Einstein's theories of relativity pose problems for certain dualistic theories, in particular, those that posit datable psychological events (e.g., thoughts) that are supposed to have no spatial location. For the theories hold that space and time are inseperable aspects or features of a single spacetime manifold. Consequently, it follows that nothing can have a temporal location without having a spatial location, and vice versa. Thus, mental events cannot have a location in physical time without having a location in physical space. This leads to some pressing questions for the dualist. If mental events do take place in physical space where they located? Are they located where their neural correlates or realizers are located? If so, they and their corresponding physical events will be compresent, both occupying the same physical space. We are then committed to holding that two things can occupy the same place at the same time. The case here is perhaps not quite so counterintuitive, since the things are events of markedly different kinds. Yet we can question whether it would make sense to hold them to be wholly distinct; perhaps we should treat this scenario as vindicating property dualism. The last question also makes a hidden assumption: that every mental event has a physical correlate. Call a mental event floating if it has no physical correlate or realization. Where are these floating events? They cannot be where their correlates are, for they have none. At first sight, assigning them a location seems rather arbitrary. However, if we're willing to abandon the causal closure of the physical, we could perhaps locate them 'between' their neural causes and effects. The question would then arise of how the laws of mental-physical interaction would "fit together" with the laws of physical-physical interaction (and mental-mental interaction, if any such there be). Conversely, if the dualist rejects the notion that mental events have a location in physical space, they must deny they have a location in physical time. They will then have to posit a purely mental or experiential 'phenomenal' time, a temporal analogue of the sense-datum theorists' phenomenal space. This time will then be disjoint from physical spacetime, making it hard to make out how events belonging to either series could have any effect on each other.
The same would also seem to hold for universals and/or properties: If they are instantiated at any physical time they are also instantiated in a physical place, and vice versa. So if one sides with Aristotle in holding that universals are present "in" things, one must also hold that they are present "at" times. If one takes a more Platonic view that universals are related to their exemplifiers or instances without being present "in" them, one must also hold that there is no time at which they are exemplified or instantiated. It would seem a change of properties would then have to be analyzed as the successive stages of an object eternally being related to different properties.