Part of the Casswiki article series Natural science
In particle physics, a particle is a basic unit of matter and energy.
From the point of view of Esoteric Science, particles can be viewed as points of harmonic stabilization that oscillate within and are bound together by webs of harmonic stability that fit within an underlying fundamental diatonic structure. Esoteric science sees this diatonic structure as mathematically revealing the scaffolding underlying the very nature of matter and even life itself. Possibly these existing harmonic stabilization points emerge from nonexistence, that is, from an unfathomable reservoir from which all possible events are made.
Fundamental particles
The concept of a particle is a natural idealization of our everyday observation of matter. Dust particles or baseballs, under ordinary conditions, are stable objects that move as a whole and obey simple laws of motion. However, neither of these is actually a structureless object. That is, if sufficiently large forces are applied to them, they can readily be broken apart into smaller pieces.
The idea that there must be some set of smallest constituent parts, which are the building blocks of all matter, is a very old one.
Democritus (born about 460 BC in Abdera, Thrace, Greece) is often credited with introducing this idea, though his concept of the building block was quite different from ours today. He introduced the word which in English translates as atom to describe the parts, whatever they might be.
History plays tricks with language, however. The word atom has acquired a meaning today that only partly matches Democritus’ idea. Certainly we know that matter is indeed composed of the objects we call atoms. Atoms were originally thought to be indivisible, that is, the smallest particle. However we now understand that atoms are built up of smaller parts. These parts are electrons and a nucleus. The nucleus is much smaller than the atom and is itself composed of protons and neutrons.
What does “fundamental” mean?
In the 1930s, it seemed that protons, neutrons, and electrons were the smallest objects into which matter could be divided and they were termed “elementary particles”. The word elementary then meant “having no smaller constituent parts”, or “indivisible” — the new “atoms”, in the original sense.
Again, later knowledge changed our understanding as physicists discovered yet another layer of structure within the protons and neutrons. It is now known that protons and neutrons are made of quarks. Over 100 other “elementary” particles were discovered between 1930 and the present time. These elementary particles are all made from quarks and/or anti-quarks. These particles are called hadrons.
Once quarks were discovered, it was clear that all these hadrons were composite objects, so only in out-dated text books are they still called “elementary”. Leptons, on the other hand, still appear to be structureless.
Today, quarks and leptons, and their antiparticles, are candidates for being the fundamental building blocks from which all else is made. Particle physicists call them the “fundamental” or “elementary” particles — both names denoting that, as far as current experiments can tell, they have no substructure.
Composite particles
Molecules are the smallest particles into which a substance can be divided while maintaining the physical properties of the substance. Each type of molecule corresponds to a specific chemical compound. Molecules are composites of one or more atoms. See list of compounds for a list of molecules.
Atoms are the smallest neutral particles into which matter can be divided by chemical reactions. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons. Each type of atom corresponds to a specific chemical element, of which 110 have been named. Refer to the periodic table for an overview.
Atomic nuclei consist of protons and neutrons. Each type of nucleus contains a specific number of protons and a specific number of neutrons, and is called a nuclide or isotope. Nuclear reactions can change one nuclide into another. See Isotope table (complete) for a list of isotopes.
Hadrons are defined as strongly interacting composite particles. Hadrons are either bosons, in which case they are called mesons, or fermions, in which case they are called baryons. Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks “aces”), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons. A “sea” of virtual quark-antiquark pairs is also present in each hadron.
Ordinary baryons contain three valence quarks or three valence antiquarks each.
Nucleons are the proton and the neutron, the fermionic constituents of normal atomic nuclei.
Hyperons such and O particles are generally short-lived and heavier than nucleons. They do not normally appear in atomic nuclei.
Ordinary mesons contain a valence quark and a valence antiquark, and include the pions, the kaons and many other types of mesons. In quantum hadrodynamic models the strong force between nucleons is mediated by mesons.
Exotic baryons have been discovered only recently.
Pentaquarks consist of four valence quarks and one valence antiquark.
Exotic mesons are predicted by new theories.
Tetraquarks consist of two valence quarks and two valence antiquarks.
Glueballs are bound states of two or more real gluons.
Hybridss consist of one or more valence quark-antiquark pairs and one or more real gluons.
Elementary particles
An elementary particle is a particle with no measurable internal structure, that is, it is not a composite of other particles. In a quantum field theory, these are the particles which are created and annihilated by the field operators in the Lagrangian. Elementary particles can be classified according to their spin.
Fermions have half-integral spin; for all known elementary particles this is 1/2. Each fermion has its own distinct antiparticle. Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the color force or not. According to the Standard Model there are 12 flavors of elementary fermions, six quarks and six leptons.
Quarks can interact via the color force. They exist in six flavors: down, up, strange, charm, bottom and top.
Leptons do not interact via the color force. They also exist in six flavorss: electron, muon, tauon, electron-neutrino, muon-neutrino and tauon-neutrino.
Supersymmetric theories predict the existence of more fermions. Their existence has not been confirmed experimentally.
The neutralino (spin 1/2) is a superposition of the superpartners of several neutral standard model particles. It is a leading candidate for dark matter. The partners of charged bosons are called charginos.
The photino (spin 1/2) is the superpartner of the photon.
The gravitino (spin 3/2) is the superpartner of the graviton boson in supergravity theories.
Bosons have integral spin. The fundamental forces of nature are mediated by gauge bosons.
According to the Standard Model, there are 13 elementary bosons:
The photon (spin 1) mediates the electromagnetic force.
The W+, W- and Z0 bosons (spin 1) mediate the weak nuclear force.
The eight gluons (spin 1) mediate the strong nuclear force.
The Higgs boson (spin 0) is predicted by standard model electroweak theory. Physicists expect the Higgs to be discovered at the Large Hadron Collider (LHC) particle accelerator now under construction at CERN.
New theories predict the existence of other bosons.
The graviton (spin 2) has been proposed to mediate gravity in a theory of quantum gravity.
The supersymmetric partners of the standard model fermions (sleptons and squarks) would also be bosons.
Other
The “Oh-My-God” particle is an extremely high-energy proton, which has been observed several times.