Does experimental physics provide facts about the natural world? Scientific realists and positivists both argue that it does. This book critically addresses the question of how experimental physics is conceptually and historically possible as a natural and empirical science. How have experimental physicists used technology to explore, model and understand nature? The argument of this book is that scientific realist and positivistic philosophies of science have both presupposed the same operational metaphysics: that natural phenomena and machine performances are consequences of the same natural principles, laws and mechanisms. This metaphysics allows the ongoing technological activities of experimentation to disclose natural phenomena in terms of mechanistic models that are tested by their implementation in future technological innovation. The origin, function and implications of this metaphysics for our understanding of the world are described and analysed in detail. It is then questionable whether physics is a natural and empirical science at all.