I disagree very much, see the other comments about Bell’s theorem.
On Google+, Matthew Leifer, a respected researcher in theoretical physics currently at University College London, replied as follows when he was asked what his conclusions were regarding the paper:
“Well, I knew this paper was coming, so it is not a surprise. Basically, it means that if you believe that quantum states are epistemic then you have two options left:
neo-Copenhagenism: Claim that a deeper realist model was never needed to support an epistemic interpretation of the quantum state. The probabilities are just about measurement results, period.
The ontological states have to be more bizarre than imagined in current approaches. For example, you could have retrocausality or “relational” degrees of freedom (whatever that means). Note that, one could also evade the theorem of this paper by claiming that quantum i.i.d. product states do not correspond to i.i.d. probability distributions in the ontological model. However, doing this does not evade a related theorem by Alberto Montina, which is based on a single system.
If neither of those options is to your taste, then you might as well become an Everettian or a Bohmian, since you are stuck with the state vector in your ontology in any case.
Overall, I would say that this result is not too surprising. I think that most people in the “psi-epistemic” camp already had the intuition that a psi-epistemic ontological model formulated in the usual way would not be possible. That is why most of us were already promoting other possibilities, e.g. Fuchs is in the neo-Copenhagen camp and Spekkens often mumbles things about relationalism. Personally, I am quite interested in the idea of retrocausal psi-epistemic hidden variable theories. It is at least a fairly clearly formulated problem to try and come up with one, whereas relationalism seems vague to me, at least as it is applied to quantum theory. If that doesn’t work out then I would probably end up being an Everettian. Despite the attraction of the Fuchsian program, realism has to win out in the end for me.”
I feel like if you understood this, you could have put it in your own words.
Did the theorem presented in this paper make any distinction between measurement with collapse and measurement without collapse? Would the proven theorem break down if collapse was how the world worked?
No. There is no such distinction between measurement mechanisms in this paper. Instead, this paper is about the difference between the wavefunction uniquely corresponding to the physical reality vs. only corresponding to physical reality “on average.”
I think your criticism here is a bit shortsighted. Just look at the longer passage that I quoted in the OP. It directly deals with some ramifications if you hold that the collapse of the wavefunction is real, namely spooky action at a distance becomes an even worse problem. It’s even harder to give an account for the physical quantum states separated by vast distance being more than just classically correlated. In the very next paragraph they mention that in interpretations in which no actual collapse has to happen, their result gives further credence to the idea that distinct quantum states are distinct physically real things.
It’s as if you just want me personally to be wrong, because both the OP and the Leifer quote above deal with ramifications in the with-collapse cases vs. ramifications in the without-collapse cases. I don’t see how you can say that choice to offer the quote means that I do not understand it. I also don’t see how you can claim that Many Worlds is unrelated when the linked paper itself mentions ramifications for that case.
I didn’t claim that this conclusively proves anything about collapse or ontological measurement, only that the ramifications do add something above and beyond Bell’s theorem. And I stick by that.
Just look at the longer passage that I quoted in the OP. It directly deals with some ramifications if you hold that the collapse of the wavefunction is real, namely spooky action at a distance becomes an even worse problem.
There is more than one interpretation of the passage you quoted, and I think a more neutral interpretation is more likely. In the first paragraph they highlight interpretations with collapse, explore the implications for interpretations with collapse, and point out an unintuitive consequence:“This is especially mysterious when two entangled systems are at separate locations, and measurement of one leads to an instantaneous collapse of the quantum state of the other.”
In the second paragraph they highlight interpretations without collapse, explore the implications for interpretations without collapse, and point out an unintuitive consequence:“But if the quantum state is a physical property of the system and apparatus, it is hard to avoid the conclusion that each marcoscopically different component has a direct counterpart in reality.”
The paragraphs have the same structure. Ramifications are mentioned for both cases. So when you say “I also don’t see how you can claim that Many Worlds is unrelated when the linked paper itself mentions ramifications for that case,” it seems to me like you’re reading asymmetrically. The authors appear to have simply explored the implications of their theorem for interpretations with and without collapse—and of course there were unintuitive bits for both, because it’s quantum mechanics.
There is more than one interpretation of the passage you quoted, and I think a more neutral interpretation is more likely.
This is a good point. I should say, “One possible interpretation is...”, but in either case I don’t think my reliance on direct quotes to try to illustrate this stronger interpretation that I advocate should qualify as failure to understand on my part. As I read the second paragraph, it seems to straightforwardly apply to Many Worlds in an important way, but I am totally willing to accept the point of view that the implications are less salient. It was just that your original comment:
Bringing up many-worlds in this article is unnecessary.
seemed unproductive to me. In what sense is it unnecessary? Unnecessary for understanding the original result? Sure… but I didn’t bring up the original result for its own sake, only to discuss implications for wave collapse.
Although there is no direct effect on the state of the evidence, I guess you’re right that there can be an indirect effect. For example, ‘collapse’ could look better than ‘no-collapse’ given wavefunction non-realism, but ‘no-collapse’ could look better than ‘collapse’ given wavefunction realism. In this case, changing our position on wavefunction realism would change the opinion on collapse vs. no-collapse.
But this effect only occurs to the extent that people already believe in the things disproved (or called into question). People who took this “statistical sort-of-nonrealism” model seriously, rather than as merely an interesting idea, are pretty rare even in the physics world*. And here on LW? Fuggedaboutit.
* I’ve never run into one, and they never came up when I talked to someone who’s working on this kind of stuff—mostly focused on the neo-Copenhagenists, to use Leifer’s term, and testing some specific sorts of collapse.
I disagree very much, see the other comments about Bell’s theorem.
On Google+, Matthew Leifer, a respected researcher in theoretical physics currently at University College London, replied as follows when he was asked what his conclusions were regarding the paper:
I feel like if you understood this, you could have put it in your own words.
Did the theorem presented in this paper make any distinction between measurement with collapse and measurement without collapse? Would the proven theorem break down if collapse was how the world worked?
No. There is no such distinction between measurement mechanisms in this paper. Instead, this paper is about the difference between the wavefunction uniquely corresponding to the physical reality vs. only corresponding to physical reality “on average.”
I think your criticism here is a bit shortsighted. Just look at the longer passage that I quoted in the OP. It directly deals with some ramifications if you hold that the collapse of the wavefunction is real, namely spooky action at a distance becomes an even worse problem. It’s even harder to give an account for the physical quantum states separated by vast distance being more than just classically correlated. In the very next paragraph they mention that in interpretations in which no actual collapse has to happen, their result gives further credence to the idea that distinct quantum states are distinct physically real things.
It’s as if you just want me personally to be wrong, because both the OP and the Leifer quote above deal with ramifications in the with-collapse cases vs. ramifications in the without-collapse cases. I don’t see how you can say that choice to offer the quote means that I do not understand it. I also don’t see how you can claim that Many Worlds is unrelated when the linked paper itself mentions ramifications for that case.
I didn’t claim that this conclusively proves anything about collapse or ontological measurement, only that the ramifications do add something above and beyond Bell’s theorem. And I stick by that.
There is more than one interpretation of the passage you quoted, and I think a more neutral interpretation is more likely. In the first paragraph they highlight interpretations with collapse, explore the implications for interpretations with collapse, and point out an unintuitive consequence: “This is especially mysterious when two entangled systems are at separate locations, and measurement of one leads to an instantaneous collapse of the quantum state of the other.”
In the second paragraph they highlight interpretations without collapse, explore the implications for interpretations without collapse, and point out an unintuitive consequence: “But if the quantum state is a physical property of the system and apparatus, it is hard to avoid the conclusion that each marcoscopically different component has a direct counterpart in reality.”
The paragraphs have the same structure. Ramifications are mentioned for both cases. So when you say “I also don’t see how you can claim that Many Worlds is unrelated when the linked paper itself mentions ramifications for that case,” it seems to me like you’re reading asymmetrically. The authors appear to have simply explored the implications of their theorem for interpretations with and without collapse—and of course there were unintuitive bits for both, because it’s quantum mechanics.
This is a good point. I should say, “One possible interpretation is...”, but in either case I don’t think my reliance on direct quotes to try to illustrate this stronger interpretation that I advocate should qualify as failure to understand on my part. As I read the second paragraph, it seems to straightforwardly apply to Many Worlds in an important way, but I am totally willing to accept the point of view that the implications are less salient. It was just that your original comment:
seemed unproductive to me. In what sense is it unnecessary? Unnecessary for understanding the original result? Sure… but I didn’t bring up the original result for its own sake, only to discuss implications for wave collapse.
Although there is no direct effect on the state of the evidence, I guess you’re right that there can be an indirect effect. For example, ‘collapse’ could look better than ‘no-collapse’ given wavefunction non-realism, but ‘no-collapse’ could look better than ‘collapse’ given wavefunction realism. In this case, changing our position on wavefunction realism would change the opinion on collapse vs. no-collapse.
But this effect only occurs to the extent that people already believe in the things disproved (or called into question). People who took this “statistical sort-of-nonrealism” model seriously, rather than as merely an interesting idea, are pretty rare even in the physics world*. And here on LW? Fuggedaboutit.
* I’ve never run into one, and they never came up when I talked to someone who’s working on this kind of stuff—mostly focused on the neo-Copenhagenists, to use Leifer’s term, and testing some specific sorts of collapse.