When I wear my hat as a philosopher of science (partially distinct from my other hat as an evolutionary biologist), I eventually run into a scientist (I could name names, but I won’t) who smugly tells me that philosophy obviously doesn’t make progress. The evidence? Philosophers disagree on all sorts of things and there is no emerging consensus—unlike in science, especially physics.

Setting aside that this kind of reasoning largely reflects ignorance of how philosophy works (surprise—it’s different from science!; see Pigliucci 2017), it turns out that there is at least one area of science where things appear to be characterized by utter confusion and lack of consensus: interpretations of quantum mechanics. And we have the empirical evidence to prove it.

Sujeevan Sivasundaram and Kristian Hvidtfelt Nielsen, of Aarhus University in Denmark, carried out a study of physicists’ attitudes concerning foundational issues in quantum mechanics (Sivasundaram and Nielsen 2016). The results are eye-opening. The survey is based on 149 responses to a questionnaire that the authors sent to 1,234 physicists affiliated with eight universities.

One obvious question posed by Sivasundaram and Nielsen was whether physicists need an interpretation of quantum mechanics in the first place. After all, quantum mechanics is a mathematical theory, and it does an incredibly accurate job of predicting the results of experiments. What else is needed? If your answer is “nothing,” then you belong to the infamous “shut up and calculate” school of thought. It’s comprised of physicists who think that it’s a waste of time to try to attach physical interpretations to the equations: the math is all there is, the rest is a waste of time. Philosophy, if you will.

The fact is, Sivasundaram and Nielsen’s results show that the shut up and calculate school is in the minority, at only 23 percent. By contrast, 65 percent of surveyed physicists responded that it’s important to arrive at a physical interpretation because it helps us understand how nature works. This difference of opinion reflects a more fundamental contrast between two attitudes about the nature of science itself. On the one hand, we have what philosophers of science call “anti-realists,” meaning people who think science is not in the business of arriving at truths about the world but can only produce empirically adequate models. The shut up and calculate people belong to this group, whether they realize it or not. The realists, by contrast, think that the whole point of science is to produce true statements about how the world actually works, so they are never going to be satisfied with just mathematical models—no matter how phenomenally accurate.

Naturally, Sivasundaram and Nielsen then asked physicists what their favorite interpretation of quantum mechanics happens to be, considering there is a large field of choices available (Lewis 2022). The responses were all over the place: 36 percent answered that they have no favorite interpretation; 39 percent preferred the Copenhagen one; 6 percent the many worlds; another 6 percent the information-theoretical; 3 percent went for a statistical interpretation; 2 percent each for De Broglie-Bohm and objective collapse; 1 percent each for modal interpretation, quantum Bayesianism, and consistent histories. The other 7 percent fell under “not sure” or “other.” Not only is there no consensus, but one may be forgiven for having assumed that the many worlds interpretation is all the rage—at least given the coverage it has gotten in recent years because of one very prominent physicist (Sean Carroll) pushing it in the public sphere.

Sivasundaram and Nielsen also wanted to know whether people change their minds about their favorite interpretation. Setting aside the 40 percent who claimed not to have a favorite, 38 percent responded “never,” 11 percent “once,” and 12 percent “several times.” The issue, it seems, is far from being settled. Indeed, one might wonder on what basis a physicist would change his or her mind about this or arrive at a particular conclusion in the first place. After all, the various interpretations are empirically equivalent, meaning that they all make exactly the same predictions about observable phenomena. Let that sink in: there is no way to empirically tell apart different interpretations of quantum mechanics. One might even suspect that this isn’t really science. It smells more like … metaphysics!

But perhaps physicists agree on more specific questions concerning quantum mechanics. For example, we often hear that the theory says that physical events are, at the fundamental level, random. Are they? It depends on whom you ask. While 67 percent of respondents agreed with the statement that randomness is a fundamental concept in nature, 12 percent thought that randomness is only apparent. Eighteen percent said that randomness cannot be removed from any physical theory, while 4 percent thought that the universe is, at bottom, deterministic, though we just haven’t gotten to the point of proving it yet.

Another thing you often hear about quantum mechanics is that it shows that objects as we understand and perceive them don’t have their properties prior to measurement. The most famous conceptualization of this notion is Schrödinger’s cat, which is both alive and dead until someone opens and looks into the infamous box in which the cat is located. Forty-seven percent of surveyed physicists agreed with this picture, but 38 percent did not. (The other 15 percent fell under “not sure” or “other.”) So which one is it? Cat lovers want to know.

Sometimes, instead of “measurements” physicists talk of the “observer” fixing the properties of objects, thus unwittingly lending apparent credence to all sorts of Deepak Chopra–style nonsense about the role of consciousness in the cosmos. But it turns out that professional opinion is divided here too. Thirty-seven percent of physicists who returned the survey said that the observer is a complex quantum system, 31 percent that it plays a fundamental role in quantum formalism but no distinguished physical role, 22 percent that it does play a distinguished physical role, and 10 percent that it plays no fundamental role at all.

One of my favorite questions, because it again strikes at the core of what physicists think about the nature of science, was “if two physical theories give the same predictions, what properties would make you support one over the other?” A whopping 87 percent picked simplicity, that is, the famous Occam’s razor. But theoretical physicist Sabine Hossenfelder has written an entire book to explain to her colleagues that simplicity, beauty, and other nonempirical criteria are simply not reliable guides to truth (Hossenfelder 2020). Plenty of simple and/or beautiful theories have been favored in the past and are now piling up in the garbage dump of the history of science.

And here is another fascinating insight from the survey conducted by Sivasundaram and Nielsen: apparently, a good number of physicists don’t know what they are talking about when it comes to quantum mechanics, which only reinforces their colleague Richard Feynman’s famous quip that if you think you understand quantum mechanics, you probably don’t. When asked what characterizes the Copenhagen interpretation, which is the oldest and most famous of them all, the responses were all over the place—including places that were mutually exclusive! And in fact, similar results were obtained when Sivasundaram and Nielsen asked the same question about the many-worlds interpretation.

I don’t mean to make (too much) fun of my colleagues in physics. But I do mean to make a couple of serious points. First, there is significant disagreement about the nature of science among professional scientists. Second, physicists are at odds with each other about several fundamental questions in their field. Reflecting on these two observations ought to invite us to practice a bit of humility whenever we are tempted to confidently talk about the scientific method, the nature of science, and the scientific view of the world.

As philosophers of science have been arguing for a while now, there is no single scientific method; the nature of science is complex and difficult to pin down. As a result, the scientific view of the world shifts all the time. This complexity and instability, however, are not bugs; they are features. Understanding the world on the basis of empirical evidence—which is what science is in the business of doing—is a hard job fraught with perils. It is arguably a miracle (in the secular sense of the term) that we do know so much about what goes on at both the cosmological and the fundamental scales of reality, given how far they are from our day-to-day experiences.

Einstein famously said that the whole of science is nothing more than a refinement of everyday thinking. If that’s true, it is a hell of a refinement. The current state of affairs in quantum mechanics seems to me to indicate that Einstein, for once, didn’t get it right.

References

Hossenfelder, S. 2020. Lost in Math. New York, NY: Basic Books.

Lewis, P.J. 2022. Interpretations of quantum mechanics. Internet Encyclopedia of Philosophy. Online at https://iep.utm.edu/int-qm/.

Pigliucci, M. 2017. On progress in philosophy: Philosophy as the evocation of conceptual landscapes. In R. Blackford and D. Broderick (eds.), Philosophy’s Future: The Problem of Philosophical Progress. Hoboken, NJ: Wiley & Sons. Online at https://bit.ly/3KqoyNC.

Sivasundaram, S., and K.H. Nielsen. 2016. Surveying the attitudes of physicists concerning foundational issues of quantum mechanics. arXiv 1612.00676. Online at https://arxiv.org/abs/1612.00676.