The Plank Epoch encompasses the time period from 0 to 10^-43 seconds.
This extremely small unit of time is aptly referred to as a "Plank Time".
Not much is truly known about this period of time, however some very interesting hypothesis have been made.
Einstein's theory of relativity proposes that a gravitational singularity may have existed. In a gravitational singularity, even the laws of quantum physics break down and the four fundamental forces (strong nuclear, weak nuclear, electromagnetic, & gravity) could be unified as one! This is an extremely odd concept to consider. It also ties into the so-called 'Theory of Everything' which states that at high enough energy levels, even gravity will combine back into one unified force with the other three.
During the Plank Era, our universe was only 10^-35 meters wide (VERY small) and 10^32 degrees celsius (VERY hot)!