If, as Richard Feyman insisted, nobody understands quantum mechanics

[rewebster]

... No energy has been created, no alternate realities have been formed.

"DeWitt admits that this constant splitting of worlds whenever the states of
systems become correlated is counterintuitive:
I still recall vividly the shock I experienced on first encountering this
multiworld concept. The idea of 10^100 slightly imperfect copies of oneself all
constantly spitting into further copies, which ultimately become
unrecognizable, is not easy to reconcile with common sense. Here is
schizophrenia with a vengeance (1973, p. 161). "

http://plato.stanford.edu/entries/qm-everett/


And to me, "Pure Math" may be rational, and there may be an enormous amount of properties known about the photon and the wave function (wave-particle function)---but, even the speed of light is still an approximation when you consider the ability to measure a second.

http://news.bbc.co.uk/2/hi/science/nature/3486160.stm


Are we supposed to inarguably 'believe' the 'math' (of MWI) when we still do not definitively 'what' the photon is, exactly, (to the point when we still can't explain some of its properties, e.g. the double slit), and go with the math that is so non-exact (an approximation, e.g. the second) ?

I know applied physicists may say 'we know a lot about ...'; and yes, I agree, and we 'have to' adhere to 'some' type of 'acceptable' knowledge, otherwise we wouldn't have been able to go to the moon, but...

--------------------------------------------------------

Here's something that doesn't relate, but if anyone is interested in Einstein memorabilia:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=010&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=200099492028&rd=1&rd=1

 

[Bertrand]

OK, OK guys,

Let's leave apart unrational arguments. Then :

- do you agree with K. Popper's argument about falsiability, that is, a theory can be considered as scientific only if some proof can be provided that it is worng ?

- If the answer is yes, then is MWI a scientific theory, according to Popper's principle ?

Besides, I will take some time to read your trillion articles about MWI, then I'll come back. By trillion, do you mean you include all versions of your articles in all universes ?

is there a universe in which you don't believe in MWI ?

Sorry, these were my last stupid jokes ...

Bertrand

 

[Tomsk]

I think the thing about MWI is, it's just an interpretation, so it is falsifiable because quantum mechanics is falsifiable. Even if you don't like to look at QM in that way, it is still possible to, as you get the same answers. In a way it is just faith to say that MWI is the *correct* interpretation of QM. But I like Carlo Rovelli's argument that if QM can be derived from physical principles, then the interpretation of it would not be an issue any more, because how it works would become obvious.

 

[JesseM]

I think the thing about MWI is, it's just an interpretation, so it is falsifiable because quantum mechanics is falsifiable.

Well, certain aspects of MWI can be falsified, but those are precisely the elements which are common to all the other interpretations because they are part of the basic structure of quantum mechanics; the things that make each interpretation unique, like the multiple versions of the same experimenter in the MWI or the hidden variables of Bohmian mechanics or the "offer waves" of Cramer's transactional interpretation, are unfalsifiable because they do not lead to any empirical predictions which are different than any other interpretation. That's exactly why they're all called "intepretations", not "theories". I think the only hope of really settling these foundational issues is if quantum gravity modifies quantum mechanics in such a way that it leads to a modified version of one of these interpretations that actually makes specific empirical predictions.

 

[rewebster]

I think the only hope of really settling these foundational issues is if quantum gravity modifies quantum mechanics in such a way that it leads to a modified version of one of these interpretations that actually makes specific empirical predictions.

OR, come up with a new 'theory' to satisfy it all (or, at least better than what is presently 'out there'*).


*(PS: 'out there'---or way, way out there)

-------------------------------------------------

just a note on the DeWitt comment--"Here is
schizophrenia with a vengeance."

I think he may of meant "split-personality disorder" (multiple personality disorder, 'Dissociative identity disorder') ---the correct definition of schizophrenia really doesn't fit the analogy. It's funny that a 'scientist' doesn't know the right definition, and uses the 'popular' erroneous one. I guess we all have 'errors'.

 

[Bob Eldritch]

Well, certain aspects of MWI can be falsified, but those are precisely the elements which are common to all the other interpretations because they are part of the basic structure of quantum mechanics; the things that make each interpretation unique, like the multiple versions of the same experimenter in the MWI or the hidden variables of Bohmian mechanics or the "offer waves" of Cramer's transactional interpretation, are unfalsifiable because they do not lead to any empirical predictions which are different than any other interpretation. That's exactly why they're all called "intepretations", not "theories". I think the only hope of really settling these foundational issues is if quantum gravity modifies quantum mechanics in such a way that it leads to a modified version of one of these interpretations that actually makes specific empirical predictions.

There could also be a way of falsifying all quantum interpretations except Bohmian mechanics. This being the only mechanics that describes the quantum wave in terms of a cause (called the quantum potential) acting in addition to the forces and its effects upon particles in motion.

So that Bohm's mechanics would be developed into a quantum hypothesis that justified and represented further details of the quantum potential cause from its effects upon particles. This hypothesis was found to be such that large scale observable natural evidence would be found of where the cause could also be justified and described as acting. This then allowed a general theory to be developed that made unique and testable predictions.

 

[Demystifier]

Why is the "multi-world hypothesis totally unacceptable" - apart from personal, intuitive preferences ?

Nothing is totally unacceptable, not even MWI.
Seriously, although MWI is also a logical possibility, there do exist arguments against it that are not purely emotional or intuitive. Perhaps the best argument is the one based on Poper falsifiability. Also, with an appropriate definition of simplicity (for example, one world is simpler than an infinite number of worlds), it can be argued that it is not in agreement with the Ocam's razor.

 

[vanesch]

Nothing is totally unacceptable, not even MWI.
Seriously, although MWI is also a logical possibility, there do exist arguments against it that are not purely emotional or intuitive. Perhaps the best argument is the one based on Poper falsifiability.

As JesseM pointed out, MWI is a *metaphysical* interpretation of a formalism, that is, it attaches ontological meanings to formal elements. In the same way as the metaphysical assumption of the existence of "spacetime" is an interpretation of the formalism of general relativity. Metaphysical concepts do not need to be falsifiable - in fact they can't. Only formalisms can be falsified because only formalisms make observational predictions. Interpretations are what comes metaphysically on top of it, and as such, two different metaphysical interpretations of the same formalism are totally empirically equivalent - by definition.

If you want to restrict yourself to Popper falsifiability, you should refrain yourself from giving ANY metaphysical interpretation of any theory. As such, this cannot be an argument against such an interpretation!

Also, with an appropriate definition of simplicity (for example, one world is simpler than an infinite number of worlds), it can be argued that it is not in agreement with the Ocam's razor.

This is a well-known argument against MWI, but it depends on what exactly one understands by Occam's razor. Usually, by Occam's razor, one doesn't consider the complexity of the *solution* but the complexity of the *axiom set*. As such, MWI has a far simpler axiom set (it is simply the unitary part of quantum theory, together with a rule (Born rule) of what will be subjectively observed) than, say Bohmian mechanics (Bohmian mechanics includes unitary QM, and has on top of it an entire Newtonian particle dynamics) ; it is also simpler than Copenhagen, because no independent classical world with its classical dynamics needs to be axiomatically postulated.

Consider Newtonian dynamics as compared to Ptolomean planetary dynamics. Ptolomean planetary dynamics has a SIMPLER solution set (namely just exactly those sets of epicycles that correspond to actual planets ; no other planets 'are possible'), than the solution set of Newtonian dynamics which contains ALL THINKABLE orbits around the sun. The solution set of Newtonian dynamics has an infinite amount of possible solutions, while the Ptolomean view has a finite number of orbits. According your view of Occam's razor, one should prefer Ptolomy's view.
But one prefers of course Newton's view, because of the *axiomatic simplicity*. You can derive that huge set of potential orbits just with a few axioms (Newton's law F = m.a, the universal law of gravity F = -G m1m2/r^2 and some other esthetics).

So from this PoV, MWI is by far the *simplest* formulation of quantum theory. No dichotomy classical/quantum, no extra dynamical elements (particles, guide fields ...). That its solution set is huge is just a consequence of its axioms, but that's not what's aimed for by Occam's razor. Occam goes for the simplest *set of rules*, not for the simplest *solution set*.

 

[vanesch]

OK, OK guys,

Let's leave apart unrational arguments. Then :

- do you agree with K. Popper's argument about falsiability, that is, a theory can be considered as scientific only if some proof can be provided that it is worng ?

- If the answer is yes, then is MWI a scientific theory, according to Popper's principle ?

I answered that in another post (MWI is not a scientific theory, but a metaphysical view on a scientific formalism, and as such, Popper doesn't apply to it).

Besides, I will take some time to read your trillion articles about MWI, then I'll come back. By trillion, do you mean you include all versions of your articles in all universes ?

is there a universe in which you don't believe in MWI ?

I don't *believe* in MWI, not more than I *believe* in a static spacetime (or in Newtonian absolute space, for that matter). I think that these are, nevertheless, good metaphysical hypotheses that go very well with the scientific theories that we have today. The reason for that is that they start from the formalism, and take "as metaphysically real" what the formalism gives us, and not the other way around, where we try to re-interpret a formalism as a function of what we intuitively WOULD LIKE things to be like. As such, these interpretations (MWI for QM, and static spacetime for GR) give us a good mental PICTURE to develop a good INTUITION for the workings of the formalism. Call it "applied philosophy" to the service of physics.

I am totally agnostic as to whether the physical theories we have today contain in them any form of "absolute truth" concerning the world around us - although I trust them a bit more than my own intuition of which I'm pretty sure that it is misleading.

 

[Demystifier]

As such, MWI has a far simpler axiom set (it is simply the unitary part of quantum theory, together with a rule (Born rule) of what will be subjectively observed) than, say Bohmian mechanics (Bohmian mechanics includes unitary QM, and has on top of it an entire Newtonian particle dynamics) ; it is also simpler than Copenhagen, because no independent classical world with its classical dynamics needs to be axiomatically postulated.

I wouldn't agree. As far I can see, both interpretations have essentially only two axioms. One is their common axiom representing the unitary part. The other axiom is either the axiom on probabilities of subjective experiences or the axiom that determines particle trajectories.

 

[Bob Eldritch]

I answered that in another post (MWI is not a scientific theory, but a metaphysical view on a scientific formalism, and as such, Popper doesn't apply to it).

I don't *believe* in MWI, not more than I *believe* in a static spacetime (or in Newtonian absolute space, for that matter). I think that these are, nevertheless, good metaphysical hypotheses that go very well with the scientific theories that we have today. The reason for that is that they start from the formalism, and take "as metaphysically real" what the formalism gives us, and not the other way around, where we try to re-interpret a formalism as a function of what we intuitively WOULD LIKE things to be like. As such, these interpretations (MWI for QM, and static spacetime for GR) give us a good mental PICTURE to develop a good INTUITION for the workings of the formalism. Call it "applied philosophy" to the service of physics.

I am totally agnostic as to whether the physical theories we have today contain in them any form of "absolute truth" concerning the world around us - although I trust them a bit more than my own intuition of which I'm pretty sure that it is misleading.

Trouble is, all quantum interpretations bar one disallow any possibility of a quantum hypthesis that could be developed into a fully justified causal theory. So that Bohmian mechanics is the only accoumt that, as I have said, descrbes a distinct cause that acts in addition to the forces. And one could think if only for this reason, the de Broglie-Bohm account is the one correct interpretation of quantum physics.

But why believe that the quantum potential is a cause that acts in the real world in addition to the forces?

Well, despite all its successes at prediction and explaining the chemical, electromagnetic and nuclear properties of many forms of matter, there is one universal feature of matter that the quantum theory of the standard model can't adequately explain, which is how matter can be and remain in its forms as atoms and molecules and organised out of its subatomic components and while the forces act just as they have been measured and described.

And it can be reasoned that even though a cause of quantum entanglement can't be measured and described in terms of it strength of effect, entanglement describes a fixed composite relationship between certain forms of behaviour such as the spin up in relation to spin down of electrons and protons. And a cause could thus be described as acting upon these objects so as to maintain or conserve this organised relationship. Also, by preventing electrons from falling into nuclei the wave property of electrons would be described as maintaining or conserving the form of atoms and molecules.

And then you could suppose that such a cause could act elsewhere in the natural world and on the large scale...

Any less likely than a many worlds interpretation?

 

[nutshell]

Hi guys I just discovered this forum and randomly wandered when I came to this extremely interesting topic (well actually they all are, as long as they concern science right ?)

Anyway it seems to me that that you guys believe (and I believe that too, to some extent) that physics can not only describe how things are but also WHY they are (ultimately this goes to the question why there is an Universe)

However, we must also consider the fact that maybe, physics cannot do that. Maybe there is no rationnal explanation at all to why things are.

Of course, one could mention the anthropic principle to get away from this difficulty...

I don't know if what I want to say is very clear but I would like to have your opinion on this.

THX

 

[NateTG]

Anyway it seems to me that that you guys believe (and I believe that too, to some extent) that physics can not only describe how things are but also WHY they are (ultimately this goes to the question why there is an Universe)

However, we must also consider the fact that maybe, physics cannot do that. Maybe there is no rationnal explanation at all to why things are.

Strictly speaking, there is no maybe about it. Physics, as a science, is about testable theories. Interpretations that deal with the why of things are primarily interesting because they can lead to testable predictions - that is, notions of how,when, or where' things happen. Science does not answer questions about why things happen.

 

[Mike2]

Strictly speaking, there is no maybe about it. Physics, as a science, is about testable theories. Interpretations that deal with the why of things are primarily interesting because they can lead to testable predictions - that is, notions of how,when, or where' things happen. Science does not answer questions about why things happen.

As I understand it. Physics can't tell us what the facts actually are. Physical theories only tell us (at best) that IF there were to exist particular circumstances, THEN particular results will follow as a consequence. In other words, physics may only be able to tell us WHY. Measurement tells us what facts exists; physical theory tells us how and why facts change.

***************************************
Can quantum mechanics be derived from logic alone?
http://www.sirus.com/users/mjake/Physlogic.htm

 

[reilly]

Seems to me that MWI is nothing more than the belief that a probability tree describes reality. There is nothing inherently quantum about this idea; works just as well for a poker game, stock market, what ever. Most, if not all, workers in math and probability for centuries never bothered with such a concept. Suggests nobody took the idea seriously -- as soon as you get to conditional probability, you have probability trees, which go back a few years.

My first reaction upon hearing of MWI is not printable. MWI seems to me to be very contrived, and an effort to get around probability -- back to the 19th century. I think this MWI stuff presents huge complications. Born may not be perfect, but no one has come up with anything practical that's better than Born.

MWI is, to me, very strange, almost like magic not physics, but it's a free country. Believe MWI if you want, but why?
Regards,
Reilly Atkinson

 

[JesseM]

Seems to me that MWI is nothing more than the belief that a probability tree describes reality. There is nothing inherently quantum about this idea; works just as well for a poker game, stock market, what ever.

The inherently quantum reason for liking the MWI is that it prevents you from having to treat measurements as fundamentally separate from the normal evolution of the wavefunction in between measurements--no need for each measurement to discontinuously "collapse" the wavefunction into an eigenstate, and this also means that classical measuring-devices are obeying the same fundamental laws that quantum systems are. Additionally, the MWI gives you a way of explaining the results of experiments on entangled particles which violate Bell inequalities without invoking nonlocal (faster than light/backwards in time) effects.

 

[Tomsk]

I don't see the problem with wavefunction collapse. It represents the reception of information describing a system by an observer. There could well be a different description of this interaction, by a second observer who does not receive the same information that the first one does. I don't see why you need parallel universes for that.

 

[JesseM]

I don't see the problem with wavefunction collapse. It represents the reception of information describing a system by an observer.

What is the physical definition of "an observer"? Assuming the observer is a large collection of quantum-sized particles interacting, why isn't the observer's behavior guided by the laws of quantum mechanics? What laws do govern the observer's behavior, exactly?

With every non-quantum theory of physics, you can have a complete description of a hypothetical universe guided by those laws, viewed "from the outside" with a Godlike perspective. With QM under the Copenhagen interpretation you can only describe individual systems being measured by some external classical system, and the behavior of the classical system, including which sets of noncommuting variables it measures, has to be put in by hand. So if our fundamental theories of physics are quantum ones, it's difficult to say what it would mean for the entire universe to be governed by those laws, with no external measuring-device. This is one of the basic problems that various "interpretations" such as the MWI and Bohmian mechanics are supposed to resolve.

There could well be a different description of this interaction, by a second observer who does not receive the same information that the first one does. I don't see why you need parallel universes for that.

If variables don't commute, there'll be uncertainty relations between them, and these apply just as much to measurements made by different observers as to those made by a single observer. If I measure a particle's spin on one axis, then measure again on the same axis, I'll get the same answer; but if I make my measurement, then unbeknownst to me someone else measures on a different axis, then I measure again on the same axis I did the first time, the spin will be randomized in just the same way as if I had made the middle measurement.

 

[vanesch]

Seems to me that MWI is nothing more than the belief that a probability tree describes reality. There is nothing inherently quantum about this idea; works just as well for a poker game, stock market, what ever. Most, if not all, workers in math and probability for centuries never bothered with such a concept. Suggests nobody took the idea seriously -- as soon as you get to conditional probability, you have probability trees, which go back a few years.

The point is, in classical probability, you can, if you want to, introduce also a "many outcomes" view, but you can also use state variables (as is done in classical statistical mechanics) which follow ONE of the several "probable" paths. There is no distinction between the "ignorance which path, but there's only one" and the "all paths simultaneously, and I only see one" view. In other words, the specific distribution of probabilities doesn't interfere with the dynamical evolution of the system: the different possible paths have their independent dynamical evolution, un-influenced by the existence, or not, of the neighbouring paths.
So, although it is entirely possible in classical probability, to have a "many outcomes-of-which-I-only-perceive-one" view, it doesn't bring in anything.
This is of course also the critique on MWI on *fully decohered branches*, but...

In quantum theory, as you know it, the wavefunction, at least as long as there is coherence, cannot be seen as an "ignorance" description: it contains essential dynamical information. This is what appears in quantum interference between "different possible paths" and follows from the fact that the probability is given by |psi|^2 and not by psi itself, psi itself containing an essential phase. As such, we cannot see |a> + |b> as simply an ignorance on our part of whether the system is in state |a> or in state |b> ; it comes down to the difference between a (coherent) superposition and a mixture (in a mixture, we can find again our traditional "ignorance" description).

This, just to outline the difference between probability as ignorance in classical theory (in which case the "many outcomes" view doesn't bring in anything new, although it can of course be considered), and the superposition in quantum theory.

My first reaction upon hearing of MWI is not printable. MWI seems to me to be very contrived, and an effort to get around probability -- back to the 19th century. I think this MWI stuff presents huge complications. Born may not be perfect, but no one has come up with anything practical that's better than Born.

I agree with you here ; I think that many MWI proponents got lost in trying to derive Born from some OTHER probability measure, such as uniform distribution. My personal opinion, like yours, is that this complicates overly the task, and is not essential, given that we'd still have to explain where this OTHER probability distribution (the uniform distribution, and state counting and so on) comes from. But to me, that's not the essence of MWI. The point is not that we can derive the Born rule from another distribution (such as uniform distribution over decohered states). The point is that there is a probability distribution which describes the observation from the state. As Born works fine, I have no problems with keeping Born! I don't see why one should first go to another distribution (uniform) and then derive Born from there. So this, to me, is a *different* aspect, and not essential to MWI.

MWI is, to me, very strange, almost like magic not physics, but it's a free country. Believe MWI if you want, but why?

I simply see MWI (with the Born rule concerning subjective observation) as the "natural" view on quantum theory as it is usually presented, in the same way as considering a static spacetime manifold is the natural way of looking upon relativity, as it is usually presented. It's a picture, that fits nicely with the ideas behind the formalism. Whether it is "true" or not, and whether one should "believe" in it or not are not considerations I want to delve into, because they are not fruitfull. As JesseM pointed out, the MWI view "explains" some apparent paradoxes in quantum theory, such as EPR/Bell and quantum erasers (simply because MWI sticks to the spirit of quantum theory). In the same way, a static spacetime view "explains" different apparent paradoxes in relativity, also because a static spacetime view sticks to the formalism. That's all. It is not a religion !
That doesn't mean that other views cannot give also satisfactory views on things. But MWI also has its merits.

 

[Demystifier]

I simply see MWI (with the Born rule concerning subjective observation) as the "natural" view on quantum theory as it is usually presented, in the same way as considering a static spacetime manifold is the natural way of looking upon relativity, as it is usually presented. It's a picture, that fits nicely with the ideas behind the formalism. Whether it is "true" or not, and whether one should "believe" in it or not are not considerations I want to delve into, because they are not fruitfull. As JesseM pointed out, the MWI view "explains" some apparent paradoxes in quantum theory, such as EPR/Bell and quantum erasers (simply because MWI sticks to the spirit of quantum theory). In the same way, a static spacetime view "explains" different apparent paradoxes in relativity, also because a static spacetime view sticks to the formalism. That's all. It is not a religion !
That doesn't mean that other views cannot give also satisfactory views on things. But MWI also has its merits.

That is perhaps one of the best explanations of MWI. I particularly like your analogy with static spacetime. Is that analogy invented by you, or first introduced by someone else? If the latter is correct, can you give me the reference where this analogy has been originally introduced?

 

[Bob Eldritch]

MWI is, to me, very strange, almost like magic not physics, but it's a free country. Believe MWI if you want, but why?
Regards,
Reilly Atkinson

Only because MWI resolves the indeterminacy problem to the extent that you can say that in the world observed the results of any quantum experiment could not be otherwise. But then, of course, the indeterminacy is thus only pushed elsewhere as the result of the inability in determining whether or not other worlds exist where the results of quantum experiments are otherwise.

 

[JesseM]

Only because MWI resolves the indeterminacy problem to the extent that you can say that in the world observed the results of any quantum experiment could not be otherwise.

As I said in my responses to reilly and Tomsk, the lack of indeterminacy is not the main reason people like the MWI--issues like the difficulty defining the boundary between quantum systems and classical measuring-system, the difficulty understanding what it would mean to have an entire universe governed by quantum laws with no external measuring system, and the problem of avoiding nonlocality are bigger reasons. A theory whose only "problem" was indeterminacy would probably bother far fewer physicists.

 

[reilly]

My suspicions about MWI were confirmed by David Deutsch's The Fabric of Reality. He talks about parallel universes in the spirit of MWI. He talks about "shadow photons", which apparently traverse universes. I ended up spending a lot of time going through his book with a fine tooth comb. He must have written it in a hurry, the book is full of contradictions, and hardly worth reading.

But, he led me to questions like ; where are these universes; do they interact; where does the energy come from to create the parallel universes; is their creation instantaneous (relativity would disaprove), or do they expand at the speed of light? Seems to me that the collection of universes form a non-separable Hilbert Space, not a nice thing.

As I've written before, my take is that wave function collapse is purely the result of neural learning. But, why is not MWI confined to our minds -- we can certainly imagine MWI, a plausible circumstance.

There are many systems in the classical world which require stochastic dynamical equations; control theory, cascades generated by cosmic rays; random walk, and so on. I see no reason at all that a MWI approach could not be used. How about breaking a membrane and allowing two gases at different temp and pressure to interact. What's the probability that a molecule could transverse the system without a collision -- how could I measure such a case? What about Kalman Filters?

Regards,
Reilly Atkinson

 

[JesseM]

As I've written before, my take is that wave function collapse is purely the result of neural learning.

And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?

 

[reilly]

[

• QUOTE=JesseM;1314060]And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?[/QUOTE]

No, of course not. In fact, quantum mechanics plays a key role in vision -- converting photons into signals that travel up the optic nerve.

Why would I think otherwise? Why do you ask?
Regards,
Reilly Atkinson

 

[JesseM]

And do you think the fundamental laws governing the brain are different from the laws governing the individual particles that make it up?

No, of course not.

Then how can the "collapse" be a consequence of anything going on in the brain, as opposed to something that must be applied to the brain by an external classical measuring-device to put it in a definite state? If you treat the behavior of the brain using the same rules as other quantum systems--constructing a wavefunction for its state and letting the state evolve according to the Schroedinger equation--then you just end up predicting a the brain is in a superposition of very different macroscopic states, nothing inherent to the system itself will cause a collapse to a single classical-looking state.

 

[vanesch]

That is perhaps one of the best explanations of MWI. I particularly like your analogy with static spacetime. Is that analogy invented by you, or first introduced by someone else? If the latter is correct, can you give me the reference where this analogy has been originally introduced?

I did find this view myself, but it might very well be that there are papers on it. I got "beaten up" by some relativists when I made those statements

 

[vanesch]

My suspicions about MWI were confirmed by David Deutsch's The Fabric of Reality. He talks about parallel universes in the spirit of MWI. He talks about "shadow photons", which apparently traverse universes. I ended up spending a lot of time going through his book with a fine tooth comb. He must have written it in a hurry, the book is full of contradictions, and hardly worth reading.

I never read it, but I find Deutsch close to a sect guru, with what I know of him.

But, he led me to questions like ; where are these universes; do they interact; where does the energy come from to create the parallel universes; is their creation instantaneous (relativity would disaprove), or do they expand at the speed of light?

You don't ask that question when, say, an electron is in a superposition of two position states, don't you ? You don't ask: where did the energy, lepton number etc... come from to have now an electron at position x1 and another (?) electron at position x2.

As I've written before, my take is that wave function collapse is purely the result of neural learning. But, why is not MWI confined to our minds -- we can certainly imagine MWI, a plausible circumstance.

Well, I could give a speculative answer to that question, but maybe this will lead us too far astray. I would say that a mind cannot at the same time have the "impression of free will" and be aware of a superposition of "states of awareness", because in that case, he could (have the impression to) act according to things observed in different branches. But if that is the case, then the physical interaction resulting from such a decision would introduce a coupling between two terms in the wavefunction, which is impossible for a linear time evolution operator. With a linear time evolution operator, you're not supposed to be able to interact with other terms. So, or you cannot be "aware" of them, or you would necessarily have the impression that you cannot "freely decide what to do".
For instance, imagine that you had a "multi-world" awareness, and you were doing a quantum experiment with the state |a> + |b>, where you measure quantity A and you'd have outcome a or outcome b.
You could say, "if I see a in one world, and b in another, I press the red button, but if I see only a, I press the green button".
Clearly, in MWI, you would both see the a and the b outcome then, and you'd push the red button.
If the incoming state would be state |a>, you'd press the green button.
But you're not supposed to be able to do this!

Indeed, let us look at the unitary evolution:
|nobutton>|a> evolves into |greenbutton>|a>
but |nobutton>(|a> + |b>) should evolve into |redbutton>(|a>+|b>).

But this can never be happening with a purely unitary time evolution operator (the |a> part should evolve into |greenbutton>|a> in any case).

There are many systems in the classical world which require stochastic dynamical equations; control theory, cascades generated by cosmic rays; random walk, and so on. I see no reason at all that a MWI approach could not be used.

MWI is not there to "explain" the randomness. It is there to explain the apparent clash between projection and unitary evolution.

 

[reilly]

Then how can the "collapse" be a consequence of anything going on in the brain, as opposed to something that must be applied to the brain by an external classical measuring-device to put it in a definite state? If you treat the behavior of the brain using the same rules as other quantum systems--constructing a wavefunction for its state and letting the state evolve according to the Schroedinger equation--then you just end up predicting a the brain is in a superposition of very different macroscopic states, nothing inherent to the system itself will cause a collapse to a single classical-looking state.

But I know several things: the brain, on an atomic scale is huge, and very complex. The brain is a classical system -- networks of non-linear electrical devices (neurons). The generation of neural pulses and neural transmission are well understood, described as they are by the Hodgkin-Huxley Eq. There's really no more practically important quantum superposition in the brain than there is in a door bell.

Note that the human mind can effectively be in what might be called a superposition of ideas. That is, "Will I make the next light?" and "What's the probability that an electron can traverse a a slab of crystal, many angstroms thick, without any collisions. That is, I can imagine both making the light and not making the light. When I get there, and say we are talking green, then our "neural pattern " collapses to " made it"-- and that's generically true for any probability situation. In other words, collapse is connected with a change of knowledge. By the way, this approach to QM came from Sir Rudolph Peierls, one of the early and prolific workers in QM, for which he won a Nobel Prize -- no crackpot he. Also, Prof. Wigner was sympathetic to Peierls poit of view.

Where is it written that QM must explain the Measurement Problem?


Regards,
Reilly Atkinson

Regards,
Reilly Atkinson

 

[Mike2]

Note that the human mind can effectively be in what might be called a superposition of ideas...In other words, collapse is connected with a change of knowledge.

Perhaps we are deceived in thinking that our mathematical models describe actual reality, when they are really a description of our understanding (perception) of it. Our equations are inventions of our minds just as much as our observations. So collapse of the wave function may be just a feature of the math, not reality itself.[/url]