Metrica
A tensor that defines space-time intervals and scalar products. Its components depend on coordinates, but the physical interval does not.
Go deeper into the topic →CONCEPT INDEX / 30 TERMS
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Brief definitions for reading complex texts. Not only the name, but also the meaning, limitations and transition to the educational article.
30 from 30 concepts
Geodetic
A curve whose tangent vector is parallel to itself. For a free test particle, this is an idealized trajectory without non-gravitational forces.
Go deeper into the topic →Curvature
A geometric property manifested in geodetic deviation. Differs from the visual curvature of the drawn surface.
Go deeper into the topic →Event Horizon
The boundary of the region from which light signals do not reach future infinity in the corresponding global formulation. Not the surface of the substance.
Go deeper into the topic →ISCO
The inner boundary of stable circular orbits of test particles in the chosen metric. Depends on the rotation and orientation of the orbit.
Go deeper into the topic →Accretion
The flow of matter to a compact object with the transfer of angular momentum and the release of energy. The disk does not have to be thin and stationary.
Go deeper into the topic →Black hole shadow
A dark area against the background of emitting gas associated with the capture and strong deflection of light. Not an image of a hard surface.
Go deeper into the topic →Quasar
Luminous active galactic nucleus. Not a "quasi-black hole": that's a different concept.
Go deeper into the topic →Spin a*
Dimensionless parameter Jc/(GM²) in the ideal Kerr metric. The rendering parameter is not the automatically measured spin of the object.
Go deeper into the topic →Eddington luminosity
Characteristic luminosity from the balance of radiation and gravitational forces for a given geometry and opacity. Not a universal hard ceiling for all flows.
Go deeper into the topic →Semiclassical approximation
Classical geometry interacts with the quantum average of the energy-momentum tensor. The geometry itself is not quantized.
Go deeper into the topic →Backreaction
The influence of fields and their quantum averages on geometry. Calculation on a fixed background is not equal to a self-consistent problem.
Go deeper into the topic →Renormalization
The procedure for determining finite observables taking into account counterterms and normalization conditions. No arbitrary deletion of inconvenient results.
Go deeper into the topic →Hadamard state
A state with the correct local short-distance structure of the two-point function necessary to determine the local renormalized observables.
Go deeper into the topic →Hawking effect
Quantum radiation in geometry with a horizon in a suitable formulation. Not direct classical radiation from the horizon surface.
Go deeper into the topic →Unruh effect
Thermal response of an ideal uniformly accelerated detector in a Minkowski vacuum. Differs from Hawking in physical staging.
Go deeper into the topic →QEI
Quantum energy inequalities for averaged energy densities. The lower bound depends on the field, geometry, state and test function.
Go deeper into the topic →NEC
Zero energy condition: Tμν kμ kν ≥ 0 for the zero vector. Can be disrupted by quantum states.
Go deeper into the topic →Flare-out
Condition for opening the neck in the class of wormholes under consideration. Formal geometry does not prove the existence of such an object in nature.
Go deeper into the topic →Global hyperbolicity
A causal property that supports the correct formulation of evolution with data on the Cauchy surface under the right conditions.
Go deeper into the topic →Tensor
A geometric object with a certain law of transformation of components. An arbitrary array of numbers does not become a tensor just because of the number of indices.
Go deeper into the topic →Connectivity
The rule for comparing tangent vectors at different points and covariant differentiation.
Go deeper into the topic →Numerical convergence
Approximation of the result to the limit when reducing the sampling step in a controlled mode. Does not equal the visual smoothness of the picture.
Go deeper into the topic →Residual
Deviation of a discrete solution from an equation or constraint. A small discrepancy does not eliminate the error in the original physical model.
Go deeper into the topic →Richardson test
Estimation of the order of convergence from results on several grids with a known step ratio. Requires an asymptotic regime.
Go deeper into the topic →FLRW
A family of background cosmological metrics using the homogeneity and isotropy of space. Real structures are described by perturbations.
Go deeper into the topic →Angular distance DA
Cosmological distance relating transverse physical size and observed angle. Differs from luminosity distance.
Go deeper into the topic →Parsec
A unit of distance determined from an astronomical unit and an angular measure. In this version pc=(648000/π) au.
Go deeper into the topic →CODATA
Consistent recommended values of fundamental constants with uncertainties. Precise determinations of SI must be distinguished from experimental estimates.
Go deeper into the topic →J2000
Reference epoch of catalog coordinates. The J2000 map itself does not provide the current visibility of an object above the local horizon.
Go deeper into the topic →Dictionary - introductory editorial navigation. For a strict definition, use the primary sources and mathematical conventions of the relevant study section.