Timeline for How does a wave become a color?
Current License: CC BY-SA 4.0
16 events
| when toggle format | what | by | license | comment | |
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| Jun 26, 2019 at 21:41 | vote | accept | Adam | ||
| May 2, 2019 at 16:36 | comment | added | anna v | @PhysicsDave see the single photon plot I edited in my answer | |
| May 2, 2019 at 16:13 | history | edited | anna v | CC BY-SA 4.0 |
addition after discussion in comments
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| May 2, 2019 at 15:59 | comment | added | PhysicsDave | @ElioFabri I found this very interesting article on quantum beats, around late 1970s. bayes.wustl.edu/etj/articles/quantum.beats.pdf | |
| May 2, 2019 at 15:51 | comment | added | PhysicsDave | @AnnaV Yes the wave packet model better explains the genesis of photon ... but can we still perceive this multifrequency photon as a single quanta. As a single quanta with a very well defined packet energy it can only be absorbed (or observed) in its entirety? | |
| May 2, 2019 at 15:37 | comment | added | PhysicsDave | @ElioFabri In the femto second laser pulse, I can understand the superposition of say 1000 photons in a small space of the EM field, can we consider this 1 photon? Or the 1000 photons in the pulse were created by roughly 1000 excited atoms and when the photons are observed they can only be absorbed one at a time ... i.e everything is still a quanta? Do the quanta have non-definite energy or is it the packet as a whole (or both)? By non-definite do you mean plus or minus 0.1%, i.e. small variation or combinations of quanta that produce higher energy photons? | |
| May 2, 2019 at 15:31 | comment | added | anna v | @ElioFabri only in wave packet models , where the frequencies are adjacent within the HUP, . When measured one frquency appears,, things that cannot be measured are mathematical constructs and are called virtual.. I am an experimentalist, , a doubting thomas " Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe" | |
| May 2, 2019 at 12:50 | comment | added | Elio Fabri | @AnnaV When caught in a spectrum, yes. Surely the've passed a grating or some other energy measuring instrument. (BTW. A grating has for non-monocromatic photons just the same effect than non-uniform field has for spin in Stern-Gerlach experiment - it entangles energy with position.) But our discussion is about photons in general, not in that special situation. The issue is: do photons with non definite energy exist? I've asserted they do. As far as I could understand, you give the opposite answer. | |
| May 1, 2019 at 8:40 | comment | added | anna v | @ElioFabri if they do not have a definite energy when caught in a spectrum, as above they are virtual and not measurable. | |
| May 1, 2019 at 8:25 | comment | added | Elio Fabri | @AnnaV 1. The spctrum may well be made by monochromatic photons but the OP in his post clearly shows he believes it's a general property of photons and this is false. 2. Quite obvious that in QED is a general practice to develop field operators in energy (and momentum) eigenstates. But this doesn't imply that photons of non-definite energy can't exist - in fact that's the rule. | |
| May 1, 2019 at 8:22 | comment | added | Elio Fabri | @PhysicsDave Look for "quantum beats" in wiki. For a different instance, think of femtosecond laser pulses, today commonplace in optics labs. A pulse 6 fs long for visible light means photons of average energy of few eV in a superposition of energy eigenstates wide about 1 eV. | |
| May 1, 2019 at 4:26 | comment | added | anna v | @PhysicsDave In general, elementary particle wave functions used in quantum field theory are plane waves, and these are not a good model for detected footprints of photons, as here sps.ch/en/articles/progresses/… . This is solved by the wavepacket as a model of a detected particle hyperphysics.phy-astr.gsu.edu/hbase/Waves/wpack.html when treated in qft | |
| May 1, 2019 at 1:05 | comment | added | PhysicsDave | @ElioFabri can you give an example of a photon in superposition? These visible photons are quantized are created by atomic transitions, are you thinking of radio waves and microwaves produced by antennas? | |
| Apr 30, 2019 at 19:03 | comment | added | anna v | @ElioFabri for the spectrum shown in the question there is monochromaticity ( withn the heisenberg uncertaint)y. In QED the operator creating a photon has a specific energy. (in the link discussing how classical fields emerger from quantum) | |
| Apr 30, 2019 at 18:57 | comment | added | Elio Fabri | The particle/photon has a fixed energy. Not true. A photon like any other quantum system, may well be in a superposition of eigenstates of energy. Even very far from a "monochromatic" photon. The widespread formula $E=h\nu$ is (approximately) true only in very special situations, e.g. in emission by transition of two discrete energy levels of an atom. | |
| Apr 30, 2019 at 12:56 | history | answered | anna v | CC BY-SA 4.0 |