Abstract
Baker (Br J Philos Sci 54:245–259, 2003) argues that quantitative parsimony—the principle that hypotheses requiring fewer entities are to be preferred over their empirically equivalent rivals—is a rational methodological criterion because it maximizes explanatory power. Baker lends plausibility to his account by confronting it with the example of postulating of the neutrino in order to resolve a discrepancy in Beta decay experiments. Baker’s account is initially attractive, but I argue that its details are problematic and that it yields undesirable consequences when applied to the case of astrophysical dark matter. Baker has not succeeded in showing why quantitative parsimony is a theoretical virtue.
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Notes
For a modern description of Beta decay, see http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/fermi2.html#c1. In Beta decay, a proton (with quarks up, down, up) decays via the weak interaction to a neutron (with quarks up, down, down), releasing an electron plus an electron anti-neutrino.
This assumes that quantitative parsimony never advises us to postulate zero entities of a kind that qualitative parsimony permits. If quantitative parsimony does tell us to postulate zero dark matter particles—that would be equivalent, perhaps, to a general injunction against unobservable entities—then quantitative parsimony would be telling us to prefer a gravitational solution to the astrophysical dynamical discrepancy. But then Baker’s explanation of the value of quantitative parsimony in terms of explanatory power cannot work: having zero dark matter particles does not explain anything. I therefore ignore this possibility in the discussion of Baker that follows.
The non-observation of dark matter is easier to explain with less massive dark matter units because more massive particles have a larger cross section of interaction and thus should be more easily detectable in particle detection schemes; they would be expected to have shorter decay times and hence would be more readily inferable from decay products such as radiation; if we are dealing with approximately Jupiter-mass objects, improved micro-lensing sensitivity will detect them or rule them out; and so on. I suppose we could say that hypotheses postulating more massive dark matter units are more testable or more falsifiable, but that in itself does not show that dark matter is in fact more likely to come in more massive units.
Thanks to a referee for this journal for pointing this out.
For these purposes I skip over secondary effects that would be produced by some of these matter distributions, on the basis of which they might be distinguished empirically. For example, some of the candidate matter solutions to Mercury’s anomalous perihelial precession would have produced effects on Venus’s orbit that were not observed.
The analogy between the Beta decay discrepancy and the astrophysical dynamical discrepancy is tighter than may at first appear. It would have been possible, before the experimental confirmation of the existence of neutrinos in 1956, to have explained Beta decay by saying that spin and mass-energy are not conserved—Niels Bohr actually proposed denying conservation of mass-energy in the quantum realm. But would such a theory be more simple or less simple than one that postulates an otherwise unknown particle to explain the same phenomenon?
Perhaps out of recognition of the difficulty of giving an explicit account of how to balance the many competing factors in theory choice situations, Duhem (1982, 216–218) declined to do so, giving authority instead to the “good sense” of experienced scientists in deciding which of the competing hypotheses to pursue or adopt.
References
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Acknowledgments
An earlier version of this paper was presented at the annual meeting of the British Society for Philosophy of Science held at Canterbury in July 2004. I thank members of the audience for questions, comments and encouragement, especially Jeremy Butterfield, Lee Smolin and James Ladyman. I am also grateful to the referees for this journal for their helpful comments.
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Vanderburgh, W.L. Quantitative Parsimony, Explanatory Power and Dark Matter. J Gen Philos Sci 45, 317–327 (2014). https://doi.org/10.1007/s10838-014-9261-9
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DOI: https://doi.org/10.1007/s10838-014-9261-9