One problem with "reality" in the context of multiverse theories is that it may mean different things to different people.
If we assume (for analytical purposes) that some form of multiverse exists, then ultimately the reality is the multiverse. But it seems that each person is constrained only to see one universe out of the multiverse. For him, that universe is all that is real, the rest of the multiverse is irrelevant. So already there is confusion over whether we should include the other worlds of the multiverse in "reality". I have been exploring the concept that the Universal Distribution exists and is "real". Reality in this model is every computer program execution, or equivalently (I would claim, but it is not too important here) every information pattern. This is a sort of "multiverse", in that it includes multiple "universes". Anything that can be created by a computer program exists, and arguably universes fall into this category. But it also includes other things. Chaotic information patterns that would not seem to possess most of the properties of a universe exist as well - without time, or causality, or dimensionality perhaps - just raw noise. And disembodied consciousnesses exist, too. We could each have our information patterns, the processes that make up our minds, be produced by programs which do not actually create the rest of the universe but simply contain hard-coded sense impressions which are delivered by clockwork. The UDist framework allows us to theoretically approximate the measure of these various information objects, so we can say that some are more "prominent" in the multiverse than others. But all exist, all are real, in this model. One of the points Bruno makes is that in these kinds of models, the reality for a given observer is pretty complicated. Much of the multiverse is irrelevant to him, but that doesn't mean he can focus on just one universe as "real". The observer spans multiple universes and multiple realities. In the UDist framework, I would say it in this way: Many programs create the information pattern corresponding to a given observer. Some of those programs create the observer as part of a relatively straightforward universe that corresponds fairly simply to his sense impressions. Some programs create the observer within a universe that has a far more subtle and complex relationship to what the observer senses. In some universes the observer is part of a simulation a la The Matrix, being run on artificial machines within that universe, so that what the observer sees has little relation to the "true reality" of that universe. And some programs create the information pattern as I described above, without a real universe at all, so that the observer in effect hallucinates the entire universe. The point is that all of these programs exist, hence all contribute measure to the observer. From the observer's perspective, all of these are in a sense "real" to him. However, he can in principle calculate (at least approximately) the numerical contribution made by each of these programs, and perhaps it turns out that the vast majority of the measure comes from just one of them. He might be justified in that case in largely ignoring the others and saying that only that one is "real" for him. But for full precision he must still take into consideration all of the programs that could create instances of his information pattern, and consider all of them to be "real" to some extent. And then, perhaps, he may choose to accept that the whole multiverse is real, even the parts which do not affect him. Otherwise he has to say that all programs exist which happen to include an information pattern corresponding to him, the observer who is making this claim. That's not a very compelling theoretical model. Hal Finney