 Since the work of Gibbons and Hawking (1977), Bekenstein (1981), Smolin (1984), Bousso (1999a), Jacobson and Parentani (2003), and Padmanabhan (2005), among others, it has been known that an entropy and a temperature can be attributed to spacetime horizons more general than just the event horizon of a black hole. From another direction, the attractiveness of Penrose's Conformal Curvature Hypothesis (Penrose 1979), discussed below in  section 7,  along with subsequent work attempting to make the Hypothesis precise, all suggest that certain types of cosmological singularities, such as the Big Bang, should themselves be attributed an entropy. This has led in recent years to several interesting proposals for a completely general measure of gravitational entropy, such as that of Clifton et al. (2013). Indeed, Anastopoulos and Savvido (2012) have even attempted to attribute entropy directly to non-cosmological singularities, those associated with collapse phenomena. Pavón and Zimdahl (2012), in a similar spirit, attempt to provide a thermodynamical analysis of future cosmological singularities and so characterize them by their thermodynamical properties. 