[baudrunner]

What is light and how does it happen?

The density of particles that exist within space is a determinant in the behaviour of energy waves in transit through it, as in the behaviour of light waves, since it is those particles which comprise the medium through which light is propagated. The only contribution that space makes to light propagation is the dimension of distance. It is the particle density in space, which increases in proportion to the proximity of a massive body due to the increased pull of its gravity, which contributes to the bending of the apparent path of light toward that body, and therefore we say that gravity bends light.

When Einstein wrote that nothing can exceed the speed of light he was, perhaps unwittingly, referring to the rate at which adjacent atoms affect each other, that is to say not how fast light travels in terms of absolute distance over time, but how fast it could propagate in the way we have described. There is a subtle difference. That rate was measured at occurring over a distance of 300,000 kilometres per second of time. This must be qualified by saying that this is the distance over which light propagates at one atmosphere of pressure on the surface of this planet, which is where all the experiments to determine the speed of light were conducted. The French physicist Jean Bernard Léon Foucault discovered in 1850 that light propagates slower in water than in air, contrary to Newton's prediction that light "corpuscles" travel faster in that medium. Since the particulate density of intergalactic space, that is the space in between galaxies, is in the order of about 1 hydrogen atom per cubic centimetre, according to the noted contemporary Italian astronomer Paolo Maffei who presented that number for the sake of discussion, one can reasonably assume that the actual distance encountered there is considerably greater than the 300,000 kilometres for every second at 1G and 1 atmosphere of pressure.

A brief explanation of the behavioural dichotomy of light or, as it is known in classical physics particle-wave duality, is in order. When an atom goes from a higher energy state to a lower energy state a quanta of photonic energy is released. An atom absorbs a quanta of photonic energy when it goes from a lower energy state to a higher energy state by the application of energy from an external source. When atoms are agitated, as when they oscillate within the range of optical frequencies, discrete quanta of photonic energy are also released and reabsorbed. Whereas the tendency of an atom is to maintain a state of equilibrium - think of a foam rubber ball that you squeeze by applying pressure and then releasing that pressure, where the ball at rest is in a state of equilibrium - any attempt to alter that state requires the application of energy which is returned as photonic energy with no loss of mass to the atom provided that the oscillations are maintained within the optical range of frequencies. It is for this reason that quanta of photonic energy are said to have no mass and where there is no mass to be affected by a change in motion, therefore we can see the light from stars many millions of light years away, without any apparent violation of the laws of motion or of the laws of conservation of mass and energy. This in effect means that the production of photonic energy in the visible optical range of frequencies does not affect the overall composition or mass of the atoms in the medium producing it.

This must be qualified by way of example in that long term storage of an object exposed to a constant source of light will result in mild erosion of the surface of the object compared to an identical object which has been stored for an equal length of time in total darkness. But this applies only to the surface atoms of the object, and not to the atoms that make up the overall composition of the object. This is the result of losses due to hysteresis. Similarly, a medium transmits laser light but a surface interrupting a laser beam may erode away very quickly depending on the intensity of the power source of the laser. In addition, the filament of a light bulb will eventually fail to produce light once it has eroded sufficiently so that it breaks and opens the electrical circuit.

In the medium through which light is propagated for the purpose of this discussion the distance between adjacent atoms is inconsequential to their tendency to affect one another, and thence to the actual rate at which they interact. Purists might take issue with this but it must be remembered that gravity wields a very slight influence over the symmetry of the atom and hence the characteristics of their oscillations and this probably has some barely measurable effect over the rate of atomic interaction. However, this is not relevant to our discussion.

When an atom in a medium oscillates it will cause adjacent atoms to oscillate as well because of like polar repulsion, since the outer orbitals of all stable atoms have like charges, and the effect is passed on until the energy producing the initial oscillations is stopped or all of the energy is absorbed by some intervening body. The intensity of the light produced by the oscillations is proportional to the amount of source energy producing the oscillations even though the frequencies produced thereby remain the same. The photonic quanti, or photons, have certain particle properties which can be demonstrated but it can be seen that the behaviour of light propagation is comparable to the wave action of water in that all adjacent components in the medium are affected, and experimentation will produce results in accordance with both particle and wave behaviour. The concept of constructive and destructive wave interference applies to the behaviour of light, as we shall see.

It should be noted here that individual photons do not actually exist as particles in the same sense that some nuclear particles exist, and this is one essential premise of the quantum theory of physics. Those who believe that discrete photons travel across the universe unimpeded the same way that neutrino particles do have trouble explaining how these photons slow down through a denser medium resulting in their refraction regardless of the presence of a source of gravity. After all, by their reckoning photons should then travel in a straight line and since they have no mass therefore should not be affected by gravity but simple observation points to a wave like behaviour. As a matter of fact the photons that allow us to see exist for a very brief instant only and the actual distance they encounter in their lifetime is measured in angstroms before they are reabsorbed.

The inability of a photon to transfer momentum because it does not have mass in no way contradicts the behaviour of a light sail since it is not light hitting the sail that gives it forward momentum but the oscillations of its surface atoms that are transferring momentum to the structure of the sail. This is supported by the fact that a black surface provides more forward momentum than a white or reflective surface. This is best demonstrated by a simple scientific toy consisting of a set of four vanes inside the vacuum of a small transparent plastic ball standing on a pedestal. When exposed to sunlight, the vanes always turn in the same direction, one side is pitch black, the other reflective. The black surfaces of the vanes invariably turn away from the observer. Black surfaces are said to absorb light but the energies that would be converted to photonic energy are instead providing momentum. If the momentum of the light sail were actually caused by light photons striking the surface then an absorbing surface would not provide nearly the momentum that a reflecting surface would but that is not the case. This can best be understood by picturing a target range consisting of two targets of identical mass but different surface properties. The first target would be a thick hard metallic plate and the other a thick plate of soft clay. When two identical guns fire identical rounds of ammunition directly at the two targets it is not hard to picture the metal sheet moving away much faster than the clay sheet. Solar sails do not move forward by way of photons striking their surface to provide momentum.

I will apply this explanation of the nature of light propagation to how we see. Our vision is the result of the oscillations of the atoms in the receiving surface of the retina. From here, the cones and rods reduce their resolution by separating sufficiently recognizable details by converting the characteristic properties of the photonic energies modulated in those oscillations in accordance with the properties of the surfacesof those objects that we see into minute electrical discharges which are received by the optic nerve. Photons do not strike our retinal receptors after bouncing off the objects that we see. It is left to our brain, most specifically the occipital cortex, to directly interpret the information that it receives via the optic nerve. We rarely look at light sources directly because the oscillations of the atoms of the medium in the direct line of sight to the source are too intense and can damage the sensitive receptors of the retina. We are generally looking at what we refer to as reflected light, that is the light produced by the excitation of the surface atoms of an object interrupting the medium by a light source such as the sun or a ceiling light or a combination of the two, and which exhibit the characteristics that we see inherent in the elemental properties of the surface of the object that we are looking at and which return the corresponding frequencies inherent in those modulations corresponding to those characteristics through the same medium.

The explanation for the behaviour of the light that is emitted from a laser beam is only slightly more complex but it works the same way. It is said that laser light is monochromatic since the photons produced by the excitation of the laser source all have the same energy and the waves producing them have the same frequency therefore the resulting wave is said to be coherent. The source of the laser light establishes a powerful resonance of the atomic oscillations in the lasing substance, be it gas or crystal, which is transferred to the medium in the direction of propagation effectively overriding any ambient frequencies produced by waves which are in the way. Laser light does have some dispersion because of the oscillations of the atoms in the medium adjacent to the coherent stream of excitation which display the properties of the ambient light in the medium and which are not affected by the direct impulse of the lased path. This causes a destructive interference of both the lased light and the ambient light along the fringe of the beam. Naturally the amount of dispersion is proportional to the distance from the source of the beam since there is a compounding effect increasing with distance, and the beam does not appear to be perfectly coherent at the edge and more so the farther from the source. Direct incidental collision with the obstructing surface of an object or any non-propagating medium by a laser beam causes the resonance to be transferred to the surface atoms of the object whereby the energies generated can produce a great deal of heat through their continual reinforcement, possibly destroying the obstruction in the laser's path depending on the power of the laser source. Remember that there is a tremendous amount of energy in an atom.

The empirical results of all the experiments ever conducted throughout history to understand the nature of light propagation support the above explanation.