The Science of Things: Unanswered Scientific Questions and Unquestioned Scientific Answers in Materials Research and Dev
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The Science of Things: Unanswered Scientific Questions and Unquestioned Scientific Answers in Materials Research and Development Robert W. Cahn “If an experiment works, something has gone wrong.” “You can never tell which way the train went by looking at the tracks.” “All’s well that ends.”
—From a poster presenting Paul Dickson’s “Murphy’s Laws on Technology”
I believe Groucho Marx pointed out that the problem with prediction is that it is about the future, and we do not know the future. But if it is unprofitable to attempt to predict what will be known in the future, I see no such objection to emphasizing what is not known yet, but which ought to be known soon. Indeed, such an enterprise has two parts. That splendid scientific cartoonist, Sidney Harris, has a lovely drawing showing the doorway of an unidentified research institute, and in front are two signs pointing opposite ways. One says “UNANSWERED QUESTIONS,” the other, “UNQUESTIONED ANSWERS.” Sometimes, the most impressive advances come from questioning unquestioned answers. A good example of an unquestioned answer that eventually was critically reexamined is the dogma that a new phase must form from an old one by the process of nucleation, a discontinuous process in a metastable starting phase with the involvement of sharp interfaces. That model was worked out over a period of years (from roughly 1910, starting with Einstein, via several other German physicists, to Charles Frank and David Turnbull in the 1950s). Then, at last in 1956, Mats Hillert showed that a new phase could form by a continuous process in an unstable starting phase, and John Cahn and John Hilliard, a few years later, took Hillert’s notion further by working out the theory of a diffuse interface that gradually thickens as the unstable parent phase decomposes continuously into regions of diverging compositions. This completely new view has been immensely influential in modern materials science and the Cahn/Hilliard papers in particular are among the most frequently cited in our field. Another example of an unquestioned MRS BULLETIN/SEPTEMBER 2000
answer was the organic chemists’ dogma that a compound must have a unique, well-defined molecular weight and melting temperature, otherwise it could not really be a compound. Polymers do not fit that dogma, so for several decades chemists insisted that polymers were, in effect, stuck-together versions of small molecules. Until that conviction was overcome, polymer science could not properly advance. That unquestioned answer delayed the progress of polymer science by at least 20 years, roughly from 1910 until 1930. The way things have been going in recent years, I would guess that the field in which the most unquestioned answers will walk the plank is the processing of materials. Modern processing can be said to have started with the invention of splatquenching in 1960 by Pol Duwez at Caltech. He wanted to find a way of enhancing effective quenching rates of alloys, with a view to examining metastable phases, and found to his surprise that quen
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