fundamental forces in nature

8/8/2019 Fundamental Forces in Nature

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Introduction To The

Fundamental Forces In NatureCompiled by Dr. Dr. Mark Brian Debowski

22/01/2009


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Matter may be viewed as consisting of fermions,

which carry properties called charges and spin.

Matter attracts or repels other material byexchanging bosons.


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In the interaction of any pair of fermions the twofermions go in interaction by boson exchangeand two changed fermions go out.


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The exchange of bosonsalways carries energyand momentum betweenthe fermions, therebychanging their speed anddirection.

The exchange may alsotransport a charge

between the fermions,changing the charges ofthe fermions in theprocess.

Bosons also carry one unit

of angular momentumand the fermion's spindirection will flip from +1/2to 1/2 (or vice versa)during such an exchange.


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As the interaction results in fermions attracting

and repelling each other, an older term for

"interaction" is force.


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There are four fundamental interactions orforces: gravitation, electromagnetism, theweak interaction, and the strong interaction.


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Every observed physical phenomenon should be

explained by these fundamental interactions.


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The quantum mechanical view of the fundamental forces(other than gravity) is that particles of matter (fermions)do not directly interact with each other, but rather carry

charge, and exchange virtual particles (gauge bosons),which are the force mediators.

For example, photonsmediate the

interaction of electric

charges, and gluons

mediate theinteraction of color

charges.


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Gravitation

Gravitation is by far the weakest of the four interactions.Nevertheless, it is important for macroscopic objects and overlong distances for several reasons.

Gravitational force:

has an infinite range; acts universally on all matter;

is permanent.

nothing "cancels" gravity.

All objects having mass are subject to gravitational force, whichworks in onl one direction: attraction.


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Gravity explains large-scale phenomena as the

structure of galaxies, black holes, and the

expansion of the universe but also explainsmore modest scale events such as planetary

orbits and objects falling. Gravitation was the

first interaction to be described mathematically.


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A theory of quantum gravity is based on

gravitational force produced by a hypothetical

massless spin 2 particle called the graviton.Gravitons have yet to be observed.


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Electroweak Interaction

At everyday low energieselectromagnetism and weakinteraction appear to be verydifferent. They can be modeledusing two different theories. Atabove unification energy, on theorder of 100 GeV, they merge intoa single electroweak force.

Electroweak theory is very importantfor modern cosmology, particularly

on how the universe was evolved.This is because shortly after theBig Bang, the temperature wasapproximately above 1015 K.Electromagnetic force and weakforce were merged into a

combined electroweak force.


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Electromagnetism

Electromagnetism is a force that acts between electrically charged particles.This includes the electrostatic force acting between charged particles at rest,and the combined effect of electric and magnetic forces acting betweencharge particles moving relative to each other.

Electromagnetism is infinite-ranged like gravity, but vastly stronger. It thereforedescribes almost all macroscopic phenomena of everyday experience,

ranging from the impenetrability of solids, friction, rainbows, lightning, andall human-made devices using electric current, such as television, lasers,and computers.

Electromagnetism fundamentally determines all macroscopic, and many atomiclevel, properties of the chemical elements, including all chemical bonding.


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Weak Nuclear ForceWeak nuclear force is responsible for some

nuclear phenomena such as beta decay.

Electromagnetism and the weak force are now

understood to be two aspects of a unified

electroweak interaction. In this theory, thecarriers of the weak force are the massive

gauge bosons called the W and Z bosons.


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Strong interactionS

trong nuclear force varies with distance. It ispractically unobservable for it holds only inside

the nucleus.


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Quantum Chromodynamics (QCD) is a theory offractionally charged quarks interacting bymeans of 8 photon-like particles called gluons.The gluons interact with each other, not justwith the quarks, and at long distances the linesof force collimate into strings. In this way, themathematical theory ofQCD not only explainshow quarks interact over short distances, butalso their string-like behavior over longerdistances.


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The Standard Model (SM) is a theory of all fundamentalforces except gravitation; however, the SM does nottie them together.

A major current research theme is Grand unified theory(GUT), under which all particles arise from a singleinteraction. GUTs predict relationships amongconstants of nature that are unrelated in the SM.

An offshoot of a GUT would be a

theory of quantum gravity. Atpresent several candidate

theories of quantum gravity,

are string theory, loop quantum

gravity, and twistor theory.


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Other theories include a hypothetical fifth force, and thesearch for such a force is an ongoing line ofexperimental research in physics.

Supersymmetric theories suggest there are particles thatacquire their masses only through supersymmetrybreaking effects and these particles, known as modulican control new forces.

The recent discovery that the

expansion of the universe is

accelerating, has given rise

to a need to explain a

nonzero cosmological

constant, and possibly to

other modifications of

general relativity.


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