On the one hand, it seems weird to say that every simulation (assuming the information it contains could, in principle, be "experienced" in some way, however simple and low-resolution the resulting "perceptions" would be) is thereby a new reality in its own right. That would seem to stretch the concept beyond all recognition. On the other hand, however, it doesn't seem that the metaphysical status of a world as "real" or not should depend on its happening to actually support conscious experiences. The material world could have existed without ever giving rise to sentient beings, so why should the same not be said of a rich Matrix-style virtual world to which nobody ever plugs in?
In Section 6 of 'The Matrix as Metaphysics', Chalmers writes:
[G]iven an abstract computation that could underlie physical reality, it does not matter how the computation is implemented.... In particular, it is irrelevant whether or not these implementing processes were artificially created, and it is irrelevant whether they were intended as a simulation. What matters is the intrinsic nature of the processes, not their origin. And what matters about this intrinsic nature is simply that they are arranged in such a way to implement the right sort of computation. If so, the fact that the implementation originated as a simulation is irrelevant to whether it can constitute physical reality.
There is one further constraint on the implementing processes: they must be connected to our experiences in the right sort of way. That is when we have an experience of an object, the processes underlying the simulation of that object must be causally connected in the right sort of way to our experiences. If this is not the case, then there will be no reason to think that these computational processes underlie the physical processes that we perceive. If there is an isolated computer simulation to which nobody is connected in this way, we should say that it is simply a simulation.
But why should we say this? The preceding sentence suggests that Chalmers is focused on the specific question of whether the processes constitute our reality. But can't we also ask the more general question of whether they constitute a genuine reality at all (regardless of whether it is ours)?
At this point one might reasonably question what hangs on whether we call something a "reality" or not. Is this merely a verbal dispute? I think the best way to avoid this danger is (as usual) to focus on the potential normative implications. Some people think that natural beauty (say) can have intrinsic value, even in a world with no conscious beings. So, the question becomes, should such people also value any similar natural beauty that is to be found within a never-experienced virtual world? Would it be worthwhile to create such worlds, just to increase the amount of natural beauty "out there"?
We might also consider less extreme versions, say where a world has been experienced in the past but never will be again. Often we care about what will happen after our deaths. Could an inhabitant of such a "dying world" reasonably care about what happens after the last conscious person leaves it?
In either case, I'm (tentatively) inclined to think that anyone who would say "yes" to the parallel question regarding a material world should likewise answer "yes" to the case involving a virtual world. But it's a little tricky, because I'm dubious about attributing value to any states of affairs that lack conscious beings or agents. (In which case, it would no longer matter whether an unexperienced world counts as "real" or not, because it lacks a crucial precondition for genuine value regardless.)
What do you think?