 Though the impression often painted of the research landscape in quantum gravity is an either/or situation between string theory and loop quantum gravity, in reality there are very many more options on the table. Some (e.g., Callender and Huggett 2001, Wüthrich 2004 (Other Internet Resources section); J. Mattingly 2005) have argued that semiclassical gravity, a theory in which matter is quantized but spacetime is classical, is at least coherent, though not quite an empirically viable option (we discuss this below). Other approaches include twistor theory (currently enjoying a revival in conjunction with string theory), Bohmian approaches (Goldstein &amp; Teufel, 2001), causal sets (see Sorkin 2003, in the Other Internet Resources section) in which the universe is described as a set of discrete events along with a stipulation of their causal relations, and other discrete approaches (see Loll, 1998). Causal set theory has begun to stimulate some philosophical interest on account of the claims, by physicists, to the effect that the theory embodies a notion of objective becoming or temporal passage based on the notion of the ‘birth’ of spacetime atoms (see, e.g., Dowker 2014; for a skeptical response, see Huggett 2014; Wüthrich, 2012, pursues instead the structuralist leanings of causal set theory). 