There are some questions in physics that no amount of physics research can answer. Why, for example, is doing string theory scientific despite its lack of empirical predictions? How should we interpret quantum mechanics? And what, while we’re at it, is so fundamental about physics? We can answer such questions dogmatically by appealing to textbooks or by making rough and ready pronouncements, but the underlying issues are best clarified with the help of the systematic, critical reflection that philosophy practises.

You’d expect me to say that; I am a philosopher after all. So I’ll ignore all the stupid and half-arsed remarks about philosophy that I’ve heard from physicists who should know better and come straight to the point: philosophers seek to understand, not what physicists know, but how they know it. And because physicists are constantly discovering new ways to know things, philosophy of physics is as alive, valuable and active as physics itself.

Three traditions

Philosophy comes in several traditions, of which three – “analytic”, “pragmatic”, and “continental” – have paid particular attention to physics. They are stylistically and methodologically divergent and, to outsiders, may erroneously look like political parties squabbling over ideological commitments. These traditions, however, have distinct perspectives on science. It’s a bit like how chemists, physicists and engineers have distinct perspectives on atoms: different features of the subject matter are put centre-stage, and analysed in different vocabularies for different ends.

Analytic philosophers, whose founding figures include logicians and mathematicians such as Rudolf Carnap and Bertrand Russell, are mainly interested in the logic of science and the meaning of its basic concepts. Starting with the language of scientific theorizing, they seek the logical conditions for its successes. Analysts tend to agree that concepts and theories are what can be known about the world, and that these are judged by testing models against observations. They focus on the “epistemology” of science – on its conceptual and methodological issues, on the logic of scientific inquiry, on evidence, and on the conceptual structure of its findings. Analysts essentially regard physicists as logicians of the world.

Pragmatic philosophers, whose founders include Charles Peirce (a physicist), William James and John Dewey, are interested in how scientists solve puzzles and what the consequences are. They know that humans don’t spring into being thinking like scientists but apprentice to become them. Pragmatists believe that true scientific ideas make a difference to the world and to science, that inquiry involves doing rather than just cognition, and that scientific work is judged by how well it explains, predicts, and gives us power over (rather than just describes) nature. Pragmatic philosophers view physicists as puzzle-solvers of the world.

Continental philosophers, whose founding figures include Edmund Husserl and Martin Heidegger, approach scientific activity as one way of life, among others, in which humans engage with the world. Continental philosophers agree that scientific activity gives a primacy to things that appear in a certain (framed) way – to things that can be measured and manipulated – and tends to ignore things that do not, such as the powerful metaphors, images and deeply embedded habits of thought that shape our thinking. Continental philosophers agree it’s a mistake to assume that the original human encounter with the world is cognitive, for all ways of being, scientific activity included, spring from a pre-scientific engagement with the world. Humans must be trained, technically and interpretatively, to think like scientists. Continental philosophers view physicists as disclosers of the world insofar as it is knowable and manipulable.

Three approaches

Philosophers of physics take their most important problems not from textbooks but from the practice of physics itself: what problems in physics can’t more research make go away? How a philosopher approaches such problems – the scientific character of string theory, say – depends on their tradition.

Analytic philosophers would start with their traditional description of scientific method – in which testability is essential – and add additional criteria to make string theory conform. Pragmatists wouldn’t be obsessed with whether string theorists were following any specific method, which might change with science itself. Instead, they’d judge string theory by whether it made a difference to physics – whether it yielded insights about existing physics (field theory for instance), and carried forward the aims of the theoretical physics community. Continental philosophers would start by investigating why physicists are stuck on this question – why one group of physicists thinks that ascertaining whether string theory is scientific should be settled by appealing to traditional concepts of “method” and “confirmation” while another group finds it sufficient to consult the actual experience of practising physicists. Each group evidently understands something about physics that cannot yet be articulated to everyone’s satisfaction, making such a controversy deeply revealing about physics itself.

The critical point

What philosophers can do, in short, is to encourage reflection on the practice of physics, especially on urgent and obstinate questions such as “Is string theory scientific?” The various philosophical approaches each bring different kinds of expertise to their analyses of this question and scrutinize in detail different features of what is taking place: logic, puzzle-solving, and interpretative and self-interpretative activity.

Analytic philosophers can stimulate the question of how much the answer has to do with methodology. Pragmatists can argue that answering such a question is less methodological and more a matter of evaluating the consequences of accepting or rejecting string theory. Continentals can point to the relevance of scientists consulting their own experience, so that they are not just reflecting on questions of method, confirmation, inquiry and community consensus, but also considering how the relationship between science and the wider world can become part of the regular practice of science itself.

Is encouraging these kinds of reflection of value to physicists? How could it not be?