Physical constant

In science, a physical constant is a physical quantity whose numerical value does not change.

Related Topics:
Science - Physical

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It can be contrasted with a mathematical constant, which is a fixed value that does not directly involve a physical measurement.

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There are many physical constants in science, some of the most famous being Planck's constant, the gravitational constant, and Avogadro's number. Constants can take many forms: the Planck length represents a fundamental physical distance; the speed of light in a vacuum signifies a maximum speed limit of the universe; and the fine-structure constant, which characterizes the interaction between electrons and photons, is dimensionless.

Related Topics:
Planck's constant - Gravitational constant - Avogadro's number - Planck length - Speed of light - Universe - Fine-structure constant - Electrons - Photons

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Beginning with Paul Dirac in 1937, some scientists have speculated that physical constants may actually decrease in proportion to the age of the universe. Scientific experiments have not yet pinpointed any definite evidence that this is the case, although they have placed upper bounds on the maximum possible relative change per year at very small amounts (roughly 10-5 per year for the fine structure constant lpha ,! and 10-11 for the gravitational constant G ,!).

Related Topics:
Paul Dirac - 1937

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Some "constants" are really artifacts of the unit system used, such as SI or cgs. In natural units, some of these supposedly physical constants turn out to be conversion factors.

Related Topics:
SI - Cgs - Natural units

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Constants that are independent of systems of units are typically dimensionless numbers, and are known as fundamental physical constants.

Related Topics:
Dimensionless number - Fundamental physical constant

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Some believe that if the physical constants had slightly different values, our universe would be so different that intelligent life would probably not have emerged, and that our universe seems to be fine-tuned for intelligent life.

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