 However, not everyone agrees that physicalism entails the impossibility of zombies. One suggestion is that physicalists can concede there are possible worlds which are exact duplicates of our world in all purely physical respects, but where the physical properties which give rise to consciousness in our world are prevented from doing so by nonphysical items which block consciousness. That would let physicalists consistently allow the possibility of zombie worlds (Leuenberger 2008. On such ‘blockers’ see Hawthorne 2002b; Chalmers 2010, 163–165). This approach, however, is obviously inconsistent with maintaining that conscious states are either identical with or constituted by physical or functional states. So it is not clear that physicalists can consistently allow the possibility of consciousness-blockers.