quantum computing Experimental method of computing that makes use of quantum-mechanical phenomena. It incorporates quantum theory and the uncertainty principle. Quantum computers would allow a bit to store a value of 0 and 1 simultaneously. They could pursue multiple lines of inquiry simultaneously, with the final output dependent on the interfer¬ ence pattern generated by the various calculations. See also DNA com¬ puting, QUANTUM MECHANICS.
quantum electrodynamics (QED) Quantum theory of the interac¬ tions of charged particles with the electromagnetic field. It describes the interactions of light with matter as well as those of charged particles with each other. Its foundations were laid by P. A. M. Dirac when he discov¬ ered an equation describing the motion and spin of electrons that incor¬ porated both quantum mechanics and the theory of special relativity. The theory, as refined and developed in the late 1940s, rests on the idea that charged particles interact by emitting and absorbing photons. It has become a model for other quantum field theories.
quantum field theory Theory that brings quantum mechanics and special relativity together to account for subatomic phenomena. In particu¬ lar, the interactions of subatomic particles are described in terms of their interactions with fields, such as the electromagnetic field. However, the fields are quantized and represented by particles, such as photons for the electromagnetic field. Quantum electrodynamics is the quantum field theory that describes the interaction of electrically charged particles via electro¬ magnetic fields. Quantum chromodynamics describes the action of the strong force. The ELECTROWEAK theory, a unified theory of electromagnetic and weak forces, has considerable experimental support, and can likely be extended to include the strong force. Theories that include the gravita¬ tional force (see gravitation) are more speculative. See also grand unified THEORY, UNIFIED FIELD THEORY.
quantum mechanics Branch of mathematical physics that deals with atomic and subatomic systems. It is concerned with phenomena that are so small-scale that they cannot be described in classical terms, and it is formulated entirely in terms of statistical probabilities. Considered one of the great ideas of the 20th century, quantum mechanics was developed mainly by Niels Bohr, Erwin Schrodinger, Werner Heisenberg, and Max Born and led to a drastic reappraisal of the concept of objective reality. It explained the structure of atoms, atomic nuclei (see nucleus), and mol¬ ecules; the behaviour of subatomic particles; the nature of chemical bonds (see bonding); the properties of crystalline solids (see crystal); nuclear energy; and the forces that stabilize collapsed stars. It also led directly to the development of the laser, the electron microscope, and the transistor.
Qu'Appelle \kwa-‘pel\ River River, southern Saskatchewan, Canada. It is about 270 mi (435 km) long and flows east through several lakes and Indian reservations and across the Manitoba border into the Assiniboine River. Its French name, meaning “who calls,” derived from its Cree Indian
name Kah-tep-was (“River That Calls”), referring to the cries of a leg¬ endary spirit supposedly haunting its waters. Once a fur-trapping region, its basin is now farmed for wheat.
quarantine Detention of humans or animals suspected to have com¬ municable disease until they are proved free of infection. The term is often used interchangeably with isolation (separation of a known infected indi¬ vidual from healthy ones until the danger of transmission passes). It derives from the 40-day ( quarantina ) isolation period instituted in an attempt to prevent spread of plague in the Middle Ages. Though appro¬ priate in some cases (e.g., diphtheria), it is ineffective for diseases that are spread by other means (e.g., plague) or are contagious before symptoms appear. In some cases, contacts (e.g., the family of a hepatitis patient) are notified, educated on precautions, and monitored for development of ill¬ ness. Quarantine is more often applied to animals (e.g., for rabies).
quark Any of a group of subatomic particles thought to be among the fundamental constituents of matter—more specifically, of protons and neutrons. The concept of the quark was first proposed by Murray Gell- Mann and George Zweig (b. 1937); its name was taken from James Joyce’s novel Finnegans Wake. Quarks include all particles that interact by means of the strong force. They have mass and spin, and they obey the Pauli exclu¬ sion principle. They have never been resolved into smaller components, and they never occur alone. Their behaviour is explained by the theory of quantum chromodynamics, which provides a means of calculating their basic properties. There are six types of quarks, called up, down, strange, charm, bottom, and top. Only the up and down quarks are needed to make protons and neutrons; the others occur in heavier, unstable particles.
Quarles, Francis (baptized May 8, 1592, Romford, Essex, Eng.—d. Sept. 8, 1644, London) English religious poet. Quarles is remembered for his Emblemes (1635), the most notable of English-language emblem books (collections of symbolic pictures, usually with verse and prose). Its success led him to produce another, Hieroglyphikes of the Life of Man (1638). Printed together in 1639, they formed perhaps the most popular volume of verse of the 17th century. He also wrote Enchiridion (1640), a highly popular book of aphorisms.
quarter horse Breed of light horse developed in the U.S. from Thor¬ oughbred, Morgan, American saddlebred, and other stock as a quarter-mile racer. Though overshadowed by the Thoroughbred, it found a place in the western and southwestern U.S. as a stock horse (see cutting horse). Mod¬ em quarter horses are short and stocky, with a muscular build and a deep, broad chest. They are noted for fast starting, turning, and stopping abil¬ ity, short-distance speed, and intelligence. They stand 14.3-16 hands (57-64 in., 145-163 cm) high, weigh 950-1,200 lbs (431-544 kg), and have a calm, cooperative temperament.
quarter-horse racing Racing of quarter horses. It originated among British settlers in Virginia shortly after Jamestown was established in 1607. The course was traditionally a quarter-mile (400 m); today there are 11 officially sanctioned races, ranging from 220 to 870 yd (201 to 796 m). Timing is to the nearest .01 second.
quartermaster Officer who oversees arrangements for the quartering and movement of troops. The office dates at least to the 15th century in Europe. The French minister of war under Louis XIV created a quarter¬ master general’s department that dotted the countryside with strategically located stockpiles of food, forage, ammunition, and equipment. By the 18th century his duties in some European countries included coordinat¬ ing marches and deployments and drafting operational orders; in the U.S. he remained a specialized administrative and logistical functionary until 1962, when the Quartermaster Corps was absorbed by other agencies.
quartz Second most abundant mineral (after feldspar) in the Earth’s crust, present in many rocks. Quartz, which consists of silica, or silicon dioxide (Si0 2 ), has great economic importance. Many varieties are gem¬ stones, including amethyst, citrine, smoky quartz, and rose quartz. Sand¬ stone, composed mainly of quartz, is an important building stone. Large amounts of quartz sand (or silica sand) are used in the manufacture of glass and ceramics and for molds in metal casting. Crushed quartz is used as an abrasive in sandpaper; silica sand is employed in sandblasting; and sandstone is used whole to make whetstones, millstones, and grindstones. Silica glass (or fused quartz) is used in optics to transmit ultraviolet light. Tubing and various vessels of fused quartz have important laboratory applications, and quartz fibres are employed in extremely sensitive weigh¬ ing devices.