MODELING IN QUANTUM FIELD THEORY
1. SOME PHILOSOPHICAL VIEWS OF EXPERIMENTS
An experiment is the manipulation of apparatus which is an arrangement of material stuff integrated into the material world in a number of different ways. I shall refer to such integrated wholes as apparatus-world complexes. In the course of the manipulation some process of interest is made to occur in an apparatus-world complex. The process more often than not results in discernible transformations of the apparatus. A close analysis of the kinds of equipment in use in the sciences will lead us see that there are two very different ways of interpreting these transformations. In those cases in which an apparatus is serving as a working model of some natural system, the changes brought about by experimental manipulations must be interpreted as analogous to states of the natural system being modeled. In those cases in which an instrument is causally affected by some natural process, the changes in the instrument are effects of the relevant state of the material world. These effects must be interpreted in terms of the causal relation presumed to hold between the process in nature and the state of the instrument. It will be convenient to use the word 'instrument' for that species of equipment which registers an effect of some state of the material environment such as a thermometer, and the word 'apparatus' for that species of equipment which is a model of some naturally occurring structure or process, such as the use of a calorimeter to study the effect of salt on the freezing point of water, or in vitro fertilization. Science has advanced so far now that there are pieces of apparatus in which processes are made to occur that have no analogues in nature, for instance the equipment used for cloning large animals.
The manipulation of material stuff extends beyond the experiment as such, into the past and into the future. The apparatus has to be created, designed and built by technicians from available material. As Toulmin (1953) pointed out, the materials used must be subjected to processes of purification. This demand covers not only the reagents used in chemistry but also the material of
176 Section Five: Introduction
which an apparatus is made. There are all sorts of presumptions then about the past of an instrument. There are also presumptions about the future of an instrument. Though a specific piece of equipment need not survive in order for an experiment to be replicated, it must be possible to reproduce versions of the material structures of the apparatus in the future. The replicability of experiments depends on that condition. Even something like a space probe that is burnt up in the Jovian atmosphere should, in principle, be able to be duplicated, and the experiment done again. If an instrument does survive to be used again it must be presumed that no radical changes have occurred during the course of the original experimental procedure.
Whether the equipment is an apparatus built to be a working model of some feature of the world, or an instrument causally transformed by processes in the world, the result of an experiment is a reading of the end state of a process. Much can happen to equipment after the moment at which the experiment ends. However, the moment at which the experiment is taken to have ended, and so which state is taken as the end state of the experiment, is not an arbitrary cut in a continuous causal process. It is determined by the project for which the experiment was undertaken.
1.1. Experiments in Logicist Philosophy of Science
The long-standing idea that philosophy of science is a branch of logic has two aspects. There is, or might be, an inductive logic that legitimizes generalizing the results of observation and experiment. These generalizations are ot~en presented as laws of nature. Scientific knowledge, so obtained, is presented in writings organized according to the principles of deductive logic. The laws of nature and other generalizations are used as axioms in the deductive process. The result of working within this framework has been the privileging of the proposition as the entity around which discussion and debate as to the acceptability of putative contributions to scientific knowledge must centre.
For the most part the discourse of 'experiments' was shaped by a standard format. According to logicism, the relation between the material world and the discourses of science was taken to be entirely captured by the relation between the propositional forms of an updated version of the Aristotelian Square of Opposition. Experiments and observations were reported in the 'Some A are B' or 'Some A are not B' forms, and general laws or law-like propositions, of the 'All A are B' or 'If x is A then x is B' forms. Occasionally the 'No A are B' propositional form was required. Philosophy of science was thought to start where the propositional universe began. All this seemed entirely natural during the domination oflogicism in philosophy of science.
Experimental results were just there to be described, brute facts, so to say. Observations were usually mentioned in the same breath as experiments. Even when the first intimations of a more subtle account of how states of the world were captured in propositions appeared, in the thesis of the theory-ladenness of descriptions, the role of the apparatus as such, as the locus of the genesis of phenomena, was ignored.
Logicist philosophy of science is the legacy of two philosophers above all, Mill and Mach.
Mill's methods ~ 1 1872) were the result of his attempt to identify the logical forms of patterns of reasoning that led from particular propositions to general propositions. His general propositions were causal laws in the Humean sense, that is they reported exceptionless correlations between types of observable states of the world. Mach's contribution was two fold.
His 'sensationalist' metaphysics confirmed a phenomenalist strand in philosophy of science, having its source in British empiricism. Science was concerned with discovering the relations between sensations. His account of laws of nature was Humean. They were nothing but summaries of instances of correlations between types of sensations, serving as mnemonics to
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recover any instance at will. The Mach-Mill analysis of scientific knowledge confirmed the project of the search for scientific rationality as the development of an inductive logic (Mach 1914).
The once popular Popperian fallibilism involved an inversion of the general schema of inductive logic--'From true statements describing the results of experiments or of observations one can infer a true general statement which can be judged to be worthy to be accepted as knowledge.' The logic of scientific discovery for Popper could be expressed as a general schema from deductive logic m 'From a true statement describing the result of an experiment or observation that contradicts a prediction deductively drawn from a general hypothesis, one can infer the falsity of the hypothesis, which must be judged worthy to be rejected as knowledge'.
Both the inductivist and the fallibilist principles are offered as rules governing scientific discourse.
Popper's only discussion of the sources of descriptive propositions is confined to a few comments on the conventionalist origins of descriptive predicates and the need to take certain basic statements to be true by convention (Popper 1967).
From a logicist point of view, experiments are simply the unproblematic sources of descriptive propositions in the Aristotelian L and 0 forms, 'Some A are B' or 'Some A are not B' The only feature of experiments that matters in logicism is the restriction of their spatial and temporal span to the here and now. This means that descriptions of empirical studies in science can exhibit only the I and 0 forms. It is also worth noting that experiments have traditionally been lumped in with observations, in the frequently recurring phrase, 'observations and experiments.' Both are cited as sources of I and 0 propositions.
The upshot is a complete neglect of the apparatus itself. Since it was never attended to the variety of kinds of apparatus was never discussed.
1.2 Experiments in Constructionist Philosophy of Science
Latour (1987) and others have discussed apparatus and experimental manipulations. I shah use his account as a stalking horse.
We can use technically crafted things to do science. The relation between apparatus and Nature needs to be analyzed. Its value to science as the best means for obtaining representations of aspects of Nature needs to be justified. Latour's move, which, as we shall see, sidelines this issue, is to delete the idea of Nature as an independent being from the account of science. In his treatment, apparatus is wholly a humanly created artifact that brings other artifacts into being.
These determine what Nature is for the scientific community.
When we use experimental equipment of either kind, apparatus or instruments, according to Latour, we are taking up material things into discourse. Here is Latour's interpretation of an experiment.
The guinea pig alone would not have been able to tell us anything about the similarity of endorphin to morphine; it was not mobilizable into a text and would not help convince us.
Only a part of the gut, tied up in a glass chamber and hooked up to a physiograph, can be mobilized in the text and add to our conviction (Latour 1987, p. 67).
The observation that Latour uses to push one towards the textual interpretation of experimental activity is his account of an instrument. It is deliberately severed from its place as a material thing integrated into a material system that includes the world. The material entity, though ultimately of natural origin, is detached from its place in nature. According to Latour, it is 'mobilized in the text'. The laboratory, he says is 'a set of new [rhetorical] resources devised in such a way as to provide the literature with its most powerful tool: the visual display (Latour 1987, p. 68).
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I will call an instrument (or inscription device) any set-up, no matter what its size.
nature or cost, that provides a visual display of any sort in a scientific text (Latour 1987, p. 68).
What is behind a scientific text? Inscriptions. How are these inscriptions obtained? By setting up instruments (Latour 1987, p. 69).
Just as in the logicist neglect of the instrument that makes it invisible, in this rendering of its role it becomes relevant only in so as it produces inscriptions. Only these are relevant to and define its importance for the enterprise of science. The triad 'world/apparatus/inscription' is replaced by a dyad, 'apparatus/inscription.' An apparatus is something that produces inscriptions, like a ticker- tape machine.
There are two obvious difficulties with this account. It does not seem to me to differ in any substantial way from the logicist account. In that too experiments are relevant only in so far as they are the source of inscriptions to be added to the text. Secondly, if inscription producing were all that apparatus is good for, then surely any material set-up that produced inscriptions would do!
By what criteria do we reject De La Warr's boxes ~ and accept Wilson's cloud chamber as genuine scientific equipment?
At the beginning of its definition the "thing" is a score list for a series of trials.., the 'things' behind the scientific texts are all defined by their performances [and are similar to the heroes of folk tales]. Thus the thing is not identified or p i c k e d out by its performance: that is a cloud chamber and it makes droplets, and that is a Geiger counter and it makes clicks' (Latour 1987, p.
89). The thing is d e f i n e d by what it does.
That is not yet all. As an ally in a scientific dispute, the cloud chamber of metal and glass dissolves not into lines of droplets, but into a visual display of subatomic particles, in short, a kind of statement. Similarly, the Geiger counter, having dissolved into clicks, dissolves even further into part of an auditory display of a wave-like distribution of particles. This raises a nice point, since the cloud chamber favours a particle interpretation and an array of Geiger counters favours the wave picture. What is the relationship between the displays? It cannot just be that one is an auditory display and the other visual. Why should they have anything to do with one another?
That this is a constructionist account is confirmed by Latour's third rule of method (Latour 1987, p. 99): 'since the settlement of a controversy is the cause of Nature's representation not the consequence, we can never use the outcome - Nature - to explain how a n d why a controversy has been s e t t l e d ' 'Nature's representation', something propositional and abstract, is equated with 'Nature' something concrete and material. This follows inexorably if we are willing to accept that it is the use of apparatus that creates Nature by displaying readable representations of nature.
The final step in assimilating the material and the propositional is Latour's special notion of the 'black box.' The story of Herr Diesel and his engine (Latour 1987, p. 105) provides the setting. For the use of the engine to spread through the world, it must be possible to treat it wholly in terms of its performance as a source of motive power. Those who use the engine need not be forever worrying about the fine details of how it works. However, to get these fine details right required the recruitment of a great many 'allies' to the project. At times these allies fell away De La Wan produced diagnostic 'machines' that were made of odds and ends. They were shown to be worthless.
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and the engine's fate was uncertain. Only as a umfied whole with all the components working properly did it make its way into the practical world. According to Latour a 'black box' exists when many elements are brought together to act as one.
This step having been taken the reconstitution the formerly material thing, the apparatus, as text seems to be a natural step. As Latour says, 'no distinction has been made [by him] between what is called a "scientific fact" [a proposition] and what is called a "technical object" or
"artifact'" (Latour 1987, p. 131).
There is only one difference between colleagues as allies and machines as allies in settling scientific controversies, according to Latour. It is easier to see that the gathered resources are made to act as one unified whole in the case of machines and pieces of hardware than in the case of colleagues and communities and runs of learned journals.
Latour has attended to the importance of practical skills, in such matters as 'making the equipment work.' However, these appear as bargaining encounters in social competition for community hegemony. Such skills are defined in a quite complex way with respect to the material nature of experimental equipment and the tasks of technicians in using it to display what it is expected to display, and sometimes does not. Failures are not always due to incompetent manipulations but to the intransigence of Nature which, as integrated with this apparatus, is other than the scientific community thought it to be. In Latour's treatment, it is hard to see that any distinction between these/grids of failures can be made.
No doubt we get the idea of what Nature is like from experiments. However, it is not that idea that is integrated with a bit of itself in a laboratory apparatus. Despite attention to the real world of the laboratory, Latour (and others) do not clearly distinguish the role of people talking and writing and so producing 'science', in the sense of a community discourse from the role of people making and manipulating material things and using them. The former are manipulating an idea or representation of Nature, the latter are manipulating Nature. It is evident that Latour does not treat these as different. He is led by the illuminating power of his metaphors, especially 'ally', to assume an identity. Nevertheless, the fact that a metaphor 'sticks' does not justify taking the similarity of source and subject that the metaphor makes visible to be an identity.