  Gilbert and Troitzsch argued that “[t]he major difference is that while in an experiment, one is controlling the actual object of interest (for example, in a chemistry experiment, the chemicals under investigation), in a simulation one is experimenting with a model rather than the phenomenon itself.” (Gilbert and Troitzsch 1999, 13). But this doesn’t seem right. Many (Guala 2002, 2008, Morgan 2003, Parker 2009a, Winsberg 2009a) have pointed to problems with the claim. If Gilbert and Troitzsch mean that simulationists manipulate models in the sense of abstract objects, then the claim is difficult to understand—how do we manipulate an abstract entity? If, on the other hand, they simply mean to point to the fact that the physical object that simulationists manipulate—a digital computer—is not the actual object of interest, then it is not clear why this differs from ordinary experiments. 