Quantum entanglement in the MWI

[PeterDonis]

I don't think I did make a positive claim.

Here is what you said:

It is sufficient to identify a subsystem in which "which-branch" information is not available. This can be personified as an observer who is ignorant of the branch in which they are embedded.

That's a positive claim. Either give a reference to back it up or retract it.

It's no good just throwing my post back at me verbatim, saying "it's in there".

Um, yes, it is. What I quoted was all of your post except the first sentence, which just said you were disagreeing with me. If you don't think that two declarative assertions by you are a positive claim, then I am very confused about what language you think you are speaking.

 

[kered rettop]

That's a positive claim. Either give a reference to back it up or retract it.

Neither of those is going to happen, are they?

 

[PeterDonis]

Neither of those is going to happen, are they?

If not, then the subject is off topic for this thread and I will delete both of our posts that refer to it.

 

[kered rettop]

I just don't see how one could possibly pull off this trick in general.

Would it help to recognise that there is a difference between dividing a world-state using arithmetic and dividing it by means of decoherence?

With arithmetic, the amplitude is divided by a real number, N, to produce N identical micro-world-states. Phase is retained: the micro-world-states are coherent. So they are indistinguishable and it doesn't make any sense to assign probability to them individually. Though if you did, it would be original/N^2. However, when you add a bunch of them together, they interfere constructively.

Decoherence works the opposite way. The process leads directly to N orthogonal micro-world-states. You can calculate the required probabilities using the Born Rule and there is no interference. Obviously the amplitudes are not original/N but original/sqrt(N).

Edit - It seems to me that what you call fundamental branching doesn't enter into any of this.

 

[PeterDonis]

You can calculate the required probabilities using the Born Rule

But in the MWI, there is no accepted derivation of the Born Rule. And if you adopt it as an extra assumption, you can't then use it to justify a concept of probability in the MWI; that would be arguing in a circle.

 

[kered rettop]

But in the MWI, there is no accepted derivation of the Born Rule. And if you adopt it as an extra assumption, you can't then use it to justify a concept of probability in the MWI; that would be arguing in a circle.

No, the context was arguments based on world-counting, specifically about how to count worlds correctly. One criterion, pointed out by the previous poster, PeroK, is that world-counting must sucessfully reconcile amplitudes with probabilities. The correct probabilities are given by the Born Rule. The Born Rule is thus an objective of the argument, it has no place as an assumption of the argument. That's why I said "required probabilities".

 

[PeterDonis]

the context was arguments based on world-counting

Which means the MWI. Which means you can't just take the Born Rule as given.

The Born Rule is thus an objective of the argument

Are you claiming that this argument is a valid derivation of the Born Rule in the MWI? On what basis? Do you have a reference?

 

[PeterDonis]

One criterion, pointed out by the previous poster, PeroK, is that world-counting must sucessfully reconcile amplitudes with probabilities. The correct probabilities are given by the Born Rule.

In the context of the MWI, before you can even get to this point, you have to justify how the concept of "probability" even makes sense.

 

[kered rettop]

In the context of the MWI, before you can even get to this point, you have to justify how the concept of "probability" even makes sense.

If by "you", you mean the formulator of the candidate argument, then sure, of course they do.

 

[PeterDonis]

If by "you", you mean the formulator of the candidate argument, then sure, of course they do.

Where do they do that?

 

[kered rettop]

Which means the MWI. Which means you can't just take the Born Rule as given.

Oh I see what you mean. Yes, I was assuming that the desired probabilies would be the Born Rule. I should have left it at "desired probabilites" and left it to the formulators or PeroK to decide and justify what they should be.

 

[kered rettop]

Where do they do that?

Oh good grief!
"do have to justify" not "do justify"!!!

 

[kered rettop]

Are you claiming that this argument is a valid derivation of the Born Rule in the MWI?

No.

 

[PeroK]

Would it help to recognise that there is a difference between dividing a world-state using arithmetic and dividing it by means of decoherence?

Take Schrodinger's cat as an example. But, instead of the 50-50 probability of decay, make it 10%. There should only be two decohered worlds. The fundamental branching of the radioactive sample is fundamental to the experiment. And, yet, there would have to be 9 times as many decohered worlds with a live cat than a dead one. Unless that ratio is driven by an initial weighted or probabilistic branching, how can it be otherwise conjured?

Moreover, the probabilistic explanation is simple. The sample has a probability of $p$ to decay; the probability the cat dies is $p$.

 

[kered rettop]

Moreover, the probabilistic explanation is simple. The sample has a probability of $p$ to decay; the probability the cat dies is $p$.

It depends what you mean by simple. Introducing probability as a primitive complicates the fundamentals of the theory. It may simplify the development of the theory. Occam's Razor vs Shut Up And Calculate.

 

[PeroK]

It depends what you mean by simple. Introducing probability as a primitive complicates the fundamentals of the theory. It may simplify the development of the theory. Occam's Razor vs Shut Up And Calculate.

I don't see how what is proposed can claim the moral high ground and insinuate a shut up and calculate accusation against a probabilistic theory. You need a constructive argument to support the MWI counting process. Throwing mud in the form of cheap soundbites doesn't cut it.

 

[PeterDonis]

Oh good grief!
"do have to justify" not "do justify"!!!

Sorry, I misinterpreted your post.

 

[kered rettop]

I don't see how what is proposed can claim the moral high ground and insinuate a shut up and calculate accusation against a probabilistic theory.

Hardly a theory. Just the status of probability.

You need a constructive argument to support the MWI counting process.

Somebody might. I don't, since I am not advocating anything.

Throwing mud in the form of cheap soundbites doesn't cut it.

Oh, it's much worse than that. I have only just realized what you've been talking about. Even if I'd used a phrase which you found acceptable, my point would have been invalid. SUAC isn't so bad in the context of my misundertanding.

And yes, this means that my suggestion won't be helpful either.