Bohm trajectories and protective measurements?

[lugita15]

Now consider the total wave function for the whole Universe. It is reasonable to expect that the total energy of the whole Universe has some definite value E. But then it is a simple consequence of the Schrödinger equation that the wave function does not depend on time. On the other hand, we see that the Universe does depend on time. This is not a problem for other interpretations, because either there is something else which depends on time, or the wave function itself depends on time because it does not really evolve according to the Schrödinger equation. But it is a problem for MWI, because MWI rejects both possibilities.

Why isn't the conclusion simply that the "reasonable" expectation is wrong?

 

[lugita15]

Nevertheless, those who do know will say the following: The time independent wave function psi(x1,...,xn) depends, among other things, on positions which represent readings of clocks. So even if wave function does not depend on the evolution time t, it does depend on the clock time. In other words, there is no time without a clock. Of course, not everybody is satisfied with it, but this seems to be the best what can be done within MWI.

Could you elaborate on this? You can have the wave function depend on the position of a clock pointer, but then you're just pushing the question one step back: why does the pointer state of a clock ever change?

 

[Lord Crc]

Energy of MATTER ALONE is tricky in GR. But total energy-density in GR of matter and gravity together is not tricky at all. It is exactly zero.

Ah ok, thanks for clearing that up :)

 

[Demystifier]

Why isn't the conclusion simply that the "reasonable" expectation is wrong?

It is explained in the Introduction of the paper. See also post #30.

 

[Demystifier]

Could you elaborate on this? You can have the wave function depend on the position of a clock pointer, but then you're just pushing the question one step back: why does the pointer state of a clock ever change?

It is a different type of question. If some quantity depends on t, it does not help to understand why t "changes", or even what does it mean that t "changes". Similarly, if another quantity depends on x, where x is the position of needle of a clock, it does not help to understand why x "changes".

MWI, but also physics in general, usually does not attempt to explain why things change. It only explains why values of some quantities depend on values of some other quantities.

 

[lugita15]

Demystifier, instead of using the word "change", what about this: why does the clock's pointer have more than one state? Isn't it conceivable that the clock would just show a single time, and thus time would stand still so speak?

 

[Demystifier]

Demystifier, instead of using the word "change", what about this: why does the clock's pointer have more than one state? Isn't it conceivable that the clock would just show a single time, and thus time would stand still so speak?

Well, in MWI a clock shows all the values for which the wave function does not vanish.

 

[Quantumental]

Demystifier: what do you think of Deutsch's "answer" to this in the link supplied by Bohm2 ?

Does this make any sense or is this a "serious flaw" like Born Rule in MWI?

 

[Demystifier]

Demystifier: what do you think of Deutsch's "answer" to this in the link supplied by Bohm2 ?

Does this make any sense or is this a "serious flaw" like Born Rule in MWI?

As far as I can see, neither of the answers linked by Bohm2 is written by Deutch. Can you be more specific?

 

[Quantumental]

As far as I can see, neither of the answers linked by Bohm2 is written by Deutch. Can you be more specific?

The quote given by Bohm2 is from a chapter written by Deutsch.

 

[Demystifier]

The quote given by Bohm2 is from a chapter written by Deutsch.

Well, that quote is essentially the same what I said that the MWI resolution of the problem of time is. So it does make sense to me, even though I find the Bohmian solution much more convincing.

 

[Quantumental]

Well, that quote is essentially the same what I said that the MWI resolution of the problem of time is. So it does make sense to me, even though I find the Bohmian solution much more convincing.

Ok, thanks. So there are no objections to their solution in other words.
It seems the Everettians has done a good job in "solving" their problems with the exception of Born Rule (though there are several attempts).
Not really seeing any benefit for Bohmians here

 

[bohm2]

It seems the Everettians has done a good job in "solving" their problems with the exception of Born Rule (though there are several attempts).

In one of his more recent papers, Wallace points out some other problems with MWI which he tries to address:

Furthermore, and quite apart from the intrinsic interest of the question, it might be thought that we cannot be confident in any story of emergence unless we are confident what it is emerging from. Maudlin (2010), in particular, criticises the Everett interpretation for having an inappropriate micro-ontology to appropriately ground macro-level facts...In particular, normally our concepts of space and time are treated as constant between higher-level and lower-level theories, so that for (e.g.) some higher-level object to exist in spacetime region K it must be instantiated not just by any old objects and properties in the lower-level theory, but by objects and properties themselves located in K.

A prolegomenon to the ontology of the Everett interpretation
http://philsci-archive.pitt.edu/8892/1/alyssa_volume.pdf

In Wallace's et al. book on MWI (Ch. 4-"Can the world only be wavefunction?") Maudlin makes this point:

In sum, any theory whose physical ontology is a complete wavefunction monism automatically inherits a severe interpretational problem: if all there is the wavefunction, an extremely high-dimensional object evolving in some specified way, how does that account for the low-dimensional world of localized objects that we start off believing in, whose apparent behavior constitutes the explanandum of physics in the first place?

I. Schemelzer has also raised some arguments against MWI arguing that pure wave function monism is not enough but I just skimmed through them so I'm not sure I really understand his arguments very well or if they are similar to Maudlin's?

About the relation between pilot wave beables and decoherence
http://lanl.arxiv.org/pdf/0907.5284.pdf
Why the Hamilton operator alone is not enough
http://lanl.arxiv.org/pdf/0901.3262.pdf
Pure quantum interpretations are not viable
http://lanl.arxiv.org/pdf/0903.4657.pdf

 

[Quantumental]

Regarding Maudlins objections, I am aware of them and I have communicated with him earlier in attempts to understand these worries, but I cannot comprehend them.
It seems the Bohmian camp deny functionalism and I suspect that his objection arises from this and that the emergence would become natural if he accepted functionalism.
But I might be very wrong, so if I am, feel free to correct me.

I. Schemelzer has also raised some arguments against MWI arguing that pure wave function monism is not enough but I just skimmed through them so I'm not sure I really understand his arguments very well or if they are similar to Maudlin's?

About the relation between pilot wave beables and decoherence
http://lanl.arxiv.org/pdf/0907.5284.pdf
Why the Hamilton operator alone is not enough
http://lanl.arxiv.org/pdf/0901.3262.pdf
Pure quantum interpretations are not viable
http://lanl.arxiv.org/pdf/0903.4657.pdf

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.
It would be very nice to see the main opponents and proponents of MWI all participate in a thread regarding MWI. To see what the true unsolved issues are once and for all.
Usually there is only 1 proponent and 1 opponent arguing back and forth, it would be nice to see more input from more angles

 

[bohm2]

Regarding Maudlins objections, I am aware of them and I have communicated with him earlier in attempts to understand these worries, but I cannot comprehend them. It seems the Bohmian camp deny functionalism and I suspect that his objection arises from this and that the emergence would become natural if he accepted functionalism. But I might be very wrong, so if I am, feel free to correct me.

I'm not sure if there is any connection between Maudlin's position and functionalism. I've always assumed that his argument against wave function monism is based on his belief on the requirement of any theory to be able to explain the macroscopic 3-D world we are familiar with: the primitive ontology (PO). See the 2 papers by Valia Allori discussing the concept of PO:

The notion of primitive ontology was first proposed in Dürr et al. 1992 and Goldstein 1998, and then discussed in a little more details in Allori et al. 2008. The main idea is that all fundamental physical theories, from classical mechanics to quantum theories, share the following common structure:
-Any fundamental physical theory is supposed to account for the world around us (the manifest image), which appears to be constituted by three-dimensional macroscopic objects with definite properties.
-To accomplish that, the theory will be about a given primitive ontology: entities living in three-dimensional space or in space-time. They are the fundamental building blocks of everything else, and their histories through time provide a picture of the world according to the theory (the scientific image).
-The formalism of the theory contains primitive variables to describe the primitive ontology, and nonprimitive variables necessary to mathematically implement how the primitive variables will evolve in time.
-Once these ingredients are provided, all the properties of macroscopic objects of our everyday life follow from a clear explanatory scheme in terms of the primitive ontology.

Primitive Ontology and the Structure of Fundamental Physical Theories
http://www.niu.edu/~vallori/AlloriWFOlast-dopo%20editing%20finale.pdf

On the Metaphysics of Quantum Mechanics
http://www.niu.edu/~vallori/Allori%20-%20LeBihan-On%20the%20Metaphysics%20of%20Quantum%20Mechanics-finale.pdf

Myself I'm not a big fan of functionalism. Functionalism has many problems, in my opinion.

 

[Demystifier]

Let me use a simple analogy. If functionalism was right, then we could solve the problem of hungry people in Africa by sending them a cookbook.

In other words, in Bohmian mechanics a wave function without a particle is like a cookbook without food.

 

[Quantumental]

Let me use a simple analogy. If functionalism was right, then we could solve the problem of hungry people in Africa by sending them a cookbook.

In other words, in Bohmian mechanics a wave function without a particle is like a cookbook without food.

I really can't phatom that there are physicists in 2012 that do not accept functionalism.
If the wavefunction is ontological in Bohm, then the many worlds are there. You would have to go with a nomological WF to avoid it.

 

[Quantumental]

I don't quite see Vallori's arguments against the emergence of worlds in these papers.
She says she is against it, but never really comes up with a logical or technical argument as to why...

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

Myself I'm not a big fan of functionalism. Functionalism has many problems, in my opinion.

What problems? Never heard of one

 

[Demystifier]

I really can't phatom that there are physicists in 2012 that do not accept functionalism.
If the wavefunction is ontological in Bohm, then the many worlds are there. You would have to go with a nomological WF to avoid it.

So I go with nomological WF, just as in classical Hamilton-Jacobi mechanics I go with nomological PF (principal function), which is a solution of the Hamilton-Jacobi equation. What's wrong with that?

 

[Quantumental]

So I go with nomological WF, just as in classical Hamilton-Jacobi mechanics I go with nomological PF (principal function), which is a solution of the Hamilton-Jacobi equation. What's wrong with that?

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.

 

[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 occurred, 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 occurred, 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 Schrödinger’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 occurred, 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.