Lifetime (physics)

Lifetime in physics is the mean time of existence of any member of an assembly of identical physical objects, each instance of which lives for a duration that follows a given distribution of which the mean is the lifetime (sometimes calls for this reason the mean lifetime).

Typically one speaks of lifetime for unstable particles, for which the time elapsed before the disintegration follows the exponential distribution (resulting from the fact that a particle has no memory of its past in regard of its lifetime):

with the associated decay constant (cf. exponential decay). Stated another way, P(t) is the probability that the particle has not yet disintegrated at time t. Therefore, in an assembly of particles, there remains at time t.

Computing the average links the lifetime to the decay constant constant :

The probability for one given atom to disintegrate in any infinitesimal interval of time is .

Another quantity of common use is the half life time , which is the time required for half of the population to disintegrate. It is linked to the lifetime through