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----------I understand that we consider light as a transverse wave in the sense that light is composed of E&M fields oscillating perpendicular to each other and the direction of propagation. And I understand how we get from here to the idea of photons as 'wave packets.' The problem I have is in regards to how we often visualize light diffraction. For example, I've only ever seen the double slit experiment explained with a drawing of longitudinal waves (like sound waves). This explains the double slit experiment well, but to me, seams to be inconsistent with our understanding of light as a transverse wave, and also confuses me in terms of ray/geometric optics. Is this contradictory? Can someone offer me a more comprehensive/visual explanation of the complete nature of light?

EDIT: thank you for the clarification in the comments. I think I understand better and this image below helps me bridge the gap in terms of my visualization issues.

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    $\begingroup$ "For example, I've only ever seen the double slit experiment explained with a drawing of longitudinal waves (like sound waves)." Would you elaborate on this. I suspect that you are mis-interpreting a drawing as meaning something other than what is intended. In particular a sketch of the surfaces of constant phase may look similar to diagrams of density distributions in sound waves, but that's just because they are both about waves and has nothing to do with transverse or longitudinal nature. $\endgroup$ – dmckee --- ex-moderator kitten Feb 20 '19 at 1:34
  • $\begingroup$ I think I have a better understanding now. I added two images to sort of give a better understanding of my confusion, and a third that helps me bring these two images together in a more satisfying manner. Thank you for the help. $\endgroup$ – physicsTom Feb 20 '19 at 22:10
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Sound waves are scalar waves. Light is a vector wave, but it can also be desrcibed as a scalar wave in some cases, for example when you have translational invariance along one of your dimensions: Transverse Electric (TE) and Transverse Magnetic (TM) diffraction. So it is possible to use scalar wave arguments to explain diffraction of full vectorial EM-waves under certain conditions.

Regarding the geometric optics. Wave propagation in situations where all relevant dimensions are much larger than wavelength can be described through Eikonal approximation (https://en.wikipedia.org/wiki/Eikonal_approximation https://en.wikipedia.org/wiki/Eikonal_equation). This provides a justified way of going from wave optics to ray optics.

"Complete nature" of light, or anything else, is not what science is generally about. But if you want to have a good understanding of what light does in most cases, then I suggest concenrating on Maxwells Equations and their solutions.

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The diagrams of diffraction you have shared don't show light as a longitudinal wave, they are a completely different representation of waves. The lines represent wave fronts NOT compression & rarefaction. Wave fronts can be thought of as corresponding to wave crests, but really mean points on waves that are in phase with one another.

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