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Physical constant

Frae Wikipedia, the free beuk o knawledge
(Reguidit frae Pheesical constant)

A physical constant is a physical quantity that is generally believed tae be baith universal in naitur an constant in time. It can be contrasted wi a mathematical constant, which is a fixed numerical value, but daes nae directly involve ony pheesical measurement.

Thare are mony physical constants in science, some o the maist widely recognised bein the speed o licht in vacuum c, the gravitational constant G, Planck's constant h, the electric constant ε0, an the elementary charge e. Pheesical constants can tak mony dimensional furms: the speed o licht signifies a maximum speed leemit o the Universe an is expressed dimensionally as length dividit bi time; while the fine-structur constant α, which characterises the strength o the electromagnetic interaction, is dimensionless.