## Planck Energy

• The Planck energy is the unit of energy in the system of Planck units. It has the value:

Ep = 1.96 × 109J

In SI units, measurements of energy are made in Joules (usually given the symbol J). The Joule is convenient for everyday usage, such as measuring the energy produced by eating different types of foods (eating 1 gram of a carbohydrate provides around 16,000 J of energy) or determining the energy requirements of a light globe (a 60 W globe uses 60 J every second). We can also write Joules in terms of the units of length, time and mass:

1 Joule = 1kg m2 s-2

A consequence of SI units is that the fundamental constants take on values that are not always convenient for including in equations:

Speed of lightc = 299792458 m s-1
Gravitational constantG = 6.673(10) x 10-11 m3 kg-1s-2
Plank's constant (reduced) = h/2π = 1.054571596(82) x 10-34 kg m2 s-1
Boltzmann constantk = 1.3806502(24) x 10-23kg m2 s-2K-1

The Planck energy is found using Einstein's famous formula relating energy and mass: Ep = mpc2, with the Planck mass defined as:

By redefining the base units for length, mass and time in terms of the Planck units, the fundamental constants have the values:

c = G = = k = 1.