 Turning to 15, there seem to be good reason for accepting gunky possibilities. The best tests for whether a scenario is possible are whether it is conceivable, logically consistent, and posited in serious scientific theories. Gunk passes every test (Schaffer 2003). It is conceivable. For instance, it is conceivable that everything is extended, and that everything that is extended has two extended halves. This generates a Zeno sequence of halvings without limit. Further, gunk is logically consistent. Or at least, there are gunky models of classical mereology (Simons 1987: 41). Finally, gunk is scientifically serious. In this vein Georgi (1989: 456) has suggested that effective quantum field theories might form an infinite tower which “goes down to arbitrary short distances in a kind of infinite regression… just a series of layers without end.” Perhaps there are competing considerations that weigh against the possibility of gunk. Here we enter into deep issues concerning the extent of what is  possible.[46]