A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that cannot be explained by a theory and therefore must be measured experimentally. It is distinct from a See more

Physical constants are parameters in a physical theory that cannot be explained by that theory. This may be due to the apparent … See more

The number of fundamental physical constants depends on the physical theory accepted as "fundamental". Currently, this is the theory of general relativity for gravitation and the See more

Any ratio between physical constants of the same dimensions results in a dimensionless physical constant, for example, the proton-to-electron mass ratio. The fine-structure constant α is the best known dimensionless fundamental physical constant. It … See more

Numerical values
Whereas the physical quantity indicated by a physical constant does not depend on the unit system used … See more

By definition, fundamental physical constants are subject to measurement, so that their being constant (independent on both the time and position of the performance of the measurement) is necessarily an experimental result and subject to verification. See more

Some physicists have explored the notion that if the dimensionless physical constants had sufficiently different values, our Universe would be so radically different that … See more