In this introductory note we identify some of the problems with *time*.
Though intuitively familiar, time is a mystery. Time is a variable throughout physics: classical mechanics, thermodynamics, quantum mechanics (QM), and general relativity (GR) all include it. Yet the constructs in each are very different. Time is a topic that flow through many discourses and fields of study other than pure physics. It has implications in philosophy for how life exists in the framework of finite time, theological questions about what existence there might be beyond time and this universe, and psychological questions about how we perceive time in a cognitive sense. There are also unsolved integrative problems, like how the time that emerges at the level of atomic clocks transfers to the world at large, whether there is an absolute time, how time started, how time dilation works, and how the arrow of time arises.
All these approaches, physics, psychology, philosophy, have models for time. Yet they are poorly integrated, indeed sometimes in conflict. Nor are those constructs always coherent with humans’ personal cognitive perception of time. For example, the idea that time runs differently depending on gravitation or velocity, or that time may have had a beginning (and therefore not existed before the universe), is deeply puzzling to the mental model of most people.