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These are excerpts and elaborations from my book "The Nature of Consciousness"
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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 Diracin 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-Mannwhen he hypothesized the breakdown of the nucleus into quarks
("A Schematic Model of Baryons and Mesons", 1964). It follows from
Diracs 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 Planckconstant, 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 Bosewho 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 Yukawain 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 dont carry and dont 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 dont
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 Higgsfield, mediated by the Higgs boson (an idea proposed in 1964 by
the British physicist Peter Higgsand 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 |
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