Talk:Modal realism

message: I am new to this talk section, so please mail me at henry.story@bblfish.net if I make a mistake. 
In his collected papers, David Lewis defines causality as a relation between events such that
  e1 causes e2 if and only if
     if e1 had not happened then e2 would not have happened
which due to his analysis of counterfactuals comes to 
  e1 causes e2 if and only if
    in the closest possible worlds in which e1 does not happen, e2 does not either
In this sense possible worlds in David Lewis' sense are not really causally isolated, since causality is a relation between possible worlds. In other words saying that something causes something else is to make a statement of the relation between possible worlds.
Now it is true that doing something in this world does not cause it to happen in another world. But that is just because that statement does not make sense.--Bblfish 13:32, 15 October 2006 (UTC)
thread_title:  On causal isolation 

message: I removed the statement "and thus far has resisted all attempts at definitive refutation" -- that is, and I think will be for a long long time -- a matter of opinion.  Moreover, I agree that we need criticisms *other than* those enumerated (and then refuted) by Lewis himself.  I'm thinking off the top of my head of Stalnaker and Kripke, but I'm sure there are others that are worth citing here; I'll see what I can find and add them in. In that case the current section with Lewis' arguments should be shortened to give due weight. BrideOfKripkenstein (talk) 20:27, 24 July 2010 (UTC)
thread_title:  Criticisms 

message: Under "The term *possible world*" it says "To note, however, though the concept does sound similar to modern notions of a multiverse, in reality these two concepts are quite distinct – a multiverse would constitute (or be part of) a single possible world." Doesn't this really depend on whether dufferent parts of such a multiverse can causally affect one another? The difference between the Copenhagen and Many Worlds interpretation of quantum mechanics, is that Copenhagen is essentially the same as Many Worlds except that it asserts that only the part of the multiverse that can directly affect the observer is "real". Modal Realism would unite the two interpretations into one. Similarly, these String Theory notions that universal constants could take on many different values don't imply that there is any way to communicate information between universes. The only motivation for saying they arevall "real" rather than merely "possible" is solve the perceived issue of "fine-tuning", whereby most "possible" universes supposedly could not possibly support anything like intelligent life, or even atoms. Thus, couldn't these multiverse theories constitute subsets or sub-continua of the set of all possible worlds, rather than single ones? Also, the entire section I refer to contains no citations, like much of the article. DubleH (talk) 22:05, 21 August 2021 (UTC)
replies: text: Thanks for pointing this out. The claim in the article about the relation between the concepts of possible world and multiverse is not obvious. Unless a source can be found, I suggest that we remove the sentence: "To note, however, though the concept does sound similar to modern notions of a multiverse, in reality these two concepts are quite distinct – a multiverse would constitute (or be part of) a single possible world." If there is a source, it might be a good idea to explain how the term multiverse is defined to show how they are different. Phlsph7 (talk) 05:23, 22 August 2021 (UTC)
thread_title:  Multiverses