Constants

A constant is a value that does not change within a given context. In mathematics, constants are fixed numbers or symbols representing fixed quantities. In science and engineering, constants may refer to quantities whose values are universal or defined by convention.

Mathematical constants include pi, e, and the golden ratio. They arise from geometric or algebraic definitions and are independent of units.

Physical constants are quantities that appear in fundamental laws and are experimentally determined. Universal physical constants have the same value everywhere in the universe (within experimental limits). Examples: the speed of light in vacuum c, the Planck constant h, the gravitational constant G, the elementary charge e, and Boltzmann constant k_B.

Some constants are dimensionless, meaning they are pure numbers not dependent on unit choices. Examples: the fine-structure constant α, and ratio-based constants such as electron-to-proton mass.

Constants can be distinguished from variables; constants are fixed across a context, though some constants are defined by convention in units. In computing, constants are values stored and not changed by programs.

The study of constants includes metrology, unit systems, and explorations of possible variations of fundamental constants in physics, though such variations are debated.