Page 16

2

Chapter 1

From the initial meaning4 of the Italian word modello, the term “model” was applied, as early as 1563, to “any simplified representation of a construction or object that is to be reproduced at a larger scale”. At the abstract level, it was applied to something or someone exhibiting to the highest degree the characteristics of a species, category or quality. In the 17th century, the word was used in the vocabulary of the arts with the meaning: “Someone who poses for a painter or sculptor”, from which then came: “Real person providing the inspiration for a writer”. It also slipped into the world of fashion before being overtaken by mannequin. In the scientific world, the idea of a model is strongly linked to that of representing something. The idea of formalizing this representation by a mathematical expression based on the tools of logic sprung forth from the intellectual eruptions of the 19th century. It also took advantage of the needs of physics to match observations with theory. Nor did the world of economics stay silent on the matter. In particular, econometrics attached very early importance to the use of models. This was further amplified in the middle of the 20th century, particularly by U.S. laboratories which received the support of scientists fleeing Nazism. Under the pressure of events related to World War II, military research acted as a favorable catalyst to the development of new disciplines such as game theory and operations research. In particular, it led John von Neumann and Oskar Morgenstern to publish their Theory of Games and Economic Behavior, a book that became an essential reference to many researchers of the time. Sociology, linguistics, and many more areas also turned with success to the use of models. But it is from astronomy and geodesy that we pluck the fascinating example that will hold our attention from here on in.

1.3

Modeling in astronomy

Astronomy appears to have been the first discipline to build a parametric model and fit it to data. The idea of using a model originated in questions studied by astronomers on the movements of celestial bodies in the sky and the need to understand them by defining systems. Take the example of the theory that the sun revolves around the Earth. This model prevailed in ancient times before the other way around was proposed. It is not surprising that the simplest model imagined at the time assumed that the sun went through a circular orbit around the Earth at a constant speed. Another way of saying the same thing was to say that the angular position of the sun was a linear function of time, a proposal that ensured Hipparchus’ fame5 . 4 The

various meanings of the word model are taken from Rey et al. [1992]. in Nicaea in the 2nd century BC, Hipparchus is often described as the greatest

5 Born

Model Choice and Model Aggregation, F. Bertrand - Editions Techip  

For over fourty years, choosing a statistical model thanks to data consisted in optimizing a criterion based on penalized likelihood (H. Aka...

Model Choice and Model Aggregation, F. Bertrand - Editions Techip  

For over fourty years, choosing a statistical model thanks to data consisted in optimizing a criterion based on penalized likelihood (H. Aka...

Advertisement