Subatomic particles which make up protons, neutrons and other exotic matter. They come in 6 flavors: up/down, charm/strange, and top/bottom. The 1st of each pair has a charge of +2/3 and the 2nd having -1/3. Quarks are bound together via the strong nuclear force.

Software company that is famous for Quark XPress, probably the most widely used professional DTP program available for Wintel PCs and Macintoshs.

Also: German name for a dairy product similar to Yoghurt.

Also an all-purpose editing tool for Quake/Q2/Q3 engine game editing. Originally started as a level editor for Quake, named QuakeMap. Then expanded to be a model editor, level editor, pak editor, and various other handy utilities/features were added. It's a freeware program, and highly recommended, although it is taking a while for full Q3 support.

Freeware by Armin Rigo, and is currently open-sourced on Sourceforge
Up
Symbol: u
Spin: 1/2
Charge: +2/3 e
Baryon Number: 1/3

Down
Symbol: d
Spin: 1/2
Charge: -1/3 e
Baryon Number: 1/3

Strange
Symbol: s
Spin: 1/2
Charge: -1/3 e
Baryon Number: 1/3

Charmed
Symbol: c
Spin: 1/2
Charge: +2/3 e
Baryon Number: 1/3

Bottom/Beauty
Symbol: b
Spin: 1/2
Charge: -1/3 e
Baryon Number: 1/3

Top/Truth
Symbol: t
Spin: 1/2
Charge: +2/3 e
Baryon Number: 1/3

GeneralWesc was a little off when he said that quarks 'form all elementary' particles.

First off, the quarks ARE (some of) the elementary particles, and they combine in various ways to form the the next level up, the hadrons, or quark-aggregates, made up of either a quark and an antiquark (mesons), or three of the same (baryons) -- quark-quark-quark or antiquark-antiquark-antiquark. Here are some examples of hadrons:
The positive pi-meson is an up quark and an antidown quark.
The proton is two ups and a down
(each for a total charge of +1, see Jesler's post.)

There are two other types of fundamental entities, the leptons and the bosons. The leptons include the electron, the muon, and the tau lepton -- the latter two being unstable more massive 'cousins' of the electron. Each of these three has an associated neutrino (these neutrinos are also considered leptons). All six of these have an associated antiparticle (just like with the quarks). On the other hand, there are the bosons. These are the particles which transmit the four forces of nature. They are: the photon (transmits the electromagnetic force), the W+, W-, and Z bosons (transmit the 'weak nuclear' force which is responsible for certain types of nuclear decay), the gluon (transmits the 'strong nuclear' force between quarks, and the force between the quark agreggates -- the 'hadrons' which include protons and neutrons, effectively holding atomic nuclei together), and finally the graviton, the proposed but as-of-yet-unobserved carrier of the gravitational force. Some physical theories include up to 12 other 'X bosons' which are not common in our cold boring universe because of their inherent high energy.

Once again, the leptons and the bosons are NOT quarks or made out of quarks, but they ARE fundamental elementary particles. Together, quarks, leptons, and bosons make up all the stuff in the Universe.

In the wake of the success of Star Wars in 1977 came a flood of science fiction-related movies, television shows, toys, games, music, clothing, and all sorts of cultural bric-a-brac, the likes of which had not been seen since the 1950s. For the first time in ages SF was It and everyone wanted to jump on the gravy train. Naturally, 90% of this was crap. But here and there one could find jewels of brilliance lodged therein.

Quark, a short-lived humorous SF television series created by Buck Henry and starring Richard Benjamin, was one of these. For a mere nine episodes in 1978 Benjamin played Adam Quark, captain of a spacegoing garbage scow of the United Galaxy Sanitation Patrol. His crew consisted of Ficus, the ship's coolly logical, deceptively human-looking science officer (he was actually an alien species of fern); Gene/Jean, the half male, half female First Mate whose temperament swung widly back and forth between macho aggression and cloying sensitivity; Betty I and Betty II, gorgeous identical twins who eschewed the standard uniform worn by everyone else in favor of skimpy silver halter tops and short shorts; and Andy the Android.

The crew received its orders from the head of the Federation, who was in fact a disembodied head with a gigantic brain called "The Head", as well as Palindrome, the architect of the ship who was played by the ever-fussy Conrad Janis of Mork and Mindy fame. Though it contained allusions to Star Wars (particularly the characters' references to a mystical power called the Source) and other works of science fiction, the show was more than anything a parody of Star Trek. There was even an episode where the crew landed on a planet where all their wishes came true and which paralleled the Trek episode Shore Leave.

Sources:
TVParty.com
iMDb.com
and my own memories of the show

What is it?
Quark is a dairy product found in much of Europe: Germany, Denmark, the UK, the Netherlands, Belgium and France (perhaps elsewhere too, do tell me if you know more!). It is called fromage frais (fresh cheese) in French, platte kaas (flat cheese) in Flemish, and that is exactly what it is: a very fresh kind of cheese.

Quark is made by adding rennet or another souring agent (like buttermilk) to milk. The milk then separates into whey and curds. The whey is poured off or drained. The remaining curds are stirred until a smooth consistency is reached: this is quark.

What does it taste like?
Quark has a distinctive sour, slightly bitter taste that some people don't like. When sugar is added, this taste is somewhat hidden and the quark comes to taste more like yoghurt.
In the Netherlands quark is available in different flavours (plain or with fruit flavour) and with different fat contents, depending on the fat content of the milk it was made of. There is also 'cream quark', to which cream was added. Quark can be made of different sorts of milk, cow's, goat's or sheep's milk to name some, but most quark is made with cow's milk.

Uses
Quark can be used in many different recipes, sweet or savoury. In this it's very similar to yoghurt. You can eat it for breakfast or as dessert, with fruit and/or cereal, you can use it in quark pie, as a base for dips, you can add garlic and herbs and use it as a low-fat substitute for tzatziki or with a baked potato... it is even used in baking, the possibilities are almost endless.

But what if I don't live in the Netherlands?
This of course is a problem in itself...You could try making quark yourself if you need it for a certain dish and can't find it in a store. You need a recipe for making cheese (perhaps substitute the rennet in the recipe with buttermilk), and follow it up until the point where you have drained off the whey and should start pressing and salting and such. Just do the draining and then stir smooth the product you end up with, you'll have made quark. Unfortunately I've not managed to find any good recipes for this, so you'll have to experiment. Or you could make do with thick yoghurt.

Particle physicists treat all matter as being composed of elementary particles; the most complicated (and most whimsically-named) of these are the six quarks. The two lightest quarks make up most of the ordinary matter in the universe, while the other four combine to make exotic, short lived particles only found using particle accelerators and in the earliest instants following the Big Bang. Despite their ubiquity, we never see quarks on their own, or 'bare', rather, they appear in composite particles called 'hadrons'. The most common hadrons are the proton and the neutron, which together compose the nuclei of atoms.

The History of the Quark

Early in the development of subatomic physics, during the 1930s, the world of elementary particles was a simple one. We had the proton, the electron, and the neutron, and these three particles made up everything we see, both in our ordinary lives and in the laboratory. The addition of antiparticles by Dirac was a relatively minor complication, and the addition of the neutrino by Pauli seemed to have no practical benefit outside of nuclear physics. Alas, this simple picture of the universe was not to last.

The 1940's saw the discovery of the first meson, predicted by Yukawa to bind the nucleus together. Or rather, the first two mesons: the pi meson or pion, which is the meson that Yukawa expected, and the mu meson or muon, which turned out to have nothing to do with the Yukawa meson and was instead a particle just like the electron, but 200 times more massive. Nobody expected to find heavy electrons; Rabi famously asked, "Who ordered that?". Soon, dozens of unstable, apparently 'elementary', particles were being discovered, mostly using with the burgeoning new technology of the particle accelerator.

This bewildering array of particles was a source of frustration to many physicists, as there initially seemed to be very little pattern to these new particles. Many, remembering the analogous case of the chemical elements and the periodic table, hoped that a system of classification would eventually present itself and lead, like the periodic table, to an explanation of the apparent complexity of the universe in terms of a much simpler set of objects.

Murray Gell-Mann finally developed a classification system in the early 1960s. By separating the known particles into groups by their intrinsic spin, and then ordering them into a two-dimensional grid by two quantum numbers, 'isospin' and 'strangeness', he found that each group (or 'multiplet') had a geometrical form predicted by the mathematics of group theory. While this is much less straightforward than the periodic table, which fell into nice columns using only the mass, it is built on powerful mathematics that were useful for making predictions. In particular, as with the periodic table a century before, there were conspicuous gaps whose notional occupants had well-defined properties. The simplest of these theorized new particles was named the 'omega-minus' by Gell-Mann, and the discovery of this particle in the laboratory was a decisive proof of the validity of Gell-Mann's "Eightfold Way", winning him the 1969 Nobel Prize in Physics.

The mathematical representation used by Gell-Mann in the Eightfold Way had a curious property; the most fundamental multiplet consisted of three particles, none of which had ever been observed. This multiplet was fundamental in the sense that all the particles in the larger multiplets could be 'assembled' from combinations of these three particles and their antimatter counterparts. Gell-Mann hypothesized that this process of assembly was the true origin of the particles described by the Eighfold Way, and named the three fundamental particles 'quarks', after a passage from James Joyce's novel Finnegans Wake:

Three quarks for Muster Mark!
Sure he hasn't got much of a bark
And sure any he has it's all a beside the mark.

But O, Wreneagle Almighty, wouldn't un be sky of a lark
To see that old buzzard whooping about for uns shirt in the dark
Or he huntin' round uns speckled trousers along by Palmerstown Park!"
The three quarks that Gell-Mann hypothesized were given the labels up, down, and strange, the latter name coming because it was the only quark with a nonzero strangeness.

For many years this 'quark model' wasn't taken very seriously in the larger world of particle physics. Experiments continued to fail at producing particles matching the descriptions of the three quarks, leading many to argue that they were merely a mathematical abstraction and an artifact of the theory of the Eightfold Way. Even the theorists that proposed a fourth quark, in all seriousness, had no objections to naming it the 'charmed' or 'charm' quark. (Some people stolidly insisted on calling the strange quark the 'sideways' quark, but no analogous term arose for the charm quark.) All of this changed with the 1974 discovery of a particle, the J/ψ meson, whose properties strongly suggested that it was composed of charm quarks. Once these properties were verified, the scientists involved concluded not only that the quark model was correct, but also that they'd discovered a new one!

Once the quark model was thus confirmed, the floodgates opened to the discovery of new particles, but with a comforting framework for understanding their properties: hadrons are made of quarks. An additional pair of quarks was postulated: the 'truth' and 'beauty' quarks, though sadly the new seriousness of the endeavour caused them to be renamed 'top' and 'bottom', respectively. The bottom quark was discovered promptly, in 1977, but the heavy top quark remained unseen until 1995. Since the discovery of the top quark, most physicists have believed that the set of quarks is now complete, and that these six quarks and their antiparticles are adequate to describe any hadron that could possibly be produced, returning the number of truly elementary particles to a manageable quantity.

Properties of Quarks

The six known quarks are, in order of mass, the down, up, strange, charm, bottom, and top quarks. The up, charm, and top quarks have a positive electric charge, 2/3 of the proton charge, while the other three quarks have a negative charge that is 1/3 of the electron charge. The quarks are paired up into three 'generations', each containing a positive and negative quark; the two quarks in each generation are relatively close in mass and they are intrinsically connected by the weak nuclear force. (There are subtleties here, see Cabibbo Kobayashi Maskawa matrix for more details)

Quarks are bound together into hadrons by the strong nuclear force, which is by far the strongest of the four fundamental forces; the next closest is the electromagnetic force at 1/137 of the strength. The strong nuclear force acts between particles that have 'colour charge', which can be one of three 'colours', usually named red, blue, and green. (We can call them whatever we want because they have nothing to do with the colours of light, despite the name.) Each quark has a single unit of colour charge, in one of the three colours. Antiquarks have negative colour charge, or 'anticolour'. All other matter particles have a colour charge of zero.

The strong nuclear force binds together quarks in combinations where the amount of each colour is the same. The two simplest way of doing this are to have one quark of each colour, or to have a quark and antiquark of the same colour. The former results in a combination of three quarks (or three antiquarks), called a 'baryon', while the latter combination is referred to as a 'meson'. Protons and neutrons are baryons: the proton is the combination of two up quarks and a down quark, and the neutron contains two down quarks and an up quark.

The binding provided by the strong nuclear force is very strong; although the force is weak between two particles when they are close together, it increases drastically with increasing distance. The energy required to remove a quark from a hadron is so large that at a certain point it will, through Einstein's equation E = mc2, produce a quark/antiquark pair from the vacuum. One of these joins the original hadron and the other joins with the quark being removed to form a new hadron. This property is called 'quark confinement'. The single exception to this situation is the top quark, which has such a short lifetime that by the time the strong force is able to 'dress' it in other quarks it has already decayed.

Quark Physics and You

For most of the activities that we, as humans, perform with matter, the existence of quarks is irrelevant. Even most of nuclear physics works just the same with the 1930s picture of the proton and neutron as elementary particles. Nevertheless, one important phenomenon that we all depend on is thought to be a consequence of quark-level physics. This phenomenon is the strange imbalance between matter and antimatter in the observable universe, namely that everything we see is made out of matter and antimatter is an exotic material produced in particle accelerators.

This is puzzling to particle physicists and cosmologists because the laws of physics are, for the most part, symmetric between matter and antimatter. Two fundamental forces are known to be completely symmetric between matter and antimatter: the strong nuclear force and the electromagnetic force. Where asymmetry between matter and antimatter appears is in the weak nuclear force; this asymmetry is referred to as CP violation.

The CP-violating part of the weak force acts directly at the quark level, and has been observed with both strange quarks and bottom quarks. This preference for quarks over antiquarks, though, is a small and subtle effect, far from the gross violations that would be necessary to produce a matter-filled universe. Violations involving other elementary particles, mainly neutrinos, have been postulated to fill this gap, but no definite evidence has yet been found.


Sources include my undergraduate and graduate particle physics courses, conversations with my thesis supervisor, and David Griffiths's text Introduction to Elementary Particles.
(CC)
This writeup is copyright 2006 D.G. Roberge and is released under the Creative Commons Attribution-NoDerivs-NonCommercial licence. Details can be found at http://creativecommons.org/licenses/by-nd-nc/2.5/ .

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