There are numerous different ways in which new universes are created.
Reality is the ways conform to the known laws of physics Creating
universes is in process as I type. Yes time in our "baby universe" had
begun at the big bang,but there has always been a multiverse that has
existed eternally. Universes beget other universes. There are as
many universes in the cosmos as flakes of snow in an endless storm. They
are exactly the same right down to the number of electrons. Reason for
that is all universes are created with the precisely the same matter
density,energy,and temperature The dimension(size) the big bang
was at the moment of creation was the Planck length 10^-33 of a
centimeter. Having universes exactly alike is all part of natures
balancing act. If my universe(Treb) was put on a balancing scale
with yours(Bert's) the scale would be just about level. That trillionth
of a second time difference(Treb's universe is that much older) is the
difference of all parrel universes. Universes are like all objects are
created in pairs. Creating in pairs is also part of natures balancing
act. Best to keep in mind for every electron created there is a
positron. TreBert