Brief extract from
Alchemical Active Imagination
Marie-Louise von Franz, Spring Publications (1979)
On the Unus Mundus and Synchronicity
Summing up, we can see that Dorn has four elements in the inner work of unification and three stages or steps. The four elements are the spiritus, anima, corpus, and the cosmos. First spiritus and anima unite and become the mens [mind]. Then the mens and corpus unite and become the vir unus and finally, in death, the vir unus unites with the Universe, though not in its visible form but as the unus mundus, its invisible potential background. Before God created the world He was with His companion, Sophia or Wisdom (cf. John 11) or the Word. She is also the soul of Christ, or Christ in His pre-existing divine form before incarnation. This Sophia is, according to some medieval philosophers, also the mental image of the creation which pre-existed in God's mind before He created the world. This is associated with the Platonic idea of a metaphysical realm of ideas. In it God conceived the idea of all real things, so that everything on earth has its archetypal model in the unus mundus.
...The idea of the unus mundus is a variation of our concept of the collective unconscious. First all archetypes are contaminated and thus the unus mundus is a unified multiplicity, a separateness of the parts and a oneness at the same time. In this fantasy world everything was conceived of as being in harmony. In the unus mundus there was no disharmony, things were separate and at the same time united. Dorn says that the state of the unus mundus only takes place after death; in other words, it is a psychological event by which man becomes one with everything existing.
Concretely the unus mundus manifests, as Jung pointed out, in the synchronistic phenomena. While we normally live in a dual world of "outer" and "inner" events, in a synchronistic event this duality no longer exists; outer events behave as if they were a part of our psyche, so that everything is contained in the same wholeness.
...This experience is the ultimate stage of the process of individuation, a becoming one with the collective unconscious...When this occurs positively, it brings about a union with the collective unconscious instead of a breaking apart, it means an enlargement of consciousness together with a decrease of intensity in the ego-complex. When this happens the ego retires in favour of the collective unconscious. To reach that point where outer and inner reality (heaven and earth) become one is the goal of individuation. Through it one also reaches some of what Jung calls the "absolute knowledge" in the unconscious.
According to an old Chinese story there were three wise old men who lived separately as hermits in caves. One day they decided to see each other and two visited the third. They walked in a little bamboo grove and had a delightful time of spiritual communication and oblation. When they just stood on a little bridge, they suddenly heard a tiger growl, and all three at once burt into laughter! Then they parted. They had understood the synchronicity, for the tiger in China is the female principle of Yin, the fourth in their spiritual male trinity, which they had ignored! So they could "read" events simultaneously, while they were happening, and draw the right conclusion. This is a stage of development man reaches when he approaches death. Perhaps death itself is nothing else than this third stage, the union with the unus mundus.