Colloquium Mathematical Philosophy, Benjamin Smart (Birmingham) gives a talk at the MCMP Colloquium (10 January, 2013) titled "The Metaphysics of Lazy Worlds". Abstract: Although it is not uncommon for philosophers to put the fundamental laws to one side and discuss, say, causal interactions concerning macroscopic objects like vases, matches and so on (Mumford and Anjum 2011), in this paper we are concerned with our most fundamental physical principles, and the universal laws that can be derived from these. When it comes to predicting ‘evolutions’ of physical systems, there seem to be two mathematically equivalent, but conceptually distinct kinds of what we might call ‘fundamental laws’: there are those laws we, it seems fair to say, are most used to talking about – Newtonian-style laws whereby we can take the state of a system at a time t, apply the relevant laws telling us what will happen next, and correctly predict the state of the system at time t+1. These kinds of law we refer to as ‘equations of motion’. But there is also a fundamental principle of a different nature – a teleological principle telling us that as a physical system evolves from one state to another, the path the system takes through velocity-configuration space is that which minimizes, or to be more precise, extremizes action. This teleological law is conceptually somewhat strange – how does the electron know where it’s going to end up, and what route it should take to take there to minimize the action? Nonetheless it is not a principle to be ignored by the metaphysician, purely because it is strange. We consider, from the viewpoint of four different metaphysical accounts of laws of nature, what this principle of least action (PLA) should be taken to be ontologically, its modal profile, and assuming that laws must have explanatory value, what kind of explanation it affords and where the PLA stands in the explanatory hierarchy.