Excerpt from

Quantum Physics, Depth Psychology,and Beyond

Thomas J. McFarlane

Synchronicity is necessarily meaningful in the sense that it is a form of unconscious compensation that serves to advance the process of individuation. It is distinguished from other forms of unconscious compensation by the fact that synchronicity involves a connection between inner psychological experience and outer experiences in the world, where the connection is acausal in the sense that the inner experience cannot have been an efficient cause of the outer experience, or vice versa.

In short, synchronicity is a meaningful, acausal connection between inner and outer events. Because the phenomenon of synchronicity involves an acausal coordination of the inner and outer worlds in a meaningful way, it is not exclusively a psychological or physical phenomenon, but is “psychoid” meaning that it somehow essentially involves both psyche and matter. Thus, Jung interpreted synchronicity to imply the existence of an extremely profound level of reality prior to any distinction between psyche and matter. In other words, synchronicity phenomena represent a manifestation in consciousness of psychoid structures present in the depths of a transcendental unitary reality Jung called the unus mundus:

Since psyche and matter are contained in one and the same world, and moreover are in continuous contact with one another and ultimately rest on irrepresentable, transcendental factors, it is not only possible but fairly probable, even, that psyche and matter are two different aspects of one and the same thing.

The unus mundus is also implied by the fact that we evidently occupy one reality that contains both psyche and matter, and that these two domains of reality are not absolutely independent and isolated, but interact with each other. As Jung says,

Psyche and matter exist in one and the same world, and each partakes of the other, otherwise any reciprocal action would be impossible. If research could only advance far enough, therefore, we would arrive at an ultimate agreement between physical and psychological concepts. Source