Part 7 (2/2)

The new experimentalism.

Introduction.

If we regard the Bayesian account of scientific inference as a failure, we still have not provided much by way of some characterisation of what it is that is distinctive about scientific knowledge. Popper posed problems for positivism and inductivism by stressing the theory-dependence of observation and the extent to which theories always transcend, and so can never be derived from, the evidence. Popper's accoun of science was based on the idea that theories are those thats urvive the severest tests. However, his account was unable to give clear guidance when a theory, rather than some element of background knowledge, should be hekd responsible for a failed test, and was unable to say something sufficiently positive about theories that happen to have survived tests. The subsequent attempts that we discussed all involved taking the idea of theory-dependence further than Popper did. Lakatos introduced research programs, and saw them retained or rejected according to conventional decisions, decisions, for example, to blame auxiliary a.s.sumptions rather than hard-core principles for apparent falsifications. However, he was unable to give grounds for those decisions, and in any case they were too weak to specify when it was time to abandon a research program in favour of another. Kuhn introduced paradigms rather than research programs thus introducing a degree of paradigm-dependence in science that was more far-reaching than Popper's theory-dependence, so much so that Kuhn was even worse off than Lakatos in giving a clear answer to the question of the sense in which a paradigm could be said to be an improvement on the one it replaced. Feyerabend can be seen as taking the theory-dependence movement to its extreme, giving up on the idea of special methods and standards for science altogether, and joining Kuhn in the portrayal of rival theories as incommen surable. The Bayesians can also be seen as part of what I am calling the theory-dependence tradition. For them the background theoretical a.s.sumptions that inform the judgments about the merits of scientific theories are brought in by way of the prior probabilities.

For one group of philosophers, the range of problems that beset contemporary philosophy of science are to be confronted by tackling the move towards radical theory-dependence at its source. Although they do not wish to return to the positivist idea that the senses provide an unproblematic basis for science, they do seek a relatively secure basis for science, not in observation but in experiment. I shall follow Robert Ackermann (1989) and refer to this recent trend as ”the new experimentalism”. According to its proponents, experiment can, in the words of Ian Hacking (1983, p. vii) have a life of its own” independent of large-scale theory. It is argued that experimentalists have a range of practical strategies for establis.h.i.+ng the reality of experimental effects without needing recourse to large-scale theory. What is more, if scientific progress is seen as the steady build up of the stock of experimental knowledge, then the idea of c.u.mulative progress in science can be reinstated and is not threatened by claims to the effect that there are scientific revolutions involving large-scale theory change.

Experiment with life of its own.

We begin this section with a historical story, drawing heavily on Gooding (1990). Late in the summer of 1820 reports reached Britain of Oersted's finding that the magnetic effect of a current-carrying wire in some way circulates the wire. Faraday undertook experimental work to clarify what this claim amounted to and to develop it further. Within a few months he had constructed what was, in effect, a primitive electric motor. A cylindrical gla.s.s tube was sealed by corks, top and bottom. A wire running through the centre of the top cork into the cylinder ended in a hook from which a second wire hung vertically. Its lower end was free to rotate around the tip of a soft iron cylinder protruding into the base of the cylinder via the bottom cork. Electrical contact between the lower tip of the dangling wire and the iron core was maintained via a pool of mercury resting on the lower cork. To activate this ”motor”, one pole of a bar magnet was held adjacent to the end of the iron core emerging from the lower cork, while a conducting wire connected the iron core to the wire emerging from the top cork via an electric cell. The ensuing current caused the lower tip of the dangling wire to rotate around the magnetised iron core, maintaining contact with the mercury as it did so. Faraday promptly sent a sample of this device to his rivals around Europe, complete with instructions on how to make it work. He pointed out to them that they could reverse the direction of the rotation either by reversing the connections to the battery or by reversing the magnet.

Is it useful or appropriate to regard this accomplishment of Faraday's as theory-dependent and fallible? It can be said to be theory-dependent in a very weak sense. Faraday's rivals on the Continent would not have been able to follow his instructions if they did not know what a magnet, mercury and an electric cell were. But this amounts to no more than a refutation of the extreme empiricist idea that facts must be established directly by the entry of sensory data into a mind that otherwise knows nothing. n.o.body need deny the claim that someone who cannot tell the difference between a magnet and a carrot is not in a position to appreciate what counts as an established fact in electromagnetism. It is surely injudicious to use the term ”theory” in such a general sense that ”carrots are not magnets” becomes a theory. What is more, construing all talk as ”theory dependent” does not help get to grips with the genuine differences between the likes of Faraday and Ampere. Faraday, as is well known, sought to understand electric and magnetic phenomena in terms of lines of force emanating from electrically charged bodies and magnets and filling the s.p.a.ce around them, while theorists on the Continent thought of electric fluids residing in insulators and flowing through conductors, with elements of fluid acting on each other at a distance. These were the theories at stake, and the appreciation of Faraday's motor effect was not ”theory dependent” in the sense that an appreciation of it depended on the acceptance of or familiarity with some version of one of the rival theories. Within electromagnetism at the time Faraday's motor const.i.tuted an experimentally established theory-neutral effect which all electromagnetic theories were obliged to take account of.

Nor is it helpful to regard Faraday's motor effect as fallible. It is true that Faraday's motors sometimes do not work, because the magnet is too weak or because the-wire is immersed so far into the mercury that the latter offers too resistance to rotation, or whatever, Consequently, the statement ”all wires situated in an experimental arrangement meeting Faraday's description rotate” is false. But this simply indicates that attempting to capture the essence of Faraday's discovery with universal statements of this kind is inappropriate. Faraday discovered a new experimental effect, demonstrated it by constructing a version of his device that did work, and gave instructions to his rivals that enabled them to build devices that worked too. The odd failure is neither surprising nor relevant. The theoretical explanation of Faraday's motor that would be accepted today differs from that offered by both Faraday and Ampere in significant respects. But it remains the case that Faraday's motors usually work. It is difficult to comprehend how future advances in theory could somehow lead to the conclusion that electric motors don't work (although they might well be rendered obsolete by future discoveries of yet other experimental effects). Looked at in this way, experimental effects that can be produced in a controlled way are not fallible, they are here for keeps. What is more, if we understand progress in science in terms of the acc.u.mulation of such effects, then we have a theory-independent understanding of its growth.

A second example supports further this way of looking at things. Jed Buchwald's (1989) detailed study of the experimental career of Heinrich Hertz indicates the extent to which Hertz aimed to produce novel experimental effects. Some of his claims to have done so did not meet with general accep tance. It is not difficult to appreciate why. Hertz had learnt his electromagnetism through Helmholtz and saw things in terms of Helmholtz's theoretical framework, which was just one of the several theoretical approaches to electromagnetism at the time (the chief alternatives being those of Weber and Maxwell). That the experimental findings of Hertz const.i.tuted novel effects could only be appreciated and defended if the fine details of the theoretical interpretation Hertz brought to his experiments were appreciated and defended. These results were highly theory-dependent, and this, a new experimentalist might well argue, is precisely why they were not generally accepted as const.i.tuting novel effects. Things were quite otherwise once Hertz had produced his electric waves. That there were such waves could be demonstrated in a way that was independent of which general theory was subscribed to. Hertz was able to exhibit this new effect in a controlled way. He set up standing waves and showed that small spark detectors showed maximum sparking at the antinodes and no sparking at the nodes of these waves. This was by no means easily achieved, nor were the results easily reproduced, as Buchwald found when he tried it. But I am not claiming the experiments were easy. I am simply claiming that the fact that the experiments demonstrated the existence of a new experimentally produced phenomenon could be appreciated in a way that did not rely on recourse to one or other of the competing electromagnetic theories, a claim borne out by the rapidity with which Hertz's waves were accepted by all camps.

The production of controlled experimental effects can be accomplished and appreciated independently of high-level theory then. In a similar vein, the new experimentalist can point to a range of strategies available to experimenters for establis.h.i.+ng their claims that do not involve appeal to high-level theory. Let us consider, for example, how an experimentalist might argue that a particular observation by way of an instrument represents something real rather than an artifact. Ian Hacking's (1983, pp. 186-209) stories concerning the use of microscopes ill.u.s.trate the point well. A miniature grid, with labelled squares is etched on a piece of gla.s.s which is then photographically reduced to such an extent that the grid becomes invisible. The reduced grid is viewed through a microscope that reveals the grid, complete with labelled squares. This already is a strong indication that the microscope magnifies, and magnifies reliably - an argument, incidentally, that does not rely on a theory of how the microscope works. We now reflect on a biologist who is using an electron microscope to view red blood platelets mounted on our grid. (Here Hacking is reporting an actual sequence of affairs reported to him by a scientist.) Some dense bodies are observable within the cell. The scientist wonders if the bodies are present in the blood or are artifacts of the instrument. (He suspects the latter.) He notes which of the labelled squares on the grid contain these dense bodies. Next he views his sample through a fluorescence microscope. The same bodies appear once again, in the same locations on the grid. Can there be any doubt that what is being observed represents bodies in the blood rather than artifacts. All that is required to render this argument persuasive is the knowledge that the two microscopes work on quite different physical principles, so that the chance of both of them producing identical artfacts can be recognised as highly improbable. The argument does not require detailed theoretical knowledge of the workings of either instrument.

Deborah Mayo on severe experimental testing Deborah Mayo (1996) is a philosopher of science who has attempted to capture the implications of the new experimentalism in a philosophically rigorous way. Mayo focuses on the detailed way in which claims are validated by experiment, and is concerned with identifying just what claims are borne out and how A key idea underlying her treatment is that a claim can only be said to be supported by experiment if the various ways in which the claim could be at fault have been investigated and eliminated. A claim can only be said to be borne out by experiment if it has been severely tested by experiment, and a severe test of a claim, as usefully construed by Mayo, must be such that the claim would be unlikely to pa.s.s it if it were false.

Her idea can be ill.u.s.trated by some simple examples. Suppose Snell's law of refraction of light is tested by some very rough experiments in which very large margins of error are attributed to the measurements of angles of incidence and refraction, and suppose that the results are shown to be compatible with the law within those margins of error. Has the law been supported by experiments that have severely tested it? From Mayo's perspective the answer is ”no” because, owing to the roughness of the measurements, the law of refraction would be quite likely to pa.s.s this test even if it were false and some other law differing not too much from Snell's law true. An exercise I carried out in my schoolteaching days serves to drive this point home. My students had conducted some not very careful experiments to test Snell's law. I then presented them with some alternative laws of refraction that had been suggested in Antiquity and medieval times, prior to the discovery of Snell's law, and invited the students to test them with the measurements they had used to test Snell's law. Because of the wide margins of error they had attributed to their measurements, all of these alternative laws pa.s.sed the test. This clearly brings out the point that the experiments in question did not const.i.tute a severe test of Snell's law. That law would have pa.s.sed the test even if it were false and one of the historical alternatives true.

A second example further ill.u.s.trates the rationale behind Mayo's position. I had two cups of coffee this morning and this afternoon I have a headache. Is the claim ”my morning coffee caused me to have a headache” thereby confirmed? Mayo's position captures the reason why the answer is ”no”, Before the claim can be said to have been severely tested, and so confirmed, we must eliminate the various ways in which the claim could be in error. Perhaps my headache is due to the particularly strong Vietnamese beer I drank last night, to the fact that I got up too early, that I am finding this section particularly difficult to write, and so on. If some causal connection between coffee drinking and headaches is to be established then it will be necessary to conduct controlled experiments that will serve to eliminate other possible causes. We must seek to establish results that would be most unlikely to occur unless coffee does indeed cause headaches. An experiment const.i.tutes support for a claim only if possible sources of error have been eliminated, and so the claim would be unlikely to pa.s.s the test unless it were true. This simple idea serves to capture some common intuitions about experimental reasoning in a neat way and is also extended by Mayo to offer some fresh insights.

Let us consider the so-called ”tacking paradox” which I ill.u.s.trate with an example. Let us imagine Newton's theory, T, has been confirmed by carefully observing the motion of a comet, with care being taken to eliminate sources of error due to attraction from nearby planets, refraction in the earth's atmosphere and so on. Suppose that we now construct theory T' by tacking a statement such as ”emeralds are green” onto Newton's theory. Is T' confii flied by the observations of the comet? If we hold the view that a prediction, p, confirms a theory if p follows from the theory and is confirmed by experiment, then T' (and a vast number of similarly constructed theories) is confirmed by the observations in question, counter to our intuitions. Hence the ”tacking paradox”. However, T' is not confirmed from Mayo's point of view and the ”paradox” is dissolved. Given our a.s.sumptions about the elimination of possible sources of error, we can say that the orbit of the comet would be unlikely to have conformed to the Newtonian prediction unless Newton's theory were true. The same cannot be said about T' because the likelihood of the comet conforming to the Newtonian prediction would be totally unaltered if some emeralds were blue and hence T' false. T' is not confirmed by the experiment in question because that experiment does not probe the various ways in which ”emeralds are green” might be false. Observations of comets can severely test T but not T'.

Mayo extends this line of reasoning to less trivial cases. She is keen to keep theoretical speculation in check by identifying theoretical conclusions that go further beyond the experimental evidence than is warranted. Her a.n.a.lysis of Eddington's test of Einstein's prediction of the bending of light in a gravitational field ill.u.s.trates the point.

Eddington took advantage of an eclipse of the sun to observe the relative position of stars in a situation where the light from them pa.s.sed close to the sun on their pa.s.sage to earth. He compared these relative positions with those observed later in the year, when the stars were no longer closely aligned with the sun. A measurable difference was detected. By looking at the details of the eclipse experiments Mayo is able to argue that Einstein's law of gravity, which is a consequence of his general theory of relativity, was confirmed by them, but the general theory of relativity itself was not. Let us see how she does so.

If the results of the eclipse experiments are to be taken as confirming the general theory of relativity, then it must be possible to argue that those results would be most unlikely to occur if the general theory is false. We must be able to eliminate erroneous links between the general theory and the results. This could not be done in the case in question because there are, as a matter of fact, a whole cla.s.s of theories of s.p.a.ce-time of which Einstein's theory is only one, all of which predict Einstein's law of gravity and hence the results of the eclipse experiments. If one of this cla.s.s of theories other than Einstein's were true, and Einstein's false, exactly the same results of the eclipse experiments would be expected. Consequently, those experiments did not const.i.tute a severe test of Einstein's general theory. They did not serve to distinguish between it and known alternatives. To claim that the eclipse experiments supported Einstein's general theory of relativity is to go further beyond the experimental evidence than is warranted.

The situation is different when we consider the more restricted claim that the eclipse experiments confirmed Einstein's law of gravity. The observations certainly were in conformity with that law, but before it is legitimate to take this as evidence for the law, we must eliminate other possible causes of the conformity. It is only then we can say that the observed displacements would not have occurred unless Einstein's law is true. Mayo shows in some detail how alternatives to Einstein's law, including Newtonian alternatives arising from an inverse square law attraction between the sun and photons presumed to have ma.s.s, were considered and eliminated. Einstein's law of gravity was severely tested by the eclipse experiments in a way that the general theory of relativity was not.

The new experimentalists are generally concerned to capture a domain of experimental knowledge that can be reliably established independent of high-level theory Mayo's position meshes well with that aspiration. From her perspective, experimental laws can be confirmed by severely testing them along the lines discussed above. The growth of scientific knowledge is to be understood as the acc.u.mulation and extension of such laws.

Learning from error and triggering revolutions.

Experimental results confirm a claim when they can be argued to be free from error, and when the results would be unlikely if the claim were false. However, there is more to Mayo's focus on the importance of experimental error than this. She is concerned with how well-conducted experiments enable us to learn from error. Looked at from this point of view, an experiment that serves to detect an error in some previously accepted a.s.sertion serves a positive as well as a negative function. That is, it not only serves as a falsification of the a.s.sertion, but also positively identifies an effect not previously known. The positive role of error detection in science is well ill.u.s.trated by Mayo's reformulation of Kuhn's notion of normal science.

Let us recall our account, in chapter 8, of the conflicting answers given by Popper and Kuhn to the question of why astrology fails to qualify as a science. According to Popper, astrology is not a science because it is unfalsifiable. Kuhn points out that this is inadequate because astrology was (and is) falsifiable. In the sixteenth and seventeenth centuries, when astrology was ”respectable”, astrologers did make testable predictions, many of which turned out to be false. Scientific theories make predictions that turn out to be false too. The difference, according to Kuhn, is that science is in a position to learn constructively from the ”falsifications”, whereas astrology was not. For Kuhn, there exists in normal science * le-solving tradition that astrology lacked. There is more to science than the falsification of theories. There is also the way in which falsifications are constructively overcome. It is ironic, from this point of view, that Popper, who at times characterised his own approach with the slogan ”we learn from our mistakes”, failed precisely because his nega tive, falsificationist account did not capture an adequate, positive account of how science learns from mistakes (falsifications).

Mayo sides with Kuhn here, identifying normal science with experimentation. Let us note some examples of the positive role played by error detection. The observation of the problematic features of Ura.n.u.s's...o...b..t posed problems for Newtonian theory in conjunction with the background knowledge of the time. But the positive side of the problem was the extent to which the source of the trouble could be traced, leading to the discovery of Neptune in the way we have already described. Another episode we have mentioned before concerns Hertz's experiments on cathode rays, which led him to conclude that they are not deflected by an electric field. J. J. Thomson was able to show that he was in error, in part by appreciating the extent to which the rays ionise the residual gas in discharge tubes, leading to a build-up of charged ions on electrodes and the formation of electric fields. By achieving lower pressures in his tubes and arranging his electrodes more appropriately, Thomson detected the influence of electric fields on cathode rays that Hertz had missed. But he had also learnt something about new effects concerning ionisation and the build-up of s.p.a.ce charge. In the context of the deflection experiments these const.i.tuted impediments to be removed. However, they also turned out to be important in their own right. The ionisation of gases by the pa.s.sage of charged particles through them was to be fundamental for the study of charged particles in cloud chambers. The experimentalist's detailed knowledge of the effects at work in an apparatus puts him or her in a position to be able to learn from error.

Mayo does more than simply translate Kuhn's notion of normal science into experimental practice. She points to the way in which the facility of experiment to detect and accommodate error can prove sufficient to trigger or contribute to a scientific revolution, a decidedly unKuhnian thesis. Mayo's best example concerns the experiments on Brownian Motion conducted by Jean Perrin towards the end of the first decade of this century. Perrin's detailed, ingenious, down-to-earth observations of the motions of Brownian particles established beyond reasonable doubt that their motion was random. This, together with observations of the variation of the density of the distribution of particles with height, enabled Perrin to show as conclusively as one could wish that the motion of the particles violate the second law of thermodynamics as well as conforming to detailed predictions of the kinetic theory You can't get much more revolutionary than that. A similar story could be told about the way in which experimental investigations of black body radiation, radioactive decay and the photoelectric effect, for instance, forced an abandonment of cla.s.sical physics and const.i.tuted important elements of the new quantum theory in the early decades of the twentieth century.

Implicit in the new experimentalist's approach is the denial that experimental results are invariably ”theory” or ”paradigm” dependent to the extent that they cannot be appealed to to adjudicate between theories. The reasonableness of this stems from the focus on experimental practice, on how instruments are used, errors eliminated, cross-checks devised and specimens manipulated. It is the extent to which this experimental life is sustained in a way that is independent of speculative theory that enables the products of that life to act as major constraints on theory. Scientific revolutions can be ”rational” to the extent that they are forced on us by experimental results. The extremes of the theory- or paradigm-dominated views of science have lost touch with, and cannot make sense of, one of its most distinctive components, experimentation.

The new experimentalism in perspective.

The new experimentalists have shown how experimental results can be substantiated and experimental effects produced by an array of strategies involving practical interventions, cross-checking and error control and elimination in a way that can be, and typically is, independent of high-level theory. As a consequence of this, they are able give an account of progress in science that construes it is the acc.u.mulation of experimental knowledge. Adopting the idea that the best theories are those that survive the severest tests, and understanding a severe experimental test of a claim as one that the claim is likely to fail if it is false, the new experimentalists can show how experiment can bear on the comparison of radically different theories, and also how experiment can serve to trigger scientific revolutions. Careful attention to the details of experiments and to exactly what they do establish serves to keep theorising in check, and helps to distinguish between what has been substantiated by experiment and what is speculative.

There is no doubt that the new experimentalism has brought philosophy of science down to earth in a valuable way, and that it stands as a useful corrective to some of the excesses of the theory-dominated approach. However, I suggest it would be a mistake to regard it as the complete answer to our question about the character of science. Experiment is not so independent of theory as the emphasis of the previous sections of this chapter might suggest. The healthy and informative focus on the life of experiment should not blind us to the fact that theory has an important life too.

The new experimentalists are right to insist that to see every experiment as an attempt to answer a question posed by theory is a mistake that underestimates the extent to which experiment can have a life of its own. Galileo didn't have a theory about Jupiter's moons to test when he turned his telescope skywards, and, ever since then, many novel phenomena have been discovered by exploiting the opportunities opened up by new instruments or technologies. On the other hand, it does remain the case that theory often does guide experimental work and has pointed the way towards the discovery of novel phenomena. After all, it was a prediction of Einstein's theory of general relativity that motivated Eddington's eclipse expeditions and it was Einstein's extension of the kinetic theory of gases that led Perrin to investigate Brownian motion in the way that he did. In a similar vein, it was fundamental theoretical issues concerned with whether the rate of change of the polarisation of dielectric media should have magnetic effects like a conduction current that put Hertz onto the experimental path that culminated in the production of radio waves, and Arago's discovery of the bright spot at the centre of a disc's shadow resulted from a direct test of Fresnel's wave theory of light.

Whether theory can sometimes guide the experimentalist in the right direction or not, the new experimentalists are keen to capture a sense in which experimental knowledge can be vindicated in a way that is independent of high-level theory. Certainly Deborah Mayo has given a detailed and convincing account of how experimental results can be reliably established using an array of error-eliminating techniques and error statistics. However, as soon as the need arises to attach significance to experimental results that extends beyond the experimental situations in which they were produced, then reference to theory needs to be made.

Mayo endeavours to show how error statistics can be applied to carefully controlled experiments to yield the conclusion that experiments of that type yield specified results with a (specified) high degree of probability. Recorded experimental results are treated as a sample of all the possible results that might be achieved by experiments of that type, and error statistics can be applied to attribute probabilities to the population on the basis of the sample. A basic issue here is the question of what counts as an experiment of the same type. All experiments will differ from one another in some respects, insofar as, for example, they are conducted at different times, in different laboratories, using different instruments and so on. The general answer to the query is that the experiments must be similar in relevant respects. However, judgments about what counts as relevant are made by drawing on current knowledge, and so are subject to change when that knowledge is improved. Imagine, for example, Galileo conduc

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