The Many-Worlds Interpretation of QM

  • Thread starter Quotidian
  • Start date

Fredrik

Staff Emeritus
Science Advisor
Gold Member
10,730
405
Not really. In order to apply QM you need a way to map the mathematical elements of its formalism to stuff out there. That's the job of an interpretation.
To me, the term "QM" refers to something that includes the correspondence rules that tell us how to interpret the mathematics as predictions about results of experiments. (QM is a theory of physics, not a piece of mathematics). So the kind of interpretation you're talking about here is already included in "QM".

So to me, an "interpretation of QM" is something else; it's an answer to the question of what's actually happening to an isolated system. But it can't be any guess. It has to be an answer that follows from QM itself*, once we have made a few statements about how to think about some of its mathematics.

Martinbn made the comment that when I tried to partially define the MWI, I seemed to be just assigning familiar but undefined terms with mathematical concepts. It seemed that way, because it was that way. I don't think there's any other way to define an interpretation of QM.
 

kith

Science Advisor
1,277
396
But in quantum mechanics, the existence of the quantum of action h implies that there is a lower limit to the interaction between the measuring bodies and the objects under investigation. One can try to control this interaction, by observing the measuring bodies themselves, but in that case those measuring bodies themselves become part of the system being observed, and the additional measuring bodies introduced will again have an uncontrollable interaction with the system.
Using a collapse interpretation like the CI here gives contradicting predictions. As soon as the internal observer performs his measurement, collapse happens and one definite outcome is selected. The external observer however will also find other outcomes with non-zero probability.

Of course, this is only a gedanken experiment. But I don't think you can get a consistent version of the CI without postulating that there is a macroscopic world which doesn't obey the rules of QM.
 

Fredrik

Staff Emeritus
Science Advisor
Gold Member
10,730
405
Using a collapse interpretation like the CI here gives contradicting predictions. As soon as the internal observer performs his measurement, collapse happens and one definite outcome is selected. The external observer however will also find other outcomes with non-zero probability.
I think this is a valid line of reasoning if we identify the state vector with the system, i.e. if we assume that it represents all the properties of the system, that it describes the system, or however you would like to put it. But I would consider that assumption to be part of the MWI, not the CI.

There are undoubtedly many people who do think of that assumption as part of the CI, but I don't think that makes sense. When I argued against this view here, I still thought that this was the CI. Since then I've learned that everyone seems to mean something different by "the CI", so I try to avoid that term.

Of course, this is only a gedanken experiment. But I don't think you can get a consistent version of the CI without postulating that there is a macroscopic world which doesn't obey QM rules.
I think it makes more sense to just drop the idea that QM is a description of what's happening, and instead view it as a way to associate probabilities with possible results of experiments.
 

kith

Science Advisor
1,277
396
Thanks Fredrik, what you write makes sense to me. So there is a more meaningful version of the CI than the one I mentioned. I agree that the term "CI" is notoriously ambigious, but somehow I still find myself using it from time to time.
 
9,184
2,095
I think it makes more sense to just drop the idea that QM is a description of what's happening, and instead view it as a way to associate probabilities with possible results of experiments.
I reached that conclusion long ago. IMHO doing otherwise simply carries too much baggage and Ballentine also makes a strong case.

Einstein returns with a vengeance - except of course he believed not only that but it pointed to the incompleteness of QM. I personally haven't reached that conclusion but it sure whispers in your ear that could be the case.

Thanks
Bill
 
70
3
On the one hand

Fredrik said:
Unfortunately I don't think philosophers are doing any of those things well. So I can't help wondering if philosophers have any relevance to science.
On the other

Fredrik said:
I think it makes more sense to just drop the idea that QM is a description of what's happening, and instead view it as a way to associate probabilities with possible results of experiments.
So, really, this amounts to the admission that "physics is not actually informing us about reality' after all, but only making statistically accurate predictions about particular things - the kind of consideration, I would suggest, which is precisely within the ambit of philosophy, as distinct from physics

I think we're losing sight of something here. In the heyday of scientific materialism, which was ended with the discovery of relativity theory and QM, the idea was that the atom was the universal explanans - that in terms of which 'everything else can be explained'. That, after all, was the basis of 'philosophical materialism'.

Now we find that nobody can actually agree on what observations of the quantum world actually mean in relation to the actual world. Of course we can speculate in terms of M-theory, or whatever it is, but all such speculations to me, seem to be grounded in mathematical abstraction, which is hardly the same kind of thing as an indivisible point particle.

Not many people seem to get that.

That is one reason why I find an irony in this remark:

Bill said:
What is fairer to say is science makes extensive use of a tiebreaker in an argument - philosophical or otherwise - actual observation - that's the real issue.
When, by definition, Everett's 'many worlds' are not even observable in principle. Yet, because it is mathematically coherent, we are willing to disregard the apparent preposterousness of such an idea. And there are many fundamental theories of physics and cosmology which entertain equally non-observable notions, from multi-dimensional strings to infinite numbers of 'universes'.

I think Lewis Carroll saw all this coming.

The only reason that most philosophers aren't doing a good job of pointing it out, is because in Anglo--American analytical philosophy, they're all in the thrall of philosophical materialism, notwithstanding the fact that the very ground has been cut out from under their feet.

So they spend most of their time arguing about the meaning of propositions. That is why they're useless, not because philosophy itself has nothing to say. Philosophy has very important questions to ask about what qualified as 'knowledge' and what role the mind has in the construction of what we regard as reality.
 
9,184
2,095
When, by definition, Everett's 'many worlds' are not even observable in principle. Yet, because it is mathematically coherent, we are willing to disregard the apparent preposterousness of such an idea.
Who is this 'we' Kemosabe?

Some are willing to accept the idea of world splitting for the sake of mathematical elegance and beauty - namely on the basis of a poll about 20% - 80% aren't - but like all things, when observation cant decide, it comes down to personal taste - there is no absolute right/wrong here - get used to it.

Although there is no agreement on this issue there is 100% agreement on the underlying math - that's pretty good compared to philosophy - in fact I don't think philosopher's can claim that distinction on any issue - but I could be wrong.

So, really, this amounts to the admission that "physics is not actually informing us about reality'
The problem with that is no one, philosophers, mathematicians, scientists - no one - can agree what 'reality' is - so its a bit hard to decide if physics is telling us anything about it.

I believe it does because I believe 'reality' is what physics tells us - but getting agreement on that is not likely - not likely at all.

And yes there is multiple views on QM that can't all be right - but the math is agreed by all so that is what I accept as realty. Actually that is something really weird - why the math of physical theories is - well - so effective:
http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html

Murray Gell-Mann thinks he knows the answer - self similarity. If true that would be a major and profound insight into 'reality'.

Thanks
Bill
 
Last edited:
70
3
Hot off the press - literally published today - http://amzn.com/019979054X [Broken] by Alyssa Ney.

This is a new volume of original essays on the metaphysics of quantum mechanics. The essays address questions such as: What fundamental metaphysics is best motivated by quantum mechanics? What is the ontological status of the wave function? Does quantum mechanics support the existence of any other fundamental entities, e.g. particles? What is the nature of the fundamental space (or space-time manifold) of quantum mechanics? What is the relationship between the fundamental ontology of quantum mechanics and ordinary, macroscopic objects like tables, chairs, and persons? This collection includes a comprehensive introduction with a history of quantum mechanics and the debate over its metaphysical interpretation focusing especially on the main realist alternatives.
OUP, too. Not some fly-by-night publishing house.
 
Last edited by a moderator:

jambaugh

Science Advisor
Insights Author
Gold Member
2,175
231
So, really, this amounts to the admission that "physics is not actually informing us about reality' after all, but only [...]
Physics informs us of actuality (what happens) rather than about reality (what is). One can only speculate about reality. Actuality slaps us in the face every morning. Which would you rather know about?

[edit] PS The philosophical issues are not lost on the Western camp. There has been a quiet battle between positivists (who stay out of philosophy departments and journals) and the post modernists who want to rebrand mysticism as science for the sake of their cherished realities.

Positivism resolves the issue nicely but in some it leaves a feeling of disquiet, like when they begin to understand that there is no Santa Claus.
 
Last edited:
9,184
2,095
OUP, too. Not some fly-by-night publishing house.
Had a look at a preview on Amazon.

It's not quackery or anything like that but it is written by philosophers for philosophers. Trouble is philosophers view of QM often (not always - but often) leaves a lot to be desired.

Its certainly cheap though and I will have a bit more of a look at its contents and may even get it.

Thanks
Bill
 
9,184
2,095
and the post modernists who want to rebrand mysticism as science for the sake of their cherished realities.
Oh dear - trouble is its probably true. Witness the popularity of consciousness causes collapse amongst SOME philosophy types that post - I rarely see it from actual practicing scientists - about the only modern adherent I know of is Penrose.

Thanks
Bill
 

jambaugh

Science Advisor
Insights Author
Gold Member
2,175
231
I think consciousness causes collapse is basically rubbish - but heresy - no.
The problem people have with orthodox CI is that indeed consciousness does cause collapse, because collapse occurs in the conceptualization, not in the material world. One as an act of consciousness collapses one's manifold of speculations about how something might behave to the singular point of how it has behaved in a given instance.

Likewise Everett's MWI is compatable with CI IF one understands that the manifold of parallel realities are parallel reality models within one's conceptualization. One should understand that we use "reality" as a model for what is out there but that the actual objective reality is a model in our heads, that "what is out there" is a system of material phenomena which at the quantum level is not a point state within a continuum sea of possibilities but just "stuff happening".

Example: A chair is a chair because we sit in it. If I hit you over the head with a chair it hasn't suddenly "collapsed" into a club in its "reality" (well actually it has but..) rather in its material actuality, it has in our conceptualization of its typical behavior. The chairness is in its function.
(And there are an infinite variety of other "objective states of utility" for that chair, such as door stop, art object, magician's prop,... the "many worlds" of the chair.)


At the quantum level material systems are "all function". Electrons are electrons because they behave like electrons and that is the sum total of their electronness. How they behave is described as precisely as can be observed by the quantum mechanical description of electron observations. One may propose a deeper quantum theory describing electrons as quantum composites of some more basic phenomenon (parton theories etc) but you can't go backwards and build quantum systems out of empirically verifiable classical (as in objective reality based) ones.

Objective reality is dead. It is only the voodoo of the intransigent metaphysicists who keep it in its current zombie state... the walking dead.
 
18
0
F.Tipler and non-locality as evidence for many-wolrds

Folks, I was going to open new thread, but maybe it is enough to ask it here. As for interpretations of QM I am open-minded agnostic.But: what about F.Tipler's article "Nonlocality as evidence of myltiverse cosmology", where he uses nonlocality and argue for MWI? Here:

http://arxiv.org/pdf/1008.2764.pdf

What is non-mwier response to that?Or -does there even NEED to be a response?...
 
706
2
Oh dear - trouble is its probably true. Witness the popularity of consciousness causes collapse amongst SOME philosophy types that post - I rarely see it from actual practicing scientists - about the only modern adherent I know of is Penrose.

Thanks
Bill




“When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth.”
― Arthur Conan Doyle, the book of Sherlock Holmes


by this i don't mean just the search for context in contextual systems in quantum mechanics(they all are, this widely agreed upon), but the lesson from the cornerstone of the quantum world - the inherent uncertainty of quantum systems. Whatever reality is, the aqcuisition of knowledge is inseparable from what it is and how it is observed. The acquisition of knowledge requires that information is meaningful to someone. Sure, one can claim that instruments completely replace the observer, but the observer is never entirely replaced by instruments; for if he were, he could obviously obtain no knowledge whatsoever. Many helpful devices can facilitate this work but they must be read! The observer’s senses have to step in eventually.The most careful record, when not inspected, tells us nothing. And in the cornerstone of quantum theory(the HUP), availablity of information about systems properties is what determines what will be observed.
 
Last edited:

jambaugh

Science Advisor
Insights Author
Gold Member
2,175
231
Another random comment. Some object to reducing the wave function to "knowledge about the system" and equally to "observer caused [physical] collapse" because they feel it smacks of solipsism. The thing to remember is that in a scientific context there is rigorous constraints on the meaning of an observation and indeed in QM the act of observing, of knowing something in a scientific sense, is a physical act. Saying I know the electron is in a spin z up "state" is saying I have via devices of some type physically interacted with the system in question.

This arises also in understanding Entropy. The proper definition of entropy is as a function of our ignorance about a system. But that doesn't mean it is subjective or meaningless. It is the function of necessary ignorance given the physical constraints in the system's definition and thus this "observer knowledge" has specific indirect connection to the physical world. Not some spooky mind over matter but the hard causal connection between the phenomena and the interaction which causes us to know in the scientific sense. I ask you metaphysicists trying for an ontological (re)interpretation to consider this and reconsider your gut objections to the orthodox non-ontological interpretation.
 
70
3
Jambough said:
Objective reality is dead. It is only the voodoo of the intransigent metaphysicists who keep it in its current zombie state... the walking dead.
whom I would have thought would be the remaining 'philosophical materialists', that is, those who advocate the view of the ultimate mind-independence of reality.

The word 'objectivity' itself was only coined in the 19th century - centuries after metaphysics in its classical sense was written down.
 
70
3
There's an interesting essay here which addresses exactly the question that I raised in the original post. It explains why 'an observing intelligence' is implicated in the 'collapse of the wave function', and concludes:

If the mathematics of quantum mechanics is right... and if materialism is right, one is forced to accept the Many Worlds Interpretation of quantum mechanics. And that is awfully heavy baggage for materialism to carry.

If, on the other hand, we accept the more traditional understanding of quantum mechanics that goes back to von Neumann, one is led by its logic ...to the conclusion that not everything is just matter in motion, and that in particular there is something about the human mind that transcends matter and its laws.
(Emphasis added.)
 
9,184
2,095
There's an interesting essay here which addresses exactly the question that I raised in the original post. It explains why 'an observing intelligence' is implicated in the 'collapse of the wave function', and concludes:
Von Neumann's argument was that the collapse could be put anywhere but if you keep tracing it back the only place that looks different to anywhere else is human consciousness (at least that's my recollection). A few bought into it including Wigner but since then great strides have been made in the understanding of decoherence.

http://en.wikipedia.org/wiki/Quantum_mind%E2%80%93body_problem [Broken]
'Decoherence does not generate literal wave function collapse. Rather, it only provides an explanation for the appearance of wavefunction collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings. A total superposition of the universal wavefunction still exists (and remains coherent at the global level), but its fundamentality remains an interpretational issue. "Post-Everett" decoherence also answers the measurement problem, holding that literal wavefunction collapse simply doesn't exist. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".'

When Wigner heard about decoherence from some early work of Zureck he realised consciousness was no longer required - it provides the natural place to put collapse - not consciousness.

I do not know much about philosophy, materialism and such but I find it hard to believe interpretations like Bohmian Mechanics, GRW etc do not satisfy its tenants just as well as Many Worlds.

Thanks
Bill
 
Last edited by a moderator:
70
3
bhobba said:
When Wigner heard about decoherence from some early work of Zureck he realised consciousness was no longer required - it provides the natural place to put collapse - not consciousness.
Be that as it may, the Wikipedia article on 'Quantum Decoherence' which the above article links to, says that:

Specifically, decoherence does not attempt to explain the measurement problem.
Besides which, as I have said before, 'quantum decoherence' is not an idea that can be meaningfully rendered in English (indeed same article is said not to be understandable to laypersons.)

But it least it serves the purpose of enabling 'the physicists' to say they can trump 'the philosophers' in arguments over 'interpretation of QM' :wink:
 
9,184
2,095
But it least it serves the purpose of enabling 'the physicists' to say they can trump 'the philosophers' in arguments over 'interpretation of QM' :wink:
There are philosophers that know the details - if you want to read what one of those think check out:
http://arxiv.org/pdf/1111.2187v1.pdf
'Decoherence explains why it is that quantum theory nonetheless works in practice: it explains why interference does not, in practice spoil the probabilistic interpretation at the macro level. But because decoherence is an emergent, high-level, approximately-defined, dynamical process, there is no hope of incorporating it into any modification of quantum theory at the fundamental level.'

Decoherence does not attempt to explain it because it doesn't need to - 'Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".'

I don't necessarily hold entirely to that - my view is its still there but now not a problem.

Thanks
Bill
 
Last edited:
70
3
Interesting article! I shall *try* and take it in. But as far as I am concerned, as long as an element of mystery remains, I sleep OK too.
 
33,366
9,095
by this i don't mean just the search for context in contextual systems in quantum mechanics(they all are, this widely agreed upon), but the lesson from the cornerstone of the quantum world - the inherent uncertainty of quantum systems. Whatever reality is, the aqcuisition of knowledge is inseparable from what it is and how it is observed. The acquisition of knowledge requires that information is meaningful to someone. Sure, one can claim that instruments completely replace the observer, but the observer is never entirely replaced by instruments; for if he were, he could obviously obtain no knowledge whatsoever. Many helpful devices can facilitate this work but they must be read! The observer’s senses have to step in eventually.The most careful record, when not inspected, tells us nothing. And in the cornerstone of quantum theory(the HUP), availablity of information about systems properties is what determines what will be observed.
Following your argument, can you show me the difference between those setups?
a) A computer records an experiment and displays the result to you
b) A human records an experiment and tells you the result
If you see a difference, where does it come from? Is there a fundamental difference between neurons and transistors?
If you do not see a difference, however, imagine a computer (with some advanced AI) asks you the same question. Is this different from me, asking the question?

There is no known physical process which makes human brains special in any way. On the other hand, there are good arguments that it is possible (at least in theory) to fully implement a human brain in electronics.
 
706
2
Following your argument, can you show me the difference between those setups?
a) A computer records an experiment and displays the result to you
b) A human records an experiment and tells you the result


These are both the same. The argument is whether a machine recording a reading and displaying it to a wall, chair or a bridge without there ever being a way for it to be read by a perceiving observer is the same as the result being read be an observer. A few experiments and the HUP suggest that classical behavior depends on knowledge about the properties of the quantum systems.



If you see a difference, where does it come from?

No. In your example there is no difference but it wasn't part of what i was discussing - the quantum mechanical counterfactual definiteness in abscence of obeserver.


There is no known physical process which makes human brains special in any way. On the other hand, there are good arguments that it is possible (at least in theory) to fully implement a human brain in electronics.
There are also good arguments why a conscious brain will never be implemented in electronics, so this point is moot.
 
Last edited:
33,366
9,095
If it does not matter if a computer or a human record the results of the observation, the human brain cannot cause a collapse when the computer does not. Unless you consider collapses are pure "personal" events - so every brain gets its own physics with different collapses. I have no idea how that should work.
There are also good arguments why a conscious brain will never be implemented in electronics, so this point is moot.
Note that "consciousness", independent of the definition (which is problematic anyway) is irrelevant to others, as you confirmed in your post. We can just ignore it for a description of the system.
I don't think that those arguments are good, however. Electronics can do the same as neurons can. Or you can build artificial neurons, if you like.
 
706
2
If it does not matter if a computer or a human record the results of the observation, the human brain cannot cause a collapse when the computer does not. Unless you consider collapses are pure "personal" events - so every brain gets its own physics with different collapses. I have no idea how that should work.


You also have no idea how the 'environment' induces collapse, so it's hardly relevant what belief you subscribe to. Believing this wonderful classical world can emerge out of potentials which are not even grounded in anything physical, is as much a fairy-tale as believing in gods. It's dubious if it's even valid philosophy.
So we have an emerging classical reality for which no straight-forward quantum mechanical explanation exists that is in accord with sensory experience, and you consider the fundamental machinery of the world to be potentials that develop in time to single outcomes. OK. The problem with that position is that it makes no sense. What about personal experience, awareness? The behavior of the so called potentials is found to be dependent on knowledge through the complementary nature of the quantum world, so knowledge and awareness cannot simply be passive, emergent phenomena of quantum potentials.

By the same metric, the so called brain is also an emergent and decoherent 'object', so i object to the inference that i ever implied that brains cause collapse. I did not.



Note that "consciousness", independent of the definition (which is problematic anyway) is irrelevant to others, as you confirmed in your post. We can just ignore it for a description of the system. I don't think that those arguments are good, however. Electronics can do the same as neurons can. Or you can build artificial neurons, if you like.

The argument only goes so far without breaking the forum rules. I've seen nothing in quantum theory that suggests or proves that personal experience is not fundamental. For that, you need to resort to sensory experience and beliefs you've been accustomed to hold by the society and which are... well, impossible to logically hold while simultaneously holding onto quantum mechanics(bad philosophy aside that is, and that includes the MWI imo)
 
Last edited:

Related Threads for: The Many-Worlds Interpretation of QM

Replies
67
Views
8K
Replies
94
Views
3K
Replies
3
Views
1K
  • Posted
Replies
0
Views
2K
  • Posted
Replies
1
Views
2K
Replies
22
Views
6K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top