[Ads-l] A theory is not complete until you can explain it to the man in the street

[Stephen Goranson]

>From Nature Nov 16 2016:

David Hilbert was extremely absent-minded, extraordinarily brilliant and the most influential mathematician of the twentieth century. His reach continues today. Among other things, he popularized a common concept in the communication of science: the ‘man in the street’, whose understanding (or not) of a problem is commonly used as a benchmark for intelligibility.
At the 1900 International Congress of Mathematicians in Paris, Hilbert set out to list the most important open problems of the field for the new century. But he also emphasized communication. “A mathematical theory is not to be considered complete,” he said, “until you have made it so clear that you can explain it to the first man whom you meet on the street.” Hilbert attributed the saying to “an old French mathematician”.
That is unusually imprecise for a mathematician. So, to complete the theory, two intrepid maths historians set out to identify Hilbert’s elderly Gallic source. As they report in this month’s Historia Math­ematica, they pursued a long paper trail, including a nineteenth-century letter published in Nature, and eventually succeeded (J. Barrow-Green and R. Siegmund-Schultze Hist. Math. 43, 415–426; 2016<https://doi.org/10.1016/j.hm.2016.08.005>).
It was indeed a Frenchman, one Joseph Diaz Gergonne (1771–1859), who first referred to the man in the street. In a letter dated 1825, Gergonne wrote that one has not said the last word on a theory until one has been able to explain it to a passant dans la rue — French for ‘passer-by in the street’. A year later, in a second letter, he went further. A formula or method that could not be explained to a passing stranger “does not deserve to see the light of day”.
Stephen Goranson
https://people.duke.edu/~goranson/

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