According to Special Relativity, a particle that can be at rest cannot move at the speed of light or beyond. Such a particle is sometimes called “massive”. Protons, neutrons, electrons, etc. all belong to this particle category. The photon, on the other hand, can’t exist at rest, and not only that, it has to move at a constant velocity, the speed of light.
This means that particles can be sorted into two categories: those always moving at the speed of light, and those always moving at a speed lower than the speed of light.
In the late 1930s, Eugene Wigner published a fascinating paper called today “Wigner’s Analysis of the Poincare Group” . He used group theory to reach a similar conclusion. This paper, refused for publication in a physics journal and finally published in a mathematical journal, is now considered as one of theoretical physics’ deepest and most impressive 20th- century papers.
Some of the massive particles are called “Hadrons”. We know today that the Hadrons are composed of even more fundamental particles, called quarks.
Vector Meson Dominance
In the late 1950s, an experiment was conducted in which protons and neutrons were “bombarded” with highly energetic photons. The photons excited the proton and the neutron and particles were emitted. The products of the collision of photons with proton and neutron were nearly identical. This was a surprising result.
Why did scientists expect anything else? Based on Maxwell Equations, developed in the 19th century, and which won the entire scientific community’s global consensus, photons interact only with electric charges. At the time of the experiment, scientists considered that the neutron’s electric structure was very different from that of the proton: the proton’s charge is positive, and the neutron has no charge at all. Today we know that the proton has two u-quarks of charge 2/3, and one d-quark of charge -1/3. The neutron, on the other hand, has two d-quarks and one u-quark.
If the nucleons are so different with respect to their electric charges, how can a photon, reacting only with electric charges, lead to such similar results?
Another unexpected issue was the magnitude of the photon- proton interaction. The photons were supposed to create an interaction only with the electric charges, but the interaction was stronger than what could be expected if it was merely based of the electric charge’s intensity, which resulted in the creation of more Hadrons than what was expected.
During the sixties, a young physicist, Jun John Sakurai published a theory claiming that the photon is not merely a massless entity, but rather a combination of a photon with a hadron at a certain probability. This theory, called Vector-Meson-Dominance (VMD), is considered today as the only theory capable of explaining the above-mentioned effect. According to Sakurai, most of the hadrons coming out of photon- proton or photon- neutron collisions derive from these hadrons attached to the photons, hence the great similarity between the collision products.
Sakurai tried to settle the contradiction between his massive photons and Special Relativity. But the compromise he found only seems to solve the problem, as Comay showed .
The scientific community has a problem with VMD as well. PACS, the Physics and Astronomy Classification Scheme, classifies the VMD concept as a model and not as a part of a theory. Some of the textbooks simply avoid mentioning the interactions between energetic photons and nucleons. A random selection of textbooks for physics [3-6] do not discuss this interaction at all. Even Wikipedia’s authors avoided getting into the details of this theory.
If it weren’t for the VMD idea, the scientific community would have no explanation for this phenomenon. Since this is not part of the syllabus anymore, it’s possible that most of the new generation of physicists is not aware to this phenomenon, and some of the older physicists already forgot it. This property has a huge significance in understanding the strong force. We will see it again in the article explaining the 3-jet event.
The Dirac monopole
Magnetic and electric forces are present in nature in a sort of “duality”: electricity in movement creates a magnetic field, and a magnet in movement creates an electric field. And they have other “dual” features. So far, only charged particles have been observed, with either positive or negative electric charges. Magnets, on the other hand, only appear with 2 indivisible poles, called “north” and “south” with respect to the direction of Earth’s magnetic field.
In 1931, Dirac tried to predict the behavior of a “magnetic monopole”, a single-pole particle never observed before. Particles may have a definite electric charge – positive or negative (for example, the electron has a negative charge), Dirac was trying to predict the behavior of a particle carrying the dual charge – the magnetic monopole.
Without being explicitly aware of it, Dirac made the assumption that all properties of an electric charge-based electromagnetic field as science knows it, would be identical in fields generated by magnetic monopoles. When reading the article, some 50 years after it had been written, Comay noticed that Dirac was making this assumption even though it wasn’t supported by any experimental evidence. Comay recalls that in his very first reading of this important article, he insolently wrote down an “X” next to the paragraph containing this hidden assumption.
In this article, Dirac pursued with the development of his theory, up to a point where he ran into a hard-to-crack mathematical nut. In order to crack it, he invented a concept called “a String”, totally foreign to the recognized theoretical structure of the electromagnetic theory. Dirac’s string defines a one dimensional curve on which the electromagnetic equations become irregular at every point. The “String” idea spread out and generalized to a point where it now constitutes a research field in itself called “String Theory”, relating to topics in Physics far off from Dirac’s monopoles.
Physicists were trying to track down Dirac’s monopoles for many decades, with no success. String theory is still considered as an asset of inalienable value, although it has no experimental validation.
By the way, Dirac continued searching for the monopoles equation for a long time. In 1948, he published yet another attempt to formulate the monopoles equation with the Variational Principle, for which he had to make some additional heavy assumptions. The paper he wrote did not result in the modification of experimental techniques, thus perpetuating the failure of the experimental endeavors to discover monopoles.
The Strong Interaction – is it a Magnetic Force?
When trying to explain the source of the Strong Interaction, holding the quarks together, physicists wondered if it was a new force, or if it derived from forces they already knew, the electric and magnetic forces. It was easily shown that it could not be an electric force, but, could it be a magnetic force? Could it be created from those magnetic monopoles described by Dirac, expected to be found within the proton and the neutron? According to the understanding of physicists who tried to examine this idea, like for example Nobel Prize laureate Julian Schwinger, magnetic monopoles should follow the equations derived from Dirac’s 1931 paper.
Based on these equations, if the Strong Interaction is a magnetic force, the electron should feel its influence when colliding with a proton or a neutron. Experimental findings deny this possibility, and this is the reason why scientists ended up believing that the Strong Interaction is not magnetic, but rather some other force acting between particles, in addition to the electromagnetic force. .
In 1982, during his stay in the University of Michigan, Comay came across a journal article describing a sensational experimental finding – a magnetic monopole. This result turned out to be wrong soon after, but it aroused Comay’s curiosity and he started reading about it. His readings lead him to Dirac’s monopole strings, which made him raise an eyebrow. So he decided to go back to the source – to Dirac’s 1931 paper. As we mentioned above, Dirac made a latent assumption in this article. Comay decided to check whether monopoles can be described without this assumption, and derive the equations merely on the basis of the Variational Principle. This principle constitutes one of physics’ solid foundations.
Within a few weeks, Comay developed the appropriate equation. If his equation is correct, then quarks are in fact magnetic monopoles, protons and neutrons are composed of such monopoles, and the Strong Interaction is nothing but a magnetic force. In particular, Comay’s equations explain why an electrically charged electron does not interact with the magnetic monopoles when colliding with a proton or a neutron.
The similarity between the electric force and the Strong Interaction has already been studied in the late ‘60s by the New-Zealander physicist, Phil Yock. His papers on this subject remained without response. Comay went further and developed the mathematical infrastructure explaining the monopoles’ properties, showing that the Strong Interaction can very well be a magnetic force carried by monopoles.
Overwhelmed by the scope of this discovery, he told one of his colleagues at the University of Michigan about it, who proposed to hold a seminar on the subject. All the local monopole experts attended the seminar, manifesting their total skepticism. Several physics journals were also skeptical about this discovery and refused to publish it. It ended up being published in a physics journal almost a year later .
Publishing a discovery does not necessarily lead to a shift of perception among professionals in the field. And it’s hard to blame them for it: there are currently some 300 new theoretical physics papers published daily. New “discoveries” are constantly being published and going through the trouble of checking which of them is correct would take more than a lifetime. Therefore, because of this abundance of papers published every day, it is natural that only papers predicting an effect which ends up being experimentally verified, would attract the scientific community’s attention and be carefully analyzed.
An explanation for the VMD phenomenon
Based on the equations developed by Comay, the magnetic field of monopoles inside the nucleon (which physicists call “the bound field”) does not affect electric charges, and therefore the electron does not react to the quarks inside the nucleons. But Comay’s equations for the Regular Charge-Monopole Theory show that quarks, i.e., the magnetic monopoles, as well as electric charges, do react to photons. Furthermore, the magnitude of the square of the quarks’ magnetic charge is much larger than that of the electric charge, about 100-fold (or, as Comay hopes, for his own reasons, 136 times…). Therefore, most of the interactions of photons colliding with protons or neutrons are the consequence of the magnetic charge, which is the same for both u- and d-quarks.
Comay’s model naturally correlates with existing experimental results, and introduces no new, unknown forces. The magnetic monopole properties do not derive from fantastic assumptions as is the case with QCD, but are based on solid physics foundations: the Maxwell Equations, the Lorenz force and the Variational Principle.
So how come it wasn’t discovered before? Indeed, all it takes is grasping the deep significance of the Variational Principle. This understanding developed and became consolidated some 90 years ago. One can argue then that it should have been obvious, that every physicist should have thought of this model in the first place. But moving in this direction implies that monopoles do not behave according to Dirac’s 1931 theory. It is likely that physicist’s attachment to Dirac’s approach to the monopole problem prevented them from pursuing the development of the idea.
 E. P. Wigner, On Unitary Representations of the Inhomogeneous, Lorentz Group, Annals of Math., 40, 149 (1939)
 E. Comay, Apeiron 10, No 2, 87 (2003). A Refutation of the VMD Idea
 Perkins, D. H., Introduction to high energy physics, 4th ed. Cambridge : Cambridge University Press, 2000.
 Griffiths, D. J., Introduction to elementary particles, 2nd, rev. ed. Weinheim : Wiley-VCH, 2008
 Halzen, F. and A. D. Martin Quarks and leptons, New York : Wiley, 1984
 Fayyazuddin and Riazuddin, A modern introduction to particle physics, 2nd ed. Singapore : World Scientific, 2000
 J. Schwinger, Phys. Rev. 173, 1536, 1968