Is the Collective Unconscious Possible?
I, for one, believe in the potential for some kind of abstract and all-pervading conscious force within the universe. Not any kind of "God", really, but more of an intangible, abstract, form of consciousness seeping throughout the cosmos (though not necessarily of a 'higher' variety). Let me tell you - very briefly - why.
Jung and the Collective Unconscious
The collective unconscious was a concept first popularized by the pre-eminent psychologist Carl Jung (1875-1961). The universal consciousness described below does not necessarily adhere to all of Jung's ideas, though it owes a debt to Jung for bringing these issues to light and developing the study thereof. Jung is commonly known as the other champion of a field of psychological theory called Psychoanalysis, right next to Freud. Psychoanalysis was big on the hidden, largely unknown forces which shape daily actions. The 'unconscious' was seen, within this camp, as a powerful force laying dormant just beneath our overt conscious attention, continually shaping our behaviors and secretly ruling our inner-most desires. Whereas Freud took the unconscious forces shaping behavior to full extremes and theorized about general psychosexual energies pervading most human ambitions, Jung took Psychoanalysis in a different direction - to a quasi-spiritual conception which included the concept of the collective unconscious.
Carl Jung
Jung believed that human consciousness unwittingly draws upon a web of knowledge and shared cultural heritage via our mutual past. Throughout his clinical career and through studies of mythology and anthropology, he noticed many of the same motifs and symbolisms used throughout human history and shared by many people.
In fact, Jung proposed that the psyche of each person shared a collective ancestry that ultimately goes back millions of years - to the beginnings of consciousness itself. He argued that the psyche is made up of what he termed archetypes, which are primordial images and associated ideas inherited from our ancestors. As support for such a theory, he spoke of the immediate attachment infants have for their mother, the inevitable fear of the dark seen in young children and how images such as the sun, moon, wise old man, nurturing mother, angels, and evil snakes all seem to be predominant themes throughout history. The connection hit upon Jung when, during a clinical study, one of his patients related a dream which carried ancient Sumerian symbolism -- despite their having no knowledge of such things.
An example diagram of levels of conscious awareness.
Reading Jung's descriptions of an intangible webbing of shared knowledge, accessible via unconscious inclinations -- immediately makes me think of the now basically-ancient debate of Hume and Locke regarding how knowledge can be acquired. Whether much of it is acquired at birth, but lays dormant -- or whether infancy is a time of impressionistic blank slates. It makes me think of the spider weaving a complex web in nature despite no previous 'training', or the bird gathering and shaping materials for a nest. This unacquired, instrinsically complex knowledge seems ingrained and accessible via species-specific birthright.
How so, with humans? What does science say about the possibilities?
It's at once a shame and a blessing that Jung was a terrible writer. His ideas were loosely stated, didn't quite flow within a rationally-constructed hypothesis and were open to about as many interpretations as you can potentially imagine. Recently, some (like famous 'biologist' Rupert Sheldrake) have linked Jung's notions of the collective unconscious with psychic abilities and shared thoughts/emotions between humans across space and time. I'll admit, it's very pseudoscientific and often based on self-fulfilling prophecies - but there are some tantalizing implications from studies like Sheldrake's and from other, more recent and less dubious studies.
One of Sheldrake's studies (popularized by a brief mention within the film Waking Life
Evidence Against: Strict Materialism
Other modern research supporting aspects of a collective (or shared) consciousness come from some of the more fringe studies in neuroscience and from quantum physics. While most of mainstream neuroscience believes that the universe is made up of only one sort of 'stuff', and that consciousness is thus biologically and chemically based, there is some mounting evidence that abstract entities like the 'mind' can still potentially exist.
I'll be honest, there is a lot of evidence for materialism and the belief that there isn't really a mind controlling your brain. If surgeons were to remove the amygdala within your midbrain, you would never feel any kind of emotion - ever again. You might even forget what emotions could or might feel like. If a neurosurgeon were to remove sections of your hippocampus, also within the midbrain, you would undoubtedly lose the ability to acquire, store and retrieve long-term memories - as well with short-term memories and areas within your forebrain. There is a rich and detailed history in neuroscience of behaviors and aspects of consciousness being inextricably linked to the correct biological function. That's strong evidence for consciousness being biologically-based and dependent upon the brain itself.
It's the same with neurochemistry. If we give you a selective serotonin reuptake inhibitor (SSRI), which is a fancier name for an antidepressant - the chemistry in your brain will be altered such that the neurotransmitter serotonin will be more available and more able to exert the influence most commonly associated with it - making happy feelings more possible. No matter what your stance on the existence of a mind is, this is strong evidence that everything that you are - mind, personality and all - is chemically and biologically determined. That doesn't really leave much room for a collective unconscious.
But that's not the whole story.