Suppose all wavefunctions encode some constant, sub-unity fraction of the information about the ‘true state’ - that all wavefunctions are equally specific. Then we should be able to tease out more of that information with some very basic experiments (edited to clarify: by measuring in multiple ways—not that the new state would be intrinsically better constrained). This contradicts the results of the many many instances of these experiments.
So you can escape by supposing that it’s possible to prepare a wavefunction that has more or less information about the ‘true state’.
It’s nice to have yet another very strong constraint to put on global hidden variables, but nothing could ever be total proof.
~~~~
edited to add: But if you pull that escape route, then it’s trivial to perform (by which I mean, they have already been done zillions of times) additional experiments showing that quantum states with different distributions of ‘real’ states (as we just allowed by the escape route) actually have identical dynamics.
The more I think about this, the less wiggle room I see.
Also note the companion article “The quantum state can be interpreted statistically,” by two of the same authors. A previous title for this paper was “The quantum state cannot be interpreted statistically,” by the way.
This heavily implies that what’s being argued here is deeply philosophical, hinging crucially on the interpretation of “statistically” and therefore has a high probability of being incorrect.
So, it turns out it is more than “just” a useful mathematical tool after all. Does this confirm the universe basically runs on maths?
Don’t lend too much credence to a single paper and don’t make far-reaching conclusions just yet. This is a nice result, but it is not of the same level as, say, the Bell inequalities.
The argument depends on few assumptions. One is that a system has a “real physical state” – not necessarily completely described by quantum theory, but objective and independent of the observer. This assumption only needs to hold for systems that are isolated, and not entangled with other systems. Nonetheless, this assumption, or some part of it, would be denied by instrumentalist approaches to quantum theory, wherein the quantum state is merely a calculational tool for making predictions concerning macroscopic measurement outcomes.
Skimming the article I haven’t found a precise definition of what having a real physical state means (which would be interesting and important in such a discussion, especially given the authors scare quotes around the term). Nevertheless, the assumption that the system has a state is quite a strong one. If one wants to deny that the wave function is real (whatever it means) one can easily deny the reality of states, and treat QM only as a tool predicting which sequences of measurements can happen and how probably.
I have an (undergraduate) degree in physics, or will at the end of the semester, and either I don’t fully understand the paper after a second read-through, or it is wrong. The claimed contradiction doesn’t seem to be particularly damning: if the measured state is excluded from being in a |0>|0> initial state, that doesn’t mean that the two cannot have started in a different state, and the excluded state will change in later measurements anyway, so the measurement is not telling you anything new.
(Motl’s explanation is harsh and caustic, but here I agree with him in interpreting the paper.)
Edit: I agree with Motl’s explanation of why the exclusion of 1 of the 4 combined states is not problematic.
Motl’s explanation is completely off-base because he’s trying to defend QM from attack when the paper is not trying to attack QM, but trying to distinguish QM from hidden-variables theories.
Of course P(i) = Tr( L | Z(i) >< Z(i) |) … that’s what QM says!
What they’ve just shown is that hidden variables theories that can’t do that, because the ‘real state’ L has specific values, and not a quantum nature.
Motl refuses to understand that they are not questioning the probabilistic nature of QM (map from amplitude to probability), but rather whether amplitude itself is only a reflection of some underlying physical state (map from unknown underlying state to amplitude). Basically, discount most of what Motl writes in this thread.
The paper authors say that if amplitude itself reflects our incomplete knowledge of the state of a physical system, and so is probabilistic in nature, then they can obtain a contradiction with the predictions of conventional QM. Unfortunately, unlike in the case of the celebrated Bell theorem, it doesn’t look to me like they are making any new predictions, only reasoning things out from what is already known.
If someone can clarify this issue (can this theorem be tested experimentally?) or link to a relevant discussion, I would appreciate it.
Yeah, that person clearly has too much of his identity tied up in this stuff. His post reads like an atheist who has been consigned to debate creationists for all his days.
The paper’s authors found that X is false, and Motl contends that in fact X is obviously false so the authors are bad people for even talking about it.
It’s as though the paper proved that if the moon were made of cheese then it could not be green, and Motl took them to task for being pro- “the moon is made out of cheese”.
Motl’s record of being wrong??? Who the hell are you to say? What is wrong with you people? The guy may have some questionable political opinions but he knows more about physics than all LW people combined ever will. What, do you think that being self-proclaimed “sane” group and having read a popular book here and there entitles you to make valid comments on scientific topics? Please note this isn’t reaction solely to paper-machine or thomblake or shminux, subset of who may actually have some rigorous physics education and who may or may not be simply wrong. This is a reaction to all of LW who apparently think that being intelligent or rational (putting aside the fact that most of their followers probably aren’t) makes them into self-taught science experts. I am posting it here because it is “closest” at the moment but this rant has been triggered by reading some other “science” posts today, most notably the quantum mechanics sequence. Which I am afraid fails terribly as an attempted first course on QM, is blatantly wrong in some parts and reflects that indeed Yudkowsky never had any proper physics education because he fails to understand even basic notions properly. LW movement, happily following this crazy narcissistic maniac, thus demonstrates level of scientific education and culture in its ranks. It’s sickening on one part and textbook example of confirmation bias on the other. If you are offended by the words chosen, know that no-one really cares. If you think the words chosen are too strong, it’s possible, I just came back from a mathematicians’ dinner where excessive, but not opinion changing, amount of wine was served. However, strong or not, you are (somewhere already, elsewhere becoming) a good source of laughs for actual scientists. Finally, if you really have to reply, please don’t try to address any of the physics criticism above, the sequences and comments under them have provided me with enough lay-people-trying-to-write-about-physics for a long time. Also, I know it is foolish to write science-LW relations rant here as no-one will read it but I don’t care. Let the down-voting commence!
most notably the quantum mechanics sequence. Which I am afraid fails terribly
as an attempted first course on QM, is blatantly wrong in some parts and
reflects that indeed Yudkowsky never had any proper physics education because
he fails to understand even basic notions properly.
I think he would like to have any mistakes pointed out. (Preferably math
mistakes rather than philosophical stuff that scientists don’t all agree on.)
LWer ciphergoth recently posted a Physics StackExchange
question
(and a corresponding LW
post)
about errors in the quantum physics sequence.
Let the down-voting commence!
It’s better to omit passive-aggressive stuff like this.
The guy may have some questionable political opinions but he knows more about physics than all LW people combined ever will.
This seems questionable. There are a variety of people here with math and physics PhDs. It might be accurate (and it wouldn’t surprise me) if by some rough metric Motl knew more about physics than any single LW regular. Claiming he knows more than everyone combined seems tough, especially given that we have subject matter experts here in subfields that are not Motl’s. The comment might be more valid if one restricted to something like “knows more particle physics” rather than physics in general, but even that seems questionable.
Motl also has a history of mixing his politics and his other views with his attitudes about physics in ways that don’t help his chances of being right. For example, see this example (one of many) where he says about a physicist that he disagrees with:
The difference between two of us is like the difference between a superman from the action movies who fights for the universal justice on one side and the most dirty corrupt villain on the other side. It’s like the Heaven and the Hell, freedom and feminism, careful evaluation of the climate and the alarmist hysteria, or string theory and loop quantum gravity.
He apparently added a few days (possibly weeks) after posting this bit a winky emoticon. There are other examples where he uses about as extreme or almost as extreme language.
Overall, Motl is not engaging in behavior and cognition that is likely to make him a reliable source.
I am honestly surprised by the reaction of people to this link.
Why is my comment being downvoted for presenting a simple source of information? You may agree or disagree with it but downvoting such a comment just shows that you don’t want to see any counter-opinions to your beliefs. You have comments to express your opinion. (Or I am totally misunderstanding karma and it actually means the level of confirmation bias participation.)
[Danger! Un-LW-orthodox opinion follows!] I am baffled by (Pusey et al, 2012) being taken seriously contrary to Lubos Motl. If the opinion of shminux, thomblake and paper-machine is representative of LW position on quantum foundations, then it seems to diverge very substantially from the general scientific consensus. But I don’t seem to find any published scientifically relevant material, only hand-waving. Prove me wrong and show me some contributions that have scientific merit.
1) Receiving a single downvote is usually not worth making another comment asking “why the downvote??” It is just one person’s opinion and you should not pay much attention to it, not the community’s. People who ask this question are often seen as whiners and downvoted more for it.
2) People saying things like “Danger! Un-LW-orthodox opinion follows!” are also at risk of downvotes, because they come of as passive-aggressive. Substantive, reasoned criticisms of LW-orthodox opinions are welcome.
(Note that I am not calling you a whiner or passive-agressive—I’m taking a guess as to how certain kinds of comments are perceived by the community.)
3) The comments on this thread by shminux, tomblake and paper-machine do not express any definite position of their own on QM foundations. They are trying to clarify what the issues at stake are, what is this new paper really saying and how relevant it is, criticizing what they see as errors of interpretation in Motl’s reading of the paper, and criticizing Motl’s general tone as overheated and unhelpful.
4) I’m not sure about the other two, but I’m certain that shminux’s position on quantum foundations is not at all representative of LW. Shminux is an instrumentalist, who adopts to QM and to science in general a shut-up-and-calculate/”reality”-is-meaningless approach. The more common LW position is realism in philosophy of science and Many Worlds in QM foundations, though there are spirited dissenters and no enforced orthodoxy.
5) I would add that contrary to your pronouncement, there is no general scientific consensus on quantum foundations questions. There is general agreement on some things, e.g. that there is no physical, objective collapse, or that there are no local hidden variables, but no consensus on more philosophical questions like MW realism vs instrumentalism.
downvoting such a comment just shows that you don’t want to see any counter-opinions to your beliefs.
Alternatively, downvoting such a comment shows that you would rather see fewer similar comments in the future, for any number of possible reasons. (I have downvoted the parent, but not the grandparent.)
Why is my comment being downvoted for presenting a simple source of information? You may agree or disagree with it but downvoting such a comment just shows that you don’t want to see any counter-opinions to your beliefs.
Do you truly believe that no post containing a link to a counter-opinion should be downvoted?
The idea is:
Suppose all wavefunctions encode some constant, sub-unity fraction of the information about the ‘true state’ - that all wavefunctions are equally specific. Then we should be able to tease out more of that information with some very basic experiments (edited to clarify: by measuring in multiple ways—not that the new state would be intrinsically better constrained). This contradicts the results of the many many instances of these experiments.
So you can escape by supposing that it’s possible to prepare a wavefunction that has more or less information about the ‘true state’.
It’s nice to have yet another very strong constraint to put on global hidden variables, but nothing could ever be total proof.
~~~~ edited to add: But if you pull that escape route, then it’s trivial to perform (by which I mean, they have already been done zillions of times) additional experiments showing that quantum states with different distributions of ‘real’ states (as we just allowed by the escape route) actually have identical dynamics.
The more I think about this, the less wiggle room I see.
Also note the companion article “The quantum state can be interpreted statistically,” by two of the same authors. A previous title for this paper was “The quantum state cannot be interpreted statistically,” by the way.
This heavily implies that what’s being argued here is deeply philosophical, hinging crucially on the interpretation of “statistically” and therefore has a high probability of being incorrect.
I’m withholding my judgment, for the moment.
Don’t lend too much credence to a single paper and don’t make far-reaching conclusions just yet. This is a nice result, but it is not of the same level as, say, the Bell inequalities.
From the article:
Skimming the article I haven’t found a precise definition of what having a real physical state means (which would be interesting and important in such a discussion, especially given the authors scare quotes around the term). Nevertheless, the assumption that the system has a state is quite a strong one. If one wants to deny that the wave function is real (whatever it means) one can easily deny the reality of states, and treat QM only as a tool predicting which sequences of measurements can happen and how probably.
I have an (undergraduate) degree in physics, or will at the end of the semester, and either I don’t fully understand the paper after a second read-through, or it is wrong. The claimed contradiction doesn’t seem to be particularly damning: if the measured state is excluded from being in a |0>|0> initial state, that doesn’t mean that the two cannot have started in a different state, and the excluded state will change in later measurements anyway, so the measurement is not telling you anything new.
(Motl’s explanation is harsh and caustic, but here I agree with him in interpreting the paper.)
Edit: I agree with Motl’s explanation of why the exclusion of 1 of the 4 combined states is not problematic.
Motl’s explanation is completely off-base because he’s trying to defend QM from attack when the paper is not trying to attack QM, but trying to distinguish QM from hidden-variables theories.
Of course P(i) = Tr( L | Z(i) >< Z(i) |) … that’s what QM says!
What they’ve just shown is that hidden variables theories that can’t do that, because the ‘real state’ L has specific values, and not a quantum nature.
http://motls.blogspot.co.uk/2011/11/nature-hypes-anti-qm-crackpot-paper-by.html
Motl refuses to understand that they are not questioning the probabilistic nature of QM (map from amplitude to probability), but rather whether amplitude itself is only a reflection of some underlying physical state (map from unknown underlying state to amplitude). Basically, discount most of what Motl writes in this thread.
The paper authors say that if amplitude itself reflects our incomplete knowledge of the state of a physical system, and so is probabilistic in nature, then they can obtain a contradiction with the predictions of conventional QM. Unfortunately, unlike in the case of the celebrated Bell theorem, it doesn’t look to me like they are making any new predictions, only reasoning things out from what is already known.
If someone can clarify this issue (can this theorem be tested experimentally?) or link to a relevant discussion, I would appreciate it.
Yeah, that person clearly has too much of his identity tied up in this stuff. His post reads like an atheist who has been consigned to debate creationists for all his days.
The paper’s authors found that X is false, and Motl contends that in fact X is obviously false so the authors are bad people for even talking about it.
It’s as though the paper proved that if the moon were made of cheese then it could not be green, and Motl took them to task for being pro- “the moon is made out of cheese”.
Given Motl’s record of being vocally wrong about many things in basic ways, this should be more or less the default position.
Motl’s record of being wrong??? Who the hell are you to say? What is wrong with you people? The guy may have some questionable political opinions but he knows more about physics than all LW people combined ever will. What, do you think that being self-proclaimed “sane” group and having read a popular book here and there entitles you to make valid comments on scientific topics? Please note this isn’t reaction solely to paper-machine or thomblake or shminux, subset of who may actually have some rigorous physics education and who may or may not be simply wrong. This is a reaction to all of LW who apparently think that being intelligent or rational (putting aside the fact that most of their followers probably aren’t) makes them into self-taught science experts. I am posting it here because it is “closest” at the moment but this rant has been triggered by reading some other “science” posts today, most notably the quantum mechanics sequence. Which I am afraid fails terribly as an attempted first course on QM, is blatantly wrong in some parts and reflects that indeed Yudkowsky never had any proper physics education because he fails to understand even basic notions properly. LW movement, happily following this crazy narcissistic maniac, thus demonstrates level of scientific education and culture in its ranks. It’s sickening on one part and textbook example of confirmation bias on the other. If you are offended by the words chosen, know that no-one really cares. If you think the words chosen are too strong, it’s possible, I just came back from a mathematicians’ dinner where excessive, but not opinion changing, amount of wine was served. However, strong or not, you are (somewhere already, elsewhere becoming) a good source of laughs for actual scientists. Finally, if you really have to reply, please don’t try to address any of the physics criticism above, the sequences and comments under them have provided me with enough lay-people-trying-to-write-about-physics for a long time. Also, I know it is foolish to write science-LW relations rant here as no-one will read it but I don’t care. Let the down-voting commence!
Scott Aaronson (who is presumably qualified) doesn’t seem to have a very high opinion of Motl either.
I think he would like to have any mistakes pointed out. (Preferably math mistakes rather than philosophical stuff that scientists don’t all agree on.) LWer ciphergoth recently posted a Physics StackExchange question (and a corresponding LW post) about errors in the quantum physics sequence.
It’s better to omit passive-aggressive stuff like this.
This seems questionable. There are a variety of people here with math and physics PhDs. It might be accurate (and it wouldn’t surprise me) if by some rough metric Motl knew more about physics than any single LW regular. Claiming he knows more than everyone combined seems tough, especially given that we have subject matter experts here in subfields that are not Motl’s. The comment might be more valid if one restricted to something like “knows more particle physics” rather than physics in general, but even that seems questionable.
Motl also has a history of mixing his politics and his other views with his attitudes about physics in ways that don’t help his chances of being right. For example, see this example (one of many) where he says about a physicist that he disagrees with:
He apparently added a few days (possibly weeks) after posting this bit a winky emoticon. There are other examples where he uses about as extreme or almost as extreme language.
Overall, Motl is not engaging in behavior and cognition that is likely to make him a reliable source.
It’s acceptable to post rants here. It’s much less acceptable to post badly written ones.
I am honestly surprised by the reaction of people to this link.
Why is my comment being downvoted for presenting a simple source of information? You may agree or disagree with it but downvoting such a comment just shows that you don’t want to see any counter-opinions to your beliefs. You have comments to express your opinion. (Or I am totally misunderstanding karma and it actually means the level of confirmation bias participation.)
[Danger! Un-LW-orthodox opinion follows!] I am baffled by (Pusey et al, 2012) being taken seriously contrary to Lubos Motl. If the opinion of shminux, thomblake and paper-machine is representative of LW position on quantum foundations, then it seems to diverge very substantially from the general scientific consensus. But I don’t seem to find any published scientifically relevant material, only hand-waving. Prove me wrong and show me some contributions that have scientific merit.
Several points here:
1) Receiving a single downvote is usually not worth making another comment asking “why the downvote??” It is just one person’s opinion and you should not pay much attention to it, not the community’s. People who ask this question are often seen as whiners and downvoted more for it.
2) People saying things like “Danger! Un-LW-orthodox opinion follows!” are also at risk of downvotes, because they come of as passive-aggressive. Substantive, reasoned criticisms of LW-orthodox opinions are welcome.
(Note that I am not calling you a whiner or passive-agressive—I’m taking a guess as to how certain kinds of comments are perceived by the community.)
3) The comments on this thread by shminux, tomblake and paper-machine do not express any definite position of their own on QM foundations. They are trying to clarify what the issues at stake are, what is this new paper really saying and how relevant it is, criticizing what they see as errors of interpretation in Motl’s reading of the paper, and criticizing Motl’s general tone as overheated and unhelpful.
4) I’m not sure about the other two, but I’m certain that shminux’s position on quantum foundations is not at all representative of LW. Shminux is an instrumentalist, who adopts to QM and to science in general a shut-up-and-calculate/”reality”-is-meaningless approach. The more common LW position is realism in philosophy of science and Many Worlds in QM foundations, though there are spirited dissenters and no enforced orthodoxy.
5) I would add that contrary to your pronouncement, there is no general scientific consensus on quantum foundations questions. There is general agreement on some things, e.g. that there is no physical, objective collapse, or that there are no local hidden variables, but no consensus on more philosophical questions like MW realism vs instrumentalism.
Very nice points, all 5 of them!
More like a recovering realist, slowly drifting toward anti-realism, but your description will do, too.
Alternatively, downvoting such a comment shows that you would rather see fewer similar comments in the future, for any number of possible reasons. (I have downvoted the parent, but not the grandparent.)
Didn’t vote on either of these, but:
Do you truly believe that no post containing a link to a counter-opinion should be downvoted?