Daughter Universes
The theory of quantum mechanics,
which reigns over the tiny world of subatomic particles, suggests another way
multiple universes might arise. Quantum mechanics describes the world in terms
of probabilities, rather than definite outcomes. And the mathematics of this
theory might suggest that all possible outcomes of a situation do occur — in
their own separate universes. For example, if you reach a crossroads where you
can go right or left, the present universe gives rise to two daughter
universes: one in which you go right, and one in which you go left.
"And in each universe, there's a copy of you
witnessing one or the other outcome, thinking — incorrectly — that your reality
is the only reality," Greene wrote in "The Hidden Reality."