Contextual Emergence in Physics

Abstract Even though physicists often claim that their theories can, in principle, be reduced to the supposedly most fundamental theory, which is quantum physics, a look at how physics is practiced reveals that this reduction is almost never performed. Instead, effective models are built that include various types of contextual information and that are often incompatible with the supposedly fundamental theory. The phenomena described by these models can be characterized as contextually emergent. This chapter illustrates contextual emergence by means of examples from different fields of physics. In quantum physics, explanations of the measurement process require the assumption of a classical context that specifies the observable being measured and that induces the measurement event. In condensed matter theory, we find many types of quasiparticles that can only exist due to the solid that embeds them and the structure of which determines the properties of the quasiparticles. In thermodynamics, state variables such as the pressure and temperature of a system are given by its environment, and its phase transitions are triggered by changes in the environment. In the early universe, the degrees of freedom and the density and temperature determine the types of particles that are found in the universe. Later, the overall properties of the universe determine whether matter can condense to form stars. From all this it follows that processes and descriptions at different scales are equally important in physics. There are even contextual influences from outside physics. The chapter will thus conclude that physics is not causally closed.