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For the novel, see The Elementary Elementary particles pdf download. A particle containing two or more elementary particles is a composite particle. Everyday matter...

For the novel, see The Elementary Elementary particles pdf download. A particle containing two or more elementary particles is a composite particle.


Everyday matter is composed of atoms, once presumed to be matter’s elementary particles—atom meaning “unable to cut” in Greek—although the atom’s existence remained controversial until about 1910, as some leading physicists regarded molecules as mathematical illusions, and matter as ultimately composed of energy. Soon, subatomic constituents of the atom were identified.

As the 1930s opened, the electron and the proton had been observed, along with the photon, the particle of electromagnetic radiation. At that time, the recent advent of quantum mechanics was radically altering the conception of particles, as a single particle could seemingly span a field as would a wave, a paradox still eluding satisfactory explanation. Via quantum theory, protons and neutrons were found to contain quarks—up quarks and down quarks—now considered elementary particles. Yet a free electron—which is not orbiting an atomic nucleus and lacks orbital motion—appears unsplittable and remains regarded as an elementary particle.

Around 1980, an elementary particle’s status as indeed elementary—an ultimate constituent of substance—was mostly discarded for a more practical outlook, embodied in particle physics’ Standard Model, what’s known as science’s most experimentally successful theory. Many elaborations upon and theories beyond the Standard Model, including the popular supersymmetry, double the number of elementary particles by hypothesizing that each known particle associates with a “shadow” partner far more massive, although all such superpartners remain undiscovered. Meanwhile, an elementary boson mediating gravitation—the graviton—remains hypothetical. All elementary particles are—depending on their spin—either bosons or fermions.

Dirac statistics and are fermions. Einstein statistics and are bosons. 1 and are therefore vector bosons. In the Standard Model, elementary particles are represented for predictive utility as point particles.

Though extremely successful, the Standard Model is limited to the microcosm by its omission of gravitation and has some parameters arbitrarily added but unexplained. Neutrons are made up of one up and two down quark, while protons are made of two up and one down quark.

Therefore, one can conclude that most of the visible mass of the universe consists of protons and neutrons, which, like all baryons, in turn consist of up quarks and down quarks. The number of protons in the observable universe is called the Eddington number. Graphic representation of the standard model.

Spin, charge, mass and participation in different force interactions are shown. Click on the image to see the full description. However, the Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, since it is not known if it is compatible with Einstein’s general relativity.

There may be hypothetical elementary particles not described by the Standard Model, such as the graviton, the particle that would carry the gravitational force, and sparticles, supersymmetric partners of the ordinary particles. The 12 fundamental fermions are divided into 3 generations of 4 particles each. Estimates of the values of quark masses depend on the version of quantum chromodynamics used to describe quark interactions.

Quarks are always confined in an envelope of gluons which confer vastly greater mass to the mesons and baryons where quarks occur, so values for quark masses cannot be measured directly. Since their masses are so small compared to the effective mass of the surrounding gluons, slight differences in the calculation make large differences in the masses. There are also 12 fundamental fermionic antiparticles that correspond to these 12 particles.

Isolated quarks and antiquarks have never been detected, a fact explained by confinement. Color-charged particles interact via gluon exchange in the same way that charged particles interact via photon exchange.

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