Interference
Constructive and Destructive Interference
This animation shows the energy flows that supply energy to the green photon. If this energy flow is interfered with, the photon becomes darker. (Destructive Interference). If the fields of a photon are in phase, then the energy flows to the two photons is combined and the light emission in that location increases. (Constructive Interference).
In this animation, the north magnetic fields are shown in red and the south magnetic fields are shown in blue. The upper row of photon fields is provided for reference. The lower row is two separate groups of photon fields as they move. This illustrates the destructive interference when the red fields overlap the blue fields. At the top are the waveforms of the two rows of photons fields. When the waveforms are in phase we see constructive interference and the light level increases. When the waveforms are 180 degrees out of phase we have destructive interference and the light goes dark. Light plus light equals dark in that situation. This darkening is due to the energy flows in the north magnetic field and the south magnetic fields canceling each other so that the energy supplied to the photon itself ceases.
This animation shows photon fields coming from two slits in a double-slit experiment. The distance between the slits is varied and as this occurs we see the changes in the interference pattern. Just as in the previous animation, when the photons’ fields are in phase with other photons’ fields, the light in that area becomes brighter. (Constructive Interference). When the photons’ fields are 180 degrees out of phase with other photons’ fields, the photons go dark. (Destructive Interference). When the photons’ fields are 180 degrees out of phase with the other photons’ fields, it causes the energy flows within those fields to “Interfere” with each other. In other words, the north energy flows and the south energy flows cancel each other out so that there is no energy flow in those photons, and the photons go dark.
Now you know why there are dark areas and bright areas in the interference patterns above. It is all about the energy flows within the fields around each photon.