I'm not commenting on the paper; I'm commenting on the notion that branches are universal. I don't think I have any comments on the paper at this time.No one is saying that Wigner has to be entangled. — Kenosha Kid
What I mean to clarify is that "universe branching" is "subject relative"; what looks like different universes to the cat isn't necessarily different universes to Schrodinger. — InPitzotl
I agree that this is nonsense, but what you said that I responded to was this:The equivalent in MWI if what's happening here is that friend measures cat, friend term in wavefunction branches, Wigner entangles with friend, but Wigner can still access both branches. — Kenosha Kid
...and there's certainly nothing universal happening in the sense that Wigner entangles with his friend when his friend entangles with the cat.When Wigner's friend measured the cat, the universal wavefunction would split then universally. — Kenosha Kid
there's certainly nothing universal happening — InPitzotl
...but you apparently agree the branches are not universal in the sense that Wigner branches when Wigner's friend branches:Any branching is universal: it is a branch in the universal wavefunction. — Kenosha Kid
After the friend measures:
(B) | not measured > X ( | measured live > | alive > + | measured dead > | dead > )/root(2) — Kenosha Kid
Right?No one is saying that Wigner has to be entangled. — Kenosha Kid
There's a part of your post in which you briefly stopped speaking of entanglement and spoke of observation. That's the part I referred to in my previous reply to you. — Kenosha Kid
What we see instead is evidence of observer-dependent collapse: Wigner knows that collapse has occurred for the friend, but for Wigner the friend is still in superposition as evidenced by interference effects between the alive and dead terms (collapse has not occurred for Wigner). — Kenosha Kid
If so, why is it difficult for you Albert to grasp that absent an observation, the moon's existence is a question mark, a very big question mark! — TheMadFool
How is it that the very method you critique derived the evidence you're using to substantiate that critique? — Isaac
Behind the Blind Spot sits the belief that physical reality has absolute primacy in human knowledge, a view that can be called scientific materialism. In philosophical terms, it combines scientific objectivism (science tells us about the real, mind-independent world) and physicalism (science tells us that physical reality is all there is). Elementary particles, moments in time, genes, the brain – all these things are assumed to be fundamentally real. By contrast, experience, awareness and consciousness are taken to be secondary. The scientific task becomes about figuring out how to reduce them to something physical, such as the behaviour of neural networks, the architecture of computational systems, or some measure of information.
Effectively that registration reduces the number of possibilities to unity for you (or it), while staying distributed for me (or some other device). So something else is going on here. — Kenosha Kid
That's the problem with asking whether things exist when we're not observing them. The things we do observe depend on the things we're not observing at the time. — Marchesk
Once, in Karl Popper's living-room, I asked him why he rejected [Kantian idealism], whereupon he banged his hand against the radiator by which we were standing and said: 'When I come downstairs in the morning I take it for granted that this radiator has been here all night'. — Bryan Magee, Philosophy of Schopenhauer
but you apparently agree the branches are not universal in the sense that Wigner branches when Wigner's friend branches: — InPitzotl
Nobody is saying it's MWI.But that's not MWI, — Kenosha Kid
Unwinding, (B) is this:that is, once entangled, there can be no interference between the live and dead terms apparent to Wigner. What the recent experiments show is that, even after Wigner's entanglement, those interference effects persist, and Wigner remains as per (B). It is only when Wigner _knows_ his friend's measurement outcome that he himself branches, i.e. the wavefunction is epistemic, not ontic. — Kenosha Kid
...for clarity I've underlined Wigner's state and bolded Wigner's friend's states.(B) | not measured > X ( | measured live > | alive > + | measured dead > | dead > )/root(2) — Kenosha Kid
But man that was quite a silly thing for Popper to argue. It takes so much for granted, which is a common mistake or so it seems to me. — Manuel
After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the non-existence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, "I refute it thus."
I know you think observation is crucial for the collapse — Manuel
Unless we build a much larger collider, we seem to be stuck. And even that might not change the results. — Manuel
Many Worlds is fully compatible with Wigner's Friend. It's just a situation where worlds not only can split but also merge again under the right conditions.
— Andrew M
That would be different to many worlds in itself. If you have to add a thing (merging criteria) that's a new theory. — Kenosha Kid
Copenhagen was originally epistemological, yes. Iirc Bohr himself went the ontological route in the end (I didn't know this until someone here found a relevant quote, should be able to dig it out if need be). — Kenosha Kid
But anyway there's a bunch of ontological Copenhagenists out there. — Kenosha Kid
Agreed, if 'reality' is left ambiguous between a unique realist objective ontology and many relativist subjective appearances. Philosophical disagreement and repeated failed attempts to discover some missing factor to make everything orthodox make all objectivist attempts suspect from the start. — magritte
I'd be interested in hearing both your thoughts on what kind of relativism this is. — Kenosha Kid
The essential idea behind RQM is that different observers may give different accurate accounts of the same system. For example, to one observer, a system is in a single, "collapsed" eigenstate. To a second observer, the same system is in a superposition of two or more states and the first observer is in a correlated superposition of two or more states. RQM argues that this is a complete picture of the world because the notion of "state" is always relative to some observer. There is no privileged, "real" account. — Relational quantum mechanics
Since the observer-dependence of collapse in these Wigner's friend experiments is essentially a disagreement between observers in their own frames as to whether something is in superposition or not, something like this might be the answer.
https://www.nature.com/articles/s41467-018-08155-0 — Kenosha Kid
Nobody is saying it's MWI. — InPitzotl
for clarity I've underlined Wigner's state and bolded Wigner's friend's states. — InPitzotl
So what do you mean by it? — InPitzotl
Proposing? What the heck are you talking about? I just described what's not a thing, and had thought you were agreeing it wasn't a thing. But given you think I'm proposing something that isn't MWI, I would say that clearly you're confused.If you agree that what you're proposing is not MWI, — Kenosha Kid
This is a handwaved concept of entanglement. Wigner and Wigner's friend have lots of states that are entangled. What constitutes being "unentangled" to you?But as I've told you, Wigner and his friend are not unentangled immediately prior to Wigner's measurement of his friend. — Kenosha Kid
No. We would expect (B). Wigner's friend entangling with the cat's life does not instantaneously make Wigner entangled with the cat's life. If Wigner hasn't done any measurements, there's no reason for Wigner to be entangled.What the Wigner's friend experiment show is that, after entanglement, after the friend has made his measurement, but before Wigner has made his measurement, when we would expect something like (C), — Kenosha Kid
I've no idea what "entangled with the lab" means, but it sounds like a fuzzy red herring. Surely Joe, who does a simple double slit experiment (or quantum erasure experiment, if that's what's confusing you), is just as entangled with his lab as Wigner is with his.Wigner is entangled with the lab insofar as communication and coordination about the experiment is ongoing between he and his friend, — Kenosha Kid
MWI has no objection whatsoever to the universal wavefunction being in a state like (B). Incidentally, (B) implies that Wigner's friend has branched. That live cat in (B) does not know what hydrocyanic acid smells like. But Wigner himself is not branched in (B). The branch is "universal" in the sense that it's a branch in the universal wavefunction (it's right there, in (B)). But it's not "universal" in the sense that Wigner's friend branching implies Wigner branched (he clearly hasn't). Having a person not branch with respect to a wavefunction that is in superposition is not a problem; how else will Joe see an interference pattern?Wigner still sees the lab in a superposition: the lab has branched for the friend, but both branches are evident to Wigner, contrary to MWI. — Kenosha Kid
For MWI, merging as well as splitting is entailed by the unitary dynamics. From the friend's perspective he has, for all practical purposes, performed an irreversible measurement - he measures spin-up in his world while his doppelganger measures spin-down in another world. But from Wigner's perspective, the friend (and his measurement) is simply in superposition (i.e., within Wigner's single world) and he can always apply a unitary transformation that reverses the friends' measurements, thus merging the friends' worlds back into one. — Andrew M
I would be interested in the quote if you can locate it. — Andrew M
I think Rovelli's relational interpretation is helpful here. It provides a clean abstraction around the idea of reference frames that covers all the issues raised by Wigner's friend: — Andrew M
I entirely agree. In fact, I see we had a brief discussion on this a year back! — Andrew M
This is a handwaved concept of entanglement. Wigner and Wigner's friend have lots of states that are entangled. What constitutes being "unentangled" to you? — InPitzotl
What the Wigner's friend experiment show is that, after entanglement, after the friend has made his measurement, but before Wigner has made his measurement, when we would expect something like (C),
— Kenosha Kid
No. We would expect (B). — InPitzotl
I imagine (because my math sucks!) the branches are like folds in an origami and the worlds of MWI are worldlines of particle-waves, that is, the many unfolded/enfolded shapes of the sheet. We 'inhabit' the edge of an unfolded shape (or worldline) that doesn't branch "into" (something else) but only branches away from other worldlines.I've long wondered about what does the MWI branch into? — Shawn
I think of it this way: the latter concerns 'variable/configurable observer-observations of one (the only) worldline' (e.g. one elephant and the many blind men) whereas the former concerns 'any one-worldline measurement of N-possible worldlines' (e.g. locked inside a completely enclosed carnival ride and looking out at the carnival through a peephole). So tell me what's wrong with this pluralism/relativism conception or why it doesn't work for interpreting fundamental physics.... I've asked this of others in the past and not quite got an answer, what differentiation do you make between a maximally pluralistic objectivity (e.g. one objectivity per reference frame) and relativism (as in frame-dependence, not subjectivity, as would apply to an atom, a device, or a point in spacetime)? — Kenosha Kid
They all probably work after a fashion (like epicycles & the aether) but I'll stick with the most parsimonious observer-invariant (my anti-idealist, anti-antirealist bias) interpretation of QM we've got which for me (as far as I know) is the MWI.P.S. I should add that observer-dependent facts is only one possible interpretation, even if it is the one that gets preferential treatment in paper titles.
The other options are non-locality (FTL communication) and super-determinism (backward or nonlocal causality). — Kenosha Kid
What you're describing art the start is two unentangled systems (B). That is not what the experiment is describing, in which Wigner and his friend are correlated (should be (C), but isn't).
As I said above, the alternative is to insist that entanglement doesn't occur just when two systems exchange information, but when an observer makes a measurement, which is not justified by the experimental setup. — Kenosha Kid
The novelty of Deutsch’s proposal [9] lies in the possibility for Wigner to acquire direct
knowledge on whether the friend has observed a definite outcome upon her measurement or not without revealing what outcome she has observed. The friend could open the laboratory in a manner which allowed communication (e.g. a specific message written on a piece of paper) to be passed outside to Wigner, keeping all other degrees of freedom fully isolated. (italics mine)
What I'm critiquing is not science but scientism. — Wayfarer
Do you recommend Daniel Dennett's approach to the subject? — Wayfarer
Get involved in philosophical discussions about knowledge, truth, language, consciousness, science, politics, religion, logic and mathematics, art, history, and lots more. No ads, no clutter, and very little agreement — just fascinating conversations.