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What happens when light hits light? 
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#37
Jan313, 05:39 PM

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PF Gold
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#38
Jan313, 06:54 PM

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PF Gold
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Before we get too far into the realm of lightbylight scattering and pair production, it's worth pointing out that this, as a practical matter, does not happen. If I have two light bulbs a meter apart and I sit and wait anxiously for a single photon to be scattered, on average I will have to wait something like 10^32 years.
If you want neutrinos to come out, add another 20 zeros on top of that. Or perhaps 40, or maybe even 80. Does it really matter? 


#39
Jan313, 07:11 PM

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When two waves collide, they get bigger as they go 'through' each other and then they just get to regular size again and move on. That's the way I learned about waves anyway. I believe they can cause interference with each other however.



#40
Jan413, 12:36 AM

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#41
Jan413, 12:54 AM

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I am not sure, whether it is free or I just have local access. There is also a good review article called "Quantum effects in onephoton and twophoton interference" by Mandel (Rev. Mod. Phys. 71, S274–S282 (1999)), but for this one I am not sure whether there is a free version or not. Back to the original question. It may be similar under some circumstances, but there are differences. First, TPI also can take place for two beams which have a fixed phase relationship with respect to each other although both beams alone are incoherent (like in down conversion or for entangled light)., Second, you also need to take the detection events into account and therefore also the backaction of the detection event on the light field. Quantum effects without classical counterpart can come into play just through the simple fact that every photon can only be detected once. 


#42
Jan413, 04:28 AM

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#43
Jan413, 04:33 AM

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There seem to be two parts to this thread. There is Interference, which gives a pattern of probabilities of a photon being detected by some detector at different points in space and there is Interaction between two photons. These are, surely, two distinct things and they seem to be used interchangeably here.



#44
Jan413, 06:15 AM

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