Rocks endure because they have built-in stability; smoke does not, for the opposite reason. Why some things are stable and others are ephemeral is not fully understood. Our knowledge of what is happening at the most fundamental level is currently in great diffi - culties, with the two most comprehensive, powerful and majestic theories of the physical world – the general theory of relativity and quantum mechanics – at odds with one another. At the intermediate level, however, things seem a little clearer. e most comprehensive account of the patterns of evanescence and endurance is the second law of thermodynamics, the supreme, perhaps the most metaphysical, of all the laws of nature. One formulation of this law is that the sum total of things tends towards thermodynamic equilibrium in which diff erences – say, of temperature, or density – are ironed out. is universal tendency towards disorder or increasing “entropy” has a simple statistical explanation: there are many more ways of being disordered than being ordered and so random change will tend towards disorder.