1 Motivation
But are there no positive arguments against scientific realism, i.e., arguments showing the benefits associated with embracing alternatives to realism (and thus with rejecting realism)? I believe that there is such an argument that has figured in the back of the realism-debate, but, to my knowledge, has nowhere been stated and defended explicitly. This is an argument from the success of quantum physics (QP) to the unlikely appropriateness of scientific realism as a philosophical stance towards science. I will state this argument in the next section, but let me first outline why I believe it has ‘figured in the back’ of the realism-debate.
Certainly the most influential anti-realist position to date is constructive empiricism (van Fraassen 1980). As is well known, constructive empiricism relies on a crucial distinction between observables and unobservables. Being in part inherited from earlier empiricisms, this divide was critically examined already by Maxwell (1962), who objected that “we are left without criteria which would enable us to draw a non-arbitrary line between ‘observation’ and ‘theory’.” (186)
The example is supposed to capture the distinction between entities that could in principle be observed with the naked eye and those that could not. However, what force would it have if the theory in question was not quantum?
Yet even here, the points made by van Fraassen remain subtle, and he does not put forward a straightforward argument directly from the success of quantum physics to an objection to realism. To my knowledge, no such argument has ever been explicitly put forward.
I shall here advance just such an argument, hoping to further—in the light of more recent developments—an understanding of the much-debated contention that quantum physics threatens realism. At the same time, this will also give critics a more solid foundation for arguing against QP’s relevance for the realism-question, as it will exhibit the detailed steps necessary for ‘transmitting the realism problem upwards’.
An important clarification should be made at this point: I here follow Wallace (2020) in distinguishing ‘quantum theory’ as a formal framework from concrete theories formulated within that framework, such as the Standard Model of particle physics or Schrödinger’s theory of the hydrogen atom. ‘Quantum physics’ will be used to refer collectively to all physical applications of the quantum framework. Hence, the argument presented should not be mistaken for the kind of simplistic view that, say, atoms do not exist and since everything is made out of them, nothing does. The point is far more subtle, and maybe better roughly summarized as the claim that, because our most predictive calculus does not really have realistic presuppositions, but is involved, in subtle ways, in much of science, we do not have a good claim to those realistic presuppositions.
2 The Argument
In its intuitive formulation, the argument is that because quantum physics is tremendously successful but (for reasons expounded on below) quite probably says nothing true about the world, its existence and success provides a positive reason to embrace alternatives to realism. However, this does not make it quite clear why the rest of science, outside those domains that cannot be handled by means other than quantum calculations, should be affected by this.
Hence, consider the following, more detailed argument:
- 1.
Scientific realism is only appropriate as a philosophy of science if science delivers approximately true explanations.
- 2.
If some scientific discipline �¯ inherits its success in no small part from another scientific discipline D, but not the other way around, �¯’s ability to deliver true explanations depends on D’s.
- 3.
The success of other scientific disciplines is in no small part inherited from physics. This is not true the other way around.
- 4.
If some field �¯ in a scientific discipline D inherits its success in no small part from another field F in that discipline, but not the other way around, �¯’s ability to deliver true explanations depends on F’s.
- 5.
The success of other fields in physics is in no small part inherited from quantum physics. This is not true the other way around.
- 6.
Quite probably, quantum physics does not deliver approximately true explanations.
- 7.
Therefore, scientific realism is quite probably not appropriate as a philosophy of science.
Because the want of a solid basis for realist commitments is transmitted ‘upwards’ from fundamental science to the special sciences, one might equally call this the bottom-up argument against realism. One can ‘grasp’ its validity, but the proof is non-trivial. Hence, a valid formalization, using a mixed notation of probability and logic, is offered in the Appendix.
I believe that this argument nicely captures and explicates several intuitions underlying that part of the realism-debate that has focussed on QP. However, its premises are certainly far from controversial, whence the remainder of the paper will be dedicated to their defence. As I said, this will at the same time highlight the argument’s potential vulnerabilities, and so give critics a chance to say exactly what they find wrong with claims to QP promoting anti-realism.
3 Scientific Realism is Only Appropriate If Science Delivers True Explanations
I claim that it is the positing of additional entities, structures, variables, beyond the purely observable domain. Thus, it was Bohr’s positing of discrete electron orbits, discrete (instantaneous) transitions between these, and the emission of radiation with the corresponding energies in these transitions that performed the explanatory work.
Now, committing to the Rydberg formula’s truth over a certain restricted domain would be fully acceptable for constructive empiricists and anti-realists of like guises, whereas committing to the truth of any of Bohr’s posits would not. Hence, despite the fact that novel predictive success is typically advanced by realists as the basis for investing epistemic commitment in a theory, model, or posit, such predictive success alone cannot define the dividing line between realism and anti-realism: It must be predictive success on account of the posited additional entities, structures, variables—success which is ipso facto also at least minimally explanatory.
This already brings a fair amount of clarity to what I am getting at here, but I believe even more headway can be made by building on some of the recent developments on scientific explanation. Crucially, I have relied on a qualifier ‘some form of’ in the above claim to an explanation being offered by Bohr’s atom model. Thus, following a mainstream trend in recent debates over scientific explanation (cf. Gijsbers 2016), I here embrace explanatory pluralism: explanations might “represent causal structure; [...] deploy asymptotic reasoning; [...] represent mechanisms; [...] represent non-causal, contrastive, probabilistic relations; [...] unify phenomena into a single framework;” and so on (Khalifa 2017, 8). However, the point is thus that on no such account does science deliver approximately true explanations, so long as explanation involves the positing of unobservables (as I have claimed).
