## Fundamental constants

The Boltzmann constant (k or kB) is the physical constant relating temperature to energy. ...more on Wikipedia about "Boltzmann constant"

The fine-structure constant or Sommerfeld fine-structure constant, usually denoted $\alpha \$, is the fundamental physical constant characterizing the strength of the electromagnetic interaction. It was originally introduced into physics in 1916 by Arnold Sommerfeld, as a measure of the relativistic deviations in atomic spectral lines from the predictions of the Bohr model. ...more on Wikipedia about "Fine-structure constant"

In physics, fundamental physical constants are physical constants that are independent of systems of units and are in general dimensionless numbers. ...more on Wikipedia about "Fundamental physical constant"

The constant of proportionality is called $\left\{G\right\} \$, the gravitational constant, the universal gravitational constant, Newton's constant, and colloquially big G. The gravitational constant is a fundamental physical constant which appears in Newton's law of universal gravitation and in Einstein's theory of general relativity. In some other theories the constant is replaced with a scalar value. See Rosen bi-metric theory of gravity. ...more on Wikipedia about "Gravitational constant"

Planck's constant (denoted h) is a physical constant that is used to describe the sizes of quanta. It plays a central role in the theory of quantum mechanics, and is named after Max Planck, one of the founders of quantum theory. A closely-related quantity is the reduced Planck constant (denoted $\hbar$, pronounced as "h-bar"), which is sometimes called Dirac's constant, after Paul Dirac. ...more on Wikipedia about "Planck's constant"