 Pearl (2000) also argues that any account of causation that closely links causal notions and the notion of interventions cannot be applied in the context of a truly fundamental physics that includes models of the universe as a whole. The reason is that global models of the universe as a whole do not have an “outside” that could be represented by an intervention variable and from which an intervention into the universe could take place. Yet Pearl’s own do-calculus first introduces interventions formally in a way that does not posit intervention variables external to the causal model of interest. Nonetheless, interventions into the universe as a whole are not physically possible. Here the question concerning interventions in fundamental physics makes contact with another issue on which there is an active debate: the question on appropriate constraints on allowable interventions and the question to what extent interventions need to be physically or conceptually possible.