
#19
Jan2313, 09:38 PM

P: 492





#20
Jan2313, 09:47 PM

P: 492





#21
Jan2313, 10:13 PM

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Even then  "particle in a box" is not a good model for the H atom.
74% yes. I don't know about "miracle" but it is certainly useful. Helium is sort of doable  it's a common exercise for senior undergrads. This allows for approximations for hydrogenic and heliumoid atoms ... varying success. Anything else does, indeed, require a numerical method. Matlab is common for a first pass  but you end up learning to program in something like c++ since the inner workings of matlab are a secret. But this is for another thread. "RungKutta" tends to imply a shooting method  there are faster methods .. also for another thread. 



#22
Jan2313, 10:53 PM

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#23
Jan2313, 11:26 PM

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If you now change the resonance wavelength by changing the distance of the mirrors, the microcavity becomes a lowreflectivity cavity for the prior resonance wavelength and photons inside will simply escape. Experiments like that have been done with acoustic strain pulses and semiconductor microcavities. 



#24
Jan2413, 09:06 AM

P: 5,634

Simon:
I have simply taken such explanations as I posted at face value...never really questioned them....I just took the view such an explanation is a simple extension of quantum confinement... I just skimmed Albert Messiah QUANTUM MECHANICS Chapter 3 regarding one dimensional quantized systems....[which I had in mind when I posted] to criticize my own post: ....there are no one dimensional systems, ....If the potential well is finite, there is a finite probability of the wave function NOT being reflected, ....If the potential well is infinite there is complete reflection and the energy levels are quantized....and we can't do infinite anything. So what about the PeterDonis explanation I posted...?? As a related suggestion, how about collapsing spacetime to 'rev up a photon'?? [If cosmological distance expansion redshifts radiation, seems like cosmological contraction should blueshift??] //// In another discussion: http://www.physicsforums.com/showthread.php?t=561511 Brian Cox claims changing the energy level of a particle changes the energy level of all its counterparts...So maybe all I have to do to excite all photons is to turn on a light bulb? Issue: Brian Cox on TV claimed…..no two electrons anywhere in the universe can be in precisely the same energy levels…. claimed to be changing the state of all electrons in the universe by warming up a diamond….a consequence of the Pauli exclusion principle proven in 1967. Synopsis [one view] : Without knowledge of Pauli's Exclusion Principle one might expect electrons arbitrarily far away from one another to have identical energy levels. Pauli, however, shows that is simply impossible. Likely too theoretical considering the OP question, but not so easily dismissed as I thought before the discussion. 



#25
Jan2413, 11:01 AM

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#26
Jan2413, 11:19 AM

P: 5,634

I'll have to catch up on it later today. 



#27
Jan2413, 11:51 AM

P: 5,634

Turns out I had in fact read almost all the posts in the BeCox thread.... I stand by my prior post: from the BeCox thread: Anyway, I'm not knowledgeable enough to take a firm position one way or the other; but I am knowledgeable enough to keep an open mind. 



#28
Jan2413, 12:32 PM

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#29
Jan2413, 05:24 PM

P: 18

You can give more energy to a photon, for instance by inelastic scatterings: Raman scattering, inverse Compton scattering. In these processes the photon is not simply absorbed and reemitted.
One also have photonphoton scattering (Delbrück scattering) and I think that in principle the photons can exchange energy. Maybe somebody from highenegy physics can give us a definite answer. 



#30
Jan2413, 08:52 PM

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(recall  time is vertical axis and space is horizontal) Would this be good enough to call "photon excitation" (see post #1) though? If we'd changed the kinetic energy of a free electron by scattering off another electron, would we call that "excitation" of the electron? Raman Scattering: is the inelastic scattering of a photon ... why not include Rayleigh scattering, which is the same thing, only elastic? Either way, the Feynman diagram similarly requires the photon to be destroyed and a new one created... the scattering particle first absorbs (annihilates) the photon, gaining energy, holds onto it for a bit, then releases the energy as another photon. If some of the energy dissipates by another means in the meantime, then less energy is available to be released. Inverse Compton scattering is the same process in a different context  this is where lowenergy photons are scattered to higher energies by relativistic electrons. Again, the electron absorbs the photon, gaining energy, and, after a bit, releases energy as a different photon. In this case it releases more energy that it received because of the context in which it happens. Remember what I said earlier about implied models? When we confine, say, an electron to a potential well, what we are actually doing is bombarding it with photons. But it is hard to talk about the process in such detail so we talk about potentials instead and so we don't have to look at each individual ##e^  \gamma## interaction. But the moment the question involves photons, explicitly, we are in a different modelframework where it is difficult to see how the language of energy level transitions applies. I'm hoping a visiting science adviser can be more clear than me. 



#31
Jan2413, 09:55 PM

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You can approximate something to an infinite square well if you are dealling with the lowenergy configuration of a big potential  then the penetration beyond the classical limits can be safely ignored. This sort of thing is done a lot in solid state physics. Oh the gravitational blue shift  I thought that was addressed by Peter? But you'd still be faced with the problem of having to "excite" the photon to a new energy level without destroying it... you've proposed somehow having the closed spacetime region shrink somehow. How? There's just a photon in it. Anyway, making a whole new universe is cheating :D There are several ways to use gravity to trap photons. Supermassive black holes spring to mind. Spacetime inside one is pretty um hard to think about. Considering GR topology requires field theory I think, rather than the photonQM/Wave mechanics we've been using ... Possibly what you've been thinking of is electromagnetic standing waves in a waveguide? 



#32
Jan2513, 12:05 AM

P: 18

All those processes involve virtual states and, as far I know, the scattering take place instantaneously. The picture that the photon is absorbed, the system holds on for a while and then reemits the photon is wrong. By "exciting a photon" he probably ment giving energy of a photon. 



#33
Jan2513, 10:01 AM

P: 5,634

All interesting comments, Simon, thanks:




#34
Jan2513, 04:17 PM

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The way to excite a photon is to have a 'hot' electron approach (an electron in whose rest frame the photon has extreme energy). Then the excited photon interacts with the hot electron, producing multiple offspring.




#35
Jan2513, 05:55 PM

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I don't know about you but I'd really hate to see how bad baby electrons misbehave.




#36
Jan2513, 06:05 PM

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"Annihilation, Jim. Total, complete, absolute annihilation."(if one is postive, the other is negative). 


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