An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A thought experiment developed in 1935 by A. Einstein (1879-1955), Boris Podolsky (1896-1966), and Nathan Rosen (1909-1995) to demonstrate that there is a fundamental inconsistency in → quantum mechanics. They imagined two physical systems that are allowed to interact initially so that they will subsequently be defined by a single quantum mechanical state. For example, a neutral → pion at rest which decays into a pair of → photons. The pair of photons is described by a single two-particle → wave function. Once separated, the two photons are still described by the same wave function, and a measurement of one → observable of the first system will determine the measurement of the corresponding observable of the second system. For example, if photon 1 is found to have → spin up along the x-axis, then photon 2 must have spin down along the x-axis, since the final total → angular momentum of the two-photon system must be the same as the angular momentum of the initial state. This means that we know the spin of photon 2 even without measuring it. Likewise, the measurement of another observable of the first system will determine the measurement of the corresponding observable of the second system, even though the systems are no longer physically linked in the traditional sense of local coupling (→ quantum entanglement). So, EPR argued that quantum mechanics was not a complete theory, but it could be corrected by postulating the existence of → hidden variables that furthermore would be "local". According to EPR, the specification of these local hidden parameters would predetermine the result of measuring any observable of the physical system. However, in 1964 John S. Bell developed a theorem, → Bell's inequality, to test for the existence of these hidden variables. He showed that if the inequality was satisfied, then no local hidden variable theory can reproduce the predictions of quantum mechanics. → Aspect experiment.

A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Phys. Rev. 41, 777 (15 May 1935); → paradox.

As great as; like or alike in quantity, degree, value.

From L. æqualis "uniform, identical, equal," from æquus "level, even, just," of unknown origin, + -alis, → -al.

Hamug, from Mid.Pers. hamôg "equal, like," from ham "the same; together; also" (O.Pers./Av. ham-; cf. Skt. sam-; also O.Pers./Av. hama- "one and the same;" Skt. sama-; Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-) + suffix -og/-ok/-uk, as in nêrog "force" (from nar "man, male"), nêvakôk "good, nice" (from nêvak "good, beautiful, nice, favorable"), mastôk "drunk" (from mast "drunk, drunken"), câpuk "quick; active," sapuk "light, brisk."

1) The state or quality of being equal.
2) Math.: A → statement of two → mathematical objects being equal. Like → equations, equalities are written as two mathematical objects connected by the → equality sign.

M.E. from L. aequalitat-, stem of aequalitats, → equal + -ity.

Hamugi noun of hamug, → equal.

Same as → equals sign.

→ equality; → sign.

The act of making equal or uniform.
Electronics: The reduction of frequency or phase distortion by introducing networks which compensate for the particular type of distortion over the required frequency band.

Noun of equalize.

To make equal; to make uniform.

From → equal + → -ize.

From hamug, → equal + sâz contraction of sâzandé "doer, maker," from sâxtan, sâzidan "to make, form, fashion, prepare" (Mid.Pers. sâxtan, sâz- "to form, prepare, build, make;" Proto-Iranian *sac- "to fit, be suitable; to prepare").

Electronics: A device, usually an electric network, designed to correct for unequal attenuation of phase shift in the transmission of signals.

Agent noun from → equalize.

A mathematical symbol (=) that indicates equality of two expressions on each side of the sign. Same as → equality sign. The equals sign appears for the first time in Robert Recorde's book The Whetstone of Witte published in 1557. He was a Welsh physician and mathematician.

→ equal; → sign.

In Ptolemy's → geocentric system, an imaginary point near the center of the → deferent but at a position opposite to that of the Earth from the center of the deferent. Ptolemy further supposed that the distance from the Earth to the center of the deferent was equal to the distance from the center of the deferent to the equant. He also claimed that the planet's deferent and the → epicycle described uniform circular motion around the equant.

L. aequant-, s. of aequans, pr.p. of aequare "to make equal."

Falak-e mo'adel (al-masir), literally "the sphere that equalizes (the path)," from Ar. falak "celestial orbit; sphere; heaven," from Babylonian pulluku + mo'adel "equalizing" (+ masir "path").

To put in the form of an equation; to state the equality of or between.

L. æquatus, p.p. of æquare "to make equal," from æquus "equal, level, even."

Infinitive form of hamug, → equal.

A statement asserting the equality of two numbers or two expressions. It consists of two parts, called sides or members of the equation, separated by the Same as → equality sign.

From L. æquation- "an equalizing," noun of → equate.

Verbal noun of hamugidan, → equate.

1) Any equation that describes the motion of objects, i.e., variation of velocity, distance covered, acceleration, etc., as a function of time; e.g., V = V₀ + at, S = Vt + (1/2)at².
2) For a fluid, a relation, in its most fundamental form, equating the rate of change of momentum of a selected portion of fluid and the sum of all forces acting on that portion of fluid.
3) In quantum mechanics, an equation that governs the time variation of the → state of the system. → Schrodinger equation. However, in the Heisenberg formulation of quantum mechanics the equation of motion does not involve the states, which in this case is time independent, but rather the → observables of the system.

→ equation; → motion.

In physics and thermodynamics, the equation that describes the relationship between pressure, density, and temperature, e.g. → ideal gas law, → van der Waals equation, → polytropic process, → virial equation of state.

→ equation; → state.

In cosmology, a → dimensionless parameter introduced by the → equation of state representing the ratio of the pressure to the energy density of a fluid, such as the → dark energy: w = p/ρ. The → deceleration or → acceleration of an → expanding Universe depends on this parameter (→ accelerating Universe). A number of numerical values of this parameter are as follows: for the → cosmological constant: w = -1, for → non-relativistic matter (present-day → baryons): w = 0, and for → relativistic matter (photons, neutrinos): w = +1/3. Together with Ω(dark energy) and Ω(matter), w provides a three-parameter description of the dark energy. The simplest parametrization of the dark energy is w = constant, although w might depend on → redshift.

→ equation; → state; → parameter.

The difference between → apparent sidereal time and → mean sidereal time. It is due to the nutation of the Earth's polar axis of rotation about its precessional motion. It ranges from +0.8 to +1.2 seconds. Also known as → nutation in right ascension.

→ equation; → equinox.

The difference, due to Earth's elliptical orbit and variable orbital velocity, between apparent solar time and mean solar time. It varies throughout the year, and slightly from year to year. At present, it reaches extremes of about -14 minutes in February, and about +16 minutes in November. The equation of time is visually illustrated by an → analemma.

→ equation; → time.

The great circle on the surface of a body formed by the intersection of the surface with the plane passing through the center of the body perpendicular to the axis of rotation. → celestial equator.

From M.L. æquator "equalizer" (of day and night, as when the sun crosses the equator), from æquare "to make equal, equate" + -tor.

Hamugâr, from hamug, → equal + -âr suffix forming agent nous (as in parastâr) or contracted present stem of âvardan "to bring; to cause, to produce."

An imaginary plane → perpendicular to the → axis of a → sphere dividing the sphere into two congruent parts.

→ equator; → plane.

A set of celestial coordinates based on the celestial equator as the primary great circle. The coordinates are → declination and → right ascension.

→ equator; → system.

Of, pertaining to, or near an equator, especially the equator of the Earth.

From → equator + -ial, variant of → -al.

Hamugâri, from hamugâr, → equator, + adj. suffix -i.