Many Worlds Interpretation and act of measuring

[rootone]

not controlling, I mean, who is "me" in another universe, I mean, this is confusing.. my brain hurts

Mine too.
Here I am writing this post in a universe that I am certain exists.
Yet I am asked to comprehend the idea that I simultaneously do not exist, or that I died last night.

 

[EmilyCA]

That I agree with. Its more or less tautological in the interpretation that you will experience one world because that's what human beings do. If that's a problem I don't really see it.

Sorry, I wasn't clear enough. I don't mean it's tautological that you experience one world - I mean it's tautological that you see whatever outcome you do see, and therefore you do not learn an empirical fact about the world when you make that observation.

I wouldn't say that we KNOW that there is a fact of the matter about such questions. We don't. As far as I can see, it's just an attitude toward the theory, it's not inherent in the theory.

Take my Newtonian universe, with infinitely many worlds that fill up all of phase space. The question is: What is "Daryl" or "Emily"? We can take an indexical approach, where we say that Daryl is defined by the person at an unobservable location in spacetime. Or we can take a subjective approach, where "Daryl" is defined by a coarse-grained equivalence class of all systems in the universe with subjectively equivalent situations. From the latter point of view, I don't have a unique location in the universe, and the future for me is nondeterministic. Mathematically, the two ways of viewing things are equivalent. Given the first, we can get to the second by taking equivalence classes, and given the second, we can get to the first by introducing a "hidden variable" that determines my first experiences (this hidden variable is equivalent to knowing my "true" location in the universe).

I agree, this is an interpretational question which depends on one's view of the nature of spacetime and of consciousness. However, I think it is at least possible to formulate a point of view whereupon the observer in the Newtonian universe may be thought of as a random sample from a reference class of observers, whereas I don't think there exists any such coherent point of view for the MWI.

It depends on what you mean. The future of the universe as a whole is definite. But if you think of your personal history as a path through the branches, then your history up to one point in time doesn't determine your future history.

But your personal history is not a path through the branches; there is nothing that goes into one branch rather than another. There is no meaningful question to be asked about which future history will be yours, and therefore there is no uncertainty here.

 

[bhobba]

Sorry, I wasn't clear enough. I don't mean it's tautological that you experience one world - I mean it's tautological that you see whatever outcome you do see, and therefore you do not learn an empirical fact about the world when you make that observation.

Cant follow that one. You learn the outcome of the world you are in.

Thanks
Bill

 

[rootone]

Yet alternative worlds where the outcome is different exists physically?
I have egg with toast for breakfast in this world, yet a world exists where Instead I ate a prawn sandwich,
Otherwise the worlds containing me are identical and not causally connected, but physically exist?

 

[bhobba]

Yet alternative worlds where the outcome is different exists physically?

What is meant by 'exists physically' is likely debatable by philosophers. But they are part of that interpretation 100% for sure.

Its a weird theory - too weird for me. But we discuss science here - not the level of weirdness - it may well be true. If you don't like it you are in good company - I don't - but one must keep an open mind. If it's too weird for you move on - check out some other interpretation. Once you understand QM better you can return to it with a better appreciation of the issues its trying to resolve as well as the very elegant, but weird, way it does it.

Just as an aside when I first leant of this interpretation I thought you would have to have rocks in your head to believe it - its nearly as bad as conciousness causes collapse. But slowly, oh so slowly, from discussion here, further reading and thinking about this issues, I grew to appreciate what it does and what it resolves. I got Wallace's book on it and saw just how beautiful mathematically it is. It even links to other interpretations like Consistent Histories, so a study of each deepens understanding of the other. In science having an open mind is very very important. That's not to say you shouldn't have an opinion - that's just as important - but it must be an informed opinion.

Thanks
Bill

 

[Rajkovic]

no one answered me, if I die here in our universe, I'm dead, right? I am not eternal?

 

[bhobba]

no one answered me, if I die here in our universe, I'm dead, right? I am not eternal?

Of course not. Don't be fooled by this quantum suicide rubbish. If someone make a duplicate of you then kills you, you are still as dead as a doornail. The duplicate is not you.

Added Later:
There is an interesting variant of this though that actually happens. You literally are not the same person you were say 50 years ago - just about every atom in your body has been replaced. That is an interesting philosophical discussion - but not for this forum. Occasionally we touch on philosophical issues - but basically we discuss science and science divorced itself from philosophy long ago.

Thanks
Bill

 

[Rodrigo Cesar]

This "theory" is hardly pseudoscience, it is pure FANTASY, it doesn't exist in reality. This is the result of trying to understand quantum mechanics, In a few years who created this crap will be ashamed.
You're only discussing it because "mathematically" is beautiful, but in reality is pure bollocks.
:Before even be found the theory of quantum mechanics, no one has ever dreamed of "parallel universes" this never existed in billions of years, now just because someone invented a math to solve something no one understands, this bull**** appears as if it were real.

 

[bhobba]

You're only discussing it because "mathematically" is beautiful, but in reality is pure bollocks.

I think you need to understand science and the scientific method a bit better. Don't be too worried - I felt in a similar way towards it - but understanding changed my view.

Thanks
Bill

 

[Rajkovic]

Of course not. Don't be fooled by this quantum suicide rubbish. If someone make a duplicate of you then kills you, you are still as dead as a doornail. The duplicate is not you.

Added Later:
There is an interesting variant of this though that actually happens. You literally are not the same person you were say 50 years ago - just about every atom in your body has been replaced. That is an interesting philosophical discussion - but not for this forum. Occasionally we touch on philosophical issues - but basically we discuss science and science divorced itself from philosophy long ago.

Thanks
Bill

you mean, my molecules changed?

 

[Rajkovic]

I know this has nothing to do with the topic, but what about people who say that we never 'touch' things, is this true?

 

[bhobba]

you mean, my molecules changed?

Yes. You literally are not the same person.

We also have a medical sciences sub forum here and that would be the appropriate place to discuss this very interesting fact.

Thanks
Bill

 

[bhobba]

I know this has nothing to do with the topic, but what about people who say that we never 'touch' things, is this true?

Yes. Solidity comes from the Pauli Exclusion principle:
http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter

Some, even some quite knowledgeable people, think its because the outer electrons of atoms repel. It isn't - as first proved by Dyson.

But pursuing it further will derail this thread. Its a legitimate topic for a new thread - although it has been discussed before.

Thanks
Bill

 

[julcab12]

As far as i go about it. Out of all the interpretation I've tried to understand on QM. For some reason, I'm more comfortable with stochastic version and CI of QM simply bec it has more emphasize on time + simultaneity of positions and velocities has a more natural(classical) take. Of course it's not w/out problem and some people might not appeal to these (ψi and ψ ∗ i , constrained by the normalization condition and treatment of K).

http://arxiv.org/pdf/1109.6462v4.pdf

"..We consider a general isolated system, which may or may not include a macroscopic measuring apparatus and/or an observer. We assume as in ordinary quantum mechanics that the state of the system is entirely described by a vector in Hilbert space. The state vector here is taken in a sort of Heisenberg picture, in which operators A(t) have a time dependence dictated by the Hamiltonian H as exp(iHt)A(0) exp(−iHt). But the state vector in this sort of theory is not time-independent; it undergoes a stochastic evolution..."

 

[stevendaryl]

As far as i go about it. Out of all the interpretation I've tried to understand on QM. For some reason, I'm more comfortable with stochastic version and CI of QM simply bec it has more emphasize on time + simultaneity of positions and velocities has a more natural(classical) take. Of course it's not w/out problem and some people might not appeal to these (ψi and ψ ∗ i , constrained by the normalization condition and treatment of K).

http://arxiv.org/pdf/1109.6462v4.pdf

"..We consider a general isolated system, which may or may not include a macroscopic measuring apparatus and/or an observer. We assume as in ordinary quantum mechanics that the state of the system is entirely described by a vector in Hilbert space. The state vector here is taken in a sort of Heisenberg picture, in which operators A(t) have a time dependence dictated by the Hamiltonian H as exp(iHt)A(0) exp(−iHt). But the state vector in this sort of theory is not time-independent; it undergoes a stochastic evolution..."

I haven't worked through the paper, but doesn't having an objective wave function collapse imply nonlocal interactions (according to Bell's theorem)?

 

[rootone]

Yes. Solidity comes from the Pauli Exclusion principle:
http://en.wikipedia.org/wiki/Pauli_exclusion_principle#Stability_of_matter

Some, even some quite knowledgeable people, think its because the outer electrons of atoms repel. It isn't - as first proved by Dyson.

But pursuing it further will derail this thread. Its a legitimate topic for a new thread - although it has been discussed before.

Thanks
Bill

Can't this be seen as the same thing though?
Two electrons can't occupy the same position, so if an electron in the shell of one atom 'attempts' to go to a position already occupied by an electron of another atom, it just can't happen, so the offending electron experiences 'repulsion', it has to go somewhere else.

You're right though, that's going off topic, I might start a new thread on that if I can't find one already that covers it.

 

[bhobba]

Can't this be seen as the same thing though?.

No.

You can't penetrate the electron cloud.

Thanks
Bill

 

[atyy]

Can't this be seen as the same thing though?

The two ideas involve some form of repulsion between electrons, but the origins are different:
(1) electrostatic repulsion - electrons repel each other due to having charge of the same sign
(2) exclusion principle repulsion - electrons repel each other due to being identical fermions

 

[Rodrigo Cesar]

in this video: watch?v=P0TNJrTlbBQ Professor Philip Moriarty explains it perfectly "Do Atoms Ever Touch?"
"Professor Moriarty's definition of contact is also the definition of contact that we all use for the Newtonian world. The attractive & repulsive forces balancing out."

 

[bhobba]

in this video: watch?v=P0TNJrTlbBQ Professor Philip Moriarty explains it perfectly "Do Atoms Ever Touch?"
"Professor Moriarty's definition of contact is also the definition of contact that we all use for the Newtonian world. The attractive & repulsive forces balancing out."

Had a look at it.

Unlike a lot of things on You-Tube this is correct.

But note - he defines contact as forces balancing ie the Van Der Walls attractive force and the repulsive force of the Pauli Exclusion Principle that is the origin of solidity. This is a LOT different from the usual conception of contact.

Thanks
Bill

 

[Ilja]

What is meant by 'exists physically' is likely debatable by philosophers. But they are part of that interpretation 100% for sure.

Its a weird theory - too weird for me. But we discuss science here - not the level of weirdness - it may well be true. If you don't like it you are in good company - I don't - but one must keep an open mind. If it's too weird for you move on - check out some other interpretation. Once you understand QM better you can return to it with a better appreciation of the issues its trying to resolve as well as the very elegant, but weird, way it does it.

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

To construct its "many worlds", it uses decoherence, but decoherence presupposes some subdivision into subsystem. Because without a restriction to subsystems there is no decoherence. Nobody explains where this subdivision comes from.

The very interpretation contradicts common sense, but to "derive" the Born rule it relies on common sense - because this is what is Bayesian probability based on. Common sense, which is based on the assumption, that we will in future, as well as now, observe only a single universe, and that the problem of rational thinking is to find out which one.

It remains to explain, why this "interpretation" is that popular. It seems to me, that this is simply the most degenerate example of what I name "mathematical mysticism". The problem here is the positivistic rejection of the discussion of philosophy/metaphysics. Self-contradictory, because it is itself philosophy, but self-defending, because it forbids discussions that criticize it (as philosophy). But, because philosophy and interpretation is a natural part of natural philosophy (the original name of physics), the result of positivistic physics will not be physics without metaphysics but physics with bad metaphysics. It is easy to predict, which type of metaphysics wins here: The one which can less than any other be accused of "containing metaphysics". This is the mystification of the mathematics of the existing theory. Once the mathematics of the theory are the part which is at least connected with observation, nobody can argue that all these equations are "metaphysics" or "philosophy". So you are free to mystify them. The equations are not simply equations which describe, approximately, the results of clock measurements, no, they define spacetime itself. The wave function is not simply a not well understood device to compute probabilities, no, they are reality itself. Some different philosophical objects or principles should not exist, because they are philosophical. So, once GR has solutions with closed causal loops which violate causality, we have to throw away causality. Some hidden preferred global time, which could easily prevent causal loops in a Lorentzian interpretation of GR, is an additional structure, thus, anathema. Some single universe, the one where we live in, which could be easily introduced like in de Broglie-Bohm theory, is an additional, new structure, thus, anathema.

Why this is not simply one, possibly unfortunate but who knows, choice of metaphysics, but bad metaphysics? Simply because it is the most inert one, the one which prevents any progress toward a more fundamental theory. For a very simple reason: A new theory needs something new - new structures, new equations, new metaphysics. These new concepts should be, of course, compatible with the existing theory, but have to go beyond it. So, there will be not only a new theory, but also a new interpretation of the old one - the interpretation, where it is the limit, the approximation of the new theory. And this will be an interpretation containing something new, something which is not part of the equations of the old theory. And one needs, together with the new interpretation, new problems - the problems which suggest how to modify the approximate equations of the new theory, which we already knew, to obtain the new, more fundamental equations. The way we can identify these problems today is also predictable: They will appear as metaphysical conflicts of the interpretation with some other, independent metaphysical principles. So, we need exactly those things which are abhorrent to mathematical mysticism.

Just as an aside when I first leant of this interpretation I thought you would have to have rocks in your head to believe it - its nearly as bad as conciousness causes collapse. But slowly, oh so slowly, from discussion here, further reading and thinking about this issues, I grew to appreciate what it does and what it resolves. I got Wallace's book on it and saw just how beautiful mathematically it is. It even links to other interpretations like Consistent Histories, so a study of each deepens understanding of the other. In science having an open mind is very very important. That's not to say you shouldn't have an opinion - that's just as important - but it must be an informed opinion.

So, please, tell me this hidden secret - I have yet been unable to see even a single piece of beauty - mathematical or otherwise - in this interpretation. As well as in inconsistent histories.

 

[Ilja]

I haven't worked through the paper, but doesn't having an objective wave function collapse imply nonlocal interactions (according to Bell's theorem)?

Every realistic/causal interpretation implies it, so what?

 

[bhobba]

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

Well you believe its nonsense. Fair enough. But I am sure you know as well as I do nonsense is in the eye of the beholder.

To construct its "many worlds", it uses decoherence, but decoherence presupposes some subdivision into subsystem. Because without a restriction to subsystems there is no decoherence. Nobody explains where this subdivision comes from.

The branching decooherence theorem on page 93 of Wallaces book may have something to do with it. But it involves studying the book with an open mind.

As I mentioned before one can define a history without reference to measurement, arbitrary division etc etc and use that to bootstrap it. Consistent Histories is similar.

So, please, tell me this hidden secret - I have yet been unable to see even a single piece of beauty - mathematical or otherwise - in this interpretation. As well as in inconsistent histories.

The secret of why I find it beautiful? There is this debate about nature vs nurture - me I believe its a bit of both - but who knows.

Thanks
Bill

 

[Quantumental]

to those of you discussing if atoms really touch: please take it to another thread

 

[stevendaryl]

This "theory" is hardly pseudoscience, it is pure FANTASY, it doesn't exist in reality. This is the result of trying to understand quantum mechanics, In a few years who created this crap will be ashamed. You're only discussing it because "mathematically" is beautiful, but in reality is pure bollocks.

To me, MWI is not so much a theory as an inevitable consequence of QM. We have plenty of evidence that electrons, atoms and molecules can be a superposition of states, because we can calculate and measure the interference effects. MWI to me is simply denying that there is a cutoff between microscopic systems, which obey quantum mechanics and can be in superpositions, and macroscopic system. It's the assumption that QM applies to everything, no matter how large.

To me, it seems that any alternative to MWI amounts to assuming without evidence a limitation to quantum mechanics. It assumes without any evidence that at some quantum mechanics is wrong.

 

[stevendaryl]

I disagree that one must keep an open mind about every piece of nonsense. The interpretation claims that the only thing which really exists is a wave function - a function on the space of all imaginable universes. I observe only one universe. So, even if there would be many different, this would be at least incomplete.

The way I see it is that the conclusion that macroscopic objects (cats, humans, the solar system, the universe) can be in quantum superpositions amounts to just assuming that quantum mechanics applies to those objects. We have plenty of evidence that QM applies to small objects (electrons, atoms, molecules), and we have zero evidence that there are any new effects or new limitations that would prevent it from applying to larger objects.

Your reasoning is something along the lines of:

1. Theory X predicts phenomenon Y.
2. I don't see Y.
3. Therefore X is wrong.

That's just not a valid argument, although it certainly is appealing. What you would need to make it valid is an additional assumption:

1. Theory X predicts phenomenon Y.
2. Theory X predicts that under circumstance Z, we would see evidence of Y.
3. In circumstance Z, we don't see evidence of Y.
4. Therefore X is wrong.

Objecting to MWI because you don't see these macroscopic superpositions is sort of like objecting to the theory that Nepal exists because I've never seen it. I've never had an opportunity to see it.

The way science works, it seems to me, is that you only observe a tiny amount of phenomena in the universe--the universe is too vast for us to observe more than an infinitesimal part of it. But based on the phenomena that we observe, we formulate theories, and we rigorously test them. At some point, we become confident that they apply even in circumstances where they have never been tested. We have confidence that Newton's physics works as well on Pluto as it does on Earth. Of course, we don't have proof of that, but we have no reason to believe otherwise.

To me, the belief that quantum mechanics applies to macroscopic objects is the same sort of case.

 

[Quantumental]

stevedaryl: then how do you explain the factorization problem?

 

[stevendaryl]

stevedaryl: then how do you explain the factorization problem?

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

To me, the stuff about trying to understand how probabilities arise in MWI is not a matter of fanciful speculation. It's an attempt to come to grips with the possibility that our theory (QM) is actually true.

I understand that what is meant by QM already includes distinctions between system and observer, between unitary evolution and measurement processes. However, the role of these special cases can be made minimal. You could, in keeping with Copenhagen, consider the entire history of the universe to be a single quantum experiment, and the only measurement is at the end, when someone is trying to put together a "history of the universe" right before the Big Crunch (if that happens--I guess they are now pretty certain it won't).

 

[Quantumental]

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

This is blatantly wrong. You can interpret the delay-erasure experiment, quantum pigeons etc. to imply that quantum mechanics is explained by retrocausality. This seems to be implied by the lack of direction in time too. You got no reason to favour MWI over this.

The factorization problem + born rule problem implies that QM does *not* imply MWI.

 

[atyy]

This is blatantly wrong. You can interpret the delay-erasure experiment, quantum pigeons etc. to imply that quantum mechanics is explained by retrocausality. This seems to be implied by the lack of direction in time too. You got no reason to favour MWI over this.

The factorization problem + born rule problem implies that QM does *not* imply MWI.

But do you have a retrocausal theory that works?

 

[TrickyDicky]

I don't have an explanation for it. I'm just saying that

1. There is no good reason to think that QM does not apply to macroscopic systems.
2. So something like MWI is true unless we discover some corrections to quantum mechanics.

IMHO your premise 1. just generalizes your own difficulties to even consider that QM might be incomplete/wrong so it isn't valid as a scientific assumption, and hinders further discussion.

 

[bhobba]

But do you have a retrocausal theory that works?

The transactional interpretation maybe?

Thanks
Bill

 

[Quantumental]

But do you have a retrocausal theory that works?

I don't. I know several people are working on assembling such theories (Huw Price, Ken Wharton, Matthew Leifer, Yakir Aharanov etc.). Some have even extended it to MWI (Lev Vaidman).
But it is what nature seems to imply in several experiments.

Similarly David Deutsch's conviction of MWI which stems back to the time he concieved of the qubit (mid 1980s). He got the idea of the speed-up being in parallel with a separate world. Today we *know* this is not the case, as has been explained thoroughly by Scott Aaronson, Andrew Steane and Michael Cuffaro. So the original motivation for MWI has been refuted.

But your own (as well as others) belief in MWI seems motivated by the simplicity of the idea that we just extend the idea of the superposition and wavefunction to entail the univere as a whole. But how would that work? There is nothing external to the universe, hence nothing to decohere it. There is also no explanation of fundamental ontology in MWI. This is where David Wallace is still struggling to come up with some deeper ontology than the wavefunction which goes far beyond the quantum formalism as is explained by Jeffrey Barrett (author of the standard entry of Everett) in this paper page 36: http://www.socsci.uci.edu/~jabarret/bio/publications/everett4.pdf
This again enters the territory of the problem of factorization too. You yourself accept that there is no solution to this at this present time, yet you don't seem troubled by it. I have to ask: Why not?

Why not just accept for instance de-Broglie Bohm then? Sure it has problems with non-locality, but it's no worse than factorization, and it does seem to be what nature tell us. Particles moving in the pattern of waves. It has no probability problems like MWI does...Or as mentioned retrocausality as several experiments seem to suggest.. Why blindly favour MWI?

 

[bhobba]

The factorization problem + born rule problem implies that QM does *not* imply MWI.

I think you are a bit confused between problem and definite refutation. Both those issues are controversial and not generally considered to be the theory killer you think it is - as I think has been pointed out to you many times.

Thanks
Bill

 

[Quantumental]

I think you are a bit confused between problem and definite refutation. Both those issues are controversial and not generally considered to be theory killer you think it is - as I think has been pointed out to you many times.

Until they have been solved they are indeed killers and is cited as the main reason why the majority of realist quantum foundation experts reject MWI. It's not just my personal opinion.