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Fr.: abondance primordiale
The relative amount of a light element (e.g. deuterium, lithium, helium) synthesized in the early Universe.
primordial black hole
Fr.: trou noir primordial
A black hole formed following the Big Bang event due to incredibly violent turbulence that squeezed concentrations of matter to high densities. These black holes, first suggested by Stephen Hawking, are expected to have a mass comparable to that of a mountain and a size as small as an atom. Same as → mini black hole.
primordial curvature perturbation
partureš-e xamidegi-ye bonâqâzin
Fr.: perturbation de courbure primordiale
In cosmological models, the phenomenon that is supposed to seed the → cosmic microwave background anisotropies and the structure formation of the Universe.
Fr.: galaxie primordiale
A high redshift, metal-deficient galaxy that formed very early in the history of the Universe.
Fr.: hélium primordial
The helium element created in the → early Universe, around 3 minutes after the → Big Bang, when the temperature dropped to 109 degrees; in contrast to the helium being synthesized in stars. Based on observations of helium → emission lines in → H II regions of metal-poor dwarf galaxies (→ metal-deficient galaxy), the primordial 4He → chemical abundance (by mass) is estimated to be YP = 0.24672 ± 0.00017. Moreover, using observations of a near-pristine → intergalactic cloud, a value of 0.250 +0.033-0.025 has been reached (Cooke & Fumagalli, 2018, Nature Astronomy, 2, 657). The theoretical He abundance predicted by → Big Bang nucleosynthesis is 0.24709 ± 0.00017 (Pitrou et al., 2018, arXiv:1801.08023).
Fr.: nucléosynthèse primordiale
The formation of → chemical elements in the → early Universe, between about 0.01 seconds and 3 minutes after the → Big Bang, when the nuclei of primordial matter collided and fused with one another. Most of the → helium in the → Universe was created by this process. Same as → Big Bang nucleosynthesis
First or highest in rank, importance, value, etc. See also → main.
M.E., from O.Fr. principal, from L. principalis "first in importance," from princeps "first, chief, prince," literally "that takes first," from primus "first" + root of capere "to take."
Farin literally "foremost," from far-, Mid.Pers. fra-; O.Pers. fra- "forward, forth;" Av. frā "forth," pouruua- "first;" cf. Skt. pūrva- "first," pra- "before, formerly;" Gk. pro; L. pro; O.E. fyrst "foremost," superlative of fore, E. fore + -in superlative suffix.
âse-ye farin (#)
Fr.: axe principal
Any imaginary line passing through the center of curvature of a
→ spherical mirror
or → lens and the corresponding geometrical center.
Principal axis is perpendicular
to the mirror or lens at the pole.
Rays of light parallel to the principal axis of a
→ concave mirror
will appear to converge on a point in front of the mirror somewhere
between the mirror's pole and its center of curvature.
Same as → optical axis.
principal quantum number
adad-e kuântomi-ye farin
Fr.: nombre quantique principal
In atomic physics, the first of a set of quantum numbers which describe an atomic orbital. Symbolized as n, it characterizes the size and energy of an orbital.
A fundamental, primary assumption, or general law from which others are derived.
From M.E., from O.Fr. principe, from L. principium "a beginning, first part," from princeps "first, chief, prince," literally "that takes first," from primus "first" + root of capere "to take."
Parvaz "origin, root, stock" (as used in particular by Ferdowsi); cf. Av. fra-vāza- "drawing from; leading onward," from Av. fra-, frā- "before; forward, forth" (fratəma- "first, front," pouruua- "first," fra-cara- "preceding;" O.Pers. fra- "forward, forth;" Mid.Pers. fra-; cf. Skt. pra- "before, formerly," prathama- "earliest, initial," pūrva- "first;" Gk. pro; L. pro; O.E. fyrst "foremost," superlative of fore) + vaz- "to draw, guide; bring; possess; fly; float," vazaiti "guides, leads" (cf. Skt. vah- "to carry, drive, convey," vahati "carries," pravaha- "bearing along, carrying," pravāha- "running water, stream, river;" L. vehere "to carry;" O.E. wegan "to carry;" O.N. vegr; O.H.G. weg "way," wegan "to move," wagan "cart;" M.Du. wagen "wagon;" PIE base *wegh- "to drive;" see also → flight).
principle of action and reaction
parvaz-e žireš va vâžireš, ~ koneš va vâkoneš
Fr.: principe d'action et de réaction
Newton's third law of motion, which states that for every action there must be an equal and opposite reaction.
principle of constancy
parvaz-e pâyâyi tondi-ye nur
Fr.: principe de la constance de la vitesse de la lumière
The second postulate in Einstein's theory of → special relativity whereby the → velocity of light in → vacuum has the same absolute value in all → inertial reference frames irrespective of the direction and speed of propagation of the light source. It should be emphasized that this constancy of the speed of light holds among → reference frames moving uniformly with respect to each other. An observer accelerated with respect to a light source will measure a speed of light that is smaller than the speed of light measured in a → rest frame. See also → principle of relativity.
principle of covariance
Fr.: principe de covariance
In special relativity, the principle that the laws of physics take the same mathematical form in all inertial frames of reference.
principle of equivalence
Fr.: principe d'équivalence
In → general relativity the principle which states that in the immediate proximity of an → accelerating system the acceleration is physically equivalent to → gravitational force. This principle also implies the equivalence of → gravitational mass and → inertial mass. Same as the → equivalence principle. See also → Einstein's elevator.
principle of excluded middle
parvaz-e miyâni sokalândé
Fr.: principe du milieu exclu, ~ ~ tiers ~
The second principle of → formal logic introduced in Aristotle's theory of the → syllogism: A statement is either → true or → false. In other words, two → contradictory → propositions cannot both be true. The truth of one implies the falsehood of the other. Also called law of excluded middle and → principle of excluded third.
principle of excluded third
parvaz-e sevomi sokalândé
Fr.: principe du tiers exclu
Same as → principle of excluded middle.
principle of identity
Fr.: principe d'identité
principle of least action
parvaz-e kamtarin žireš, ~ ~ koneš
Fr.: principe de moindre action
The principle that, for a system whose total mechanical energy is conserved, the path to be taken for the system from one configuration to another is the one whose action has the least value relative to all other possible paths and from the same configurations. Also called Maupertuis' principle, least-action principle.
principle of non-contradiction
Fr.: principe de non-contradiction
principle of relativistic causality
parvaz-e bonârmandi-ye bâzânigi-mand
Fr.: principe de la causalité relativiste
One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.