Bohm trajectories and protective measurements?

[Demystifier]

I never said there was anything wrong with a nomological approach, but then you do not run into problems with functionalism either. So I wonder why you reject it.

Perhaps we do not share the same definition of the word "functionalism". What is your definition of functionalism? For example, would you say that, according to functionalism, to have a computer program which can calculate something is the same as having the calculation of that something? (In my dictionary: yes - this is what functionalism is, and no - these two things are not the same and therefore functionalism is wrong.)

 

[Quantumental]

Perhaps we do not share the same definition of the word "functionalism". What is your definition of functionalism? For example, would you say that, according to functionalism, to have a computer program which can calculate something is the same as having the calculation of that something? (In my dictionary: yes - this is what functionalism is, and no - these two things are not the same and therefore functionalism is wrong.)

You need to be more specific. If a computer program has all the "ingredients" necessary to do all the functions as the thing does in real life, then yes it's the same.
So if I were run a fantastically complicated simulation of a mouse's mind on a supercomputer, then that would indeed be a mouse's mind.

Let's take another example: imagine a desert, imagine that a infinitely unlikely sandstorm occured, where the wind would act like a pilot-wave and guide all the grains of sand in such a manner that it would be identical to a human brain with all it's processes (yes gigantic storm), why wouldn't there be thoughts in this brain?
Just because it isn't what we call "biological" ?Your foreign-aid functionalist argument doesn't work because a book doesn't have any functions. It's not like the letters printed on paper acts like fruit for instance.

 

[bohm2]

If a computer program has all the "ingredients" necessary to do all the functions as the thing does in real life, then yes it's the same. So if I were run a fantastically complicated simulation of a mouse's mind on a supercomputer, then that would indeed be a mouse's mind. Let's take another example: imagine a desert, imagine that a infinitely unlikely sandstorm occured, where the wind would act like a pilot-wave and guide all the grains of sand in such a manner that it would be identical to a human brain with all it's processes (yes gigantic storm), why wouldn't there be thoughts in this brain? Just because it isn't what we call "biological" ?

Others like Searle would disagree with this:

The computational model of consciousness stands to consciousness in the same way the computational model of anything stands to the domain being modeled. Nobody supposes that the computational model of rainstorms in London will leave us all wet. But they make the mistake of supposing that the computational model of consciousness is somehow conscious. It is the same mistake in both cases.

The Problem of Consciousness
http://users.ecs.soton.ac.uk/harnad/Papers/Py104/searle.prob.html

Why couldn't a hyperdimensional object have things in it which appear 3D? Just like a hologram is 2D but appears 3D?

This is a difficult topic and hard to put in words (assuming I even understand their arguments) and I don't want to misinterpret their arguments so I'll post the relevant points made by Maudlin (including questions by Wallace) and other physicists/philosophers:

Maudlin video with Wallace, other physicists, etc. in the audience and question period-see transcipt below because video isn't perfectly clear with interesting comment in the discussion made by Valentini and arguably at the heart of this issue, I think:

He (deBroglie) gives some criticisms of Schrodinger’s theory and one of them is: what does it mean to say you have this wave function on a configuration space when there’re no configurations.

Can the world be only wavefunction?
http://vimeo.com/4607553
Transcript discussion Maudlin
http://everettat50.blogspot.ca/2007/09/transcript-discussion-maudlin_15.html

Advocates of the Everett interpretation of quantum mechanics have long claimed that other interpretations needlessly invoke "new physics" to solve the measurement problem. Call the argument fashioned that gives voice to this claim the Redundancy Argument, or ’Redundancy’ for short. Originating right in Everett’s doctoral thesis, Redundancy has recently enjoyed much attention, having been advanced and developed by a number of commentators, as well as criticized by a few others. Although versions of this argument can target collapse theories of quantum mechanics, it is usually conceived with no-collapse "hidden variable" interpretations in mind, e.g., modal and Bohmian interpretations. In particular, the argument is an attack against theories committed to both realism about the quantum state and realism about entities – what Bell 1987 calls "beables" – that supplement this state. Particles, fields, value states, and more have been suggested as possible ontology to supplement the quantum state. Redundancy is the argument that this supplementation is methodologically otiose, the superfluous pomp that Newton scorned.

Discussion: The redundancy argument against Bohm's theory
http://philpapers.org/rec/CALDTR

 

[Demystifier]

Let's take another example: imagine a desert, imagine that a infinitely unlikely sandstorm occured, where the wind would act like a pilot-wave and guide all the grains of sand in such a manner that it would be identical to a human brain with all it's processes (yes gigantic storm), why wouldn't there be thoughts in this brain?
Just because it isn't what we call "biological" ?

If by "thoughts" you mean physical events which process information, then they will be there. But if by "thoughts" you mean subjective conscious experiences, then I have no idea. I pretty much agree with Chalmers that physics as we understand it cannot explain the origin of subjective conscious experiences.

 

[Quantumental]

Others like Searle would disagree with this:

The Problem of Consciousness
http://users.ecs.soton.ac.uk/harnad/Papers/Py104/searle.prob.html

I disagree with Searle here. I don't even understand what he can possibly think he argues by saying "Noone gets wet from a computational rain storm". It's because we aren't *in* the simulation.
If you simulated a "reality" with people in it and then simulated them experiencing rain, then they'd experience the rain. Soo...?
Did he think that functionalism/computationalism magically transported the computation into his livingroom?

I tried making sense of the transcripts, but I couldn't.
It seems no one did, the questions etc. made it seem that no one agreed with Maudlin and not even Maudlin seemed to be able to pin down any technical faults with WF realism.

 

[Quantumental]

If by "thoughts" you mean physical events which process information, then they will be there. But if by "thoughts" you mean subjective conscious experiences, then I have no idea. I pretty much agree with Chalmers that physics as we understand it cannot explain the origin of subjective conscious experiences.

But why not? I mean, yeah consciousness *seems* very mysterious and all, but it is just neural activity in the brain. We can demonstrate this by doing drugs and scanning the brain.
We have in my opinion absolutely no reason to suspect that consciousness somehow taps into some unknown physics...

But even if you think that it may do, how does that affect the debate of whether minds can arise from a wavefunction?

 

[bohm2]

I disagree with Searle here.

I interpretated him as arguing that simulating some properties of the mind/brain is not the same thing as subjectivity/qualia/consciousness. I think he is just re-stating his "Chinese Room" argument:

The Chinese Room Argument
http://plato.stanford.edu/entries/chinese-room/

yeah consciousness *seems* very mysterious and all, but it is just neural activity in the brain. We can demonstrate this by doing drugs and scanning the brain. We have in my opinion absolutely no reason to suspect that consciousness somehow taps into some unknown physics...

The problem is one of unification. How does a brain/matter with the properties we currently understand "spit out" qualia/subjectivity? You don't literally see one's thoughts using brain scans. Many think the issue is far more complex but I probably agree with you that this issue has little to say on this topic of this thread, I think.

 

[Demystifier]

But why not? I mean, yeah consciousness *seems* very mysterious and all, but it is just neural activity in the brain. We can demonstrate this by doing drugs and scanning the brain.
We have in my opinion absolutely no reason to suspect that consciousness somehow taps into some unknown physics...

indeed, there is a lot of EXPERIMENTAL evidence that neural activity is correlated with consciousness. But it does not imply that we THEORETICALLY understand how one thing causes the other.

But even if you think that it may do, how does that affect the debate of whether minds can arise from a wavefunction?

There are many possibilities. One of them is that particle trajectories ARE consciousness:
http://arxiv.org/abs/1112.2034

 

[Quantumental]

There are many possibilities. One of them is that particle trajectories ARE consciousness:
http://arxiv.org/abs/1112.2034

This hypothesis might be the most crazy thing I've ever heard from a serious physicist.
I hope you made that paper to demonstrate a point and not that you actually consider it a serious possibility.
Superdeterminism ('t Hooft is waaay less crazy)

But I wanted to ask you something: you seem quite liberal with your ideas and open to a lot of speculation. So why aren't you pro-MWI really? What keeps you from subscribing to it's plausibility?

 

[lugita15]

So why aren't you pro-MWI really? What keeps you from subscribing to it's plausibility?

Based on past discussions with Demystifier (and he can correct me if I'm wrong), I think he rejects many worlds because it doesn't suffice to prove the Born rule for probabilities. In order to prove it, you need to make additional assumptions, and he feels that Bohmian mechanics constitutes the most plausible set of additional assumptions.

 

[Demystifier]

Based on past discussions with Demystifier (and he can correct me if I'm wrong), I think he rejects many worlds because it doesn't suffice to prove the Born rule for probabilities. In order to prove it, you need to make additional assumptions, and he feels that Bohmian mechanics constitutes the most plausible set of additional assumptions.

Yes, that's correct.

 

[Demystifier]

This hypothesis might be the most crazy thing I've ever heard from a serious physicist.
I hope you made that paper to demonstrate a point and not that you actually consider it a serious possibility.
Superdeterminism ('t Hooft is waaay less crazy)

Yes, I only wanted to demonstrate a point. But I know an even more crazy idea by a serious philosopher of physics which only serves to demonstrate a point. Do you know about the Albert fatness argument against the Born rule in MWI?

 

[Demystifier]

But I wanted to ask you something: you seem quite liberal with your ideas and open to a lot of speculation. So why aren't you pro-MWI really?

A careful reader may notice that some of my papers are quite MWI in spirit:
http://arxiv.org/abs/0905.0538
http://arxiv.org/abs/0912.1938
http://arxiv.org/abs/1101.2744

 

[Quantumental]

Yes, I only wanted to demonstrate a point. But I know an even more crazy idea by a serious philosopher of physics which only serves to demonstrate a point. Do you know about the Albert fatness argument against the Born rule in MWI?

Yes I'm aware of it. But I thought David Wallace had responded to it?

 

[bohm2]

I wish Ilja still posted here, I remember a few threads where he participated and his opinions seemed to be very interesting, but I never fully grasped them.

Ilja did discuss his criticism of MWI in this blog:

MWI in it's current form simply becomes invalid, with or without Born rule, because it does not have an additional structure which is necessary to fix the preferred basis: The papers prove that different choices are possible, and lead to different physics. The Copenhagen intepretation solves this problem with its association of the operators p, q with classical experimental arrangements, but this solution is not available in the Everett interpretation. Thus, to make MWI a (viable) intepretation, you not only have to derive the Born rule, but also have to add some new structure to fix the canonical preferred basis.

Why MWI?
http://onqm.blogspot.ca/2009/07/why-mwi.html

My first impressions is that he is echoing Maudlin's arguments but presenting them more formally, I think? Notice that Ilja also quotes deBroglie as per Valentini in that video I linked using the same type of argument:

Instead, recognizing that the configuration space is part of the definition of the physics gives more power to an old argument in favour of the pilot wave approach, made already by de Broglie at the Solvay conference 1927: “It seems a little paradoxical to construct a configuration space with the coordinates of points which do not exist.”

Why the Hamilton operator alone is not enough
http://arxiv.org/pdf/0901.3262.pdf

 

[Demystifier]

Yes I'm aware of it. But I thought David Wallace had responded to it?

I only wanted to point out that this idea is even more crazy than mine.

 

[Quantumental]

Ilja did discuss his criticism of MWI in this blog:

Why MWI?
http://onqm.blogspot.ca/2009/07/why-mwi.html

My first impressions is that he is echoing Maudlin's arguments but presenting them more formally, I think? Notice that Ilja also quotes deBroglie as per Valentini in that video I linked using the same type of argument:

Why the Hamilton operator alone is not enough
http://arxiv.org/pdf/0901.3262.pdf

I know Ilja has been on PF.com previously, it would be cool if he came back and commented some on this.
Personally I am not qualified to judge this, but I do find it interesting that it seems only 2 people bring up this...
Mallah also argues quite confidently against it

 

[bohm2]

I know Ilja has been on PF.com previously, it would be cool if he came back and commented some on this. Personally I am not qualified to judge this, but I do find it interesting that it seems only 2 people bring up this...Mallah also argues quite confidently against it

I've e-mailed Ilja. Maybe he will comment.

 

[Ilja]

Ilja did discuss his criticism of MWI in this blog:

Why MWI?
http://onqm.blogspot.ca/2009/07/why-mwi.html

My first impressions is that he is echoing Maudlin's arguments but presenting them more formally, I think? Notice that Ilja also quotes deBroglie as per Valentini in that video I linked using the same type of argument:

Why the Hamilton operator alone is not enough
http://arxiv.org/pdf/0901.3262.pdf

My argument about the Hamilton operator is indeed more formal, but it is also about a slightly different point than Maudlin. In the video lecture which has been linked here, he was ready to accept the configuration space as given as an additional structure. Then, one main argument is that the configuration space itself requires much more structure.

My point is that without additional structure you cannot identify the configuration space. This was an important point for me because it destroys claims that MWI needs less structure.

 

[Quantumental]

My argument about the Hamilton operator is indeed more formal, but it is also about a slightly different point than Maudlin. In the video lecture which has been linked here, he was ready to accept the configuration space as given as an additional structure. Then, one main argument is that the configuration space itself requires much more structure.

My point is that without additional structure you cannot identify the configuration space. This was an important point for me because it destroys claims that MWI needs less structure.

I am very interested in grasping this, but first I want to ask you if you've considered the "new" approach by Wallace and Timpson? It seems they no longer support the view of wavefunction realism in configuration space, but rather promote an idea called Space-Time state realism.
They have written a paper on it: http://philsci-archive.pitt.edu/4621/1/ststaterealism.pdf

 

[bohm2]

Just to add some more links to this topic since I'm also confused and yet very interested in trying to understand these arguments by Wallace, Ilja and Maudlin there is this series of videos by Tumulka discussing Wallace's paper that was linked by Quantumental:

This is the first part of Roderich Tumulka's talk on David Wallace's views and quantum ontology generally. Unfortunately David Wallace couldn't make the conference due to volcanic activity, so Roderich was kind enough to read his paper for him.

http://www.youtube.com/user/rutgersphilos
(The relevant videos are Tumulka 1-Tumulka 6 (6 videos) and Tumulka audiende discussion with Q & A (3 videos)

 

[Quantumental]

Just to add some more links to this topic since I'm also confused and yet very interested in trying to understand these arguments by Wallace, Ilja and Maudlin there is this series of videos by Tumulka discussing Wallace's paper that was linked by Quantumental:

http://www.youtube.com/user/rutgersphilos
(The relevant videos are Tumulka 1-Tumulka 6 (6 videos) and Tumulka audiende discussion with Q & A (3 videos)

I really struggle to grasp this.
If I remember correctly these (Maudlin, Tumulka etc) reject functionalism. So I wonder if that is their motivation, since people like Wallace etc. claims the ontology is there

 

[Ilja]

I am very interested in grasping this, but first I want to ask you if you've considered the "new" approach by Wallace and Timpson? It seems they no longer support the view of wavefunction realism in configuration space, but rather promote an idea called Space-Time state realism.
They have written a paper on it: http://philsci-archive.pitt.edu/4621/1/ststaterealism.pdf

My first impression is that this accepts some of the arguments by Maudlin. So, they accept not only that the wave function is not only an element in a Hilbert space, but a complex function on the configuration space (introducing the first additional structure) but also that the configuration space itself has a complex structure of something living on ordinary space.

Of course, because of the relativistic background, all this on spacetime instead of space.

And, once it is a many worlds variant, only with a wave function, not with a configuration itself.

So, now we have a configuration space, moreover, with a structure which makes sense for a space of configurations living in a space - and all this with all the properties we would use to describe the actual configuration of the world as we see it - but without any configutions.

I would say there was, in the past, some interesting research program: Is it possible to start, with only a Hilbert space and the Hamilton operator on it, to derive everything else, including all the physics? My argument was that this program fails because one needs additional structure, already in the first step where one wants to recover the configuration space from the Hamilton operator, a step which, from mathematical point of view, was the most promising, because the usual Hamilton operator, looking like $p^2 + V(q)$, looks very different for p and q.

As far as I understand, the very program has been given up. The subdivision into systems, which was a central element, always had a weak point: There is no natural fundamental subdivision, and the subdivisions we have in real life, into observers, devices and so on have no fundamental origin, they make sense only in an environment of a particular configuration which contains at least the Solar system with the Earth.

Maybe looking for a replacement of the subdivision into subsystems they use the subdivision into spacetime regions? That would be fine with me, it makes sense. Unfortunately not for the aim of saving relativity, because
it would be an introduction of a background in a situation where the quantum gravity guys hope for background-independent theories. But it doesn't seem to be the case - at other places, it sounds like all the decoherence stuff is used as it is, without worrying about the definition of subsystems.

I see a circularity here: To define the real objects we observe, we have to apply this decoherence machine, which depends on the subdivision into systems. But the usual subdivisions into systems come from the real objects we observe.

A problem which is absent in dBB. There we always have a configuration, and if we consider the evolution of this configuration, we have to consider its environment in the configuration space. In this environment all the visible subsystems are already present and can be used as they are.

So far some ideas immediately after reading the paper, so, not very deep.

 

[bohm2]

I tried making sense of the transcripts, but I couldn't.
It seems no one did, the questions etc. made it seem that no one agreed with Maudlin and not even Maudlin seemed to be able to pin down any technical faults with WF realism.

I'm not sure if this paragraph by Jill North makes it any easier but here's a pretty good summary (I think) of Maudlin's argument:

Think of it this way. The relation between the wave function’s space and its ontology, on the one hand, and three-dimensional space and its ontology, on the other, is analogous to the relation between particles, on the one hand, and tables and chairs, on the other. Compare: isn’t it remarkable, if particles are fundamental, that they should conspire to make it seem as though there really are tables and chairs? But of course particles conspire to form themselves into tables and chairs, if particles really are in the fundamental level of reality and the nonfundamental stuff includes tables and chairs. Since the apparent existence of tables and chairs is the starting point for our theorizing, of course the fundamental theory we are led to is one that predicts the appearances (and existence) of tables and chairs. To put it another way, our evidence for the theory, in the first place, is what we observe. But what we observe, everyone agrees, is a parochial reflection of our own situation: we are familiar with tables and chairs. It is then no great coincidence that we end up with a fundamental theory that has the power to predict the appearances for us.

The Structure of a Quantum World
http://philsci-archive.pitt.edu/9347/1/Final_QM_for_volume.pdf

 

[bohm2]

I'm still having some difficulty understanding the difference between weak versus protecive measurements although the authors in some of these papers seem to be suggesting that unlike weak measurements:

In protective measurements we obtain this value not as a statistical average, but as a reading of a measuring device coupled to a single system. A sufficient number of protective measurements performed on a single system allow measuring its quantum wave function. This provides an argument against the claim that the quantum wave function has a physical meaning only for an ensemble of identical systems.

Protective Measurements
http://lanl.arxiv.org/pdf/0801.2761.pdf

So if I'm understanding this, then, it is different than weak measurements as summarized here by Demystifier:

Weak measurements in quantum mechanics and 2.6 children in an American family
https://www.physicsforums.com/blog.php?b=1226

I'm still not sure if this scheme of protective measurements is universally accepted primarily because of some critical papers on the topic but in a recent paper by Gao, he suggests that protective measurements rule out ψ-epistemic models as per PBR:

In particular, the actual physical state of the measured system can be measured by a series of protective measurements, and the wave function turns out to be a one-to-one representation of the physical state. Therefore, the ψ-epistemic models, in which the wave
function or quantum state is not uniquely determined by the underlying physical state, can be ruled out without resorting to nontrivial assumptions beyond those required for a well-formed ontological model.

Comment on "Distinct Quantum States Can Be Compatible with a Single State of Reality"
http://philsci-archive.pitt.edu/9457/1/comments_on_PRL_v9.pdf

 

[Demystifier]

I'm still having some difficulty understanding the difference between weak versus protecive measurements

Both weak measurement (WM) and protective measurement (PM) measure an observable without destroying the state. But they achieve it in a different way.

PM does it with a single measurement. WM does it with a large number of measurements, each on another member of an ensemble of equally prepared systems.

For WM, the prepared state before the measurement may be arbitrary (but must be the same for each member of the ensemble). For PM, the prepared state before the measurement cannot be arbitrary; it must be an eigenstate of the observable which will be measured.

In a perfect measurement, one would measure an observable:
1. for an ARBITRARY initial state,
2. WITHOUT DESTROYING it, and
3. with only ONE measurement performed.
But in QM such a perfect measurement is not possible. Standard strong measurement violates 2, WM violates 3, and PM violates 1.

EDIT:
For the sake of completeness, let me also explain two additional kinds of measurement:
- first kind (FK) measurement and
- quantum non-demolition (QND) measurement.
Both FK and QND are types of standard strong measurement, so they both destroy the initial state. However, they have a nice property if, after the measurement, you measure the same observable again; they both give the same value of the observable which you obtained by the first measurement. The difference is that FK achieves this only immediately after the first measurement, while QND achieves this at an arbitrary later time. FK measurements are measurements which can be described by a wave-function collapse. Many (but not all !) actual measurements are FK. However, not many actual measurements are also QND.

 

[bohm2]

I don't fully understand this argument but this author tries to use protective measurement to rule out the MWI:

It is argued that the components of the superposed wave function of a measuring device, each of which represents a definite measurement result, do not correspond to many worlds, one of which is our world, because all components of the wave function can be measured in our world by a serious of protective measurements, and they all exist in this world.

An Exceptionally Simple Argument Against the Many-worlds Interpretation: Further Consolidations
http://philsci-archive.pitt.edu/9494/1/aa-mwi_further_v9.pdf

 

[bohm2]

Another paper came out today suggesting that ψ is ontic but relying on the concept of protective measurement:

Recently Lewis et al (2012) demonstrated that additional assumptions such as preparation independence are always necessary to rule out a ψ-epistemic model, in which the quantum state is not uniquely determined by the underlying physical state. Their conclusion is based on an analysis of conventional projective measurements. Here we will demonstrate that protective measurements (Aharonov and Vaidman 1993; Aharonov, Anandan and Vaidman 1993), which are distinct from projective measurements, already shows that distinct quantum states cannot be compatible with a single state of reality...

In conclusion, we have demonstrated that, without resorting to nontrivial assumptions such as preparation independence, the wave function or quantum state is uniquely determined by the underlying physical state, and thus distinct quantum states cannot be compatible with a single state of reality. This improves the interesting result obtained by Pusey, Barrett and Rudolph (2012). Certainly, the quantum state also plays an epistemic role by giving the probability distribution of the results of projective measurements according to the Born rule. However, this role is secondary and determined by the complete quantum dynamics that describes the measuring process, e.g. the collapse dynamics in dynamical collapse theories.

Distinct Quantum States Cannot Be Compatible with a Single State of Reality.
http://philsci-archive.pitt.edu/9609/1/dqs_v6.pdf

 

[bohm2]

Another paper came out today suggesting that ψ is ontic but relying on the concept of protective measurement...

An excellent summary by Schlosshauer and Claringbold criticising authors who try to infer interpretational insights not just from protective measurements but also from decoherence theory, Bell's and PBR theorem:

We suggest that the failure of protective measurement to settle the question of the meaning of the wave function is entirely expected, for protective measurement is but an application of the standard quantum formalism, and none of the hard foundational questions can ever be settled in this way...

Of course this is not to say that by milking the quantum formalism we cannot produce something fresh. Quantum information theory and decoherence theory are good examples, but they, just like protective measurement, have not answered the hard interpretive questions; and they, too, could not be expected to do so. Quantum information theory may have motivated new information based interpretations of quantum mechanics, but there are quantum information theorists who are Bohmians and others who are Everettians...Thus if we understand the quantum measurement problem as the question of how to reconcile the linear, deterministic evolution described by the Schrodinger equation with the occurrence of random, definite measurement outcomes, then decoherence has certainly not solved this problem, as is now widely recognized. What decoherence rather solves is a consistency problem: the problem of explaining why and when quantum probability distributions approach the classically expected distributions. But this is a purely practical problem, not a game-changer for quantum foundations. To be sure, the picture associated with the decoherence process has sometimes been claimed to be suggestive of particular interpretations of quantum mechanics or to pinpoint internal consistency issues. But it might be safer to say that certain interpretations(such as the Everett interpretation) are simply more in need of decoherence to define their structure...

Another example is Bell’s theorem , although what exactly the experimentally measured violations of Bell’s inequalities tell us about nature remains a matter of debate. Like Bell’s theorem, the PBR theorem is based on the consideration of hidden-variables models and accommodates a variety of conclusions (Colbeck and Renner 2012, Hardy 2012, Schlosshauer and Fine 2012, 2014).

Entanglement, scaling, and the meaning of the wave function in protective measurement
http://arxiv.org/pdf/1402.1217.pdf