WHAT IS DISCOVERY?
The type of discovery with which I am concerned is discovering some thing or type of thing (for example, the electron, the Pacific Ocean), rather than discovering that something is the case (for example, that the electron is negatively charged).
Later I will consider a sense of discovering some thing X that requires a knowledge that it is X, as well as a sense that does not.My view has three components, the first of which is ontological. Discovering something requires the existence of what is discovered. You cannot discover what doesn't exist—the ether, the Loch Ness monster, or the fountain of youth—even if you think you have. You may discover the idea or the concept of these things. Everyone may think you have discovered the things corresponding to these ideas or concepts. They may honor you and give you a Nobel Prize, but if these things don't exist, you haven't discovered them.
The second component of discovery is epistemic. A certain state of knowledge is required. If you are to be counted as the discoverer of something, not only must that thing exist but also you must know that it does. Crookes in 1879 did not discover electrons because he lacked such knowledge; his theoretical claim that cathode rays consist of subatomic particles, although correct, was not sufficiently established to produce the knowledge that such particles exist. Not just any way of generating knowledge, however, will do for discovery. I may know that something exists because I have read that it does in an authoritative book. Discovery, in the sense we are after, requires that the knowledge be firsthand.
What counts as “firsthand” can vary with the type of object in question. With physical objects such as electrons one might offer this rough characterization: knowledge that the objects exist is generated, at least in part, by observing those objects or their direct effects.
This knowledge may require rather strenuous inferences and calculations from the observations. (Scientific discovery is usually not like discovering a cockroach in the kitchen or a nail in your shoe.) As noted, discovery involves not just any observations that will produce knowledge of the object's existence, but observations of the object itself or its direct effects. I may come to know of the existence of a certain library book by observing a computer screen in my office which claims that the library owns it. I may discover that the book exists by doing this. But I may never discover the book itself if I can't find it on the shelf. In discovering the book at least among the things that make me know that it exists is my seeing it. Finally, for discovery, the knowledge in question involves having as one's reason, or at least part of one's reason, for believing that X exists the belief that it is X or its direct effects that have been observed. My knowledge that electrons exist may come about as a result of my reading the sentence “Authorities say that electrons exist” on my computer screen. What is on my screen is a direct effect of electrons. But in such a case, I am supposing, my reason for believing that electrons exist does not include the belief that I have observed electrons or their direct effects on the screen.[237]Putting together these features of the second (epistemic) component of discovery, we can say that someone is in an epistemic state necessary for discovering X if that person knows that X exists, observations of X or its direct effects caused, or are among the things that caused, that person to believe that X exists, and among that person's reasons for believing that X exists is that X or its direct effects have been observed. More briefly, I will say that such a person knows that X exists from observations of X or its direct effects.
The third component of discovery is priority. If I am the discoverer of something, then the epistemic state I have just described must be a “first.” I put it this way because it is possible to relativize discovery claims to a group or even to a single individual.
I might say that I discovered that book in the library last Tuesday, meaning that last Tuesday is the first time for me. It is the first time I knew the book existed by observing it, even though others knew this before I did. I might also make a claim such as this: I was the first member of my department to discover the book, thereby claiming my priority over others in a certain group. Perhaps it is in this sense that we say that Columbus discovered America, meaning that he was the first European to do so. And of course, the relevant group may be the entire human race. Those who claim that Thomson discovered the electron mean, I think, that Thomson was the first human to do so.There is a rather simple way to combine these three components of discovery, if we recognize that knowing that something exists entails that it does, if we confine our attention to discovering physical objects (rather than such things as facts, laws, or proofs), and if we employ the previously introduced concept of an epistemic state necessary for discovery. The simple way is this: P discovered X if and only if P was the first person (in some group) to be in an epistemic state necessary for discovering X. That is, P was the first person (in some group) to know that X exists, to be caused to believe that X exists from observations of X or its direct effects, and to have as a reason for believing that X exists that X or its direct effects have been observed.
Before contrasting this with opposing views, and applying this to Thomson and the electron, some points need clarification.
First, on this account, to discover X, you don't need to observe X directly. It suffices to observe certain causal effects of X that can yield knowledge of X's existence. If I see a cloud of dust moving down the dirt road that is obviously being produced by a car approaching, then I can discover a car that is approaching even though I can't see the car itself, but only the cloud of dust it is producing as it moves.
It is not sufficient, however, to come to know of X's existence via observations of just any sort. If I read a letter from you saying that you will be driving up the dirt road to my house at noon today, and I know you to be someone who always keeps his word, that, by itself, does not suffice for me to say that I discovered a car that is approaching at noon, even if I know that the car is approaching. Discovering the car requires observations of the car or its direct effects.Second, this will prompt the question “What counts as observing direct effects?” Some physicists want to say that the tracks produced by electrons in cloud chambers are direct effects, because electrons, being charged, ionize gas molecules around which drops of water condense, forming the tracks. By contrast, neutrons, being neutral, cannot ionize gas molecules and hence do not leave tracks. They are detected by bombarding charged particles that do leave tracks. More recently detected particles, such as the top quark, involve many different effects that are less direct than these.[238] This is a complex issue that cannot be quickly settled.[239] What appears to be involved is not some absolute idea of directness, but a relative one. Given the nature of the item whose effects it is (for example, if it is a neutron it cannot produce a track but must interact with charged particles that do produce tracks), this degree of directness in detecting its effects not only yields knowledge that the item exists but also furnishes the best, or one of the best, means at the moment available for obtaining that knowledge.
Third, on this account, the observations of X or its effects need not be made by the discoverer, but by others. What is required is only that the discoverer be the first to know that X exists from such observations. The planet Neptune was discovered independently by Adams and Leverrier from observations of the perturbations of Uranus caused by Neptune.
These observations were made by others, but complex calculations enabled these astronomers to infer where the new planet could be observed in the sky. The first actual telescopic observation of Neptune was made not by either of these astronomers but by Johann Galle at the Berlin Observatory. Although Galle may have been the first to see Neptune, he is not its discoverer, because he was not the first to come to know of its existence from observations of Neptune or its effects.Fourth, to discover X it is not sufficient simply to postulate, or speculate, or theorize that X exists. In 1920 Rutherford theorized that neutrons exist, but Chadwick in 1932, not Rutherford in 1920, is the discoverer of these particles. There were before 1932 no experimental results that allowed the existence of this particle to be known.
In connection with the electron, there are two physicists whose names I have not mentioned so far: Larmor and Lorentz. Both had theories about what they called electrons. Setting aside questions about whether they were referring to what we call electrons, one reason these physicists are not the discoverers of electrons is, I think, epistemic. Although their theories explained experimental results, such results were not sufficiently strong to justify a knowledge-claim about the electron’s existence. Their claims about electrons were primarily theory driven.
Fifth, this view allows there to be multiple discoverers, as were Adams and Leverrier. They came to be in the appropriate epistemic states at approximately the same time. It allows a cooperative group of scientists, rather than the scientists individually in that group, to be the discoverers— as in the case of the top quark. And it allows scientists to make contributions to the discovery of X without themselves being discoverers or part of a group that discovered X. Plucker did not discover the electron, though in 1859 he made a crucial contribution to that discovery—the discovery of cathode rays.
Sixth, we need to distinguish two ways of understanding the phrase “knowing that X exists” in my definition of discovery and hence two senses of discovery. Suppose that while hiking in the Rockies, I pick up some shiny stones. You inform me that I have discovered gold. This could be true, even if I don’t know that it is gold. In this case by observing the stones I have come to know of the existence of something that, unknown to me, is gold. That is one sense in which I could have discovered gold. Of course, I might also have come to know that these objects are gold. That is another sense in which I could have discovered gold.[240]
The same applies to discovering the electron. To say that Thomson discovered the electron might mean only that by suitable observations he came to know of the existence of something that happens to be the electron, even if he didn’t realize this. Or it might mean something stronger to the effect that he came to know that the thing in question has the electron properties (whatever those are). I shall speak here of the latter as the “stronger” sense of discovery and the former as the “weaker.”