Relation between Theories, Experiments, and Simulations of Spectral Line Shapes

Simulations of Shapes and Shifts of Spectral Lines (SSSL) are important as the third powerful research methodology-in addition to theories and experiments. However, there is a growing tendency in physics in general and in the area of SSSL in particular, to consider the ultimate test of any theory to be the comparison with results of a code based on fully-numerical simulations starting from the "scratch" rather than from some analytical advance. In this paper, we show by examples that fully-numerical simulations are often not properly verified and validated, fail to capture emergent principles and phenomena, and lack the physical insight. Physics is the experimental science. So, the ultimate test of any theory-including theories of SSSL-should be the comparison with experiments conducted in well-controlled conditions (benchmark experiments).