Instants in physics - point mechanics and general relativity (1306.0338v1)

Abstract: Theories in physics usually do not address the present''orthe now''. However, they usually have a precise notion of an ``instant'' (or state). I review how this notion appears in relational point mechanics and how it suffices to determine durations - a fact that is often ignored in modern presentations of analytical dynamics. An analogous discussion is attempted for General Relativity. Finally I critically remark on the difference between relationalism in point mechanics and field theory and the problematic foundational dependencies between fields and spacetime.