An Etymological Dictionary of Astronomy and Astrophysics
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A potential φ defined so that the → electric field  E is expressed by a combination of its → gradient and the variation of the → magnetic vector potential over time: E = -∇φ -∂A/∂t.

→ electric; → scalar; → potential.

The simplest curvature invariant for a → Riemannian manifold. It is derived from the → Ricci tensor R_μν ≡  R^α_μαν by contracting indices. Taking the trace of the Ricci tensor gives the Ricci scalar: R ≡ R_μνg^μnu; = R^μ_ν = R^αμ_αμ. Also called → scalar curvature.

→ Ricci tensor; → scalar.

Any quantity which is sufficiently defined only with its magnitude, when given in appropriate units. Compare → vector.
See also:
→ electric scalar potential, → scalar field, → scalar potential, → scalar processor, → scalar product, → scalar wave, → scalar-tensor theory, → tensor-vector-scalar (TeVeS) theory.

Of or pertaining to → scale.

A → tensor density of → order 0.

→ scalar; → density.

A → field whose value at every point of space is independent of → direction and → position. Examples include → temperature distribution throughout space and → pressure distribution in a → fluid. Similarly, a → potential field, such as the Newtonian → gravitational field or the electric potential in → electrostatics are scalar fields. In quantum field theory, a scalar field is associated with → spin zero particles, such as → mesons or → bosons. Therefore, the → Higgs boson is associated with a scalar field. The → derivative of a scalar field results in a → vector field is called the → gradient. In contrast to a vector field, a scalar field is → invariant under the → rotation of the → coordinate system. The → inflation in the → early Universe is supposed to be driven by a scalar field, called the → inflaton field.

→ scalar; → field.

The energy density fluctuations in the → photon-baryon plasma that bring about hotter and colder regions. This perturbation creates velocity distributions that are out of phase with the acoustic density mode. The fluid velocity from hot to cold regions causes blueshift of the photons, resulting in → quadrupole anisotropy.

→ scalar; → perturbation.

Computers: A type of central processing unit in which only one operation on data is executed at a time. By contrast, in a vector processor, a single instruction operates simultaneously on multiple data items.

→ scalar; → processor.

A multiplication of two vectors giving a scalar. The scaler product of V₁ and V₂ is defined by: V₁.V₂ = V₁.V₂ cos α, where V₁ and V₂ are the magnitudes of the vectors and α is the angle between them. Same as dot product. See also → vector product.

→ scalar; → product.

In theories of gravitation, a kind of → gravitational wave, transversal and/or longitudinal, characterized by → spin zero.

→ scalar; → wave.

An alternative to the standard → general relativity of gravity that contains not only the → tensor field (or → metric), but also a → scalar field. In this formalism, the → gravitational constant is considered to vary over time. As a consequence, the measured strength of the gravitational interaction is a function of time. Same as → Jordan-Brans-Dicke theory.

→ scalar; → tensor; → theory.

A theory put forward to provide a basis for a relativistic generalization of the → MOdified Newtonian Dynamics (MOND) paradigm. TeVeS is based on three dynamical fields: a tensor field, a vector field, and a scalar field. In contrast to general relativity, it has two metrics, an Einstein metric and a physical metric. TeVeS has attracted considerable attention, since it can explain many galactic and cosmological observations without the need for → dark matter. Proposed by J. D. Bekenstein, 2004, "Relativistic gravitation theory for the modified Newtonian dynamics paradigm", Phys. Rev. D, 70, 083509, arXiv:astro-ph/0403694.

→ tensor; → vector; → scalar; → theory.