Sunday, January 23, 2011

Overview of the History Comp Project

’ve worried more about the history comp than I have about the philosophy comp, because I’m primarily a philosopher by disposition and by training. However, I think I have a pretty good start on this one.

My history comp project is a piece of experimental HPS, which involves revisiting past experiments in order to address historical, philosophical, and scientific questions. I am working with Paolo Palmieri, a professor in my department, who has been a pioneer in this field. Most of his experimental HPS work has been on Galileo’s pendulum and inclined-plane experiments. There have been debates among Galileo scholars about whether Galileo actually performed certain of the experiments he reports, or whether they were merely thought experiments. Or perhaps they were somewhere in between: maybe he rolled balls down inclined planes, but he didn’t measure the times of fall precisely enough really to demonstrate the results he claims. Historical reconstructions of Galileo’s experiments can contribute to this debate by, for instance, providing evidence that he could or could not have gotten certain kinds of results using the materials and methods that were available to him.

I am planning to take an experimental HPS approach to Robert Millikan’s oil-drop experiments. These experiments—performed primarily between 1909 and 1912—convinced nearly all physicists that electricity comes in discrete units and provided the most precise measurement of the elementary unit of charge that had ever been performed.

Millikan published his first definitive paper with results from the oil drop technique in 1913. In 1923, he won the Nobel Prize for these experiments and his work on the photoelectric effect. One reason it took ten years for him to win the Nobel was that his work was challenged by Felix Ehrenhaft, a Viennese physicist who claimed to find evidence in experiments similar to Millikan’s for “subelectrons,” units of charge smaller than Millikan’s supposedly fundamental units. Millikan argued that Ehrenhaft was generating artifacts by using bits of metal and other materials that, Millikan claimed, could not have spherical, unlike Millikan’s oil drops. Ehrenhaft argued that his materials were in fact spherical, and that Millikan begged the question in favor of the existence of a fundamental unit of charge in the way he analyzed his data. Millikan published his last, rather cranky paper on this debate in 1925, while Ehrenhaft continued to argue his case into the 1940s. By that time the mainstream physics community had accepted Millikan’s results and rejected Ehrenhaft. Ehrenhaft did not help his cause by claiming to have created other anomalous effects, such as magnetic monopoles and magnetolysis.

Although Millikan won the day, questions remain about what Ehrenhaft was observing that made him think that he had found subelectrons and about why the physics community chose to accept Millikan’s results and reject Ehrenhaft’s. These questions became more complicated and more pressing in the 1960s, when historian Gerald Holton reviewed Millikan’s laboratory notebooks from the experiments that made it into his 1913 paper. He found that Millikan selectively excluded some of his experimental results from publication. Holton argues that Millikan was just doing what all good experimentalists do—making reasoned judgments about which results were reliable and which were unreliable. However, the results he threw out included a small number of runs that seemed fine except for the fact that they would have seemed to support Ehrenhaft’s subelectron hypothesis. Moreover, Millikan did not just fail to report that he discarded anomalous results; he says explicitly says that he did not do so: “It is to be remarked, too, that this is not a selected group of drops but represents all of the drops experimented upon during 60 consecutive days” (Millikan 1913, 138). It is hard to interpret these words in a way that doesn’t make Millikan out to be a liar. Daniel Goodstein has tried, but I’ve yet to understand his explanation.

There is a fairly large literature on the Millikan-Ehrenhaft dispute and on the issue of Millikan’s alleged fraud. I aim to contribute to this literature with insights derived from working with a scaled-down version of Millikan’s apparatus. (I also have high-quality scans of Millikan’s laboratory notebooks that I have begun to examine.) It is hard to know in advance what these insights will be, but I have a few guesses. First, I want to compare the phenomenology of the experiment to Millikan’s remarks on it. Millikan speaks as if the experiment essentially speaks for itself. “One who has seen this experiment,” he says, “has SEEN the electron.” I’ll be interested to find out whether doing the experiment feels like seeing the electron. I’ll explain in a forthcoming post what the experiment involves and why I think it might feel this way. If it does, then it would be a plausible conjecture that the experience of doing the experiment played a major role in convincing Millikan that the theory of a fundamental unit of charge was correct—perhaps to the point that he saw the data as a tool for displaying the correctness of the theory, rather than as the primary epistemic basis on which the theory should rest. I think there is some textual support for this conjecture, but it would be greatly strengthened if the experience of doing the experiment turns out to be rather striking. If the experience of doing the experiment bears out this conjecture, then it would, I think, give some grounds for being a bit more lenient regarding Millikan’s data manipulation than we might otherwise be. Why report data that seemed to speak against the electron hypothesis when he had SEEN the electron, and thus knew that it was real?

Second, it would be quite interesting if we could reproduce anomalous observations akin to some of those the results from which Millikan discarded. For instance, Millikan says at a couple points in the notebook that a drop “flickers” as though “unsymmetrical in shape.” (He threw out the results from those drops.) What do such drops look like? Is the flickering obvious? Do the flickering drops seem different from the oil drops in other ways? Can we make any reasonable conjectures about what the flickering drops are, e.g. specks of dust or multiple drops stuck together? It would be even more interesting, if we could do it, to run the experiment using some of the materials Ehrenhaft used. Would we get the same anomalous results? Is there any way we could use modern tools to investigate whether these materials were in fact spherical or not? Could we use computer simulations to investigate how departures from sphericality should affect the results?

In the long run, it would be fantastic to do a plausible re-creation of some of Ehrenhaft’s experiments. Trying to explain Ehrenhaft’s results is the kind of project that one would like HPS scholars to pursue—a side-trail in the history of science that’s quite interesting and unresolved, but that working scientists don’t have time for. However, the practical obstacles are daunting. Ehrenhaft’s apparatus was more complicated than Millikan’s and, as I’ll explain in the next post, we’re not even doing a full-fledged re-creation of Millikan’s. I’ll see how this relatively easy Millikan re-creation goes, and then perhaps think about a more ambitious project on Ehrenhaft.

Hey look, I’m already at over 1,000 words—1/7 of the way to my history comp! I’ll be done in a week. Or not.

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