Thomas McFarlane - Quantum Physics, Depth Psychology, and Beyond


If a union is to take place between opposites like spirit and matter, conscious and unconscious, bright and dark, and so on, it will happen in a third thing, which represents not a compromise but something new.[1] - C. G. Jung

The modern worldview of Western culture is characterized by an implicit division between the objective or physical realm of existence and the subjective or psychic realm of existence, with the objective or physical realm generally dominating the subjective or psychic realms to the point of virtual exclusion, as in the materialistic worldview which considers mind to be a mere epiphenomenon of matter. The dominance of modern materialism is due in large part to its association with the remarkable theoretical and practical power of classical physics as developed by Newton and his successors. According to this model, reality consists of a fixed and passive space containing localized material particles whose movement in time is deterministically governed by mathematical laws. Consequently, mental phenomena, in this picture, are nothing more than the complex functions of the material brain governed by physical laws.

Although scientific materialism provided the dominant worldview of modern Western culture, it did not exist to the total exclusion of other alternatives. Nevertheless, these alternatives did not succeed in fundamentally challenging the dominance of materialism. Instead, this challenge largely came from within empirical science itself. In the 20th century the modern materialistic worldview began to unravel in the face of scientific developments, particularly in physics. In physics, the development of relativity and quantum theory served to radically undermine various fundamental assumptions at the base of the materialistic model. For example, the special and general theories of relativity forced physicists to revise their basic conceptions of space, time, movement, gravitation, matter, energy, and the nature of the cosmos as a whole. Quantum theory, on the other hand, forced a revision of the concepts of causality, determinism, and locality. Perhaps most importantly, it even challenged the idea that properties of matter have an objective existence independent of observation. As a result, 20th century physics undermined the very basis for materialism, and suggested to some thinkers that the  psyche may be involved, in some mysterious way, with the determination of the observed properties of matter.

Meanwhile, developments in psychology during the 20th century explicitly introduced the psyche into the domain of scientific inquiry. In particular, Freud's psychoanalytic theory demonstrated the reality of a psychological unconscious, an unobservable psychic reality which contains repressed personal impulses and desires. These hidden psychic contents exert their influence upon consciousness and thus can be indirectly known by us through a study of various conscious contents, such as our dreams. Although the concept of the psychological unconscious did not initially challenge materialism, the discovery of the transpersonal depths of the unconscious by Jung (i.e., the collective unconscious and psychological archetypes) presupposed a psychic reality that was difficult to reconcile with any strictly materialistic understanding of human nature. Moreover, Jung's later work with the phenomenon of synchronicity provided evidence that the deepest regions of the unconscious (i.e., the  unus mundus) consists of " psychoid" structures that transcend the distinction between psyche and matter altogether.

The above developments in 20th century physics and psychology have analogous implications: just as psychology revealed in the deepest regions of psyche a profound connection with matter, physics revealed in the depths of matter a profound connection with the psyche. Although the precise nature of these connections remains elusive and controversial, the provocative possibility of transcending the dualism of mind and matter has provided motivation for the development of a more comprehensive and unified worldview. As Jungian psychologist Marie-Louise von Franz says,

The unexpected parallelisms of ideas in psychology and physics suggest, as Jung pointed out, a possible ultimate oneness of both fields of reality that physics and psychology study. . . . The concept of a unitarian idea of reality (which has been followed up by Pauli and Erich Neumann) was called by Jung the unus mundus (the one world, within which matter and psyche and are not yet discriminated or separately actualized).[2]

The remainder of this paper will explore in more detail some of these developments during the 20th century, with a particular emphasis on depth psychology and quantum physics. Because this paper does not presuppose familiarity with quantum physics or depth psychology, a brief exposition of some basic concepts in these two areas of research will precede the discussion of their connections.

Quantum Physics

The existing scientific concepts cover always only a very limited part of reality, and the other part that has not yet been understood is infinite. Whenever we proceed from the known into the unknown we may hope to understand, but we may have to learn at the same time a new meaning of the word `understanding'.[3] - Werner Heisenberg

The fundamental laws of quantum physics were discovered independently in 1925 by Werner Heisenberg and in 1926 by Erwin Schrödinger in response to puzzling experimental evidence that contradicted the fundamental concepts of classical physics. For example, electrons (which were previously thought to be particles) were found to exhibit properties of waves. Conversely, light (which was previously thought to be waves) was found to exhibit properties of particles. This confusion of classical distinctions between particles and waves was resolved by Niels Bohr's principle of complementarity, according to which the wave and particle concepts are understood to be mutually exclusive but both necessary for a complete description of quantum phenomena.
A consequence of this wave-particle duality is that all matter has a wave aspect, and cannot be said to have a definite localized position at all times. Moreover, by virtue of their nonlocal wave properties, pairs of spatially separated particles sometimes exhibit nonlocal correlations in their attributes. Another consequence of the wave-particle duality is a corresponding duality between the unobserved and the observed. This duality raises puzzling questions regarding the nature of measurement in quantum mechanics: how is it that the wave suddenly changes into a particle, and how is this sudden transformation related to observation?

A deeper understanding of these subtle issues requires some basic understanding of the way quantum physics describes phenomena. According to quantum physics, the state of an unobserved quantum of matter or light (such as an electron or photon) is represented by a solution to Schrödinger's wave equation. This solution is a quantum wave function y(x) whose intensity |y(x)|2 at any particular position x represents the probability of observing the quantum at that position. When the quantum is observed, however, it is seen to have a definite actual position, and the wave function no longer properly describes the quantum. Thus, when the quantum is unobserved, it is a nonlocal wave of probable positions; and when the quantum is observed, it is a particle having a definite localized position. As a result, both the particle and wave concepts are required to completely characterize a quantum: the particle concept is required to describe its particle-like behavior when observed, while the wave concept is require to describe its wave-like behavior when unobserved. The particle and wave concepts are called "complementary" descriptions because they are both needed to characterize the observed and unobserved aspects of any quantum, as illustrated in the following table.


wave functions
unobserved quanta

observed quanta


Although observation is evidently necessary to bring about the transition from possible to actual, the fundamental nature of observation in quantum theory remains somewhat mysterious. This problem of measurement derives from the fact that, prior to observation the quantum is described as being a nonlocal wave of probability spread throughout space, while after observation only one of the possible values is actualized. Thus, observation involves a discontinuous "collapse" (also called a "projection") of the quantum wave function from a continuum of possibilities to a single actualized value. This projection, however, is an ad hoc element of the formalism, and is not a lawful transformation that is governed by Schrödinger's wave equation. There is no explanation for how, when, or where this mysterious projection happens. Moreover, when the projection takes place, the laws of quantum physics do not predict which of the possible values will be actualized in any given observation, thus violating classical determinism and introducing an element of acausality and spontaneity into the theory at a fundamental level.

In a fundamental analysis of the quantum measurement process, John von Neumann argued that consciousness is required to explain the projection of the wave function from possibility to actuality. In particular, he reasoned that because all physical interactions are governed by Schrödinger's wave equation, the projection that is associated with observation must be attributed to a non-physical consciousness that is not governed by physical law. According to von Neumann, this activity of consciousness only serves to cause the projection, and does not select or influence the particular value actualized. There is thus a spontaneity inherent in the projection that takes place in the transition from the unobserved to the observed.

Jungian Psychology

Since the stars have fallen from heaven and our highest symbols have paled, a secret life holds sway in the unconscious. ...Our unconscious...hides living water, spirit that has become nature, and that is why it is disturbed. Heaven has become for us the cosmic space of the physicists, and the divine empyrean a fair memory of things that once were. But "the heart glows," and a secret unrest gnaws at the roots of our being.[4] - C. G. Jung

The notion of the psychological unconscious was first extensively developed in Freud's The Interpretation of Dreams, published in 1900, and further developed in his Three Essays on the Theory of Sexuality, published in 1905. In addition to the contents of our conscious awareness, Freud considered the psyche to also contain an unconscious region whose contents are hidden and cannot be directly observed. These unconscious contents, according to Freud, consist of previously conscious contents that have been repressed and forgotten. The unconscious is thus a kind of `skeleton closet' containing personal psychological contents that were conscious in the past but then hidden away. Although they are no longer directly observable, these unconscious contents can be indirectly known through their effects on consciousness, such as their influence on our dreams. In Freud's conception, the unconscious contains only personal psychic contents that were previously conscious, but then repressed, typically during childhood.

After studying with Freud, Carl Jung deepened and expanded Freud's notion of the unconscious, most notably in his Psychology of the Unconscious, published in 1912, and his Archetypes of the Collective Unconscious, published in 1934. According to Jung, the unconscious contains, in addition to repressed personal contents, a deep and vast region of collective psychic contents, called the collective unconscious. In contrast to the personal unconscious contents that were previously conscious, the collective unconscious contents do not derive from previously conscious personal contents. Instead, the collective contents are innate and universal. In Jung's words,
We have to distinguish between a personal unconscious and an impersonal or transpersonal unconscious. We speak of the latter also as the collective unconscious, because it is detached from anything personal and is common to all men, since its contents can be found everywhere, which is naturally not the case with the personal contents.[5]

Although the collective unconscious is present in the depths of each individual psyche, it is not subjective in the sense of being different from person to person. Because the collective unconscious is common to all individuals, it is objective in the sense that all individuals share these same deep psychic structures. As Jung writes,
The collective unconscious stands for the objective psyche, the personal unconscious for the subjective psyche.[6]

In short, the door to the unconscious does not open up to a skeleton closet, as Freud proposed, but opens up to a larger world beyond the walls of the conscious psyche.
It is important to note that between the personal and collective regions of the psyche there are various intermediate levels of depth, each having its share of universality and particularity. Jung explains:

In as much as there are differentiations as corresponding to race, tribe, and even family, there is also a collective psyche limited to race, tribe, and family over and above the "universal" collective psyche.[7]

The unconscious, in other words, is not divided into distinct personal and collective regions, but rather is a continuum with the personal and universal contents at each extreme. Jung's most important contribution and his primary interest, however, is in the deeper regions of the collective unconscious, whose structures Jung calls archetypes. Like Plato's Ideas, the archetypes of the collective unconscious are universal patterns that shape our experience of the world and provide it with common elements. Following Kant, however, Jung considers the archetypes as epistemological structures rather than independent ontological entities:

The collective unconscious, being the repository of man's experience and at the same time the prior condition of this experience, is an image of the world which has taken eons to form. In this image certain features, the archetypes or dominants, have crystallized out in the course of time.[8]
According to Jung's conception of the collective unconscious, the archetypal structures are not fixed, but dynamic. Not only do the archetypes evolve over time, but they also have dynamic and creative activity in the present. Moreover, this activity is not merely a reaction to the activities of consciousness, but is inherent in the unconscious itself. As Jung explains,

If [the unconscious] were merely reactive to the conscious mind, we might aptly call it a psychic mirror world. In that case, the real source of all contents and activities would lie in the conscious mind, and there would be absolutely nothing in the unconscious except the distorted reflections of conscious contents. The creative process would be shut up in the conscious mind, and anything new would be nothing but conscious invention or cleverness. The empirical facts give the lie to this. Every creative man knows that spontaneity is the very essence of creative thought. Because the unconscious is not just a reactive mirror reflection, but an independent, productive activity, its realm of experience is a self-contained world, having its own reality, of which we can only say that it affects us as we affect it--precisely what we say about our experience of the outer world. And just as material objects are the constituent elements of this world, so psychic factors constitute the objects of that other world.[9]

The objective psychic world, or collective unconscious, is thus similar to the objective physical world in that both worlds have objective structures and both worlds have autonomous activity independent of our personal will. For example, just as the objective physical world serves as a creative impetus for the development of our scientific worldviews, the psyche develops and evolves because the objective psyche is not merely repressed conscious contents, but has an autonomous activity that is relatively independent of our personal consciousness. Because this activity of the unconscious is relatively autonomous, it often manifests as a compensation or correction to our conscious views or beliefs. The result is an evolution of the psyche toward wholeness and integration, a process Jung called `individuation'.

In an unconscious compensation, some unconscious content is spontaneously expressed or manifested in consciousness, such as in a dream, and provides the psyche with an opportunity to integrate the unconscious content into consciousness. One of the most interesting and dramatic types of unconscious compensation is the phenomenon Jung calls synchronicity. 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.[10]

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.[11]
Jung's concept of the unus mundus, therefore, not only shows how matter is implicated in the depths of the psyche, but also provides a framework for integrating our understanding of psyche and matter. In this framework, both the objective psychic and objective physical worlds are rooted in a common unity at the depths of reality. Because the unus mundus is normally unconscious, it is experienced as the mysterious Other that is the infinite unseen context of our finite conscious experience. Viewed in its subjective aspect, this unified reality takes the form of a psychic domain containing psychological archetypes that manifest in our inner experience. Viewed in its objective aspect, the unus mundus takes the form of a physical domain containing the archetypal laws of nature that govern manifestations in our outer experience. If psyche and matter are, as this suggests, a single reality viewed from different perspectives, then a comparison of their common elements as revealed in physics and psychology may provide insight into the nature of reality at its deepest and most universal level.

Modern science may have brought us closer to a more satisfying conception of this relationship [between psyche and physis] by setting up, within the field of physics, the concept of complementarity. It would be most satisfactory of all if physis and psyche could be seen as complementary aspects of the same reality.[12] - Wolfgang Pauli

Microphysics is feeling its way into the unknown side of matter, just as complex psychology is pushing forward into the unknown side of the psyche. Both lines of investigation have yielded findings which can be conceived only by means of antinomies, and both have developed concepts which display remarkable analogies. If this trend should become more pronounced in the future, the hypothesis of the unity of their subject-matters would gain in probability. Of course there is little or no hope that the unitary Being can ever be conceived, since our powers of thought and language permit only of antinomian statements. But this much we do know beyond all doubt, that empirical reality has a transcendental background.[13] - C. G. Jung

In attempting to understand the deepest levels of reality, it is wise to take note of Jung's observation that our concepts are imperfect instruments, and that any conceptual representations we may form of these regions of reality will likely involve antinomies, and should be taken as being essentially symbolic rather than literal. For example, progress in the conceptual understanding of the nature of quanta was accomplished by acknowledging the principle of complementarity, which states that mutually exclusive sets of concepts must be used to completely characterize quantum phenomena in all their aspects. As Marie-Louise von Franz tells us, Jung recognized that this principle of complementarity applied to psychology as well as to physics:
Bohr's idea of complementarity is especially interesting to Jungian psychologists, for Jung saw that the relationship between the conscious and unconscious mind also forms a complementary pair of opposites.[14]

The analogy suggested here is that the wave-particle complementarity in quantum physics parallels the unconscious-conscious complementarity in psychology. Indeed, just as the wave is the unobserved aspect of the quantum and the particle is the observed aspect, so the unconscious is the unobserved aspect of the psyche and the conscious is the observed aspect. Moreover, the wave is continuously spread throughout space, while the particle has a limited location. Similarly, Jung states that

The area of the unconscious is enormous and always continuous, while the area of consciousness is a restricted field of momentary vision.[15]
The analogy goes even further. The quantum wave function represents probabilities, as contrasted to the actualized particle. Similarly, the archetypal structures of the unconscious represent fundamental potentialities of psychic manifestation, while conscious contents are actualizations of these potentialities. As von Franz explains,

What Jung calls the archetypes...could just as well be called, to use Pauli's term, "primary possibilities" of psychic reactions.[16]

This suggests that the unus mundus behind both psyche and matter is also a continuous world of potentiality. Jung elaborates:

The common background for microphysics and depth-psychology is as much physical as psychic and therefore neither, but rather a third thing, a neutral nature which can at most be grasped in hints since in essence it is transcendental. The background of our empirical world thus appears to be in fact an unus mundus. ... The transcendental psychophysical background corresponds to a `potential world' in so far as those conditions which determine the form of empirical phenomena are inherent in it.[17]

The following table summarizes the correspondence between complementary principles in psyche and matter:





unconscious contents
unmanifest archetypes

unobserved quanta
wave functions


conscious contents
manifest images

observed quanta


Extending the analogy between psyche and matter further, physicist Victor Mansfield points out a similarity in the manner in which potentialities are transformed into actualities in the two realms:
In physics the irreversible measurement process transforms the potentialities into actualities. What is the corresponding psychic function that transforms `the potential world...' into the world of multiplicity? It is reflective consciousness, the association of knowing with the ego, which makes the empirical world possible and brings the transcendental into the empirical world of multiplicity. The primordial unity of the unus mundus is shattered by reflective consciousness-a point agreed upon in most mystical traditions.[18]

In quantum mechanics it's only when an individual observes that an acausal spacetime event manifests. Our participation through measurement generates acausality. Analogously, when a unique center of consciousness, a specific individual, actualizes a possibility in the unus mundus, acausality enters our world. Introducing a particular perspective, a finite center of consciousness, inevitably brings acausality into the transition from possibilities to actualities.[19]
Similarly, Jung has made a correspondence between the indeterminacy inherent in quantum measurement and the attempt to consciously determine unconscious contents:
Any attempt to determine the nature of the unconscious state runs up against the same difficulties as atomic physics: the very act of observation alters the object observed. Consequently, there is at present no way of objectively determining the real nature of the unconscious.[20]

It should be pointed out here that Jung's characterization of quantum measurement requires clarification. The quantum measurement does not alter the actual properties of the object being observed since these properties do not have determinate existence prior to measurement. More accurately, the measurement is the occasion for the determination of the actual properties of the object. There is thus a spontaneity that enters nature in quantum measurement. Similarly, the manifestation of unconscious contents within consciousness also has an element of spontaneity, insofar as the particular conscious image manifesting an archetype is not completely determined by previous conscious contents. This type of spontaneity is especially evident in synchronicity.
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