In physics, the Planck time (t_P), is the natural unit of time. Eponymously termed for Max Planck, it is considered to be the smallest possible interval of time.

$t\_P\; =\; \backslash sqrt\{\backslash frac\{\backslash hbar\; G\}\{c^5\}\}\; \backslash approx$ 5.39121(40) × 10⁻⁴⁴ seconds

where:

$\backslash hbar$ is the reduced Planck constant (h / 2π which is also called Dirac's constant)

G is the gravitational constant

c is the speed of light in a vacuum

The two digits between the parentheses denote the uncertainty (standard deviation) in the last two digits of the value. The Planck time is the time it would take a photon travelling at the speed of light to cross a distance equal to the Planck length, and is thus considered to be a "quantum of time".

The estimated age of the Universe in the big-bang theory (4.3 × 10¹⁷ s) would be roughly 8 × 10⁶⁰ Planck times.

External links

• Shortest time interval measured - coverage of 2004 event on BBC news.
• Fastest view of molecular motion - BBC news.

See also

• Planck epoch

Natural units | Units of time | Physical constants

Temps de Planck | Tiempo de Planck | Temps de Planck | Tempo di Planck | Tempus planckianum | Planck-idő | Plancktijd | プランク時間 | Planck-tid | Plancktid | Czas Plancka | Planckin aika | Thời gian Planck | 蒲朗克時間