Disclaimer: this is a short reflexion that I have tried to put under 1000 words. The subject is vast and this post should be understood as a synopsis introducing more detailed future reflexions on important sub-questions involving the intricate relationship between science and philosophy.
I was asked recently to tell in which way philosophy contributed to the physical sciences.
I felt that the question was ironic to some extent since, although philosophy has greatly contributed to modern branches of physics like cosmology (for example by answering questions like: is it a science? what does it tell us about the world? what constitutes a satisfactory explanation? etc..), some authorities in this field and astrophysics have been clear on the total absence of contribution of philosophy to their daily work. Just to name a couple of (very visible) extreme cases:
- In his book “Dreams of a final theory”, S. Weinberg (1979 Nobel prize in physics) has a dedicated chapter called “Against Philosophy” where he is appalled by the “unreasonable ineffectiveness of philosophy” in the physical sciences in a joking comparison with Wigner’s awe at the “unreasonable effectiveness of mathematics” in the physical sciences.
- In at least two occasions, renown physicist S. Hawking has claimed that “philosophy is dead” to such an extent that it cannot even answer the questions that are philosophical by their nature and so physics must take care of it in its stead.
- The popular cosmologist L. Krauss has repeatedly claimed that philosophy was not only obsolete for science (and physics in particular) but also for anything else .
- To some extent, there is a trend to take and re-use literally a provoking joke from R. Feynman (1965 Nobel prize in physics) claiming that “Philosophy of science is as useful to science as ornithology is useful to birds”.
So, in light of these strong opinions voiced by leading figures in cosmology and physics, how should one reply to the initial question?
I think it is a fair point to say that some (maybe most) physicists do not use philosophical thinking (or at least not consciously) on a daily basis. In a Kuhnian sense, they mostly work in the context of normal science. But then, do they ever need to take (knowingly or not) a philosophical stance? And to this question I would say they do and in at least 2 different ways:
- In deciding what do the contemporary physical sciences tell us about the world (implicitly here scientific realism is adopted to some degree). This has to do with spelling out as clearly as possible the worldview(s) that emerges from currently accepted theories and models in all their possible nuances. For example, physicists might disagree on the fundamental ontologies one should be talking about: fields or particles? Or about the nature and function of time in physics (see for example Rovelli or Smolin). In cosmology this plays a big role when understanding what people mean by vacuum or beginning for example. These could also encompass decisions regarding what questions are worth answering (often because no answer is provided by the currently accepted theory or framework) and sometimes goes back to the “typicality” of the phenomenon to be explained. Hence, J. Kepler tried to relate a nested arrangement of the Platonic solids to explain the size of the various orbits of the planets relative to the Sun while Newton, in his third book of Principia, simply stated that these observations relied on historical contingency. To some extent, resorting to the anthropic principle to address the fine tuning problem is of the same nature. And as one may know there are plenty of ongoing debates with regards to what quantum mechanics tells about the world.
- Physicists also use philosophical arguments in a broader context when physics or the future of a branch of physics is concerned. This again has two aspects: on the one hand when deciding for a change of paradigm (as it has happened multiple times within the 20th century), physicists do actually appeal to criteria of what is a “better” claim than another: they can resort to aesthetics, simplicity (via Ockham’s razor), number of new predictions, practical testability, plausibility of the theory (Bayesian inference) and backward compatibility with previously held ideas to name a few. The above mentioned criteria can for example be used to claim a non-equivalence between the concordance model of cosmology and rival theories for dark matter and dark energy, thus solving in a certain way the underdetermination problem of theories by empirical evidence. On the other hand, physicists and scientists use philosophical arguments when it comes to the legitimacy of scientific claims with regards to objective truths or even absolute truths when employed outside of the scientific “playing field”. These claims usually put science on a pedestal to inform the civil society or more broadly policy making agencies in modern societies and usually require that we are able to discriminate science from pseudo-science (something that looks like science but is not science). In this case, scientists must resort to philosophical arguments like K. Popper’s to justify the legitimacy of their claims (while putting on the side other contributions like Kuhn’s…see link about Weinberg above). It is interesting (and deplorable) to see that this demarcation is also often done between scientific disciplines whereby the more mathematical sciences would have a stronger pretence to truth at the expense of other scientific disciplines less mathematically versed ranging from biology to sociology. But highly mathematical branches of science are not safe either. One remarkable case happened 2 years ago when physicists and philosophers joined forces to discuss whether string theory could be considered proper science or not. Here again the motivations appeared to be societal and related to the funding of a given research programme considered useless by some physicists and the possible devaluation of the image of “truth giving discipline” of physics in the public eye.
Overall, philosophy in a broad sense does contribute to the physical sciences but, more often than not, without the physicists themselves being fully aware of it or even denying they resort to it. This state of affairs can be a consequence of the overspecialisation of the sciences already deplored by physicist and philosopher C. F. von Weizsacker more than 40 years ago and characterises how the great successes of the physical sciences of the last three centuries may have made its practitioners forget what constitute its intellectual foundations so that only relics of them remain to this day. In fact, the sciences have progressed so fast in the 20th century that there is a need for philosophy to serve both as a safeguard with regards to some claims made by scientists (and the physical sciences in particular) in the public sphere (e.g. claims and a critic with respect to ethics) and inform physicists (and other scientists) about puzzles they might have overlooked (an example in quantum mechanics) in their haste.