The Planck energy is the natural unit of energy, denoted by E_P.

$E\_p\; =\; \backslash sqrt\{\backslash frac\{\backslash hbar\; c^5\}\{G\}\}\; \backslash approx$ 1.956 × 10⁹ J $\backslash approx$ 1.22 × 10¹⁹ GeV $\backslash approx$ 0.5433 MWh

where

$c$ is the speed of light in a vacuum

$\backslash hbar$ is the reduced Planck's constant

$G$ is the gravitational constant

The Planck energy is equivalent with the Planck mass - in terms of energy-mass equivalence -, corresponding to about the mass of a small flea. The Planck energy equals approximately the electricity consumed by an average person in 12 weeks, or by an average US citizen in two weeks (2001 figures). The Oh-My-God particle observed in 1991 with some 50 joules contained about 25 billionths of the Planck energy.

While the Planck energy equals an already macroscopic amount of energy, it is nevertheless thought to be an important quantity in particle physics - as soon as gravitation is taken into account. The Planck energy is not only the energy (in principle) necessary to probe the Planck length, but it is probably also the maximum energy that can fit into a region of that scale - which in this case will immediately collapse to a (very hot) Black Hole.

Particle physicists and cosmologists often use the reduced Planck energy, which is

$\backslash sqrt\{\backslash frac\{\backslash hbar\{\}c^5\}\{8\backslash pi\; G\}\}$ ≈ 0.390 × 10⁹ J ≈ 2.43 × 10¹⁸ GeV

Including the additional factor of 8π simplifies several equations in gravity.

See also

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• Planck's constant
• Holographic principle

Units of energy | Natural units

Énergie de Planck | Energia di Planck | Planck-energia | Energia Plancka