# Planck temperature

## Description

Planck temperature, denoted by T_{P}, is the unit of temperature in the system of natural units known as Planck units.

It serves as the defining unit of the Planck temperature scale. In this scale the magnitude of the Planck temperature is equal to 1, while that of absolute zero is 0. Other temperatures can be converted to Planck temperature units. For example, 0 °C = 273.15 K = 1.9279*10^{-30} T_{P}.

In SI units, the Planck temperature is about 1.417*10^{32} Kelvin (equivalently, degrees Celsius, since the difference is trivially small at this scale), or 2.55*10^{32} degrees Fahrenheit or Rankine.

**History**

What today is known as the Planck temperature was first introduced in 1899 by Max Planck together with his introduction of what today is known as the Planck length, the Planck mass and Planck time.

**Significance**

As with most of the Planck units, a Planck temperature of 1 (unity) is a fundamental limit of quantum theory, in combination with gravitation, as presently understood. In other words, the wavelength of light emitted by an object can be calculated by its temperature. If an object were to reach the temperature of 1.42*10^{32} Kelvin (T_{P}), the radiation it would emit would have a wavelength of 1.616*10^{-35} m (Planck length), at which point quantum gravitational effects become relevant. At temperatures greater than or equal to T_{P}, current physical theory breaks down because we lack a theory of quantum gravity.

## Variables

T_{p} | Planck temperature (K) |

m_{p} | Planck mass |

c | Speed of light |

k | Boltzmann constant |