Spis treści Rodzaje oddziaływań podstawowych [edytuj]

Oddziaływania podstawowe Z Wikipedii
Oddziaływania podstawowe (fundamentalne) – oddziaływania fizyczne obserwowane w przyrodzie, nie dające się sprowadzić do innych
oddziaływań.
Spis treści
[ukryj]
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1 Rodzaje oddziaływań podstawowych
2 Główne cechy oddziaływań podstawowych
3 Opisy oddziaływań
4 Próby unifikacji
Rodzaje oddziaływań podstawowych [edytuj]
Obecnie znamy następujące rodzaje oddziaływań podstawowych:
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oddziaływanie elektromagnetyczne
oddziaływanie słabe
oddziaływanie silne
oddziaływanie grawitacyjne
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Główne cechy oddziaływań podstawowych [edytuj]
Zasięg oddziaływań
silne
˜10 − 15 m
elektromagnetyczne
słabe
˜10 − 18 m
grawitacyjne
KaŜdemu typowi sił odpowiada stała sprzęŜenia mnoŜąca funkcję opisującą zaleŜność siły od odległości.
Rząd wielkości stałych sprzęŜenia oddziaływań
silne
˜1
−2
elektromagnetyczne
˜10
słabe
˜10 − 5
grawitacyjne
˜10 − 38
Opisy oddziaływań [edytuj]
W fizyce klasycznej oddziaływania między obiektami obdarzonymi masą bądź ładunkiem opisywane są najczęściej za pomocą potencjałów lub
pól wytwarzanych przez jeden z obiektów i oddziałujących na drugi. Przy czym zakłada się, Ŝe pole przenika całą przestrzeń wokół obiektu,
który je wytwarza.
Innym sposobem opisu oddziaływania jest tzw. oddziaływanie przez wymianę. W tym wypadku między oddziałującymi obiektami zostaje
wymieniona pewna cząstka, (kwant pola), charakterystyczna dla danego typu oddziaływania. Jak wiadomo kwanty niosą ze sobą energię oraz
pęd. Z zasady nieoznaczoności Heisenberga:
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wynika, Ŝe proces ten moŜe zajść w czasie nie dłuŜszym, niŜ ∆t
Wymieniane bozony nazywane są cząstkami wirtualnymi. MoŜna je pośrednio zaobserwować w róŜnych eksperymentach.
Oba opisy oddziaływania są równowaŜne a z matematycznego punktu widzenia identyczne. Jedno zakłada, Ŝe cząstki poruszają się w
zakrzywionej przestrzeni (przy czym jest to pewna abstrakcyjna przestrzeń matematyczna a nie fizyczna czasoprzestrzeń), natomiast drugie
mówi, Ŝe przestrzeń jest płaska, ale występują w niej poprawki zmieniające wartości pochodnej pól cząstek, co ma identyczny efekt jak
przestrzeń zakrzywiona.
Próby unifikacji [edytuj]
Historycznie rozróŜniano wiele oddziaływań podstawowych. Za oddziaływania fundamentalne uwaŜano oddziaływanie elektryczne,
magnetyczne, grawitacyjne, słabe i silne. W procesie rozwoju nauki doszło do tak zwanej unifikacji opisu oddziaływań i zaczęto postrzegać
niektóre oddziaływania jako formy występowania pewnych ogólniejszych oddziaływań.
I tak oddziaływanie magnetyczne i elektryczne James Clerk Maxwell opisał jako komplementarne aspekty oddziaływania elektromagnetycznego.
Był to pierwszy historyczny przypadek unifikacji opisu sił uwaŜanych wcześniej za fundamentalne i rozłączne. Kolejny przykład unifikacji opisu
oddziaływań dotyczy oddziaływań elektromagnetycznych i słabych, które zintegrowano w ramach tzw. teorii oddziaływań elektrosłabych.
Dokonali tego Weinberg i Salam.
Unifikacja opisu oddziaływań jest przyjęta obecnie za paradygmat fizyki: dąŜy się do jak najściślejszej integracji opisów róŜnych oddziaływań.
Fizycy starają się zunifikować wszystkie siły w jedną, co pozwoliło by na opisanie całego Wszechświata praktycznie jednym wzorem.
Dotychczas udało się stworzyć następujące teorie:
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teoria oddziaływań elektrosłabych – łącząca oddziaływania elektromagnetyczne i słabe
Model Standardowy – opisujący oddziaływania silne i elektrosłabe w mało elegancki sposób
teorie wielkiej unifikacji – unifikujące oddziaływania silne i elektrosłabe, niepotwierdzone doświadczalnie
Teoria superstrun – unifikująca wszystkie siły, wykraczająca daleko poza ramy współczesnej fizyki, niepotwierdzona doświadczalnie
supersymetria – łącząca oddziaływania elektrosłabe, silne i grawitację, niepotwierdzona doświadczalnie
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Źródło: "http://pl.wikipedia.org/wiki/Oddzia%C5%82ywania_podstawowe"
Kategoria: Fizyka
Fundamental interaction
From Wikipedia, the free encyclopedia
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In physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other, and which cannot be
explained in terms of another interaction.
Contents
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1 Overview
2 The interactions
o 2.1 Gravitation
o 2.2 Electromagnetism
o 2.3 Weak interaction
o 2.4 Strong interaction
3 Current developments
4 See also
5 Notes
6 References
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[edit] Overview
In the conceptual model of fundamental interactions, everything in nature consists of fermions, which carry properties called charges and 1/2 of
a unit of angular momentum (spin of 1/2 * reduced Planck's constant). They attract or repel each other by exchanging bosons.
The interaction of any pair of matter particles can then be modeled this way:
two fermions go in
interaction by boson exchange
two changed fermions go out
The exchange of bosons always carries energy and momentum between the fermions, thereby changing their directions of flight and their
respective speed. It may transport a charge between the fermions, changing the charges of the fermions in the process (e.g. turn them from one
type of fermion to another type of fermion). Since bosons carry one unit of angular momentum, the fermion's spin direction will flip from +1/2 to
-1/2 (or vice versa) during such an exchange (in units of reduced Planck's constant).
Because fermions can attract and repel each other due to an interaction, such an interaction is sometimes called a "force".
Efforts of modern physics are directed at explaining every observed physical phenomenon by these interactions. Moreover, one tries to reduce
the number of different interaction types (like unifying the electromagnetic interaction and the weak interaction into the electroweak interaction,
see below). For an introductory explanation, four fundamental interactions (forces) may be assumed: gravitation, electromagnetism, the weak
interaction, and the strong interaction. Their magnitude and behavior vary greatly, as described in the table below. Both magnitude ("relative
strength") and "range", as given in the table, have some meaning only within a rather complex framework of ideas.
It should be noted that the table below lists properties of a conceptual model that is still subject to research in modern physics.
Interaction
Current Theory
Quantum chromodynamics
Strong Nuclear
gluons
(QCD)
Electromagnetic
Relative Strength[1] Long-Distance Behavior Range(m)
1
1038
10-15
(see discussion below)
Mediators
Quantum electrodynamics
photons
(QED)
1036
5
infinite
1025
Weak
Electroweak Theory
W and Z bosons
Gravitation
General Relativity
(GR)
gravitons (not yet discovered) 1
10-18
infinite
The modern quantum mechanical view of the three fundamental forces (all except gravity) is that particles of matter (fermions) do not directly
interact with each other, but rather carry a charge, and exchange virtual particles (gauge bosons), which are the interaction carriers or force
mediators. For example, photons are the mediators of the interaction of electric charges; and gluons are the mediators of the interaction of color
charges.
[edit] The interactions
[edit] Gravitation
Main article: Gravitation
Gravitation is by far the weakest interaction, but at long distances is the most important force. There are two reasons why gravity's strength
relative to other forces becomes important at long distances. The first is that gravity has an infinite range, like that of electromagnetism. The
second reason why gravity is important at long distances is because all masses are positive and therefore gravity's interaction can not be screened
like in electromagnetism. Thus large celestial bodies such as planets, stars and galaxies dominantly feel gravitational forces. In comparison, the
total electric charge of these bodies is zero because half of all charges are negative. In addition, unlike the other interactions, gravity acts
universally on all matter. There are no objects that lack a gravitational "charge".
Because of its long range, gravity is responsible for such large-scale phenomena as the structure of galaxies, black holes and the expansion of the
universe, as well as more elementary astronomical phenomena like the orbits of planets, and everyday experience: objects fall; heavy objects act
as if they were glued to the ground; people are limited in how high they can jump.
Gravitation was the first kind of interaction which was described by a mathematical theory. In ancient times, Aristotle theorized that objects of
different masses fall at different rates. During the Scientific Revolution, Galileo Galilei experimentally determined that this was not the case — if
friction due to air resistance is neglected, all objects accelerate toward the ground at the same rate. Isaac Newton's law of Universal Gravitation
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(1687) was a good approximation of the general behaviour of gravity. In 1915, Albert Einstein completed the General Theory of Relativity, a
more accurate description of gravity in terms of the geometry of space-time.
An area of active research today involves merging the theories of general relativity and quantum mechanics into a more general theory of
quantum gravity. It is widely believed that in a theory of quantum gravity, gravity would be mediated by a massless spin 2 particle which is
known as the graviton. Gravitons are hypothetical particles not yet observed.
Although general relativity appears to present an accurate theory of gravity in the non-quantum mechanical limit, there are a number of alternate
theories of gravity. Those under any serious consideration by the physics community all reduce to general relativity in some limit, and the focus
of observational work is to establish limitations on what deviations from general relativity are possible.
[edit] Electromagnetism
Main article: Electromagnetism
Electromagnetism is the force that acts between electrically charged particles. This phenomenon includes the electrostatic force, acting between
charges at rest, and the combined effect of electric and magnetic forces acting between charges moving relative to each other.
Electromagnetism is also an infinite-ranged force, but it is much stronger than gravity, and therefore describes almost all phenomena of our
everyday experience, ranging from the impenetrability of macroscopic bodies, to lasers and radios, to the structure of atoms and metals, to
phenomena such as friction and rainbows.
Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 1800s that scientists discovered that electricity
and magnetism are two aspects of the same fundamental interaction. By 1864, Maxwell's equations had rigorously quantified the unified
phenomenon. In 1905, Einstein's theory of special relativity resolved the issue of the constancy of the speed of light, and Einstein also explained
the photoelectric effect by theorizing that light was transmitted in quanta, which we now call photons. Starting around 1927, Paul Dirac unified
quantum mechanics with the relativistic theory of electromagnetism; the theory of quantum electrodynamics was completed in the 1940s.
[edit] Weak interaction
Main article: Weak interaction
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The weak interaction or weak nuclear force is responsible for some phenomena at the scales of the atomic nucleus, such as beta decay.
Electromagnetism and the weak force are theoretically understood to be two aspects of a unified electroweak interaction — this realization was
the first step toward the unified theory known as the Standard Model. In electroweak theory, the carriers of the weak force are massive gauge
bosons called the W and Z bosons. The weak interaction is the only known interaction in which parity is not conserved; it is left-right
asymmetric. It even breaks CP symmetry. However, it does conserve CPT.
[edit] Strong interaction
Main article: Strong interaction
The strong interaction, or strong nuclear force, is the most complicated force because it behaves differently at different distances. At distances
larger than 10 femtometers, the strong force is practically unobservable, which is why it wasn't noticed until the beginning of the 20th century.
After the nucleus was discovered, it was clear that a new force was needed to keep the positive protons in the nucleus from flying out. The force
had to be much stronger than electromagnetism, so that the nucleus could be stable even though the protons were so close together, squeezed
down to a volume which is 10-15 of the volume of an atom. From the short range of the force, Hideki Yukawa predicted that it was associated
with a massive particle, whose mass is approximately 100 MeV. The pion was discovered in 1947 and this discovery marks the beginning of the
modern era of particle physics.
Hundreds of hadrons were discovered from the 1940s to 1960s. An extremely complicated theory of the strongly interacting particles, known as
hadrons, was developed. Most notably, the pions were understood to be oscillations of vacuum condensates, the rho and omega vector bosons
were proposed by Sakurai to be force carrying particles for approximate symmetries of Isospin and hypercharge, and the heavier particles were
grouped by Geoffrey Chew and Steven Frautschi into families that could be understood as vibrational and rotational excitations of strings. None
of these approaches led directly to the fundamental theory, but each of these were deep insights in their own right.
Throughout the sixties, different authors considered theories similar to the modern fundamental theory of QCD as simple models for the
interactions of quarks, starting with Murray Gell-Mann who along with George Zweig first proposed fractionally charged quarks in 1961. The
first to suggest the gluons of QCD explicitly were the Korean physicist Moo-Young Han and Japanese Yoichiro Nambu, who introduced the
quark color charge and hypothesized that it might be associated with a force-carrying field. but at that time, it was difficult to see how such a
model could permanently confine quarks. Han and Nambu also assigned each quark color an integer electrical charge, so that the quarks were
only fractionally charged on average, and they did not expect the quarks in their model to be permanently confined.
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In 1971, Murray Gell-Mann and Harald Fritsch proposed that the Han/Nambu color gauge field was the correct theory of the short-distance
interactions of fractionally charged quarks. A little later, David Gross, Frank Wilczek, and David Politzer discovered asymptotic freedom in this
theory, which allowed them to make contact with experiment. They came to the conclusion that QCD was the complete theory of the strong
interactions, correct at all distance scales. The discovery of asymptotic freedom led most physicists to accept QCD, since it became clear that
even the long-distance properties of the strong interactions could be consistent with experiment if the quarks are permanently confined.
Assuming that quarks are confined, Mikhail Shifman, Arkady Vainshtein, and Valentine Zakharov were able to compute the properties of many
low-lying hadrons directly from QCD with only a few extra parameters to describe the vacuum. First-principles computer calculations by
Kenneth Wilson in 1980 established that QCD will confine quarks, to a level of confidence tantamount to certainty. From this point on, QCD was
the established theory of the strong interactions.
QCD is a theory of fractionally charged quarks interacting with 8 photon-like particles called gluons. The gluons interact with each other, not just
with the quarks, and at long distances the lines of force collimate into strings. In this way, the mathematical theory of QCD is not only
responsible for the short-distance properties of quarks, but for the long-distance string-like behavior discovered by Chew and Frautschi.
[edit] Current developments
The Standard Model is a theory of three fundamental forces — electromagnetism, weak interactions and strong interactions; however, these three
forces are not tied together. Howard Georgi, Sheldon Glashow and Abdus Salam discovered that the Standard Model particles can arise from a
single interaction, known as a grand unified theory. Grand unified theories predict relationships between otherwise unrelated constants of nature
in the Standard Model. Gauge coupling unification is the prediction from grand unified theories for the relative strengths of the electromagnetic,
weak and strong forces and this prediction was verified at LEP in 1991 for supersymmetric theories.
Currently, there is no complete theory of quantum gravity. There are several candidates for a framework to fit quantum gravity, including string
theory, loop quantum gravity and twistor theory.
In theories beyond the Standard Model, there are frequently fifth forces and the search for these forces is an on-going line of experimental
research in physics. In supersymmetric theories, there are particles that only acquire their masses through supersymmetry breaking effects and
these particles, known as moduli can mediate new forces. Another possible motivation for new forces is related to the accelerating expansion of
the universe. The most concrete examples of new forces from the cosmological expansion result from modifications of General Relativity.
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[edit] See also
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Standard Model
o Strong interaction
o Electroweak interaction
o Weak interaction
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Gravity
o Quantum gravity
o String Theory
o Theory of Everything
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Grand Unified Theory
o Gauge coupling unification
o Unified Field Theory
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Quintessence, the proposed fifth force.
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People: Isaac Newton, James Clerk Maxwell, Albert Einstein, Sheldon Glashow, Abdus Salam, Steven Weinberg, Gerardus 't Hooft,
David Gross, Edward Witten, Howard Georgi
[edit] Notes
1. ^ Approximate. The exact strengths depend on the particles and energies involved.
[edit] References
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Feynman, Richard P. (1967). The Character of Physical Law. MIT Press. ISBN 0-262-56003-8
Weinberg, S. (1993). The First Three Minutes: A Modern View of the Origin of the Universe. Basic Books. ISBN 0-465-02437-8
Weinberg, S. (1994). Dreams of a Final Theory. Vintage Books USA. ISBN 0-679-74408-8
Padmanabhan, T. (1998). After The First Three Minutes: The Story of Our Universe. Cambridge University Press. ISBN 0-521-62972-1
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•
Perkins, Donald H. (2000). Introduction to High Energy Physics. Cambridge University Press. ISBN 0-521-62196-8
[hide]
v•d•e
The Four Fundamental Interactions of Physics
Strong interaction · Electromagnetism · Weak interaction · Gravitation
Retrieved from "http://en.wikipedia.org/wiki/Fundamental_interaction"
Categories: Interaction | Force
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This page was last modified on 30 April 2008, at 19:08.
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