Planck energy
Template:More citations needed In physics, Planck energy, denoted by Template:Math, is the unit of energy in the system of natural units known as Planck units.[1]
Template:Math is a derived, as opposed to basic, Planck unit. It is defined by:
where Template:Math is the speed of light in a vacuum, Template:Math is the reduced Planck's constant, and Template:Math is the gravitational constant.
Substituting values for the various components in this definition gives the approximate equivalent value of this unit in terms of other units of energy:
An equivalent definition is:
where Template:Math is the Planck time.
Also:
where Template:Math is the Planck mass.
The ultra-high-energy cosmic ray observed in 1991 had a measured energy of about 50 joules, equivalent to about 2.5×10−8 Template:Math.[2] Theoretically, the highest energy photon carries precisely 1 Template:Math of energy (see Ultra-high-energy gamma ray). Most Planck units are extremely small, as in the case of Planck length or Planck time, or extremely large, as in the case of Planck temperature or Planck acceleration. For comparison, the Planck energy is approximately equal to the energy stored in an automobile gas tank (57.2 L of gasoline at 34.2 MJ/L of chemical energy).
Planck units are designed to normalize the physical constants Template:Math, Template:Math and Template:Math to 1. Hence given Planck units, the mass-energy equivalence Template:Math simplifies to Template:Math, so that the Planck energy and mass are numerically identical. In the equations of general relativity, Template:Math is often multiplied by 4π. Hence writings in particle physics and physical cosmology often normalize Template:Math to 1. This normalization results in the reduced Planck energy, defined as:
See also
Template:Planck's natural units Template:Portal bar