ziggurat in #2 View Post
And in order for light to interact directly with itself, that would require electromagnetic fields to be nonlinear. There is no evidence that either occurs. ... Maxwell's equations for electromagnetism are explicitly linear. They would need to be wrong in order for photons to interact directly. There's no evidence they are.

You cannot argue from Maxwell's equations to the invalidity of Einstein's photon concept. In the same way, you cannot argue to the impossibility that under certain conditions (e.g. high densities), photons with similar properties exchange energy and momentum, in order to become mutually coherent or to align propagation direction. And even in mainstream physics, interaction of photons is a reasonable hypothesis:
"Planck believed that in a cavity with perfectly reflecting walls and with no matter present, the electromagnetic field cannot exchange energy between frequency components. This is because of the linearity of Maxwell's equations. Present-day quantum field theory predicts that, in the absence of matter, the electromagnetic field obeys nonlinear equations and in that sense does self-interact. Such interaction in the absence of matter has not yet been directly measured because it would require very high intensities and very sensitive and low-noise detectors, which are still in the process of being constructed." (Source)
Originally Posted by ben m in #3 View Post
If there is a force between photons, we would be able to measure it. Many, many experiments have searched for this "force" at optical wavelengths, and all have shown that photon-photon interactions are incredibly small.

I don't think we are able to reproduce by experiment e.g. the gamma photon densities of a neutron star surface just after formation by collapse. If the fissures in the previously homogeneous gamma ray field only occur far away from the source, then very small cohesive forces between neighboring photons are enough for the gamma ray fragment to remain a detectable unit, as they fly in almost the same direction (see #1).

Cheers, Wolfgang
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Old 14th September 2014, 01:00 PM   #23
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Very-high-energy gamma ray could be further evidence for photon-cohesion. Attributed with energies of 1011 to 1014 electronvolts, very-high-energy gamma photons are considered the highest-energy photons currently detectable from astronomical sources. As the energy-equivalent of a silver atom is around 1011 eV, one single gamma photon would contain the mass of up to 1000 silver atoms! At the same time the wavelength of such a 1000-silver-atom photon would be near 10-17 meter, which is a thousandth part of the diameter of only the nucleus of a silver atom (around 10-14 m).
"Instruments to detect this radiation commonly measure the Cherenkov radiation produced by secondary particles generated from an energetic photon entering the Earth's atmosphere. This method is called imaging atmospheric Cherenkov technique or IACT. A high-energy photon produces a cone of light confined to 1 of the original photon direction. About 10,000 m2 of the earth's surface is lit by each cone of light."
If we assume photon cohesion, then there is no need to explain such a cone of secondary radiation by a single gamma photon. Many individual photons travelling close together like a flock of birds can be at the origin of the cone of secondary radiation.

Cheers, Wolfgang
http://www.internationalskeptics.com...d.php?t=281031

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Old 14th September 2014, 04:17 PM   #24
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Originally Posted by wogoga View Post
Very-high-energy gamma ray could be further evidence for photon-cohesion. ...
Except your "photon-cohesion" is a complete fantasy, wogoga. The ignorance of thinking that stars are lasers has already been pointed out to you.

The Wikipedia article states:
Quote:
A high-energy photon produces a cone of light confined to 1 of the original photon direction.
This is an observed physical phenomena with an actual physical cause (not your imaginary "photon-cohesion").
If a high energy particle such as a cosmic ray or gamma ray hits a particle in the atmosphere, it produces a cascade of particles in a cone shape. This is known as an air shower. The Cherenkov radiation produced by these particles is also within the cone.
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Old 14th September 2014, 04:27 PM   #25
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Originally Posted by wogoga View Post
I don't think we are able to reproduce by experiment e.g. the gamma photon densities of a neutron star surface just after formation by collapse.
A fantasy about "the gamma photon densities of a neutron star surface just after formation by collapse" producing your ""photon-cohesion" is just that, wogoga.
We can actually predict what the interactions are between photons using little things calls laws of physics .
Classically there can be no EM interactions between photons (they have no charge). But QED shows that there are extremely weak EM interactions between photons: http://en.wikipedia.org/wiki/Two-photon_physics

Reproduction by experiment is not needed - the universe runs experiments with neutron stars all of the time! We can observe real nova, supernova and neutron stars to see what they do. If your idea was more than a fantasy then you could tell us what we would detect, wogoga.
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Old 15th September 2014, 06:34 AM   #26
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Originally Posted by wogoga View Post
In the same way, you cannot argue to the impossibility that under certain conditions (e.g. high densities), photons with similar properties exchange energy and momentum, in order to become mutually coherent or to align propagation direction.
First off, I'm not arguing that photons do not interact. I'm arguing that the interaction which exists (and which we understand) cannot account for what you want it to do.

Secondly, in regards to aligning their propagation direction, we know that this cannot happen because it would violate momentum and/or energy conservation.

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And even in mainstream physics, interaction of photons is a reasonable hypothesis:
Quite so. But again, the fact that they interact (weakly) doesn't mean that they interact the way that you want them to. They do not.
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Old 18th September 2014, 04:08 PM   #27
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Originally Posted by Ziggurat in #26 View Post
First off, I'm not arguing that photons do not interact. Secondly, in regards to aligning their propagation direction, we know that this cannot happen because it would violate momentum and/or energy conservation.

The objection that propagation alignment of photons violates momentum and /or energy conservation is indeed serious. The bigger the changing angles, the more convincing the objection.

Let us assume that two photons with each the same energy E are close to one another, and that the angle between their propagation directions is 120. If they want to move in the same direction, then each photon has to change its direction by 60 into the new intermediate propagation direction.

Because of symmetry, the two photons cannot exchange energy, and propagation speed is always c. Before propagation alignment, combined momentum in the new direction:
2 * E/c^2 * 0.5 c = E/c
The factor 0.5 is the result of cos 60. After alignment, momentum in this new direction:
2 * E/c^2 * c = 2 E/c
Therefore, combined momentum in the new direction would double during propagation alignment.

This problem can be solved by a simple ad-hoc-hypothesis. During alignment, radiation (in the form of one or more photons) with energy 0.5 E is emitted in the direction opposite to the new propagation direction, and each of the original two photons loses 25% of its energy E. Then total momentum in the new direction will be again:
2 * 0.75 E/c 0.5 E/c = E/c
As seen from two such photons:
The attempt not to drift apart leads by momentum conservation to an attempt to reduce propagation speed. There are only two solutions: either to give up the attempt to align propagation direction, or to gain forward momentum by emitting radiation backwards.
In any case, the momentum-compensation hypothesis for aligning photons implies:
  • Overall redshift for the interacting photons
  • Release of low-frequency radiation (lost in background)
Cheers, Wolfgang
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Old 18th September 2014, 05:17 PM   #28
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Originally Posted by wogoga View Post
This problem can be solved by a simple ad-hoc-hypothesis....
No, wogoga: an assertion that photons spontaneously emit photons whenever you want and at any energy you want is not "a simple ad-hoc-hypothesis" - it is a fantasy.
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Old 30th September 2014, 06:57 AM   #29
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Originally Posted by wogoga in #9 View Post
So, in the case of starlight we get:
Huge areas of mutually coherent photons separated by "fissures", i.e. boundaries between photons of different phase shift (and maybe of slightly different frequencies).
Originally Posted by Ziggurat in #10 View Post
This makes no sense whatsoever.

Let us imagine a frequency-stabilized 632.8 nm HeNe laser with a (longitudinal, temporal) coherence length of around 100 meter. Optical output power is assumed to be 1 Milliwatt. As the energy per photon is around 3x10-19 Joule, the laser output consists of 3x1015 photons per second, or 10 million photons per meter beam.

If we split our beam into two sub-beams and reunite them (Michelson Interferometer), then interference depends on the pathlength difference between the two sub-beams. If the pathlength difference is more than 100 m, (almost) no inference between the two sub-beams can be detected. For pathlength differences less than 100 m, inference is the stronger, the shorter the difference.

So in our example, a coherence length of 100 m means that we have groups with on average around 1 billion* coherent photons, separated by "fissures".

Cheers, Wolfgang

* 1 billion = 100 m times 10 million photons per meter beam
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Old 30th September 2014, 09:04 AM   #30
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Originally Posted by wogoga View Post
So in our example, a coherence length of 100 m means that we have groups with on average around 1 billion* coherent photons, separated by "fissures".
No. There are no fissures in your example. There is merely a continual drift in phase/frequency over time.
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Old 30th September 2014, 09:09 AM   #31
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Originally Posted by Monketey Ghost View Post
Have you guys looked at the OP date on this zombie or am I missing something?
I guess he went on vacation in the mean time.
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Old 30th September 2014, 12:55 PM   #32
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Originally Posted by wogoga View Post
Let us imagine a ...
No, wogoga: Let us imagine that you can understand that other posters here probably know about fairly basic physics such as a Michelson Interferometer !
The interference fringes in a Michelson Interferometer do not magically vanish for a difference in path length longer than the coherence length of a laser - the interference is just weaker.
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Old 2nd October 2014, 09:13 AM   #33
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Originally Posted by Ziggurat in #30 View Post
No. There are no fissures in your example. There is merely a continual drift in phase/frequency over time.

A continual drift in frequency would imply that laser light becomes more and more incoherent after leaving the source. Only photon groups of exactly the same frequency can remain coherent.

Let us assume an infrared laser with a wavelength from 999.999 to 1000.001 Nanometer. For simplicity, let us further assume that photon frequencies are equally distributed in this spectral bandwidth of 10-6 +- 10-12 Meter.

I suppose we agree that the photons are (normally) in phase when leaving the laser. Having the same phase is a prerequisite for photons being part of coherent light.

What is the situation after propagation of 50 cm? For a 1000 nm photon this distance corresponds to 500,000 wavelengths, for a 999.999 nm photon the 50 cm result in 500,000 plus half a wavelength, and for a 1000.001 nm photon we get 500,000 minus half a wavelength.

From the premise of equal distribution within the bandwidth, we conclude that at a distance of 50 cm from the laser, our light is completely incoherent, as photon phases are equally distributed in the range from -500 nm to +500 nm.

Even without our simplifying assumptions (and depending on the definition of coherence length), at the latest at a distance of several coherence-lengths, laser light would become incoherent (despite remaining highly monochromatic and collimated.)

So, from the fact that laser light remains coherent during propagation, we conclude that laser light consists of groups of coherent photons of the same frequency, separated by jumps in phase (and frequency).

Cheers, Wolfgang

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(*currently prevailing, authoritative mainstream science or religion)

Last edited by wogoga; 2nd October 2014 at 09:27 AM.
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Old 2nd October 2014, 01:14 PM   #34
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Originally Posted by wogoga View Post
A continual drift in frequency...
No wogoga: You have a laser beam that shifts frequency and that is that. There are no imaginary gaps, fissures, jumps or even dancing the fandango in the frequency .
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Old 2nd October 2014, 05:32 PM   #35
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Originally Posted by wogoga View Post
A continual drift in frequency would imply that laser light becomes more and more incoherent after leaving the source.
It implies nothing of the sort. This is not a change in the frequency of light that has already been emitted, that light retains its same frequency. It's merely that light emitted at a later time has a slightly different frequency than light emitted at an earlier time.
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Old 6th October 2014, 05:21 AM   #36
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Originally Posted by wogoga in #33 View Post
A continual drift in frequency would imply that laser light becomes more and more incoherent after leaving the source.

Originally Posted by Reality Check in #34 View Post
No wogoga: You have a laser beam that shifts frequency and that is that.
Originally Posted by Ziggurat in #35 View Post
It implies nothing of the sort. This is not a change in the frequency of light that has already been emitted, that light retains its same frequency. It's merely that light emitted at a later time has a slightly different frequency than light emitted at an earlier time.

You either confuse longitudinal (temporal) coherence with spatial (transverse) coherence, and/or you confuse continuity of phase with continuity of frequency. The only logical possibility of a stable continual drift in phase is a constant frequency.

And even so, by assuming that photons emitted at the same time will remain in phase, you admit the existence of coherent photon groups (emitted at the same time). The slightest difference in frequency between neighboring photons will lead to arbitrary phase shifts after long enough propagation.

Let us again deal with a hypothetical 1000 nm laser, this time assuming a frequency drift of +-10-8 (relative change) per meter beam. Let us examine a one-meter-piece of beam consisting of light emitted 1 m earlier to light just leaving the laser. The difference in wavelength within this 1-m-piece is 1000 nm x 10-8 = 10-14 m. As one meter is filled with 1 million wavelengths this leads to a phase shift of 1 million x 10-14 m = 0.01 wavelengths. (Under more realistic premises: phase shifts fluctuating from -0.01 to +0.01 wavelengths.) So, light at the ends of this 1-m-piece of beam would be highly coherent.

However, what is the situation after further propagation of 1000 m? As 1 km can be filled with one billion wavelengths, the wavelength difference of 10-14 m between front and back end of the 1-m-piece leads to a phase shift of 1 billion x 10-14 m = 10 wavelengths (i.e. more realistically: to phase shifts fluctuating from -10 to +10 wavelengths).

So, laser light of coherence length far more than 1 meter would become after propagation of 1 km laser light of coherence length far less than 1 m.


If you cannot accept the simple and obvious hypothesis of groups of coherent photons separated by (variable) phase shifts, then you have to adopt the absurd and refuted claim of Dirac that every photon only interferes with itself.

Cheers, Wolfgang

It is an irony of history that it was just Albert Einstein who reopened (with his relativity theories discrediting common sense) the door into physics for the resurrection of religious concepts (e.g. that a photon angel-like can use very different paths at the same time)
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Old 6th October 2014, 06:23 AM   #37
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Originally Posted by wogoga View Post
You either confuse longitudinal (temporal) coherence with spatial (transverse) coherence, and/or you confuse continuity of phase with continuity of frequency.
I have done nothing of the sort. Shifting the phase is the same thing as shifting the frequency. If you remain at the same frequency, the phase is stable.

Quote:
The only logical possibility of a stable continual drift in phase is a constant frequency.
A constant-rate phase shift is exactly the same as being at a slightly shifted (but constant) frequency. But the drift is not stable. The phase change is random, and it's caused by random fluctuations in the frequency. It's only constant in the sense that it's always changing, not in the sense that its rate of change is constant.

Plus, you're wrong about superpositions decohering over a distance. They don't. The longitudinal wave profile of plane-wave radiation traveling through a vacuum, whether it's monochromatic or not, will not change as it propagates, because a vacuum is non-dispersive. You have a fundamental misunderstanding of wave mechanics.
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Old 8th October 2014, 03:23 AM   #38
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Originally Posted by wogoga in #33 View Post
So, from the fact that laser light remains coherent during propagation, we conclude that laser light consists of groups of coherent photons of the same frequency, separated by jumps in phase (and frequency).
...
Confusing reality with orthodoxy has always been widespread in human history

I should have written: Confusing reality with one's own reasoning has always been widespread in human history.


Originally Posted by wogoga in #36 View Post
You either confuse longitudinal (temporal) coherence with spatial (transverse) coherence, and/or you confuse continuity of phase with continuity of frequency.
Originally Posted by Ziggurat in #37 View Post
I have done nothing of the sort.

Sorry for having accused you and Reality Check of confusion, here it is me who has become fully confused (in trying to transform a reasoning concerning incoherent photons emitted by stars becoming more or less coherent, into an analogue reasoning for laser radiation).

Yes, it is obvious that photons emitted in phase with slightly different frequencies will remain in phase during propagation. Maxima and minima of all photons propagating in the same direction have the same speed c, so the distances between such maxima and minima of different photons remain constant.

I also have to admit that continuous phase shifts caused by slightly changing frequencies can explain longitudinal coherence of laser light. So, the hypothesis of fully coherent laser-beam pieces (separated by phase shifts) is not necessary in order to explain that laser-light coherence does not decrease with increasing distance from the laser.


Originally Posted by Ziggurat in #37 View Post
Shifting the phase is the same thing as shifting the frequency. If you remain at the same frequency, the phase is stable.

Isn't this only correct in the case of classical wave mechanics? Photons (independently emitted in the same direction) of the same frequency can be in-phase or out-of-phase, can't they?

Quotes from Wikipedia -> Coherence -> Talk:
"How can a small slit in front of a light source produce coherence? Consider the source behind the slit. Each atom in the light source is working away independently and so photons arrive at the slit with every possible phase. How does the slit put them in phase? Somehow the photons get in step."

"Consider the colors in a film of gasoline on water. One photon that was in phase with another interferes with another after reflecting off a different surface. This should only work if a significant proportion of the photons were in phase. How can the sun be considered as a coherent source in this instance? No coherence can occurs because the photons are emitted thousands of miles apart and so they will arrive with totally random phases."
Quote from Nick Herbert on The Van Cittert-Zernike Theorem:
"Light emitted from a star is completely incoherent. Yet by the time that starlight reaches the Earth it has somehow in its long journey organized itself into co-ordinated patches of waviness similar to the patches of coherent water waves in the ocean. How does initially incoherent starlight become coherent simply by travelling from there to here?"

Originally Posted by Ziggurat in #37 View Post
Plus, you're wrong about superpositions decohering over a distance. They don't. The longitudinal wave profile of plane-wave radiation traveling through a vacuum, whether it's monochromatic or not, will not change as it propagates, because a vacuum is non-dispersive.

I have to agree.

Cheers, Wolfgang
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Old 8th October 2014, 06:30 AM   #39
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Originally Posted by wogoga View Post
Isn't this only correct in the case of classical wave mechanics?
No. That applies to quantum mechanical waves as well.

Quote:
Photons (independently emitted in the same direction) of the same frequency can be in-phase or out-of-phase, can't they?
Sure. But that doesn't change what I said.

The superposition (quantum or classical) of two monochromatic waves of the same wavelength and frequency will produce a wave of the same wavelength and frequency. This superposition wave will have a phase intermediate between the two superimposed waves, but that phase will not change over time if the two component waves remain at their original fixed frequency. It will be stable.

Quote:
The slit doesn't put them in phase. What it does is make the phase difference at the slit the only relevant phase difference, because the waves are blocked everywhere else. In contrast, if you have two spatially separated sources with nothing blocking them, then the phase difference will change from location to location.

Once you've selected that single spatial phase difference at the slit, it will not change as the superimposed waves propagate outward from the slit. This is the sense in which the slit becomes a coherent source. But if the waves are completely out of phase at the slit, then nothing will get through at all. So the slit doesn't make them get in phase. It can't.

This is a classical effect. It applies to quantum waves as well, but you can observe it with purely classical waves.

Quote:
Again, this too is a classical effect. Light from different parts of the star do NOT get put in the same phase. Rather, because they must be traveling basically parallel to each other in order to get from a distant star to earth (even if they're emitted from opposite sides of the star), whatever their phase difference is becomes constant over our region of observation. Two superimposed waves with a constant phase difference will act the same as a single wave with a phase intermediate between them.
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Old 21st October 2014, 08:55 AM   #40
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Originally Posted by Ziggurat in #37 View Post
Shifting the phase is the same thing as shifting the frequency.
Originally Posted by wogoga in #38 View Post
Isn't this only correct in the case of classical wave mechanics?
Originally Posted by Ziggurat in #39 View Post
No. That applies to quantum mechanical waves as well.

I don't know for what kind of "quantum mechanical waves" your statement may be true.

In the case of Einstein's photon concept however, a difference between shifting frequency and shifting phase exists. Photons of the same frequency emitted later can be in-phase or out-of-phase with previously emitted photons. A continuous drift in phase without frequency-change is therefore at least logically possible.


Originally Posted by Reality Check in #34 View Post
There are no imaginary gaps, fissures, jumps or even dancing the fandango in the frequency .

Do you have some evidence that phase jumps do not occur?

From Encyclopedia of Laser Physics and Technology:
Phase noise may occur in the form of a continuous frequency drift, or as sudden phase jumps, or as a combination of both.
From Noise effects in injection locked laser simulation: Phase jumps and associated spectral components:
When light from an external source is injected into a laser oscillating above threshold, the injected radiation competes with the spontaneous emission of the laser for being amplified. If the optical frequency of the injected light is close to the eigenfrequency of the unperturbed laser, the laser will adjust its frequency and coherence properties to those of the injected light.
You deny the existence of coherent photon groups separated by phase jumps only because I use it as evidence for a gamma-ray-burst hypothesis not (yet) existing in textbooks or peer-reviewed articles.

There is a lot of further evidence suggesting the existence of coherent photon groups, e.g. Astrophysical maser, or Random Laser:
These spontaneously emitted photons will then stimulate other radiative transitions in the gain medium to take place, unleashing yet more photons. This is, in many ways analogous to the chain reaction that occurs in the fission of neutrons in a nuclear reactor and has been referred to by R.H. Dicke as an optical bomb.
Cheers, Wolfgang
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