Radiation Era
The Radiation Era contains the moments after the
big bang and lasted for about 50000 years, during this era there
were no atoms formed or forming and the universe was dominated
by radiation and particles and all four fundamental forces at
the beginning of
this era were unified under what is known as the Grand Unified
Force (GUT) or during the short Planck Epoch it could also have
been known as super gravity.
Planck Epoch
The Planck Epoch is the period of time right after the Big Bang (ending around 10^-43 seconds after the big bang) and thus due to the universe having very little time to expand it was the hottest and densest time for the universe. Physics during the Planck Epoch is very interesting, during this time it is theorized that all four fundamental forces merged into one super force, however, the exact behavior or model of this super force is still unknown.
GUT Epoch
Notable because this is when gravity broke off
from this super force while the strong, weak, and
electromagnetic forces were still one unified force. During this
time the universe experienced a rapid inflation, "in a mere
10^-36 seconds...[the size of the universe was an] atomic
nucleus might have grown to the size of our solar system"
(web.njit.edu). Why did this happen? The transition of gravity,
and towards the end of the GUT era, the strong force was
starting to separate as well which released a lot of energy.
Like the Planck Epoch this ended very quickly, 10^-35 seconds
after the big bang.