If you were to poll a thousand physicists, you’d find no consensus. This assertion applies to a multitude of subjects, including the nature of the universe, the composition of dark matter, and the quest for perfectly efficient wiring. Recently, the team at Nature raised inquiries that sharply delineated the field’s divisions. They conducted a survey of 1,100 physicists regarding their preferred interpretations of quantum mechanics. The outcome? They exhibited “significant disagreement.”

This does not surprise me. In my reporting, I frequently encounter physicists who interpret the results of quantum experiments in varied ways. They might all analyze the same equation or experimental outcome but arrive at different narratives about reality.

So, how significant is this discord, and what does the quest for interpretation really entail? To begin with, it’s peculiar how things unfold within quantum mechanics, a discipline we’ve explored for over a century amid a plethora of unfortunate tests. There’s no denying the robust success of quantum mechanics, a remarkable framework governing the actions of the extremely small or the extremely cold. This theory not only passes all evaluations with distinction but also leads to technological innovations like transistors that power electronic devices and fiber optics for the internet. “Quantum mechanics is remarkably successful, both theoretically and practically,” asserts Peter Lewis from Dartmouth College in New Hampshire.

However, while physicists can articulate equations and construct devices, if I may put it bluntly, they don’t always agree on what these equations signify. They fail to reach consensus on how quantum mechanics describes the observable realities of our world. Research published in Nature indicates that the Copenhagen interpretation of quantum mechanics discourages contemplation on the nature of quantum entities, prompting physicists to focus merely on calculations. Others endorse the many-worlds interpretation, which necessitates belief in an infinitely expansive universe or a hyper-deterministic theory. Notably, only 24% of physicists expressed complete confidence in their chosen interpretations.

Discrepancies also surfaced regarding fundamental aspects of quantum theory, such as wave functions, the enigmatic link between particles referred to as quantum entanglements, and the iconic double-slit experiment that confirmed all matter possesses hidden wave-like attributes. “Moreover, some scientists, even those in similar camps, exhibit varied understandings of their chosen interpretations,” Elizabeth Gibney highlighted in her analysis of the research.

Lewis observes that this scenario—a blend of extraordinary technical advancement and complete philosophical bewilderment—is unparalleled in the annals of science. Navigating this situation remains a challenge. Some physicists perceive it as a discredit to the field, while others argue it’s a positive aspect of scientific diversity. I found myself wrestling with the term “interpretation” to discern which viewpoint I align with the most. What does this term actually imply, and what criteria make an interpretation viable or competitive? Ultimately, I returned to the source material.

“For me, interpreting quantum mechanics transcends mere physics; it veers into philosophy or perhaps psychology,” noted Jeffrey Harvey from the University of Chicago. I recall his class as being a mathematical challenge, and I vividly remember the excitement of discovering that the waves in the abstract Hilbert space “exist.” However, I struggle to remember any clear arguments surrounding the interpretations of the complex mathematical outcomes we examined. Harvey expresses hesitance in teaching various interpretations, citing competition from established “mental models” over experimentally discernible frameworks. When two interpretations stem from the same equation and yield identical experimental predictions, why favor one over the other? “This reflects an agnostic stance. I’d prefer to keep an open mind rather than feel compelled to choose,” Harvey explained.

Jontae Hans, located at the University of Newcastle in the UK, contends that the term interpretation is often utilized too broadly. Some interpretations effectively extend quantum mechanics by adding or modifying core equations. “The challenge lies in the fact that interpretations are viewed differently, as well as the specific issues faced by quantum mechanics,” Lewis states. The Nature survey revealed respondents’ insights across eight interpretations, some of which augment the foundational quantum mechanics rules, while others simplify them, leaving the question of their necessity open for debate, as seen in the Copenhagen interpretation.

To grasp this distinction, consider the famous Schrödinger equation. This is the equation physicists employ to predict outcomes related to quantum objects. Several interpretations of quantum mechanics (e.g., the many-worlds interpretation) rely on the original Schrödinger equation as it was initially formulated. Conversely, a theory termed “decoherence” seeks to uncover why quantum effects are infrequently observed in our macroscopic world, incorporating additional symbols and numbers into the Schrödinger equation that signify new physical processes. Hans asserts that this technically renders the latter an extension rather than merely an interpretation. In such cases, experimental tests could potentially reveal whether our reality necessitates modification of the Schrödinger equation.

This could provide evidence compelling researchers like Harvey to abandon agnosticism. Hans suggests that a successful extension of quantum mechanics could explain numerous experiments whose predictions are already highly accurate, while also insisting that different interpretations can yield clearly distinct and testable predictions.

At the same time, all three researchers acknowledged that many physicists manage to perform their daily tasks without delving into the complexities of quantum mechanics interpretations. This partly explains why my class with Harvey didn’t cover quantum mechanical interpretations; I was primarily taught how to apply the theory. “I don’t perceive it as a problem in terms of innovation and applications in most areas of quantum mechanics. [Interpretation] is mainly a philosophical concern,” Lewis remarks.

Nonetheless, it doesn’t mean that interpretations lack merit, even when competing interpretations don’t yield differing experimental predictions. “While physicists may find interpretations less integral to physics, they can significantly influence how innovative ideas emerge. In that regard, I believe the diversity of mental models fosters exploration of new concepts arising from quantum mechanics,” says Harvey.

Moreover, even philosophical perspectives hold weight, especially regarding the growth of quantum mechanics. For Lewis, this historically unprecedented divide between utility and meaning in quantum mechanics might offer insights into the limitations of science and the philosophical boundaries regarding what can or cannot be understood. The fact that quantum mechanics, a mathematical model explaining the world exceptionally well, still lacks consensus on its significance is telling.

Hans similarly argues that assigning meaning is a fundamental aspect of physics. When discussing this, they often reference social media posts from people like Elon Musk. While I may not have seen them, I’m struck by the tremendous simplifications in their claims. “For me… it’s all about developing equations; it’s about engineering. While some are inclined to pursue engineering careers, I haven’t followed that path. This doesn’t imply engineers lack curiosity; rather, I feel some tension stemming from existential concerns. It’s a question that has kept physicists awake for centuries, and it will likely persist into the future.