In lieu of an abstract, here is a brief excerpt of the content:Preface: Virtual Entities in ScienceRobert Harlander, Jean-Philippe Martinez, Friedrich Steinle, and Adrian WüthrichIt is not only since the sudden increase of online communication due to the COVID-19 situation that the concept of the “virtual” has made its way into everyday language. In this context, it mostly denotes a digital substitute for a real object or process. Virtual reality is perhaps the best-known term in this respect. With these digital (...) connotations, “virtuality” has also been used in science and research: Chemists use virtual laboratories, biologists do virtual scanning of molecular structures, and geologists engage in virtual field trips. But the concept of the virtual has a much longer tradition, dating back to long before the dawn of the digital age. Virtual images and virtual displacements were introduced in classical physics already in the late seventeenth and eighteenth centuries, respectively. They represent auxiliary objects or processes without instantiation, with the purpose of efficiently describing specific physical systems. In today’s physics, the term “virtual” is mostly associated with the quantum world, first and foremost with the “virtual particle” of quantum field theory. It has become such an integral part of modern high energy physics that its ontological character may be considered to go beyond the purely auxiliary, which is typically associated with the virtual. [End Page 263]In other disciplines, however, use of the term virtual without a digital connotation is much rarer. While concepts like “virtual adrenaline” show up in physiological research around 1940s, and Charles Darwin, in a private note in January 1840,1 spoke of “virtual change” in the context of embryology, these examples seem to be singular occurrences of entities that were explicitly called “virtual.” The basic idea behind the terminology of the virtual, however, might be much more common, even outside of physics. The “invisible hand” in economics, or the “vital force” in biology, for instance, may carry aspects of a virtual entity, even if they have not been referred to that way.These different observations raise several questions about the status of virtual entities in science. What has led scientists to call one entity “virtual” and not another? Do all virtual entities in science have the same roots and meet the same characteristics? Are they more than auxiliary objects or processes? Why does physics seem to occupy a specific position with respect to the use of the notion of virtuality? These are some points that led us to discuss virtual entities in science during a workshop, out of which grew the present collection. We invited contributions that addressed the historical formation and philosophical interpretation of concepts of virtual entities in physics and other disciplines—in whatever terms they may come. The main goal of the workshop was to bring to the fore similarities and differences in the meanings and functions of these concepts, so as to be able to precisely characterize why certain entities are considered virtual in specific contexts, why a different terminology was often used in each individual case, and in what sense the virtual entities relate to the real world.The organization of the workshop was part of our project “The formation and development of the concept of virtual particles,” a subproject of the Research Unit “The Epistemology of the Large Hadron Collider,” funded by the Deutsche Forschungsgemeinschaft (DFG) and Der Wissenschaftsfonds (FWF). The workshop took place online on four consecutive Fridays in March 2021. It brought together contributors who discussed the role of the concept of the virtual in theoretical as well as experimental activities, and investigated into the origins of the terminology of the virtual as it was applied to the various disciplines of natural science. Dealing with historical, philosophical, but also methodological questions, the presentations covered a wide time range, from the Middle Ages to the present day. While physics naturally emerged as the dominant field, natural philosophy, computer science and biology were also addressed. The papers in this volume were contributed by participants in this workshop and approach the subject from different angles. [End Page 264]First, Friedrich Steinle provides us with an introductory piece that reflects on the specific meaning of the use of the term ‘virtual’ in science. He highlights and... (shrink)