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Natural Science Forum / Physics / Research / August 2008Is there any proof that electrons can absorb photons?
Is there any proof that electrons can absorb photons or emit photons? Can someone prove to me its the electrons and not the bonds or holes that absorb, emit or hold the photon? Has anyone ever seen with an instrument an electron absorb or emit a photon? Do electron beams ever absorb photons or emit photons if you cross them with laser beams? > Is there any proof that electrons can absorb photons or emit photons? > [quoted text clipped - 6 lines] > Do electron beams ever absorb photons or emit photons if you cross > them with laser beams? <http://www.phys.ualberta.ca/~gingrich/phys512/latex2html/node102.html>  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > Is there any proof that electrons can absorb photons or emit photons? > [quoted text clipped - 6 lines] > Do electron beams ever absorb photons or emit photons if you cross > them with laser beams? Synchrotron and cyclotron radiation, bremsstrahlung processes, etc. would seem to provide experimentally observed instances of emission and absorption of radiation from electrons (not bound to an atom). charlie torre On Aug 21, 12:55=A0am, johndev...@iprimus.com.au wrote: > Is there any proof that electrons can absorb photons or emit photons? > [quoted text clipped - 6 lines] > Do electron beams ever absorb photons or emit photons if you cross > them with laser beams? What exactly do you mean by saying that "an electron absorbs a photon"? Experiments for measuring absorption/emission lines of atoms, show that electrons absorb/emit energy in quantized amounts. And photon is nothing more than a packet of quantized electromagnetic energy. So, in that sense all experiments on measuring absorption or emission lines of atoms prove that an electron absorbs/emits photons. And there is also something called single photon detector. With this one can measure single photon events. Kushal. > What exactly do you mean by saying that "an electron absorbs a > photon"? I'm not sure, goes into or wraps around an electron maybe? How does a photon even find an electron in a probability cloud? How do the sizes of a photon and an electron compare to each other? >> What exactly do you mean by saying that "an electron absorbs a >> photon"? > > I'm not sure, goes into or wraps around an electron maybe? Well, you're completely mixing metaphors there. Electrons clearly do emit photons -- that's quite well established from atomic transitions to synchrotron light sources. In a sensible theory the equations are time-reversible, so an electron must be able to absorb a photon as well -- certainly in QED they do so. Hmmm. It could be argued that in every case there is a SYSTEM that emits the photons (an atom, a synchrotron, etc.), so perhaps it is not established after all. It's not easy to support that argument -- basically one would need to construct a theory that does this and still satisfies the experimental record. Good luck.... Experimentally it is observed that sufficiently-dense plasmas are opaque, and the electrons are in general far more likely to be involved in absorbing the photons than any ions. I'll bet there is a reference to electrons in an atomic trap (e.g. a Penning trap) absorbing radiation. You can use Google and scholar.google.com and SPIRES as well as I (this is far from my experience). > How does a photon even find an electron in a probability cloud? There's no need to "find" it, interactions simply happen (with various probabilities, of course, which depend on the overlap of their wavefunctions). As a rule of thumb: anything that is not prohibited is mandatory. > How do the sizes of a photon and an electron compare to each other? The question does not make sense, as neither has a definite "size". The regions over which their wavefunctions are nonzero depend more on the sources of photons and electrons than on the particles themselves. Tom Roberts >>> What exactly do you mean by saying that "an electron absorbs a >>> photon"? [quoted text clipped - 10 lines] > absorb > a photon as well -- certainly in QED they do so. Electrons do not technically emit or absorb photons. The energy-momentum from/to photon is absorbed or emitted and photons are either destroyed or created in the interaction. Best, Fred Diether Co-moderator sci.physics.foundations >> Electrons clearly do emit photons [...] > > Electrons do not technically emit or absorb photons. The > energy-momentum from/to photon is absorbed or emitted and photons are > either destroyed or created in the interaction. Quibble all you like about words. In QED, when a 3-point vertex has two electron legs and a photon leg, and the time ordering is such that the photon and one electron leg are incoming and the other is outgoing, we say "the electron absorbed the photon" [#]. Similarly, in an experiment, when photons impinge on an electron plasma and do not emerge, we say "the electrons absorbed the photons". And when a synchrotron has an orbiting electron beam, radiation emerges from the bending magnets and we say "the electrons emitted the photons". Quibble all you like about words, but this is how they are actually used. "Absorbed" and "emitted" are merely two more names for the "interaction". [#] Of course this statement is not frame independent. Tom Roberts >>> Electrons clearly do emit photons [...] >> [quoted text clipped - 21 lines] > used. "Absorbed" and "emitted" are merely two more names for the > "interaction". Yes, that is true but as you can see this sloppy use of language that is prevalent caused some confusion with the OP in his statement "I'm not sure, goes into or wraps around an electron maybe?". Photons are clearly created or destroyed at the interaction vertex. I just wanted to make that point clear to the OP and others. I know that you know that. Best, Fred Diether Co-moderator sci.physics.foundations On Aug 25, 1:07 am, johndev...@iprimus.com.au wrote: > > What exactly do you mean by saying that "an electron absorbs a > > photon"? [quoted text clipped - 4 lines] > > How do the sizes of a photon and an electron compare to each other? It will not be correct to think of the photon as having a definite size and shape. It is just a packet of energy and not really a particle in the sense of an electron. When we say that "an electron absorbs a photon", all that we mean is that the electron has gained some quanta of energy which was in the form of electromagnetic radiation. So, its all about the absorption or emission of energy. Nothing more. Kushal. On Aug 24, 10:07=A0pm, johndev...@iprimus.com.au wrote: > I'm not sure, goes into or wraps around an electron maybe? > > How does a photon even find an electron in a probability cloud? > > How do the sizes of a photon and an electron compare to each other? In QED the (virtual) photons are emitted from a so called "transition current". This is an interference pattern between the initial and final state of an electron. An electron cloud represents a continuous charge- and spin-density distribution. An interference pattern represents an alternating charge and spin density. This alternating pattern is the source of the (virtual) photon. You can obtain the interference current by working out the Dirac algebra. The photon is then obtained with the Lienard Wiechert potentials. For instance, It's the alternating spin density pattern which is responsible for the transverse components of the photon. Regards, Hans de Vries ----------------------------------------------------- http://www.physics-quest.org science advisor since 2005 at http://www.physicsforums.com [ Mod. note: In the future, please quote the context you are replying to. Otherwise, it is not obvious what you are referring to. -ik ] I agree with the above. But I do not think these are the type of answers were what he was aiming for. I think his question goes more along the lines of Feynman's dialogue with his father, when the latter asked him if an electron emitted a photon, had the photon been somewhere inside the electron before emition. > Is there any proof that electrons can absorb photons or emit photons? > [quoted text clipped - 6 lines] > Do electron beams ever absorb photons or emit photons if you cross > them with laser beams? Apparently one can accelarate an electron using an EM field. As the field is quantised accelaration of the electron obviously follows via absorbtion of photons. ilper wrote: >johndev wrote: >> Is there any proof that electrons can absorb photons or emit photons? [quoted text clipped - 11 lines] >field is quantised accelaration of the electron obviously follows via >absorbtion of photons. Aren't you effectively talking about low-energy Compton scattering? If you put some numbers in you might be able to figure out how easily it can be observed. as I see it the electron is a boat and the photon is the wake it creates as it passes through the medium. holog > Is there any proof that electrons can absorb photons or emit photons? > [quoted text clipped - 6 lines] > Do electron beams ever absorb photons or emit photons if you cross > them with laser beams? > as I see it the electron is a boat and the photon is the wake it creates > as it passes through the medium. Medium? Are you now proposing that Maxwell's aether has reality, afterall? |
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