I Sean Carroll podcast on many worlds interpretation

[Elias1960]

He claims interpretations other than MWI have to "work hard" to get rid of the many worlds.

This sounds like an echo of the "BM is many worlds in denial" argument made by Deutsch iirc. It presupposes, of course, that MWI makes sense at all (which most of those preferring other interpretations doubt). Then it presupposes that the other interpretations use the ideas of MWI, which they don't.

So, the MWI guys completely miss the role of the configuration trajectory $q(t)\in Q$ in BM. It defines what we are ourselves, it defines what we see in the macroscopic domain, and the effective wave function of a quantum system is defined by that trajectory of the measurement device,
$$ \psi(q_{sys},t) = \psi_{all}(q_{sys},q_{device}(t),t). $$
Instead, MWI seems to think that BM guys would have a problem to observe any trajectories at all, all that can be measured are wave functions, as it has to be in MWI, while in BM the wave function can be defined only based on observing the trajectories.

 

[vanhees71]

The maximum entropy of one bit is $k_B \ln 2$ in the standard definition. But a qubit is not a bit. A bit can only have two values, $0$ or $1$. A qubit's wave function can have any value on the Bloch sphere. Measuring a qubit can only result in one of two values, but a single measurement on a qubit is not sufficient to tell you its exact wave function. Strictly speaking, it takes an infinite number of measurements (on an ensemble of identically prepared qubits) to do that.

That, at least, is how I understand Motl's argument, and it seems at least worth enough consideration for somebody to have written a paper on it at some point; that's why I asked if anyone knows of such a paper.

The state of maximum entropy for a qubit is $\hat{\rho}=\hat{1}/2$ and the von Neumann entropy is $S=-k_{\text{B}} \mathrm{Tr} \hat{\rho} \ln \hat{\rho}=k_{\text{B}} \ln 2$.

Of course, state determination can usually not achieved by a single measurement, but what has this to do with the (useful) definition of von Neumann entropy?

 

[vanhees71]

If you measure a PVM, for a POVM in general you do not. I don't think that affects your main point much, just a technicality.

I'm not sure what you mean by QM not needing collapse. I mean after an observation you update the state, right?

The question is for what purpose you are "updating the state". Collapse in the sense of some Copenhagen flavors is a clear contradiction of the standard local relativistic QFT constructions, which don't allow for an instantaneous action at a distance. So it cannot be part of any interpretation that pretends to interpret standard local QFTs.

But indeed, there's no need for a collapse. All there is are probabilities calculated using Born's rule, given the state preparation. These probabilities refer to PVM's, i.e., precise measurements. To blur the subject with weak measurements, which can be understood when needed using the minimal interpretation, but are not important for the interpretational argument at all.

Now, when do you need an "update of the state"? It's when you do a preparation. A preparation, as any other manipulation we can do, is a local interaction between some "object" with some matter set up by us to prepare it. Since these manipulations are local, it's no collapse either, and the collapse is not needed to understand the preparation procedure.

Then there's simply a (PVM) measurement, where the measurement device provides a pointer reading, we get notice of (maybe decades later after the experiment is dismantled already) by reading off some measurement protocol (nowadays usually a computer file from some detector). There's no more mystery in that than taking notice of the outcome of the lottery drawing each Saturday. Nothing collapses here at all.

 

[DarMM]

Certainly, it's more so that I'm wondering by "collapse" does @bhobba mean just plain old state reduction, which I'd be surprised if he were saying we don't need it, or a physical nonlocal collapse which certainly we don't need.

These probabilities refer to PVM's, i.e., precise measurements. To blur the subject with weak measurements, which can be understood when needed using the minimal interpretation, but are not important for the interpretational argument at all

POVMs aren't weak measurements. Could you explain how they blur the subject? To me they add a lot. For example that most measurements are not actually quantizations of classical quantities, also POVMs are not equivalent to PVMs but are in fact more general. They're the same relation to PVMs that density matrices are to pure states. So it would be equivalent to saying density matrices "blur" the subject or are irrelevant. Rather I think they are an important part of the modern formalism.

Also I should say I was just pointing the fact out to @bhobba that the results of measurements are not always related to the eigenvalue of an observable. That's a fact, not really tied to the interpretation.

 

[akvadrako]

To my knowledge Carroll doesn't invoke consciousness. Nor does he endorse a special role for consciousness. I think he has argued that consciousness emerges from physics, not the other way around. (I don't want to speak for him but I seem to remember him talking along those lines.)

It depends what you mean by physics. If you mean objective reality then consciousness is irrelevant. If you mean what's measurable then it depends how subjective experience emerges. We have a rough idea how this works in day to day life, but things get hairy when you consider the experience of Wigner's friend or other circumstances when subjective experience differs greatly from two different viewpoints. Maybe Wallace was on the right path when we tried to derive the Born rule from decision theory, though he only considered one aspect of experience.

 

[akvadrako]

Motl's argument is basically that the MWI, or indeed any interpretation that treats the wave function as real, must answer "yes" to the above question. If that is true, then, whether the proponents of such interpretations realize it or not, or have even considered it or not, their interpretation actually isn't just an interpretation; it makes a testable physical prediction about entropy that is different from standard quantum statistical mechanics.

Motl claims this is a testable prediction but how do you propose to test it? Even if by some measure the entropy is different, it's inaccessible.

 

[vanhees71]

Certainly, it's more so that I'm wondering by "collapse" does @bhobba mean just plain old state reduction, which I'd be surprised if he were saying we don't need it, or a physical nonlocal collapse which certainly we don't need.POVMs aren't weak measurements. Could you explain how they blur the subject? To me they add a lot. For example that most measurements are not actually quantizations of classical quantities, also POVMs are not equivalent to PVMs but are in fact more general. They're the same relation to PVMs that density matrices are to pure states. So it would be equivalent to saying density matrices "blur" the subject or are irrelevant. Rather I think they are an important part of the modern formalism.

Also I should say I was just pointing the fact out to @bhobba that the results of measurements are not always related to the eigenvalue of an observable. That's a fact, not really tied to the interpretation.

For the interpretational issues we discuss you don't need the very complicated description of weak measurements by POVMs. Of course they are useful, when needed, but not for the purpose to discuss the interpretational foundations.

 

[DarMM]

For the interpretational issues we discuss you don't need the very complicated description of weak measurements by POVMs. Of course they are useful, when needed, but not for the purpose to discuss the interpretational foundations.

I don't know about that.

First I wouldn't say they are very complicated, or at least more so than PVMs. Both are ultimately just decompositions of the identity operator on a Hilbert space. A POVM is just the more general case when the elements of the decomposition don't commute. Also I wasn't speaking of weak measurements, but POVMs. POVMs are not weak measurements.

Secondly I think they do have a major impact on interpreting QM as they show you most measurements are not associated to the quantization of a classical quantity. So in many cases what we are measuring cannot be called angular momentum, position or any other quantity that appears in classical physics. Indeed in most cases we are simply measuring that POVM for which we have no name in general. That's quite a big deal in my opinion.

 

[vanhees71]

We have zillions of real-lab measurement devices described by PVMs. Recently we had the debate of POVMs, and I still have not a single example for a real-lab apparatus and its description by a POVM. The math is indeed simple enough to understand it, but the link to real measurement devices is still not clear to me.

I'm also not sure what POVMs have to do with "quantization of a classical quantity" or not. The observable algebra cannot be derived from classical physics of course. One has to rely on mathematical arguments like symmetry principles. Then you build a model and check, whether it describes real-world phenomena correctly. An example for an observable which for sure is not derivable by some "quantization of a classical quantity" is spin.

I think to make physical sense of POVMs you need no more and no less than the standard postulates and the minimal interpretation including Born's rule for the measurement in the usual PVM sense.

 

[Minnesota Joe]

This sounds like an echo of the "BM is many worlds in denial" argument made by Deutsch iirc. It presupposes, of course, that MWI makes sense at all (which most of those preferring other interpretations doubt). Then it presupposes that the other interpretations use the ideas of MWI, which they don't.

Yes, that attitude is what I had in mind. Not just BM though but all interpretations QM except MWI are in denial according to Carroll.

So, the MWI guys completely miss the role of the configuration trajectory $q(t)\in Q$ in BM. It defines what we are ourselves, it defines what we see in the macroscopic domain, and the effective wave function of a quantum system is defined by that trajectory of the measurement device,
$$ \psi(q_{sys},t) = \psi_{all}(q_{sys},q_{device}(t),t). $$
Instead, MWI seems to think that BM guys would have a problem to observe any trajectories at all, all that can be measured are wave functions, as it has to be in MWI, while in BM the wave function can be defined only based on observing the trajectories.

In de Broglie-Bohm, as I understand it, the particles are actually what you observe and you can retrodict their trajectories though you can't predict them because of ignorance of initial conditions. So if a particle goes through a Stern-Gerlach (SG) device, it matters which side of the direction of propagation axis it was on: above or below. The the SG separates the wave function into two packets, one containing the particle and one empty. Does that sound right so far? So is it the empty packet that the MWI people are calling a "world" or is it something else do you suppose?

 

[Minnesota Joe]

It depends what you mean by physics. If you mean objective reality then consciousness is irrelevant. If you mean what's measurable then it depends how subjective experience emerges. We have a rough idea how this works in day to day life, but things get hairy when you consider the experience of Wigner's friend or other circumstances when subjective experience differs greatly from two different viewpoints. Maybe Wallace was on the right path when we tried to derive the Born rule from decision theory, though he only considered one aspect of experience.

Really I just wanted to make sure Carroll wasn't characterized incorrectly--there are already people accusing him of engaging in woo--because as far as I know consciousness doesn't enter at all into what he is trying to do.

 

[DarMM]

We have zillions of real-lab measurement devices described by PVMs. Recently we had the debate of POVMs, and I still have not a single example for a real-lab apparatus and its description by a POVM

Really? They're incredibly common. See here:
https://arxiv.org/abs/1501.05096
He even lists the device explicitly. This is just one of several such papers. Very common in anything associated with quantum information. POVMs are decades old, I find the discussions on this forum as if they were some weird esoteric idea very odd.

I'm also not sure what POVMs have to do with "quantization of a classical quantity" or not. The observable algebra cannot be derived from classical physics of course. One has to rely on mathematical arguments like symmetry principles. Then you build a model and check, whether it describes real-world phenomena correctly. An example for an observable which for sure is not derivable by some "quantization of a classical quantity" is spin

That's not really what I mean. Spin is still connected to angular momentum and there is a classical notion of spin in terms of spinor bundles. I mean some POVMs are even more non-classical than that. The quantum observable algebra of PVMs is often connected to some classical observable algebra via a process we call quantization, but POVMs are more general than this.

I think to make physical sense of POVMs you need no more and no less than the standard postulates and the minimal interpretation including Born's rule for the measurement in the usual PVM sense

Some POVMs are not reducible to PVMs though. The rule for POVM detection event probabilities has Born's rule as a special case.

 

[vanhees71]

So is the "theorem" proven in Pere's book wrong?

Also, don't get me wrong. I've nothing against POVMs, why should I? But where do you need them for the discussion on foundations?

 

[DarMM]

So is the "theorem" proven in Pere's book wrong?

Also, don't get me wrong. I've nothing against POVMs, why should I? But where do you need them for the discussion on foundations?

I assume you mean Neumark's theorem. No that is a correct. As Peres himself says though it doesn't mean every POVM is a PVM. It means for non-QFT systems it is possible to realize a POVM as a PVM on the system + ancilla.

As for where they are needed, this is why Peres includes discussion of them in his book and many of his papers, because they give a very different picture of what a quantum measurement is. So different that many (including Peres in his monograph) propose to rename them quantum tests. This is related to what I mentioned about them and classical quantities above. See here for example:
https://arxiv.org/abs/quant-ph/0207020

 

[Minnesota Joe]

This is never answered by any of these dogmatic Everettians

I'm not an MWI proponent, but I don't get the sense that Carroll is dogmatic. On Mindscape and elsewhere he interviews way too many people with directly opposing viewpoints and really allows them to have their say for me to label him dogmatic. Go listen to the David Albert interview where Albert pinpoints for Carroll what is wrong with the probability interpretation in MWI for example. Carroll is trying to overcome those objections so he listens to people and acknowledges he might fail.

Contrast his behavior with some of the physicists linked to in this thread if you dare. You could do a simple experiment and count the ad hominem attacks and other statements irrelevant to the truth or falsehood of their claims in what they write. They are obviously smart and have good ideas, but so do lots of people and I don't like wading through the terrible to get to the good stuff. I'll take Carroll's attitude any day.

 

[atyy]

I assume you mean Neumark's theorem. No that is a correct. As Peres himself says though it doesn't mean every POVM is a PVM. It means for non-QFT systems it is possible to realize a POVM as a PVM on the system + ancilla.

Does it not hold for QFT systems because of the type III algebras that don't have have pure states?

 

[Demystifier]

But where do you need them for the discussion on foundations?

One example would be measurement of time, given that there is no time observable.

 

[Demystifier]

It means for non-QFT systems it is possible to realize a POVM as a PVM on the system + ancilla.

Whenever someone tells that something which is true for QM is not necessarily true for QFT, my first instinctive gut reaction is - that's because something in QFT is not mathematically well defined due to the infinite number of degrees of freedom, implying that it is really true for physical QFT as well, provided that one finds a way to define it precisely in a physically sensible way. And in 99% cases my first instinctive gut reaction turns out to be right.

 

[DarMM]

Does it not hold for QFT systems because of the type III algebras that don't have have pure states?

Yes exactly.

 

[DarMM]

Whenever someone tells that something which is true for QM is not necessarily true for QFT, my first instinctive gut reaction is - that's because something in QFT is not mathematically well defined due to the infinite number of degrees of freedom, implying that it is really true for physical QFT as well, provided that one finds a way to define it precisely in a physically sensible way. And in 99% cases my first instinctive gut reaction turns out to be right.

The fact that QFT has type-III C*-algebras is rigorously established.

 

[Demystifier]

The fact that QFT has type-III C*-algebras is rigorously established.

I don't see how is that related to physics. Can you give example of a physical measurement described by QFT where it would imply POVM that cannot be reduced to PVM?

 

[Quanundrum]

I'm not an MWI proponent, but I don't get the sense that Carroll is dogmatic. On Mindscape and elsewhere he interviews way too many people with directly opposing viewpoints and really allows them to have their say for me to label him dogmatic. Go listen to the David Albert interview where Albert pinpoints for Carroll what is wrong with the probability interpretation in MWI for example. Carroll is trying to overcome those objections so he listens to people and acknowledges he might fail.

I still maintain that his attitude is dogmatic. He is on record repeatedly saying that the state of Quantum Foundations is "embarrassing" for not having solved the measurement problem in a century, and then concludes every time that one should naturally choose Everett. He's not as straightforward as David Deutsch in his insistence, but sometime around 2010 he started insisting on Everettian QM.

The reason he has people like David Albert on his podcast and treats them respectfully is tied to the fact that these people have contemplated and published on the topic of Everett since before Carroll graduated. However, in all his blog posts over the past ~9 years, all the interviews and recently published book he insists that Everett is simply "taking the physics seriously", echoing the arrogant sentiment from the Oxford camp over the past 20 years. That is dogma.

You have Saunders, Deutsch and Wallace in the Decision Theoretic camp, you have Sean Carroll and Lev Vaidman in the Self-Location Uncertainty camp, but Vaidman rejects Carroll and Sebens 'proof' of derivation of the Born Rule. Similarly you have Wallace and Timpson in the State Space camp versus Carroll and Singh in their Mad Dogg Everettian camp. Add to this the Splitting vs Divergence. And then finally add to this the whole extravaganza of "Multiverse = Many Worlds" that Susskind, Tegmark and sometimes Carroll espouse. The Everettian program is littered in unanswered questions and indicators that it is far from as simple as "taking the math/physics" seriously. If he had acknowledged this, I'd respect him a lot more. Instead he feels comfortable dogmatically going into interviews and proclaiming that Everett is "just QM taken seriously" and then extrapolating claims from there, even though the myriad of different Everettian readings wildly disagree on those claims...

 

[DarMM]

I don't see how is that related to physics. Can you give example of a physical measurement described by QFT where it would imply POVM that cannot be reduced to PVM?

QFT implies it for all POVMs, such as the one given in the paper above in #62

 

[Demystifier]

QFT implies it for all POVMs, such as the one given in the paper above in #62

How can that be rigorous in general, given that interacting QFT itself is not rigorous in general?

 

[DarMM]

How can that be rigorous in general, given that interacting QFT itself is not rigorous in general?

The existence of type-III algebras requires the existence of the continuum limit. For 4D Yang-Mills Balaban has established enough to show Type-III algebras hold.

 

[atyy]

@DarMM, at the non-rigorous physics level there are also arguments against associating pure states with local subsystems, eg. https://arxiv.org/abs/1406.7304 and https://arxiv.org/abs/1601.04744

Is this related to the Type III algebras or is it a different issue?

 

[Demystifier]

The existence of type-III algebras requires the existence of the continuum limit. For 4D Yang-Mills Balaban has established enough to show Type-III algebras hold.

OK, my gut intuition then tells me that there should be some kind of weak equivalence between POVM's and PVM's. Perhaps something like - there is no PVM that is exactly equivalent to the POVM, but the POVM can be approximated arbitrarily well with a PVM, with a suitable definition of "approximated arbitrarily well". Could something like that be true?

 

[bhobba]

I'm not sure what you mean by QM not needing collapse. I mean after an observation you update the state, right?

If that's what you man by collapse the yes, but some include things like the state instantaneously changing. I am not going to argue one way or the other on that - its similar to when you throw a dice the outcome is 1-6 - is that collapse? Just something to think about, I am not taking any side.

Thanks
Bill

 

[DarMM]

If that's what you man by collapse the yes, but some include things like the state instantaneously changing. I am not going to argue one way or the other on that - its similar to when you throw a dice the outcome is 1-6 - is that collapse? Just something to think about, I am not taking any side.

I just meant state reduction, usually that's what people mean by collapse. I was just checking what you meant.

That state reduction is like bayesian updating, such as in your dice example, is a well known aspect of viewing QM as a generalization of probability theory.

 

[vanhees71]

State reduction and collapse is usually used synonymous. If you interpret as a Bayesian updating, it's no problem. The problem arises, and this made obviously a big part of the debate beween Einstein and Bohr, when one assumes that the collapse is a physical process acting instantaneously on the entire universe. This is neither a necessary assumption to use QT to describe observations (state preparation and measurements) nor is it consistent with the mathematical features built in the usual local relativistic QFTs, according to which space-like separated events cannot be causally connected since the Hamilton density commutes by construction with all local operators with space-like separated arguments.

 

[Michael Price]

The maximum entropy of one bit is $k_B \ln 2$ in the standard definition. But a qubit is not a bit. A bit can only have two values, $0$ or $1$. A qubit's wave function can have any value on the Bloch sphere. Measuring a qubit can only result in one of two values, but a single measurement on a qubit is not sufficient to tell you its exact wave function. Strictly speaking, it takes an infinite number of measurements (on an ensemble of identically prepared qubits) to do that.

That, at least, is how I understand Motl's argument, and it seems at least worth enough consideration for somebody to have written a paper on it at some point; that's why I asked if anyone knows of such a paper.

The answer is that the infinite information stored on the Bloch sphere is spread across the infinity of mutually inaccessible worlds that split off from an idealised measurement. No single world can access this infinity of information or entropy.

 

[Swamp Thing]

https://www.quora.com/How-does-the-...ding-to-the-Born-rule/answer/Michael-Price-29

How does this work when we look at a continuously distributed observable?
And in a rigorous formulation, would the term "overlap" be well defined?

 

[Michael Price]

How does this work when we look at a continuously distributed observable?
And in a rigorous formulation, would the term "overlap" be well defined?

Overlap is a well defined (and elementary) procedure for producing a complex number from two wave vectors.
The continuous case is just the limit of the discrete case - nothing fancy or controversial.

All undergrad stuff.

 

[pinball1970]

Overlap is a well defined (and elementary) procedure for producing a complex number from two wave vectors.
The continuous case is just the limit of the discrete case - nothing fancy or controversial.

All undergrad stuff.

The discussion has been above my pay grade for the most part but fascinating none the less.
Thanks for making the thread lively.
I am off to Waterstones to get the hardback and had a quick look at the reviews while I was checking if they have it in stock
Jim Al Kalili and Brian Greene gave good reviews
https://www.waterstones.com/book/something-deeply-hidden/sean-carroll/9781786076335

 

[Heikki Tuuri]

One can say that the Copenhagen interpretation is an MWI "in denial".

Think of the thought experiment which I mentioned earlier. We have a physicist performing measurements in an isolated laboratory. For outside observers, the wave function of the lab, including the physicist, develops smoothly. There is no collapse.

The wave function can be input to the Bohm model, and there we can calculate a continuum many branches in the wave function. If we consider these branches "really" existing, then we have an MWI where we have used the Bohm model to pick the branches, that is, the worlds.

If we take the ontology above, then a wave function always involves many worlds.

But is Newtonian mechanics an MWI? We initialize some particles in the system and let it develop in time. If we would have chosen different initial values, we would have had a different history. A Platonist might claim that the alternative histories do exist. We just happen to live in this particular history.

The big difference between the Newtonian model and quantum mechanics is that we need the wave function in quantum mechanics. The development of a single branch cannot be calculated from the branch alone. We need to know the wave function.

 

[vanhees71]

Think of the thought experiment which I mentioned earlier. We have a physicist performing measurements in an isolated laboratory. For outside observers, the wave function of the lab, including the physicist, develops smoothly. There is no collapse.

The problem with such statements in quantum-foundations discussions is that it is self-contradictory. If there are outside observers being able to observe anything what the physicist in his lab is doing, this physicist's lab is no longer isolated but is interacting with the outside observer. Not taking this into account easily leads to paradoxes and endless discussions.

 

[Heikki Tuuri]

The problem with such statements in quantum-foundations discussions is that it is self-contradictory. If there are outside observers being able to observe anything what the physicist in his lab is doing, this physicist's lab is no longer isolated but is interacting with the outside observer.

I am sorry. I was careless with my words. The lab is isolated. Only at a later time, an observer opens the lab. It is just like Schrödinger's cat, except that we have put a physicist inside the box.

 

[PeterDonis]

The development of a single branch cannot be calculated from the branch alone. We need to know the wave function.

This is not correct for a branch that has decohered. For a decohered branch, you can just use the term in the wave function that corresponds to that branch to predict all future measurement results in the branch. You don't need to know the entire wave function. If this were not true, MWI would not work as an interpretation.

 

[Heikki Tuuri]

This is not correct for a branch that has decohered. For a decohered branch, you can just use the term in the wave function that corresponds to that branch to predict all future measurement results in the branch. You don't need to know the entire wave function. If this were not true, MWI would not work as an interpretation.

Decoherence makes it possible to discard conflicting branches, in practice. For example, if we find Schrödinger's cat alive, we do not need to think about dead cat branches any more.

But theoretically, we do need the entire wave function. Nothing can be discarded. This assumes that the whole universe is one giant box with a single wave function.

The wave function of the universe involves philosophical as well as practical problems, though. Are we sure that a physicist living within that wave function observes things like we observe now?

 

[DarMM]

@atyy and @Demystifier , both your questions are very interesting. I want to speak to former colleagues first, as I'm not entirely sure my intuitive answers are correct and up to date. Apologies for the delay.

A difficulty with your question @Demystifier is that there simply are no local PVMs in QFT, so we need a way of characterizing "PVM-like" in a theory with no PVMs.

 

[PeterDonis]

theoretically, we do need the entire wave function

Not if all you are doing is predicting further measurement results on a single decohered branch. And that's what you were talking about in the post of yours that I responded to: "development of a single branch". You don't need to know the entire wave function to calculate that. You only need to know that particular branch.

 

[Heikki Tuuri]

Not if all you are doing is predicting further measurement results on a single decohered branch.

Decoherence is never perfect. The idea is that one degree of freedom interacts with a large number of other degrees of freedom. For example, a single photon changes the state of a large number of silver and bromine atoms in a photographic film.

At which point the scientist inside the lab would be allowed to discard part of the wave function? The scientist himself may be a particle which is used in a double slit experiment. There is always a minuscule chance that the scientist will interfere with another version of himself who took a different route but arrived on the screen in the same state.

 

[PeterDonis]

Decoherence is never perfect.

It's perfect enough for us to make accurate predictions.

At which point the scientist inside the lab would be allowed to discard part of the wave function?

At the point when he can make accurate predictions by doing so.

The scientist himself may be a particle which is used in a double slit experiment.

No, he can't. The scientist has many orders of magnitude too many degrees of freedom which cannot be kept coherent for such an experiment.

 

[Minnesota Joe]

Like the GRW and de Broglie-Bohm people, in Something Deeply Hidden Sean Carroll writes that he seeks a "complete, unambiguous, realistic" theory but is discouraged by the difficulties of extending the theory once you add something in addition to Schrodinger equation. (pg 31-32).

He writes, "But we should also admit that the whole picture might be wrong, and something very different is required" page 40 and "I am defending one particular view of that reality...This shouldn't be taken to imply that the Everettian view is unquestionably right." pg 42. So I take him to be undogmatically defending his favorite.

At least some of the meaning of the statements he makes in his podcast are clearer. He reinterprets the solutions to the Schrodinger equation so of course all the other interpretations have "worlds" from that point of view, but that doesn't at all change my position that the claim is question-begging and he should stop using it.

I can see how the minimalism is attractive but on the flip side it means that if your interpretation is incorrect, you just carry the incompleteness of quantum mechanics forward.

Another attractive feature of MWI apparently is locality. Can someone please explain to me in what senses MWI is local if so? People sometimes conflate the various senses of 'local' and this caused all manner of confusion for me when I started reading quantum foundations. In particular, is it fair to say the violations of Bell's inequality are merely apparent under MWI? Or does it just mean Lorentz invariant? (I could be botching things myself I freely admit.)

 

[pinball1970]

Like the GRW and de Broglie-Bohm people, in Something Deeply Hidden Sean Carroll writes that he seeks a "complete, unambiguous, realistic" theory but is discouraged by the difficulties of extending the theory once you add something in addition to Schrodinger equation. (pg 31-32).

He writes, "But we should also admit that the whole picture might be wrong, and something very different is required" page 40 and "I am defending one particular view of that reality...This shouldn't be taken to imply that the Everettian view is unquestionably right." pg 42. So I take him to be undogmatically defending his favorite.

At least some of the meaning of the statements he makes in his podcast are clearer. He reinterprets the solutions to the Schrodinger equation so of course all the other interpretations have "worlds" from that point of view, but that doesn't at all change my position that the claim is question-begging and he should stop using it.

I can see how the minimalism is attractive but on the flip side it means that if your interpretation is incorrect, you just carry the incompleteness of quantum mechanics forward.

Another attractive feature of MWI apparently is locality. Can someone please explain to me in what senses MWI is local if so? People sometimes conflate the various senses of 'local' and this caused all manner of confusion for me when I started reading quantum foundations. In particular, is it fair to say the violations of Bell's inequality are merely apparent under MWI? Or does it just mean Lorentz invariant? (I could be botching things myself I freely admit.)

You should have put a spoiler on this post, I got the hard back yesterday. I am going to read it and possibly post a review on pf if that is allowed. This is a pop Science book after all.
He is doing real physics in this area so published paper references may let this through.
That's if I understand enough of it to review.

 

[Heikki Tuuri]

@Minnesota Joe ,

in the EPR experiment, Copenhagen people think that the measurement apparatuses at both ends "collapse" into definite classical states.

They kind of discard large parts of the wave function of the whole system, which includes also the measurement apparatuses.

In MWI there is never any collapse. When a scientist compares the results from the both ends in his mind, it is local operation.

The wave function in the Schrödinger equation develops in a local manner, and the hidden variables in the Bohm model develop locally.

But the Schrödinger equation is not relativistic. Locality is more a thing of Special relativity. We would need a relativistic wave function and a relativistic Bohm model.

 

[Minnesota Joe]

You should have put a spoiler on this post, I got the hard back yesterday.

Yes, my apologies, I'll try to remember that in the future, thank you.

 

[Minnesota Joe]

in the EPR experiment, Copenhagen people think that the measurement apparatuses at both ends "collapse" into a definite classical states.

They kind of discard large parts of the wave function of the whole system, which includes also the measurement apparatuses.

In MWI there is never any collapse. When a scientist compares the results from the both ends in his mind, it is local operation.

If I understand what you wrote correctly, that is what I meant by the violations being only apparent. Because we only see the set of statistics in our branch. Do you agree?

The wave function in the Schrödinger equation develops in a local manner, and the hidden variables in the Bohm model develop locally.

But the Schrödinger equation is not relativistic. Locality is more a thing of Special relativity. We would need a relativistic wave function and a relativistic Bohm model.

So do we prefer to use 'locality' to mean relativistic? What word do we use for instantaneous influence at large distances? Or, rather, the idea discussed long before Einstein that you ought not be able to influence a system without propagating some signal to where that system is? (Implying both finite time and intervening causes.)

 

[OCR]

You should have put a spoiler on this post. . .

Lol. . . ah, c'mon now pinball.

Spoiler: 👀

You would have looked, anyway. . . .

.

 

[pinball1970]

Lol. . . ah, c'mon now pinball.

Spoiler: 👀

You would have looked, anyway. . . .

.

Yes I still looked.
I saw a quote from page 32 on post #94 and I was barely through the introduction. My spoiler post was half in jest, it's not like @Minnesota Joe gave away the end of House season 4 or anything.