Expansionsfart

Expansionsfart is a term used to describe the rate at which the size of a system increases due to an expansion process. In practice, it is expressed as a speed or as the time derivative of a characteristic length, and it can be context-dependent, taking different mathematical forms in cosmology, materials science, or mathematical modeling. The term is not standard in most technical literatures, but it appears in some German- and Danish-language sources as a direct translation of the more common phrase expansion rate or expansion velocity.

In cosmology, the expansion rate of space is commonly described by the Hubble parameter H = (1/a) da/dt, where a(t) is the scale factor. Expansionsfart can be used informally to refer to da/dt or H, depending on normalization. In other domains, such as simulative growth models, expansionsfart may refer to the rate at which a simulated region grows with time or the rate at which a physical foam or crystal expands after a change in conditions.

Measurement relies on time-resolved observations or simulations. In cosmology, distances and redshifts yield H0, constraining expansionsfart of the universe. In materials science, imaging methods quantify growth rates of domains or voids. Anisotropic expansions are described by tensorial rates rather than a single scalar.

See also expansion rate, Hubble constant, scale factor, inflation, growth rate, expansion velocity.