Subatomic particle

A subatomic particle is a particle smaller than an atom. It may be (a) an elementary (or fundamental) particle, or (b) a composite particle. An electron is an example of an elementary particle; protons and neutrons are examples of composite particles. Researchers in particle physics and nuclear physics study these various particles and their interactions.

The elementary particles fall into one of two classes: fermions and bosons. It may be helpful to think of fermions as "pixels of matter"—fundamental particles normally associated with matter. Bosons, on the other hand, may be thought of as "pixels of force"—particles associated with fundamental forces.

Overview of fermions and bosons

There are a dozen fundamental fermions, also referred to as "12 flavors" of fermions. In addition, there are four fundamental bosons, with another two proposed in theory. Out of these basic components, an essentially unlimited number of composite particles can be assembled. Everyday matter is made up of three fermions (electron, up quark, and down quark) and two bosons (photons and gluons).

• Fermions:

Quarks — up, down, strange, charm, bottom, top

Leptons — electron, muon, tau, electron neutrino, muon neutrino, tau neutrino

• Bosons:

Gauge bosons – gluon, W and Z bosons, photon

Other, theoretically proposed bosons — Higgs boson, graviton

The fermions and bosons have very different natures and can be distinguished as follows:

• A boson is ephemeral, and is easily created or destroyed in any number. A photon of light is an example. A stable fermion, such as an electron in regular matter, is essentially eternal. The stability of matter is a consequence of this property of the fermions. While creating a single electron is currently thought impossible (see the Standard Model), making a particle-pair of matter-antimatter out of energy is an everyday occurrence in science and the more extreme corners of the universe. A gamma photon of sufficient energy, for example, will regularly separate into an electron and positron pair which take off as quite real particles. When the positron meets an electron, they merge back into a gamma photon.

• When a boson is rotated through a full circle of 360°, it behaves quite normally—it ends up just as it started. This is called "quantum spin 1" behavior. By contrast, when a fermion is rotated a full circle, it turns upside down. A fermion must be rotated two full circles (or 720°) to get it back as it started. This is known as "quantum spin 1/2" behavior. (A Moebius twisted strip illustrates such behavior, as shown below in the Example of the hydrogen atom.)

• A boson "pixel of force" going forward in time is exactly the same as when it goes backward in time (which is quite common on subatomic scales). They are identical. A fermion going forward in time is a "pixel of matter," while a fermion going backward in time is a "pixel of antimatter." They are exactly opposite each other, and, when they meet, they cancel, or anhiliate, and become an energetic "spin 1" photon. The fury of the atomic bomb dropped at Nagasaki would be matched if just 1 gram of matter united with 1 gram of antimatter. That our universe is composed entirely of matter (fermions going forward in time) is one of the great questions of cosmology. This asymmetry between matter and antimatter is seemingly connected to the left-handedness of the Weak Force, and is a topic at the frontier of current understanding. Theory suggests that in the hot Big Bang, the ratio of matter to antimatter fermions was 100,000,000,001/100,000,000,000. The matter fermions remaining after the mutual anhiliation phase gave rise to the matter in the universe.

• Bosons come in a wide range of sizes, from large to small. A radio wave photon can stretch for miles, while a gamma photon can fit inside a proton. By contrast, fermions are so ultratiny that current experiments have placed only an upper limit on their size. The electron and quark are known to have a diameter that is less than 1/1,000,000 the diameter of a proton, which itself is 1/10,000 the size of an atom. While electrons or quarks may well be described as a "pixels of matter," they do not contribute much directly to the spatial extent of matter—they contribute only indirectly by their overall history over time, as directed by the quantum wavefunction, or orbital as it is called in atoms and molecules. This aspect of matter encapsulates all of what is called 'quantum weirdness' and there is much disagreement in the science world as to how to translate the concepts expressed in precise, and flawless, universal mathamatics (that everyone agrees on) into the vague and fuzzy concepts of a natural language such as English. The quantum wavefunction is a extended abstarct aspect of particles that determines the probability of what history in time they will follow. So, for example, a tiny proton (trillionths of a centimeter) is swathed by a acomparitively imensnse abstract construct (that, like an iceberg, only shows the tip of its complex poly-dimensional, hierarchical probability amplitudes, as the real probability that rules the electron in the external 3-D world of spacetime. This vast abstract construct about a single proton extends for [at least] centimeters (see Rydberg Atoms in which an excited electron is in, say, the 756s level of the quantum wavefunction orbital and is centimeters away from the proton genrating the orbital). When all the levels of this abstract orbital constrct are empty, the proton is a hydrogen ion. When a single electron occupies the very lowest energy, and the smallest at one millionth of a centimeter, of the levels in the orbital wavefunction generated by the proton—the 1s orbital—the combination is called a ground-state hydrogen atom.

• In the theory of General Relativity, space and time are united as one, to form spacetime. While bosons and fermions have the same overall velocity, they move through the spatial and temporal components of spacetime in opposite ways. A boson, such as a photon of light, moves with through space at velocity c (the speed of light) and moves through time with velocity zero. (This is why reversing time has no effect on bosons. This is not true for the Weak Bosons which are slow in space and fast in time as they have mass. The W comes in both poitive and negative time directions —the W+and W-, while the Z, like the photon, is symetrical in time. ) Fermions do the opposite, the fermions move through space with velocity that, compared to the speed of light, is essentially zero for the ones we are made off. The still have their original velocity of c, but are now doing it solely along the time axis. The fermions we are made of move through time with velocity essentially c—this is what we call the passage of common time. In one second, we fermion-based being cover the distance c in time and rarely approch even a tiny fraction of lightspeed in space) When the fermions do speed up in space, however, they slow down in time. The velocity is still c in spacetime, it is just the spatial and temporal components that have shifted as explained by the theory of Special Relativity. While time will actually run slower when flying the Pacific, the effect is in the sixteenth decimal place and imperceptable. At speeds approaching c in space, however, such fermions will travel through time at a speeds approaching zero. See the twin paradox form of time travel into the future.

Particles and the four fundamental interactions (forces)

Fermions are essentially eternal, but they are not static, they interact with each other. They do this by exchanging or coupling with the ephemeral bosons they are able to generate. The consequences of such exchange of bosons between fermions is what science calls the 'four fundamental forces.

The exchange of photons of light underlies the 'electromagnetic force.'

The exchange of gluons is the 'color strong force' that confines quarks within protons and neutrons.

The 'weak force' involves 'weak bosons.' Unlike its photon and gluon cousins, these bosons have mass and are slow in space so do not get very far away from a fermion, even on the scale of the proton. This sluggish behavior plays a central role in the slow and steady energy generation in the core of the Sun.

Gravity is still a mystery and has been described either as a global phenomenon involving spin-0 bosons and spacetime curvature (see Mach's Principle and General Relativity), or as a local phenomenon involving coupling with spin-2 cousins called gravitons. The final answer will probably embrace both these perspectives.

Quantum particles in Matter

Everyday matter is made up of two types of fermions—quarks and electrons—and two types of bosons—photons and gluons. Each of these has a history that is determined, over time, by an abstract quantum wavefunction or orbital.

The quarks are capable of creating and absorbing both photons and gluons, they have both electric and color charge. A proton (or neutron) is a composite subatomic particle that contains three ultra small quarks immersed in the intense field of gluons they have generated. The exchange of gluons is very vigorous and confines the quarks to a tiny volume 1/10,000th the size of an atom. The energy of this 'color force field' is large, and is responsible (by Einstein's equivalence of energy and mass) for 99.9% of the mass of the proton/neutron and hence is responsible for the mass of all material objects. The rest mass of the bare quarks and electrons together make up the other 0.01%.The size of the proton is that of this gluon field, while the much greater size of the atom reflects the much less intense photon field between the quarks in the nucleus and the electrons the periphery.

The electrons are only capable of coupling with photons. The energy in the photon field of the atom is 1/1,000,000,000 of that in the gluon field and contributes little to the atom's mass.

Three families in three generations

While all are not involved in the structure of everyday matter, there are other fundamental fermions and bosons that are all related in a simple way. There are three 'families' of fermions:

First Family: The simplest member of the first generation of this family is the electron neutrino. This is like a tiny moebius-like twist in one of the spatial extensions of the Planck Scale 'pixels of spacetime.' This twist has a very fast spin and, being a fermion, takes two revolutions to get back to its initial state. Next is the electron which has spin and 'electric charge' (couples with photons). It can be conveniently thought of as a neutrino with a twist to it. Last is the quark which has spin, electric charge and 'color charge' (couples with gluons) and can be thought of as an electron with an extra twist that can go in two directions, the U and D quarks.

All of these are moving in the 'normal' direction of time. When they go in the opposite direction they are called antiparticles, such as the anti-neutrino, the anti-electron (or positron) and the anti-quarks. While the physical universe is all matter, antimatter can be readily created in the lab. When matter and antimatter fermions meet each other they 'untwist' each other and their energy is liberated as high-energy photons (gamma rays).

There are three 'generations' of fermions that can be thought of as non-oriented twists (see Moebius strip) in spacetime.

The 1st generation is based on the electron neutrino which can be thought of as a quantum twist/spin in 1 spatial dimension. The electron, and U / D quarks are derived from this as above.

The 2nd generation is based on the muon neutrino which can be thought of as a twist/spin in 2 dimensions. The muon and S/C quarks are founded on this as in the 1st generation. All the members of this generation have more mass/energy than the first generation.

The 3nd generation is based on the tauon neutrino which can be thought of as a twist/spin in all 3 dimensions. The tauon and B/T quarks are founded on this. All the members of this generation have more mass/energy than the second generation.

There are three families of bosons that can be thought of as simple waves in spacetime:

1. The photon which is a (complex) wave in 1 dimension.
2. The 'weak bosons' which are (complex) waves in 2 dimensions.
3. The gluons which are (complex) waves in all 3 dimensions.

There is also the (theoretical) Higgs Boson which can best be thought of as a wave or excitation in 0 dimensions. Gravity can be described either as a global phenomenon involving the Higgs and the bending of spacetime, or as a local phenomenon involving the graviton or 'spin-2' boson.

Example of the hydrogen atom

The above illustration shows the components of the hydrogen atom (not drawn to scale). The proton at the center is made up of three quarks that have shed all their concentrated color charge into a halo of intense-colored gluons. If the quarks are considered on the scale of three fireflies, the overall proton would be on the scale of Manhattan Island. The quarks in the colorless center are just responsive to the photons. They couple with each other and with the distant electron. The electron (on the scale of another firefly) is in quantum motion in an abstract "1s" orbital (on the scale of the solar system). Being a fermion, it has to make two full circuits of this orbital to end up as it started (as suggested by the Moebius strip cross-section).

History of dividing the atom

The study of electrochemistry led G. Johnstone Stoney to postulate the existence of the electron (denoted e⁻) in 1874 as a constituent of the atom. It was observed in 1897 by J. J. Thomson. Subsequent speculation about the structure of atoms was severely constrained by the 1907 experiment of Ernest Rutherford which showed that the atom was mostly empty space, and almost all its mass was concentrated into the (relatively) tiny atomic nucleus. The development of the quantum theory led to the understanding of chemistry in terms of the arrangement of electrons in the mostly empty volume of atoms. Protons (p⁺) were known to be the nucleus of the hydrogen atom. Neutrons (n) were postulated by Rutherford and discovered by James Chadwick in 1932. The word nucleon denotes both the neutron and the proton.

Helium atom (schematic)
Showing two protons (red), two neutrons (green) and two electrons (yellow).

Electrons, which are negatively charged, have a mass of 1/1836 of a hydrogen atom, the remainder of the atom's mass coming from the positively charged proton. The atomic number of an element counts the number of protons. Neutrons are neutral particles with a mass almost equal to that of the proton. Different isotopes of the same nucleus contain the same number of protons but differing numbers of neutrons. The mass number of a nucleus counts the total number of nucleons.

Chemistry concerns itself with the arrangement of electrons in atoms and molecules, and nuclear physics with the arrangement of protons and neutrons in a nucleus. The study of subatomic particles, atoms and molecules, their structure and interactions, involves quantum mechanics and quantum field theory (when dealing with processes that change the number of particles). The study of subatomic particles per se is called particle physics. Since many particles need to be created in high energy particle accelerators or cosmic rays, sometimes particle physics is also called high energy physics.

History

J. J. Thomson discovered electrons in 1897. In 1905 Albert Einstein demonstrated the physical reality of the photons which were postulated by Max Planck in order to solve the problem of black body radiation in thermodynamics. Ernest Rutherford discovered in 1907 in the gold foil experiment that the atom is mainly empty space, and that it contains a heavy but small atomic nucleus. The early successes of the quantum theory involved explaining properties of atoms in terms of their electronic structure. The proton was soon identified as the nucleus of hydrogen. The neutron was postulated by Rutherford following his discovery of the nucleus, but was discovered by James Chadwick much later, in 1932. Neutrinos were postulated in 1931 by Wolfgang Pauli (and named by Enrico Fermi) to be produced in beta decays (the weak interaction) of neutrons, but were not discovered till 1956. Pions were postulated by Hideki Yukawa as mediators of the strong force which binds the nucleus together. The muon was discovered in 1936 by Carl D. Anderson, and initially mistaken for the pion. In the 1950s the first kaons were discovered in cosmic rays.

The development of new particle accelerators and particle detectors in the 1950s led to the discovery of a huge variety of hadrons, prompting Wolfgang Pauli's remark: "Had I foreseen this, I would have gone into botany". The classification of hadrons through the quark model in 1961 was the beginning of the golden age of modern particle physics, which culminated in the completion of the unified theory called the standard model in the 1970s. The discovery of the weak gauge bosons through the 1980s, and the verification of their properties through the 1990s is considered to be an age of consolidation in particle physics. Among the standard model particles the existence of the Higgs boson remains to be verified— this is seen as the primary physics goal of the accelerator called the Large Hadron Collider in CERN. All currently known particles fit into the standard model.

See also

• Poincare symmetry, CPT invariance, spin statistics theorem, bosons and fermions.
• Particle physics, list of particles, the quark model and the standard model.

External links

• particleadventure.org: The Standard Model
• particleadventure.org: Particle chart
• University of California: Particle Data Group
• Annotated Physics Encyclopædia: Quantum Field Theory
• Jose Galvez: Chapter 1 Electrodynamics (pdf)

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