Abstract
H. Collins has challenged the empiricist understanding of experimentation by identifying what he thinks constitutes the experimenter’s regress: an instrument is deemed good because it produces good results, and vice versa. The calibration of an instrument cannot alone validate the results: the regressive circling is broken by an agreement essentially external to experimental procedures. In response, A. Franklin has argued that calibration is a key reasonable strategy physicists use to validate production of results independently of their interpretation. The physicists’ arguments about the merits of calibration are not coextensive with the interpretation of results, and thus an objective validation of results is possible. I argue, however, that the in-situ calibrating and measurement procedures and parameters at the Large Hadron Collider are closely and systematically interrelated. This requires empiricists to question their insistence on the independence of calibration from the outcomes of the experiment and rethink their position. Yet this does not leave the case of in-situ calibration open to the experimenter’s regress argument; it is predicated on too crude a view of the relationship between calibration and measurement that fails to capture crucial subtleties of the case.
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Notes
The broader philosophical motivation for advocating such a view, especially the claim that epistemological criteria cannot be disentangled from the social context, is motivated in part by Wittgenstein’s mature philosophical views and the understanding of epistemological criteria it condones (Collins 2002). Yet focusing on Wittgesteinian traits of Collins’s argument does not answer the question of whether Franklin’s reading of the argument as hopelessly social constructionist is correct. For gesturing to late Wittgenstein’s philosophy implies little more than a vague view that social practices and sound epistemological criteria are entangled. Wittgenstein himself spent decades trying to understand either how they could be entangled, or why they cannot be disentangled even for the purposes of the analysis—depending on which interpretation of his philosophy one subscribes to.
We will see that a number of techniques applied at the LHC can be defined as calibration precisely in light of sharing this particular key aspect.
Franklin and Howson (1984) explain why experimenters prefer to vary rather than simply reproduce well known phenomena.
He also suggests strategies other than calibration that brake the experimenter’s regress.
In addition, there is more statistical data coming from this channel, allowing for a more precise disentanglement of signal and backgrounds as harsher cuts can be applied.
Because the Higgs boson couples with the top quark, in combination with the W boson mass, we can determine the Higgs’ mass.
“Both the commissioning as well as the measurement of b-tagging efficiencies and jet energy corrections from data are crucial for the searches for new physics phenomena.” (Van Mulders 2010, p. 15)
Early commissioning calibration is done in-situ, based on the parameters of each detector, as well as with cross-checking detectors, where a parameter for a detector is calibrated against the parameters provided by other detectors.
In order to extract the pole mass of the top quark the mass of W boson is constrained by world average value, a value obtained from all relevant experiments (with its corresponding uncertainty).
Similarly, the Monte Carlo simulations are tuned to data in order to provide appropriate corrections of parton collisions. (Van Mulders 2010, p. 83)
For instance, a mercury-based thermometer can be calibrated with a constant volume gas thermometer, a completely different apparatus that works on a different physical principle. But it can also be calibrated against other mercury based thermometers by using containers made of materials with different thermal coefficients. The commissioning calibration is more closely analogous to the former case, while the in-situ calibration to the latter.
“Currently the most precise measurements of Mt are performed by the Tevatron experiments, but the ATLAS and CMS results are getting more and more precise.” (Blyweert 2012, p. 5)
Although Franklin may not object to any of the points I will make individually, his account does not emphasize them and does not assimilate them into a general account or into conclusions concerning the relation between the calibration and the outcome.
This insight illustrates why the case-studies that identify various strategies of validation, rather than vacuous conceptual discussions and distinctions, are the most reliable and effective way of refining the empiricist viewpoint.
See Karaca (2013) for an insightful discussion of the distinctive layers of theories used in high-energy physics experimentation.
References
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Acknowledgments
This work was supported by the project “Dynamic Systems in nature and society: philosophical and empirical aspects” (evidence # 179041) financed by the Ministry of Education, science and technological development of the Republic of Serbia. I am grateful to Helge Kragh, Brian Hepburn, Samuel Schindler, John Norton, and graduate students in the course I taught at the Department of the History and Philosophy of Science at the University of Pittsburgh for commenting on the very first draft of the manuscript; Allan Franklin and Harry Collins for their encouragement and gentle criticism; and especially two anonymous referees for an outstanding effort to improve my argument.
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Perovic, S. Experimenter’s regress argument, empiricism, and the calibration of the large hadron collider. Synthese 194, 313–332 (2017). https://doi.org/10.1007/s11229-015-0749-6
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DOI: https://doi.org/10.1007/s11229-015-0749-6