expansion

Expansion is the process of increasing in size, volume, quantity, or scope. It can refer to physical growth of matter, the growth of a system or economy, or the development of a concept or structure. In many disciplines, expansion is described by rate, drivers, and constraints.

In physics and engineering, expansion describes how materials change size with conditions such as temperature. Thermal expansion occurs when substances expand upon heating, with coefficients of linear, area, or volumetric expansion. Gases may show large expansions with pressure and temperature changes, while solids and liquids have smaller coefficients. Expansion can be restrained by constraints, producing stress.

In cosmology, the expansion of the universe refers to increasing distances between distant galaxies over time, a phenomenon evidenced by redshift and modeled by the metric expansion of space. The rate is described by the Hubble constant and influenced by the energy content of the universe, including dark energy.

In economics, expansion denotes a period of rising economic activity, typically measured by GDP growth, employment, and industrial output. It can be driven by demand, investment, and policy, and ends with a contraction or recession.

In biology and ecology, expansion can describe growth of cells, tissues, populations, or the geographic spread of species. Growth rates depend on resources, genetics, and environmental factors.

In mathematics, expansion refers to representing a function as a series, such as a Taylor or Fourier expansion, or to asymptotic expansions. These tools approximate complex functions near a point or over an interval.

Across fields, expansion involves the addition of new space, capacity, or scope, and is often analyzed in terms of rate, constraints, and impacts on systems and structures.