In this chapter we shall examine the role of the experiment of Christenson, Cronin, Fitch, and Turlay in refuting the concept of invariance of physical processes under CP (combined space inversion and particle–antiparticle interchange). We shall see that this experiment was a “convincing” experiment. It persuaded most of the physics community that CP was violated. There were, however, several alternative explanations offered to explain this result, and we shall also discuss the role that experiment played in refuting or eliminating these alternatives. We begin with the historical background of the experiment and then examine both the experiment itself and the reaction of the physics community to it.

HISTORICAL BACKGROUND

From the time of their discovery in 1947 by Rochester and Butler, the neutral K mesons, or kaons, have exhibited odd features. One puzzle, that certain K particles of equal masses and lifetimes (called θ and τ) seemed to decay into states of opposite parity, was resolved by the discovery of parity nonconservation (see Chapter 1). An equally puzzling observation concerning the kaons was put this way by C. N. Yang: “While the [se] strange particles are produced quite abundantly (say 5% of the pions) at BeV energies and up, their decays into pions and nucleons are rather slow (10−10 sec). Since the time scale of pion-nucleon interactions is of the order of 10−23 sec, it was very puzzling how to reconcile the abundance of these objects with their longevity (1013 units of time scale).”

In the previous chapter I argued that there is an epistemology of experiment, a set of strategies that are used to provide rational belief in an experimental result. These strategies distinguish between a valid observation or measurement and an artifact created by the apparatus. One such strategy, suggested by Hacking, is intervention. Hacking's example involves use of the microscope, with the experimenter “intervening” (i.e., staining, injecting fluid) and in other ways manipulating the object under observation. This is a special case of a more general strategy in which we predict what will be observed if the apparatus is working properly or is working as we expect it to. When the observation is made, we increase our belief in the proper operation of the apparatus and in its results. Hacking also suggests that we believe in an observation if it can be made using “different” microscopes (i.e., optical, polarizing, phase-contrast, etc.) or if it is independently confirmed. If the apparatus is based on a well-corroborated theory, we also have good reason to trust its results. Even without such a theory we can validate observations. Sometimes the phenomena themselves provide such evidence. The observations of the moons of Jupiter by Galileo were extremely unlikely to have been artifacts of the telescope, as suggested by Cremonini, because they appeared to represent a consistent planetary system and even obeyed Kepler's Third Law (R3/T2 = constant).

If all plausible sources of error and all alternative explanations can be eliminated, then an observation is valid.

I would hope that after reading this study the reader will have an increased appreciation of the varied and important roles that experiment plays in physics. The reader should conclude that experiment has a philosophically legitimate role in the choice between competing theories and in confirmation of theories or hypotheses and that there are good reasons for believing in experimental results. These are rather commonplace and obvious conclusions. Why should one write or, perhaps more important, read a book that concludes so little? I believe that detailed historical study of actual, as opposed to mythical, experiments is worthwhile. Some philosophers and sociologists of science have sought to deny, or to minimize, the role that experiment plays in theory choice and to cast doubt on the validity of experimental results. This book is my attempt to answer them.

One of the great anticlimaxes in all of literature occurs at the end of Shakespeare's Hamlet. On a stage strewn with noble and heroic corpses – Hamlet, Laertes, Claudius, and Gertrude – the ambassadors from England arrive and announce that “Rosencrantz and Guildenstern are dead.” No one cares. A similar reaction might be produced among a group of physicists, or even among historians and philosophers of science, were someone to announce that “Lummer and Pringsheim are dead.” And yet they performed some of the most important experiments in the history of modern physics. It was their work on the spectrum of black-body radiation, along with that of Rubens and Kurlbaum, that showed deviations from Wien's Law and formed an important part of the background to Planck's introduction of quantization.

This is symptomatic of the general neglect of experiment and the dominance of theory in the literature on the history and philosophy of science. In Thomas Kuhn's history of quantization, Black-Body Theory and the Quantum Discontinuity, 1894–1912, Lummer, Pringsheim, Rubens, and Kurlbaum are, at best, peripheral characters. The title indicates what Kuhn thinks is important. We never see what the experimental results were or find a discussion of how they were obtained.

But, it might be said, that is only an isolated case. Surely everyone is aware of the famous experiments of Galileo and the Leaning Tower of Pisa, of Thomas Young's double-slit interference experiment, and of the Michelson–Morley experiment.

Another possible problem concerning the role of experiment in physics is that of scientific fraud. Accusations of fraud have recently received considerable publicity in both the scientific literature and popular literature. Such accusations have raised serious questions concerning science policy and the funding of research, and several United States congressional committees have held hearings on the subject.

More important for the philosophy of science, and science itself, are the doubts such accusations raise concerning the reliability of experimental data. If a large majority of scientists do not subscribe to Merton's norm of “disinterestedness,” the honest reporting of experimental results, then science may be faced with an insoluble problem. Which experimental claims are to be believed – those that report a result or those that contradict it? Merton stated that “The virtual absence of fraud in the annals of science, … appears exceptional when compared with the record of other spheres of activity…,” but the accusations mentioned earlier may cast doubt on that assertion. Although no significant data on the prevalence of scientific fraud currently exist, Golley has expressed the view that these rather sensational cases are but “the tip of an iceberg.”

The question at issue here, however, is whether or not the normal procedures of science provide sufficient safeguards against fraud. It seems clear that some safeguards were operating in the cases noted earlier, because the fraud (or alleged fraud) was disclosed. In this chapter I shall examine four cases from the history of physics, involving not only possible fraud but also questionable analysis of data, to see if the existing procedures did work, and, if so, why.

Although all scientists and philosophers of science are agreed that science is based on observation and experiment, very little attention has been paid to the question of how we come to believe rationally in an experimental result, or, in other words, to the problem of the epistemology of experiment. How do we distinguish between a result obtained when an apparatus measures or observes a quantity and a result that is an artifact created by the apparatus? In this chapter I suggest that there are various strategies that both provide justification for rational belief in an experimental result and are used by practicing scientists. We shall be concerned here primarily, although not exclusively, with observations or results that are interpreted within an existing theory. Although a devout skeptic might doubt the validity of pointer readings or chart recordings, I do not believe that is the important question about the validity of experimental results.

Ian Hacking has made an excellent start on discussing these issues. He points out that most modern experiments involve complex apparatus, and so, at the very least, the results are loaded with the theory of that apparatus. Dudley Shapere has extended the idea of “direct observation” to include theoretical beliefs explicitly. In his discussion of the solar neutrino experiments, he stated that “X is directly observed if (1) information is received, by an appropriate receptor and (2) that information is transmitted directly, i.e. without interference, to the receptor from the entity X (which is the source of the information).”

When I first came to Rome I found certain physicians who avoided phlebotomy so sedulously that sometimes even when a person was suffocating from plethos they refused to use the remedy. In the case of a woman almost twenty-one years old, who had a red face and a slight cough and already some difficulty in breathing, as a result of suppression of the menstrual catharsis, I found them lightly binding her limbs with woollen bandages and ordering her to fast, but neither using phlebotomy themselves nor permitting me to do so. Since they were more trusted than I was because of their intimacy with the woman's family and their seniority, I gave up for the time being the attempt to convince them concerning phlebotomy; I did, however, enquire whether there would be any objection to provoking a flow of blood to the uterus by means of drugs with the power to effect this. When they agreed, I at once sought out the patient's usual midwife and urged her to make use of them. She told me, however, that she had used them as the occasion demanded, when the monthly purgation was expected to occur, and mentioned the drugs she had applied to the woman; they were all of approved quality, so that no one could think the treatment had failed because of their weakness.

It seems to me to be a question well worth investigating, why on earth Erasistratus, who was, after all, so competent in the other branches of the Art, and so meticulous about the minutest detail as to describe even the boiling of certain vegetables and of plasters – matters on which it would have sufficed any one else just to say what was essential and to omit the mode of preparation, as a minor point which anyone could pick up as he went along – why Erasistratus, in the case of such a powerful and important remedy as phlebotomy, and one that was esteemed by the ancients as in no way inferior to the most effective of all, has nothing to say. The fact is that the word K148 phlebotomy is scarcely to be found in any work of his; the one exception is in his book on bringing up blood, but even here he mentions it more, it would seem, in passing than as something he was considering with the care it deserves.

Galen (c. ad 129–200) was a Greek from Pergamon in Asia Minor. Because of his habit of putting autobiographical details into his works, we know that he was the son of a prosperous architect, Nikon, who named him Galenos (mild), perhaps in the hope that he would turn out different from his mother, who was a shrew. He speaks of his father with respect; he gave him an excellent education in literature, philosophy and the sciences, and finally sent him to Alexandria to study medicine after being advised in a dream to make him a physician. After a spell in Pergamon as medical officer to the gladiators, Galen went to Rome in 162 and quickly established a large and fashionable practice; the second bloodletting work gives a lively account of how he did it. It was not long before he was attending the emperor Marcus Aurelius, who had, if we can believe Galen, some very complimentary things to say about him. Galen wrote a short work, That the Best Physician is also a Philosopher, in which he condemned the ignorant and materialistically-minded doctors of his time, and urged physicians to emulate Hippocrates, who, at least according to Galen, had despised possessions and the pleasures of the table and the bed, and laboured unceasingly in the pursuit of knowledge.

No attempt at an exhaustive analysis of the writers between Hippocrates and Galen will be made here. Only a few will be considered; the aim is merely to illustrate the divergent opinions that were prevalent.

Whether or not Celsus was himself a physician, and whether his work is his own or a translation of a lost Greek original, it is of the greatest value in reconstructing medical opinion between the Hippocratic writers and Galen. In addition to many incidental references he devotes a chapter to venesection, which opens with the significant remark: ‘It is not new to let blood by cutting a vein; but that there is hardly any disease in which blood is not let, is new.’ This is, in effect, Galen's indication from the severity of the disease, regardless of its nature; his primary indication for bloodletting is the presence, or indeed only the expectation, of any severe disease whatsoever. According to Celsus this was in his time – some two centuries before Galen, unless he is reproducing an earlier work – a new concept. It cannot be Hippocratic, since Celsus describes Hippocrates as ‘the most ancient author’. As we have seen, the idea appears in the Corpus only in the Appendix to Regimen in Acute Diseases, which most scholars think spurious, although Galen says that this particular statement is good Hippocratic doctrine; this does not apply, however, to everything else in the treatise. It has already been shown that the Hippocratic writers used venesection far less extensively than Galen did, though Galen would like us to think otherwise; Celsus confirms this opinion.

It has been shown in the previous chapter that although the Hippocratic writers unquestionably made use of venesection, they mention it only briefly and in passing, neither offering a rational explanation for its use nor listing the indications. Galen is more systematic. From a study of all his references to venesection it is possible to extract a good deal of information on his practice, and to determine not only what he did but also sometimes why he did it. His indications will be considered first.

In brief, Galen regards venesection as an evacuant remedy to be used in certain patients with plethos, though not in all. Suppression of wonted evacuations of blood, such as the menses or bleeding piles, may lead to plethos, which in turn, if not dispersed, may result in inflammation. Apart from these considerations, any severe disease is an indication for venesection, not only when established, but even when foreseen or expected; thus venesection may be used prophylactically in healthy subjects. Galen employs the remedy widely in fever. It is further used as a revulsive or derivative remedy, to direct blood away from or towards a particular part; and a number of pathological conditions are specifically mentioned in which it is applied. These indications will now be considered in more detail.

As an evacuant, Galen says, venesection is selective; it empties only the veins, whereas starvation leads to the evacuation of the whole body, a process attended with many troubles for the patient. Besides, venesection acts at once, whereas starvation is slow and the weakest of all evacuant remedies; Galen remarks later that it does not evacuate directly at all.

In the foregoing chapters Galen's opinions on venesection have been collected from his surviving works and compared with the views of the Hippocratic writers and of some of his other predecessors and contemporaries. What has not been resolved, and probably cannot be certainly decided at all, is the origin of Galen's opinions. Although he has a profound respect for Hippocrates, his opinions on venesection are Hippocratic only in the sense that they are those of a fictitious Hippocrates whom Galen has constructed for himself. Although the seeds of his ideas are to be found in the Corpus, they have grown by the time of Galen into something far bigger and more organised than is found in the Hippocratic writings. It is not clear where and when this growth took place. Although Celsus, like Galen, makes more extensive use of venesection than the writers of the Corpus do, his practice is in many ways quite different from Galen's, and the same can be said of Aretaeus, Antyllus and Soranus. What, then, was the origin of Galen's peculiar methods and beliefs? They are not truly Hippocratic, and a study of a few surviving sources between the writers of the Corpus and Galen suggests that they were far from universal among practitioners of ability and reputation. Where, then, did they come from, and why did he hold them so tenaciously?

This question might best be answered with another: Why did Galen succeed in his practice?