I Consciousness and quantum mechanics

[PeroK]

If that is the case then how is it that natural processes cause wave function collapses?

I guess that, in a nutshell, is the measurement problem.

 

[PeterDonis]

On the one hand, the argument has been made that consciousness is not necessary for causing wave function collapse because natural processes not involving conscious beings cause collapses.

On the other hand you seem to say that a natural process cannot be simulated as a sequence of wave function collapses.

No. Only some natural processes--the ones that do not involve decoherence--cannot be simulated as a sequence of wave function collapses. The orbit of the Moon is a natural process, and can be simulated just fine with a classical model, which is equivalent to a continuous infinity of wave function collapses.

 

[Stephen Tashi]

No. Only some natural processes--the ones that do not involve decoherence--cannot be simulated as a sequence of wave function collapses.

Being mathematically inclined, I'm curious about how such a claim ("cannot be simulated" - in any manner whatsoever) would be stated as a theorem.

The orbit of the Moon is a natural process, and can be simulated just fine with a classical model, which is equivalent to a continuous infinity of wave function collapses.

Is there no way to simulate non-decoherent processes as stochastic realization of a continuous infinity of wave function collapses? For example Brownian motion is such a model. I assume people have tried it and failed, but "no known way" is not the same as "no way".

 

[PeterDonis]

I'm curious about how such a claim ("cannot be simulated" - in any manner whatsoever) would be stated as a theorem.

I'm taking "simulated" to be basically equivalent to "apply some particular mathematical model to make predictions". The mathematical model that makes accurate predictions about the double slit experiment results does not include any wave function collapse within the experiment (although it does at the end when the particle makes a dot on the detector screen). The mathematical model that makes accurate predictions about the motion of the Moon does include continuous wave function collapse (since that is what using classical equations amounts to in quantum terms).

Is there no way to simulate non-decoherent processes as stochastic realization of a continuous infinity of wave function collapses?

I'm not aware of any such model.

For example Brownian motion is such a model.

Brownian motion can't reproduce quantum interference phenomena such as those in the double slit experiment. The phenomena for which Brownian motion makes accurate predictions, such as large molecules in suspension in a fluid, are decoherent processes in quantum terms (since the underlying statistical mechanics that is used is classical).

 

[allisrelative]

Summary:: I am reading a book which quotes from Wigner “Remarks on the Mind-Body Question”. Would appreciate someone’s comment on them.

Reading book, “God? Very Probable”. The author quotes Wigners comments in his book, “Remarks on the Mind- Body Question” 169, 171, 173. “The very study of the external world led to the conclusion that the content of consciousness is an ultimate reality. Given the ultimate priority of consciousness, the quantum physics understanding of reality leads to an intellectual outcome where “solipsism may be logically consistent” with the current state of scientific thinking in physics but it is beyond doubt that “monism in the sense of scientific materialism is not” compatible with contemporary physics.
The author, Robert Nelson, then goes on to quote a similar conclusion from Wheeler in “At Home in the Universe” , 181.
I ask, how do these ideas stand in today’s Theories of quantum mechanics?

Good Quote from Wigner.

To answer your question, it doesn't really stand with today's strict materialist view of QM that wants to reduce the observer to basically nothing and hysterics ensue whenever anyone tries to connect QM and consciousness.

The Founders of QM saw a connection to consciousness.

[Off topic content removed.]

I think the simple solution is to redefine consciousness separate from awareness of consciousness. In the recent experiment around Wigner's Friend, they defined an observer as any mechanical or biological system that can record the quantum state in it's memory.

Using this definition, the universe, a measuring device, animals and humans are all conscious of their environment and the quantum state. Humans have awareness of consciousness which allows us to build civilizations.

The definition of consciousness which includes awareness of consciousness isn't an objective truth. If you just separate the two, all of the confusion goes away.

 

[atyy]

I don't think you can get the prediction that the Moon behaves classically without applying the "collapse" postulate of QM to the Moon even when no one is looking at it.

I agree. So is the difference in our views that I wouldn't mind using "measurement", "observer", "conscious observer" in a related way with regards to the quantum formalism, but you would?

 

[Lord Jestocost]

Summary:: I am reading a book which quotes from Wigner “Remarks on the Mind-Body Question”. Would appreciate someone’s comment on them.

I ask, how do these ideas stand in today’s Theories of quantum mechanics?

For example: "The mental Universe" by Richard Conn Henry, Nature, volume 436, 29 (2005)

Abstract:
The only reality is mind and observations, but observations are not of things. To see the Universe as it really is, we must abandon our tendency to conceptualize observations as things.

 

[PeterDonis]

is the difference in our views that I wouldn't mind using "measurement", "observer", "conscious observer" in a related way with regards to the quantum formalism, but you would?

I'm not sure if we have different views about that. My only concern was to make clear the point that you say you agree with in your latest post. None of the words "measurement", "observer", "conscious observer" can make that clear by themselves.

 

[f95toli]

The Founders of QM saw a connection to consciousness.

It is important to realize that what the founder thought about QM is -quite generally- essentially irrelevant. They did most of their work about a 100 year ago at at time when QM was brand new and nowhere near fully developed; and where most "foundational" experiments had not yet been done. Hence, there was no way they could have an informed opinion about anything.
Some of them also went a bit mad as they got older and came up with all sorts of nonsense. The latter seems to be a almost an occupational hazard for successful scientist (although it could also be that we have a tendency to assume that everything they said was somehow "profound" when we would have just ignored a "normal" person) .

 

[Lord Jestocost]

It is important to realize that what the founder thought about QM is -quite generally- essentially irrelevant.

@f95toli
When making such claims about the founders of QM, it would be helpful when you point to some corresponding texts or articles published by, for example, Werner Heisenberg, Erwin Schrödinger, Max Born, Pascual Jordan, Wolfgang Pauli, Paul Dirac, John von Neumann, Niels Bohr etc. in order to support your claim.

 

[Lord Jestocost]

The Founders of QM saw a connection to consciousness.

Not only some founders of QM were pondering. For example, David Bohm and Basil J. Hiley in “The Undivided Universe: An Ontological Interpretation of Quantum Theory (Routledge 1993)”:

"Several physicists have already suggested that quantum mechanics and consciousness are closely related and that the understanding of the quantum formalism requires that ultimately we bring in consciousness in some role or other (e.g. Wigner [17], Everett [18] and Squires [19]). Throughout this book it has been our position that the quantum theory itself can be understood without bringing in consciousness and that as far as research in physics is concerned, at least in the present general period, this is probably the best approach. However, the intuition that consciousness and quantum theory are in some sense related seems to be a good one, and for this reason we feel that it is appropriate to include in this book a discussion of what this relationship might be."

 

[edmund cavendish]

In the early stages of this discussion Sir Roger Penrose's name was mentioned. Given his views on the relationship between QM and the origins of consciousness it seemed that they deserved a bit more of an airing hence the link and extract from the article below. I personally feel that a lot of the language about the "observer" is also tied up with issues around Free will and Determinism, explaining why some are uneasy with the idea of a universal system observation as distinct from a chosen act..to open the lid of the box or not. Penrose also writes/talks extensively about the non computability of consciousness, referencing Godel and it seems likely that the AI debate may also add to this current discussion, which I have enjoyed reading.

http://nautil.us/issue/47/consciousness/roger-penrose-on-why-consciousness-does-not-computeExtract from the above.

"Penrose’s theory promises a deeper level of explanation. He starts with the premise that consciousness is not computational, and it’s beyond anything that neuroscience, biology, or physics can now explain. “We need a major revolution in our understanding of the physical world in order to accommodate consciousness,” Penrose told me in a recent interview. “The most likely place, if we’re not going to go outside physics altogether, is in this big unknown—namely, making sense of quantum mechanics.”

He draws on the basic properties of quantum computing, in which bits (qubits) of information can be in multiple states—for instance, in the “on” or “off” position—at the same time. These quantum states exist simultaneously—the “superposition”—before coalescing into a single, almost instantaneous, calculation. Quantum coherence occurs when a huge number of things—say, a whole system of electrons—act together in one quantum state."

 

[PeterDonis]

Extract from the above

This is not really a good reference. If Penrose has published an actual peer-reviewed paper, that is what we should be using as a reference for what he is proposing.

 

[allisrelative]

In the early stages of this discussion Sir Roger Penrose's name was mentioned. Given his views on the relationship between QM and the origins of consciousness it seemed that they deserved a bit more of an airing hence the link and extract from the article below. I personally feel that a lot of the language about the "observer" is also tied up with issues around Free will and Determinism, explaining why some are uneasy with the idea of a universal system observation as distinct from a chosen act..to open the lid of the box or not. Penrose also writes/talks extensively about the non computability of consciousness, referencing Godel and it seems likely that the AI debate may also add to this current discussion, which I have enjoyed reading.

http://nautil.us/issue/47/consciousness/roger-penrose-on-why-consciousness-does-not-computeExtract from the above.

"Penrose’s theory promises a deeper level of explanation. He starts with the premise that consciousness is not computational, and it’s beyond anything that neuroscience, biology, or physics can now explain. “We need a major revolution in our understanding of the physical world in order to accommodate consciousness,” Penrose told me in a recent interview. “The most likely place, if we’re not going to go outside physics altogether, is in this big unknown—namely, making sense of quantum mechanics.”

He draws on the basic properties of quantum computing, in which bits (qubits) of information can be in multiple states—for instance, in the “on” or “off” position—at the same time. These quantum states exist simultaneously—the “superposition”—before coalescing into a single, almost instantaneous, calculation. Quantum coherence occurs when a huge number of things—say, a whole system of electrons—act together in one quantum state."

Good points about Penrose.

Penrose is talking about the science of consciousness and for some reason it's not seen as "mainstream" science but it's actually more science involved than a lot of other theories that have no scientific basis. Here's a couple of papers talking about Penrose's theory.

Emergent Consciousness: From the Early Universe to Our Mind

In a previous paper (gr-qc/9907063) we described the early inflationary universe in terms of quantum information. In this paper, we analize those results in more detail, and we stress the fact that, during inflation, the universe can be described as a superposed state of quantum registers. The self-reduction of the superposed quantum state is consistent with the Penrose's Objective Reduction (OR) model. The quantum gravity threshold is reached at the end of inflation, and corresponds to a superposed state of 10^9 quantum registers. This is also the number of superposed tubulins-qubits in our brain, which undergo the Penrose-Hameroff's Orchestrated Objective Reduction, (Orch OR), leading to a conscious event. Then, an analogy naturally arises between the very early quantum computing universe,and our mind.

https://arxiv.org/abs/gr-qc/0007006

Consciousness in the universe: A review of the ‘Orch OR’ theory

Abstract

The nature of consciousness, the mechanism by which it occurs in the brain, and its ultimate place in the universe are unknown. We proposed in the mid 1990's that consciousness depends on biologically ‘orchestrated’ coherent quantum processes in collections of microtubules within brain neurons, that these quantum processes correlate with, and regulate, neuronal synaptic and membrane activity, and that the continuous Schrödinger evolution of each such process terminates in accordance with the specific Diósi–Penrose (DP) scheme of ‘objective reduction’ (‘OR’) of the quantum state. This orchestrated OR activity (‘Orch OR’) is taken to result in moments of conscious awareness and/or choice. The DP form of OR is related to the fundamentals of quantum mechanics and space–time geometry, so Orch OR suggests that there is a connection between the brain's biomolecular processes and the basic structure of the universe. Here we review Orch OR in light of criticisms and developments in quantum biology, neuroscience, physics and cosmology. We also introduce a novel suggestion of ‘beat frequencies’ of faster microtubule vibrations as a possible source of the observed electro-encephalographic (‘EEG’) correlates of consciousness. We conclude that consciousness plays an intrinsic role in the universe.

https://www.sciencedirect.com/science/article/pii/S1571064513001188?via=ihub

Their predictions were corroborated by Anirban Bandyopadhyay a Senior Scientist at the National Institute for Material Science when he found quantum vibrations in microtubules. Here's Anirban talking about these vibrations.



So Penrose and his theories of the Quantum Mind are based in science that can be tested and observed. The thoeory makes predictions that we should soon be able to test. Michio Kaku calls himself a String Theorist and Sean Carroll is a proponent of many worlds. Both of these things have features that aren't scientific and can't be tested. This is why speculation about String Theory has been around for 40-50 years and many worlds is centered around a global physical wave function that can never be observed or tested yet the Quantum Mind isn't "mainstream" science and these things are?

The only reason this is the case is because Penrose is connecting features of QM to the brain and talking about consciousness.

 

[allisrelative]

Not only some founders of QM were pondering. For example, David Bohm and Basil J. Hiley in “The Undivided Universe: An Ontological Interpretation of Quantum Theory (Routledge 1993)”:

"Several physicists have already suggested that quantum mechanics and consciousness are closely related and that the understanding of the quantum formalism requires that ultimately we bring in consciousness in some role or other (e.g. Wigner [17], Everett [18] and Squires [19]). Throughout this book it has been our position that the quantum theory itself can be understood without bringing in consciousness and that as far as research in physics is concerned, at least in the present general period, this is probably the best approach. However, the intuition that consciousness and quantum theory are in some sense related seems to be a good one, and for this reason we feel that it is appropriate to include in this book a discussion of what this relationship might be."

Good quote and it's true.

Recent studies really hurt Many Worlds and some Decoherence interpretations of QM.

They say collapse doesn't happen just the "appearance of collapse." I agree with this. Wigner's Friend in the lab just appears to collapse the wave function from his point of view. Relational interpretation of QM says it's because his friend is now a part of an S+O system and has a lack of information about the state of the overall system. You still need his awareness of consciousness to say if he's in a universe where he measures vertical polarization or if he's in a universe where he measures horizontal polarization. Wigner outside of the lab isn't a apart of the S+O system and can measure interference.

What M.W.I. and some Decoherence interpretations say is the observer is basically meaningless and this global physical wave function splits or decohere's when the system interacts with it's environment. If this is the case Wigner shouldn't be able to measure interference. This is because Wigner's Friend measuring vertical or horizontal polarization is an objective truth of the branching of this global physical wave function. Observers have nothing to do with it yet Wigner in the lab is aware of this appeareance of collapse and records the results while Wigner can see interference.

Is this global physical wave function schizophrenic? How can Wigner measure interference outside of the appearance of collapse which is objectively real due to the evolution and branching of this global physical wave function? Wigner should have no choice but to see what his friend in the lab sees because according to M.W.I. and some Decoherence interpretations it's not about Wigner or his friend. Sean Carroll said in one program that the observer was like a rock. The recent Wigner's Friend experiment shows the observer playing a role because it can extract information and record that information in it's memory about the state of the quantum system. How can that be seen as compatible with M.W.I. and some Decoherent interpretations?

When Wigner's Friend measures vertical polarization that's a decoherent history that Wigner and his friend are now in yet the experiment shows Wigner can't be shown to be in a universe where his friend measures vertical polarization or a universe where his friend measures horizontal polarization until he gains knowledge about the state his friend observed.

 

[PeterDonis]

What M.W.I. and some Decoherence interpretations say is the observer is basically meaningless and this global physical wave function splits or decohere's when the system interacts with it's environment. If this is the case Wigner shouldn't be able to measure interference.

I think this is an important point. My impression from previous discussions on PF of Wigner's Friend type expeirments is that the people who claim Wigner can measure interference want to have it both ways: they want to call the friend's observation an actual outcome, while at the same time they want Wigner to be able to measure interference between multiple "outcomes" for his friend. The latter would require Wigner to be able to do unitary operations on his friend that are equivalent to quantum erasure of the friend's memory. But those kinds of operations are incompatible with decoherence, and therefore with actual outcomes.

In other words, if Wigner can actually keep the friend and his entire lab and experimental apparatus in a state of sufficient quantum coherence to be able to measure interference, then the friend will never have actually observed anything, because no decoherence will ever have occurred.

 

[PeterDonis]

Their predictions were corroborated by Anirban Bandyopadhyay a Senior Scientist at the National Institute for Material Science when he found quantum vibrations in microtubules.

While such vibrations have been observed, that is still far short of corroborating Penrose's larger model; we have no real evidence about the role, if any, that such vibrations play in consciousness. I absolutely think such research should be continued, but it's way too early to say that it has confirmed Penrose's overall model.

Michio Kaku calls himself a String Theorist and Sean Carroll is a proponent of many worlds. Both of these things have features that aren't scientific and can't be tested.

I certainly agree that many physicists make claims about the MWI and string theory that go way beyond what has actually been established by experiment.

 

[allisrelative]

I think this is an important point. My impression from previous discussions on PF of Wigner's Friend type expeirments is that the people who claim Wigner can measure interference want to have it both ways: they want to call the friend's observation an actual outcome, while at the same time they want Wigner to be able to measure interference between multiple "outcomes" for his friend. The latter would require Wigner to be able to do unitary operations on his friend that are equivalent to quantum erasure of the friend's memory. But those kinds of operations are incompatible with decoherence, and therefore with actual outcomes.

In other words, if Wigner can actually keep the friend and his entire lab and experimental apparatus in a state of sufficient quantum coherence to be able to measure interference, then the friend will never have actually observed anything, because no decoherence will ever have occurred.

How do you define an actual outcome? How are you defining decoherence?

I know some people have a more expansive view of decoherence that's not supported by any evidence. Here's a good publication on this:

Decoherence and definite outcomes

In the last few years the general notion of decoherence in quantum mechanics has become increasingly common among physicists, philosophers of physics and quantum information scientists. And rightly so, because it represents both a further application of the predictive and explicative power of quantum theory, and an attempt to break the stalemate situation with respect to the interpretation of quantum mechanics. Powerful as it might be, however, the decoherence programme has not solved the measurement problem yet. Specifically, and contrary to some claims, it has not solved the definite outcomes problem, better known as the problem of the wave function collapse. Due to the wide scope of the decoherence programme, which could be summarized as the attempt to recover the classical phenomena from quantum physics, the problem of definite outcomes happens to be often confused with other, loosely related, issues. Such a confusion is the main motivation of this study.

It has been already stressed that the appearance of definite outcomes in single measurements does not follow from the decoherence mechanism, but, in light of the many contradictory or misleading statements present in the relevant literature, the author feels that such a point is never highlighted enough. In fact, up until the first half of the 2000’s, it was not uncommon to find such statements as: “...In particular ‘reduction of the wave packet’, postulated by Von Neumann to explain definiteness of an outcome of an individual observation, can be explained when a realistic model of an apparatus is adopted” [57]; or “...the word ‘decoherence’ which describes the process that used to be called ‘collapse of the wave function’...” [66].

Some of the authors, expressing the view that the decoherence programme has somehow solved the definite outcomes problem, actually base their position on sophisticated assumptions which, unfortunately, they often fail to expound. Some others, such as for example W. Zurek, later on acknowledged the incorrectness of their statement and clarified which particular interpretation they were adopting, even proposing new solutions [31].

http://philsci-archive.pitt.edu/9947/1/decoherence_and_definite_outcomes.pdf

I never used the words "actual outcome" but what do you mean by it? Also, how exactly are you relating decoherence to observation?

 

[allisrelative]

While such vibrations have been observed, that is still far short of corroborating Penrose's larger model; we have no real evidence about the role, if any, that such vibrations play in consciousness. I absolutely think such research should be continued, but it's way too early to say that it has confirmed Penrose's overall model.

I agree. This just corroborates a prediction made by Penrose and Hameroff.

The overall theory of Penrose-Hameroff really hinges upon self collapse connected to quantum gravity which also gets into his cyclical model of the universe. He has proposed ways to test these things and maybe we will be able to in the future.

My point was the Quantum Mind of Penrose-Hameroff is based in science and should be explored with an open mind. This was in contrast to theories that some scientist accept that aren't based in science and are outside the bounds of observation.

 

[Stephen Tashi]

My impression from previous discussions on PF of Wigner's Friend type expeirments is that the people who claim Wigner can measure interference want to have it both ways: they want to call the friend's observation an actual outcome, while at the same time they want Wigner to be able to measure interference between multiple "outcomes" for his friend.

Does a "Wigner's friend experiment" imply repetitions of some experiment - call it "the basic experiment" - so that statistics from the basic experiment can be used to demonstrate interference?

 

[PeterDonis]

How do you define an actual outcome?

An outcome that cannot be reversed.

How are you defining decoherence?

Loss of quantum coherence due to entanglement spreading out among a large number of untrackable degrees of freedom.

You are correct that a single definite outcome, by itself, does not follow from decoherence alone. All decoherence ensures is that the outcomes are definite, i.e., there is no interference between them and each one is irreversible. But decoherence by itself does not rule out interpretations like the MWI where all possible outcomes actually occur, not just one of them. It just says that, even in interpretations like the MWI, the outcomes are irreversible and don't interfere. So if Wigner's friend undergoes decoherence, Wigner can't observe interference between different outcomes for his friend.

 

[PeterDonis]

Does a "Wigner's friend experiment" imply repetitions of some experiment - call it "the basic experiment" - so that statistics from the basic experiment can be used to demonstrate interference?

Not as I understand it. A Wigner's friend experiment requires Wigner to be able to, in a single run of the experiment, subject the friend, along with his entire lab and the observations he makes in it, to something like a Mach-Zehnder interferometer, where Wigner can cause the different "branches" of the friend/lab wave function to recombine, as an MZI does at the second beam splitter, and thus enable interference between the branches.

 

[allisrelative]

An outcome that cannot be reversed.
Loss of quantum coherence due to entanglement spreading out among a large number of untrackable degrees of freedom.

You are correct that a single definite outcome, by itself, does not follow from decoherence alone. All decoherence ensures is that the outcomes are definite, i.e., there is no interference between them and each one is irreversible. But decoherence by itself does not rule out interpretations like the MWI where all possible outcomes actually occur, not just one of them. It just says that, even in interpretations like the MWI, the outcomes are irreversible and don't interfere. So if Wigner's friend undergoes decoherence, Wigner can't observe interference between different outcomes for his friend.

Undergoes decoherence? What does that mean? I know you undergo anesthesia but I never heard of someone that undergoes decoherence.

Let's answer it though using your vernacular.

Wigner's Friend "undergoes" decoherence not Wigner which is illustrated by Rovelli's Relational interpretation. This is only occurring in Wigner's Friend's frame of reference not Wigner's.

All physical interactions are, at bottom, quantum interactions, and must ultimately be governed by the same rules. Thus, an interaction between two particles does not, in RQM, differ fundamentally from an interaction between a particle and some "apparatus". There is no true wave collapse, in the sense in which it occurs in the Copenhagen interpretation.

Because "state" is expressed in RQM as the correlation between two systems, there can be no meaning to "self-measurement". If observer O measures system S, S's "state" is represented as a correlation between O and S. O itself cannot say anything with respect to its own "state", because its own "state" is defined only relative to another observer, O'. If the S+O compound system does not interact with any other systems, then it will possesses a clearly defined state relative to O'. However, because O's measurement of S breaks its unitary evolution with respect to O, O will not be able to give a full description of the S+O system (since it can only speak of the correlation between S and itself, not its own behaviour). A complete description of the (S+O)+O' system can only be given by a further, external observer, and so forth.

Taking the model system discussed above, if O' has full information on the S+O system, it will know the Hamiltonians of both S and O, including the interaction Hamiltonian. Thus, the system will evolve entirely unitarily (without any form of collapse) relative to O', if O measures S. The only reason that O will perceive a "collapse" is because O has incomplete information on the system (specifically, O does not know its own Hamiltonian, and the interaction Hamiltonian for the measurement).

https://en.wikipedia.org/wiki/Relational_quantum_mechanics

So for Wigner's Friend he "undergoes" decoherence and becomes part of an S+O system when he gains knowledge of the state the quantum system is in. What do I mean by gains knowledge?

It means Wigner's Friend gains knowledge of both states of the quantum system. You have a Wigner's Friend that records vertical polarization of the photon in his memory and Wigner's friend who records horizontal polarization in his memory. The interference between these two states decoheres but not because any wave function collapse. It's because both versions of Wigner's Friend has a lack of information about the overall S+O system and they perceive "collapse" and record the outcome.

The wave function has not collapsed so why shouldn't Wigner(O') be able to measure interference of the S+O system as long as he doesn't gain knowledge about his friend's state?

I think confusion comes into play because you're equating loss of intereference with collapse of the wave function.

 

[PeterDonis]

Undergoes decoherence?

If you are not familiar with decoherence theory, I would recommend taking some time to learn about it. It is an important part of our current understanding of QM.

Decoherence is a physical process, and a person is a physical system, so I don't see anything at all wrong with saying that a person undergoes decoherence.

The wave function has not collapsed so why shouldn't Wigner(O') be able to measure interference of the S+O system

Because the S+O system has a huge number of degrees of freedom, most of which cannot be tracked. The process of the friend (O) observing the system (S) spreads entanglement among all of those degrees of freedom. That is the physical process of decoherence.

The effect that that physical process has is to make it impossible for Wigner to, in the terminology of the Wikipedia article, have "full information" about the S+O system, because such information would have to include the information that has been spread by decoherence among the huge number of mostly untrackable degrees of freedom in the S+O system.

If, on the other hand, we stipulate by fiat that, however infeasible it is given the huge number of degrees of freedom in the S+O system, Wigner does have "full information" about that system, then we are stipulating that decoherence has not occurred in that system, and that in turn means the friend has not made any actual observation of anything. The "S" subsystem might have interacted with the "O" subsystem, but that is not the same as an actual observation being made. It is no different from the interaction of an electron with a Stern-Gerlach magnet, which by itself is not a measurement of the electron's spin; it just entangles the electron's spin with its momentum. Similarly, whatever is going on in the S+O system that does not lead to decoherence can't be a measurement of anything; it is just entangling some degrees of freedom in S with some degrees of freedom in O. And since that entanglement is reversible (because we have stipulated, however unrealistically, that decoherence has not occurred), it is not a measurement.

In other words, you can't have it both ways. You can't both say that the friend has actually made an observation, which requires decoherence to occur, and also say that Wigner can measure interference, which requires decoherence to not occur.

I think confusion comes into play because you're equating loss of intereference with collapse of the wave function.

No. See above.

 

[PeterDonis]

I think confusion comes into play because you're equating loss of intereference with collapse of the wave function.

Perhaps it's worth elaborating on my "no" response to this a little more.

In a no collapse interpretation, such as the MWI, decoherence still occurs--more precisely, decoherence is still required for "splitting" into multiple "branches" to occur. If interference between different alternatives is still possible, decoherence has not occurred, and those alternatives are not separate "worlds" or "branches" according to the MWI.

So in a Wigner's friend experiment where we stipulate by fiat (however unrealistically) that Wigner can detect interference, the MWI will agree with interpretations that do have collapse, because both kinds of interpretations will say that no measurement by the friend occurred at all--the friend, once again, is no different from an electron that has gone through a SG magnet but has not yet hit any detector screen.

 

[allisrelative]

Perhaps it's worth elaborating on my "no" response to this a little more.

In a no collapse interpretation, such as the MWI, decoherence still occurs--more precisely, decoherence is still required for "splitting" into multiple "branches" to occur. If interference between different alternatives is still possible, decoherence has not occurred, and those alternatives are not separate "worlds" or "branches" according to the MWI.

So in a Wigner's friend experiment where we stipulate by fiat (however unrealistically) that Wigner can detect interference, the MWI will agree with interpretations that do have collapse, because both kinds of interpretations will say that no measurement by the friend occurred at all--the friend, once again, is no different from an electron that has gone through a SG magnet but has not yet hit any detector screen.

Decoherence is still required for splitting into multiple branches?

Where's the scientific evidence for this? Is this speculation or observed evidence you're talking about?

You said:

If interference between different alternatives is still possible, decoherence has not occurred, and those alternatives are not separate "worlds" or "branches" according to the MWI.

What about many interacting worlds theory? Which speculative theory are you saying is the final word when it comes to decoherence?

Quantum Phenomena Modeled by Interactions between Many Classical Worlds

We investigate whether quantum theory can be understood as the continuum limit of a mechanical theory, in which there is a huge, but finite, number of classical “worlds,” and quantum effects arise solely from a universal interaction between these worlds, without reference to any wave function. Here, a “world” means an entire universe with well-defined properties, determined by the classical configuration of its particles and fields. In our approach, each world evolves deterministically, probabilities arise due to ignorance as to which world a given observer occupies, and we argue that in the limit of infinitely many worlds the wave function can be recovered (as a secondary object) from the motion of these worlds. We introduce a simple model of such a “many interacting worlds” approach and show that it can reproduce some generic quantum phenomena—such as Ehrenfest’s theorem, wave packet spreading, barrier tunneling, and zero-point energy—as a direct consequence of mutual repulsion between worlds. Finally, we perform numerical simulations using our approach. We demonstrate, first, that it can be used to calculate quantum ground states, and second, that it is capable of reproducing, at least qualitatively, the double-slit interference phenomenon.

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041013

Which speculative theory do you want me to go by?

Yes, Wigner can measure interference. That was the whole point of the published paper. If you want to refute it, then write a paper and get it peer reviewed.

Again, you're making the mistake that Wiki doesn't even make by confusing decoherence with collapse of the wave function.

Decoherence has been used to understand the collapse of the wave function in quantum mechanics. Decoherence does not generate actual wave-function collapse. It only provides an explanation for apparent wave-function collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wave function are decoupled from a coherent system and acquire phases from their immediate surroundings. A total superposition of the global or universal wavefunction still exists (and remains coherent at the global level), but its ultimate fate remains an interpretational issue. Specifically, decoherence does not attempt to explain the measurement problem.

https://en.wikipedia.org/wiki/Quantum_decoherence

So I ask again.

If the wave function hasn't actually collapsed for Wigner's friend and he just perceives collapse then why couldn't Wigner measure interference between the S+O system as long as he doesn't have knowledge of the state his friend observed?

 

[PeterDonis]

Decoherence is still required for splitting into multiple branches?

Yes.

Where's the scientific evidence for this?

There can't be any scientific evidence for one interpretation of QM over another.

The statement I said "yes" to above is a postulate of the MWI. It's not something that can be proved or disproved by evidence. It's part of the interpretation.

Which speculative theory do you want me to go by?

In this thread and this forum, none. In this thread and this forum, we are discussing interpretations of QM. Not interpretations of some other speculative theory.

If you want to talk about some other speculative theory, please start a new thread (with appropriate references) in the appropriate forum, which will probably be the Beyond the Standard Model forum.

Wigner can measure interference. That was the whole point of the published paper.

You can certainly stipulate that Wigner can measure interference in a particular thought experiment. What you can't do is stipulate that and then make use of intuitive arguments that assume that Wigner's friend has made an actual observation, the same way that we would make an actual observation in ordinary life.

If you search these forums, you will find plenty of previous threads on the Wigner's friend experiment, in which references to multiple papers are given that make arguments on both sides of questions like this.

 

[allisrelative]

What? You said:

You can certainly stipulate that Wigner can measure interference in a particular thought experiment. What you can't do is stipulate that and then make use of intuitive arguments that assume that Wigner's friend has made an actual observation, the same way that we would make an actual observation in ordinary life.

First, it wasn't just a thought experiment it was an actual experiment.

Next you said the way we make an observation in ordinary life? Are you talking about local realism? What exactly do you mean? Explain the science of "ordinary life."

Death by experiment for local realism

A fundamental scientific assumption called local realism conflicts with certain predictions of quantum mechanics. Those predictions have now been verified, with none of the loopholes that have compromised earlier tests.

https://www.nature.com/articles/nature15631

So scientifically, what do you mean by "ordinary life.?"

So you used an intepretation that you admit has no evidence to equate decoherence with wave function collapse?

Again, it's not a thought experiment, it's an actual experiment. The paper ended like this:

Because quantum theory does not distinguish between information recorded in a microscopic system (such as our photonic memory) and in a macroscopic system, the conclusions are the same for both: The measurement records are in conflict regardless of the size or complexity of the observer that records them. Implementing the experiment with more complex observers would not necessarily lead to new insights into the specific issue of observer independence in quantum theory. It would, however, serve to show that quantum mechanics still holds at larger scales, ruling out alternative (collapse) models (20). However, this is not the point of a Bell-Wigner test—less demanding experiments could show that.

https://www.researchgate.net/publication/335953720_Experimental_test_of_local_observer_independence

I'm not talking about "ordinary life" whatever that means or speculation about self collapse theories that could be right but at this point there's no evidence to support them. I'm talking about science that has been observed and tested.

Why don't you just admit that you used speculative M.W.I. to confuse decoherence with the collapse of the wave function?

 

[PeterDonis]

it wasn't just a thought experiment it was an actual experiment.

There have not been any actual Wigner's friend experiments involving people. There have been "Wigner's friend" experiments involving qubits. Qubits have only one degree of freedom. People have something like $10^{25}$. Big difference.

 

[PeterDonis]

quantum theory does not distinguish between information recorded in a microscopic system (such as our photonic memory) and in a macroscopic system as long as the system remains isolated and quantum coherence is maintained.

See my bolded addition in the quote above. It makes a big difference.

 

[allisrelative]

There have not been any actual Wigner's friend experiments involving people. There have been "Wigner's friend" experiments involving qubits. Qubits have only one degree of freedom. People have something like $10^{25}$. Big difference.

You're not debating science, you're speculating.

It's not a big difference according to Quantum Theory. Let me quote from the published paper again:

Because quantum theory does not distinguish between information recorded in a microscopic system (such as our photonic memory) and in a macroscopic system, the conclusions are the same for both: The measurement records are in conflict regardless of the size or complexity of the observer that records them. Implementing the experiment with more complex observers would not necessarily lead to new insights into the specific issue of observer independence in quantum theory. It would, however, serve to show that quantum mechanics still holds at larger scales, ruling out alternative (collapse) models (20). However, this is not the point of a Bell-Wigner test—less demanding experiments could show that.

https://www.researchgate.net/publication/335953720_Experimental_test_of_local_observer_independence

Your claim that it makes a big difference is just speculation. Does it make a big difference because of self collapse or M.W.I.?

You're not being very scientific. You use M.W.I. to confuse decoherence with wave function collapse. Now you claim there's a BIG DIFFERNCE without any evidence. Quantum Theory doesn't make a distinction between information recorded in a microscopic or macroscopic system.

Your BIG DIFFERENCE has to come from speculation just like your "Ordinary Life."

 

[PeterDonis]

You're not debating science, you're speculating.

No, I'm making valid points which you are not even responding to, you're just repeating the same claims over and over again.

Let me quote from the published paper again

Repeating the same quote over and over again is pointless.

Thread closed.