What is Planck time?

Planck time is a unit of time representing the smallest meaningful duration that can be measured, roughly equivalent to 5.4 x 10^-44 seconds. It's defined as the time it takes light to travel one Planck length in a vacuum. This unit is derived from fundamental constants like the speed of light, the gravitational constant, and Planck's constant. Planck time is roughly 10−43 seconds. However, to date, the smallest time interval that was measured was 10−21 seconds, a "zeptosecond." One Planck time is the time it would take a photon travelling at the speed of light to cross a distance equal to one Planck length.

The shorter the wavelength of the photon, the smaller the object that photon can interact with — if it can't interact, you can't detect it. The Planck length is so short that we could never create a photon with a short enough wavelength to interact with it — therefore, we can never measure anything smaller than it.

The smallest measurement of length is the 'Planck length,' named after Max Planck. It is approximately equal to 1.6 x 10-35 meters. It is so small that it is about 10-20 times the size of a proton. In other words, it is a millionth of a billionth of a billionth of a billionth of a centimeter!