Visible light energy radiations are just a tiny part of the electromagnetic radiation spectrum. We are able to see this small band of radiations and so it has been the most studied. Whilst this blog is about visible light much of what is said is applicable to the rest of the spectrum.
If you have not red my blog on radiation I there explained that photon energies are energy pulses and that they, like particles, are composed of energy fragments and that they proactively interact by exchanging energies. Photons energies come together in coherence but they are also influenced by particle energies. So let us consider cohered light passing an edge or through a slit. It diffracts but why?
Diffraction is most evident with monochromatic light that is cohered with plain wavefronts. These are shown in blue in the diagram, which also shows and identifies just 6 of the millions of photon energies in the light beam.
What appears to us as a sharp material edge is in reality a photon exchanging particle structure and it bears influence on and attracts the passing photons, highly attracting those closest to it, less so those furthest from it. The structure attractions are why the photons follow a curving path.
The photons want to maintain both their independence and spatial coherence but to achieve that for the whole light beam bundle the photons represented by a would have to slow substantially whilst the bundle represented by f, would need to speed up substantially. They cannot do that and what happens is that photon bundles break up. Bundles a and b do succeed in staying cohered by exchanging energy, They are most influenced by the edge particles and turn the most. Bundles c and d cohere and turn less whilst e and f cohere and turn least. If we observe the output light on a screen it displays a pattern of light and dark bands.
When we observe light that has passed through a glass or water, the observed object is seen to be displaced from where we know it to be. This is due to a similar bending of light called refraction. The cohered photons from each and every tiny point on the viewed object follow their own unique and bent path to our eye retina rods and cones as shown for just one such object point.
Being cohered means the photons want to stay together but, because they approach the glass at an angle, some are nearer to the glass than others and they are attracted to the glass energies and turn toward it. The light photons want to remain cohered and by exchanging energies they succeed in doing that. Our wavefronts now travel through the glass at that changed angle.
Glass has a very rigid particle structure. Its electrons are held quite firmly in place and are limited in their ability to move toward and collect photons. It is why light passes through glass. But that does not mean to say that they do not attract photons. They do so and more so than the more sparse particles of atmospheric gases. Photons that had a slight wiggling motion through the atmosphere have a more pronounced wiggling motion through the glass. It is why photon speed appears slowed in glass.
When the wiggling and cohered photons reach the glass to air structure, they again do so at an angle and those arriving their first are first freed from the higher attractions of the glass particles and so they speed up. But their still slower colleagues want to stay with them and remain cohered. Exchanges of energy occur that result in the light bundle moving off into the air in a changed direction and as cohered photon wavefronts to our eyes. Our eyes see the point location on the object, and all other point locations on the object, as in the direction of the incoming photons and displaced from the real position of the object.
White light we see is actually a combination of spectrum frequencies. Watch a piece of iron being heated. Its surface particles are interacting with environmental energies in excess of their needs, processing them and dispersing them to other particles and back to the atmosphere. At first we see lower energy photons as red and then as higher energy photon are released we see the mixture that is orange before the yellows dominate . We don’t see the hotter blue photons because unlike those emitted when we burn natural gas they are mixed with all of the other photon energies coming to our eyes so we see white.
It may puzzle you as to why white light refracted through a glass block as above does not break up into colours, yet when passed through a prism it does just that as shown in the illustration. My blogs on gravity and on particles explained how attractions and repulsions at the macro and particle levels were about particle desires and repulsions of photon energies. Larger bodies of energy (larger masses) were more attracting of photon energies than smaller bodies of energy.
What we perceive to be white light is the result of a number of photon energies acting on our eye retinas. Light we see as violet has the highest visible photon energy whilst light we see as red has the lowest visible energy. After being refracted at the first prism surface the photon energies that constitute white light have to pass between the more energy attracting base of the prism with its higher energy and mass content.
All photon energies are attracted to the base energies but they cannot all move toward the base as photons of light, like particles, use their distance apart to control their energy exchanges. The more dense violet and blue energies get priority in moving toward the prism base displacing the yellow and red frequencies upward and encouraging their attraction to the prism top. The displacement is not unlike that experienced by less dense atmosphere molecules that in competing with others for earth’s “gravitational attraction” energy find themselves pushed to higher levels.
On being refracted at the second surface the colours become more deviated. The mix of yellow and blue photon mix we see as green whilst the red and yellow junction mixes to orange and the violet blue to indigo.