Lee Corbin writes: > Why not instead adopt the scientific model? That is, that > we are three-dimensional creatures ensconced in a world > governed by the laws of physics, or, what I'll call the > "atoms and processes" model. About observer-moments, I would > say what LaPlace answered to Napoleon about a deity: > "I have no need of that hypothesis".

Observer moments are more than a hypothesis, they are our raw experiences of the world. It is more the world that is the hypothesis to explain the observer moments, than vice versa. "I think, therefore I am... an observer moment," as Descartes meant to say. However, given the strong evidence we have for the world's existence and the explanatory power it gives for our experience, I don't think there is a problem with treating it as fundamental. This leads to a model of world -> observers -> observer-moments. A world maintains and holds one or more observers, which can themselves be thought of as composed of multiple observer moments. A key point is that the mapping is not just one-to-many. It is many-to-many. That is, an observer moment is shared among multiple observers; and an observer exists in multiple worlds. To explain the first point, observers merge whenever information is forgotten. And they diverge whenever information is learned. This means that each observer-moment is a nexus of intersection of many observers. The observer moment has multiple pasts and multiple futures. To explain the second point, observers exist in any world which is consistent with their observations. The amount of information in an observer is much less than the amount of information in a world (at least, for observers and worlds like our own). So there are many worlds which are consistent with the information in an observer, and the observer can be thought of as occupying all of those worlds. In this sense, the mapping above might be better expressed as world <-> observers <-> observer-moments. It is many-to-many in both directions. I see both views - worlds as primary, or observers and observer-moments as primary - as playing an important role in understanding our relationship to the multiverse. In terms of choosing actions or making predictions, we need methods for making quantitative estimates of what is likely to happen. This requires us to take into consideration the set of worlds which our observer-moments span, and the set of possible future observer-moments which we care about. To calculate, we need a measure over observer-moments. Then we can have a greater expectation of experiencing observer moments with higher measures. So how do we do this calculation? I start by calculating the measure of universes. Using an arbitrary, simple, universal computer, I would calculate the minimum program size for creating a given universe. (Yes, I know this is non-computable, but we can approximate it and use that for our estimates.) The program size gives the measure of that universe, and then that measure should lead us to a measure for the observers and observer-moments in that universe. This step of going from universe-measure to observer-measure seems a bit problematic to me and I don't have a completely satisfactory solution, but I won't go into the details of the problems right now. Anyway, once you have the measure for an observer moment in a given universe, you can sum the measures over all universes that generate that particular observer moment, to get the measure of the observer moment. Then, with a measure over observer-moments, you can take your current observer moment, look at ones that you identify with in the future, and consider the measure of those observer moments in helping you to choose what actions to take. This is how one should behave in a multiverse. This approach seems to require acknowledgement of the fundamental importance both of worlds and observer-moments. We use worlds to calculate measure; we use observer-moments to constrain the set of worlds that we occupy, now and in the future. A world-only approach would seem to pin us to a single world and not recognize that we span all worlds which contain identical observer-moments; an observer-only approach does not seem to give us grounds to estimate measure a priori (although I think Bruno may have a method which is supposed to do that). We have to use both concepts to get a complete picture of what is going on. Hal Finney