The 2023 Lecture
The maggot in the apple: peaceful coexistence between incompatible theories
Michael Berry, University of Bristol, Europe
Abstract: Most phenomena can be understood in more than one way: the gas in an engine obeys the laws of thermodynamics and also those of the motion of its molecules. The different understandings correspond to different levels of description. Theories must overlap, but their consilience is far from straightforward because they are usually based on seemingly incompatible concepts. The discordance arises from a fact that was unappreciated until recently: the limit in which the more general theory reduces to the less general (usually older) theory is mathematically singular. One consequence is a range of phenomena, of intense current interest, inhabiting the borderlands between the theories. I will explore this theme with examples from the physics of fluids, light and the quantum world. The abundance of singular limits prompts a meditation: Physics is True but not Real.