by Daniel Ranard
Nearly anyone who tells you about quantum mechanics is quick to tell you how weird it is. And perhaps any science that ventures outside the realm of the visible or the human is bound to be strange. Our universe is a strange place, filled with exotic objects whose undeniable strangeness is blunted only by familiarity: the double helix, rippling force fields, supernovae. But physicists will tell you that quantum mechanics is even stranger. They explain that distant photons may be intimately entangled, or that an electron may exist in a superposition of two places at once. They describe a world not only strange in its particulars but strange in its way of being. According to quantum theory, particles may lack definite properties until measured, and the outcomes of quantum experiments are fundamentally uncertain.
What should we make of these claims? Perhaps we should be deeply impressed. After all, quantum mechanics is not some niche of modern physics; physicists expect that the rules of quantum theory underlie all physical phenomena. And if taken seriously, these claims about quantum weirdness are claims about the nature of knowledge or existence itself. Philosophers and thinkers should take note.
But even though we might be impressed, we should also be suspicious. No definite properties, fundamental uncertainty… what could it all mean? It's hard to imagine how scientific experiments (or any line of investigation, really) might yield such bold claims. You worry that the physicists have taken their equations and their metaphors too seriously. Here it's helpful to borrow a perspective from operationalism, a school of thought in the philosophy of science. A staunch operationalist might say the real content of a physical theory lies only in the list of experimental predictions it makes: “If you build an experiment in this way, you will see result X; if you build an experiment in that way, you will see that result Y,” and so on. Any talk about invisible particles or fields then serves only to package and describe these predictions. Most philosophers agree this view is too simple, but it contains a point of truth: the language and concepts we use to describe our predictions are often a matter of taste and historical contingency. In fact, we expect that our most fundamental physical theories will be revealed as only useful approximations, undergirded by new theories with new descriptions.
Before we take claims of quantum weirdness seriously, we must ask whether the weirdness is a property of nature itself or only of our current description. This question is rarely broached in popular explanations of physics, or even in most physics classes. But the question stands: how do we know quantum theory will never be rephrased or replaced, that quantum weirdness is not just a figment of our odd descriptions?
