I have a two-part question about the definition of a possible world. I will make the assumption that time is tensed.
First of all, is a possible world a complete list of all propositions that are true now (at the time of the present temporal event), or a complete list of all temporal events and a complete list of all propositions that are true of each event? For example, if one gave a list of propositions that precisely described the position and motion of every fundamental particle at the present instant, and analogously described any additional mental or supernatural realities at the present instant, would this be a different possible world than a similar list describing an instant one year ago, or would these (along with all other instants) be part of the a single possible world?
EDIT: It seems I worded the first question a bit clumsily; I didn't mean to give such special weight to the "now" event. My point was to ask what the temporal scope of a possible world is. Is it a maximal description of reality during a single hypothetical (or actual) event, or a maximal description of a hypothetical (or actual) reality throughout its full duration?
Secondly, if the latter is correct, is the objective "now" part of the description of a possible world? If two descriptions of reality are identical, except that in one, 1990 is now, and in another, 2000 is now, do these constitute one or two distinct possible worlds?