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Where does the energy go when two photons interfere destructively at a point on a screen in Young's double slit experiment ?

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    If energy simply redistributes itself , then what is the explanation of this ? http://physics.stackexchange.com/questions/23930/what-happens-to-the-energy-when-waves-perfectly-cancel-each-other Anna v's answer ? –  May 03 '13 at 10:55
  • You might as well ask "Where does the energy go at the nodes of a vibrating string?". Answer: to places where the interference is not so destructive. – dmckee --- ex-moderator kitten May 03 '13 at 17:42
  • @dmckee What if it is destructive everywhere ? Answer: Energy stays in the very same places , but it changes to other forms . For example suppose I send 2 out of phase waves to a person . The person won't see the waves coming to him but will be getting the energy at the other end of the string. –  May 04 '13 at 05:22
  • " What if it is destructive everywhere ?" In general that's not how it works. You seem to be assuming that the classical description of E&M and the quantum description will give different results in a realm where they are both valid. They won't. They describe the same physics and where their regions of applicability overlap they give the same predictions. – dmckee --- ex-moderator kitten May 04 '13 at 06:07
  • @dmckee When I said destructive everywhere , I was replying in the context of string and not EM waves . Like you said for vibrating string . –  May 04 '13 at 07:10

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Each photon leaves its energy in the molecules of the screen. Destructive interference observed at the line x=1mm for example , means that the probability of finding a photon at x=1 is close to zero. Instead, the photon has very high probabiliy of depositing its energy at the construcive interference fringe.

anna v
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  • Yes , supposedly , the YDSE happens adzactly according to what we predicted using probabilities, then there'll be no heat/energy at the dark fringes ? –  May 03 '13 at 12:45
  • Also , I'd very grateful if you could once have a look here and tell me if I am correct here or not ? Kindly read the transcript once . Sorry for wasting your time , but kindly read and tell me if there's something that I am understanding .http://chat.stackexchange.com/transcript/71/2013/5/1 –  May 03 '13 at 12:49
  • Yes, in a double slit expriment the dark fringe means no energy deposited there. Luboš Motl in his blog has a good formulation of how the individual photon fields build up the classical electromagnetic field http://motls.blogspot.com/2011/11/how-classical-fields-particles-emerge.html . Sound is different. The energy of sound is propagated on the medium. EM needs no medium. – anna v May 03 '13 at 13:14
  • But I think you wrote in that post in my question's comment ," when alignment was right , heat was observed at a region of dark fringe ?" –  May 03 '13 at 13:26
  • That was a possible hypothesis for total destructive interference, no bright fringes. a very special experimental setup, http://www.wired.com/wiredscience/2011/02/real-live-antilaser/ . I was exploring alternatives, and my answer was not popular."Or the truth is in between that the energy propagates and we can only see interference if the beams impinge on a medium, which will take care of energy conservation" – anna v May 03 '13 at 16:55
  • Still , you're somehow answering in both sides , please choose one (?) –  May 04 '13 at 05:20
  • There I am giving alternatives, that is why i did not get votes, I was thinking online :). I am sure of the answer i gave above.In the case of two collinear totally out of phase beams in vacuum I think that if there is no medium to observe them they go on their path merrily along. if they impinge on matter the energy conservation will be taken up by the medium, as the experiment with lasers shows. – anna v May 04 '13 at 06:13