Carl Jung was a pupil of Sigmund Freud but they were quite different in their views of the world.
Jung was very interested in Eastern spirituality. He also recognized the existence of some psychic phenomena which he called “significant coincidences.” You’ve probably experienced a coincidence such as thinking of a friend who you rarely see or speak with and suddenly the friend calls on the phone. But Jung was thinking about ones that were not so random. One example he wrote about was when he was taking notes about a patient’s dream about a particular type of beetle when at that moment that exact beetle came in through his window.
One of Jung’s patients in 1932 was Wolfgang Pauli, a pioneer in quantum physics. Their relationship helped lead him to his concept of synchronicity. Jung’s theory was that sometimes events attract each other without any obvious connection. Why? Because they are connected on a level deeper than normal reality. Their attraction is not a coincidence but more like something described by quantum physics. For example, Jung was interested in entanglement which is when a particle can influence another instantaneously even if very far from it. This has been verified in tests a number of times.
Pauli and Jung combined quantum physics and psychiatry to explain things like déjà vu. Jung was convinced that these significant coincidences were connected at some deeper level. He also believed that mankind had created a huge common library where the oldest symbols resided, which he called archetypes.
He believed minds could be connected because everything in the universe is connected. In his Jung’s last major work, Mysterium Coniunctionis, which was completed in his 81st year, he wrote about the synthesis of the opposites in alchemy and psychology.
“We do not know whether what we on the empirical plane regard as physical may not, in the Unknown beyond our experience, be identical with what on this side of the border we distinguish from the physical as psychic. Though we know from experience that psychic processes are related to material ones, we are not in a position to say in what this relationship consists or how it is possible at all. Precisely because the psychic and the physical are mutually dependent it has often been conjectured that they may be identical somewhere beyond our present experience, though this certainly does not justify the arbitrary hypothesis of either materialism or spiritualism.” – Carl Jung, Mysterium Coniunctionis: Inquiry into the Separation and Synthesis of Psychic Opposites in Alchemy