Planck mass - Definition and Overview

The Planck mass is the natural unit of mass, denoted by m_P.

m_P = (c <math>\hbar<math>/ G)^1/2 ≈ 2.176 × 10^-8 kg = 21.76 µg

where:

c is the speed of light

<math>\hbar<math> is Dirac's constant

G is the gravitational constant

The 2002 CODATA recommended value for the Planck mass is 2.176 45(16) × 10^-8 kg where the part in parentheses indicates the uncertainty in the last digits shown. This is 21.7645 µg ± 0.0016 µg.

Unlike most of the other Planck units, the Planck mass is on an approximately human scale, being roughly the mass of some fleas. The issue is that general relativity predicts that smaller black holes can exist within an event horizon of radius less than the Planck length, while quantum mechanics predicts that the mass would probably be outside the event horizon.

See also

• Natural units
• Orders of magnitude (mass)
• Planck length
• Planck time

External links

• The NIST Reference on Constants, Units, and Uncertainty (http://physics.nist.gov/cuu/Constants/index.html)

Example Usage of Planck