Light as waves
According to all physics books, light is an electromagnetic wave described by the four Maxwell equations. These equations were formulated in 1865 by James Clerk Maxwell. The solutions to these equations describe electromagnetic (EM) waves – oscillating electric and magnetic fields – which, without the need for a medium, advance at 300,000 km / sec, which is the speed of light. The confirmation of light as a wave phenomenon was already done by Thomas Young. Maxwell’s laws are the result of classical physics and are commonly considered fundamental. EM waves will – if unhindered – expand spherically in three dimensions where the energy received on a surface of a fixed size decreases with the square of the distance to the source.
Maxwell based his equations on the results of research into electrical and magnetic phenomena by, among others, Michael Faraday. The existence of electric and magnetic fields, states of empty space resulting from electrical and/or magnetic charges present therein was assumed. How that state of empty space came about was and still remains unknown. However, in quantum physics nowadays EM-fields are considered to be the result of elementary particles, photons, interacting with other matter.
Light as photons
However, in 1900 Max Planck saw that the EM radiation emitted by so-called black emitters should be quantized, that is EM radiation was emitted and absorbed in packets with an energy that was directly proportional to their frequency. Planck thus laid the foundation for quantum physics and at the same time a bomb under Maxwell’s chair. Planck’s hypothesis was confirmed countless times in the course of the following century. EM energy is emitted and absorbed in the form of quanta, later called photons. This was in direct contradiction with the Maxwell wave image. The energy of a photon does not decrease with the distance to the source. A light source of 1 Watt that emits all that energy as light of 500 THz (orange-yellow) emits 3.1021 photons per second. Because of these unimaginable huge numbers, the behavior of light on our normal scale of observation will be so close to that spherical expansion of energy that it can no longer be distinguished from the Maxwell EM wave. However, at the atomic level, light therefore exhibits a totally different image: energy packages, photons.
Wave-particle paradox?
According to the one view, light is therefore a wave, a fact that already seemed to be confirmed by Young’s double-slit experiment. According to the other view, light consists of particles, quanta or photons. Those two ideas cannot be combined. For instance, the energy of a photon only depends on its frequency and therefore does not decrease with the distance to its source like a wave does. We thereby experience a paradox. Now be aware that a paradox is the result of a hidden, false premise, unless we assume that nature is fundamentally paradoxical. But we don’t give up that easily. Can we find that hidden, false premise?
A metaphysical state wave
In the Copenhagen interpretation of Bohr and Heisenberg, the quantum state wave that follows from the Schrödinger equation is a probability wave that is not physical. Only upon measurement does the quantum object physically manifest itself. The quantum state wave is therefore metaphysical, something that is not physical but does affect the physical. That interpretation has been confirmed by all Bell Tests and various delayed choice experiments. What a measurement exactly is, is extremely important but nevertheless poorly defined and even controversial. But that’s not the point now.
Bosons and EM-fields
The photon is considered nowadays as an elementary particle, one of the bosons, an element of the Standard Model. Bosons are particles that represent the field forces. They make up one of the two classes of particles, the other being fermions. The mutual repulsion of two electrons is depicted in a Feynman diagram by the exchange of a photon. In the image below of that process, the location in space is displayed horizontally and the time is displayed vertically increasing from bottom to top.
An electron comes from the left and a second electron comes from the right. When they approach each other, up to a certain distance, they exchange a photon, which causes them to reverse direction and by that exchange, their momentum and speed. This idea of exchanging particles replaces the field idea by mutual interactions between particles, here two fermions (electrons) and a boson (photon). In that way we have rid physics of that misunderstood and uncomfortable field as a mysterious state of empty space. Field forces can now be explained as just particles that collide with each other exchanging their impulses, something that we understand very well. By that view the billiard ball model is back in physics and everything seems explained by direct particle interactions.
Now think about how those electrons sense each others nearness so they can decide to exchange a photon. Physicists now suppose that traveling electrons continuously eject and absorb virtual photons by which their explanation has become virtually virtual.
The photon is not physical, ever
As stated in the Copenhagen interpretation of quantum physics and later confirmed by experiments, a quantum object, which a photon is, is not physical until it is detected in the measuring instrument. Not physical means here that a physical description has no meaning and that observation is not possible. There is only a non-physical, therefore metaphysical, quantum state wave, a probability wave, that, according to current interpretations, extends from the source to the measuring instrument. Upon detection of the photon, however, the energy of the photon is instantaneously converted into an excited electron and the photon is annihilated. Did it appear physically at the same moment of its annihilation? At the source, precisely the opposite happened, an excited electron that released its energy in the form of a photon that only exists in the form of a state wave which means that it does not physically exist.
The question then arises: at what moment does the photon actually exist physically? Well, never.
The speed of light
It must have become clear that the Maxwell Equations are descriptions of large-scale behavior of billions times billions of photons but that they cease to be valid at the atomic level. Just like fluid mechanics, even though it is still valid at the macro level, it ceases to be valid at the level of the water molecules. And also just like the ideal gas law, which is the result of huge numbers of gas molecules, will loose its sense and validity at the level of the gas molecules. Viewed in this way, the paradox of light wave and photon is no longer a real paradox. Maxwell’s laws are no longer valid at the photon level.
But then the wave behavior of individual photons should be not interpreted as EM-behavior, but as the behavior of a metaphysical quantum wave. It also becomes important to realize that the fact that the speed of light is always and everywhere the same is not a result of electric and magnetic fields and their properties, but that it must be a result of metaphysical quantum wave behavior. With that, the speed of light loses the physical foundation it had in the results of the Maxwell equations which in turn provided Einstein with a foundation in setting up his special theory of relativity.
The metaphysical properties of light
Thus the experience of light is nothing more than the experience of an energy transfer from one electron to another. Regardless of their distance. As Planck stated. As Bohr had already realized with his atomic model in which he stated that the jump from the electron from one orbit to the other had to be instantaneous. This discrete package of energy, the so-called photon, is not physically on its way from source to destination. There exists only a metaphysical quantum state wave that can best be interpreted as a probability distribution in time and space. And what are probabilities? They are expectations, thoughts about the physical world. Metaphysics. No more. No less.
Maxwell’s laws are thus no longer fundamental in this view, but merely a model that only makes reasonably correct predictions on a scale that is many orders of magnitude higher than the atomic domain. With that insight, the particle-wave paradox of light has disappeared.
So, how do we explain single photon interference?
You may now ask how it is possible when light consists of particles, that is, photons, and the EM wave at atomic level is no longer a good description of the behavior of light, how it is possible that interference occurs with single photons when we send them photon by photon through a double slit. The answer is now actually relatively simple. The interference should not be seen as an effect of overlapping physical EM waves but of overlapping metaphysical state waves. If metaphysical waves do exist, they will also show interference, as this is inherent in wave behavior.
The challenge lies in accepting the idea that reality is not limited to the strictly material physical.
The next subject in the guided tour is: Relativity, Quantum Gravity and Black Holes.