Quantum Mechanics and the (Coming) Demise of Materialism

Why do so many physicists and philosophers try to save classical realism?

Materialism is founded on several assumptions. One of these assumptions is notably the idea of a strictly deterministic and, at least in theory, entirely predictable universe. It is a worldview based on a causality principle of physical causal realism where, once the initial and boundary conditions of a system are fixed, for every cause (in the past), there can be one and only one effect (in the present). This belief system can be traced back to the ‘Laplace’s demon’ thought experiment, introduced in 1814 by the French mathematician and philosopher Pierre-Simon Laplace. It has persisted as the implicit assumption of modern materialism and all sciences, representing a form of strict determinism and reductionism in conceptual terms.

Pierre Simon Laplace (1749-1827)

Laplace’s famous line of reasoning was the following:

“We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect that at a certain moment would know all forces that set Nature in motion, and all positions of all items of which Nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.”

In the 20th century, quantum mechanics, the theoretical framework in physics that elucidates the behavior of particles ranging from the subatomic to molecular scales, shattered this conception into pieces. However, it remains the (albeit mostly unconsciously) assumption that drives all reductionist scientific thinking. Let me first make a brief and as simple as possible technical introduction so that you might get an intuitive feeling of what this is all about.

Quantum physics is rife with numerous counterintuitive aspects. For instance, the well-known ‘wave-particle duality’ explains the behavior of particles such as electrons and photons, which exhibit characteristics of both waves and particles.

Fig. 2 The wave-particle duality is shown with the double-slit experiment.

In the renowned double-slit experiment, particles exhibit wave-like behavior, seemingly passing through both slits simultaneously. However, when observed on a detecting screen, they manifest as discrete spots. Put plainly, the experiment suggests that when a particle isn't observed, it behaves like a wave. Yet, once you attempt to determine its location, it ‘collapses’ into a single point in space. The question arises: Is it a wave or a particle?

There's also the equally well-known ‘quantum superposition principle’¹, which suggests that a single particle acts as though it could exist in multiple places or even in a combination of different energy states simultaneously. Translating this to our everyday macroscopic world implies that, for instance, one could not only occupy various locations at the same time but also move at two or more different speeds simultaneously. This concept starkly contrasts with our everyday realism; yet, whether we accept it or not, such states are perfectly ordinary in the quantum realm.

Fig. 3 An atom in energy superposition: *Not* E1 or E2, but E1 *AND* E2.

And who has never heard about ‘quantum entanglement’? When two particles become entangled, they behave as if they are no longer separate entities but rather a singular, undifferentiated whole. However, upon measurement, this ‘entity’ appears to ‘collapse’ into two distinct particles with correlated properties. This phenomenon suggests that the state of one particle in one location instantly influences the state of the other particle, even if they are separated by vast distances, an idea that Einstein discredited as "spooky action at a distance." This concept is known as ‘quantum non-locality’: two or more particles can act as a singular and interconnected entity, no longer defined by their individual properties and correlated over considerable distances.

Here, the non-reductionist facet of quantum physics emerges: a system of entangled particles cannot be simply reduced to the sum of its parts. Under specific conditions, these particles behave as if they exist in a physical state lacking a precise location in space and time. This challenges the conventional understanding based on local realism, which relies on our reductionist viewpoint of particles as distinct entities with specific positions and properties.

Fig.4 Left: Wrong understanding of quantum entanglement as two particles interacting with each other. Right: Correct quantum entanglement depiction of a probability wave expanding throughout space: there is no “particle” to begin with.

Most depictions of quantum entangled particles typically portray two particles as two ‘marbles’ connected by an odd string or energy beam (Fig. 4, left). However, this representation doesn't accurately capture the situation. According to quantum physics, it’s not that there are two individual particles; instead, there exists a singular wave function in one unified quantum state. For example, the decay of an atomic nucleus emitting two entangled particles is represented by a spherical probability wave extending throughout space (Fig. 4, right). There are no interconnected particles or separate entities yet; rather, there is a unified and undifferentiated whole that expands in time isotropically. It's only upon measurement that this wave ‘collapses’ into two distinct particles somewhere on the expanding spherical surface.²

What about ‘Heisenberg’s uncertainty principle’? It dictates that the position and momentum (which relates to speed) of a particle cannot be simultaneously known with absolute precision, not even in theory (and that's why it's called a ‘principle’). The more precisely you attempt to determine its position, the less accurately you can discern its momentum, and vice versa. It is essential to understand that this principle isn't a result of measurement errors from your measuring device (and, no, here I come to the skeptic’s defense: it isn’t influenced by your mind or consciousness). It's an inherent ‘quantum indeterminism’ imposed by Nature, irrespective of how rigorously you strive to define a particle’s position and momentum. It's not due to our lack of knowledge about a particle’s location, but rather because the particle itself lacks a definite and precise position and momentum to begin with. In the realm of quantum physics, things lack inherent definiteness. There's no conventional understanding of a point-particle possessing precise properties. Instead, everything appears a bit nebulous and uncertain, conflicting with our intuitive grasp of particles moving along specific and deterministic paths.

Fig. 5: Classical (point-like) particle vs. quantum (fuzzy) “particle.”

Put simply, every measurement inherently reveals ‘quantum randomness’ and unpredictability. During each measurement, the particle will ‘appear’ in a slightly different position each time with certain probabilities, illustrated by the blue ‘probability cloud’ in the figure above (right). Contrary to common belief, this variability isn’t due to the interaction with a measurement device that supposedly ‘pushes’ the particle away; rather, it’s an intrinsic property of the particle (or perhaps we should term it a ‘probability cloud'?)

In philosophical parlance: The uncertainty principle isn’t about an epistemic lack of knowledge, but an ontological or ‘ontic’ uncertainty.

Epistemic (from Greek ἐπιστήμη - epistḗmē) means “relating to cognition or knowledge.” For example, an object may have some property or be in some specific physical state, but we have no means to know what property it has or in which state it actually is. Unfortunately, the uncertainty principle is interpreted much too often as an epistemic lack of knowledge. This makes people believe (sometimes even physicists think in this misleading way) that the uncertainty principle tells us our knowledge about the position or momentum of a particle is uncertain due to our inability to observe it with greater accuracy, but that, nevertheless, the particle has some definite, precise position and momentum. We just don’t know where it is and what speed it has, but it still truly possesses some (for us unknown and unknowable) position and speed. This is the wrong understanding of the uncertainty principle.

While quantum uncertainty reflects an ontological lack of knowledge, ontological (from ancient Greek ὤν, ὄντος - ṓn, óntos) means “being,” “existing,” or “essence” and is about the being of things—that is, about the essential nature of things in themselves, as they truly are as entities, inherently and fundamentally, independent from our models based on deceiving senses or conceptual constructs. In the quantum context, an ontological lack of knowledge expresses the fact that there is no particle to begin with. The idea of a particle is only a fictitious model, a mental conceptual construct that has no counterpart in the microscopic physical reality. It makes no sense to talk about the position of a particle because the idea of a point particle is a mathematical human mental abstraction. It started with Descartes, who began to draw his Cartesian grid system in a coordinate space with infinite coordinate points. However, the inherent nature and essence of what we call a quantum ‘particle’ have nothing to do with points. To use a metaphor: What we call a particle stands for the real intrinsic nature and essence of the phenomenon, just as the 2D disk or square shadows projected by a cylinder on a surface stand to the cylinder itself. The ontological, or ontic, nature of the object is the cylinder; its shadows are our modeled epistemic knowledge. Asking for the exact position of a particle in the quantum uncertainty principle is like mistaking the surface of the square or disk for the volume of the cylinder and expecting to get an answer in square meters.

In a similar manner, we can question whether the collapse of the wave function, along with all the other quantum weird phenomena and properties we describe with quantum theory, represents only an epistemic description of reality (the mathematical theory of quantum mechanics works perfectly well; it will tell you everything you need to know for making measurements), or whether it tells us something about the ontology of things (for example, is the wave function a real object “out there” in the world, or is it only a mathematical abstraction?).

Fig. 6: The cylinder represents the ‘thing in itself,’ the square and the disk are dimensional reductions

Thus, in quantum mechanics, the distinction between epistemic and ontological is something reminiscent of Plato’s cave allegory or Kant’s distinction between noumenon and phenomenon. If you really want to understand what quantum mechanics is trying to tell us about the nature of reality, I strongly suggest reading my post that addresses the question, ‘Is reality an illusion.’ You won’t fully grasp the philosophical implications of quantum mechanics unless you recognize the relationship between our sensory representations of the world and the world itself.

In the following, I will use the word ‘particle’ only for linguistic convenience. However, you must always keep in mind that the word doesn’t reflect the ontology for which it stands.

Despite this inherent uncertainty, quantum mechanics still enables predictions by employing statistical calculations. Although we can't accurately predict specific outcomes (such as precisely determining when the next atomic decay will occur), we can make statistical predictions using a powerful and successful mathematical formalism. For instance, we will never know the exact time of decay of a single carbon-15 atom isotope or which of the N atoms in a sample is going to decay next, but we can predict that in approximately 2449 seconds, about half of all these N atoms will have decayed.

This raises significant questions about our understanding of cause and effect. What prompts atoms to decay at one moment instead of another, or particles to seemingly ‘quantum fluctuate’ erratically throughout space without any discernible external cause? Where does this quantum uncertainty, randomness, or ‘fluctuation’ stem from if there’s no apparent triggering cause?

As per the traditional formulation of quantum mechanics, it’s considered a ‘theory without hidden variables.’ This implies that there’s no intrinsic yet unknown reason or concealed cause determining a particle’s unpredictable behavior. The effect merely exists without a discernible reason.

Moreover, there are other perplexing quantum phenomena, such as the ‘quantum tunneling effect.’ This effect suggests that particles might traverse barriers even without possessing the energy that classical mechanics would traditionally deem necessary to overcome these obstacles. Instead, they ‘tunnel’ through potential barriers (here the ‘hill’) that, in theory, should be impenetrable.

Fig. 7: Simplified view of the quantum tunneling effect.

In a more detailed and realistic portrayal, consider the next animated gif. The particle is represented by a ‘probability wave’ (resembling the fuzzy, ghostly blob seen in the previous Fig. 5 right) with a portion that gets reflected while another part is transmitted through a potential barrier. Upon close inspection, you’ll notice a less intense yet substantial probability wave making it through the barrier and appearing on the right side. Essentially, in practical terms, this means that in the majority of instances, we’ll observe the particle being reflected by the ‘wall.’ However, there’s also a smaller probability that it will traverse or ‘tunnel’ through it, despite lacking the necessary energy according to classical mechanics.

Fig 6: The somewhat more realistic depiction of the quantum tunneling effect.

These were only a few of the aspects that challenge our conventional understanding of how the world is supposed to work, especially regarding what constitutes reality.³

So, what is left of Laplace’s idea of a universe where we can know “all positions of all items of which Nature is composed,” and that we could “embrace in a single formula” with nothing of the past, present, and future remaining uncertain? And is the quantum universe “the effect of its past and the cause of its future”?

These odd quantum effects challenge our human-centered macroscopic worldview. The understanding of the world in terms of concrete objects having definite properties, that are in a specific place and can jump over walls only with sufficient energy, following precise paths like pinpointed particles in a mathematical diagram and ruled by a strict principle of classical cause and effect, no longer stands. This kind of Cartesian, Galilean, Newtonian, and Laplacian mechanistic realism, based on a reductionist, deterministic, local worldview made of unconscious matter following classical laws of physical causality, and that has been so tremendously successful for almost three centuries, is now under serious question. The dream of reducing reality to a completely predictable unconscious and mechanistic clockwork universe is no longer tenable.

The quantum revolution that came about a century ago with scientists like Max Planck, Werner Heisenberg, Erwin Schrödinger, Max Born, Albert Einstein, and several others suddenly tells us a very different story about reality. The inherent quantum randomness makes particles seem to behave as if they are making ‘choices’ by themselves, independently of our knowledge, no matter how precise we try to pin them down. The principles of cause and effect, with laws describable in terms of particles subjected to an initial boundary condition—that is, one cause—leading to one and only one possible effect, are no longer a certainty. What causes a particle traversing the double slit to hit one place on a detecting screen, while the next particle starting from exactly the same initial conditions as the first one nevertheless hits another point on the screen? If quantum mechanics is a theory without hidden variables, then the answer is: Nothing. It is just so.

So much for the technical aspects of quantum mechanics. Now let us examine the sociological implications. Nature is telling us something here. There is a message to acknowledge and a lesson that Nature would like us to learn. Are we listening? Did we learn the lesson?

When you talk to physicists, you will hardly find anyone still believing in a naive mechanistic Newtonian and Laplacian realism that imagines elementary particles as marbles or bouncing billiard balls. There is a general recognition that our everyday macroscopic perception of reality no longer holds.

But what is the primary emotional instinct when a scientific fact dismisses your belief system and worldview? You might fall into a state of denial and ignore the facts (something quite in fashion nowadays), or you might try to recast the new findings in the frame of the old paradigm instead of accepting the new one. Humanity has already seen this with the transition from the geocentric to the heliocentric model of the universe. For a long time, people tried to explain the strange looping path of the planet’s motion observed on the celestial sphere. They resorted to contrived theories that added deferents and epicycles upon epicycles, insisting on placing the Earth at the center of all there is. They couldn’t wrap their heads around the idea that we are not at the center of the universe. And indeed, it works! You can accurately depict the planet’s motion if you carefully choose the right size and angular speed of these circles moving on other circles.

Fig. 7: The Ptolemaic geocentric model with its deferents and epicycles.

The same is happening again with indeterministic and non-local realism because it was and still is at the basis of all materialistic understanding (not only in physics but in biology, medicine, and neuroscience as well). Most scientists and philosophers will tell you that they know how quantum physics challenges our everyday notions, but they will also tell you how many are trying hard and doing their utmost to find deeper layers—that is, the ontology—underneath quantum mechanics that restore some form of classical realism in line with our everyday human-centered experience. For decades, very smart physicists have developed a plethora of interpretations of quantum mechanics that could somehow, at least partially, rewind the film of history to a 19th-century form of realism. And indeed, it works again! Alternative explanations and so-called “loopholes” in the orthodox interpretation of quantum mechanics have been found, which could, at least in principle or partially, reestablish our everyday human form of realism made of solid stuff that behaves nicely, without being in superposition states, collapsing to infinitesimal dots, tunneling through walls like ghosts, or zigzagging its way randomly all over the place.

For example, David Bohm developed a theory that remains non-local but at least recovers determinism if we imagine those tiny point particles having definite positions. This can be done by imagining a universal ‘pilot wave’ that keeps particles as particles but allows them to behave as waves.

Then there’s the infamous ‘Many Worlds Interpretation’ that imagines a deterministic and locally realistic universe, but at the cost of multiplying it into innumerable ‘worlds’ every time someone makes a measurement. This means that there doesn’t arise any superposition of states; rather, the present universe branches into two or more twin ‘worlds’ where you will find one state in one world and another in a different world, with yourself being multiplied and copied in all these worlds simultaneously as well! I don’t know about you, but I don’t like the idea of someone or something being able to multiply me. Ultimately, this worldview is much more absurd than the quantum weirdness it sought to eliminate. Determinism and locality are recovered, but at a high price.

What about ‘superdeterminism’? The name itself speaks volumes: if one assumes that the state of the measurement device is correlated with the particles determining the outcome of the measurement result, one may be able to recover the neat world described by a local, deterministic theory without hidden variables.

Other interpretations do not imply any form of determinism or locality; however, they come up with other scarcely credible ideas, such as the observer's role or consciousness collapsing the wave into a particle (again, I discussed this here), or making waves collapse spontaneously (whose spontaneity is it?), or other theories like Qbism that suggest it is all about your beliefs and that you shouldn’t look further for contrived ontologies.

However, the major shortcoming of all these interpretations of quantum mechanics is that they don’t predict anything new. They are just different models of reality that make no testable predictions that allow us to verify them and distinguish one ontology from another. They only tell us something we already know, placing it into different ‘theaters of reality’ but mimicking the very same quantum theory without adding much that is substantially new.

Therefore, despite all these speculations, there has been little progress in the foundations of quantum mechanics over the past decades. Most of the progress comes from applied physics, but not much has come from the domain of the conceptual foundations. That’s why the vast majority of physicists are pragmatists (“Shut up and calculate! Who cares about the ontology of quantum physics?”)

Why then did generations of physicists put so much effort into developing interpretations that try to recover the deterministic and reductionist worldview? Because, deep down, even if they might not admit it openly, all this quantum weirdness is something annoying for the naturalist’s mind. It clashes with their (more or less undeclared) hope and faith that we would sooner or later be able to explain away everything in mechanistic terms that leave no room for any uncertainty, indefiniteness, and unpredictable behaviors, leaving us with none other than an inert, unconscious, lifeless, and ultimately meaningless universe. Psychologically and subconsciously, there is a reason why so many would like to get there: because it would finally allow them to get rid of any speculations about supernatural causes. Deep down, it is about the desire to eliminate all ideas of final causation, purpose, and direction, and to keep everything within material and efficient causation.

Unfortunately for them, the long-awaited triumph of a physicalist science over religion and spirituality that seemed to be so close at the end of the 19th century, if not quashed forever, has at least been delayed by quantum physics beyond the presently visible horizon.

This is why you will hear most physicists talk about a theory without hidden variables or say that in quantum physics some phenomena are just “random,” carefully avoiding any further reflection on what this implies. But the word “random” is a buzzword that doesn’t mean much when we try to answer deeper philosophical questions. Sticking to “randomness” or a “hidden variables” narrative only betrays the subconscious desire to avoid calling it by its name: it is a ‘non-causal paradigm.’ There are quantum effects that can take place without a cause. Ask them. You will see them rejecting this almost angrily and keep saying, “quantum mechanics is without hidden variables; it is random, but not ‘non-causal’!” Eventually, they will begin to talk about one of the above interpretations, pointing out that we can think of it in other terms. But the truth of the matter is that if quantum mechanics is without hidden variables, it precisely means that there are aspects of the world that are non-causal, or should we label them ‘self-causal’? Something that could potentially become the backdoor for divine causation. Scientists feel that and, therefore, must reject it. If you would like to know more about this and how it might be even connected to free will, you can read my paper here.

This is also the (more sociological than scientific) reason why you will find most materialists trying to recast quantum physics in the naïve forms of human realism, while those who have a more spiritual or idealist worldview show less resistance toward the ‘spooky actions’ and quantum superposition, randomness, and the like.⁴ Unfortunately, the latter, especially if not professionals, falls into misunderstandings and develops pseudo-scientific theories. However, the crackpot theorists have been largely exposed by the so-called 'skeptics' and rarely receive attention from serious scientists. Therefore, I will not double down on them here again. But this psychological phenomenon that affects materialists sometimes leads them to equally crackpot speculations as well.

Thus, the reason why philosophers and some physicists are so obsessed with saving determinism and/or locality in quantum mechanics is purely sociological. It is a desperate attempt to preserve our naïve human-centered realism and models of reality conflating the epistemic with the ontic—no more and no less than those who tried to save geocentrism because of their religious beliefs and desperately needed to preserve their human-centered universalism. It is an ideological reaction that has little to do with science.

But Nature’s message is loud and clear: “No matter how hard you try to imagine yet another ontology, no matter how long you look for yet another loophole, no matter how many times you come up with yet another interpretation: I am indeterministic, I am non-local, I am irreducible. Get over it!”

If you would like to know more about quantum physics from a non-academic but not too simplistic perspective, you might like to check my series in two volumes “Quantum Physics: An Overview of a Weird World.”

1. I won’t discuss the famous ‘Schrödinger’s cat experiment’ here which is, of course, related to this.

2. People sometimes entertain the notion that this ‘spooky action’ could be employed to instantaneously transmit information faster than the speed of light across the universe. Unfortunately, the reality is more complex. Primarily, there is no direct ‘action’ or ‘interaction’ taking place; rather, it’s a correlation (or anti-correlation) of particle properties that manifest only at the moment of measurement, not before. Additionally, the determination of which particle will assume a particular state is entirely random and beyond our control. Consequently, quantum entanglement cannot be harnessed for transmitting information.

3. Why didn’t I mention the so-called “observer effect”? This is, to a great extent, a myth that I tried to deflate here, and will no longer consider in the present context.

4. I say “most” because the only exception I’m aware of is David Bohm.