Dear Simon, On Tue, Jan 22, 2013 at 4:44 AM, Matthew West <dr.matthew.west@xxxxxxxxx> wrote: That is precisely the problem with NULL. You don't know if it means not known, or does not exist. In principle it could mean either in any situation.
There is an analogous issue when relating 3+1D ontologies of Space+time to 4D ones when it comes to entities might be considered to exist in time, but which may have no meaningful spacial extent. An good example of this are Fictional people (in worlds in which they are fictional, not in their fictional worlds). These entities have a temporal extent, but assigning them to a spacial location is problematic. MW: I don’t see a problem. There simply is a possible world in which they do exist and have a location. You can’t place them in the “real” world simply because they do not exist there, and the one they do exist in can be arbitrarily similar to the real world that we are in and they are not. Regards Matthew West Information Junction Tel: +44 1489 880185 Mobile: +44 750 3385279 Skype: dr.matthew.west matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx http://www.informationjunction.co.uk/ http://www.matthew-west.org.uk/ This email originates from Information Junction Ltd. Registered in England and Wales No. 6632177. Registered office: 2 Brookside, Meadow Way, Letchworth Garden City, Hertfordshire, SG6 3JE. One could specify that they have a height, width, and length of 0, and unspecified x,y,z co-ordinates, but that does not distinguish them from a point whose location is happens to be unknown. One could give them infinite spacial extent, so that they supervene upon the entire universe, but that is somewhat arbitrary, requires that answers to questions about what exists in any given 3-space region as of the now include Pegasus (and Fluttershy). One could stipulate that fictional characters supervene on physical things where information about them is held, but the act of thinking about Fluttershy activates different neurons, and requires one to accept that you can move Fluttershy with your mind. If one wants to say that x,y,and z extents/locations are meaningless for some types of abstract entities that can nevertheless have temporal extent, surely one needs to some sort of distinct value in ones coordinate space indicating that there is known to be no meaningful value (e.g. $\mathbb{R}_{\bot}$). This avoids confusion with epistemic issues, but changes the commitments of ones ontology. |