Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Physics of Elementary Particles: Close Encounters with Matter
Quantum Theory redrew our picture of nature and started a race to discover the ultimate constituents of matter. This program culminated in the formulation of theories of Quantum Electrodynamics, virtually invented by the British physicist Paul Dirac in 1928 when he published his equation for the electron in an electromagnetic field (which combined Quantum Mechanics and Special Relativity) and Quantum Chromodynamics, virtually invented by the US physicist Murray Gell-Mann when he hypothesized the breakdown of the nucleus into quarks ("A Schematic Model of Baryons and Mesons", 1964).
It follows from Dirac’s equation that for every particle there is a corresponding anti-particle which has the same mass and opposite electric charge, and, generally speaking, behaves like the particle moving backwards in space and time.
Forces are mediated by discrete packets of energy, commonly represented as virtual particles or “quanta”. The quantum of the electromagnetic field (e.g., of light) is the photon: any electromagnetic phenomenon involves the exchange of a number of photons between the particles taking part in it. Photons exchange energy in units of the Planck constant, a very small value, but nonetheless a discrete value.
Other forces are defined by other quanta: the weak force by the W particle, gravitation by the graviton and the nuclear force by gluons.
Particles can, first of all, be divided according to a principle first formulated (in 1925) by the Austrian physicist Wolfgang Pauli: some particles (the “fermions”, named after the Italian physicist Enrico Fermi) never occupy the same state at the same time, whereas other particles (the “bosons”, named after the Indian physicist Satyendra Bose who made the discovery in 1924) do. The wave functions of two fermions can never completely overlap, whereas the wave functions of two bosons can completely overlap (the bosons basically lose their identity and become one).
(Technically, "boson" is the general name for any particle with an angular momentum, or spin, of an integer number, whereas "fermion" is the general name for any particle with a odd half quantum unit of spin).
It turns out (not too surprisingly) that fermions (such as electrons, protons, neutrons) make up the matter of the universe, while bosons (photons, gravitons, gluons) are the virtual particles that glue the fermions together. Bosons therefore represent the forces that act on fermions. They are the quanta of interaction. An interaction is always implemented via the exchange of bosons between fermions.
(There exist particles that are bosons but do not represent interactions, the so called "mesons", first hypothesized by the Japanese physicist Hideki Yukawa in 1935. Mesons decay very rapidly. No stable meson is known).
Three forces that act on elementary particles have been identified: the electromagnetic, the “weak” and the “strong” forces. Correspondingly, there are bosons that are weak (W and Z particles), strong (the gluons) and electromagnetic (the photon).
Fermions can be classified in several ways. First of all, the neutron and the proton (the particles that made up the nuclei of atoms) are not elementary: they are made of 18 quarks (six quarks, each one coming in three "colors"). Then there are twelve leptons: the electron, the muon, the tau, their three neutrinos and their six anti-particles. A better way to organize Fermions is to divide them in six families, each led by two leptons: the electron goes with the electron's neutrino, the down quark and the up quark. This family makes up most of the matter we know. Another family of Fermions is led by the muon and contains its neutrino and contains two more quarks. The third family contains the tau particle, its neutrino and two more quarks (bottom and top).
Particles made of quarks are called "hadrons" and comprise "baryons" (made of three quarks, and therefore fermions, such as the proton and the neutron) and "mesons" (made of one quark and one antiquark, and therefore bosons). These particles are kept together by the strong forced mediated by gluons.
The electromagnetic force between leptons is generated by the virtual exchange of mass-less particles called “photons”. The weak force is due to the W and Z particles (there are two W particles). The “strong” force between quarks (the one that creates protons and neutrons) is generated by the virtual exchange of “gluons”. Quarks come in six “flavors” and three “colors”. Gluons are sensitive to color, not to flavor. The “strong” force between protons and neutrons is a direct consequence of the color force mediated by gluons. Note that gluons, unlike photons, also interact among themselves because they carry and react to color charges (photons don’t carry and don’t react to the electric charge).
Leptons do not have color, but have flavor (for example, the electron and its neutrino have different flavors). The “weak” force is actually the flavor force between leptons. W+ and W- are the quanta of this flavor force.
Before the discovery of quarks, we knew of no force that grows with distance. Quarks don’t exist as individual particles because they can never be separated: the stronger you pull them apart, the stronger their interaction.
From the point of view of Quantum Field Theory, quantum fluctuations cause vibrations that we perceive as attributes of particles: mass, spin, charge, etc. Thus a particle (e.g., an electron) can be viewed as a vibrational pattern (a pattern of vibrations in a quantum field). Vibrations interact among themselves. When we observe this interaction, we perceive it as particles interacting with each other by exchanging virtual particles (that we interpret as forces, e.g. electromagnetism).
This model explains what we know of matter. It does not explain why there are four forces, 6x3 quarks, six leptons, four bosons for leptons, and eight gluons for quarks. The numbers seem to be arbitrary.
In particular, it does not explain why particles have the masses they have; rather arbitrary numbers that span ten orders of magnitude, the top quark being about 100,000 times “heavier” than the electron, and more than one trillion times heavier than the electron-neutrino. A field called the Higgs field, mediated by the Higgs boson (an idea proposed in 1964 by the British physicist Peter Higgs and possibly confirmed experimentally in 2012) is supposed to permeate the universe, and the mass of a particle is supposed to be a measure of the intensity of its interaction with the Higgs field. Mass would therefore be an emergent property rather than a fundamental property of matter.
The Higgs boson would be the only particle equipped with mass from the beginning. The US physicist William Bardeen showed that the mass of the Higgs boson could be a consequence of scale-symmetry breaking ("On naturalness in the standard model", 1995) and scale-symmetry breaking could also explain the exponential inflation that followed the Big Bang, argued by the Italian physicists Alberto Salvio and Alessandro Strumia ("Agravity", 2014). Bardeen's idea is that scale (size) would not be an inherent feature of nature (galaxies would not necessarily be bigger than stones) but would emerge spontaneously from the interaction of the particles constituting the universe. According, instead, to the theory of the US physicist Peter Graham ("Cosmological Relaxation of the Electroweak Scale", 2015) , the Higgs mass is due to a field dubbed the relaxion which pervades all space.
Nor does the theory explain why this universe needs three fundamental forces (weak, strong and electromagnetic). Roughly, the strong force (that acts only between quarks) creates nuclei. The electromagnetic force (that acts only between charged particles) creates atoms (and whatever is left of it creates molecules). Together these two forces create the matter that we see. The weak force is responsible for the decay of quarks and leptons into different kinds of quarks and leptons. When a quark or lepton decays, it is said to change “flavor”. While it is difficult to visualize the weak interaction, it is quite important for our being here because it transforms elements into other elements that account for stars and life (the thermonuclear fusion that transforms hydrogen into deuterium and fuels the Sun is a weak-interaction process, and the life forms of the Earth were made possible by the production of carbon and heavier elements inside stars). Basically, the strong force holds particles together inside the nucleus of the atom, whereas the weak force changes the nature of those particles.
Alternatively, leptons and quarks can also be combined in three families of fermions: one comprising the electron, its neutrino and two flavors of quarks (“up” and “down”); one comprising the muon, its neutrino and two flavors of quarks (“strange” and “charmed”); and one comprising the tau lepton (“tauon”), its neutrino and two flavors of quarks (“bottom” and “top”). Plus the three corresponding families of anti-particles. Eight particles per family (each flavor of quark counts as three particles). The grand total is 48 fermions. The bosons are twelve: eight gluons, the photon and the three bosons for the weak interaction. Sixty particles overall.
The profusion of particles is simply comic. Quantum Mechanics has always led to this consequence: in order to explain matter, a multitude of hitherto unknown entities is first postulated and then “observed” (actually, verified consistent with the theory). More and more entities are necessary to explain all phenomena that occur in the laboratory. When the theory becomes a self-parody, a new scheme is proposed whereby those entities can be decomposed in smaller units. So physicists are already, silently, seeking evidence that leptons and quarks are not really elementary, but made of a smaller number of particles. It is easy to predict that they will eventually break the quark and the electron, and start all over again.
Several other characteristics look bizarre. For example, the three families of fermions are very similar: what need did Nature have to create three almost identical families of particles?
The mass of the muon is 209 times the mass of the electron, and the mass of the tau lepton is 3478 times the mass of the electron. Why?
The spins of these particles is totally arbitrary. Fermions have spin 1/2 and bosons have integral spin. Why?
The whole set of equations for these particles has 19 arbitrary constants. Why?
Gluons are fundamentally different from photons: photons are intermediaries of the electromagnetic force but do not themselves carry an electric charge, whereas gluons are intermediaries of the color force that do carry themselves a color (and therefore interact among themselves). Why?
Also, because color comes in three varieties, there are many gluons, while there is only one photon. As a result, the color force behaves in a fundamentally different way from the electromagnetic force. In particular, it extends to infinite. That confines quarks inside protons and neutrons. Why?
Back to the beginning of the chapter "The New Physics" | Back to the index of all chapters