CONTRASTING VIEWS OF DISCOVERY

The present view of discovery will now be contrasted with several others, including ones suggested by two historians of science who have discussed the history of the discovery of the electron.

Manipulation-and-Measurement View

At the end of her important 1987 paper on Thomson, Isobel Falconer writes:

In the light of this reinterpretation of Thomson's work is there any sense remaining in which he can be said to have “discovered the electron”? Arriving at the theoretical concept of the electron was not much of a problem in 1897. Numerous such ideas were “in the air.” What Thomson achieved was to demonstrate their validity experimentally. Regardless of his own commitments and intentions, it was Thomson who began to make the electron “real” in Hacking's sense of the word. He pinpointed an experi­mental phenomenon in which electrons could be identified and methods by which they could be isolated, measured, and manipulated.^[241]

Several things are suggested here, but one is that Thomson discovered the electron because he was the first to design and carry out experiments in which electrons were manipulated and measured. We might recall that, on Hack­ing's view, to which Falconer alludes, “if you can spray them they are real.”^[242] On the more sophisticated version suggested by Falconer in this passage, if you can manipulate them in such a way as to produce some measurements they are real; and if you are the first to do so, you are the discoverer.

Important Classification View

This view is suggested by an earlier passage in Falconer's paper. Discussing the experimental work of Wiechert, she writes:

Wiechert, while realizing that cathode ray particles were extremely small and universal, lacked Thomson's tendency to speculation. He could not make the bold, unsubstantiated leap, to the idea that particles were constitutents of atoms. Thus, while his work might have resolved the cathode ray contro­versy, he did not “discover the electron.”^[243]

This suggests that, despite the facts that both Wiechert and Thomson manipulated the electron in such a way as to obtain a mass-to-charge ratio and that both physicists claimed that cathode particles were “extremely small and universal,” Thomson, and not Wiechert, is the discoverer of electrons because Thomson but not Wiechert got the idea that cathode particles are constituents of atoms. Although Falconer does not say so ex­plicitly, perhaps what she has in mind is that Thomson's identification of cathode particles as universal constituents of atoms is what is important about electrons. Generalizing from this, you are the discoverer of X when you are the first to arrive at an important (and correct) classification of X. The question remains as to what counts as an “important” classification—a major lacuna, as I will illustrate in a moment. However this is understood, it should include Thomson's classification of electrons as constituents of atoms.

Social Constructivist View

Social constructivism is a broad viewpoint pertaining to many things, in­cluding the reality of scientific objects themselves such as electrons (they are “socially constructed” and have no reality independently of this).

A final approach [to discovery]—and the one I favour—takes as central to the account the perspectives of the relevant historical actors and tries to re­main as agnostic as possible vis-a-vis the realism debate. The criterion that this approach recommends is the following: since it is the scientific community (or its most eminent representatives) which adjudicates discovery claims, an entity has been discovered only when consensus has been reached with respect to its reality. The main advantage of this criterion is that it enables the reconstruction of past scientific episodes without presupposing the res­olution of pressing philosophical issues. For historical purposes, one does not have to decide whether the consensus reached by the scientific com­munity is justifiable from a philosophical point of view. Furthermore, one need not worry whether the entity that was discovered (in the above weak sense) can be identified with its present counterpart.^[244]

Although in this passage Arabatzis claims that there is a discovery only when the community believes there is, he also says that the main advantage of his criterion is that it avoids the issue of whether the con­sensus reached is justified, and the issue of whether the entity that was discovered is the same as the one scientists now refer to. Accordingly, the view suggested is a rather strong one, to the effect that consensus is both necessary and sufficient for discovery. (At least, that is the social construc­tivist view about discovery that I will consider here.) Thomson discovered the electron if he is generally regarded by physicists as having done so.

Different Contributions View

According to this idea, there are discoveries in science, including that of the electron, that are not made by one person, or by several, or by any group, but involve various contributions by different people. We need to replace the question “who discovered the electron?” with more spe­cific questions about who made what contributions to the discovery. We might note that in 1855 Geissler contributed by inventing a pump that allowed much lower gas pressures to be produced in electrical discharge tubes; that in 1859 using this pump, Plucker found by experiment that when the pressure is reduced to 0.001 mm of mercury, the glass near the cathode glows with a greenish phosphorescence and the position of the glow changes when a magnetic field is introduced; that in 1869 Plucker’s student Hittorf found that if a solid body is placed between the cathode and the walls of the tube it casts a shadow, from which he concluded that rays are emitted from the cathode that travel in straight lines. This story could be continued with experimental and theoretical contributions by Crookes, Larmor, Lorentz, Hertz, Goldstein, Schuster, and so forth, cul­minating with the experiments of Thomson—or well beyond if you like.

Now, it is not that all the people mentioned, or even several of them, or a group working together, discovered the electron. Plucker didn't discover the electron, nor was he one of several people or a group that did. Still the electron was discovered, but it was not the sort of discovery made by one individual, or several, or a group. Rather it was the sort of discovery that involved different contributions by different persons at different times.

Several historical actors provided the theoretical reasons and the experi­mental evidence which persuaded the physics community about its [the electron's] reality. However, none of those people discovered the electron. The most that we can say is that one of those, say Thomson, contributed significantly to the acceptance of the belief that “electrons” denote real entities.^[245]

True Belief View

According to this view, you have discovered something only if what you believe about it is true or substantially true. Despite Lord Kelvin's claim to know various facts about the luminiferous ether,^[246] that entity was not discovered by nineteenth-century wave theorists (or by anyone else), since what was believed about it, including that it exists and that it is the medium through which light is transmitted, is false. Similarly, in this view, Thomson did not discover the electron since quite a few of his core beliefs about electrons (or what for many years he called corpuscles) were false. His corpuscles, he later thought, were entirely electrical, having no inertial mass; they were arranged in stationary positions throughout the atom; they were the only constituents of atoms; they were not waves of any sort; and they were not carriers of the smallest electric charge. So, if he discovered anything at all, it was not the electron.

Now, I reject each of these five views about discovery, both in the generalized forms I have given them and as ones applicable to the case of Thomson and the electron. Although manipulation and measurement are frequently involved in a discovery, they are neither necessary nor suf­ficient. Galileo discovered mountains and craters on the moon without manipulating or measuring them (in any reasonable sense of these terms). Moreover, the manipulation and measurement view would too easily de­throne Thomson. Many physicists before Thomson in 1897 manipulated electrons in the sense that Thomson did; that is, they manipulated cath­ode rays, and did so in such a way as to produce measurements.

The second view—“important classification”—fails to provide a suf­ficient condition for discovery since you can arrive at an important classification of Xs without discovering them. You can postulate their ex­istence on largely theoretical grounds, and describe important facts about them, without “confronting” them sufficiently directly to count as having discovered them. In the early 1930s Pauli hypothesized the existence of a neutral particle, the neutrino, in order to account for the continuous distribution of energy in beta decay. But the neutrino was not discovered until there was a series of experiments, beginning in 1938, that estab­lished its existence more directly.

Whether the important-classification view fails to provide even a necessary condition for discovery is more difficult to say because of the vagueness in the notion of important classification. Roentgen discovered x-rays in 1895 without knowing that they are transverse electromagnetic rays. Although he speculated that they were longitudinal vibrations in the ether, he did not claim to know this (nor could he know this) and for this reason, and to distinguish them from other rays, he called them x-rays. Did he fail to arrive at a sufficiently important classification? Or shall we say that the fact that he discovered that x-rays are rays that travel in straight lines, that have substantial penetrating power, that cannot be deflected by an electric or magnetic field, and so forth, is sufficient to say that he arrived at an important classification?

Similarly, in the case of the electron, isn't the fact that the constit­uents of cathode rays are charged particles smaller than ordinary ions an important classification? If so, then Crookes in 1879 deserves the title of discoverer. Is it that the classification “constituent of all atoms” is more important than “being charged particles smaller than ordinary ions,” and so Thomson rather than Crookes deserves the honor? Crookes, indeed, claimed that he, not Thomson, first arrived at the classification “constit­uent of all atoms.” Moreover, why choose this classification rather than something more specific about how these constituents are arranged in atoms? If so, then Rutherford or Bohr should be selected, not Thomson, whose plum-pudding model got this dead wrong.

The crucial question concerning the present view is whether you could know that X exists from observations of X without knowing an important classification of X. In the weaker sense of discovery I distinguished earlier, one could discover X without knowing very much about X, including that it is X. (Recall my discovering gold.) The stronger sense involves knowing that it is X. But what important classification one needs to know to know that something is X I'll leave to important classification theorists.

The view I propose also contradicts the social constructivist account of discovery, since in my view there is, or at least can be, a fact of the matter about who discovered what that is independent of who the sci­entific community regards as the discoverer. This is because there is, or can be, a fact of the matter about who was the first to be in an epistemic state necessary for discovery. Being regarded by the scientific community as the discoverer of X is neither necessary nor sufficient for being the discoverer of X. No doubt scientific discoverers wish to be recognized by the scientific community for their discovery. Perhaps for some a dis­covery without recognition is worthless. But this does not negate the fact of discovery itself. Nor is this to deny that a discovery that is and remains unknown except to the discoverer will have little chance of advancing science, which depends on public communication. That is one reason scientists make their discoveries public. Although publicity helps to pro­mote the discovery and the recognition for it, neither publicity nor rec­ognition creates the discovery. Finally, one can relativize discovery claims to a group. I can be the first in my department to discover a certain book in the library, Columbus the first European to discover America, and so forth. This is not social constructivism, however, since there is a fact of the matter about discovery within a group that is independent of the be­liefs of the members of the group. Either I was or I wasn't the first in my department to discover that book, no matter what views my colleagues have about my discovery.

Two of the views of discovery that contrast with mine deny the claim that Thomson discovered the electron: the “different-contributions” view and the “correct-belief” view. Briefly, my response to these views is this. The fact that various people made contributions to the discovery of the electron does not, on my account, necessarily preclude the fact that Thomson discovered the electron. All this means is that various people helped make it possible for Thomson to be the first to achieve an epistemic state necessary for discovery. Nor, finally, does getting into that epistemic state about some X require that all or most of your beliefs about X be true. Suppose that while walking along a road I discover a person lying in the ditch beside the road. Suppose that, after observing the per­son, I come to believe that the person is a woman, quite tall, at least fifty years old, with blond hair, and wearing a gray jacket. Suppose, finally, that I am quite wrong about these beliefs. The person in the ditch is actually a man, five feet tall, thirty years of age, with dark hair, and wearing no jacket at all. I can still be said to have discovered the person in the ditch, despite the fact that what I believe about the person in the ditch is substantially false. So I reject the general rule that you have discovered X only if what you believe about X is true or substantially true.