Counterfactual Definiteness and MWI in Wiki

[TunnelingthuWorlds]

TL;DR

Counterfactual Definitiveness and Many World's Interpretation

Summary: Counterfactual Definitiveness and Many World's Interpretation

Sorry for all these threads, my noetic fluids and bursting.

Wiki states the following:

In quantum mechanics, counterfactual definiteness (CFD) is the ability to speak "meaningfully" of the definiteness of the results of measurements that have not been performed (i.e., the ability to assume the existence of objects, and properties of objects, even when they have not been measured). The term "counterfactual definiteness" is used in discussions of physics calculations, especially those related to the phenomenon called quantum entanglement and those related to the Bell inequalities.[1] In such discussions "meaningfully" means the ability to treat these unmeasured results on an equal footing with measured results in statistical calculations. It is this (sometimes assumed but unstated) aspect of counterfactual definiteness that is of direct relevance to physics and mathematical models of physical systems and not philosophical concerns regarding the meaning of unmeasured results.
"Counterfactual" may appear in physics discussions as a noun. What is meant in this context is "a value that could have been measured but, for one reason or another, was not.Then proceeds to state in regards to the import of CFD to MWI:

The Many Worlds interpretation rejects counterfactual definiteness in a different sense; instead of not assigning a value to measurements that were not performed, it ascribes many values. When measurements are performed each of these values gets realized as the resulting value in a different world of a branching reality. Thus although unperformed experiments have values, they cannot be used in statistical calculations as one would the single value of a performed experiment. As Prof. Guy Blaylock of the University of Massachusetts Amherst puts it, "The many-worlds interpretation is not only counterfactually indefinite, it is factually indefinite as well." [19]

Can someone help me understate the part Prof. Guy Blaylock is pointing towards, and whether or not you agree with everything as stated?

 

[PeterDonis]

Wiki states the following

What Wikipedia article are you quoting from? Please provide a link.

 

[TunnelingthuWorlds]

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

 

[PeterDonis]

Can someone help me understate the part Prof. Guy Blaylock is pointing towards

He's saying that the MWI is not "factually definite" because it does not assign a single unique result to a measurement that is performed; it assigns multiple results.

whether or not you agree with everything as stated?

The statement about the MWI not being "factually definite" in the sense I described above is correct.

I don't think the statement about how the MWI denies counterfactual definiteness is correct. The MWI does not assign any result to measurements that are not performed. It assigns multiple results to measurements that are performed.

 

[TunnelingthuWorlds]

He's saying that the MWI is not "factually definite" because it does not assign a single unique result to a measurement that is performed; it assigns multiple results.

But, I thought MWI was superdeterministic. Hence, the decidability of outcomes is predetermined, are they not?

 

[PeterDonis]

I thought MWI was superdeterministic

Why do you think that?

 

[TunnelingthuWorlds]

Why do you think that?

Wiki again:
The many-worlds interpretation (MWI) is an interpretation of quantum mechanics that asserts that the universal wavefunction is objectively real, and that there is no wavefunction collapse.[2] This implies that all possible outcomes of quantum measurements are physically realized in some "world" or universe.[3] In contrast to some other interpretations, such as the Copenhagen interpretation, the evolution of reality as a whole in MWI is rigidly deterministic.[2]

Click on [2]

 

[TunnelingthuWorlds]

From the Preface:

In 1957, in his Princeton doctoral dissertation, Hugh Everett, III, proposed a new interpretation of quantum mechanics that denies the existence of a separate classical realm and asserts that it makes .sense to talk about a state vector for the whole universe. This state vector never collapses, and hence reality as a whole is rigorously deterministic. This reality, which is described jointly by the dynamical variables and the state vector, is not the reality we customarily think of, but is a reality composed of many worlds. By virtue of the temporal development of the dynamical variables the state vector decomposes naturally into orthogonal vectors, reflecting a continual splitting of the universe into a multitude of mutually unobservable but equally real worlds, in each of which every good measurement has yielded a definite result and in most of which the familiar statistical quantum laws hold.

 

[Dr.AbeNikIanEdL]

None of your quotes contain the word “superdeterministic”...

 

[Demystifier]

But, I thought MWI was superdeterministic. Hence, the decidability of outcomes is predetermined, are they not?

In MWI the outcomes are predetermined, meaning that it is deterministic. But it is not superdeterministic. Superdeterministic means that initial conditions are fine tuned so that the particular solution (of the equations of motion) associated with those initial conditions obeys a rule that most other solutions do not obey.

 

[TunnelingthuWorlds]

In MWI the outcomes are predetermined, meaning that it is deterministic. But it is not superdeterministic. Superdeterministic means that initial conditions are fine tuned so that the particular solution (of the equations of motion) associated with those initial conditions obeys a rule that most other solutions do not obey.

But, if the wavefunction keeps on evolving, then each iteration or (insert word for a system that evolves on its own without external input), then doesn't that mean that the initial conditions were fine-tuned?

 

[Demystifier]

But, if the wavefunction keeps on evolving, then each iteration or (insert word for a system that evolves on its own without external input), then doesn't that mean that the initial conditions were fine-tuned?

Not really. It is quite a generic property for all solutions with a low coarse-grained entropy. Of course, most solutions do not have a low coarse-grained entropy, so there is some "fine tuning" involved. Essentially, that's the "fine tuning" that is needed for the emergence of the 2nd law of thermodynamics. But apart from the 2nd law, there is no any other independent law that emerges from such "fine tuning". Hence it is a rather mild form of "fine tuning" so it is usually not viewed as superdeterminism. A more precise way to express this idea is to note that a low entropy initial state has low complexity, while a truly fine tuned initial condition has to have a large complexity.

 

[TunnelingthuWorlds]

Not really. It is quite a generic property for all solutions with a low coarse-grained entropy. Of course, most solutions do not have a low coarse-grained entropy, so there is some "fine tuning" involved. Essentially, that's the "fine tuning" that is needed for the emergence of the 2nd law of thermodynamics. But apart from the 2nd law, there is no any other independent law that emerges from such "fine tuning". Hence it is a rather mild form of "fine tuning" so it is usually not viewed as superdeterminism. A more precise way to express this idea is to note that a low entropy initial state has low complexity, while a truly fine tuned initial condition has to have a large complexity.

So, didn't you just describe the dynamics of the wavefunction here or can it possibly be a top-down approach instead of a bottom-up one in this case?

 

[Demystifier]

So, didn't you just describe the dynamics of the wavefunction here

Yes I did.

or can it possibly be a top-down approach instead of a bottom-up one in this case?

It's a bottom-up description.

 

[TunnelingthuWorlds]

It's a bottom-up description.

Without deviating from this great thread, what is the consensus amongst physicists, and mathematicians?

 

[Demystifier]

Without deviating from this great thread, what is the consensus amongst physicists, and mathematicians?

Consensus about what? Perhaps you mean consensus about whether physics should be done bottom-up or top-down? In that case the consensus is that the fundamental laws are to be searched in a top-down manner, but once they are found they are to be used in the bottom-up manner.

 

[PeterDonis]

Wiki again

None of what you quote says that the MWI is superdeterministic, just that it is deterministic.

 

[TunnelingthuWorlds]

None of what you quote says that the MWI is superdeterministic, just that it is deterministic.

I'm churning through this thread.:

https://www.physicsforums.com/threads/many-worlds-superdeterministic.831205/
Anyone welcome to comment or revise beliefs held since some long 4 years.

 

[PeterDonis]

I'm churning through this thread

Which also doesn't say the MWI is superdeterministic. The thread title asks a question, and the answer to the question is no.

 

[TunnelingthuWorlds]

Ok, then it's rigidly deterministic.

Can we stop the pissing contest?

 

[DarMM]

Ok, then it's rigidly deterministic.

Can we stop the pissing contest?

Superdeterministic and deterministic are different terms with very different implications, they have to be kept separate. And @PeterDonis is correct, Many Worlds is not superdeterministic.

 

[PeterDonis]

Can we stop the pissing contest?

You're the one that raised the issue of the MWI being superdeterministic. We are simply answering your question. This attitude is not called for, and has just got you a warning and your thread closed (and your original question has been answered anyway).