Alexander Christian - Philosophy of Science

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Paul Hoyningen-Huene

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There is a plausible prima facie answer to the title question whether there are good arguments against scientific realism, which simply is no! The source for this answer is the ubiquitous behavior of scientists, more specifically of physicists: they are usually straightforward realists when it comes to discussing scientific results. Good physicists have a solid education, are usually diligent, rational, intelligent, and self-critical people (at least as long as they talk science, not necessarily when they talk about science). Here is an example from recent, very topical science (suspect of earning some of its authors a Nobel Prize in physics). The upper half of Fig. ). The interpretation of these data is summarized in the conclusion of the paper: The language of this conclusion (and of the whole body of the paper) is uncompromisingly realist: they have observed gravitational waves, the existence of binary stellar-mass black hole systems is demonstrated, gravitational waves have been directly detected, and a binary black hole merger has been observed for the first time. There is no talk of or any argument for the given realist interpretation of the data: no other possibility is mentioned, let alone explicitly discarded based on some argument. Therefore, for the physicists involved more than 1000 figure as authors of the paper the case seems clear: they just detected really existing gravitational waves and observed the really existing merger of a pair of really existing black holes. Any argument for the evidently realist interpretation of the data is lacking. This suggests that the authors deem such an argument just totally unnecessary. If we stick to the hypothesis that this group of physicists is a bunch of fairly rational people, we must conclude that there simply are no serious arguments against the realist stance taken up in the paper, otherwise these arguments would have been confronted (and possibly disproved). Therefore, in the view of physics, as implicitly contained in the cited paper, the case seems clear: there are no serious arguments against scientific realism.

However, there seem to be serious dissenting voices: there are quite a few statements by (theoretical) physicists and chemists exactly to the contrary. A prominent example is Stephen Hawking: This statement seems to be in blatant contradiction with the realist stance of the physicists who discovered gravitational waves. Is Hawking perhaps fundamentally different from these physicists? It may come as a surprise that he is not, at least as far as black hole physics and gravitational waves are concerned. In the context of the 1960s and 1970s discussion about the possible detection of gravitational waves, Hawking published a paper entitled Gravitational radiation from colliding black holes (Hawking ). Its abstract reads: Hawking refers to gravitational radiation emitted and collapsed object[s] (i.e., black holes), and there is no sign in the paper that these things are only calculational devices with no reality content, as one would expect from an instrumentalist. Instead, he speaks about them in the same language as one speaks about any ordinary real physical object. Hawkings stance in this paper is thus purely realist. However, what shall we make of this apparent contradiction between a purely realist and a radically instrumentalist stance occurring in the same author?

My suggestion is that we should distinguish, in somewhat fashionable terminology, different discourses, or: ways of reasonably discussing things (or language games). I shall describe the differences between these discourses as differences in the levels of their philosophical radicality . There is a ground level, or level zero, of philosophical radicality in which nothing is put into question for philosophical motives. On this level, nothing is doubted beyond what is doubted in normal scientific practice (or in everyday discourse, for that matter). For instance, in cutting edge scientific discourse about new hypothetical objects, many things are taken for granted, for instance realistically interpreted established theories and those parts of the experimental equipment that have been exhaustively tested. Taken for granted only means that these things are not questioned in the given context which does not, of course, exclude their being questioned in other contexts, be it scientific or philosophical contexts (more on the latter see below). For instance, in the recent discovery of gravitational waves and of inspiraling black holes, it was taken for granted (among many other things) that the theory on which the design of the lasers was based was correct, that the data that the two detectors produced were the result of optical interference, and that General Relativity Theory was the right theory to interpret the data (see Abbott et al. The question in focus was the existence of gravitational waves and, for any particular case, their concrete sources. Clearly, this is a thoroughly realist stance: the pertinent scientific theories are interpreted realistically, and the question is whether gravitational waves really exist and what their sources are. Thus, the enterprise is a purely scientific one, devoid of any additional philosophical questioning.