PHILOSOPHY TO THE RESCUE: What quantum mechanics is cannot be understood by physicists alone?

Photo source: fau.eu

This year, the scientific world marked the centenary of quantum mechanics. Yet after a century, experts are forced to admit that different scientists understand its meaning in different ways. Its history and current status remain a battlefield for subjective interpretations. This became clear as a result of the largest survey of scientists conducted by the international scientific journal Nature.

QUANTUM THEORY HAS MANY “MEANINGS”

If you ask a group of physicists to explain a quantum experiment, you are unlikely to hear the same description twice. At the same time, all of them would agree that the mathematical foundation of quantum mechanics brilliantly predicts the results of experiments in the subatomic world. It is used to create a wide range of technologies — from computer chips to lasers and atomic clocks. Yet, paradoxically, its practical usefulness does nothing to clarify for scientists the physical meaning of this theory. Hence, there is a large number of subjective interpretations of this mystery. Over the past 100 years, physicists have still failed to reach a consensus on the fundamental nature of reality, the particles, and the forces that shape it. This has happened for a whole range of reasons.

A VERY NARROW CONSENSUS

Quantum mechanics allows researchers to match expected observational results with exceptional precision. And this is not only impressive but also profoundly strange. Experiments point to an indeterminate and probabilistic quantum world. The phenomenon of entanglement can bind the fates of particles together even when they are physically separated by great distances. They appear to behave like waves, interfering with one another and with themselves until they are measured. But as soon as a measurement is made, their behavior becomes more ordered. Then, it seems, the outcomes of experiments are governed by statistical rules. But at that point, one could say, the scientific consensus comes to an end.

WHAT THE SURVEY OF SCIENTISTS REVEALED

The largest survey of scientists in the history of science, conducted by the journal Nature, showed that disagreements arise immediately when physicists are asked what exactly they mean by all of the above. For example, there are different answers to the question: what happens to quantum objects between measurements? Or what underlies phenomena such as randomness? Likewise, there is almost no consensus on other questions. Can a particle truly exist in two places at once? Do multiple universes exist? And, in general, do the mathematical quantities underlying quantum mechanics correspond to anything real?

“REALISTS” AND “EPISTEMOLOGISTS”

Alas, the survey results raise more questions than answers. However, if one attempts to classify the many subjective interpretations, they can be conventionally divided into two large groups. The first are the “realists”, who believe that quantum physics can and should provide a visualizable description of the world. The second are supporters of the “epistemic” view (from the Greek episteme — knowledge), who interpret the theory solely as concerning knowledge and the prediction of experimental results.

AWAITING A NEW THEORY

The disputes between these two groups of scientists create tremendous confusion in the minds of “ordinary” people, opening wide space for all kinds of pseudoscientific theories and speculation. But on the other hand, this lack of agreement may be highly beneficial, since it objectively drives science forward. This is especially true in the case of technologies such as quantum computers and quantum cryptography. Scientists hope that their debates will ultimately help uncover a path toward resolving physics’ seemingly unsolvable mysteries. For example, understanding the nature of gravity, the only fundamental force of nature that quantum theory is currently unable to explain. According to the Naturesurvey, about 75% of researchers believe that quantum theory will inevitably be fully or partially replaced by another, more complete theory.

A BET ON INTUITION AND IMAGINATIVE THINKING

While waiting for a new theory to emerge, physicists rely not so much on experiments and calculations as on imagination and intuition. Thus, Alain Aspect of Paris-Saclay University, who received the Nobel Prize in Physics in 2022, considers the diversity of views on quantum foundations to be a wonderful source of imagery. And imaginative thinking, in Aspect’s view, in turn stimulates intuition. Thought experiments are precisely what help modern scientists make progress in understanding the foundations of quantum physics. Here, one may mention Renato Renner and Daniela Frauchiger of ETH Zurich. Their thought experiment imposed limits on what different interpretations can simultaneously regard as true.

HOW TO SHED LIGHT ON DARK MATTER

Today, not only thought experiments but real ones are reaching a grand scale. A highly significant event was the experiment involving the world’s largest dark matter detector, XENONnT, located beneath Gran Sasso in Italy. With its help, a group of scientists from the United States, Europe, and Asia attempted to detect dark matter particles that interact with atoms of liquid xenon. According to current understanding, dark matter makes up about 85% of the matter in the Universe, does not emit light, and barely interacts with ordinary matter. Dark matter itself was not detected during the experiment. However, scientists succeeded in obtaining the strictest limits to date on the interaction of light dark matter with electrons.

THE COPENHAGEN INTERPRETATION

To create a less blurred picture of the quantum world, scientists propose deepening the dialogue between physicists and philosophers. This would make it possible to better understand the different linguistic interpretations and assumptions used in quantum theories. Let us recall that one of the most widespread approaches to understanding quantum theory is the Copenhagen interpretation. It emerged as the result of combining the views of two founders of the field — Niels Bohr and Werner Heisenberg — who by no means always agreed with one another. However, both believed that the theory should not be based on what cannot be observed, and that it is better to focus on what can be tested experimentally.

PHYSICS AND PHILOSOPHY NEED EACH OTHER

True, as the Nature survey showed, the approach of Niels Bohr and Werner Heisenberg is not especially popular among those concerned with the philosophical foundations of quantum theory. In turn, physicists, unlike “philosophers”, rarely agree that certain “radical” theories can explain their observations. For example, theories such as the many-worlds interpretation which assumes the existence of a vast number of universes. Nevertheless, a growing understanding is emerging within the scientific community that physics and philosophy are necessary to one another. They are closely intertwined, interconnected, and there is no clear boundary between them. It is possible that precisely at the intersection of these disciplines, imaginative thinking and intuition may give rise to outstanding scientific concepts that go beyond the limits of today’s narrow consensus.

Original research: