 Another way in which this assumption is complicated is that different physical theories often seem to imply different things about the nature of time. Consider, for instance, the fact that in general relativity there is sometimes (though not always!) a preferred way of “foliating” spacetime into instants of time and thus reintroducing a notion of absolute simultaneity, or the fact that on some interpretations of quantum mechanics, the dynamical laws seem to require a notion of absolute simultaneity.