Are there "Particles of Light?"

A Realist Picture of Light:

Light is Made of Waves!

Milk is Made of Molecules.  Light is made of waves.  "Wave-Particle Duality" is a nonsensical explanation of light forced on us during the 1920's.   New research is finally beginning to make sense out of the nonsense.

It looks like light is not made of tiny indivisible "quantum" objects or particles or "corpuscles" after all. New research says it was all a misunderstanding, an enormous mistake.   There aren't any bizzare quantum particles of light after all.   What about "single photon counters?"  What about Einstein's "Photoelectric Effect?"  Misinterpretations of the data, according to researchers at the University of Texas at Austin.

Some ideas are just wrong.  Is the Moon made of cheese?   Is the earth flat?  Is Elvis alive?

Everyone knows milk is made of water molecules, lactose molecules, salt, proteins, fats and many other molecules.   But no matter how far we zoom in on light, there aren't any particles.  Light is made of smooth continuous electromagnetic waves just like radio waves and microwaves even at atomic scale.

Light waves have frequency and wavelength.  Light waves, like radio waves, spread out in all directions by diffraction.  Light waves go through glass, plastic, water, diamonds and air.  When light is absorbed it is converted to heat or other forms of energy, like chemical energy in plant photosynthesis.

Dipole radio waves radiating from an antenna [Wikipedia]

On the other hand, a particle doesn't spread out.  Particles can be counted.  Particles collide.  Most particles have some mass and size and shape.  Particles can stand still.   Light doesn't stand still.

Light doesn't collide with other light, it just adds up.   Maxwell's electromagnetic wave equations are linear.

The particle vs. wave debate goes back thousands of years.  

The history of light is fascinating and fun to read.  Ancient Greece and ancient Rome believed that light is made of particles.   Robert Hooke said light was a wave (1665) and it was generally accepted.  Isaac Newton published his light particle theory in his book "Optiks" in 1704 and it became the dominant picture for a century.  Then came Huygens, Foucault, Michelson-Morley, Maxwell, Young, Einstein, Dirac, and many other scientists and theories.

Is light made of particles? [Tenor Gif]

Today everyone accepts "Duality"  

 All our science textbooks, university classes, schools, scientists and engineers universally accept that light is BOTH a wave and a particle.  To me "Wave-particle Duality" a very confusing idea and full of mystery and controversy.  I think it's nonsense because  it seems to violate basic logic, causality and reality.  How can we picture one particle going through both slits and then interfering with itself?  [Wikipedia Quantum Paradoxes] We have two incompatible, conflicting models trying to explain the same reality.  Yet everyone seems to think "wave-particle duality" as an acceptable explanation for how light works.  Look at any science textbook, any science magazine, any scientist or engineer anywhere.  

Here is the definition: [Wikipedia]

Wave–particle duality is the concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave. It expresses the inability of the classical concepts "particle" or "wave" to fully describe the behaviour of quantum-scale objects. As Albert Einstein wrote in 1938:

"It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do."

What's New?

Now the understanding of light is changing.   The experimental evidence that light is explained by indivisible particles (the particle picture) is steadily being debunked.  It is starting to look like the particle explanation is the result of incorrect interpretation of optical phenomena.  What's left is Maxwell's original electromagnetic field equation, a pure wave model.   His classical wave model can fully describe the behavior of light even at the quantum scale.  This is new and astonishing!  Most of us still believe, like the Einstein quote above,  "there are two contradictory pictures of reality."  (Micro vs. Macro).

Photographic Film

Until recently everyone interpreted the dots on photographic film as evidence of particles.  Each black dot was believed to be the location where a particle of light hit the film.  Now we understand the dots are just crystal grains that had a chemical reaction.  Each silver halide grain is different.  The most sensitive grains react first.  The "graininess" of a photograph is explained by the chemical crystal grains, not by graininess of light.  Light is a smooth continuous electromagnetic wave.  The film is grainy.

What about Compton Scattering and the Photoelectric Effect?

The Compton Scattering "proof" was refuted by P.A.M. Dirac in 1926.  

P.A. M. Dirac. The Compton Effect in Wave Mechanics. Proc. Cambr. Phil. Soc. V. 23. P. 500-507 (1926). 

Einstein's photoelectric effect "proof" was refuted by Lamb & Scully in 1969.   

W.E. Lamb and M.O. Scully: The photoelectric effect without photons. In: Polarization, Matter and Radiation. Jubilee volume in honour of Alfred Kasiler, pp.363-369. Press of University de France, Paris (1969).   Discussion.

"Single Photon Detectors"

Do the "clicks" in a single-photon detector actually count individual particles?  Researchers at the Applied Research Laboratory at the University of Austin, Texas say no.  Their data indicates that the light follows a continuous classical (Maxwell) model.  The clicks are due to noise, not "single photons."  How could they tell the difference between single photons and noise?  They did it by comparing the statistics   They confirmed their result with simulations (Maxwell's wave model).  Details are here:  

Do photon-number-resolving detectors provide valid evidence for the discrete nature of light?

Morgan C. Williamson,  Gabriel D. Ko, and Brian R. La Coury

Applied Research Laboratories, The University of Texas at Austin, Austin, TX 

(Dated: October 11, 2021)

So is All Quantization Wrong?  

Of course not!  Atoms and electrons are certainly quantized, meaning that they have precisely fixed energy levels (states).  When an atom emits a "photon" it is transmitting a burst of electromagnetic waves, exactly the same thing as infrared, radio, microwaves, and radar.  The energy levels in atoms and molecules are quantized because they act as resonators (resonant cavities).  The statistics are described and modeled very accurately by eigenvalues and operators, expectation values and quantum statistics.  The text books and scientific literature just need to adapt to our new understanding of "photons" as waves, not point particles.

Why can't we just have 2 or 3 models for light?

You like the particle (QM) model, I like the classical (Maxwell) wave model.  Maybe both explanations are right -- for different situations.  Why not?  What's wrong with two explanations?  We could choose when and where to use them.  In fact the "Ray Tracing" model is often used for optical calculations, because it's fast, easy, and accurate enough for many purposes.  We should use quantum mechanics for transitions if it is faster or easier.  So yes, we can have 3 models.  

Models are not right or wrong,  they are just tools like shovels.  Shovels are neither right nor wrong.
But be careful -- don't use the wrong model for the wrong situation.  Newton's gravity model is wrong (unusable) for black holes because it leads us to wrong answers.   Shovels are not hammers.

The ray tracing model is great for trajectories but fails to explain interference.  There is no interference in ray tracing.  It doesn't deal with wave effects.  It's the wrong model for interference.

The QM model fails to explain particle trajectories.  There are no trajectories.  There is an initial state and a final state.  QM does not give any path or position along the way.    It only calculates the statistical probability of an outcome.  Asking for the position of a single photon half way through a double slit experiment is a nonsensical question for QM.   Since there is no position, obviously asking for the evolution of that position with time, i.e. the trajectory, is also nonsensical.

QM is a Statistical Model

If you just want to calculate the statistical probability of a transition from state A to state B, the quantum (particle) formula obviously works.  It's right.  It gives the right energy levels for atoms.  It predicts the probability of an outcome correctly if you follow the formalism.  The QM (Quantum Mechanics) math formulas are accurate and correct for statistics.  You will get the right answer, statistically.  

But it is mind-boggling to talk about "Schrödinger probability waves"  because probability does not travel through space in waves.  Probability waves can't carry energy and momentum and spin.  Does a probability wave packet travel at the speed of light?  Or faster?  Can a mirror reflect probability?  Can two packets of probability collide?  It seems nonsensical.   Probability is just statistical information in your head or my head.   

If we want to explain how light got from A to B, if we want to understand what's happening along the way, the trajectory, process, how it works, we have to picture it in terms of waves, not particles.  When a radio wave is transmitted, it is not made of many "particles."  When starlight comes from a distant galaxy it is just a radio wave, not tiny marbles or bullets of light.

The particle picture is wrong for double slits. [from the web]

This is the wave picture.
[Wikipedia] Thanks to Fu-Kwun Hwang for this image.

Reference

Here is just one recent article in Physics Review A showing that light behaves as a classical wave, not an indivisible particle.

https://www.researchgate.net/publication/352273487_Classical_model_of_a_delayed-choice_quantum_eraser