To the extent that I'm aware of it, yes — Isaac

In that case, nothing to discuss.

In that case, nothing to discuss. — Wayfarer

Ah yes, I forgot your aversion to talking with anyone who disagrees with you. My apologies. No doubt I just don't understand the issue. In fact, have you got a massive quote from someone to that effect you can paste in lieu of an actual response, by any chance?

There is no privileged, "real" account. — Relational quantum mechanics

That's due to the subject matter, which has no ultimate nature. Science went searching for the ultimate basis of matter, and this is what it found.

You've basically disproven your point. — Isaac

That's Wayfarer's m.o. for sure.

Ah yes, I forgot your aversion to talking with anyone who disagrees with you. — Isaac

Yep, that too.

Science went searching for the ultimate basis of matter, and this is what it found. — Wayfarer

Yep. Which it then had the decency to admit to, investigate and form models based on.

What happened when Plato, Buddha, Mohammed,...etc went in search of the really real essence of reality? A similar admission, or thousands of year's worth of woo?

Yeah, frustrating as hell. I can't get my head around why someone would come on to a public forum and then not do the one thing the forum is designed to do, I mean, it's not as if there aren't hundreds of topic-specific forums in which people can discuss the details of issues they're all in broad agreement on. This approach of launching into a topic with a very strong claim, knowing it will be contested, and then backing out almost as soon as it actually is contested is really intriguing. It's the main reason I keep engaging, I'm hoping one time I'll understand a little more about the thought processes here.

Well, good luck. I've been there and done that, and have taken an uncharitably dim view of such dogmatic, or evasive, tactics. I'm noticing it more and more lately and this wears my patience thin to the point where for stretches of days I don't bother to login at all.

I can't get my head around why someone would come on to a public forum and then not do the one thing the forum is designed to do, — Isaac

There are a number of people here that never respond to my posts. The reason it’s pointless to debate you, is because you have a fundamentally positivist attitude which is never going to be shifted by anything I have to say.

The reason it’s pointless to debate you, is because you have a fundamentally positivist attitude which is never going to be shifted by anything I have to say. — Wayfarer

Why would you want to shift my attitude? Are you recruiting?

Notwithstanding, I've a couple of questions about this approach of yours...

Why 'attitude'? Are approaches for you clearly divided into 'attitudes' and conclusions (the former intractable, the latter the result of reasoned thought)? How do you distinguish an 'attitude' from a conclusion, such that you might find it worthwhile debating a wrong conclusion, but not a wrong 'attitude'? Surely persistence in the face of counter-argument can't be a measure alone as one would presumably persist no less with a well-reasoned and right, conclusion.

If someone disagrees with you and that's because you're actually wrong, then their position isn't going to shift is it, yours is. So by saying it's pointless to debate someone who position doesn't seem to be shifting no matter what you say is a self-immunised assumption that your position simply must be right. What if I'm not changing my position because all of your arguments are weak and unpersuasive? Does that bother you at all? What if I'm not changing my position because it's more resilient to counter-argument than yours? Is that something you just assume couldn't possibly be the case from the outset?

Responded here.

I'm not sure whether we're referring to the same experiment. — Andrew M

So the experiment has actually been done several times and, unless I made a mistake, one of the links was to one of those reports. So yes, same thing.

So the upshot is that the friend has made a definite measurement and reported that she has done so to Wigner, without telling him what the result was. At the same time the lab remains in superposition for Wigner, per your (B). — Andrew M

But at this point at the very latest Wigner and his friend should be entangled as they are exchanging information, i.e. they are not two independently evolving systems. This is how they'd appear, for instance, to an outside observer whose lab includes Wigner and Wigner's lab. In reality, Wigner and his friend were correlated well before. But then in reality we don't expect humans to be entangled at all (classical limit).

So tell me what's wrong with this pluralism/relativism conception or why it doesn't work for interpreting fundamental physics. — 180 Proof

I was just asking what the difference is.

I stated the difference as I understand it and that's why I asked whether or not you think it makes sense with respect to the variety of interpretations of QM, and if you find it does not maybe tell me why not. (I'm not looking to argue the point, just learn more about the science that's being so wildly interpreted by some scientists and too many "philosophers".)

And most of all, is this just a ruse to shoehorn in a third pomo-friendly thread to annoy ssu? Oh, more pluralism, more diversity, yes, very clever. (It's not, honest.) — Kenosha Kid

Not annoyed, but thank you for the thought. :smirk:

I actually had moral pluralism versus relativism in mind when I asked, but I see no reason not to translate to something more on-topic.

The difference as I understand it is this:

Relativism
"The cat is dead" is true for Wigner's friend but not for Wigner.

Plural realism
"The cat is dead is true for Wigner's friend" is true for everyone.

In one, the facts are observer-dependent; in the other, everyone has their own observer-independent facts. (An actual observer isn't necessarily required in either case, just a frame of reference.)

MWI doesn't help here because it branches on observations, not observers. When Wigner's friend makes a measurement of a superposed cat, the universal wavefunction branches into alive and dead branches. Wigner later makes his measurement but a version of him does so in each one of those branches. There is no observer-dependence here since, within a given branch, nothing is in superposition any more. In fact, MWI was formulated in part to explicitly exclude observer-dependence.

If I follow him rightly, @Andrew M is arguing for a conceptually modified MWI in which branching is observer-dependent, something along the lines of: before Wigner makes his measurement, his part of the wavefunction remains separable from the lab's. Within the lab there's a sort of miniverse that's cut off from the rest of the universe, within which the alive and dead branches evolve independently, but from the outside it's the whole that's evolving, including cross-terms | alive > | dead > and | dead > | alive > (which is where the interference effects come from). I'm not sure how that's going to work out, but could be the kind of pluralist realist thing you're looking for.

Not annoyed, but thank you for the thought. — ssu

Out of interest, and before the real third and final part of my pomo triptych, what did they say? (Why am I anticipating the answer "They said as long as he doesn't do a third"? :rofl: )

Now you are too p0m0 for me to understand.

But I'm not the brightest guy anyway...

MWI doesn't help here because it branches on observations, not observers. — Kenosha Kid

It seems to me that in the MWI 'observers and observations' are identical.

Relativism — Kenosha Kid

Pluralism:
"The cat is dead" is true for Wigner's friend but not for Wigner.
is equivalent to
"The cat is dead [is true] for Wigner's friend"
Realism:
The cat is dead [is true for everyone].

In addition to pluralism, relativism whether ontological [dead] or logical [true] requires a second higher level functor.

Not mentioned yet is the even more radical alternative: the worlds that branch out are made of words. That is, at bottom, you actually see text in the wave function!

:cool:

It seems to me that in the MWI observers and observations are identical. — 180 Proof

No, not at all. Branching occurs when a system in superposition is "decohered" (not necessarily by a mind, just whatever is sufficient to cause collapse or branching). Basically as long as the superposition coheres, you can get interference effects (e.g. in the double slit experiment, there isn't branching as the electron goes through each slits, as each branch must evolve as if the other didn't exist, so you couldn't get that interference pattern), but once it decoheres, no interference can occur (such as on the back screen of the double slit experiment, where the prior possibility of finding the electron in one position cannot impact the probability of finding it in another).

In MWI, when the friend measures the cat, he can only measure one possible outcome, which is a sign of decoherence. In one branch he measures alive cat, in the other dead cat. In each of these branches, Wigner then comes along and measures his friend's results. In alive branch, Wigner must measure the alive result; in the dead branch he must measure the dead result. So one wouldn't expect in either branch for Wigner to be able to detect interference patterns (a sign of coherence) or, to put it another way, one wouldn't expect any observer-dependence: in each branch, the state of the cat is an objective fact.

We need a matrix... But I just can't MathJax on this crappy phone :cry:

Pluralism:
"The cat is dead" is true for Wigner's friend but not for Wigner.
is equivalent to
"The cat is dead [is true] for Wigner's friend" — magritte

Yes, I think this is what I meant. The first is relativism, the second pluralism, and they are equivalent. As I said, I encountered this first in a discussion on moral relativism versus objectivity, including pluralism, and I understood how the latter isn't just the former insisting it's the latter.

My brain's not working hard enough to grok this. You seem to me to be imposing an instrumentalist interpretation on the MWI realism. :confused:

I actually had moral pluralism versus relativism in mind when I asked ... — Kenosha Kid

We did this little dance a while back

https://thephilosophyforum.com/discussion/comment/433376

and it never crossed my mind until you just mentioned them in moral terms.

NB:

• relativism – subject-variant paths / values
• pluralism – X out of N-possible subject-invariant paths / landscape of values

My brain's not working hard enough to grok this. You seem to me to be imposing an instrumentalist interpretation on the MWI realism. :confused: — 180 Proof

The basic principle of MWI is: whatever the math says is what's happening. So you follow the math, and there ain't no observer-dependence in there.

We did this little dance a while back — 180 Proof

Ah it was YOU!!! What are the odds. Aye, that. Reminds me, I said I'd dig out a post for Andrew.

Rovelli doesn't agree with the MWI, not that that means I agree with him or not. His idea is that we should let the science say what the metaphysics is, not let our metaphysics guide our science. I take him mean that people who adhere to MWI have the intuition that the world must be deterministic, but the world isn't so.

How'd you think about this?

In each of these branches, Wigner then comes along and measures his friend's results. — Kenosha Kid

Can you at least look it up on Wikipedia or something? — Kenosha Kid

In 1985, David Deutsch proposed a variant of the Wigner's friend thought experiment as a test of many-worlds versus the Copenhagen interpretation. It consists of an experimenter (Wigner's friend) making a measurement on a quantum system in an isolated laboratory, and another experimenter (Wigner) who would make a measurement on the first one. According to the many-worlds theory, the first experimenter would end up in a macroscopic superposition of seeing one result of the measurement in one branch, and another result in another branch. The second experimenter could then interfere these two branches in order to test whether it is in fact in a macroscopic superposition or has collapsed into a single branch, as predicted by the Copenhagen interpretation. Since then Lockwood (1989), Vaidman and others have made similar proposals. These proposals require placing macroscopic objects in a coherent superposition and interfering them, a task now beyond experimental capability. — Many-Worlds interpretation

https://en.wikipedia.org/wiki/Many-worlds_interpretation

ETA: Just to nip another misunderstanding in the bud, don't assume that my discussion style matches the typical "random internet person"; I'm not out to "win" an argument... my goal here isn't to "prove MWI" to you, or "prove you wrong" (i.e., I'm not "proposing" anything... except that MWI is as I understand it, as far as I understand it). My goal is to simply understand what you're saying. My issue is that your description of MWI makes no sense to me, and doesn't match my understanding of it.

Does not every observation, as an interaction, cause entanglement? (Leaving room still for partial observation; see below). — Pfhorrest

Sorry Pfhorrest, I missed this. Yes, but not the other way around: not every entanglement is an observation. Entanglement occurs when two bodies or systems communicate or share a history. This doesn't have to involve a measurement. Indeed, something like the EPR paradox is about an entangled, unmeasured spin pair.

Is this while Wigner and his friend are already entangled? — Pfhorrest

Should be, yes: Wigner and his friend are exchanging information. But yes the experiment shows that Wigner still observes interference effects, which suggests he is not entangled with his friend. Which is tricky because every branch his friend is communicating with him in should be completely independent.

I’m getting the sense that this new evidence is of the possibility of SOME information from inside the box being communicated to the friend without it being enough of the right information to collapse the wavefunction — Pfhorrest

Yes, and maybe this is what Andrew had in mind too. It's worth remembering that from the friend's point of view, his branch is an independent universe and he is in contact with Wigner before branching has occured for Wigner. His universe should go something like:

| Wigner before update > | Friend measured alive > | Alive cat >

to

| Wigner updated > | Friend measured alive > | Alive cat >

This is reality in his branch, and it's completely independent of the existence of any other branch. But Wigner can assuredly tell his friend that Wigner has detected the other branch:

| Wigner detects superposition > | Friend measured alive > | Alive cat >

This is weird, no? There is definitely evidence in the friend's branch that another branch exists.

... we should let the science say what the metaphysics is, not let our metaphysics guide our science — Manuel

It's not as simple as reversing these terms. Science is already a 'defeasible (hypothetical / statistical) metaphysics of reality' which must be accounted for, in order to be self-consistent, by a more general, indefeasible (categorical / modal) metaphysics of the real. Even 'fundamental sciences' can no more ground themselves than Rovelli (I'm a huge fan, btw) can rewrite his own/the past; physics is a 'mapmaking map' but is not the territory itself or the encompassing horizon.

Yeah, I agree. I don't necessarily follow Rovelli, particularly with his view that there isn't a metaphysical substrate or existence absent relations. I think physical stuff exists independent of us.

But I also appreciate someone trying to make sense of QM as is, which makes for an interesting thought process when taken seriously, as opposed to Chopra-style woo.

It's also not clear to me that we actually can suspend metaphysical inclinations: even the most avowed anti-metaphysician has a metaphysics, sometimes a variety of positivism or some kind of view related with sense data.

So the upshot is that the friend has made a definite measurement and reported that she has done so to Wigner, without telling him what the result was. At the same time the lab remains in superposition for Wigner, per your (B).
— Andrew M

But at this point at the very latest Wigner and his friend should be entangled as they are exchanging information, i.e. they are not two independently evolving systems. — Kenosha Kid

Wigner and his friend don't become entangled because the friend is sending exactly the same piece of information to Wigner from both branches, i.e., that a definite result has been obtained. So no which-way information is being sent. It's only when the actual result is measured by Wigner, thus distinguishing the branches, that entanglement occurs.

In other words, that single piece of information that is identical in both branches factorizes out and is what is measured by Wigner, leaving all other degrees of freedom (such as the alive/dead result itself) fully isolated.

I’m getting the sense that this new evidence is of the possibility of SOME information from inside the box being communicated to the friend without it being enough of the right information to collapse the wavefunction
— Pfhorrest

Yes, and maybe this is what Andrew had in mind too. — Kenosha Kid

Yes (in this case, it's information communicated from the friend to Wigner).

In fairness, the deterministic part of the wavefunction is the only thing that encodes any physics. So Everett was, to this extent, taking the physics seriously.

The point of this discussion is precisely the ramifications of the lab _not_ being an isolated experiment by virtue of the fact that Wigner and his friend are exchanging information. On which...

Wigner and his friend don't become entangled because the friend is sending exactly the same piece of information to Wigner from both branches, i.e., that a definite result has been obtained. — Andrew M

If this was just a story about the friend telling Wigner that the measurement has been done by, say, sending a photon, ignoring everything else, even that the measurement was a quantum one, would you say that this process of sending a photon from one system to another didn't entangle the two systems? Because that doesn't appear right. This is a three-body problem and will be correlated. The point here is that this entanglement is occurring after branching, and what's going on in each of these branches is independent.

I think perhaps the correct MWI answer is that this entanglement has already branched the wavefunction. It's not that entanglement hadn't occurred, it's that any entanglement pertinent to the the uncertainty in the signal has already decohered, making Wigner effectively separable from the lab across branches because the signal is the same in all of them.

In reality, that kind of separability isn't realistic. Maybe for a macroscopic Wigner and friend, but not for the quantum observers of the experiment.