With MWI, this is incorrect—we do predict the outcome: all the branches.
The MWI gives an illusion of predictability (“Everything possible happens! We just don’t see it because nearly all of it happens somewhere else to some other ‘us’!”). Unfortunately, it can no more answer the question of which outcome an experiment will measure in “this world” than any other interpretation.
Even more unfortunately, and at a risk of a massive downvote, I hate to say it, but the MWI has become an official LW religion:
proclaimed to be true true by the founder: check
provides comfort to the masses: check
sets the group apart from others: check
impossible to falsify: check
makes one feel superior because of “deeper understanding of the world”: check
How does MWI provide comfort to the masses? Michael Vassar is hardly the masses, but it makes him extremely uncomfortable—he called Quantum Immortality the most horrifying idea he’d ever had to take seriously, and I agree.
I would think that most people would find the idea of living forever in some of the worlds at least somewhat comforting. It is even better than having an immortal soul: you get to live forever in the flesh, and you do not need to pay a tithe in any of the worlds.
That said, I was referring to something else, namely to the major discomfort of the essential unpredictability of any quantum experiment. In the MWI (or at least in some versions of it) the parallel worlds come into existence and sail apart as the decoherence takes hold and the off-diagonal contribution to the joint system/detector state decays away rapidly.
Everything seems predictable and some day maybe even computable. The only minor caveat is that you never get to observe these other worlds and bless your surviving copies with your dying breath (or receive the blessing of those gone before you).
Unfortunately, it can no more answer the question of which outcome an experiment will measure in “this world” than any other interpretation.
It doesn’t fail to give an answer to the question—it makes the question incoherent.
“Which outcome an experiment will measure” is sitting before the experiment looking forward. With MWI, there is no world after the experiment looking backwards with a unique claim on being “this world.” The answer to “will there be a me observing result X” will of course be yes. The question of which of those mes is the “real” one is misleading. What quantum theory does tell us, in MWI, is the total amount of surprise in the mes looking back.
...And we are back to square one, the unfalsifiability of an interpretation, which makes the adepts feel good about their “knowledge” without running any risk of it being shattered.
For your information: Not voting you down because you disagree with the MWI, but because you made a silly argument and then immediately replaced it with an entirely different argument with no acknowledgement that your original argument had been shown to be silly.
I wasn’t feeling superior to you because you chose to reference non-MWI QM—I’m not confident about MWI myself, and would prefer we keep other interpretations alive until we can distinguish on the basis of evidence (or at least have a strong argument that space complexity deserves no place at all in our priors).
I am feeling superior to you now because you ignored a prevalent interpretation without giving mention to what interpretation you were using, and then when I tried to clarify you launched into a rant.
Generally? No, not at all. Here, it was specifically a response to statements to the effect of “you’re only bringing up MWI as an excuse to feel superior.”
Still, I find it preferable if people keep their potentially offensive feelings private, even if these feelings arose as a reaction to being accused of having such feelings.
I offered the above more as explanation than defense. I certainly respect your point of view here; I have some further thoughts, but I’d rather sift through them a bit as I’m not sure they’re actually coherent.
Quantum Mechanics is a classic counterexample, as far as we know, in a sense that there is no deeper underlying theory that would predict an outcome of a measurement when QM says it cannot be determined.
This is not refraining from picking a model—this is choosing to reify certain classes of interpretation. If you are saying, “The math is just what the math is, and says nothing more” then it doesn’t purport to be complete in the first place, and isn’t a counterexample.
Quantum Mechanics is falsifiable; MWI vs Copenhagen is mathematically equivalent. I’d call it a preference rather than a religion.
[edit] Poster below states that they’re not mathematically equivalent. I think a better way of saying it is “MWI is related to Copenhagen so that observable evidence for or against one is always and exactly observable evidence for or against the other as well. ”
Unfortunately, it is not treated as a preference. People use magic words like Occam’s razor, Solomonoff induction and Kolmogorov complexity to justify why the MWI is better, without any attempt to quantify it. Well, I did make an attempt to quantify the complexity in one of my comments. Predictably, at least in the hindsight, there was little interest in discussing the validity or the consequences of this approach.
I suspect that he misinterprets, as it were, what an interpretation is, namely, a way of thinking that elucidates the underlying mathematical framework. He seems to think that different interpretations can make different predictions based on the same math:
We are led by the Copenhagen Interpretation to expect that the positions of the interference minima should have no particular significance, and that the wires should intercept 6% of the light they do for uniform illumination.
...
Thus, it appears that both the Copenhagen Interpretation and the Many-Worlds Interpretation have been falsified by experiment.
Does this mean that the theory of quantum mechanics has also been falsified? No indeed! The quantum formalism has no problem in predicting the Afshar result. A simple quantum mechanical calculation using the standard formalism shows that the wires should intercept only a very small fraction of the light. The problem encountered by the Copenhagen and Many-Worlds Interpretations is that the Afshar Experiment has identified a situation in which these popular interpretations of quantum mechanics are inconsistent with the quantum formalism itself.
I would say that, more likely than not, his mental model of what an interpretation is is different from what physicists tend to mean. It does not help that he has an ax to grind, as the author of his pet “transactional” interpretation.
Reread this statement, which you quoted: “The problem encountered by the Copenhagen and Many-Worlds Interpretations is that the Afshar Experiment has identified a situation in which these popular interpretations of quantum mechanics are inconsistent with the quantum formalism itself.”
The implication is that Copenhagen and Many-Worlds are not valid interpretations, since (he claims) they are inconsistent with the formalism. (I’m not sufficiently well-versed in QM to evaluate this claim, unfortunately.)
Copenhagen and Many Worlds do not employ the same math. Many Worlds posits a single dynamical evolution law, given by Schrodinger’s equation. Copenhagen supplements this with an intermittent stochastic collapse process (Von Neumann’s Process 2). So Copenhagen vs. MWI is a question open to empirical test.
There are certain interpretations that are empirically indistinguishable from MWI. Bohmian mechanics is an example, although even here the math is different but this difference is postulated to be epistemically inaccessible.
EDIT: I think calling Copenhagen, MWI, Bohm, GRW, etc. different interpretations of a single theory is pretty misleading, suggesting that they are different models of the same axiomatic system. They should really be regarded as different theories, with a large amount of overlap in their mathematical structure.
There is no “intermittent stochastic collapse process” anywhere in the math of QM. The measurement is a black box with the Born rule to decide the outcome. Bohm is a different story, and not a happy one.
The measurement process in the orthodox interpretation isn’t just a means for determining outcomes. It also has an effect on the subsequent evolution of the wave function. There is a discontinuity in the dynamics before and after a measurement. I don’t see how that wouldn’t count as part of the math of the theory.
True, but there is nothing stochastic about this. Measurement is an external event controlled by an observer. The Born rule and the jump into an eigenstate is the math of it, nothing more, nothing less. The “Von Neumann’s Process 2” is an unnecessary interpretational mumbo-jumbo.
The MWI gives an illusion of predictability (“Everything possible happens! We just don’t see it because nearly all of it happens somewhere else to some other ‘us’!”). Unfortunately, it can no more answer the question of which outcome an experiment will measure in “this world” than any other interpretation.
Even more unfortunately, and at a risk of a massive downvote, I hate to say it, but the MWI has become an official LW religion:
proclaimed to be true true by the founder: check
provides comfort to the masses: check
sets the group apart from others: check
impossible to falsify: check
makes one feel superior because of “deeper understanding of the world”: check
How does MWI provide comfort to the masses? Michael Vassar is hardly the masses, but it makes him extremely uncomfortable—he called Quantum Immortality the most horrifying idea he’d ever had to take seriously, and I agree.
I would think that most people would find the idea of living forever in some of the worlds at least somewhat comforting. It is even better than having an immortal soul: you get to live forever in the flesh, and you do not need to pay a tithe in any of the worlds.
That said, I was referring to something else, namely to the major discomfort of the essential unpredictability of any quantum experiment. In the MWI (or at least in some versions of it) the parallel worlds come into existence and sail apart as the decoherence takes hold and the off-diagonal contribution to the joint system/detector state decays away rapidly.
Everything seems predictable and some day maybe even computable. The only minor caveat is that you never get to observe these other worlds and bless your surviving copies with your dying breath (or receive the blessing of those gone before you).
It doesn’t fail to give an answer to the question—it makes the question incoherent.
“Which outcome an experiment will measure” is sitting before the experiment looking forward. With MWI, there is no world after the experiment looking backwards with a unique claim on being “this world.” The answer to “will there be a me observing result X” will of course be yes. The question of which of those mes is the “real” one is misleading. What quantum theory does tell us, in MWI, is the total amount of surprise in the mes looking back.
...And we are back to square one, the unfalsifiability of an interpretation, which makes the adepts feel good about their “knowledge” without running any risk of it being shattered.
If you suppose “interpretation” to be a distinction that can’t be settled by observation, and simultaneously that any distinction must be settled by observation, then it’s not clear what you’re objecting to. These posts seem relevant: Belief in the Implied Invisible, You’re Entitled to Arguments, But Not (That Particular) Proof.
For your information: Not voting you down because you disagree with the MWI, but because you made a silly argument and then immediately replaced it with an entirely different argument with no acknowledgement that your original argument had been shown to be silly.
I wasn’t feeling superior to you because you chose to reference non-MWI QM—I’m not confident about MWI myself, and would prefer we keep other interpretations alive until we can distinguish on the basis of evidence (or at least have a strong argument that space complexity deserves no place at all in our priors).
I am feeling superior to you now because you ignored a prevalent interpretation without giving mention to what interpretation you were using, and then when I tried to clarify you launched into a rant.
Is it really necessary to publish one’s superior feelings?
Generally? No, not at all. Here, it was specifically a response to statements to the effect of “you’re only bringing up MWI as an excuse to feel superior.”
Still, I find it preferable if people keep their potentially offensive feelings private, even if these feelings arose as a reaction to being accused of having such feelings.
I offered the above more as explanation than defense. I certainly respect your point of view here; I have some further thoughts, but I’d rather sift through them a bit as I’m not sure they’re actually coherent.
Fair enough.
The math of QM does not require an interpretation, so I refrain from using any.
Then refrain.
This is not refraining from picking a model—this is choosing to reify certain classes of interpretation. If you are saying, “The math is just what the math is, and says nothing more” then it doesn’t purport to be complete in the first place, and isn’t a counterexample.
Seems like we are talking past each other (happens quite often whenever the MWI is mentioned), so I will disengage.
Quantum Mechanics is falsifiable; MWI vs Copenhagen is mathematically equivalent. I’d call it a preference rather than a religion.
[edit] Poster below states that they’re not mathematically equivalent. I think a better way of saying it is “MWI is related to Copenhagen so that observable evidence for or against one is always and exactly observable evidence for or against the other as well. ”
Unfortunately, it is not treated as a preference. People use magic words like Occam’s razor, Solomonoff induction and Kolmogorov complexity to justify why the MWI is better, without any attempt to quantify it. Well, I did make an attempt to quantify the complexity in one of my comments. Predictably, at least in the hindsight, there was little interest in discussing the validity or the consequences of this approach.
At least one well-known physicist not only believes that the MWI can be falsified… he suggests that it has been falsified:
http://www.analogsf.com/0409/altview2.shtml
I suspect that he misinterprets, as it were, what an interpretation is, namely, a way of thinking that elucidates the underlying mathematical framework. He seems to think that different interpretations can make different predictions based on the same math:
...
I would say that, more likely than not, his mental model of what an interpretation is is different from what physicists tend to mean. It does not help that he has an ax to grind, as the author of his pet “transactional” interpretation.
Reread this statement, which you quoted: “The problem encountered by the Copenhagen and Many-Worlds Interpretations is that the Afshar Experiment has identified a situation in which these popular interpretations of quantum mechanics are inconsistent with the quantum formalism itself.”
The implication is that Copenhagen and Many-Worlds are not valid interpretations, since (he claims) they are inconsistent with the formalism. (I’m not sufficiently well-versed in QM to evaluate this claim, unfortunately.)
Copenhagen and Many Worlds do not employ the same math. Many Worlds posits a single dynamical evolution law, given by Schrodinger’s equation. Copenhagen supplements this with an intermittent stochastic collapse process (Von Neumann’s Process 2). So Copenhagen vs. MWI is a question open to empirical test.
There are certain interpretations that are empirically indistinguishable from MWI. Bohmian mechanics is an example, although even here the math is different but this difference is postulated to be epistemically inaccessible.
EDIT: I think calling Copenhagen, MWI, Bohm, GRW, etc. different interpretations of a single theory is pretty misleading, suggesting that they are different models of the same axiomatic system. They should really be regarded as different theories, with a large amount of overlap in their mathematical structure.
There is no “intermittent stochastic collapse process” anywhere in the math of QM. The measurement is a black box with the Born rule to decide the outcome. Bohm is a different story, and not a happy one.
The measurement process in the orthodox interpretation isn’t just a means for determining outcomes. It also has an effect on the subsequent evolution of the wave function. There is a discontinuity in the dynamics before and after a measurement. I don’t see how that wouldn’t count as part of the math of the theory.
True, but there is nothing stochastic about this. Measurement is an external event controlled by an observer. The Born rule and the jump into an eigenstate is the math of it, nothing more, nothing less. The “Von Neumann’s Process 2” is an unnecessary interpretational mumbo-jumbo.