Talk:Photon

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Untitled[edit]

please add new talk topics at the bottom

Photon structure[edit]

Would it be acceptable for me to add [1] to the other references page section? The work is a significant advance with relevance to many other pages. Reference to it in those pages would augment this project's value. HCPotter (talk) 08:25, 23 October 2011 (UTC)]

This article proposes a new theory, but is published in Apeiron, which is not indexed by Web of Science (thus has no impact factor) and is considered as a "dissident journal". We need reliable secondary sources establishing the notability of this theory. Materialscientist (talk) 08:34, 23 October 2011 (UTC)
Withouth reading the paper in detail, (I pretty much stopped when I saw this was published in Apeiron, which isn't considered a reliable source by our standards), the jist of it is that this is original material, thus shouldn't be included per our policy on original research. First get those claims published in a reputable journal. Then it needs to be reviewed/endorsed as mainstream by the physics community. Then it could be included. But not before. This is not a judgment on whether your paper has merits or not, simply that its inclusion in Wikipedia would be premature at this point in time. Headbomb {talk / contribs / physics / books} 10:43, 6 November 2011 (UTC)

On 17:11, 25 May 2013, I gave a contribution which was reverted by Materialscientist on 18:18, 25 May 2013‎ by the reason Not a reliable source yet. Maybe in a few years. I wish to inform that an English translation version of the source reference was posted on http://arxiv.org/abs/1305.3602 (same link of the cited reference). Now anyone can read and verify that the physics therein is consistent and supports that the photon may be composed by pairs of flux quanta. The source reference at arXiv.org reproduces the version accepted for publication on the next issue of Rev. Bras. Ens. Fis., ISSN 1806-1117 (print), 1086-9126 (online). It is a peer reviewed publication, the source reference for this add to Photon at Wikipedia was submited to analysis under neutral point of view and fully accepted. User:Celso ad 23:27, 5 June 2013 (UTC)

So now it has become a wp:primary source, but we need wp:secondary sources. Is the paper significantly cited elsewhere yet? - DVdm (talk) 07:02, 6 June 2013 (UTC)

Incorrect diagram[edit]

This diagram needs correcting, fails to show 90 degree phase shift between E-M waves. I'll replace sometime, unless someone else does first. Here's a correct diagram: [2]. Tom Ruen (talk) 04:09, 25 January 2012 (UTC)

In 1900, Maxwell's theoretical model of light as oscillating electric and magnetic fields seemed complete. However, several observations could not be explained by any wave model of electromagnetic radiation, leading to the idea that light-energy was packaged into quanta described by E=hν. Later experiments showed that these light-quanta also carry momentum and, thus, can be considered particles: the photon concept was born, leading to a deeper understanding of the electric and magnetic fields themselves.
Correct me if I'm wrong - but I think both images are incorrect in that they give the incorrect wave direction. I'm assuming that the arrow and word 'distance' in the present image is referring to the direction of wave propagation. The proposed image is much nicer looking, except for the direction which should be the cross product of E and B. The animation on the electromagnetic radiation page is correct.PhySusie (talk) —Preceding undated comment added 20:32, 25 January 2012 (UTC).
There is no phase shift (see e.g. Sinusoidal plane-wave solutions of the electromagnetic wave equation or Electromagnetic wave equation), but the propagation direction is indeed wrong in most images on Commons (as they are derivatives of this one). Correct images are File:Tem wave.gif File:Onda e y ma 20.JPG File:Onda electromagnetica1.jpg [3] [4], etc. I might have known why there are two types of images, but completely forgot. Materialscientist (talk) 07:45, 27 January 2012 (UTC)

If the diagram is correct, and E & B are 'in phase', then the energy formula for a photon (e = hv) is plainly wrong and must be re-written as a time varying formula. Further, 'why' do the E & B fields ever 'recover' from the point at which both fields are zero (explanations that invoke the 'storage' of energy 'in the aether' are not acceptable :-) ) and if the energy varies how do we explain the photo-electric effect ? — Preceding unsigned comment added by 62.3.239.168 (talk) 14:49, 23 March 2013 (UTC)

Your question has a hidden assumption, which is that one field (E or B) or a change in it, causes the other field (B or E) to "recover." Not your fault, as generations of students are told that a varying E "causes" a B, and vice versa, and that is how EM waves are made. Wrong. But Maxwell's equations for B and E are not causal. They demand a certain association between E and B, but associations between two variables can be caused by a third Main Cause, and in this case, they are. In Maxwell's equations, E and B are both caused by charges and they literally have nothing to do with each other. They are both caused by an accelerated charge at the source, and by the time you get very far away from the charge, E and B are in fixed ratios to each other because they are both a product of this same acceleration. And not the charge's density or velocity (current), which can be arbitrary, and produce arbitrary E/B ratios close to the source charges and currents. But that doesn't mean E causes B in an EM wave (EMR), which is made of photons.

There's also an enormous amount of confusion caused by the fact that displacement currents in a capacitor (the term in Maxwell's equations that suggests an EM wave) give E and B fields that are NOT in phase. In fact, E and B in a capacitor gap are exactly out of phase, even though described by the same equations. But the changing EM field inside a capacitor (mostly what we call the near-field) is not the same changing EM radiation that you see far away from the capacitor (the far-field), and the phase is not the same. Inside the capacitor the ratio of E to B can be anything you like (depends on the design or the capacitance of the capacitor, even if you specify vacuum dielectric). Far away from a capacitor, in the direction of x propagation in vacuum it must be the case for linearly polarized plane waves that [dx/dt]^2 dE/dx = dE/dt, and the same equation for B, so that E = (dx/dt) B where dx/dt is some constant wave speed determined by the permittivity and permiability of vacuum. This velocity turns out to be dx/dt = c. Please note the form of the equation. It is not true that E = dB/dt or that B = dE/dt, which are the Faraday's law looking things, even though you will be told that this is the "mechanism" by which EM waves are made. For sine or cosine waves this would give a phase difference, as sine of B would be cosine of E, and vice versa. But the correct single differentiation on both sides (one for space and one for time) gives the same phase of E and B in the far-field.

As for the precise "where" in space that the energy of EM radiation is stored, that is related to the uncertainty principle. You can't point to a specific place on a wave antinode and say "what is there no energy THERE?" The energy of the wave is spread out along the EM wave (many wave peaks), so you can ignore places where the E and B fields go to zero. That's true even for a single photon, which isn't composed of just one peak-- it's a whole train of them. If you want to squeeze a photon in space (along the direction of travel) the frequency of the waves making it up get uncertain, and so does its energy. SBHarris 23:40, 14 April 2013 (UTC)

Is the photon elementry?[edit]

A photon is made of one electron and one anti-electron so how can photons be described as elementry? EveryThingIsRelative (talk) 10:07, 20 April 2012 (UTC)

Questions like that are best put at the wp:reference desk/science. Article talk pages are for discussions about the content and format of the article, not for discussions or questions about the subject. See wp:talk page guidelines. Cheers - DVdm (talk) 11:15, 20 April 2012 (UTC)

Photons inside superconductors[edit]

The following sentence is missing a reference: """Photons inside superconductors do develop a nonzero effective rest mass; as a result, electromagnetic forces become short-range inside superconductors.""" — Preceding unsigned comment added by 213.136.58.100 (talk) 10:40, 29 July 2012 (UTC)

Yes check.svg tagged - DVdm (talk) 10:54, 29 July 2012 (UTC)

Photons CAN be localized, EM field IS closely related to schrodinger wave function[edit]

I removed a longish paragraph in edit http://en.wikipedia.org/w/index.php?title=Photon&oldid=509261917 just now. Please see http://physics.stackexchange.com/a/34966/8841 for my description of why. In addition to what I wrote there, you can read discussions of how the EM waves ARE very close to "Schrodinger" wave functions in [1], and [2]. Briefly, a "complex" electromagnetic field is used as a matter of course in quantum electronics and engineering, in the dynamic field case, the imaginary part of the dynamic electric field is within a constant of the dynamic magnetic field (and vice verse). The localization of the photon is completely possible, but the localized states cannot be stationary in free space. But is a car moving 100 kph any less localized at any instant in time than a car parked?

Mwengler (talk) 15:50, 26 August 2012 (UTC)

  1. ^ Marcuse, D., Principles of Quantum Electronics, 1980
  2. ^ Yariv, A., Quantum Electronics, 1975
Regardless of validity of the paragraph removed (and reinserted by an unreg), the electromagnetic field is not a wave function. This does not preclude the photon to have its wave function, but one just has to realize that it is not the same as a field strength, in the same way as a quantum mechanics is not a quantum field theory. There exists a simple thought experiment to check the difference. Wave function is a quantity those linear combinations correspond to quantum superposition. If a particle's wave function is, say, doubled (in some piece of a space), this does not mean that we now have more particles. And what does a doubled field strength mean? IMHO it means 4 times more photons. Incnis Mrsi (talk) 10:18, 29 August 2012 (UTC)
If a (bosonic) particle's wave function is doubled in all of space, you have four particles instead of one particle, just as with the photon. I am not claiming that the E-field is the Schrodinger wave. I am claiming that the exact same thing that allows a wave packet description of the electron to demonstrate so clearly the Heisenberg uncertainty principle allows it to be demonstrated for the photon. The photon cannot be localized and stationary, but every time a photodetector is triggered, it is with a photon quite localized in x, y, z, and t. If one of the fans of non-localisability of photons could explain the very obvious and trivially achieved "real" localization of em energy in that context, that would be very helpful.
On a related subject, just how much should I respect an uncommented untalked about undo by an unreg? Mwengler (talk) 19:23, 29 August 2012 (UTC)

Attribution[edit]

The article states "...the modern concept of the photon was developed gradually by Albert Einstein..."

This conflicts with another Wikipedia article on Electromagnetic radiation that states, "An anomaly arose in the late 19th century involving a contradiction between the wave theory of light on the one hand, and on the other, observers' actual measurements of the electromagnetic spectrum that was being emitted by thermal radiators known as black bodies. Physicists struggled with this problem, which later became known as the ultraviolet catastrophe, unsuccessfully for many years. In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum. Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta." — Preceding unsigned comment added by 70.189.252.150 (talk) 00:02, 1 February 2013 (UTC)

Please, read Photoelectric effect and Bose–Einstein statistics articles. It may help to realize the difference between Planck’s raw thoughts about “discrete bundles” and the actual theory of photons. Incnis Mrsi (talk) 08:46, 1 February 2013 (UTC)

If photons have 0 displacement[edit]

In a wave the particles do not displace. But according to this article EM waves have photons and they displace at speed of 3.0 X 108 m/s. I assume that photons do not travel but only show their energy through vibrations like ordinary matter. So only energy is travelling at the speed of 3.0 X 108 m/s. Therefore the whole universe would be filled with photons and they show different energy intensities by their vibrations just like ordinary matter. I think all should consider this. — Preceding unsigned comment added by G.Kiruthikan (talkcontribs) 11:07, 2 February 2013 (UTC)

Added a formula that describes mass of phothon(sic)[edit]

[5] This (second) IP addition

  1. is redundant and off-topical (I already said: the infobox shows the invariant mass);
  2. written (and added) in poor English;
  3. uses a translated text from Spanish Wikipedia without attribution.

If one is willing to investigate what “Algunas fuentes” should mean in Spanish and to fix the IP’s “wavelenght” and so, then feel free to reintroduce it, but in some less prominent spot than the infobox. BTW, in es:Fotón this footnote was referred only from the body text for many years, and only recently was included to infobox. Incnis Mrsi (talk) 05:48, 14 April 2013 (UTC)

The photon mass is already discussed in the Physical properties section, with a nearly identical footnote, which I suspect is where the Spanish version came from. There's no need for an attempt to translate the footnote back (even if that was successful), and there's no need to link it in the infobox. The word "Mass" in the infobox already links to Invariant mass, and readers can be expected to look in the main article for further details and explanations regarding the material summarized in the infobox. — HHHIPPO 10:16, 14 April 2013 (UTC)
Thanks Hhhippo, now I learned that they accustomed to infringe Wikipedians’ copyright in both directions, and probably inside their wiki as well. Sorry, I can’t deter myself from this attack. Incnis Mrsi (talk) 10:38, 14 April 2013 (UTC)

Where does the version of the uncertainty principle in this article come from[edit]

Looks like it should actually be ≥hbar/2 — Preceding unsigned comment added by 128.223.131.219 (talk) 05:59, 20 April 2013 (UTC)

Photon is described by exactly three continuous parameters[edit]

Sure, I realize that author(s) of Photon #Physical properties thought about the momentum representation but forgot to say it explicitly. BTW, they actually forgot polarisation which is not derivable from a 3-vector, is it? But for a person not advanced in quantum mechanics all this should look very confusing, in any case. Imagine an analogous text for an arbitrary massive particle ¤ (such as electron, proton, neutron, pi-meson…):

An ¤ particle has (number of) possible spin states and is described exactly by its spin quantum number s¤, a discrete parameter, and its momentum vector p¤, three continuous parameters. Components of the momentum vector uniquely determine velocity vector v¤ and kinetic energy E¤.

Would it be useful for a reader who does not know what is a quantum state, wave function, and Fourier transform? Incnis Mrsi (talk) 08:56, 6 June 2013 (UTC)

WP:PHYSICS review: A-level article[edit]

I'm beginning a sort of WP:Expert review process for articles independent of the featured article system which I've realized has problems. As such, I've rated this article a level 'A' which means it is of the quality that would be expected from a professional reference work on the subject. I say this as a person with graduate degrees in astrophysics, but I encourage others who have similar qualifications to make comments if they believe my judgement to be incorrect.

jps (talk) 02:19, 12 September 2013 (UTC)

I don't agree. It is a mash-up which in my opinion lacks clarity. Level 'A' means it has the 'quality' of a 'professional reference work'? Please provide references to this claim. ThanksAbitslow (talk) 23:41, 12 December 2013 (UTC)

Merge discussion of material from Photon molecule and Photonic matter[edit]

This was a recently created article that, based on it current content and sourcing, might be better merged here. Do folks have any particular objections to including its material here? I, JethroBT drop me a line 16:38, 27 September 2013 (UTC)

In my opinion, Photon molecule should definitely not be merged here. It is not particularly relevant to this article, and if it were to be merged, there would be hundreds or thousands of other esoterica that would qualify to be merged on the same criteria: photons are fundamentally involved in almost every physical phenomenon that we observe. — Quondum 17:30, 27 September 2013 (UTC)
Agree. PM is a new form of matter, not a detail to a particle. I'll be adding more detail over the coming days. Lfstevens (talk) 17:52, 27 September 2013 (UTC)
What about Photonic matter? — Reatlas (talk) 02:58, 28 September 2013 (UTC)
Every photon is a form of matter. Lfstevens (talk) 07:36, 28 September 2013 (UTC)
I have proposed that Photon molecule be merged into Photonic matter, since this was mentioned by Reatlas. I feel that the original merge proposal into Photon should be removed. — Quondum 02:11, 29 September 2013 (UTC)
Interestingly, the two pieces were created within one hour of each other. (GMTA) I chose molecule rather than matter for the reason stated above: the discovery wasn't that photons are a type of matter. It's that they can act as a molecule. Since the two discuss the same phenomenon some merger is clearly called for. Hopefully, more will chime in. Cheers! Lfstevens (talk) 04:50, 29 September 2013 (UTC)
One must forgive a certain amount of hype and grantsmanship on the part of the inventors. It's all well to say you've discovered a new state of matter but it's something else to get you colleagues to agree. Matter is not well defined and when it is , photons are most often given as examples of non- matter . It's not even clear here if the reference is to photon " molecules " in free space, or to their theoretical existence as part of an ensemble (like a Cooper pair of electrons in a superconductor ). In the latter case a whole lot of atomic matter is also part of the package . The idea of "crystals" of pre photons holding together is hyperbole and approaches what you might hear in an ad campaign for a product or politician. Come, now. A little less Star Wars light saber, before I gag. Some scientist needs to step away from his rubidium and perhaps try a few clarifying weeks of lithium! SBHarris 06:28, 29 September 2013 (UTC)
I think this is better discussed at state of matter. Paradoctor (talk) 15:47, 30 September 2013 (UTC)
I just found out that "photonic molecule" seems to have an established second meaning, I'll make a few edits. Paradoctor (talk) 15:47, 30 September 2013 (UTC)
Looks like merge is out of the question now. If nobody beats me to it, I'll move to photonic matter what belongs there. Paradoctor (talk) 16:23, 30 September 2013 (UTC)
This whole discussion of "matter" versus "molecules" (media speak) completely misses the point. The original title of the nature paper was "Attractive photons in a quantum nonlinear medium". So this is about photon interactions, similar to stimulated emission. It probably belongs in a subsection of Two-photon physics or Rydberg atom instead. — Preceding unsigned comment added by 91.176.150.45 (talk) 17:50, 30 September 2013 (UTC)

Edit Request[edit]

I tried to correct the table of properties to correctly link to the Charge parity article. My change resulted in the entire line no longer appearing. Specifically, the table links c parity to the article on c symmetry, not to the article on Charge_parity (c parity). I also tried to change the Parity line to Intrinsic Parity which should appear there (either in addition to or instead of "Parity"), but was unable to do that also. Several other problems with the article: 1) reference for these two lines is to a cryptic web page that does not provide any more information than that in the table, and in addition the page (in my web browser,(FireFox)) contains garbled characters. 2) Also, the link if you click on Parity (intrinsic) links you NOT to the intrinsic parity article, but to the article on parity {in (quantum) physics}. This also needs to be fixed. Other problems include 3) the statement that photons are stable. Is a virtual photon "stable"?? 4) Virtual photons are common enough to require the article to distinguish between the various 'flavors' of photons. Two other issues I found which need some attention (imho) are: 5) the implied claim that Maxwell's equations are only appropriate for semiclassical treatments. As is probably obvious, I'm not an expert on this but: its my understanding that appropriately modified, Maxwell's equations are perfectly compatible with quantum field theory. 6) I don't think this article appropriately or sufficiently handles the fact that in modern applications electromagnetic theory must include Maxwell's equations. 7) Another error is the claim that the pictured light cone (2d representation of a 3d cone) IS the light cone. The cone is 4d, of course, best depicted as a series of (3d) spheres. 8) Finally, this article has NO mention of classical (optical) rays, and the relationship between rays and ((9) classical waves) and photons ((10)not to mention the 'classical' quantum mechanics and quantum field theory differences).Abitslow (talk) 00:10, 13 December 2013 (UTC)

A photon is not necessarily massless[edit]

In the "Physical Properties" section it says "A photon is massless", and in Note 2 that "The mass of the photon is believed to be exactly zero, based on experiment and theoretical considerations described in the article"

The article quoted does not say any of this. http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

The article actually says that "Photons are traditionally said to be massless. This is a figure of speech". It also states "It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero."

You can never measure a zero mass, that idea is absurd because there's nothing to measure!

All they can do is say the mass is less than a very small amount. It could turn out that the mass is much smaller than the currently measurable limit. Effectively, you can never say it is zero until you have infinite measuring capability, which we will never have.

I wrote all this into the section but it has been reverted.

The article is being used as a false reference for an author's personal views.88.203.90.14 (talk) 18:14, 6 January 2014 (UTC)

lazy photon[edit]

I expected to find something about lazy photons on wikipedia, but could not find anything. There was a reference to lazy photons at LHC in New Scientist. Could some professional/amateur particle physicist please explain for me... 80.4.63.73 (talk) —Preceding undated comment added 01:19, 19 February 2014 (UTC)

Hi 80.4.63.73. Please ask this question on Wikipedia:Reference desk/Science, and I'm sure someone will be happy to help you. This page is for discussing what should appear in the photon article; it's not for talking about photons generally. --Trovatore (talk) 04:06, 19 February 2014 (UTC)

Light Cone Diagram[edit]

The light cone diagram seems very strange, or at least the caption does. The caption says the green and indigo areas represent polarization of light, but it sure looks to me like they represent past and future. Can someone clear this up? — Preceding unsigned comment added by 172.251.246.55 (talk) 14:20, 26 April 2014 (UTC)

The diagram is a little confusing, but if you read the section carefully, you'll see that it makes some sense. The axes in the diagram are mislabelled, though: it is not time and space, but rather frequency in the time and spatial directions respectively. It is a matter of convention which direction of the frequency-in-time axis would correspond with which circular rotation. Ideally the axes should be relabelled, and the caption made clearer. —Quondum 15:38, 26 April 2014 (UTC)
I've tried to make this clearer in the caption, but the axes in the diagram should really be relabelled. Well spotted on the part of the OP. —Quondum 16:00, 26 April 2014 (UTC)

Nomenclature/history of the term[edit]

Acoording to this arxiv paper the history of term is a bit more involved than currently described in the article.--~~