Quantum mechanics works very well. Its predictions are remarkably precise, and a large part of modern advanced technology is based on it. In the century since its inception, it has established itself as one of the most successful theories in the history of science.

Yet, this extraordinary success conceals a fundamental dilemma: we still do not know precisely what quantum mechanics actually describes. What is the reality it purports to reveal? This, however, is not its weakness, but rather a sign that physics must also openly confront questions that cannot be resolved by measurements and equations alone, but demand thorough conceptual analysis.

The question of interpreting quantum mechanics has been important from the very beginning, yet for a long time, it was pushed to the margins as something deemed outside the scope of legitimate scientific inquiry. Today, it is increasingly apparent that such avoidance of philosophical questions is no longer tenable, as interpretational problems have become a legitimate and essential part of the debate on the foundations of physics.

Questions such as: what truly exists (particles, wave functions, parallel worlds?) and how nature operates (deterministically or randomly? locally or non-locally?), are an inseparable part of the physical theory itself. Every interpretation has its advantages, but also its "price"—either in the form of additional, hard-to-justify assumptions or in consequences that many find difficult to accept.

Philosophy as a Tool for Understanding the Quantum World

Philosophy can play a significant role in understanding quantum mechanics—not as an external arbiter dictating rules to scientists, but as a set of conceptual tools for clarifying fundamental assumptions and assessing their soundness. It offers help precisely where experiment and calculation no longer suffice.

One of philosophy's key tasks is to highlight the assumptions we often take for granted. Every interpretation of quantum mechanics rests on certain suppositions about the nature of the world, and philosophical analysis allows us to make them explicit and critically examine them. At the same time, it promotes a more precise use of language by revealing that terms like "measurement," "observer," or "state of a system" are not as self-evident as they might seem, and thus demand clear and consistent application.

It is also crucial for evaluating the philosophical consequences of various interpretations. Whether we accept the existence of parallel worlds or the idea that events are not predetermined, these are not merely abstract possibilities but concepts that profoundly shape our understanding of reality. Philosophy enables us to comprehend and weigh such consequences.

Finally, philosophy serves a critical function as a safeguard. It helps maintain a clear distinction between scientific hypothesis and speculation, particularly where the physical theory leaves its explanations open. Without such reflection, these conceptual gaps are quickly filled by untestable claims—often from physicists themselves—that verge on mysticism or esotericism. Here, philosophical tools act as a filter, ensuring logical rigor and conceptual discipline.

Physicists are often already engaged in work that is, in many respects, philosophical—typically without being aware of it and without the proper conceptual tools. The question, therefore, is not whether a philosophical approach belongs in physics, but how to integrate it thoughtfully and with the necessary rigor. Ultimately, philosophy can contribute to a better understanding of the world described by quantum mechanics—a world that may be strange and counter-intuitive, but is no less real for it.

When Physical Phenomena Become Philosophical Problems

In a conventional physics education, concepts such as superposition, entanglement, and measurement are presented as part of the standard formalism of quantum mechanics. Physicists learn to apply them as tools for solving specific problems. Philosophical inquiry, however, begins where the textbook typically ends: by treating these phenomena as questions that probe the very foundations of our understanding of nature.

Superposition is a prime example. It is not merely a matter of a particle existing in a state that encompasses multiple possibilities simultaneously—such as being in two places at once. The crucial question is what this implies for our very notion of what a "property" is. Does a physical object—an electron, for instance—possess definite properties in and of itself, at all times? Or do these properties only come into being when the object interacts with something else, such as a measuring apparatus? Superposition, therefore, compels us to question whether the world possesses fixed, independent features, or if its properties are instead contingent on context and relationships.

Entanglement goes a step further. Here, we are no longer dealing with a single object, but with two or more whose states are so inextricably linked that they cannot be described independently. In entangled pairs, the state of the entire system—all particles together—is something more than just the sum of the states of its individual parts. This has been confirmed by numerous experiments, which show that the predictions of quantum mechanics hold true even when they defy the fundamental assumptions of classical physics. If we take these results seriously, we must abandon at least one of two classical assumptions: that influences cannot propagate faster than light (locality), or that particles possess definite properties independent of observation (realism).

The most enduring and prominent debate, however, revolves around the measurement problem. In quantum mechanics, there are two different rules for describing the evolution of a system over time. The first is the Schrödinger equation, which describes the deterministic evolution of a state. The second is the so-called "collapse of the wave function," which, upon measurement, abruptly singles out one result from many possibilities—and does so in a way that is random and inherently unpredictable. These two processes are fundamentally different, yet the theory does not explain the transition from one to the other. The key question is whether both processes are equally fundamental, or if one is merely an approximation arising from our limited perspective. In any case, this creates a tension within the theory itself: quantum mechanics describes the world with the immense precision of the Schrödinger equation, yet it simultaneously includes a mechanism that is inconsistent with its own fundamental description.

Three Philosophical Interpretations of Quantum Mechanics

The various interpretations of quantum mechanics are not merely different perspectives on the same thing. They are distinct philosophical approaches to understanding what the theory actually says about the real world. Each interpretation adopts certain presuppositions about the nature of reality—that is, a particular view on what exists in the world and how—while relinquishing others. Since, for now, none of these interpretations can be distinguished by direct observation, the choice between them is fundamentally philosophical, not empirical.

The most widespread approach in the history of quantum theory is the so-called Copenhagen interpretation. It attempts to resolve the problem by declaring it irrelevant. According to this view, physics should limit itself to predicting the results of measurements and not concern itself with questions about what is really happening "behind the scenes." In this sense, it is a strategy of philosophical restraint that avoids untestable claims and emphasizes that only what can be measured is important. But the price of such an approach is the surrender of the ambition for science to describe the world as it exists independently of the observer and the act of measurement.

At the opposite end of the spectrum is the Many-Worlds Interpretation, which does away with the wave function collapse problem by simply rejecting it: the collapse never happens. Instead, all possible outcomes of a system's quantum evolution are in fact realized—each in its own branch of a diverging multiverse. This approach takes the mathematical structure of quantum mechanics as a direct description of reality and requires no additional mechanisms or interventions. It is elegant and internally consistent, but it comes at a high price: we must accept the existence of an infinite number of parallel worlds that we can never directly perceive.

A third path involves interpretations that attempt to supplement or modify quantum mechanics to reconcile it with a more classical worldview. The first of these are hidden-variable theories, which postulate that quantum theory is incomplete and that there are yet-undiscovered factors—the hidden variables—that actually determine the outcomes of measurements. If we knew them, we could predict events with complete determinism. The second are objective-collapse theories, which introduce additional laws into the formalism of quantum mechanics, causing the wave function to collapse spontaneously under certain conditions—not due to observation, but because of the system's own intrinsic properties. Both of these approaches preserve the classical idea that the world has an objective, observer-independent structure. But these approaches, too, have their price: as of now, we have no empirical evidence that hidden variables or objective collapses actually exist. If they are to become part of accepted physics, they will have to be confirmed by new experiments.

When Contradiction Is Not a Flaw, but a Feature of the World

But what if the very premise of all the interpretations so far is flawed? What if the assumption that there must be a single, fully coherent, and logical explanation for reality simply isn't true? A philosophical shift emerging in contemporary debates about quantum mechanics offers another possibility: that the problem lies not with the interpretation, but with the very nature of reality itself. Perhaps reality, at its most fundamental level, is simply not something that can be described without contradiction.

From this perspective, the contradictions revealed by quantum mechanics are not a sign of the theory's inconsistency but are instead an inherent feature of reality itself. The world, at its most profound level, is inherently indeterminate—and perhaps even contradictory. Within this framework, a paradox is no longer a problem to be solved, but a source of insight. The fact that we cannot consistently describe an electron as either a particle or a wave might not mean that our theory is missing something; it might mean that this very duality is an intrinsic part of its nature. This approach does not resolve contradictions but embraces them as a fundamental feature of reality. A paradox is therefore no longer an obstacle to understanding, but the very means by which we achieve it.

The mechanism of decoherence, which is well-known to physicists, holds an important place in this discussion. This is the phenomenon whereby a quantum system loses its distinctively quantum properties, such as superposition, through its interaction with the environment. Decoherence explains why we do not observe quantum effects in the everyday world, and why the world appears "classical" to us, even though it is fundamentally governed by quantum laws. However, decoherence does not solve the measurement problem—it does not explain why we get one specific result in any individual measurement. Instead of explaining how a single actuality emerges from a multitude of possibilities, it merely shows how quantum uncertainty is, in a sense, dissipated into the environment.

The philosophical task is to highlight this difference: between what suffices "For All Practical Purposes" (FAPP) and what would constitute a genuine, fundamental understanding. This distinction is crucial for any serious treatment of the conceptual meaning of decoherence. A practically useful solution is not the same as an explanation of what actually happens.

The Quantum Computer as a Practical Test of Philosophical Paradoxes

The debate over the fundamental concepts of quantum mechanics does not end in a lecture hall or a philosophical essay—it has very concrete consequences. One of these is quantum computing. At first glance, it appears to be a technically sophisticated technology of the future, but a closer look reveals that the quantum computer is also a philosophically sensitive instrument. It doesn't just operate according to quantum principles—it operates within them.

The fundamental difference between a classical bit and a quantum bit (qubit) is deep and conceptual. A classical bit can take one of two values: 0 or 1. A qubit, however, exists in a superposition of both—its state is not "either/or" but "both at the same time." This means that a quantum computer does not calculate with fixed facts but with possibilities that are omnipresent until they are observed. The computation takes place in a field of potentiality that exists as potentiality—a state that classical logic once deemed an impermissible contradiction. Yet it is precisely this state of contradiction, where something is simultaneously 0 and 1, that forms the basis of quantum computational power.

This difference is not merely mathematical or engineering-related. It is the embodiment of the idea that the world, at its core, can be ontologically indeterminate—as we saw in the philosophical approach that does not seek to eliminate contradiction but accepts it as a real feature of nature. The quantum computer not only confirms this idea but re-enacts it with every operation. Its computational process is based on the system existing in many possibilities at once—every computational path is simultaneously present and active until a measurement is performed.

But it is precisely here that the fundamental tension, already familiar from the discussion of decoherence, becomes apparent. For a quantum computer to function at all, it must remain isolated from its environment—it must maintain its coherence. Any contact with the classical world, whether a measuring device or thermal noise, causes decoherence—the loss of superposition and thus the collapse of quantum potentiality. In this sense, the fight against decoherence is actually a fight against the world's pressure to turn potentiality into actuality too soon. A quantum computer is not just a machine; it is a physical experiment to create a controlled "bubble" of quantum reality within the classical world. It is a practical demonstration of a contradictory state that works—but only as long as it can hold the influence of the classical view of the world at bay.

Ultimately, however, comes the measurement—the moment the quantum computer delivers a result. At that point, the superposition collapses, and we are left with a single, classical answer. In a philosophical sense, this is the moment of "collapse": from a space of rich, co-existing possibilities, only one actuality remains. All other possibilities, which were realistically present in the wave function, have vanished. With this, the quantum computer stages one of the most fundamental problems of quantum mechanics—the measurement problem—not as an abstract question, but as part of its everyday function.

Therefore, quantum computing is not just a useful technology for faster calculations but something far more significant: it is a laboratory in which we test our deepest notions of what it means for something to exist, for us to know something, and for us to measure something. A quantum computer operates on foundations that are not self-evident to classical logic, as it enables a state in which mutually exclusive possibilities are simultaneously present. According to classical logic, something cannot be both 0 and 1 at the same time. In quantum reality, however, this is not only possible but essential for its operation.

Every quantum algorithm runs in this space of possibility. During the algorithm's execution, the system simultaneously "considers" all possible paths without committing to any single one. But to get a concrete answer from the system, we must finally perform a measurement. At that moment, the wave function collapses—and we get a single result. Philosophically speaking, this is the moment when actuality emerges from potentiality. But this transition is neither smooth nor fully explained: all other outcomes, which were realistically present as possibilities just moments before, disappear—as if they never existed.

The essence is this: a quantum computer does not work in spite of the paradoxes of quantum theory, but because of them. Its power lies precisely in its ability to temporarily manage this tension: it allows contradictory possibilities to be sustained long enough to participate in a calculation and then—at the right moment—enables their conversion into a single result. This is a technology based not on avoiding the philosophical problems of quantum mechanics, but on taking them seriously and integrating them into its very operation.

Why Physics Needs Philosophy

The aim of this text has been to show that physics is already engaged with philosophical questions—often unconsciously and without the proper conceptual tools. The debate over the interpretations of quantum mechanics is not something marginal or academically exotic; it is a debate about the very picture of reality we are trying to construct when developing a theory of its most fundamental laws.

In this context, philosophy is not an outside observer of science but a toolkit essential for clarifying foundational concepts. It helps reveal hidden presuppositions, check the internal logic of arguments, evaluate the price of different explanations, and better understand what is truly at stake in fundamental scientific debates. When interpretations speak of the world—and not merely of equations—they are engaging in philosophy. And this is precisely the case with quantum physics today.

Furthermore, philosophy performs another, perhaps less obvious, but crucial role: it acts as a defense mechanism against conceptual slippage. Wherever a physical theory leaves a vacuum—as it does with the measurement problem—that vacuum is often filled by speculations bordering on mysticism, sometimes even from physicists themselves. Talk of the "role of consciousness" in creating reality or of direct links to spiritual traditions are common symptoms of this phenomenon. A rigorous philosophical approach acts as a filter here: it demands that every claim be clearly defined, logically consistent, and that its ontological commitments be made explicit. By doing so, it separates a legitimate—albeit speculative—scientific hypothesis from ill-defined statements that are, in fact, untestable. Philosophy, therefore, not only opens new avenues of thought but also offers the tools to close off those that lead nowhere, thereby safeguarding the integrity of the scientific debate.

The collaboration between philosophy and science is therefore no longer a matter of personal curiosity, but an essential part of any serious engagement with questions that probe the very foundations of nature. Philosophy will not provide new physical equations—that is, and will remain, the task of physics. But it can offer the conceptual clarity, terminological precision, and intellectual rigor needed to navigate a theory that resists everyday intuition and challenges our notions of reality. Quantum mechanics reveals a world that is not merely strange, but profoundly different from anything we have ever imagined. To truly understand it, we need more than tools for measuring—we also need tools for thinking.

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Translated from the Slovene original, available here:

ANATOMIJA VEDNOSTI / Sašo Dolenc

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