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What is a Quark?

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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 09 November 2016
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A quark is a tiny theoretical particle that makes up protons and neutrons in the atomic nucleus. Along with gluons, quarks also make up more exotic hadrons such as mesons, which are not stable. It is called theoretical because while assuming its existence makes for a better physics theory, it has never been observed directly.

Along with leptons — electrons, muons, the tau, and their associated neutrinos and antiparticles — quarks make up all the visible matter in the universe. They are the only fundamental particles which interact with each other through all four fundamental forces: strong nuclear force, weak nuclear force, electromagnetic force, and gravity. A basic property of these particles is confinement — all quarks make up hadrons, and are necessarily never independent. Descriptions of their physical properties emerged from quantum chromodynamics (QCD), the theory of the strong nuclear force which holds the atomic nucleus together.

Like all other subatomic particles, quarks may be described exhaustively by three quantum numbers: spin J, parity P, and mass m. Because they are never isolated, these properties must be inferred by observing the larger particles they make up. There are six known types: up, down, charm, strange, top, and bottom. These names are purely arbitrary and do not suggest anything about each quark's properties.

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The normal matter that makes up the majority of the universe is made of up and down quarks, which are the lightest of the particles. A proton is made of two up and one down quark, while a neutron is made of two down and one up quark.

Quarks have varying masses, which are measured in GeV (giga electron-volts) over the speed of light squared. Subatomic particles are measured in terms of the energy they produce rather than mass in grams. The down quark is about twice as massive as the up. The strange is about 20 times as massive as the down quark. The charm quark is about 10 times as massive as that, followed by the bottom, which is about three times as massive as the last, and finally the top quark, which is the most massive of all. Increasing mass tends to correspond to scarcity of the particle, and necessitates more exotic physical conditions for its manifestation.

Physicists are on the lookout for theorized quark matter, a hypothetical lattice made of continuous quarks connected by gluons. It is not yet known whether this type of matter is physically possible. If so, it would probably be found in the core of extremely compact stars that have not yet collapsed into a black hole.

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FitzMaurice
Post 5

@arod2b42

I think that the fact that rules change should not discourage scientists from seeking to find rules which explain things. The rules are out there, even though they may be infinite, and vary infinitely. The more we discover, the more we will advance, and I don't think we will ever finish discovering all there is to know. In fact, I think we barely know anything compare to all there is to know. That is why science needs to remember that it is far from exhaustive.

arod2b42
Post 4

@Renegade

As we progress downward to understand the building blocks of reality, the rules change completely. This makes the whole "science" very unscientific and unpredictable. Upon observing light to discover its true nature, we realize that light changes patterns upon observation. If things change when we observe them, how will we ever comprehend the deepness of understanding and how the universe works?

GigaGold
Post 3

As we delve deeper into the elements which make up the basic building blocks of atoms and of all things, the logic seems to get more and more complicated. There seems to be an infinitesimal amount of detail among these round objects which orbit and interact with each other. Just like the infinite magnitude of the sky and orbiting masses, these small orbiting objects have a profound depth of detail and pragmatic beauty.

Renegade
Post 2

String theory postulates that all of the forces of the universe are supported and fueled by strings of varying lengths and levels. These strings are immensely powerful, and comprise the core of the smallest quarks. They are the basic elements of reality, on which all of reality is based. Cosmologists believe that understanding these is the only way to ultimately manipulate the space-time continuum.

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