An interview with David Lindley
Astrophysicist and author David Lindley has been charting changing currents in science since 1993. His latest book, Degrees Kelvin: A Tale of Genius, Invention and Tragedy, examines the vigorous life of William Thomson, Lord Kelvin, the Victorian prodigy whose brilliant contributions to classical physics were somewhat overshadowed by his later doubts about the progress of scientific inquiry.
American Scientist Online managing editor Greg Ross asked Lindley to discuss his impressions of Thomson, whose story touches on themes of genius, the enterprise of physics and the construction of scientific reputation.
Thomson was an intellectual butterfly in classical physics, alighting everywhere, drawing connections and resolving confusion among his colleagues. But it's hard to point to a contribution that is uniquely his own. Why is this?
In the early part of his career, his greatest work was in thermodynamics and electromagnetism, and these were subjects that many others in the middle of the 19th century were thinking about. So Thomson was one of several great scientists who built these subjects into what we now know. But it's also true, as your question implies, that Thomson was not the kind of person to stick with any one subject until he had brought it to completion. Having solved the immediate problem, he moved quickly on to something else.
For example, he introduced in one paper a definition of what looks like entropy but apparently didn't think hard enough about what he had done to see its larger significance. Similarly, he was the first to devise a mathematical portrayal of Michael Faraday's electric and magnetic lines of forces, but it was James Clerk Maxwell who built on that foundation to create a full theory of electromagnetism.
On the other hand, remember that Maxwell spent 10 years, much of it in solitary fashion, coming up with that theory. Thomson simply didn't have the personality or psychology to do that. He had an amazingly fertile and quick mind, but I would say he was not deep in the sense that Maxwell was, for example.
Thomson was also a pioneering educator in science. He was among the first to conceive of classical physics as a unified discipline; he collaborated on the field's first comprehensive undergraduate textbook; and he introduced student experimentation to the classroom. Do you think he would have been a good teacher?
As a teacher he was earnest and enthusiastic; he found the old-style Cambridge system, under which he had learned, abstract and arid; he embraced, arguably even invented, a new style of practical science teaching that mixed theory and experiment. He was a great believer in learning by doing. The brighter of his students remembered his lessons with great fondness and admiration.
On the other hand, his enthusiasm sometimes got the better of him. I think he genuinely couldn't grasp that not everyone was as quick as he was, and he was inclined to rush off on diversions and digressions as he lectured, because he was forever glimpsing some new idea as he spoke and couldn't resist chasing after it.
Nevertheless, his textbook with P. G. Tait was truly innovative and influential. Until then no one had put a synopsis of all of physics, theoretical and experimental, between one set of covers. What Thomson and Tait produced was a recognizably modern style of teaching that in some respects is still with us today.
It struck me that Thomson held strangely mixed feelings about mathematics. He used math brilliantly to understand the world, but he would not always follow where it led. For example, his ideas contributed to Maxwell's theory of electromagnetism, but he seemed to regard that theory as suspiciously abstract. Is this a contradiction?
For Thomson, mathematics always had to have a practical purpose. He was very adept at the subject, but I don't think it meant much to him unless the symbols represented physical entities. For that reason he distrusted mathematical reasoning when it wasn't attached to a physical model he could understand.
He was at first not all that impressed with Faraday's ideas but soon grasped that Faraday was thinking about electromagnetic phenomena in a way that had great explanatory power. So translating Faraday's notions into the language of mathematics was a practical step forward. It's also true that Thomson, following Faraday's lead, embraced the idea of an electromagnetic influence that pervaded space. Where he parted company eventually with Maxwell was that Maxwell was content to let the electromagnetic field be defined largely by its mathematical properties, leaving its physical basis unclear. Thomson wanted something more concrete—hence all the mechanical models of the ether that seem so bizarre to us nowadays.
Thomson was consistent in always disdaining as “metaphysics” any mathematical theory that wasn't clearly based on established physical facts. So his wariness about Maxwell's electromagnetism was entirely in character.
Thomson's contributions to 19th-century science were dazzling, but in later years he seemed increasingly contrary. He doubted the existence of atoms, he would not wholly accept radioactivity, and he opposed the theory of evolution. Was this personal stubbornness, or something larger?
Lord Rayleigh had a nice line to the effect that older physicists could still make themselves useful as long as they stuck to what they knew and refrained from commenting on what their younger colleagues were up to. Of course Thomson, especially after he became Lord Kelvin in 1892, always wanted to be in the thick of things. By the end of the 19th century, Kelvin was in his 70s, and that's a little late to see your physical understanding of the world ripped up and rebuilt.
It's worth noting that ideas about atoms, radioactivity, x rays and so on were in their infancy in Kelvin's later years, and his objections were not unreasonable. Nor did he only criticize—he proposed alternatives, rooted in his own understanding of the physical world. But of course his thinking was rather antiquated by then.
It's worth noting also that he didn't wholly object to evolution. He liked the idea of a mechanistic explanation for survival and failure. Where he had trouble was in understanding how new species arise, and particularly how inanimate processes could produce intelligent life. He was asking too much for evolution to explain all that from the outset, but his questions and criticisms were often acute.
Much of Thomson's later critical thinking came from his dissatisfaction with partial answers. But that's an ambiguous virtue—to make progress in science you often have to be satisfied with half a loaf. More than stubbornness, I think he suffered at times from excessive perfectionism.
Thomson argued strenuously that the Earth and Sun could not be more than 100 million years old, and later said he thought this the most valuable work of his career. Why do you think this argument was so important to him?
Today we take it for granted that geology must incorporate some basic physics, but as late as the 1880s eminent geologists acted as if conservation of energy, important though it might be for physics, had nothing to do with their science. The 19th century saw not only the rise of physics, chemistry, geology and so on in their modern forms, but also their integration. Thomson was always a proselytizer for basic physics, and his argument about the age of the Earth was for him an illustration of the universality of scientific reasoning. It galled him that many geologists ignored him for a long time, or acted as if understanding a little quantitative reasoning were beyond (or perhaps beneath) them. Of course Thomson was wrong in the specifics of his argument about the age of the Earth, and he tended to be heavy-handed in laying down the laws of physics to other disciplines. But in the end he got across the point that physics mattered to geology, and that gave him a great deal of satisfaction.
You write that Thomson's greatest flaw as a scientist was his conviction that every theory is "merely a combination of established truths." He seemed most comfortable fitting empirical knowledge into theoretical systems, but that prevented him from guessing larger truths. Did this conservatism increase as he grew older, or was the practice of science changing?
What impresses me most is the consistency of Thomson's viewpoint throughout his life. In his early work on thermodynamics and electromagnetism, he made great progress by fitting experimental knowledge into a simple mathematical framework. At the time (in the 1840s) this was a somewhat novel way of doing science. Mathematical science of the then-dominant French school tended to be axiomatic, trying to explain established phenomena by proceeding a priori from principles.
But there was a substantial change in the style of physics during Thomson's lifetime. As mathematical theories became more sophisticated, they began to include theoretical entities that were not empirically verifiable in any direct way. That's how atoms began, after all, and why they were so controversial for a long time.
Thomson's way of mathematizing physics was enormously productive and useful for the middle few decades of the 19th century, but it represented a transitional stage on the road to theoretical physics as we now understand it. In that sense he remained consistent in his attitude, but physics moved on.
Do you think those who followed Thomson slighted his contributions because he was disagreeable or seemed shortsighted? It seems unfair. His early contributions were undeniable, whatever his later positions.
The simple answer is—what have you done for me lately? By the early 20th century most young physicists took conservation of energy entirely for granted, so it was hard for them to imagine that here at their meetings was a white-haired old man who had actually had something to do with establishing it. They only knew that Kelvin was pronouncing antiquated ideas and strange opinions on subjects he didn't appear to know too much about.
I don't think anyone ever thought Kelvin was disagreeable—only that he was out of touch. He made the mistake of remaining lively and engaged right up until he died, at 83, so that he was remembered by his much younger colleagues for what he was saying in 1907, not what he had done half a century earlier. Unfair maybe, but not surprising.
What lessons does Thomson's story have for modern scientists?
It's easy to look at the last decades of Thomson's career and imagine that he went off the rails. But on closer inspection, some of his criticisms of the directions physics was going in were on the mark. He didn't like the disembodied nature of the electromagnetic field in Maxwell's theory and wanted a concrete model for how an electromagnetic influence gets from one place to another. I'm not sure he would be altogether enchanted by quantum mechanics as a whole, but I think Thomson would like the picture of a field as an aggregation of virtual particles. The pendulum has swung back: The classical field now seems old-fashioned, and especially with string theory and its offspring we have come back to a localized, broadly mechanical picture of fundamental theory.
So I'd like to end on a positive note. Thomson stuck to his guns, never worried too much about what other people thought, and as far as I can tell enjoyed his life immensely.