On Thursday, January 23, 2014 5:15:58 PM UTC+11, Liz R wrote: > > On 23 January 2014 18:09, meekerdb <[email protected] <javascript:>>wrote: > >> >> Yeah, but decoherence just makes things look classical at a >> coarse-grained level (when we trace over the environment). Microscopically >> it's spreading the superposition. >> >> Yes, I guess that makes sense. All those quantum entities will be fuzzing > out, regardless of what we do - so I assume the answer to the original > question is that the multiverse differentiates like his "old method" of > backing up files - taking complete snapshots of everything - rather than > using the "version control system" method of only storing differences? > I had a long think about this while walking on the beach this morning and I still think not, though the picture is more complicated than your spreading local changes scenario suggests. If you read the paper I cited above you'll see that there is a method to rescue locality, but it comes at a fairly steep price, conceptually. Each particle has to carry "labels" with it, essentially a memory of prior interactions, so that it knows what states are permitted when it interacts with another system. This sounds about as bad as the whole universe duplicating when you consider that its history goes right back to the Big Bazoom, as you point out, so effectively it carries the weight of the entire world on its tiny subatomic shoulders. However there's another way of conceptualizing it I think which rescues the parsimony of the source control type system while keeping the interaction history.
Essentially yu have to stop thinking of the particle as an isolable entity. Its entire history *define* its position, location and properties, and at the same time in a sense define the whole universe. This is not quite as mystical as it sounds (though it's still pretty mystical!). I'll explain. When I make a change in git (my clever source control system), it records the delta between the old code and the new - i.e., the changes only. This is maximally parsimonious. I can make two branches in my code, say to explore some new feature or way of doing things, and both branches link back to a common root in the tree of deltas. Now later, because the system retains full information about all the changes (interactions), I can merge these branches and all changes will be incorporated into the one new branch. This is the exact equivalent of MWI universes re-merging. But let's say I made a change to the *same line* in both code branches. Then I can't merge automatically any more because there's a conflict. I have to choose which version of the line I want. This is the equivalent of decoherence. Now the point here is that if I was someone who wanted to study a node in isolation, I'd see some information, but only a very small amount. The rest of the information is kept in the previous node that it links back to, and the node it links back to, and the one before, and so on. The node makes no sense in isolation and seems not to contain enough information to reconstruct a coherent code base (universe), but it does in the context of the whole tree. The information about what changed where is kept at the point of interaction, not needing to be copied forward. The system can always know when to decohere in order to maintain internal consistency. Whaddya reckon? To me it makes an elegant sense, though I have no idea of its testable. I suspect not, but it seems a lot cleaner than the "entire backup" idea, OR the idea of a particle that carries its autobiography under its arm. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
