Tree Of Life

The Four Worlds of the Qabalah are:

ATZILUTH	Archetypal — Pure Deity
BRIAH	Creative — Archangelic
YETZIRAH	Formative — Angelic
ASSIAH	Action — Matter, Man, Shells, Demons

Before creation there was No-thing, the infinite God. In Kabbalah beginning in Kether (Ke-ter) the hightest sphere-the crown there wass oneness, unity.
At the moment of creation  everything separated and became duality.

In Genesis chapter one we see the world  (universe) was without form and void but when Spirit moved upon it  the waters separated from the land, day separated into light and dark. male into female and so on. No longer was there unity.
On the Tree of Life duality is first observed in the opposites of Chokmah and Binah=Wisdom and Understanding.
Though you don't find much written about it, there is what is known as the invisible sphere known as Daath which is the great  Abyss. Daath  is (Hidden) Knowledge.