The Huygens–Fresnel principle has every point on a wavefront become the source of spherical waves, and different points mutually interfere, and they sum to a new wavefront. This seems to conserve the momentum for a beam of photons. What happens to the momentum during diffraction? Same question for electrons in the double slit experiment when interference pattern appears, is the momentum conserved in some way?
Dear I. Chavdarovski
The main law in physics, the law of conservation of energy, can be seen as “the law of conservation of quanta (Planck’s constant)”. The transfer of every quantum has a direction thus all the “directions of the transfer of fixed amounts of energy” are conserved too (conservation of “momentum”).
But is the conservation of momentum helpful to understand diffraction or the double slit experiment? It is obvious that the transfer of a quantum is a local change within the electric field. This local fixed change creates a corresponding vector within the magnetic field and visa versa.
But diffraction – and the double slit experiment – shows that this corresponding mechanism is locally forced “out of sync”. The velocity of a single quantum in vacuum space is the speed of light. But vectors don’t transfer energy so vectors are not bound to the speed of light. Vectors are only limited by opposite vectors. Thus under certain conditions it is obvious that we can observe a divergence of the usual properties of both corresponding fields. Like a local rearranging of the correspondence between the electric and the magnetic field, forced by e.g. 2 beams of photons.
Maybe this point of view is a bit helpful.
With kind regards, Sydney
Well the presence of boundaries implies that momentum conservation is modified-that's what boundaries do and that's what leads to the interference pattern, after all. If there weren't any boundaries, there wouldn't be any interference. And all that's described by the transmission and reflection coefficients and, in more detail, by the interference pattern. The presence of the boundaries actually appears in the boundary conditions, of course.
Dear Chavdarovski: The photon can be described as a packet of grains mass moving all in the same direction with the velocity of the light. The photon has no inert mass but the sum of its grains amounts to an equivalent mass making up the energy. During the emission the emitting electron and the nucleus around which it is orbiting, lose a given momentum p, the same which will be transmitted to the electron and atom going on to absorb the photon afterwards.
Photons will be reemitted, soon or late after absorption. In order that the photon is reemitted leaving the electron in a synchronous motion with other non-absorbent electrons in the atoms nearby, it is necessary that the electron orbital components are the same that before absorption. This process can occur if the additional parallel translational component given by the photon at the absorption can be subtracted at the emission. This implies that the photon leaves the electron with a reflection angle equal to the incidence one. Thus, it gives raise to the reflected beam implying the reflection law by the notion of photon.
The X diffraction is governed by the same reflection law with a restrictive condition because of the deep penetration of X photons. Let us consider an X-rays beam reaching on a crystal, X rays penetrate the crystal. Every crystal plane can reflect the beam; the reflected photons by different planes will be reemitted in the same direction of reflection, if the time interval between the planes is equal to an integer number of periods. See: “Bragg’s law, continuity and discreteness”
The question is mixing models - is light photon particles or wave. light interference present a problem for particle models. Indeed, I know of only 1model of light as photons.
Scalar Theory of Everything (STOE) unites the big, the small, and the four forces (GUT) by extending Newton's model
https://www.researchgate.net/publication/344442808_Scalar_Theory_of_Everything_STOE_unites_the_big_the_small_and_the_four_forces_GUT_by_extending_Newton's_model
https://www.youtube.com/watch?v=0YlJGdTvuTU
There are several experiments that reject wave-like light. 2 are particularly convincing:
the Afshr experiment
and
Interference Experiment with a Transparent Mask Rejects Wave Models of Light
https://www.scirp.org/journal/paperinformation.aspx?paperid=93056
which is described in the above video.
This model answers your question but, perhaps, in an indirect way. The potential momentum change in the question is one of a changed direction not of a changed speed or mass. The model is one of forces, not energy or momentum.
- Badges
- Science topic