tânsor-e Einstein (#)
Fr.: tenseur d'Einstein
A mathematical entity describing the → curvature of → space-time in → Einstein's field equations, according to the theory of → general relativity. It is expressed by Gμν = Rμν - (1/2) gμνR, where Rμν is the Ricci tensor, gμν is the → metric tensor, and R the scalar curvature. This tensor is both symmetric and divergence free.
Named after Albert Einstein (1879-1955); → tensor.
marpel-e zamâni-ye Einstein
Fr.: échelle de temps d'Einstein
The time during which a → microlensing event occurs. It is given by the equation tE = RE/v, where RE is the → Einstein radius, v is the magnitude of the relative transverse velocity between source and lens projected onto the lens plane. The characteristic time-scale of → microlensing events is about 25 days.
Fr.: ascenseur d'Einstein
A → thought experiment, involving an elevator, first conceived by Einstein to show the → principle of equivalence. According to this experiment, it is impossible for an observer situated inside a closed elevator to decide if the elevator is being pulled upward by a constant force or is subject to a gravitational field acting downward on a stationary elevator. Einstein used this experiment and the principle of equivalence to deduce the bending of light by the force of gravity.
Bâlâbar, → lift.
Einstein's field equations
hamugešhâ-ye meydân-e Einstein
Fr.: équations de champ d'Einstein
A system of ten non-linear → partial differential equations in the theory of → general relativity which relate the curvature of → space-time with the distribution of matter-energy. They have the form: Gμν = -κ Tμν, where Gμν is the → Einstein tensor (a function of the → metric tensor), κ is a coupling constant called the → Einstein gravitational constant, and Tμν is the → energy-momentum tensor. The field equations mean that the curvature of space-time is due to the distribution of mass-energy in space. A more general form of the field equations proposed by Einstein is: Gμν + Λgμν = - κTμν, where Λ is the → cosmological constant.
Einstein's gravitational constant
pâyâ-ye gerâneši-ye Einstein (#)
Fr.: constante gravitationnelle d'Einstein
Einstein's theory of specific heat
negare-ye garmâ-ye âbize-ye Einstein
Fr.: théorie de la chaleur spécifique d'Einstein
Same as → Einstein model.
Einstein-de Sitter effect
oskar-e Einstein-de Sitter
Fr.: effet Einstein-de Sitter
Same as → geodetic precession.
Einstein-de Sitter Universe
giti-ye Einstein-de Sitter
Fr.: Univers Einstein-de Sitter
The → Friedmann-Lemaitre model of → expanding Universe that only contains matter and in which space is → Euclidean (ΩM > 0, ΩR = 0, ΩΛ = 0, k = 0). The Universe will expand at a decreasing rate for ever.
Fr.: action de Einstein-Hilbert
Fr.: paradoxe Einstein-Podolsky-Rosen
→ EPR paradox.
A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Phys. Rev. 41, 777 (15 May 1935); → paradox.
Fr.: pont d'Einstein-Rosen
A hypothetical structure that can join two distant regions of → space-time through a tunnel-like shortcut, as predicted by → general relativity. The Einstein-Rosen bridge is based on the → Schwarzschild solution of → Einstein's field equations. It is the simplest type of → wormholes.
Albert Einstein & Nathan Rosen (1935, Phys.Rev. 48, 73); → bridge.
Fr.: relativité einsteinienne
The laws of physics are the same in all → inertial reference frames and are invariant under the → Lorentz transformation. The → speed of light is a → physical constant, i.e. it is the same for all observers in uniform motion. Einsteinian relativity is prompted by the → Newton-Maxwell incompatibility. See also: → Galilean relativity, → Newtonian relativity.
A radioactive metallic → transuranium element belonging to the → actinides; symbol Es. → Atomic number 99, → mass number of most stable → isotope 254 (→ half-life 270 days). Eleven isotopes are known. The element was first identified by A. Ghiorso and collaborators in the debris of first hydrogen bomb explosion in 1952.
To throw out material, for example by a massive star through stellar wind, or by a volcano in eruption.
From L. ejectus, p.p. of eicere "to throw out," from → ex- "out" + -icere, comb. form of jacere "to throw."
Ešândan, from Hamadâni ešândan "to throw out;" Pashto aestal, wištal "to throw, project;" Laki owštan "to throw, to shoot (with bow and arrow);" Lori šane "throwing," šane kerde "to throw;" Av. ah- "to throw," pres. ahya- "throws," asta- "thrown, shot," astar- "thrower, shooter;" cf. Khotanese ah- "to throw, shoot," Skt. as- "to throw, shoot," ásyati "throws," ásana- "throw, shot."
Material, in solid, liquid, or gaseous form, thrown out by a body, especially as a result of → volcanic eruption, → meteoritic impact, or → supernova explosion. See also: → ejecta blanket, → supernova ejecta.
Plural of L. ejectus, → eject.
Ešânâk "that which is ejected," from šân present stem of šândan→ eject + suffix -âk.
Fr.: couverture d'éjecta
Act or instance of ejecting; the state of being ejected.
Verbal noun of → eject.
Fr.: couche d'Ekman
A kind of viscous → boundary layer in a rotating fluid system. Such a layer forms over a flat bottom that exerts a frictional → stress against the flow, bringing the velocity gradually to zero within the layer above the bottom. An Ekman layer occurs also on the fluid surface whenever there is a horizontal frictional stress, for example along ocean surface, when waters are subject to wind stress.
Named for Vagn Walfrid Ekman (1874-1954), Swedish oceanographer, who studied the phenomenon originally in his doctoral thesis (1902) and later developed it (1905, 1906); → layer.
Fr.: nombre d'Ekman
A → dimensionless quantity that measures the strength of → viscous forces relative to the → Coriolis force in a rotating fluid. It is given by Ek = ν/(ΩH2), where ν is the → kinematic viscosity of the fluid, Ω is the → angular velocity, and H is the depth scale of the motion. The Ekman number is usually used in describing geophysical phenomena in the oceans and atmosphere. Typical geophysical flows, as well as laboratory experiments, yield very small Ekman numbers. For example, in the ocean at mid-latitudes, motions with a viscosity of 10-2 m2/s are characterized by an Ekman number of about 10-4.
Fr.: Univers ekpyrotique
A cosmological model in which the → Big Bang is not the beginning of the → Universe, but a transitory phase in a more global scenario. The ekpyrotic Universe model is fundamentally different from the → standard cosmology and offers radically different explanations for the cosmological problems (→ homogeneity, → isotropy, → flatness, → magnetic monopoles, etc.). In this highly speculative model → space-time has five dimensions, four spatial and one temporal. Two three-dimensional → branes, one visible and one hidden, collide following the contraction of the extra dimension. The contraction produces a blue shift effect that converts gravitational energy into brane kinetic energy. Some fraction of this kinetic energy is converted into matter and radiation that can fuel the Big Bang. The movement of the hidden brane prior to the collision is under the influence of a potential created by the exchange of appropriate M-theory fields between the branes. The resulting temperature is finite, so the hot Big Bang phase begins without a → singularity. The Universe is homogeneous because the collision and initiation of the Big Bang phase occur nearly simultaneously everywhere. The energetically preferred geometry for the two branes is flat, so their collision produces a flat Big Bang Universe. According to → Einstein's field equations, this means that the total energy density of the Universe is equal to the → critical density. Massive → magnetic monopoles, which are over-abundantly produced in the standard Big Bang theory, are not produced at all in this scenario because the temperature after collision is far too small to produce any of these massive particles. A new version of the model provides the possibility of a cyclic Universe in which the fifth dimension undergoes a cycle of contraction and expansion a number of times, or indefinitely. The Big Bang is therefore not a special event and can happen again and again. Each cycle begins with a Big Bang and ends in a → Big Crunch. At the transition between the Big Crunch and Big Bang, matter and radiation are created, restoring the Universe to the high density required for a new Big Bang phase. In this scenario, the → dark energy that is causing the cosmic acceleration of the Universe today is inter-brane potential energy. Apart from speculation, this model suffers from several fine tunings (J. Khoury et al. 2001, Phys. Rev. D64, 123522 (hep-th/0103239); P. J. Steinhardt & N. Turok, 2002, Phys. Rev. D65, 126003 (hep-th/0111098), and references therein).
Ekpyrotic is inspired by the ancient Stoic doctrine according to which the world ends in a supreme conflagration, called ekpyrosis, and then reborns from the fire (palingenesis), only to be destroyed again at the end of the new cycle; ekpyrosis, from Gk. ek- "out of," → ex-, + → pyro- combining form of pyr, → fire, + -sis a suffix used to form nouns of action, process, state, condition, such as thesis, analysis, catharsis; → Universe.