# Dictionary

## Planck time

Natural interval of time that can be obtained by combining the fundamental natural constants that govern spacetime, the strength of gravity and the quantum world: the gravitational constant, Planck’s constant and the speed of light. It amounts to about 5·10^{-44 }seconds [see exponential notation] and is the time it takes light to traverse one Planck length’s worth of distance.

At such time scales – for instance: at cosmic time comparable to the Planck time in the big bang models – both the effects of quantum theory and those of general relativity should become important, in short: such time intervals and what happens in them can only be described adequately using a theory of quantum gravity.

Compare: Planck length, Planck energy, Planck mass.