Physicists face an array of different kinds of challenges. Some involve research—measuring a key parameter, elaborating a theory, or solving some other research puzzle. Other challenges have to do with securing equipment, materials or funding. Yet a third set of problems stems from questions that no amount of physics expertise or resources can make go away. Examples include the following: Why is doing string theory scientific despite its lack of empirical predictions? How to interpret quantum mechanics? What is the nature of time and space? What constitutes fundamental physics? Controversies about these and similar issues have recently riled not only physics but also affect how outsiders view the discipline.

These kinds of controversies arise because physics is a highly complex activity made possible by inherited concepts and convictions that sometimes collide with each other or with developments or discoveries in a way that cannot be resolved by more laboratory research. These clashes can often be handled in a rough and ready practical way by scientists, but the issues behind them also can often be significantly clarified by critical reflection. Because philosophy is the systematic process of critical reflection, this kind of controversy is a place where physics and philosophy overlap, so we can call this third category of issues ‘philosophical challenges’. Examining a few such philosophical challenges is a good way to illustrate what philosophy of physics is about, and its value for physicists.

To get an idea of how this overlap can happen, think of the realm of physics as like a giant workshop, a specialized and regulated environment where it is possible to create and study things and events—Higgs bosons, rare isotopes, superfluids—that do not appear, or appear crudely and rarely, in the surrounding world. Inside the workshop, we can be in near-complete control of the things and events we stage to try to understand ‘the complicated array of moving things’, as Richard Feynman says at the beginning of his lectures on physics. Inside the workshop, we can make sure that the results are general and do not depend on features of the world outside. Inside the workshop, researchers can put questions to nature, in Galileo’s words, or question it like a court witness, in Immanuel Kant’s. Nature is silent to those who would understand it unless it is probed. But there are no blank or formless questions; questions are always ‘from somewhere’, given specific form by the particular inherited concepts and practices that make meaningful both the questions and the responses. This inheritance consists of certain fundamental and generally unquestioned assumptions about matters taken for granted in the scientific quest for knowledge. Questions arise when mismatches occur between what is found in the world and physicists’ expectations, and the answers may call into doubt aspects of the inheritance. Physics grows by answers that modify the workshop traditions—by the introduction of new concepts, such as the Higgs field, that change the tradition—or by seeking out and discovering some piece of evidence that the tradition says should be there: the Higgs field itself.

Philosophers of physics—and to some degree, all philosophers of science, though I will focus here only on philosophers of physics—are interested in the interactive activity of the workshop. But philosophers pay attention to this process differently than physicists do. I’ll ignore the ignorant and half-witted remarks about philosophy that I’ve encountered by physicists who should have known better, and get right to it: philosophers seek to understand, not what physicists know, but how they know it. They study the back-and-forth cycle of interpretation and inquiry, which they call ‘the hermeneutic circle’, in a technical way. Philosophers investigate matters taken for granted in the workshop, such as the role of the tradition, different manners of questioning, the changing practices and assumptions of those who question, the nature of inquiry, and the way of life that finds it important to inquire into nature. This makes for enormous differences between physics and philosophy, and means that physics and philosophy of physics have different concepts, methods, standards, interests and literature. It also ensures that philosophy of physics is as alive, relevant and as full of active questions as physics itself.

There is a danger that philosophers may try to make the workshop interactions fit a single image or model. They may fall victim to the temptation, for instance, to try to capture what is happening in the workshop in terms of a characterization like ‘realism’ or ‘instrumentalism’ or ‘nominalism’ or ‘idealism’, and then try to shoehorn what they see of workshop activity into it. This is not only a bad way to inquire into something, but can lead physicists to suspect the wrong-headedness or irrelevance of philosophy. The first duty of a philosopher, like that of any scientist, is to look and describe rather than judge and prescribe. When this happens, it can help resolve the philosophical challenges mentioned above.

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