On 4/15/2022 2:36 PM, George Kahrimanis wrote:

Bruce wrote> [...] Since I have not been able to formulate an argument that has convinced Saibal, there seemslittle point in continuing the discussion.Not yet, because I just got an idea of what went wrong in thecommunication. Part of it was the understanding (maybe it was justme!) of "local splits" as propagating on light cones, which now makesme laugh.> The argument that MWI is strictly local is just a mistake, and not an argument against MWI itself.Let me try to back this claim. In the example with Alice and Bob, thesplits arise in the description ("wavefunction") of a superobserver,George, who only knows that, first Alice then Bob, measure entangledspins on two pre-set axes, without him knowing the outcomes. Insteadof the superobserver, you may think of an impersonal quantumdescription of the whole system, but I wonder what does it mean, toassume a quantum description without a subject, so I will keepspeaking of a superobserver.When Alice becomes entangled with the spin, and the record becomespractically permanent (by decoherence in her head), then in George'sdescription the whole system splits.

`"In George's description" means George knows...what? Does he know the`

`setting of Alice's polarizer? Does he know that she got 1 or know that`

`she got 0, on only that she got a result? Some of these he can know`

`without being the forward light cone of Alice's measurement.`

Not separately Alice or Bob; the whole system. We should not beconfused by the fact that at first the two Bobs are exactly identical,until Bob eventually learns Alice's record -- but the split hadoccured earlier, in George's description (of the whole system).When, in turn, Bob (that is, both Bobs) measures the spin with hisequipment, George's description splits again; so George counts fourBobs now. (If the two axes are parallel, then one of the twocomponents of the second split has measure zero.) This split alsoaffects each Alice, who becomes two IDENTICAL copies (total: four!),until she (that is: each Alice) learns Bob's record, and then thereare no more identical Alices -- but the split had ocurred earlier.

`That seems pretty much the same as Bruce's account. Whatever the`

`polarizer settings, there are four result pairings, while QM only`

`predicts two in case the polarizers are parallel.`

Brent

So, "local split" makes no sense: each split arises in the descriptionof a superobserver. Without a superobserver, it is unclear whetherAlice will regard herself as split by her measurement. Bob will tellher "Alice, now you are split", but so what? Alice (both of them) mayreply "I know that I am counted as double by anyone who knows of mymeasurement without knowing the record, but I assure you that I amonly one of the two Alices you have in mind". (No wonder that manypeople hate MWI!) And she may add "If I am split then you are too!".I could say more about needing a superobserver -- maybe in anotherposting.George K. --You received this message because you are subscribed to the GoogleGroups "Everything List" group.To unsubscribe from this group and stop receiving emails from it, sendan email to everything-list+unsubscr...@googlegroups.com.To view this discussion on the web visithttps://groups.google.com/d/msgid/everything-list/eaca7767-1024-41c5-b9e4-c685dd3af3ban%40googlegroups.com<https://groups.google.com/d/msgid/everything-list/eaca7767-1024-41c5-b9e4-c685dd3af3ban%40googlegroups.com?utm_medium=email&utm_source=footer>.

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