It provides you a distribution of outcomes that can be compared with the predictions of usual QM. It may match or not match the predictions depending on what you assume are the weights (again in Carroll's sense of weights).PeterDonis said:
It does not!pines-demon said:
In QM interpretations, one can only hopekered rettop said:
No, it doesn't. The "distribution of outcomes" that we measure (in the context of the MWI) is relative frequencies in one world. It is not the relative weightings of different worlds in the wave function. So any claim about "distribution" that involves relative weightings is irrelevant to comparing our measurements with predictions. I pointed this out a while ago in the thread.pines-demon said:
I know that you are unconvinced but see it this way, if they repeat the experiment many times, for most observers at the end of the branch in a given world, both their past branch frequencies and the weights for the different branches for a given future measurement will agree.PeterDonis said:
Exactly. If it looks like probability and quacks like probabiity then it...pines-demon said:
Well, there shouldn't be any assumption, other than that the probabilities are equal. The thing is - and I think I may have to set up a hotkey to write this, it comes up so often - to derive a probability rule using counting, you have to add the microstates i.e. their amplitude vectors, and add the unknown but equal probabilities. It's not hard. If the microstates arise because of decoherence, they are orthogonal and the Born Rule jumps right out. Carroll's psuedo-branches are not orthogonal, in fact they are parallel. But the outcomes are not independent, they are 100% correllated. You have to use the rule for combining correlated probabilities. And that's assuming you can find a meaning for probability that includes psuedo-branches.pines-demon said:
The argument you are making here has been made in the literature by multiple people, going back, IIRC, some decades. I am not the only one who is not convinced by it. In any case, it is not something we are going to resolve here. Putting the various viewpoints on record here is fine, but we should not expect to actually reach a resolution when the community as a whole has not done so despite discussing this for far longer than we have here.pines-demon said:
I was trying to contest the general idea that probabilities cannot be defined. Putting that term probability aside, there are proposals to do get different distributions that can be compared with usual QM. This last part that does not seem to be a huge point of disagreement between the advocates of MWI. What seems to be a problem is if those proposals derive the Born rule (I am far from being the only one that has arrived to this conclusion here). Anyway, outside advocates of MWI, I do agree that sources disagree in many things.PeterDonis said:
Not sure I am following. I will answer to a few things. As I read it from the pdf, I think the pseudo-branches are indeed orthogonal (do not ask me to justify that!). I am also avoiding to discuss "probabilities" as it seems to convey a specific nuance that I have not been able to narrow down in this conversation.kered rettop said:
Yes, and as I said, that debate has been ongoing in the literature for decades now. Your point of view certainly has proponents in the literature, but it also has opponents. The issue is still open.pines-demon said:
No, they're not, because they are all associated with the same outcome (and in fact "they" are just one actual branch, which can't possibly be orthogonal to itself--that's mathematically impossible).pines-demon said:
Then I am very confused about why you are even posting in this thread, which, as its title explicitly says, is about the meaning of probability in the MWI.pines-demon said:
Sure but that does not say much, that's why we are exploring those issues.PeterDonis said:
Read the pdf, see the probabilities that they get and make you own mind about the orthogonality. These seem to be different branches with similar results. Postulate a hidden quantum number if you will, again it is worked out to reobtain the Born rule.PeterDonis said:
I have explained what I meant by it, that is to provide some measure that can be compared with QM. I just trying to formulate something pragmatic, I do not want to enter into these ontic-epistemic debates just by saying the term, I leave that to you.PeterDonis said:
I have. Its argument has, again, been made in the literature multiple times over decades, and has not resolved the issue (and, as I've said, I don't find it convincing). The reference is given and readers can make up their own minds.pines-demon said:
To be clear I am not necessarily inviting you to adhere to it. In this specific exchange I was just trying to clarify a remark by another user related to the paper. Let us not dig too much into the intricacies of the paper.PeterDonis said:
You smuggled a lot of hidden assumptions in this comment, i.e., that we are a single entity after branching.PeterDonis said:
I made no such assumption. In at least one other post (not in response to you) I acknowledged that after the branching, each "we" is different to the extent that "we" have observed a different measurement outcome. I also said that no "we" is privileged over any other; they are all on the same footing and they all have the same "we" before branching in their past. When I talked about the "we" in every world, in what you quoted, that was all I meant.jbergman said:
I'm not. See above.jbergman said:
There is only the wave function in the MWI. That and the dynamics of the wave function always being unitary (no collapse) are the MWI's primary features. There isn't some other version of the MWI where there is something else in addition to the wave function. The wave function is all there is in the MWI.jbergman said:
Sure, decoherence is what defines "branching" in the MWI (more precisely, it cleared up what used to be a serious missing piece of the MWI, namely what did define "branching"). That doesn't contradict anything I said above or in my previous posts.jbergman said:
It's still there!PeterDonis said:
I kind of agree except I would say that they cannot be treated the same way as worlds in a world-counting derivation of the Born Rule. Therefore either Carroll isn't doing that, or he has made a giant mistake, or my assertion is wrong.PeterDonis said:
Nobody is denying that it is an unconvincing way to get the Born rule, is cooked that way. Also to be fair, that pdf is not exactly Carroll's. He does not call them pseudo-branches, here is Carroll's take (see section 3.2):kered rettop said:
It would be nice to know why they cannot reach consensus though. Perhaps someone should start a thread on it.PeterDonis said:
Not the post where you used the words "SEP definition" and then cut it off. That's been deleted.kered rettop said:
I don't think there is even consensus on that.kered rettop said:
That can be expected to happen when you are dealing with questions that cannot be resolved by experiment, in a domain where what can be resolved by experiment is highly counterintuitive and is known not to have any simple resolution that meets our natural classical expectation.So it would seem, assuming PF users are representative. Still, putative explanations and meta-explanations do shed some light on the physics issues even if the reason for there being no consensus remains a mystery.PeterDonis said:I don't think there is even consensus on that.
Yes.jbergman said:
No, it isn't. Every possible outcome happens. So the probability of any outcome with a nonzero amplitude in the wave function happening is ##1##. It doesn't matter what the weight of that particular outcome is, since that weight makes no difference to whether the outcome happens or not. It always happens as long as there is any nonzero weight at all.jbergman said:
We have discussed it and I see how it could be a definitional issue, but is it a point of non-consensus though? Does criticism in literature centers about this? Clearly this is no point of conflict between MWI advocates so I guess it is brought by detractors?PeterDonis said:
It is one of multiple points that are not resolved in the literature.pines-demon said:
Yes, it is. That's part of the problem: even MWI advocates don't all agree on these questions.pines-demon said:
As far as I can tell from Carroll's "self-locating uncertainty" paper, he isn't. His approach there is different.kered rettop said:
Could you provide some sources about this criticism? From what I can read from Wikipedia or Carroll's differences between MWI proposals are not based at all on the problem of branch counting being an issue. What seems to matter is if their respective ways of counting really derive the Born rule or not.PeterDonis said: