The Many-Worlds Interpretation of QM

[bhobba]

The Schlosshauer quote talks about "the preferred states of a system" and how they are determined by the system's interactions with its environment. So it only says that given a decomposition, there's a preferred basis. It doesn't suggest that there's a preferred decomposition.

It becomes clearer as you read more of the reference I quoted from. But basically it singles out the basis of observables that commute with the interaction Hamiltonian between the system and the environment that is causing the decoherence - obviously they are the ones that don't vary with time. Mostly, from what I have read, that is something like a coulomb interaction and evidently the observable that tends to commute with is position.

I guess the assumption is given any interaction Hamiltonian a unique observable and hence basis exists that it commutes with. That at least one exists is the problem of any outcomes at all - but there is another one - there may be more than one - although I am unaware of any such cases.

Regarding the other stuff such as a unique set of worlds I think we run into semantic issues with MWI. Basically there is really only one universe but when decoherence occurs the basis it produces as the mixture that continues to evolve is thought of as separate worlds. This however is just a way to describe the situation - its not really a separate world - there is really only one world or universe. This doesn't mean I hold to the MWI - its far too 'extravagant' as one guy I seem to recall said about it with all these new 'worlds' being created exponentially and with a different version of me in every one of them.

Thanks
Bill

 

[HomogenousCow]

QM is bizzare

-Is QM a true theory?, i.e. is the universe probabilistic at the core?
I find this question and its implications highly disturbing. Now if it were true that QM is simply a "front" for a true deterministic theory, where did we go wrong? How did we stumble upon a completely statistical theory when we were not even looking for one? One would expect that we would simply have a less accurate theory, not a theory with a completely different structure and physical output.

-Are interpretations simply human rationalizations?
I find this possibility even more disturbing, the fact that perhaps we will never understand the true nature of nature, because it is simply inaccessible to our intuition, if not our mathematics.

-Just what exactly is a measurement?
If I walk into a room with electrons, in a sense I am preforming a measurement on all of them, in the sense that my body is interacting with the electrons. The point is that we can always deduce something about a system no matter what, hence we are always measuring everything. The measurement axiom of QM is probably the least mathematically well defined axiom in all of physics.

 

[Fredrik]

It becomes clearer as you read more of the reference I quoted from.

I disagree. I mean, you're talking about things that we all agree about, but these are things that can't shed any light on the issue that I've brought up. I don't know what I should try to explain better, since we're talking about two different things.

I think you, me, Schlosshauer and that MWI article are all in complete agreement that the interaction between subsystems of the universe selects a basis. But you can't even begin to talk about the interaction between the subsystems until you have chosen a decomposition of the universe into subsystems. So the preferred basis is only preferred relative to that decomposition, and the decomposition is arbitrary.

Note that the subsystems are not the worlds. They are things like "the cat" and "the cat's environment". "Bill + Bill's environment" is one decomposition. "Fredrik + Fredrik's environment" is another. Both are equally valid. Each one gives us a preferred basis for the Hilbert space of "the system", but these are different systems, and their Hilbert spaces are two different subspaces of the Hilbert space of the universe. So a basis for one of them isn't a basis for the other one.

But basically it singles out the basis of observables that commute with the interaction Hamiltonian between the system and the environment that is causing the decoherence - obviously they are the ones that don't vary with time. Mostly, from what I have read, that is something like a coulomb interaction and evidently the observable that tends to commute with is position.

I understand these things, but the "interaction Hamiltonian between the system and the environment" will depend on which part of the universe that you choose to call "the system". Given a decomposition of the universe into "the system" + "its environment" , the interaction selects a basis. But the decomposition is an arbitrary choice made by the person doing the calculation.

Regarding the other stuff such as a unique set of worlds I think we run into semantic issues with MWI. Basically there is really only one universe but when decoherence occurs the basis it produces as the mixture that continues to evolve is thought of as separate worlds. This however is just a way to describe the situation - its not really a separate world - there is really only one world or universe. This doesn't mean I hold to the MWI - its far too 'extravagant' as one guy I seem to recall said about it with all these new 'worlds' being created exponentially and with a different version of me in every one of them.

I chose to call the single physical system that QM supposedly describes "the universe", lacking a better word. Penrose has suggested "the omnium", but I haven't seen anyone else use it. In my usage, a "world" is not synonymous to "the universe", because the latter refers to a single physical system, and the (many) "worlds" are aspects of its properties.

 

[Fredrik]

-Is QM a true theory?, i.e. is the universe probabilistic at the core?
I find this question and its implications highly disturbing. Now if it were true that QM is simply a "front" for a true deterministic theory, where did we go wrong? How did we stumble upon a completely statistical theory when we were not even looking for one? One would expect that we would simply have a less accurate theory, not a theory with a completely different structure and physical output.

If there's a deterministic underlying theory, then I think "what went wrong" is just that it was much easier to find a theory that assigns probabilities to measurement results than to find one that describes what's actually happening.

-Are interpretations simply human rationalizations?
I find this possibility even more disturbing, the fact that perhaps we will never understand the true nature of nature, because it is simply inaccessible to our intuition, if not our mathematics.

I find it pretty disturbing too. Even if it's accessible to intuition and mathematics, it may still be inaccessible to science, in the sense that we may find several theories that look like they might be descriptions of what's actually happening, but they that don't give us any new predictions.

-Just what exactly is a measurement?
If I walk into a room with electrons, in a sense I am preforming a measurement on all of them, in the sense that my body is interacting with the electrons. The point is that we can always deduce something about a system no matter what, hence we are always measuring everything. The measurement axiom of QM is probably the least mathematically well defined axiom in all of physics.

The problem is that each theory consists of a purely mathematical part and a set of correspondence rules that tell us how to interpret the mathematics as predictions about results of experiments. The correspondence rules are always non-mathematical, and never really well-defined. This is disturbing too, but it's just the way it is, and we will never be able to do anything about it.

The funny thing about correspondence rules is that so far, science has done pretty well without ever writing down a complete set of correspondence rules for any theory. It would actually be really hard to write them down. Consider e.g. a correspondence rule about how to measure time. It would have to describe what sort of things we are allowed to think of as "clocks", and tell us how to build clocks. So how do we do write down this rule for classical SR, when the best clocks rely on QM? The only answer I've been able to come up with goes like this: We define a hierarchy of theories. In the level 0 versions of SR and QM, we describe measuring devices that are extremely easy to build, but probably not very accurate. For every positive integer n, when we write down the level n versions of SR and QM, the correspondence rules must be such that they can be followed by a person who understands the level n-1 theories and has access to level n-1 measuring devices.

 

[Maui]

The only thing you can do with experiments is to find out how accurate the theory's predictions are.

No, there exist interpretations that are not part of the perdictive theory and these interpretations can be tested for viability in experiements. Look at the quantum eraser by Kim et al and you'll notice how there are detectors(D0--D0) at all possible photon paths all the time but you only get quantum behavior(interference pattern)when the which-way information cannot be obtained(D1 and D2). Whenever the which-way information can be obtained(D3 and D4) for the idler photon, there is no interference pattern when compared at the coincidence counter with the signal photon. So it cannot be the detector nor its photons that cause the wavefunction to collapse to an eigenstate of the observable. It makes no sense to apply a world splitting to something so obvious as the quantum eraser as it would explain nothing about why the interference pattern happens to disappear whenever information about what the system was doing between observations was available.

They can't possibly tell us anything else. What you're saying is clearly impossible.

No, the role of the interpretations is to tell us more than the theory(qm). They don't have any other role and they actually tell us a lot more about the inner workings of the world that is not visible in the theory. If one believes it though.

 

[kith]

No, there exist interpretations that are not part of the perdictive theory and these interpretations can be tested for viability in experiements.

Please provide a peer-reviewed reference for this, especially for your claim that the MWI is falsified by Kim's experiment. I think you either have a serious misconception about the scientific use of the word "interpretation" or don't understand how the MWI works.

 

[bohm2]

No, the role of the interpretations is to tell us more than the theory(qm). They don't have any other role and they actually tell us a lot more about the inner workings of the world that is not visible in the theory. If one believes it though.

I'm not sure if I understand you but I think I agree with you, for the most part. I think interpretation is important because it seems that there is something more to physical reality (or even our models of physical reality) over and above the mathematics. Surely, "...it is because of the unbending nature of the world that we find the need to move, for example, from classical to quantum physics; that we find the need to revise our theories in the face of recalcitrant experience." But the problem is that we can't get to the physical world without using mathematics because non-mathematical versions of scientific theories just seem to be practically very difficult to do. But, even though the mathematics may be indespinsible and the mathematical equations we use ultimately decide what we believe about the physical world there still seems to be this difference between the mathematics and what the mathematics represents and this just adds fuel to many of the interpretative debates in quantum mechanics because there seems to be many interpretations that are arguably equally compatible (or relatively so) with the math.

 

[Maui]

Please provide a peer-reviewed reference for this, especially for your claim that the MWI is falsified by Kim's experiment. I think you either have a serious misconception about the scientific use of the word "interpretation" or don't understand how the MWI works.

Which part of what i said about the which-path information causing wavefunction collapse in the Kim experiement didn't you understand, so i can focus on it? Here is the original peer-reviewed paper with detectors at all photon paths in case you need a reference:

http://arxiv.org/pdf/quant-ph/9903047v1.pdf

To be sure the interference
pattern disappears when which-path information is obtained.
But it reappears when we erase (quantum erasure)
the which-path information [3,4]. Since 1982, quantum
eraser behavior has been reported in several experiments
[5];

 

[mfb]

The impression I've been getting from the MWI stuff I've read (admittedly not that much, because I got frustrated over how badly written everything was) is that its supporters do think that there's a unique set of worlds that make up the universe.

I think that some (many?) opponents of MWI get the impression that supporters claim that, and argue against that self-made claim.

 

[kith]

Which part of what i said about the which-path information causing collapse in the Kim experiement didn't you understand, so i can focus on it?

This is not about your description of Kim's experiment. You claim that Kim's experiment refutes the MWI, correct? I just ask you to back this claim up by a reference.

 

[Maui]

This is not about your description of Kim's experiment. You claim that Kim's experiment refutes the MWI, correct? I just ask you to back this claim up by a reference.

I claim that in the Kim experiement it's the which-path information that causes wavefunction collapse. This is also what the authors claim and is visible from the setup and the results. From it follows that NEITHER detectors NOR interactions between photons in this particular setup creates or destroys the interference pattern.

It seems that since you cannot explain the results of this experiment in terms of the MWI(you would have if you could), you hope you can just skip the technical details of the experiement and appeal to authorities. Physics does not deal with interpretations and their refutals, so you are free to continue to stick to whatever interpretation you think is peer-reviewed or favored by a your chosen group. I am done here.

 

[mfb]

I claim that in the Kim experiement it's the which-path information that causes wavefunction collapse.

To rephrase this, you use a non-MWI interpretation (collapses), and get results different from MWI.
How does this invalidate MWI?

It seems that since you cannot explain the results of this experiment in terms of the MWI(you would have if you could)

Just let the wave function evolve unitarily (and calculate amplitude-squares after the experiment if you like), it will give the same result.

 

[Maui]

To rephrase this, you use a non-MWI interpretation (collapses), and get results different from MWI.
How does this invalidate MWI?

You can control the collapse and when it happens, so yes it's experimentally observed. See the paper i cited earlier.

Just let the wave function evolve unitarily (and calculate amplitude-squares after the experiment if you like), it will give the same result.

This is not an interpretation of the repetive no interference results when which-path information is available. It's a restatement of the shut up and calculate approach, which is most definitely not an interpretation of quantum theory.

 

[Fredrik]

I think that some (many?) opponents of MWI get the impression that supporters claim that, and argue against that self-made claim.

As I wrote that line, I was thinking about the many false claims about what MWI supporters believe that had already been made in this thread, and I was wondering if I was doing the same. That's why I used weak phrases like "it seems to me".

The main reason why it seems that way to me is that even the MWI supporters are talking about "the preferred basis problem" as if it really is a problem. I don't see any reason why someone who isn't assuming that there's only one set of worlds that make up the universe would consider "the preferred basis problem" anything more than an interesting feature.

There's also the fact that no one ever talks about worlds that don't correspond to possible measurement results (not even to dismiss them as irrelevant), or worlds that correspond to a different choice of decomposition of the universe into subsystems. OK, the guy who wrote that article did, but he was using it to argue against the MWI.

 

[Fredrik]

No, there exist interpretations that are not part of the perdictive theory and these interpretations can be tested for viability in experiements.

If you mean that there are interpretations that make different predictions than the theory, then I would consider them different theories. And this is irrelevant to what we've been talking about anyway.

If you mean that experiments can test an assumption that has no effect on the theory's predictions, then this is obviously incorrect.

Look at the quantum eraser by Kim et al and you'll notice how there are detectors(D0--D0) at all possible photon paths all the time but you only get quantum behavior(interference pattern)when the which-way information cannot be obtained(D1 and D2).

So? This is just what the theory predicts. So it's obviously consistent with all interpretations of the theory.

No, the role of the interpretations is to tell us more than the theory(qm). They don't have any other role and they actually tell us a lot more about the inner workings of the world that is not visible in the theory. If one believes it though.

Right. But they don't change the theory's predictions, and experiments only check the accuracy of the predictions. Experiments test theories, not interpretations.

 

[Maui]

If you mean that there are interpretations that make different predictions than the theory, then I would consider them different theories. And this is irrelevant to what we've been talking about anyway.

If you mean that experiments can test an assumption that has no effect on the theory's predictions, then this is obviously incorrect.

I stated clearly what i mean but you keep shifting the focus and misinterpreting my words.

So? This is just what the theory predicts. So it's obviously consistent with all interpretations of the theory.

Incorrect. The interpretation is not the theory(of quantum mechanics). I must have pointed out this very obvious fact more than a dozen times now. If you think otherwise, show me a textbook that talks about the MWI on equal footing with quantum theory. The theory surely doesn't predict > 99 trillion worlds.

Right. But they don't change the theory's predictions, and experiments only check the accuracy of the predictions. Experiments test theories, not interpretations.

This might have been the case in the 1950's but experiments get more sophisticated and their outcomes can only be interpreted as 'which-path information causing wavefunction collapse' or by appealing to superdeterminism, which seems to be the new religion of physics these days.

 

[Fredrik]

I stated clearly what i mean but you keep shifting the focus and misinterpreting my words.

What are you talking about? I haven't shifted anything. The only thing we've been talking about is whether an additional assumption that's added to the theory without changing its predictions can be falsified by experiments. It can't. This is an obvious fact that has has nothing to do with technological advances or how well we understand the theory.

And I don't always know what you mean. What did you mean by an "interpretation that's not part of the predictive theory"? What does it have to do with the possibility of disproving the MWI by experiment?

Look at the quantum eraser by Kim et al and you'll notice how there are detectors(D0--D0) at all possible photon paths all the time but you only get quantum behavior(interference pattern)when the which-way information cannot be obtained(D1 and D2).

So? This is just what the theory predicts. So it's obviously consistent with all interpretations of the theory.

Incorrect. The interpretation is not the theory(of quantum mechanics). I must have pointed out this very obvious fact more than a dozen times now. If you think otherwise, show me a textbook that talks about the MWI on equal footing with quantum theory. The theory surely doesn't predict > 99 trillion worlds.

How am I supposed to answer this? Your answer has nothing to do with what I said, or with your previous statement that I was responding to. You said that we only get quantum behavior when which-way information cannot be obtained. So when I quoted that statement and said that "this" is just what the theory (i.e. QM) predicts, I was obviously talking about the quantum behavior and the which-way information. So when you're quoting that and saying "incorrect", your statement can only be interpreted as saying that QM's prediction is something other than this, so that the experiment actually falsifies QM. I don't think that's what you meant, but that's what you're saying. So it's impossible to respond.

What do you mean by the suggestion that you have pointed out that the theory isn't the interpretation? That's one of the things I've been saying. An interpretation is defined by non-mathematical, non-scientific assumptions that are made in addition to the assumptions that define the theory and determine all the predictions. That's why they aren't testable even in principle. It doesn't matter how sophisticated our experiments get.

"> 99 trillion worlds" is not a prediction. A prediction is an assignment of a probability to a possible result of a measurement.

 

[bhobba]

If I understand it correctly (and it's certainly possible that I don't), it says that decoherence does select a preferred basis, given a decomposition into subsystems. But there's no preferred decomposition. I don't know if the article explains clearly why it considers that a problem. Personally, I think the only "problem" with it is that it prevents us from saying that a preferred basis identifies "the worlds that make up the universe"

Get where you are coming from now.

My opinion is the breaking of a system into subsystems is entirely arbitrary - basically you choose it for convenience. You can choose not to break it into subsystems, or into as many as you like with any boundaries you like. If however you choose a not particularly good one then the interaction Hamiltonian, Lagrangian, or whatever formalism you use is more complicated, however if you break it into subsystems such that the interaction term (or terms) is non existent or at least simple then you have chosen a good one. You would, or should anyway, obtain exactly the same results either way - its just a suitable choice will make life easy.

As far measurements are concerned before the measurement apparatus is used generally there is no interaction so breaking the system into apparatus and what is being measured looks a good choice. Once they interact then the interaction Hamiltonian will single out the preferred basis. I think any breaking of what is being measured and measurement apparatus into subsystems, or even if to break it at all, is arbitrary - you can choose not to do it - or break into anything you like - but your analysis becomes a lot more complicated - or easier - depending on you choice.

Thanks
Bill

 

[bhobba]

No, the role of the interpretations is to tell us more than the theory(qm). They don't have any other role and they actually tell us a lot more about the inner workings of the world that is not visible in the theory. If one believes it though.

Yes - sometimes. But there is also a role for simply mapping the mathematical objects of the theory to something out there. The MSI does that and is not particularly illuminating about inner workings. Others like BM give a lot of detail about those inner workings. I would say the MWI is actually fairly close to the MSI in what it does - it really does take the formalism to its logical conclusion - its just the way it does it is unappealing in its 'weirdness' to many.

Thanks
Bill

 

[bhobba]

I claim that in the Kim experiement it's the which-path information that causes wavefunction collapse.

But what does that have to do with MW since it doesn't have wavefunction collapse.

That said prior to decoherence creating a mixed state whose basis is the new worlds it splits into which path information is used. But be careful here - MWI being a decoherence based interpretation does not consider probabilities assigned by the Born rule to states independent of decoherence to be of any real value - they are called pre-probabilities in such interpretations and are basically of academic use only - they play no real part in the interpretation so which path information is not really the way MWI looks at it.

Thanks
Bill

 

[mfb]

You can control the collapse and when it happens, so yes it's experimentally observed. See the paper i cited earlier.

Sorry, but you need a collapse interpretation to say that. It is obvious that the interpreted results of collapse interpretations are not compatible with MWI. No, there was NO observed process of collapses. Collapses are just a possible interpretation of the results.

The main reason why it seems that way to me is that even the MWI supporters are talking about "the preferred basis problem" as if it really is a problem.

I don't see it as a real problem, but it would be nice to have an obvious way to get bases which have some similarity to classical physics.

There's also the fact that no one ever talks about worlds that don't correspond to possible measurement results (not even to dismiss them as irrelevant)

I'm sure I am not the first one to do that.

or worlds that correspond to a different choice of decomposition of the universe into subsystems

Well, I don't care about them.

 

[HomogenousCow]

MWI seems like a theoretical dead-end to me, it is impossible to test, it adds nothing to the theory and seems like a non-answer to me. How does one mathematically define the phrase "The Universe just splits into two"?

 

[mfb]

MWI seems like a theoretical dead-end to me, it is impossible to test, it adds nothing to the theory and seems like a non-answer to me.

The same can be said about all other interpretations of QM.

How does one mathematically define the phrase "The Universe just splits into two"?

You do not have to. But if you like, with decoherence: In your favorite basis (actually, in many bases), the wavefunction splits in two parts with negligible cross-terms.

 

[bhobba]

MWI seems like a theoretical dead-end to me, it is impossible to test, it adds nothing to the theory and seems like a non-answer to me. How does one mathematically define the phrase "The Universe just splits into two"?

Well it actually doesn't split in two, or even split really - it simply keeps evolving.

After decoherence a superposition is converted to a 'improper' mixture that has the form sum pi |bi>|ri> where |bi> is the outcome of the observation and |ri> is the rest of the world. Now in a collapse interpretation pi gives the probability of the outcome |bi> and after the observation the outcome and the rest of the world has state |bi>|ri> that keeps on evolving. This is the collapse of the wavefunction issue and depending on your interpretation may or may not be an issue. If it was a real mixture it wouldn't be an issue since a mixture is the outcomes randomly presented but having the outcome there prior to observation - its like selecting a random marble out of a hat that has been placed there. However its an 'improper' mixture meaning its mathematically the same but is not physically the same - its observationally exactly the same but has not been physically prepared the same way. You can assume it is and hold it has that outcome prior to observation but in reality how it selected that outcome is a mystery. I hold to a modified MSI that does just that - simply assumes it observes an outcome already there but what it is has probability pi. But what I have really done is hidden the collapse issue - however its still there - just swept under the rug.

MWI is a twist on this - the mixture keeps on evolving as is and each of the |bi>|ri> continues to evolve. However to an observer in the |ri> its as if an observation was made and the outcome |bi> occurred. No collapse occurred and everything continues to evolve deterministically. Of course we are left with the issue of how probabilities enters into it and various researches such as David Deutch have their own take on it that you can read about.

Very very elegant - no collapse, totally deterministic - all issues resolved. But can you stomach all these exponentially increasing multiple you's - that's the question.

Thanks
Bill

 

[bhobba]

The same can be said about all other interpretations of QM.
You do not have to. But if you like, with decoherence: In your favorite basis (actually, in many bases), the wavefunction splits in two parts with negligible cross-terms.

That's true - you don't have to evoke decoherence but it does help in explaining why observers in each of the worlds experiences it like a collapse. Its the way I prefer to look at it.

Thanks
Bill

 

[Fredrik]

My opinion is the breaking of a system into subsystems is entirely arbitrary - basically you choose it for convenience. You can choose not to break it into subsystems, or into as many as you like with any boundaries you like. If however you choose a not particularly good one then the interaction Hamiltonian, Lagrangian, or whatever formalism you use is more complicated, however if you break it into subsystems such that the interaction term (or terms) is non existent or at least simple then you have chosen a good one. You would, or should anyway, obtain exactly the same results either way - its just a suitable choice will make life easy.

I would expect the results (the preferred bases) corresponding to two different decompositions to not be exactly the same. In fact, I would expect them to have almost nothing in common. For example, I don't see any reason to think that "the silver atom in my Stern-Gerlach experiment + everything else" and "an iron atom in the sun + everything else" should give us similar results. That article seems to confirm that, by showing that there's always a decomposition such that the two subsystems do not interact with each other. If we choose that decomposition, no preferred basis will emerge.

What I expect all this to mean (this is what I've been thinking for a few years, so it doesn't have anything to do with that article) is e.g. that a claim that a classical world is being split in two is never objectively true or false. It can be true relative to one decomposition, and false relative to another. Worlds can be splitting in one way relative to one decomposition, in an entirely different way relative to another.

I also expect this "non-objectiveness" to go very far beyond this. The worlds relative to one decomposition could perhaps be very different from the worlds relative to another decomposition. Note that a decomposition doesn't have to be "this chunk of matter + everything else". Every countable orthonormal basis and every bijection from $\mathbb Z$ (the set of integers) into $\mathbb Z\times \mathbb Z$ defines a decomposition, as described (briefly and not very pedagogically) in the article. Basically, you take a basis $\{e_i\}$ and relabel the basis vectors $\{e_{ij}\}$. Then for each j, $\{e_{ij}\}_{i=1}^\infty$ spans a subspace, and if I understand this idea correctly, the original Hilbert space can be viewed as a tensor product of (something isomorphic to) that subspace and (something isomorphic to) its orthogonal complement. These spaces can then be considered the Hilbert spaces of "subsystems".

There could be decompositions such that a description of what's happening is completely different from what we'd get from a typical decomposition. It seems entirely plausible to me that such a description could describe worlds where you and me don't even exist. The "exponentially multiplying" copies of you will only exist in the descriptions corresponding to a specific sequence of decompositions. Relative to other decompositions, you may not be splitting in the same way, and you may not even exist. Since these ideas haven't been explored (as far as I know) it's hard to tell how deep this goes. Is it possible that the same chunk of matter that we think of as "bhobba", is a Coca-Cola machine relative to another decomposition? I have no idea, and I think its funny that I can't even tell if such things can be ruled out.

Note that I'm not saying that this is what's actually happening. I still prefer to think of QM as just an assignment of probabilities to possible results of experiments. I'm just saying that it seems to me that the consequences of assuming that QM describes what's actually happening are very different from what people seem to think.

I don't consider this a reason to dismiss the MWI. I don't consider it a reason to favor the MWI. I just think it makes the MWI much more fascinating than it seemed at first.

 

[Maui]

What are you talking about? I haven't shifted anything. The only thing we've been talking about is whether an additional assumption that's added to the theory without changing its predictions can be falsified by experiments. It can't. This is an obvious fact that has has nothing to do with technological advances or how well we understand the theory.

The assumption is falsified if it cannot explain experimental results which can otherwise quite easily be explained without making the assumption.

And I don't always know what you mean. What did you mean by an "interpretation that's not part of the predictive theory"? What does it have to do with the possibility of disproving the MWI by experiment?

The MWI is not part of quantum theory. Do you understand thus far? It's your fantasy that it's somehow the same as quantum theory but it is not. It's fantasy proposed by a propminent figure, that's all.

How am I supposed to answer this? Your answer has nothing to do with what I said, or with your previous statement that I was responding to. You said that we only get quantum behavior when which-way information cannot be obtained. So when I quoted that statement and said that "this" is just what the theory (i.e. QM) predicts, I was obviously talking about the quantum behavior and the which-way information. So when you're quoting that and saying "incorrect", your statement can only be interpreted as saying that QM's prediction is something other than this,

Definitely no, quantum theory does not make predictions in the sense of classical mechanics but assigns probabilities. You most definitely cannot predict outcomes 1:1 but only approximately for large ensembles. So the fact that you misrepresent qm as predicting the results of the quantum eraser is enough for me to stop responding to your posts(especially since human choice enters the experimental setup which cannot be modeled by the SE). QM does not describe how you get no interference pattern when which-path information is available, this can only be 'explained' via superdeterminism and the SE.

Sorry that was my last post arguing religious beliefs.

 

[Maui]

Sorry, but you need a collapse interpretation to say that.

No, you can choose whether to look at detectors that can in principle provide which-path information or you can choose to look at the detectors that don't provide the information. By doing this many times, you can choose what behavior you want to observe - you can 'cause' collapse just by choosing the right set of detectors.

 

[Nugatory]

The assumption is falsified if it cannot explain experimental results which can otherwise quite easily be explained without making the assumption.

That's not sufficient to falsify an assumption; it shows that the assumption is unnecessary but does not show that the asumption is untrue. Falsification requires a stronger criterion: the assumption must lead to a prediction that can be shown to be false.

 

[Fredrik]

The assumption is falsified if it cannot explain experimental results which can otherwise quite easily be explained without making the assumption.

See nugatory's reply.

The MWI is not part of quantum theory. Do you understand thus far?

Of course, that's why I've been saying that many times.

It's your fantasy that it's somehow the same as quantum theory but it is not.

This is a lie. I don't have a problem with you making incorrect statements about QM or its interpretations, or with you using words like "prediction" and "falsified" incorrectly, but now you're lying about me. That's very far from acceptable behavior in this forum.

Definitely no, quantum theory does not make predictions in the sense of classical mechanics but assigns probabilities.

Why are you telling me this? This is something I'm saying all the time. I'm sure I've said it more times than anyone else in this forum.

You most definitely cannot predict outcomes 1:1 but only approximately for large ensembles. So the fact that you misrepresent qm as predicting the results of the quantum eraser is enough for me to stop responding to your posts(especially since human choice enters the experimental setup which cannot be modeled by the SE). QM does not describe how you get no interference pattern when which-path information is available, this can only be 'explained' via superdeterminism and the SE.

Wait, you're actually suggesting that what I said in my previous post implies that QM doesn't assign non-trivial probabilities to possible results of measurements? That's so far from the truth that I don't even know where to begin.