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

Lack of symmetry; not symmetrical.

Gk. asymmetria "lack of proportion," from asymmetros "ill-proportioned," from → a- "not" + symmetros "commensurable, symmetrical."

Nâhamâmuni, from nâ- "not" + hamâmuni "symmetry," from ham- "together = syn" + -â-, euphonic affix, + mun "measure" + -i, noun affix.

A symmetry with respect to a line. A geometric configuration is said to have axial symmetry if it remains unchanged when rotated about a given line.

→ axial; → symmetry.

Same as → axial symmetry.

The observation that in the present → Universe there is → matter but not much → antimatter. Observations do not show the presence of galaxies made of antimatter, nor gamma rays are observed that would be produced if large entities of antimatter would undergo → annihilation with matter. However, the → early Universe could have been baryon symmetric, and for some reason the matter excess has been generated, through some process called → baryogenesis. → Sakharov conditions.

→ baryon; → asymmetry.

Same as → charge conjugation and → charge symmetry.

→ charge; → symmetry.

Same as → charge conjugation and → C-symmetry.

→ charge; → symmetry.

The laws of physics should be the same if a particle is interchanged with its → antiparticle (→ charge conjugation), or swapped for its mirror image (→ parity symmetry). It is known that charge-parity (CP) symmetry holds for interactions involving → electromagnetism, → gravitation, and → strong interactions, but CP violation is known to occur during → weak interactions involved in → radio decay. Same as → CP-symmetry.

→ charge; → parity; → symmetry.

Same as → charge-parity symmetry.

→ charge; → parity; → symmetry.

Absence or lack of symmetry

From → dis- + → symmetry.

Nâhmâmuni, from nâ- "non, un-," → a- + hmâmuni→ symmetry.

A principle underlying the quantum-mechanical description of the three non-gravitational forces. It allows a system to behave in the same way even though it has undergone various transformations. The earliest physical theory which had a gauge symmetry was Maxwell's electrodynamics.

→ gauge; → symmetry.

Same as → parity symmetry.

→ parity; → symmetry.

The invariance of physical laws under a transformation that changes the sign of the space coordinates. Parity symmetry is sometimes called mirror symmetry. It is known that the parity symmetry is violated in some weak interactions, while it is well preserved in all other three interactions (gravitational, electromagnetic, strong). Same as → P-symmetry and → parity conservation.

→ parity; → symmetry.

A configuration in which the constituting parts are arranged concentrically around the center of a sphere.

→ spherical; → symmetry.

A physical phenomenon whereby a symmetric system becomes permanently asymmetric. A simple example is a ball lying on top of a hill in equilibrium. The hill-ball system is symmetric about the vertical axis through the top of the hill. Moreover, there is no preferred horizontal direction to the system. However, its state is unstable, since the slightest perturbing force will cause the ball to roll down the hill in some particular direction. The system becomes permanently asymmetric because the ball will not roll uphill by itself. Symmetry breaking is found in several fields of physics, for example in → magnetism (→ ferromagnetism), → thermodynamics (→ crystallization), and → particle physics, where it constitutes the basis of → electroweak interactions. In cosmology, according to the → Big Bang model, the fundamental forces of the Universe split off from one another in a form of spontaneous symmetry braking. If a single, unified force existed with a certain symmetry just after the Big Bang, if that symmetry were somehow broken so that the unified force were fractured, then the result might be several fundamental forces. See also → grand unified theory, → theory of everything, → phase transition.

→ spontaneous; → symmetry; → break.

A class of theories that seek to unify the four fundamental forces of nature. It proposes symmetrical relationships linking fermions and bosons (particles of half integer spin, like electrons, protons, and neutrinos) with particles of integral spin (like photons and gluons).

→ super; → symmetry.

1) A quality of a geometric figure that has exactly similar parts with respect to a point, a line, or a plane of its own.
2) A geometric transformation that does not alter neither the shape nor the size of a figure.
3) A property of a mathematical function whose value does not change when its variables are interchanged.
4) Of physical phenomena, the property of remaining invariant under certain changes (as of rotation, reflection, inversion in space, the sign of the electric charge, parity, or the direction of time flow). See also → Noether's theorem.
See also:
→ asymmetry, → axial symmetry, → axisymmetry, → baryon asymmetry, → charge-parity symmetry, → dissymmetry, → gauge symmetry, → parity symmetry, → spherical symmetry, → spontaneous symmetry breaking, → supersymmetry, → symmetry group, → T-symmetry.

From L. symmetria, from Gk. symmetria "agreement in dimensions, due proportion, arrangement," from symmetros "having a common measure, even, proportionate," from → syn- "together" + metron "meter;" PIE base *me- "to measure;" cf. O.Pers., Av. mā- "to measure;" Skt. mati "measures;" L. metri "to measure."

Hamâmun from ham-, → syn- "together," + -â- epenthetic vowel + mun, variant mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," from O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure."

A group of symmetry-preserving operations composed of all rigid motions or similarity transformations of some geometric object onto itself.

→ symmetry; → group.

The symmetry of physical laws under a time reversal transformation.

T for → time; → symmetry.