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9 The Great Deluge Simulation Modeling and Scientific Understanding j o H a n n e S L e n H a R d L Recently, a friend went to see her general practitioner in order to give her thyroid gland a checkup. The doctor took a blood sample to test a few parameters in the laboratory, and she performed an ultrasound scan on the thyroid gland. The result was not completely clear, and the doctor referred my friend to a specialized radiologist with the necessary instruments for a reliable diagnosis. She said that while my friend could simply hand over the results of the blood tests, she thought the radiologist would have little use for the ultrasound printout. This was not because it was irrelevant, but because the radiologist would certainly want to carry out his own test. Indeed, this is exactly what happened. This suggests a consensus among physicians that blood tests performed in a laboratory provide objective and communicable information, whereas this is not quite the case for an ultrasound printout. Anyone who has ever seen an ultrasound printout knows how necessary it is to interpret the structures and shadings it reveals. Nonetheless, it is not the case that the ultrasound scan is of decreasing information value, because the radiologist did not drop it in favor of some other procedure. Quite the opposite, he performed a second scan himself. My friend could well have brought the radiologist an X-ray, for example, as a source of information just like the results of the blood tests. However, what makes the diagnostic content of an ultrasound printout so much less transportable ? And why did the physician prefer to do his own scan? 169 the great deluge de Regt Txt•.indd 169 9/8/09 11:27:08 AM 170 It is not the mere printout, the snapshot that my friend could have brought with her, that delivers the information. The benefits of an ultrasound test are gained through a complicated interaction: namely, the physician’s hand with its changing position when guiding the probe and the accompanying changes on the screen. It is only through a temporal sequence of controlled movement and observation that the specialist can learn which imaged effects remain invariant, which are perhaps only blurred shadings, and so forth. The full diagnostic potential of the ultrasound scan can only be exploited through multidimensional movement and through observing the relation between movement and image over a certain period of time. The procedure draws on an essentially dynamic aspect; hence, it is basically not a single representation, but a relational tableau with which the physician gradually becomes familiarized through the temporally extended interaction of body movement, instrumental evaluation, and its visualization—an orientation is gained through a sequence of images that the physician can influence through his or her own movement. Dynamics, iteration , and visualization are essential aspects of the instrumental access through the ultrasound scan that could never be conveyed, even in principle, through a single image. This chapter considers which kind of understanding (a certain class of typical ) computer simulations can provide, and how they do so. Discussing these issues will reveal major parallels to the ultrasound scan scenario sketched above because dynamics, feedback with visualization, and the orientation that can be attained in a model characterize the understanding that researchers can obtain in computer simulation as well.1 Models come in different types. Basically, we can distinguish between theoretical models (in mathematical language), simulation or computational models (for example, discretized versions of a theoretical model), and algorithmical implementation (sometimes also called the computational model). Simulation modeling involves going back and forth between all of them. The modeling process, however, can be described with more levels of modeling (Winsberg 1999), with emphasis on experimental aspects (Dowling 1999; Winsberg 2003; Lenhard 2007), or by analyzing whether theoretical models may be dropped entirely in certain circumstances (Keller 2003). The details do not matter here (see Lenhard et al. 2006 for a sample of the modeling discussion specializing in simulation). Simulations weaken the link between theory and understanding. In this book, Tarja Knuuttila and Martina Merz’s “Understanding by Models” points out the affinities between studies of modeling and of understanding. However, if the investigation of scientific understanding should be located in the context of modeling, what distinguishes simulation models from models in general, if such characteristics exist at all? Knuuttila and Merz claim that the “workable johannes lenhard de Regt Txt•.indd 170 9/8/09 11:27...

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