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Yes there are. Even without invoking any philosophical issues, quantum mechanics admits it's not self-contained. It takes measurement - the act of an outsider i

by mjfl 8y ago

Yes there are. Even without invoking any philosophical issues, quantum mechanics admits it's not self-contained. It takes measurement - the act of an outsider interacting with a system, which collapses the wavefunction, as a postulate. Measurement is not described by quantum mechanics.

btilly 8y ago
No, there is not. The Everett aka many-worlds interpretation demonstrates that you can explain the observed effects of measurement without invoking "collapse" of the wave function, and without reference to anything outside of QM.
- whatshisface 8y ago
  To further build on what you're saying, by bringing in the concept of a measure-er we have already entered the domain of philosophy, because the special class "measure-er" belongs to the Copenhagen interpretation and the interpretation of quantum mechanics is a philosophical issue by virtue of the fact that it will never be decided experimentally.
  - mjfl 8y ago
    Philosophical issues mean that the theory is wrong and new physics will come from their resolution, and thus philosophical issues can be decided experimentally.
    - whatshisface 8y ago
      We may be using different definitions of the word philosophical. I'm classifying anything that can be decided experimentally as scientific. These interpretations are identical from an experimental standpoint.
      - TheOtherHobbes 8y ago
        That's a circular argument. It doesn't prove that experimental differences between interpretations are impossible. The existence of such a proof would provide a genuine scientific basis for not continuing to address the problem. Without that proof, the problem remains open.
        whatshisface 8y ago
        It will surprise you to hear, just as it suprised me, that MWI and Copenhagen have been axiomatically identical from day one. I know what you are thinking, something like, "if the problem was closed we wouldn't be talking about it, so it must be open." Yeah, well... There is a list of axioms of quantum mechanics, Copenhagen and MWI disagree only on how you get to them. (And also on their conceptual interpretation). That's why they're called interpretations of quantum mechanics, not theories of quantum mechanics.
- gowld 8y ago
  Requiring the existence of something that is fundamentally impossible to detect, is a poor resolution to the problem. If there are many worlds, how is it decided which one we are in? MWI is scientifically equivalent to collapse, it's just imagined as a branching instead of a selection among alternatives.
  - firethief 8y ago
    MWI is what happens when you don't require the existence of anything extra (collapse phenomenon). It's like how <the way sound emitters change pitch when the observer is moving> isn't an unexplained phenomenon--it results from the evolution of the observer's perspective. In MWI there is no event corresponding to collapse for the same reason that Gallileo's model doesn't have any correlate of epicycles.
    - TheOtherHobbes 8y ago
      In MWI the event corresponding to collapse is the supposed appearance of an entire universe, which is - conveniently - impossible to detect. And which "explains" any one timeline of experience as "Actually, that's still just random." So MWI goes from "That's random and we don't know why" to "That's random, we don't know why, but now we've added a universe too, although we can't prove it exists." Something about this doesn't seem entirely convincing.
      - btilly 8y ago
        And yet there is an intermediate version. Which is that we can have an "observer" that is a moderately complex QM system where further post-observations are possible though difficult. And we can conduct experiments along that line and observe the growing difficulty of future interaction as systems get complex. Unsurprisingly, these experiments with "partial collapse" produce exactly the predicted results of QM. And are exactly in line with, "And if the system gets more complicated still, collapse becomes irreversible." (Where "more complicated still" is very simple compared to ordinary macroscopic objects.)
      - dghf 8y ago
- ttctciyf 8y ago
  Many Worlds still owes us an explanation of the apparently huge difference between this, the actual, world and all the other apparently not quite so actual ones, does it not? The two most promising ideas (IMO) are the idea that the "wave function collapse" is a non-physical event describing a change in our knowledge, the quantum informatics approach as per Philip Ball's recent RI lecture,[1] and the "Relational" interpretation[2] which observes that a measurement always entangles the measuring system with the measured system, and is best treated as such - i.e. as an entanglement relationship; though it seems that this leads to an "entanglements all the way down" view in which these relationships are the ultimate physical reality, rather than the conventional picture of the relationships being secondary to the things which are so related. The "measurement as entanglement" view is, I know, notably supported by at least one HN poster[3], who I hope will be on hand to correct my no-doubt erroneous rendition :) 1: https://www.youtube.com/watch?v=q7v5NtV8v6I https://www.youtube.com/watch?v=q7v5NtV8v6I 2: https://en.wikipedia.org/wiki/Relational_quantum_mechanics https://en.wikipedia.org/wiki/Relational_quantum_mechanics 3: https://news.ycombinator.com/item?id=12657447 https://news.ycombinator.com/item?id=12657447
  - btilly 8y ago
    Many Worlds still owes us an explanation of the apparently huge difference between this, the actual, world and all the other apparently not quite so actual ones, does it not? No. For a start, there is no evidence that the ones you are calling "not quite so actual" are any less actual than the one we share an experience of. Continuing on, the interpretation does not attempt to explain the phenomena of perceived consciousness. That is as much out of its remit as abiogenesis is out of the remit of Darwin's theory of evolution. Those problems are different in kind, much harder, and have to be addressed by very different theories. Everett addressed a precise problem. That problem is explaining why, to the extent that QM describes an observer, the act of observation must turn that observer into a superposition of observers. Each of which has observed an apparent collapse, and none of which can interact further in any meaningful way.
    - ttctciyf 8y ago
      > For a start, there is no evidence that the ones you are calling "not quite so actual" are any less actual than the one we share an experience of. Well, there is evidence of the one I'm calling "actual" - if it's evidence you want, there's no evidence at all of the "not so actual" ones - citing the MW interpretation as evidence of these is purely circular. Regards not explaining perceived consciousness.. If MW is shunting off questions of actuality into something to be resolved by a theory of consciousness isn't it leaving behind centuries of consensus belief in the objective observer-independent existence of a physical world ontologically prior to consciousness?
- ddxxdd 8y ago
  Last time I checked, the Everett interpretation has yet to reproduce the "Born Rule" equation for wavefunction collapse. The Many-Worlds interpretation is nice and fun to talk about, but it hasn't done any heavy lifting in terms of reducing the number of postulates required to describe quantum mechanics.
philipov 8y ago
Yes it is. Measurement is entanglement between the observed system and the observing system. Wave function collapse is an illusion caused by the two systems no longer being separable. They have entered a mixed state. It looks like information is lost in the observed system only because you are ignoring the observer.
- mjfl 8y ago
  You've just replaced the problem of collapse with the problem of which universe we transition to. We are only in one.
  - atq2119 8y ago
    To be more precise, we are in all of them, but our consciousness only perceives one of them. So the real problem isn't in quantum mechanics, it's in what the hell consciousness is and why it works the way it does. However, note that you can have observations performed by a computer which e.g. counts events, and the counter will exist in all "worlds" (branches of the universal wave function, really), while each incarnation of it only "perceives" one such "world". So the physics works just fine even while we don't fully understand consciousness.
    - philipov 8y ago
      Why is it necessary for consiousness to be any different from that computer counter? It seems to me that the paradoxical idea is not quantum mechanics, but rather conciousness.
      - atq2119 8y ago
        I actually agree with you. If you can accept that consciousness is basically a computer, then there isn't really anything mysterious going on. I probably could have phrased that better.
- rohit2412 8y ago
  How does that measurement occur? Since all particles interact via gravitational and electromagnetic Force all the time, why aren't they always entangled. I never see a definition of measurement, or observation.
SubiculumCode 8y ago
There is only one system. There are no outsiders. These are dichotomies of convenience.
ttlei 8y ago
The act of making a measurement/observation is nothing more than an interaction where the system is exchanging information or this this case quantum states which is described by quantum mechanics. I don't get where this "special/outside" observer coming from.

by mjfl 8y ago

btilly 8y ago

No, there is not. The Everett aka many-worlds interpretation demonstrates that you can explain the observed effects of measurement without invoking "collapse" of the wave function, and without reference to anything outside of QM.

whatshisface 8y ago
To further build on what you're saying, by bringing in the concept of a measure-er we have already entered the domain of philosophy, because the special class "measure-er" belongs to the Copenhagen interpretation and the interpretation of quantum mechanics is a philosophical issue by virtue of the fact that it will never be decided experimentally.
- mjfl 8y ago
  Philosophical issues mean that the theory is wrong and new physics will come from their resolution, and thus philosophical issues can be decided experimentally.
  - whatshisface 8y ago
    We may be using different definitions of the word philosophical. I'm classifying anything that can be decided experimentally as scientific. These interpretations are identical from an experimental standpoint.
    - TheOtherHobbes 8y ago
      That's a circular argument. It doesn't prove that experimental differences between interpretations are impossible. The existence of such a proof would provide a genuine scientific basis for not continuing to address the problem. Without that proof, the problem remains open.
      - whatshisface 8y ago
        It will surprise you to hear, just as it suprised me, that MWI and Copenhagen have been axiomatically identical from day one. I know what you are thinking, something like, "if the problem was closed we wouldn't be talking about it, so it must be open." Yeah, well... There is a list of axioms of quantum mechanics, Copenhagen and MWI disagree only on how you get to them. (And also on their conceptual interpretation). That's why they're called interpretations of quantum mechanics, not theories of quantum mechanics.
gowld 8y ago
Requiring the existence of something that is fundamentally impossible to detect, is a poor resolution to the problem. If there are many worlds, how is it decided which one we are in? MWI is scientifically equivalent to collapse, it's just imagined as a branching instead of a selection among alternatives.
- firethief 8y ago
  MWI is what happens when you don't require the existence of anything extra (collapse phenomenon). It's like how <the way sound emitters change pitch when the observer is moving> isn't an unexplained phenomenon--it results from the evolution of the observer's perspective. In MWI there is no event corresponding to collapse for the same reason that Gallileo's model doesn't have any correlate of epicycles.
  - TheOtherHobbes 8y ago
    In MWI the event corresponding to collapse is the supposed appearance of an entire universe, which is - conveniently - impossible to detect. And which "explains" any one timeline of experience as "Actually, that's still just random." So MWI goes from "That's random and we don't know why" to "That's random, we don't know why, but now we've added a universe too, although we can't prove it exists." Something about this doesn't seem entirely convincing.
    - btilly 8y ago
      And yet there is an intermediate version. Which is that we can have an "observer" that is a moderately complex QM system where further post-observations are possible though difficult. And we can conduct experiments along that line and observe the growing difficulty of future interaction as systems get complex. Unsurprisingly, these experiments with "partial collapse" produce exactly the predicted results of QM. And are exactly in line with, "And if the system gets more complicated still, collapse becomes irreversible." (Where "more complicated still" is very simple compared to ordinary macroscopic objects.)
    - dghf 8y ago
ttctciyf 8y ago
Many Worlds still owes us an explanation of the apparently huge difference between this, the actual, world and all the other apparently not quite so actual ones, does it not? The two most promising ideas (IMO) are the idea that the "wave function collapse" is a non-physical event describing a change in our knowledge, the quantum informatics approach as per Philip Ball's recent RI lecture,[1] and the "Relational" interpretation[2] which observes that a measurement always entangles the measuring system with the measured system, and is best treated as such - i.e. as an entanglement relationship; though it seems that this leads to an "entanglements all the way down" view in which these relationships are the ultimate physical reality, rather than the conventional picture of the relationships being secondary to the things which are so related. The "measurement as entanglement" view is, I know, notably supported by at least one HN poster[3], who I hope will be on hand to correct my no-doubt erroneous rendition :) 1: https://www.youtube.com/watch?v=q7v5NtV8v6I https://www.youtube.com/watch?v=q7v5NtV8v6I 2: https://en.wikipedia.org/wiki/Relational_quantum_mechanics https://en.wikipedia.org/wiki/Relational_quantum_mechanics 3: https://news.ycombinator.com/item?id=12657447 https://news.ycombinator.com/item?id=12657447
- btilly 8y ago
  Many Worlds still owes us an explanation of the apparently huge difference between this, the actual, world and all the other apparently not quite so actual ones, does it not? No. For a start, there is no evidence that the ones you are calling "not quite so actual" are any less actual than the one we share an experience of. Continuing on, the interpretation does not attempt to explain the phenomena of perceived consciousness. That is as much out of its remit as abiogenesis is out of the remit of Darwin's theory of evolution. Those problems are different in kind, much harder, and have to be addressed by very different theories. Everett addressed a precise problem. That problem is explaining why, to the extent that QM describes an observer, the act of observation must turn that observer into a superposition of observers. Each of which has observed an apparent collapse, and none of which can interact further in any meaningful way.
  - ttctciyf 8y ago
    > For a start, there is no evidence that the ones you are calling "not quite so actual" are any less actual than the one we share an experience of. Well, there is evidence of the one I'm calling "actual" - if it's evidence you want, there's no evidence at all of the "not so actual" ones - citing the MW interpretation as evidence of these is purely circular. Regards not explaining perceived consciousness.. If MW is shunting off questions of actuality into something to be resolved by a theory of consciousness isn't it leaving behind centuries of consensus belief in the objective observer-independent existence of a physical world ontologically prior to consciousness?
ddxxdd 8y ago
Last time I checked, the Everett interpretation has yet to reproduce the "Born Rule" equation for wavefunction collapse. The Many-Worlds interpretation is nice and fun to talk about, but it hasn't done any heavy lifting in terms of reducing the number of postulates required to describe quantum mechanics.

philipov 8y ago

Yes it is. Measurement is entanglement between the observed system and the observing system. Wave function collapse is an illusion caused by the two systems no longer being separable. They have entered a mixed state. It looks like information is lost in the observed system only because you are ignoring the observer.

mjfl 8y ago
You've just replaced the problem of collapse with the problem of which universe we transition to. We are only in one.
- atq2119 8y ago
  To be more precise, we are in all of them, but our consciousness only perceives one of them. So the real problem isn't in quantum mechanics, it's in what the hell consciousness is and why it works the way it does. However, note that you can have observations performed by a computer which e.g. counts events, and the counter will exist in all "worlds" (branches of the universal wave function, really), while each incarnation of it only "perceives" one such "world". So the physics works just fine even while we don't fully understand consciousness.
  - philipov 8y ago
    Why is it necessary for consiousness to be any different from that computer counter? It seems to me that the paradoxical idea is not quantum mechanics, but rather conciousness.
    - atq2119 8y ago
      I actually agree with you. If you can accept that consciousness is basically a computer, then there isn't really anything mysterious going on. I probably could have phrased that better.
rohit2412 8y ago
How does that measurement occur? Since all particles interact via gravitational and electromagnetic Force all the time, why aren't they always entangled. I never see a definition of measurement, or observation.

SubiculumCode 8y ago

There is only one system. There are no outsiders. These are dichotomies of convenience.

ttlei 8y ago

The act of making a measurement/observation is nothing more than an interaction where the system is exchanging information or this this case quantum states which is described by quantum mechanics. I don't get where this "special/outside" observer coming from.