I Consciousness and quantum mechanics

[rasp]

TL;DR 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?

 

[Fred Wright]

“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.

I find this to be quite annoying. Wigner makes the assertion, "that the content of consciousness is an ultimate reality", playing fast and easy with non falsifiable, philosophical arguments which have nothing to do with quantum mechanics. No one knows what consciousness is, where it is, when it begins or when it ends. Imo Wigner's argument is merely a wordy justification for self-worship.

 

[PeterDonis]

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

The ideas you mention are from pop science books, not textbooks or peer-reviewed papers. If you look in actual textbooks or peer-reviewed papers, you will only very rarely see these ideas mentioned at all, and they are never used to make actual predictions.

 

[rasp]

I find this to be quite annoying. Wigner makes the assertion, "that the content of consciousness is an ultimate reality", playing fast and easy with non falsifiable, philosophical arguments which have nothing to do with quantum mechanics. No one knows what consciousness is, where it is, when it begins or when it ends. Imo Wigner's argument is merely a wordy justification for self-worship.

You may be right Fred, but I’m surprised your so sure of yourself. Isn’t there a basis in science to presume that nothing can be said about the existence of a quantum object until it is observed by a consciousness. Thereby making consciousness as Wigner asserts , “an ultimate reality”?

 

[rasp]

The ideas you mention are from pop science books, not textbooks or peer-reviewed papers. If you look in actual textbooks or peer-reviewed papers, you will only very rarely see these ideas mentioned at all, and they are never used to make actual predictions.

Your right about the pop science source. But Even they still require a rational Response. I’m not asking about Actual predictions. I’m asking about Theoretical fundamentals.

 

[PeterDonis]

Isn’t there a basis in science to presume that nothing can be said about the existence of a quantum object until it is observed by a consciousness.

No. This was a common misconception up until the theory of decoherence was worked out. Decoherence theory makes it obvious that quantum systems are being "measured" all the time by interactions with their environment, without any conscious observation being required.

Even they still require a rational Response.

Not here. We don't accept pop science sources as a basis for discussion since they are not reliable sources about actual physics.

I’m asking about Theoretical fundamentals.

And the place you should look for those is in textbooks and peer-reviewed papers, not pop science books.

 

[rasp]

I find this to be quite annoying. Wigner makes the assertion, "that the content of consciousness is an ultimate reality", playing fast and easy with non falsifiable, philosophical arguments which have nothing to do with quantum mechanics. No one knows what consciousness is, where it is, when it begins or when it ends. Imo Wigner's argument is merely a wordy justification for self-worship.

The ideas you mention are from pop science books, not textbooks or peer-reviewed papers. If you look in actual textbooks or peer-reviewed papers, you will only very rarely see these ideas mentioned at all, and they are never used to make actual predictions.

I understand your reluctance to comment on pop science. However, in my case I’m Not quoting the pop science writer but quoting Wigner. What I’m asking is is his restatement In English language of the observer’s role, in fact still an accurate portrayal of at least some interpretation of QM?

 

[DaveC426913]

...the observer’s role, in fact still an accurate portrayal of at least some interpretation of QM?

Technically, you are probably correct - there is probably at least one person out there who thinks so.

A better question would be is there any such hypothesis being seriously researched and published in peer reviewed papers?

 

[StevieTNZ]

You might find this paper interesting -- https://arxiv.org/abs/1609.00614

 

[haushofer]

No. This was a common misconception up until the theory of decoherence was worked out. Decoherence theory makes it obvious that quantum systems are being "measured" all the time by interactions with their environment, without any conscious observation being required.

Mmm. How to reconcile this with the fact that decoherence doesn't solve the measurement problem?

A measurement "collapses" the wavefunction, while environmental interactions don't, right? I always found this a bit confusing.

 

[atyy]

No. This was a common misconception up until the theory of decoherence was worked out. Decoherence theory makes it obvious that quantum systems are being "measured" all the time by interactions with their environment, without any conscious observation being required.

Although the environment is said to "measure" the system, it is only a pre-measurement. There are no outcomes with decoherence alone, and a measurement is still needed to discuss outcomes.

 

[PeterDonis]

in my case I’m Not quoting the pop science writer but quoting Wigner.

Your references are not pop science because they are written by "pop scientists" instead of "real scientists". They are pop science because they are not textbooks or peer-reviewed papers, so they have not gone through the kind of critical scrutiny that textbooks and peer-reviewed papers get. That means the authors can get away with saying things they know they would never get away with saying in a textbook or peer-reviewed paper. And experience shows that they do in fact do just that.

What I’m asking is is his restatement In English language of the observer’s role, in fact still an accurate portrayal of at least some interpretation of QM?

It might be, but his claim was not about some particular interpretation of QM; his claim, as you quoted it in the OP, was a general claim that, if it were true, would have to apply to QM itself, as a theory, independent of any interpretation. And as such a general claim, the claim is false.

 

[PeterDonis]

A measurement "collapses" the wavefunction, while environmental interactions don't, right?

As far as decoherence theory is concerned, no; environmental interactions are the same as "measurements" done as experiments in the lab. In both cases, entanglement is spread over a very large, untrackable number of degrees of freedom. That is the key.

Although the environment is said to "measure" the system, it is only a pre-measurement.

No, it is a measurement. The only difference is that in interaction with the environment, there are no particular degrees of freedom that are picked out as "the ones being measured", while in a lab measurement, there are. But in both cases, outcomes occur without any conscious observers needing to be involved. Or more precisely, the basic rules of QM do not require any conscious observers to be involved in order to treat outcomes as having occurred (i.e., "collapsing" the wave function to be used for making future predictions). Some interpretations might say that "in reality" no outcome occurs until a conscious observer has observed it, but that is interpretation-dependent; there is no such requirement in the basic rules of QM, and in practice nobody imposes any such requirement when actually using QM.

 

[atyy]

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?

Quantum mechanics as usually presented does depend on a subjective concept of "measurement", as something in addition to unitary time evolution of the quantum state. In that sense, "measurement" seems somewhat like "consciousness". However, it is difficult to discuss the link or non-link between "measurement" and "consciousness" since both words are not well understood. Apart from Wigner, you may like to know about the comments of von Neumann in his classical text https://en.wikipedia.org/wiki/Von_Neumann–Wigner_interpretation.

The special status of measurement in quantum mechanics is called the measurement problem: https://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf. There are attempts to solving the measurement problem, such as Bohmian mechanics. In Bohmian mechanics, "measurement" does not have a special status. However, it is not known whether Bohmian mechanics can explain the full range of quantum phenomena, and even if it could, we do not know whether it is true. Another major attempt to solving the measurement problem by removing the special status of "measurement" is the Many-Worlds Interpretation.

 

[atyy]

No, it is a measurement. The only difference is that in interaction with the environment, there are no particular degrees of freedom that are picked out as "the ones being measured", while in a lab measurement, there are. But in both cases, outcomes occur without any conscious observers needing to be involved. Or more precisely, the basic rules of QM do not require any conscious observers to be involved in order to treat outcomes as having occurred (i.e., "collapsing" the wave function to be used for making future predictions). Some interpretations might say that "in reality" no outcome occurs until a conscious observer has observed it, but that is interpretation-dependent; there is no such requirement in the basic rules of QM, and in practice nobody imposes any such requirement when actually using QM.

No, you are wrong. Decoherence is not a measurement. We are not able to discuss definite outcomes with decoherence alone.

 

[PeterDonis]

Quantum mechanics as usually presented does depend on a subjective concept of "measurement"

In the sense that the theory does not tell you what a "measurement" is, but just tells you to use your best judgment in putting "measurements" wherever you need to to make correct predictions, yes.

We are not able to discuss definite outcomes with decoherence alone.

I didn't say we were. I simply said that the rules of basic QM don't care whether the "measurement" process that produces definite outcomes occurs in a lab or not, or whether it involves human observers, or whether it was purposely set up by humans as a "measurement".

For example, as far as the basic rules of QM are concerned, the Moon is there even if nobody is looking at it, because the Moon's interaction with its environment (which includes itself--the huge number of degrees of freedom in the Moon are continually interacting with each other) is just as good as a detector in a lab at producing a definite outcome. There is no special status accorded to "detectors" that humans just happen to be looking at, or that humans have set up in labs and labeled as "experiments". Hence, we can treat the Moon as a classical object without having to worry about whether someone happens to be doing something to it that counts as a "measurement".

The role decoherence theory plays is to give a detailed explanation of how the interactions among all of these degrees of freedom that can't be individually tracked make the quantum interference terms in the overall wave function disappear, so that we have well-defined classical alternatives. You are correct that decoherence alone cannot pick just one alternative as the outcome; for that we need additional rules, which basic QM provides. But, as above, there is no need to have a human observer present or to set up a particular experiment in a lab in order to apply those additional rules. You do it, as basic QM says, wherever you need to to make good predictions. Applying the rule to assign a single outcome to what the Moon is doing even when no one is looking at it makes good predictions; hence, basic QM tells us it's fine to apply the rule in that case.

 

[PeterDonis]

The role decoherence theory plays is to give a detailed explanation of how the interactions among all of these degrees of freedom that can't be individually tracked make the quantum interference terms in the overall wave function disappear, so that we have well-defined classical alternatives.

I should add that decoherence theory also shows how, for example, what happens when the electron makes a spot on the detector screen in a Stern-Gerlach experiment is the same kind of process that happens inside the Moon, or any ordinary object, when it interacts with its environment. In both cases, you have entanglement spreading over a very large number of untrackable degrees of freedom. The fact that this process is similar in both cases explains why classical alternatives get picked out in both cases.

 

[atyy]

@PeterDonis, what you are saying seems implicitly Bohmian-like - the moon is there when no one is looking (ie. particles have trajectories or hidden variables). I agree that if you apply a Bohmian interpretation, then it may be that the measurement problem is solved and we don't need to give a special status to "measurement" or "consciousness" or whatever we may like to call this extra element with fundamental status in the theory. However, we do not yet know whether a Bohmian-like theory can even in principle cover all quantum phenomena, so I think what you are saying is speculative.

As long as the measurement problem is open, and there is the subjectivity as to when a measurement occurs, I think one has to grant that von Neumann and Wigner did have a point.

 

[Stephen Tashi]

A related question to whether consciousness is required for a measurement is whether consciousness itself is a measurement - i.e. does the presence of consciousness imply that at least a few physical things have taken on specific values from the many possible values that are possible in their quantum state?

As has been said, nobody knows what consciousness is. However, if we are thinking of it as some physically implemented phenomena, it seems to fair to think of its physical process as being similar to other complex phenomena like the weather, city traffic, or "the environment" in general. Do we regard complex physical processes like that as being equivalent to a large number of measurements? - or no particular measurement?

 

[PeterDonis]

what you are saying seems implicitly Bohmian-like

No, it's just the basic rules of QM, as I said.

As long as the measurement problem is open, and there is the subjectivity as to when a measurement occurs

The measurement problem is the problem of explaining why the basic rules of QM work, or, if you like, putting the basic rules on a firmer conceptual foundation than just "apply the collapse postulate wherever it gives the best predictions". But the fact that they work--that we make good predictions by treating objects like the Moon classically, hence applying the "collapse" postulate of basic QM to them continuously to assign a definite outcome to where they are and how they are moving, even when no conscious observer is watching them--is not in question.

 

[EPR]

If we can make macroscopic stuff behave quantum mechanically and observe the process with human vision, it would clearly mean we are not the measuring apparatus.
We can observe such behavior - hence the argument that consciousness measures quantum states must be false.

https://www.newsweek.com/fifth-state-matter-iss-1510436

 

[atyy]

No, it's just the basic rules of QM, as I said.

I don't think the basic rules of QM say the moon is there when one isn't looking. I think they are silent on that issue.

 

[Stephen Tashi]

If we can make macroscopic stuff behave quantum mechanically and observe the process with human vision,

With vision, do we observe quantum mechanical behavior except by repeatedly making things is a quantum state take specific values and then compiling the statistics of these results?

 

[EPR]

With vision, do we observe quantum mechanical behavior except by repeatedly making things is a quantum state take specific values and then compiling the statistics of these results?

We.can observe it directly with some setups. Superfluidity: How Quantum Mechanics Became Visible.

https://link.springer.com/chapter/10.1007/978-94-007-7199-4_6

 

[AndreasC]

In the sense that the theory does not tell you what a "measurement" is, but just tells you to use your best judgment in putting "measurements" wherever you need to to make correct predictions, yes.
I didn't say we were. I simply said that the rules of basic QM don't care whether the "measurement" process that produces definite outcomes occurs in a lab or not, or whether it involves human observers, or whether it was purposely set up by humans as a "measurement".

For example, as far as the basic rules of QM are concerned, the Moon is there even if nobody is looking at it, because the Moon's interaction with its environment (which includes itself--the huge number of degrees of freedom in the Moon are continually interacting with each other) is just as good as a detector in a lab at producing a definite outcome. There is no special status accorded to "detectors" that humans just happen to be looking at, or that humans have set up in labs and labeled as "experiments". Hence, we can treat the Moon as a classical object without having to worry about whether someone happens to be doing something to it that counts as a "measurement".

The role decoherence theory plays is to give a detailed explanation of how the interactions among all of these degrees of freedom that can't be individually tracked make the quantum interference terms in the overall wave function disappear, so that we have well-defined classical alternatives. You are correct that decoherence alone cannot pick just one alternative as the outcome; for that we need additional rules, which basic QM provides. But, as above, there is no need to have a human observer present or to set up a particular experiment in a lab in order to apply those additional rules. You do it, as basic QM says, wherever you need to to make good predictions. Applying the rule to assign a single outcome to what the Moon is doing even when no one is looking at it makes good predictions; hence, basic QM tells us it's fine to apply the rule in that case.

I am a little bit confused. It might be a very dumb question but in the case of, say, the double slit experiment, the way it is usually explained is that the lack of measurement is fundamental to the interference pattern observed, and that if you made a measurement about which slit the photon passed through before the slit, the pattern would be destroyed. This always seemed kinda weird to me, I guess there is something that I haven't understood properly. When light passes through one slit, it may interact, no matter how weakly, with a bunch of air particles around it, right? So if that counts as a rough position "measurement", shouldn't light be "measured" no matter what before it gets to the slit? How is it that we still see the interference pattern then?

 

[Lord Jestocost]

I am a little bit confused. It might be a very dumb question but in the case of, say, the double slit experiment, the way it is usually explained is that the lack of measurement is fundamental to the interference pattern observed, and that if you made a measurement about which slit the photon passed through before the slit, the pattern would be destroyed.

There is no need to "make a measurement" about which slit the photon passed through to blurr the interference patter. Have a look at chapter 3-2 "The two-slit interference pattern" of The Feynman Lectures on Physics, Volume III. As stated by Časlav Brukner in "Elegance and Enigma, The Quantum Interviews" (edited by Maximilian Schlosshauer):

"... any increase of partial information about the particle’s path will always mean a corresponding loss in visibility of the interference pattern, and vice versa. Most importantly, it is not relevant whether we read out that information. All that is necessary is for the information to be present somewhere in the universe."
[Bold by LJ]

 

[Lord Jestocost]

Although the environment is said to "measure" the system, it is only a pre-measurement. There are no outcomes with decoherence alone, and a measurement is still needed to discuss outcomes.

There is another problem. Quoting Ruth E. Kastner ( ‘Einselection’ of pointer observables: The new H-theorem?, https://arxiv.org/abs/1406.4126 ):

"It is often claimed that unitary-only dynamics, together with decoherence arguments, can explain the ‘appearance’ of wave function collapse, i.e, that Schrodinger’s Cat is either alive or is dead. This however is based on implicitly assuming that macroscopic systems (like Schrodinger’s Cat himself) are effectively already ‘decohered,’ since the presumed phase randomness of already-decohered systems is a crucial ingredient in the ‘derivation’ of decoherence. Thus decoherence arguments alone do not succeed in providing for the emergence of a classical world, nor for the necessary preferred basis of splitting in an Everettian account, and their explanatory benefit is illusory.”

 

[AndreasC]

There is no need to "make a measurement" about which slit the photon passed through to blurr the interference patter. Have a look at chapter 3-2 "The two-slit interference pattern" of The Feynman Lectures on Physics, Volume III. As stated by Časlav Brukner in "Elegance and Enigma, The Quantum Interviews" (edited by Maximilian Schlosshauer):

"... any increase of partial information about the particle’s path will always mean a corresponding loss in visibility of the interference pattern, and vice versa. Most importantly, it is not relevant whether we read out that information. All that is necessary is for the information to be present somewhere in the universe."
[Bold by LJ]

Right, but that's my issue. How is it possible that we observe such patterns at all if it is this easy for them to get blurred?

 

[Lord Jestocost]

Is it easy? You have always to estimate the probability that a 'Wich path information?' could remain somewhere in the universe. Have a look at Chapter 3 "Probability Amplitudes" of The Feynman Lectures on Physics, Volume III.

 

[AndreasC]

Is it easy? You have always to estimate the probability of "A 'Wich path information?'" which could present somewhere in the universe.

I'm a bit confused by this comment. It seems easy to me because if the photon interacting with any particle at all counts as a "measurement", as it was claimed, then surely the photons or electrons or whatever interacting with, say, the air molecules just before the slit would be enough to destroy it.

 

[PeterDonis]

I don't think the basic rules of QM say the moon is there when one isn't looking.

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.

 

[PeterDonis]

if the photon interacting with any particle at all counts as a "measurement"

That's not what is being said. What is being said is that spreading entanglement due to interactions over a very large number of untrackable degrees of freedom counts as a "measurement".

 

[EPR]

I'm a bit confused by this comment. It seems easy to me because if the photon interacting with any particle at all counts as a "measurement", as it was claimed, then surely the photons or electrons or whatever interacting with, say, the air molecules just before the slit would be enough to destroy it.

Weak interactions(photon and air molucules) do not generally produce collapse. Molecules of metals, plastics, etc. are another matter.

 

[AndreasC]

That's not what is being said. What is being said is that spreading entanglement due to interactions over a very large number of untrackable degrees of freedom counts as a "measurement".

Alright, so doesn't that happen in the case of the interactions before the slit?

 

[AndreasC]

Weak interactions(photon and air molucules) do not generally produce collapse. Molecules of metals, plastics, etc. are another matter.

Why is that? Where is the boundary?

 

[PeterDonis]

Where is the boundary?

The interactions with the air molecules are far too weak to cause decoherence (loss of phase coherence). The interactions with something like a detector screen are not, due to the screen's much higher density.

 

[f95toli]

Right, but that's my issue. How is it possible that we observe such patterns at all if it is this easy for them to get blurred?

It is only "easy" if you use light since photons do not really interact very much with their environment when traveling in vacuum. Generally speaking it is very hard to get a systems to exhibit "quantum behaviour". This is not for any "philosophical" reason but simply because you need to isolate the system extremely well to avoid decoherence.
These days we have a very good understanding for which interactions cause decoherence and we are getting better and better at isolating our systems using ultra high vacuum, low temperatures, ultra-clean materials etc

There are no conceptual problems here; it is just that it is technically very hard.

 

[Stephen Tashi]

We.can observe it directly with some setups.

If we call watching a video "observing directly", we could say that looking at the interference pattern forming in a double slit experiment is observing quantum behavior directly. When things like this happen are we observing Nature doing measurements?

I suppose one could go back and forth on that question depending on whether we think of dots on a screen or cells in the retina reacting to photons as completely specific events (in the classical sense) or whether there are aspects of these events, such as their position, that do not have unique values.

 

[EPR]

I think you can be allowed near the glass and see for yourself water flowing upwards due to quantum superfluidity. This counts as direct observation.
Macroscopic superposition phenomena(BEC's incusive) tend to be less weird than the behaviour of single particles. Perhaps because of averaging.

 

[PeroK]

If we call watching a video "observing directly", we could say that looking at the interference pattern forming in a double slit experiment is observing quantum behavior directly. When things like this happen are we observing Nature doing measurements?

I suppose one could go back and forth on that question depending on whether we think of dots on a screen or cells in the retina reacting to photons as completely specific events (in the classical sense) or whether there are aspects of these events, such as their position, that do not have unique values.

Anything you see involves absorption of photons by your retina. You don't get more quantum than that!

 

[Stephen Tashi]

I think you can be allowed near the glass and see for yourself water flowing upwards due to quantum superfluidity. This counts as direct observation.

I agree that if we have a theory that predicts a measurement then doing the experiment and observing that the measurement agrees with theory is (in a manner of speaking) directly observing the theory.

However, I think you are saying we observe the predictions of QM by doing an experiment and somehow observing something that is not a measurement.

 

[Stephen Tashi]

Anything you see involves absorption of photons by your retina. You don't get more quantum than that!

My question isn't whether such outcomes obey statistics predicted by QM. The question is whether the individual outcomes are particular outcomes from the set of possible outcomes. I gather that the conventional view is that they are not. If they were, we'd have to say which observables take on specific values. Then other non-commuting observables would not have particular values.

Of course their might be salvation through mathematics. Perhaps we can analyze complex physical process by picking a set of observables arbitrarily and modeling a specific occurence of the process as those observables taking on specific values. If the statistical predictions for replications of the process agree no matter which set of observables is chosen, then we are free to imagine the process as sequence of wave function collapses in various ways.

I don't know whether the Monte-Carlo method is used in QM models of phenomena. If it is used, what events define a specific realization of the phenomena? Are the events effectively wave function collapses?

 

[PeroK]

My question isn't whether such outcomes obey statistics predicted by QM. The question is whether the individual outcomes are particular outcomes from the set of possible outcomes.

How can they be anything else? If they are outcomes, they must be from the set of possible outcomes.

 

[Stephen Tashi]

How can they be anything else? If they are outcomes, they must be from the set of possible outcomes.

Yes, if we begin by accepting that a "real" occurrence of a physical process must be a set of particular outcomes from a set of possible outcomes - i.e. a sequence of wave function collapses. But do we accept this type of model?

 

[PeroK]

Yes, if we begin by accepting that a "real" occurrence of a physical process must be a set of particular outcomes from a set of possible outcomes - i.e. a sequence of wave function collapses. But do we accept this type of model?

I'm not sure I understand the question. QM is a model. Whether we accept it is largely down to its predictive capacity. Everything else is inferred.

 

[Stephen Tashi]

I'm not sure I understand the question. QM is a model. Whether we accept it is largely down to its predictive capacity. Everything else is inferred.

To put the question in concrete terms, suppose I want do a Monte Carlo simulation of a double slit experiment. One approach is to compute the probability density for the particle landing at location (x,y) on the screen that is implied by its wave function. Another approach would be to imagine that there are intermediate stages to the process and that the particle is actually somewhere before it hits the screen. For example, it is well known (I think) that simulating the position of the particle with the model that gives it a 0.5 probability of passing through either slit at a non-random time doesn't work. (I don't know whether there is a joint distribution of which-slit and what-time that does.)

Generalizing to complex phenomena like the weather, can we (theoretically) model a particular occurrence of the weather at time T5 by modeling some initial state of a system at time T0 and Monte Carlo-ing the evolution of the system as a sequence of wave function collapses between T0 and T5? Or would we always get different statisics than those implied by computing the evolution of the wave function from T0 to T5?

The way the question is posed, it doesn't specify a particular method for continuing the simulation after a wave function collapse occurs at an intermediate time T2, T0 < T2 < T5. So a proof that there is no possible way to model the evolution of the system as a sequence of wave function collapses would be a strong result.

 

[PeroK]

One approach is to compute the probability density for the particle landing at location (x,y) on the screen that is implied by its wave function.

That's right.

Another approach would be to imagine that there are intermediate stages to the process and that the particle is actually somewhere before it hits the screen.

That won't work. You can't imagine the particle takes a well-defined path and a sequence of wave function collapes.

 

[Stephen Tashi]

You can't imagine the particle takes a well-defined path and a sequence of wave function collapes.

A well defined path would be an infinite sequences of wave function collapses, wouldn't it?

 

[PeroK]

A well defined path would be an infinite sequences of wave function collapses, wouldn't it?

It doesn't really matter whether it's an infinite or finite sequence, it's not the way QM works.

The Feynman path integral formulation works on probability amplitudes, but those are not wave function collapses.

 

[Stephen Tashi]

It doesn't really matter whether it's an infinite or finite sequence, it's not the way QM works.

I agree, but I think you have in mind a particular way of simulating a process as a sequence of intermediate wave collapses - not the question of whether it can be done if we are allowed complete freedom of choice in how to do this and how to model the process after the collapse.

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. If that is the case then how is it that natural processes cause wave function collapses? To model how natural processes cause wave function collapses, must we model the process by stochastically picking times when it will cause a collapse? Or does the consciousness-causes-collapse theory get a second wind by virtue of the fact that a conscious observer must choose when to observe the process?