Why quantum mechanics needs philosophy

Author: Bethany Terris, PhD Philosophy of Physics, France Ambassador

Quantum mechanics is an incredibly successful scientific theory. Its applications are vast, ranging from high-precision lasers to high-performance computing. Despite this success, over 100 years since the conception of quantum theory, physicists still disagree on its meaning and consequences for the world we live in.

In most areas of science, we expect successful theories to eventually settle disagreements; if a theory makes accurate predictions, then it must say something about the world. Quantum theory is different. While those studying the theory may agree on the mathematics and the outcomes of experiments, they disagree about what lies beneath those results. Does the wavefunction describe something physically real, or is it simply a tool for making predictions? Does a quantum system possess definite properties before it is measured? What role, if any, does an observer play in determining physical reality?

These questions are loaded with philosophical nuance, it is impossible to answer them with just mathematics or experiment alone. They require us to examine the concepts that lay beneath the mathematics, and this is where philosophy comes in.

When people hear the word “philosophy”, they often imagine abstract debates completely disconnected from scientific practice. They may imagine ancient scholars, draped in robes, debating life’s deepest questions: What makes a good life? What is knowledge? What is justice? Or, more recently, perhaps they think of seminar rooms filled with young, hopeful students, debating the very same questions that have been debated for millennia, with no chance of finding a concrete solution. Although the pragmatically inclined may see such debates as frivolous, these debates do matter; not only are they intellectually stimulating and pleasurable to engage in, philosophy also extends its influence into many modern disciplines: law, political science, economics, education, and ethics to name a few.

Quantum mechanics is one such area to benefit from the work of the philosopher. The questions raised by quantum theory are fundamentally philosophical. They concern the nature of reality, observation, explanation, causation, and probability. Such questions are reminiscent of those being debated in university philosophy departments throughout history, across the globe.

Consider the wavefunction, the mathematical object at the heart of quantum mechanics. Everyone agrees on how to use it. However, physicists disagree on what it represents. According to some interpretations, it corresponds to a real physical entity. According to others, it merely encodes an observer’s information about a system [1], while others suggest that every possible outcome of a quantum measurement actually occurs in different branches of reality [2]. Remarkably, these interpretations often make the same experimental predictions. The disagreement is therefore about how we should understand and interpret the theory itself.

This is one of the most visible examples of where philosophy enters quantum theory. However, the role of philosophy extends far beyond choosing between interpretations. More broadly, it seeks to understand the very foundations on which modern physics is built.

One of the most important contributions of philosophy is the clarification of concepts. Before scientists can answer a question, they must first understand what the question means. Philosophy helps clarify fundamental concepts such as space, time, causality, information, and measurement. These concepts are often taken for granted, yet quantum mechanics has challenged many of them in unexpected ways. What exactly counts as a measurement? What is information, and can it be considered a physical quantity? While they may sound abstract, these questions lie at the very foundations of quantum theory.

Philosophy also helps uncover assumptions that might otherwise go unnoticed. Throughout history, scientific progress has oftentimes required questioning ideas that once seemed obvious. Newton’s theory challenged traditional views of motion, Einstein transformed our understanding of space and time, and quantum mechanics forced physicists to reconsider assumptions about determinism and locality. By identifying and examining these underlying assumptions, philosophy encourages scientists to think critically about the frameworks in which they work. Philosophy is not only concerned with analysing existing theories; it can also help to generate new scientific questions. Careful philosophical investigation has frequently inspired new experiments and theoretical developments. A famous example comes from the work of Bell, who questioned whether quantum mechanics could be explained by hidden variables while preserving locality. His analysis led to Bell’s theorem [3], transforming what at first appeared to be a philosophical debate into a question that could be tested experimentally. Today, Bell tests play a central role in quantum information theory.

At this point, you may still be wondering why any of this actually matters; if quantum technologies can be built successfully just using quantum theory as it stands, why should anyone working in quantum computing, sensing, or communication care about philosophy?

The answer is that science is more than calculation and experimentation. While these methods lead to outcomes, innovation often comes from understanding concepts deeply enough to ask new questions. The history of physics shows that progress is frequently driven not only by technological advances, but also by conceptual breakthroughs.

For those working in quantum technologies, philosophy can provide valuable tools for critical thinking, problem-solving, and communication. It encourages us to examine assumptions, distinguish between what we know and what we merely believe, and think carefully about the concepts underlying our best scientific theories. These skills are increasingly important in a rapidly developing field where scientific, technological, and societal questions often intersect.

Many of today’s emerging research areas sit at the boundary between physics and philosophy. Questions about the nature of information, the foundations of quantum computing, and the role of causality in quantum systems continue to inspire both theoretical and experimental research. Engaging with philosophical inquiry does not inhibit scientific or technological progression, nor is philosophy a pointless pursuit for the idleminded. It is a tool for navigating questions that lie beyond the reach of theory or experiment alone. As quantum technologies continue to advance, philosophy remains an invaluable companion, propelling the science forward, and helping us understand not only how quantum mechanics works, but what it means.

References

[1] Fuchs, Christopher A., and Asher Peres. “Quantum theory needs no ‘interpretation’.” Physics today 53, no. 3 (2000): 70–71.

[2] Everett III, Hugh. ““Relative state” formulation of quantum mechanics.” Reviews of modern physics 29, no. 3 (1957): 454. [3] Bell, John S. “On the Einstein Podolsky Rosen paradox.” Physics 1, no. 3 (1964): 195.