Max Karl Ernst Ludwig Planck’s (1858-1947) work with black-body radiation is considered today to be the birth of quantum physics. His research in this field led him to create three fundamental units of mass, length, and time. Each of these units demonstrate, quite literally, the smallest measurement you can make of that subject. Planck time is, therefore, the smallest amount of time.
To understand what this means, you must first understand a Planck length (ℓP). Planck length is 1.6 x 10-35 meters. Written out, this number truly begins to reveal it’s small stature:
This is a hundred-million-trillion times smaller than a proton (who’s size is 1.6 x 10-15 meters). But where did he find this absurdly small measurement? From an equation using three fundamental constants: the gravitational constant (G), Planck’s Constant (the reduced Planck’s Constant in the equation ħ), and the speed of light in a vacuum (c).
This is the smallest measurement that will ever be measured, even with advances in technology. A unit of Planck Time is the smallest amount of time that can be measured. It is the amount of time a photon of light takes to travel a Planck Length. Due to the fact that no smaller measurements of length can be made beyond Planck Length, and that nothing can travel faster than light: no smaller amount of time can be measured. It is the basic unit of time itself.
Personally, I like to think that if contact is made with extraterrestrial life, these constants will be used for better communication between two very different societies. Martians are not going to know what a second or a meter is!