I'm a staunch atheist, but I've often considered the possibility of a god running a computer simulation that is completely deterministic in nature: every time a random value was needed (like when the wave function representation derived from Schroedinger's equation collapses), the simulation would read it off of an arbitrarily large CD-ROM (say) containing a set of random or seemingly-random numbers. That simulation would, of course, be our universe and would account for the quantum indeterminacy we see. This very review could be encoded in that simulation!
On the flip side, it's easily possible we will be able to represent information contained in our genomes, and even our brains, in virtuo, and create "computing clones" of ourselves. If done to an accurate enough detail they may well have human-like properties, including human-like sentience and human-like consciousness.
It hasn't escaped my mind that, ironically enough, both scenarios (or even variances of this consistent with many hierarchies) could be true. We could be simulations attempting to simulate intelligent systems which in turn simulate intelligent systems and so on. The Thirteenth Floor explores this notion in a thought-provoking manner, with a fairly cohesive plot. However, it is lacking in terms of acting, direction, and effects.
In the film, Hammond Fuller (Armin Mueller-Stahl) and Douglas Hall (Craig Bierko) have created a virtual reality simulation of 1937 Los Angeles complete with sentient agents that act out the people from that era. Fuller is able to "jack in" to this world and interact with the agents just as he would in his world. Complications arise when Fuller is killed just as he tries to tell Hall a truth about their world. Furthermore, Hall becomes the chief murder suspect. To make matters worse, one of the sentient agents in the simulation, a bartender named Whitney (Vincent D'Onofrio), discovers that he is not "real" and proceeds to find a way to "escape" to the real world.
The movie is extremely predictable. Both the major plot "twists" (the discover of the simulation within the simulation and how Hall manages to make it to a world one layer above his (which may also be a simulation for all we know)) were choreographed by me well in advance. A plot device necessary for the movie (driving past the borders of Southern California to discover the truth about one's world) does not stand up to scrutiny (is this like The Truman Show where phobias were programmed in to make people not leave L.A.? If they could create an elaborate version of 1937 L.A., why not just create an imagined loop that goes on for eternity). The acting, consisting of relatively new faces, isn't anything terrific, and neither is the character development.
The movie has been compared to The Matrix, and while the genre is the same, I think that the paradigms being addressed by the two films are completely different. In The Matrix, it is the humans who want to be left alone by the sentient agents. In this film, the sentient agents want to be left alone by the aliens. The degree of philosophising in this film is very limited, unlike The Matrix. But, like I say above, the consequence is that the storyline ends up being thought-provoking and definitely worth the matinee fare.