…specifically, as it relates to the conservation of energy. When two laser beams destructively interfere, leaving only darkness… where does the energy go?
In: 3
In destructive interference, the energy isn’t lost but redistributed. The dark areas occur where waves cancel out, but there are also bright areas where they add together, resulting in an overall conservation of energy.
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The energy is literally going into each wave and scattering them.
Imagine a child on a swing with a parent behind them pushing them. As long as the parent pushes while the child is starting to move forward, they are performing constructive interference and the child will go higher and higher. But if they push while the child is coming towards them that creates destructive interference that slows the swinging. And when that happens the extra energy is channeled into the body of the child and the arms of the parent. This could even potentially injure one or both of them if enough force is involved.
Different photon will not be able to interact with each other due to superposition (not quite correct because of non-linear phenomenon but close enough), and in particular there are no interferences. (if there are interactions due to non-linear phenomenon, they could create particles with mass)
When you see an interference pattern, each photon is interfering with *itself*. In fact, the same photon going through different slits give a wavefunction for each slit and these wavefunctions are always orthogonal.
If there’s destructive interference, somewhere else there is constructive interference. The energy just shifts around.
For a given source you can actually make destructive interference everywhere. This is where the fun begins: if you achieve this the source won’t emit energy.
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