Talk:Photon/Archive 1

message: This article and the vast majority of other such material about light, overlook completely what a photon actually is.
Firstly, a charged particle is surrounded by an electric field, which extends outwards in all directions, reaching a distance of at least 13.7 billion light years. When a charged particle is accelerated, due to conservation of energy and angular momentum, the change in movement must be conveyed to the electric field which surrounds it. This change propagates at the speed of light, and is in fact, what we call light. Any light we see is caused by a change in an EXISTING electric field. Thus, a photon probably should be called a virtual particle, since it does not really exist like a regular particle independent of its creator. It is as virtual as other such particles like phonons, solitons, or polaritons. If we observe a photon emitted long ago from a distant star, we are observing the change in the electric field of the particle which emitted the photon. There is no particle which is a photon. The quantization of light is solely an effect of the quantization of charge and the particulate nature of the electrons used to observe and emit light. There might, however, be a quantization of space-time, which would also lead to the observation of quantized light.
Furthermore, a photon is not a packet of energy with a simple frequency or polarization. A wave of light can find itself in any shape allowed by the propagation of change in an electric field. This means that a photon isn't necessarily a sine wave, or even periodic. It just so happens that we are designed to detect periodically changing electric field in a certain range of frequencies called visible light. And we've created devices which are designed to detect light of many other frequencies. But we shouldn't limit our thoughts to the special (albeit useful) case of the periodically changing electric field.
I use the term electric, rather than electromagnetic field, since it has been shown that the observation of a magnetic field is a special relativistic effect upon charged particles in motion with respect to an electric field.
In view of quantum theory, the electromagnetic field is made of truly virtual photons, and when a change is propagated through the field we observe "real" photons.
Would anyone else like to comment? Like why aren't these ideas common knowledge? And why does the idea of a photon as corpuscle still exist? (please spare commentary on the photoelectric effect, unless it can be shown that this is not the result of interaction with particles of definite charge and cross-section)
--D. Estenson II 08:20, Mar 22, 2005 (UTC) (BTW,IANAP,BWBSS)
: Yes, "photon" carries misconceptions, and even physicists aren't immune.  Photons are quanta, not particles, since "particle" carries conceptual baggage (the word "particle" unfortunately implies something like a very small grain of sand.)   
: A good collection of recent articles by physicists is from the Optical Society of America : THE NATURE OF LIGHT: WHAT IS A PHOTON?    
: The articles have some some suprising stuff: the Photoelectric Effect does not prove the existence of photons, Nobelist W. Lamb takes a very dim view on the whole photon concept, and even as late as 1966 some physicists had a running bet whether quantum phenomena (Lamb Shift) could be calculated without recourse to quantized EM fields.  Other articles in the collection show where the "photon" concept is crucial in physics.  --Wjbeaty 04:16, Mar 23, 2005 (UTC)
:: FYI, here is a link to the abstract for the original article from the Optical Society of America. The Nature of Light: What is a Photon?.  There you can find a link to the article in pdf format.  Thanks for pointing out these articles. --D. Estenson II 10:08, Mar 23, 2005 (UTC)
:::I support most of the said. Even if we don't know, what a electromagnetic field oder matter is, and even, if we don't know, what momentum and energy is, we believe: the amount of energy and momentum doesn't change, but can be moved from field to matter. This exchange of energy and momentum we call a photon. This will solve some problems with imagination. Field no longer consist of photons, but are excitated by "photonic events". Such an event is a change in action of size h. Action is, according to my knowledge, the only appearance, that is realy quantisized. Energy quantization depends on the properties of a "measuring instrument". Quantisation of action NOT. This is the key! ErNa 08:48, 14 November 2005 (UTC)
thread_title: what is a photon, really 

message: Wave-Particle duality is not unique to the photon and the EM field in QM. Every particle, for example the electron, behaves like a wawe and under the right conditions this can be (and was) detected experimentally.
Elad Tsur 13:30, 1 June 2004 (UTC)
thread_title:  Who named the photon?

message: Is it true, that, whenever a photon is emitted or absorbed, the emitter/absorber state changes by h (Planck's quantum of action)?217.229.215.59 14:35, 17 May 2005 (UTC)
thread_title:  Photon and Action 

message: This article could use some content on the history of the photon, or at least some links.  See e.g. photoelectric effect. -- Beland 06:30, 14 August 2005 (UTC)
thread_title: History

message: If I'm reading this article right, light is made out of photons, and photons cannot decay on their own. So why is it that when I turn a flashlight off, the light goes away? What happens to all the photons that had been produced by the flashlight? -- Mwalcoff 00:00, 20 October 2005 (UTC)
replies: text: Photons can be absorbed (and turned into kinetic energy) when they collide with normal matter.  (Sometimes an electron is knocked free by this process, hence the photoelectric effect.)  --Jasonuhl 07:39, 14 November 2005 (UTC)
thread_title:  What am I missing? 

message: The caption says that photons can be perceived as particles or waves.  "Perceived" implies with our senses.  Should this be changed to detected?  Experimentally observed?  Bubba73 (talk), 05:43, 12 January 2006 (UTC)
replies: text: No, perception reflects how the experimenter interprets what is detected. The photons are not "detected" as either particles or waves, but one may interpret or perceive the detected result to imply a wave-like or particle-like nature.--Srleffler 06:43, 12 January 2006 (UTC)
replies: text: How about "observed" then?  Or how about rephrasing it to say that they can behave as particles or as waves, depending on the experiment/situation?    Bubba73 (talk), 16:03, 12 January 2006 (UTC)
replies: text: The thing is that photons are neither particles nor waves, but those are abstractions that allow us to think about it more easily. In some situations the wave model is simpler, and in others, a particle model is. Fresheneesz 23:28, 7 April 2006 (UTC)
thread_title:  Perceived?  Detected? 

message: isnt there somthing to do with seperatin photons, and then when one gets annilated, so does the other one, no matter how far apart they are, this recently came up while taking to a physicit i know.—The preceding unsigned comment was added by 172.202.236.88 (talk • contribs) .
:Not exactly, but it sounds like you're talking about quantum entanglement. --Jasonuhl 22:37, 19 January 2006 (UTC)
replies: text: Not sure what you're talking about. Quantum entanglement is well established and has been demonstrated in many labs worldwide.--Srleffler 04:15, 14 February 2006 (UTC)
thread_title: Quantum entanglement

message: Most of what's written in this article about "photons" is equally true about light in general and classical electrodynamics specifically.  Radiation pressure is a classical effect.  Calling an antenna or my microwave oven an emitter of photons seems to be an abuse of the language that brings to mind billiard balls.  Similarly, talking about photons in the context of General Relativity, a nonquantum theory, is odd.
Why not merely devote this article to treating the photon as a fundamental particle (gauge boson/force carrier) and as the quantum of light?
Does Willis Lamb read Wikipedia?
09:30, 20 February 2006 (UTC)
thread_title:  Article unnecessarily long and potentially confusing 

message: The article says ...always move at a constant speed with respect to all observers, even when those observers are themselves moving.  With respect to what are these observers moving? Should it say "with respect to each other"? Bubba73 (talk), 17:01, 24 February 2006 (UTC)
replies: text: With respect to whatever you please. That's part of the point: there is no absolute reference for motion. You always have to specify with respect to what you are moving. Light is special, in that no matter what you pick as your reference, and no matter which direction you move in or how fast, the speed of light that you observe is always the same. You can be moving toward the source at 90% of the speed of light, and the light will be coming towards you at the speed of light relative to you. A friend can be moving away from the same source at the same time, and she will percieve the light overtaking her from behind, moving at the speed of light relative to her. This is extremely odd and unexpected behavior, but there is solid evidence that it's true, and relativity theory explains how it all works in a consistent way.--Srleffler 03:58, 25 February 2006 (UTC)
replies: text: Yes, but the old version that you reverted to is still wrong. I'll take a crack at it. Melchoir 04:13, 25 February 2006 (UTC)
replies: text: I like your version.--Srleffler 06:05, 25 February 2006 (UTC)

text: But my point is that if you have an observer and a photon and nothing else in the universe, you can't tell if the observer is moving.  Bubba73 (talk), 04:25, 25 February 2006 (UTC)
replies: text: Yes. I reverted your change, though, because it's irrelevant whether the observers are moving with respect to one another. You can pick any reference you please. Melchoir's new wording is better: instead of referring to the observers as moving, he merely says that the speed of light is constant regardless of their velocity. That covers all cases.--Srleffler 06:05, 25 February 2006 (UTC)
replies: text:  I like the new version better too.  The old version said that they were moving, but not with respect to what.  It could have specified "the light source', "other inertial reference frames", or something - but it idn't specify anything.  It mentioned only a photon and observer.  You and I known what the article intended to say (but didn't say), but many people viewing the article wouldn't know that. (i.e. "You can pick any reference you please." - the article didn't say that, but needed to say something to clarify that.)  Bubba73 (talk), 01:00, 26 February 2006 (UTC)
thread_title:  moving 

message: I don't think this a good example of wave behaviour. Imaging can be described with ray optics and thus is amenable to a particle description.  This only breaks down when the diffraction-limit is reached but that is a secondary effect to the actual image formation.  Why don't we use the standard example of interference (e.g. Young's double slit or diffraction at the edge of a shadow)?--J S Lundeen 22:15, 13 April 2006 (UTC)
thread_title:  Imaging in a camera does not require a wave description of photons 

message: Can anybody confirm/refute this (somewhat paradoxical) interpretation of the photon? Consider a single photon emitted from some source. Is it not true that light is by definition EM radiation that ALWAYS propagates in every direction? (Every direction in a vacuum assuming no matter blocks it.) This means that the "particle" interpretation of a photon is quite misleading as the single photon is ALWAYS as sphere of EM disturbance whose radius increases with time (at the speed of light), which means the photon "exists" everywhere on the sphere at once. This is quite difficult to imagine if thinking of a photon as what most people consider a particle (a very small thing moving about in space with a definate position at any given time). Is this sort of like what is meant when, in explaining the wave/particle duality of matter/light, that the particle is "smeared" out over the wave front?
It is also interesting to consider the photon after a long time, when the radius of the EM sphere is very very large, meaning the photon "particle" exists simultaneously over an ever increasing spatial area. Because of this, I would almost expect that the energy of the photon decrease with time, as it has to "cover" more area. Is it not true though that in any given direction the energy of a photon does not decrease with time (or stated another way the magnitude of the EM disturbance does not decrease?) as the wave continues to propagate forever? It seems almost like getting something for nothing: while the energy at every point on the ever increasing sphere remains the same, the amount of space affected by this energy is ever increasing implying that the total energy of the photon in all of space is ever increasing with time. Perhaps this is just a property of PURE energy (which if I understand correct is what light is) as it relates to space and time that just does not sit well if one tries to give matter-like properties (a particle) to something that is just not matter. Is this a seriously flawed interpretation of quantum theory or an illumination of the paradoxical nature of it all? -Kyp4 19:51, 28 April 2006 (UTC)
replies: text: Yes it is : ) . The photon model says that light does *not* "always propoage in every direction". However, for a point source, the probability that the photon will travel in any given direction is the same - thus for a large number of particles, statistics dictates that the light will form a virtual sphere of photons. Fresheneesz 06:15, 8 May 2006 (UTC)
thread_title:  A single photon 

message: It seems to me that this article is not in very good shape. One of the first things that needs to be done to clean it up is to decide whether this is an article about photons or an article about light. (Obviously, it should be the former.) As an article about photons, we really ought to throw out all the bits dispersion and whatnot that are related to classical optics (except as it pertains specifically to the quantization of light). Also, the parts about the speed of light (in vacuum or not) are pertinent to light rays, but irrelevant to the photon. As a massless particle, the photon must always travel at c. The superposition of photons with some excited states of condensed matter are interesting, but need to be better phrased in the language of quantum mechanics, not of optics, to be appropriate for this article. Anybody agree or disagree? -- Xerxes 18:34, 1 May 2006 (UTC)
replies: text: I completely agree. Melchoir 19:46, 1 May 2006 (UTC)
replies: text:  I agree too. However, I think we should have some explanation as to how the photon model agrees with the wave model. Fresheneesz 06:30, 8 May 2006 (UTC)
thread_title: Cleaning up the photon article

message: The original Wikipedia article was correct. The term "photon" was coined by Gilbert Lewis in a 1926 letter to the editors of the journal Nature. The 1920 lecture by Planck, as posted by nobelprize.org, is a translation from the original German. In German, Planck uses the term "lichtquantum", meaning literally "light quantum". So this usage does not pre-date Lewis's 1926 coining. -- Xerxes 14:32, 18 May 2006 (UTC)
replies: text: Yes. I've actually looked at the 1926 article. I don't have it right now, but I can vouch that it does say something like "I hereby propose the term 'photon'[...]" (paraphrased from memory). Itub 18:31, 18 May 2006 (UTC)
thread_title: Origin of the term photon

message: Good for you, Xerxes. What a needless word. Sounds like the particles that come out of the top of the big black pyramid casino in Las Vegas. Luxons. Yeah. And I may add to critics that while luxon may be a perfectly cromulent word, its use does not embiggen this article. Steve 00:28, 26 June 2006 (UTC)
replies: text: I actually cannot see why luxon is not in this article...it gets its definition by photons and gluons alone. I also like how photons being gauge bosons gets like no play. --HantaVirus 20:33, 9 August 2006 (UTC)
replies: text: In 100,000 physics papers I searched, there are 2 mentions of this word. So it's a word for which there is no pressing need (physicists say "massless" when they need to lump gluons and photons together), and which isn't much used. Let's not use Wikipedia to give it any airtime, or soon it will creap into the language like some horrid particulate neologism the writers of ST:TNG made up, especially for use by Ensign Crusher to save the day with. One of the papers which used it had a scheme for making tachyons too, which lets you know how odiferous the associations are. And let us not forget tardyons, which sound like something from Dr. Who. Or maybe they are the guage particle which explain school lateness, something like Higgs do for inertia. Surely a grand unified theory of this is needed . And bradyons as the field particle of bad 70's TV sitcoms.  But opinions differ. If you think the word is cool, start your own website for it. As for myself, you remind me to tag the luxon wiki article for deletion, unless somebody can come up with a physics literature reference for it. I'm sure one exists (so it will be kept, probably), but having to FIND it may teach luxon-boosters out there a lesson. SBHarris 21:45, 9 August 2006 (UTC)
thread_title: Luxons??

message: X-ray photons are created whenever a charged particle accelerates, a well-known process called synchrotron radiation.  When we even have an article at Wiki devoted to this very subject, how could x-ray photon production by this well-known process get overlooked? I've added a comment in the "creation" section about the production of x-ray photons by synchrotron radiation.  Also, photons are also created in particle collisions, also called particle annihilation.  This isn't mentioned either but I hesitate to add a comment for it because we have a section in this article specifically labeled "annihilation" and I feel it may be confusing to some readers without knowledge of particle physics.  What are your thoughts on how to include photon-production from different kinds of particle annihilation (there are many)? Thanks. Cheers, Astrobayes 22:33, 26 June 2006 (UTC)
replies: text: One final comment on my addition: while I know the article *did* mention the acceleration of charged particles, my desire and intention is to illuminate that this is an x-ray photon production process that is so widely familiar and used that it has a name - and this information is important for anyone who has either not taken a modern physics course or who is not familiar with advanced electromagnetism or particle physics. My addition was not to suggest that the article did not contain a cursory reference to acceleration of charged particles but rather that the link between this general process, and the popular method of producing x-rays was highlighted. Cheers, Astrobayes 22:38, 26 June 2006 (UTC)
replies: text: Go for it. Be bold in edits-- they can only get reverted by others if wildly unpopular. And if good additions, they stay. I recall once being given a tour of the LLNL national synchrotron light source, which is basically this big electron synchrotron in UC Berkley, run to do nothing but produce X-rays, which are tapped off in beamlines for various materials science projects which need them. Whole thing was run by one master 486 computer at the time. :)   These days I'm sure it takes a supercomputer, at least.  But of course you're right that synchrotrons are very important sources of high intensity coherant X-rays. The mechanism is acceleration of charge, but the frequencies obtaineds are due to odd and specific relativistic effects, as you know. So they are worth mentioning for that alone.Steve 23:25, 26 June 2006 (UTC)
thread_title: Photon Creation Section Missing Critical Information

message: Are photons in matter really polaritons? A polariton is the composite particle that results from strong coupling between a dipole carrying particle (usually a quasi-particle) and a photon. The characteristics of the polariton are a combination of the composite particles. So in the case of matter, this other particle would in general be an atom (or molecule). But the dispersion of a photon in a matter is not a combination of the atomic dispersion and the vacuum photon dispersion. Moreover, I've never heard anyone refer to a photon travelling through matter as a polariton (other than very particular situations such as in EIT, or in a cavity).  Could someone provide a reference?  --J S Lundeen 17:48, 22 July 2006 (UTC)
thread_title:  Polaritons 

message: I'm a bit unclear on the uncertainty relations section.  It says: "...quantum mechanics forbids the simultaneous measurement of the position and momentum of a particle in the same direction. Similarly, it forbids simultaneous measurement of the number of photons in an electromagnetic wave and the phase of that wave." I'm familiar with the first part, but how are phase and number of photons conjugate variables?  It also constrains the uncertainty of the product of energy and time.  Is it fair to say that since the photon's momentum and energy are definite and known values (in some situations, at least), that the position and time are completely unknown?  Is there a sensible way to temper this somewhat absurd-sounding statement, or does it have some deep meaning? Dicklyon 01:26, 9 August 2006 (UTC)
replies: text: See Coherent state#Coherent states in quantum optics. "Specifically, coherent light is thought of as light that is emitted by many such sources that are in phase." "Contrary to the coherent state, which is the most wave-like quantum state, the Fock state (e.g. a single photon) is the most particle-like state." "Mathematically, the coherent state |\alpha\rangle is defined to be the eigenstate of the annihilation operator a \!." In other words, measuring the phase assumes a coherent state which requires changing the number of photons so that that number cannot be measured simultaneously. JRSpriggs 05:36, 10 August 2006 (UTC)
replies: text: OK, I see the point now.  But the way it is written, I don't think "the number of photons in an electromagnetic wave" makes much sense as a way to describe those incoherent states.  At the least, come clarification is needed. Dicklyon 06:49, 10 August 2006 (UTC)
replies: text: Making quantum mechanics clear is beyond my abilities. However, let me add that instead of "electromagnetic wave", one could refer to "a vibrational mode of the electromagnetic field". Instead of "photon", one could say "excitation of the mode" or "energy level" (actually \frac{E}{h \nu} - \frac{1}{2}). Instead of "phase", one could speak of "time since the beginning of a cycle divided by the period of the cycle" or "time since the beginning of a cycle times the frequency". So  you see that this is equivalent to the uncertainty relationship between energy and time in the context of quantum field theory. JRSpriggs 04:07, 11 August 2006 (UTC)
thread_title: Uncertainly relations

message: So I'd been thinking about WillowW's challenge, and my eye happened to wander across a Scientific American compilation on "Particles and Fields" in my bookcase, and I wondered idly if I could find it there. Wasn't very hard:
:The photon always travels at the speed of light (denoted by the letter "c"); it can never be at rest. Because of its motion it possesses energy. It therefore also possesses mass, according to the famous relation E=mc2. 
Now, strictly speaking, this is a "popularization"; no one is going to claim that Scientific American is a physics research journal. Still, when I hear "popularization", I think Asimov in F&SF, or maybe even Hofstadter, but not Gell-Mann in SciAm. I think this is good enough evidence for going back to my earlier version of the footnote, the one that spoke of relativistic mass for the photon as an "older notion ... now little used". --Trovatore 04:26, 21 August 2006 (UTC)
thread_title: Reference for application of relativistic mass to photon