Many Worlds Interpretation and act of measuring

[RUTA]

The "correct distribution" INCLUDES a nonzero probability of weird initial conditions. If something has a nonzero probability, and you repeat the experiment infinitely often, then it will almost certainly happen (unless there is some unknown conservation law that prohibits it).

For example, the odds are 1 in 2^{10^6} that flipping a coin one million times will end up "heads" each time. If you assume that relative frequencies are always equal to theoretical probabilities, then that implies that it will happen roughly once in every 2^{10^6} worlds. To assume that it never happens, on any world, is to contradict your assumption that relative frequencies approach the theoretical probability.

I should've said every planet will discover the correct probability, not distribution. Of course in establishing the correct probability, everyone will see the correct distribution. Again, you're just making an assumption otherwise. There's no logical reason that has to be the case. Given your assumption for the way the probability of classical physics is instantiated in reality, then I agree, MWI is no worse off.

 

[stevendaryl]

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In contrast, with ordinary probability, we don't have to be optimists about it, we can quantify it using probability, eg. using a Frequentist p value or a Bayesian posterior.

I disagree. For probability theory to be HELPFUL, in the sense of providing useful tips on how to bet on future occurrences (I'm using "bet" in a loose sense here--if I take a plane, I'm betting my life that it won't crash), the future relative frequencies should be roughly what is predicted by my probability theory. If that isn't the case, then I've wasted my time computing probabilities. But whether the future turns out the way probabilities predict is luck. They may not.

I think a major question is whether such optimism is rational. In Deutsch-Wallace MWI, the unique rational assignment of weights is according to the Born rule of the true amplitudes.

If a counting assignment of weights is rational, then it would seem that the Deutsch-Wallace assignment is not unique, contrary to their claim.

I'm only claiming that a counting assignment of weights is AN approach to dealing with nondeterminism. If all you have to go on is a set of possibilities, and you have no basis for distinguishing the different possibilities, then a counting weight is as good as anything. It's sort of a "minimalist" assumption.

The case of quantum mechanics is a little more complicated, because we do have other information that simply the number of possible outcomes. We have the amplitudes, as well. Various people have argued that if we assume that a weight is derivable from amplitudes, then something like the Born rule is the only possibility consistent with certain other criteria for reasonableness.

Basically, we decide that a particular way of assigning weights is best because the other alternatives have unmotivated, ad-hoc elements that we find objectionable. There's the same sort of thing going on in statistical mechanics. We compute such things as entropy by making the assumption (or maybe definition) that for a thermally isolated system in equilibrium, all states with the same energy are equally likely. We don't really know that that's the case, but we have no basis for assuming anything different.

But that doesn't address how we could come to know the weights in the first place - how we could come to their definition of a rational behaviour?

I don't think that that's mysterious, at all. We perform the same experiment a bunch of times, and compute relative frequencies. Then we assume that they reflect some kind of probability, and we develop a theory to allow us to calculate it. If the relative frequencies hadn't turned out that way, we would have discarded the theory.

How could you know whether you are in a good world or bad world, in at least a probabilistic sense?

I think it's just an assumption. If we don't assume that future relative frequencies can be calculated, then we can't make predictions about the future. We can't do science. We can't do technology. We can't do medicine. So we assume that we live in a nice, predictable world, because we have no other way to reason about it. If our assumption is wrong, then we're screwed. But as I said, we might as well be optimists about it.

 

[EmilyCA]

'You' means what you experience as a sequence of worlds. You never experience more than one world at a time.

Thanks
Bill

In that case, it is true as a matter of definition that `you' see whatever outcome it is that you see. Therefore there is nothing to be learned in a measurement: you are defined as the agent who sees outcome A, so the measurement yields only the tautology, `The agent who sees outcome A sees outcome A.' This sort of fact cannot possibly confirm or falsify a scientific theory.

 

[bhobba]

In that case, it is true as a matter of definition that `you' see whatever outcome it is that you see. Therefore there is nothing to be learned in a measurement: you are defined as the agent who sees outcome A, so the measurement yields only the tautology, `The agent who sees outcome A sees outcome A.' This sort of fact cannot possibly confirm or falsify a scientific theory.

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.

Thanks
Bill

 

[stevendaryl]

I think the difference here is that we can give a non-indexical account in terms of the physical locations of thought-events: when I have the thought 'I wonder which outcome I am going to see?' there is a fact about where in spacetime that thought-event occurs, and so there is a unique answer to this question, since there is a unique outcome that is going to occur in the vicinity of the thought. In the Everettian case this isn't possible: if prior to the measurement we wonder which outcome we're going to see, there is no unique answer since there is only one thought-event but many different outcomes that are going to be seen.

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).

 

[stevendaryl]

What, precisely, do you mean by `you'? If `you' are merely a person-at-a-time rather than a continuant over time, then there is no fact of the matter about which outcome `you' will see when you perform the measurement. Whereas if `you' are an entity that persists over time, then it seems that `you' will indeed experience all the worlds, since the observers who see the different outcomes are not distinct before the time of the measurement.

Either way, it seems that there is nothing here which can play the necessary stochastic role.

If the future is not determined, then it seems that, by definition, there is no "fact of the matter" about future events. They become facts when they happen, and get entered into our memories. So the only facts are facts about the past (and possibly facts that hold in all possible futures). I don't see that branching or stochastic events makes any difference. In both cases, the past is definite, and the future is indefinite.

 

[Quantumental]

If the future is not determined, then it seems that, by definition, there is no "fact of the matter" about future events. They become facts when they happen, and get entered into our memories. So the only facts are facts about the past (and possibly facts that hold in all possible futures). I don't see that branching or stochastic events makes any difference. In both cases, the past is definite, and the future is indefinite.

In MWI the future is definite. You know that pre-branching that you will see all outcomes post-branching.

 

[bhobba]

In MWI the future is definite

Yes - but what you experience isn't.

Thanks
Bill

 

[stevendaryl]

In MWI the future is definite. You know that pre-branching that you will see all outcomes post-branching.

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.

 

[atyy]

I disagree. For probability theory to be HELPFUL, in the sense of providing useful tips on how to bet on future occurrences (I'm using "bet" in a loose sense here--if I take a plane, I'm betting my life that it won't crash), the future relative frequencies should be roughly what is predicted by my probability theory. If that isn't the case, then I've wasted my time computing probabilities. But whether the future turns out the way probabilities predict is luck. They may not.

All observations are consistent with complete randomness and no laws of physics. But why do we act as if Copenhagen quantum mechanics or equilibrium statistical mechanics are better theories than complete randomness? The reason is that we are typical in Copenhagen and equilibrium statistical mechanics, but we are not typical in complete randomness. So MWI has to find some way of arguing that the results we see are "typical" in some sense, otherwise we could not choose between MWI and complete randomness.

One way to argue that we are "typical" in MWI in some sense is to assign a weight, such as the branch counting measure you mention. But there are potential problems with this.

(1) It is unclear whether we are typical given a branch counting measure, and some argue that we are not typical given such a measure.

(2) It seems to conflict with the Deutsch-Wallace argument. At the very least, it would seem that MWI does not make sense unless additional structure is introduced, such as the branch-counting measure. Maybe this would be ok, if we start with the branch counting measure as a guess, and then are able to update it as one gets more data. I think this is what Greaves and Myrvold try to do.

 

[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