Using two mutually inconsistent models for light is unsatisfactory. A century ago the great scientists of the day could not reconcile the two models of light and decided to park the issue in the form of wave-particle duality. It was a temporary expediency but it is now taught as an unfathomable truth. It isn’t. It is time to for clever fresh thinking to develop a comprehensive, internally consistent model for light.

This essay argues that self-consistent model for light should be possible. Abandon misleading analogies and focus on the evidence with an open mind. Logically follow the evidence until a new model starts to take shape. By way of example the essay makes a start on prototype it calls ‘phots’. Following essays start testing the emerging phot model against the major categories of optical experiments.

Introduction

We observe the Universe almost entirely through electro-magnetic radiation (‘light’). Our standard model for the Universe is struggling to explain some key recent experimental/observational discoveries. So maybe it is a good time to check what we think we know about light.

When the platypus was first discovered it was described as being part beaver and part duck. This description was pragmatic at the time but has limited value for the proper appreciation of a platypus. A platypus is not a bird or a rodent. It is what it is – an egg laying mammal now classified as a monotreme.

Similarly light has been described as a wave and also as a particle. This is inherently self-contradictory. It is confused and confusing. It was an expedient compromise over a hundred years ago, but that is no reason to keep on putting up with it.

Light (i.e. electromagnetic radiation generally) is the main way we perceive the Universe and everything in it. It is essential that we understand it better.

Some questions

If you think that you understand light perfectly well, answer the following simple sample questions:

Once light has escaped the gravity well of a distant quasar and travels billions of miles through space, does it get any redder?
Why is some starlight coherent?
Did light travel more slowly in the early Universe?
Can a photon interfere with itself in a two slit experiment?
In a medium other than a vacuum, why do the higher energy photons/waves travel more slowly than the lower energy photons/waves?
In a spectrum, why are more energetic red photons refracted less than blue ones?
Why does low energy light pass through matter more easily than high energy light?
Do photons bounce off a mirror or are they absorbed and reformed?
If a photon is a massless particle, why does it have momentum?
If a photon is absorbed into the electron shell of an atom, where does its momentum go?
When photons reach an interface with a less dense medium they sometimes reflect back into the denser medium? Why?
In the three polarizers experiment, why does introducing the third filter between the other two filters increase the overall throughput?
In experiments using entangled photons, what conditions are required for the photons to stay entangled?

Introducing Phots

This essay is going to make a start on assembling the evidence about light into a logical framework. It will also illustrate the recommended approach by allowing the evidence to start to suggest a new prototype for light. It may not be right, but at least is illustrates an approach that might eventually work.

One thing we need to do is escape the baggage of the past. We need to escape old fashioned thinking and misleading ideas caused by misleading analogies. As soon as we use words like wave and particle we automatically inherit a whole set of concepts which bias our thinking and swamp the mental space required to allow new ideas to develop. Accordingly this example of a bottom up attempt to describe light is going to give it a new name … phots. Light consists of phots.

The description of phots starts with a blank sheet of paper. The description will be built up using hard evidence from real experiments. In due course a picture will emerge and that will evolve into the new model.

Basic Properties of Phots

A phot can only be detected once. You can infer its path if you know where it came from, or from the location of things that did not absorb it, but you cannot watch a phot in action. You can only detect its demise. To detect it is to destroy it. What you can observe is an effect of the phot’s destruction. You can only measure one of these effects at a time.
Because of the above we can never be sure exactly where a phot is until we detect it. This is not some profound mystery about reality only becoming reality when it is observed. The phots have a perfectly well defined place in the scheme of things. They are not lost, undefined or spread out over multiple universes. But while they might know exactly where they are – we don’t and we can’t. We can only determine where the phot was when it turned into something else.
Phots can die in many ways. They can cause an electron to move into a higher energy state. Or they interact with sub atomic particles. Or even another phot. Or they cause the phenomenon called reflection. One phot dies, another is born.
A phot carries energy away from its source and imparts it to whatever it interacts with. The amount of energy is small, but occurs over an incredibly wide range, from gamma rays through to radio waves.
The detection/destruction of a phot can create electro-magnetic disturbances with a sinusoidal pattern. Such patterns have a frequency. Experiments show that the energy carried by a phot is directly proportional such frequency effects. The constant of proportionality is called Planck’s constant .
Planck’s constant, symbolized as h, relates the energy of a phot to the frequency of the effects observable in its destruction. In the International System of Units (SI), the constant value is 6.62607015×10⁻³⁴ Joule-seconds.
As with the speed of light and various other constants, we measure h in our infinitesimal corner of the Universe, in an infinitesimal period of time, using units of space and time we have only recently begun to understand, and we proclaim them to be Universal Constants which are the same throughout the Universe and have been throughout the entire history of the Universe. Perhaps we should keep a more open mind.
Phots travel very fast – as fast as anything can travel.
Experiments designed to measure the speed of light in a vacuum are best conducted using an inertial reference frame. In such frames the measured result for the speed of light is always the same. It makes no difference if the source is moving towards the detector or away from the detector. It makes no difference if the detector is moving towards the source or away from the source.
In practice there are no reference frames which are perfectly inertial. Nearly everything in the Universe is spinning or orbiting or both, and nearly everything in the Universe is experiencing gravity from multiple sources.
We think that the speed of phots is constant (in vacuum) throughout the Universe and throughout the history of the Universe.
We now know that gravity slows down time. Which is awkward when we discuss the speed of light because speed is distance (properly measured) divided by intervals of time (properly measured). And our standard unit of distance is defined by how far light goes in an interval defined by an agreed number of vibrations within certain crystals. It is all a bit circular.
If you emit a phot from a source that is moving towards the detector, all that happens is that the detected phot will have a higher energy level upon detection. Likewise if the detector is moving towards the source.
If you emit a phot from a source that is moving away from the detector, all that happens is that the detected phot will have a lower energy level upon detection. Likewise if the detector is moving away from the source.
You can’t make a phot go faster by bouncing it off a fast moving reflector.
If we measure the speed of phots in a particular direction we need to measure the distance carefully and we need to have well coordinated clocks at the start and finish. This is called a one way measurement. Or we can reflect the phots back to where they started. Then we can use just one clock. This is called a two way measurement.
Experiments to measure the speed of phots are tricky. Most of the early experiments were designed on the basis that phots were waves. They relied heavily on interference effects. Most of the later experiments were designed on the basis that the phots are particles. These experiments often use detectors based on the photo-electric effect. Two-way experiments are easier than one-way experiments, but are also less clear cut.
Phots are not waves and they are not particles and they are not a wave and a particle simultaneously or alternatively. However, they can exhibit wavelike properties or particle-like properties when they are detected. This says as much about the detectors as it does about the phots.
You can draw sinusoidal wave along the path of light if you like, but it is quite misleading. You can’t watch a phot in flight. The drawing is supposed to show the intensity of an electric field as the light moves forward. Chopping the drawing up suggests the vector blinks into and out of existence. Trying to show the quantum nature of light by chopping a wave drawing into short segments just makes a bad analogy even worse.
You cannot dissect a phot. Observing it destroys it. If you are careful you can deduce which direction it has come from, and the centre of such a path. Or what its energy level is. Or you can determine its polarization. Or get a good estimate for when it arrived. Or what direction its spin is. But you cannot discover more than one of these properties for the same phot. See Heisenberg Uncertainty Principle.
Phots do not spread out like a water wave or sound wave. They do not dilute with distance. They travel in a definite direction. They travel in straight lines. In fact their paths can be thought of as defining a straight line. And they can be thought of as having a centre.
The path of phots bends (refracts) when they pass close to the edge of a material object. This indicates that they have a spatial size (or presence) in directions orthogonal to their path. If you must use analogies, think if them as have a presence in a plane orthogonal to the line of travel and that such presence decreases radially with distance away from the centre of their path.
Radio phots can be detected when they are focused between two vertical metal poles or wires places placed some distance apart. This confirms that phots have a sideways presence, or ‘effective width’. Low energy phots have greater width than high energy phots. Note that the effective width of a photon is rarely discussed in the literature, and discussions about width using the particle model are completely different.
If phots travelling in air encounter a transparent medium such as water or glass they slow down. Higher energy phots slow down more than low energy phots. They no longer all travel at the same speed.
If phots travelling in air encounter a transparent medium such as water or glass at angle, their paths bend down (see Snell’s law). Higher energy phot paths bend the most. This produces the rainbow spectra Newton demonstrated with his famous prism. The lower energy red light is at the top. This simple experiment is more profound than you might think.
Upon detection, phots can cause polarized effects. In other words the effects are greater in some directions than others. It is reasonable to deduce that these effects come from something encoded in the phots themselves. The direction showing the greatest effects is called the plane of polarization of the phots. Also known as its orientation.
Sometimes a group of identical phots interacting with a detector show effects that vary in magnitude and direction and the effects change if the detector is moved a bit closer to the source or further away from it. This gives rise to a variety of effects called circular and elliptical polarization. Explaining all this is quite instructive for building a bottom up model for phots. It seems that when a phot hits a detector it becomes a driver of not one, but two electro-magnetic disturbances with sinusoidal time variance in intensity. If the two patterns are in phase the effect is plane polarized. If the two patterns are plus or minus 90 degrees out of phase the resultant effect is clockwise or anticlockwise circular polarisation. At phase differences less than ±90 degrees the result is elliptical polarisation.
Bear in mind that a phot can only be observed once. Also note that just because the destruction of a phot suggest two sine wave drivers are at work does not necessarily mean that a phot has two sine waves operating “in flight”. It might or it might not. It is unwise to jump to conclusions. However, at this stage we can conclude that phots embody something that will result in two sine wave drivers upon impact. A double something that is usually coincident but does not have to be.
It is also possible to describe the polarisation effects created by an incident phot as being the sum of two identical circularly polarised waves, except that one is left handed (clockwise) and the other is right handed (anti-clockwise). If these have zero phase difference between them the resultant vector is linearly polarised.
Phots have no inertial mass but they do deliver linear momentum. Put enough of them together and they can exert some pressure. This is perplexing and the some sources make a mess of explaining it. They sometimes use the E= mc² formula, overlooking that this only applies to an entity at rest.
Phots also transfer angular momentum. A phot can make an electron go from negative half unit of spin to a positive half units of spin. They can deliver extra angular momentum if their source was orbiting something.
The transmission, absorption and re-emittance of phots are all affected by external electric or magnetic fields. For example see the Kerr effect where a strong electric field can change the refractive index of fused silica, or the Faraday effect where a strong electric field can change the polarization of phots during absorption and transmission.
On encountering a substance, a phot may eventually be absorbed in it. The depth over which this occurs is called the extinction length. It is well defined for certain crystals.
If a set of phots is directed around a closed path in both directions, the time of travel in each direction is not the same if the apparatus is rotating with respect to the fixed stars (see Sagnac effect). Such as device can be used as a gyroscope with no moving parts.

This is not an exclusive list of the properties of phots, but it is enough to start with.

Applying Special Relativity to Phots

As discussed the speed of phots in a vacuum and measured from an inertial reference frame is always the same. Close to 300 million metres/second. It makes no difference if their source is moving with respect to the detector or not.

This leads to the remarkable conclusions of Special Relativity, as developed by Einstein at the start of the 19th century. In summary: If we observe a moving system from a properly designed inertial reference system, then time in the moving system runs slower, lengths in the moving system contract in the direction of the movement and a body of matter at rest in the frame has total energy proportional to its mass.

So what if the moving system is a group of phots? What does Special Relativity tell us?

Taken to its limit, Special Relativity implies that time in the moving set of phots is infinitely dilated, i.e. at a standstill. Phots travel at the speed of light, so it can be inferred that from the perspective of any and all inertial observers, there is no progression of time in a system comprised of phots all moving in one direction.

Consider a tube with a mirror at either end and a photon bouncing back and forth between the two mirrors. Then move the tube sideways in your reference frame. Conceptually the path of the photon in your frame is a saw tooth zig-zag. Move the tube faster and faster until it approaches the speed of light. The saw tooth is stretched out until it approximates a straight line going sideways. In the limit it is a straight line going sideways. If you were using the beat of the photon as a clock, you would observe that the clock has stopped.

Hence we should not think of phots in fight as being oscillating fields or wriggling electro-magnetic disturbances – they are not doing anything except travelling very fast. A phot is a carrier for a future electromagnetic disturbance, but this is only manifest when it interacts with something.

How wide is a phot? The evidence suggests that phots have some sort of lateral presence that fades out with orthogonal distance from the line of travel. For example, phots do not have to hit a detector directly in order to be detected.

Consider two vertical radio masts placed some meters apart and direct a focused beam of radio frequency phots between the two masts. Radio phots can easily be detected. Less so if the antenna are moved further apart. Then try a beam of higher energy phots, such as microwaves. The detection will be poor until the masts are brought close together.

Another experiment involves passing a beam of phots close to a sharp edge. The beam is diffracted downwards.

Another experiment involves passing x-ray phots through a cloud of free electrons (Compton Scattering). The level of interaction is higher than if the phots were particles with very small effective widths.

Note that in special relativity, lengths orthogonal to the line of travel are not contracted.

How long is a phot? In Special Relativity objects moving at speeds approaching that of light contract by the Lorentz gamma factor in the direction of travel. Taken to the limit, this implies that a phot does not have any length in its direction of travel. It can have spatial extent in the plane orthogonal to its direction of travel. That is all. It has width but not length.

Some explanations of light depict it as a sort of electromagnetic worm wriggling through spacetime at the speed of light. Phots do not do anything but travel very fast.

Some sources about the light waves being stretched as the Universe expands. Phots do not have any length in the direction of travel, so there is nothing to stretch.

Summary

This essay argues that it might be possible to develop a better understanding of light that is an improvement over the internally inconsistent wave-particle approach. It suggests abandoning misleading analogies and mental baggage from the past, starting with a fresh sheet of paper and building up a picture based purely on the evidence of experiments. As an example it starts to build up a description of light it calls phots.

A phot cannot be observed in flight. The things we can discover about a phot come from the effects of its destruction, and then only one property at a time. It is better to focus on what can be observed than on what cannot. Hence it is inherently misleading to draw pictures of phots are assumed to be doing in flight. It is better to focus on what phots do and let that define them.

However we can infer the path of a phot from things it did not run into and we can infer a set of properties for phots emanating from a particular source by observing rays of phots produced in identical ways and measuring all the relevant properties one at a time. The picture that starts to emerge is of a ‘whip crack’ of pure energy travelling as fast as anything can. A phot has no length but it does have a sideways presence. It has an orientation around its line of travel. It does not ‘do’ anything in flight except travel, and maybe rotate.

When a phot hits something it delivers linear momentum and a discrete amount of spin (plus or minus 1) and maybe a bit of extra angular momentum as well. It does this electro-magnetically. It delivers two sine wave drives of electric intensity. These two drivers are orthogonal to each other and have a phase difference between then ranging between -90degrees to +90degrees. The combined effect has a frequency. The frequency is proportional to the energy of the phot. The combined effect can be different for different phots in the same ray, and this suggests that phots have a phase angle that may have varied as the phot travelled.

The phot model will be further developed in some following essays (see index of essays on the homepage). There are thousands of relevant experiments so the essays will use a sample of the main phenomena – reflection, refraction, absorption, diffraction, various interference effects, various polarization effects, scattering experiments, Hall and Kerr effects and photo-electricity etc.

The challenge is to develop a self-consistent model that can explain the all relevant experimental results in a satisfactory way. Only then can we say that we truly understand light.

Reference

Van de Vusse, Sjoerd B.A., 2024, Some ideas and experiments for issues affecting modern physics, https://hereticalphysics.com.au
Author contact: SBAvan@utas.edu.au
Author’s location: Hobart, Australia

Unifying Light