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

The incompatibility between → Galilean relativity and Mawxell's theory of → electromagnetism. Maxwell demonstrated that electrical and magnetic fields propagate as waves in space. The propagation speed of these waves in a vacuum is given by the expression c = (ε₀.μ₀)^-0.5, where ε₀ is the electric → permittivity and μ₀ is the magnetic → permeability, both → physical constants. Maxwell noticed that this value corresponds exactly to the → speed of light in vacuum. This implies, however, that the speed of light must also be a universal constant, just as are the electrical and the magnetic field constants! The problem is that → Maxwell's equations do not relate this velocity to an absolute background and specify no → reference frame against which it is measured. If we accept that the principle of relativity not only applies to mechanics, then it must also be true that Maxwell's equations apply in any → inertial frame, with the same values for the universal constants. Therefore, the speed of light should be independent of the movement of its source. This, however, contradicts the vector addition of velocities, which is a verified principle within → Newtonian mechanics. Einstein was bold enough to conclude that the principle of Newtonian relativity and Maxwell's theory of electromagnetism are incompatible! In other words, the → Galilean transformation and the → Newtonian relativity principle based on this transformation were wrong. There exists, therefore, a new relativity principle, → Einsteinian relativity, for both mechanics and electrodynamics that is based on the → Lorentz transformation.

→ Newton; → Maxwell; → incompatibility.

A method for finding roots of a → polynomial that makes explicit use of the → derivative of the function. It uses → iteration to continually improve the accuracy of the estimated root. If f(x) has a → simple root near x_n then a closer estimate to the root is x_n + 1 where x_n + 1 = x_n - f(x_n)/f'(x_n). The iteration begins with an initial estimate of the root, x₀, and continues to find x₁, x₂, . . . until a suitably accurate estimate of the position of the root is obtained. Also called → Newton's method.

→ Newton found the method in 1671, but it was not actually published until 1736; Joseph Raphson (1648-1715), English mathematician, independently published the method in 1690.

A prefix meaning "not."

From O.Fr. non-, from L. non "not," from Old L. noenum "not one;" in some cases perhaps from M.E. non "not" (adj.), from O.E. nan.

Nâ- "no, not," variants na, ni, ma- (prohibitive) "not;" from Mid.Pers. nê, ma "no, not;" O.Pers. naiy, nai "not;" Av. nôit, naē "not;" cf. Skt. ná "not;" cf. L. ne-, in-, un-; Gk. ni; Lith. nè; O.C.S. ne "not;" PIE *ne-.

A → transcendental function. Examples are: exponential, logarithmic, and trigonometric functions.

→ non-; → algebraic + → function.

→ Dark matter composed of → non-baryonic particles.

→ non-; → baryonic; → dark; → matter.

Matter that, unlike the ordinary matter, is not made of baryons (including the neutrons and protons). It is proposed as a possible constituent of dark matter.

→ non-; → baryonic matter.

Radiation having waves that are out of phase in space and/or time; radiation which is not → coherent.

→ non-; → coherent; → radiation.

Describing a → proposition that is either → true in every possible circumstance or → false in every possible circumstance. A proposition that is not → contingent.

→ non-; → contingent.

A medium in which the → phase velocity is independent of frequency.

→ non-; → dispersive; → medium.

Any of several geometries which do not follow the postulates and results of Euclidean geometry. For example, in a non-Euclidean geometry through a point several lines can be drawn parallel to another line. Or, the sum of the interior angles of a triangle differs from 180 degrees. According to Einstein's general relativity theory, gravity distorts space into a non-Euclidean geometry.

→ non-; → Euclidean geometry.

A → multiple star system that lacks the characteristics of a → hierarchical multiple system.

→ non-; → hierarchical; → multiple; → system.

A → magnetohydrodynamics approach dealing with → plasmas which is an improvement with respect to → ideal magnetohydrodynamics. Non-ideal magnetohydrodynamics allows for a drift between particles, redistributing the → magnetic flux and acting on both the → angular momentum and magnetic flux conservation issues.

→ non-→ ideal; → magnetohydrodynamics.

Any frame of reference in which the law of inertia does not apply, such as in accelerating and rotating frames. For example, the Earth is a non-inertial frame because it is rotating about its axis. But the rotation is so slow that the associated acceleration is negligible compared to other accelerations commonly encountered in everyday life. However, the non-inertial nature of the Earth appears in, e.g., the → Coriolis effect. → inertial reference frame.

→ non-; → inertial; → frame.

Not ionized, → neutral.

→ non-; → ionized.

A physical condition in which the assumption of the → local thermodynamic equilibrium does not hold.

→ non-; → local thermodynamic equilibrium.

Not ordinary matter. Same as → dark matter.

→ non-; → luminous; → matter.

A → tumbling motion of an → asteroid. See also → tumbling asteroid.

→ non-; → principal axis; → rotational; → motion.

A type of stellar pulsation in which waves run in different directions on and beneath the surface of a star.

→ non-; → radial; → pulsation.

An process in which an excited state returns to the ground state without emitting radiation. → radiative process.

→ non-; → radiative; → process.

Not concerned with or based on the → theory of relativity. See also:
→ non-relativistic electron, → non-relativistic mechanics, → relativistic.

→ non-; → relativistic.