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Yes. Mathematical frameworks that assume Quantum Systems are deterministic (only being in state A or B) during unobserved periods have never been validated by

Yes. Mathematical frameworks that assume Quantum Systems are deterministic (only being in state A or B) during unobserved periods have never been validated by experiment. It is great if you have a model, but if that model fails to agree with experimental results.

SomeStupidPoint 10y ago
But as I understand it, this is because of technical lock-in: physicists had to choose between non-locality and indeterminism, chose indeterminism, got forced in to non-locality for other reasons, and never went back to re-examine the model, because it was getting decent computational results, and it would be a lot of work to rebuild. I've never seen a solid argument for indeterminism being anything but an extraneous assumption in QM. Entanglement (and other behaviors at low temperature) necessitates non-locality, which means the most parsimonious model would also use that, rather than indeterminism, to resolve Bell's inequality. So is there any reason besides "it predicts good enough" and "technical lockin" to keep using models with indeterminism? (Physics actually seems a hodgepodge of random philosophical assumptions no one bothered to ever review because they're deep in the model. Not unlike code suffering from code rot.)
- malkarouri 10y ago
  (Physics actually seems a hodgepodge of random philosophical assumptions no one bothered to ever review because they're deep in the model. Not unlike code suffering from code rot.) This..
- codethief 10y ago
  Entanglement doesn't require non-locality.
  - SomeStupidPoint 10y ago
    Does it not? Can you explain how entanglement works as an entirely local phenomenon?
    - codethief 10y ago
      (Sorry for replying so late, I hope you'll still see this.) Well, the situation of entanglement is not really* different from the following one: Imagine you have two pairs of socks, a red pair and a blue pair. Now, certainly you only wear a red (blue) sock on your left foot iff you wear one of the same color on your right foot, right? So, consider the measurement of your left sock's color by pulling up the leg of your pants and looking at your sock. If it is red, you can be 100% sure you will measure your right sock to be "red" as well, and, similarly, if it is blue you will measure blue on the right, too. Now, in order to explain this phenomenon, do you need faster-than-light travel of your left sock's color to your right sock at any point? No. The results of the color measurements on both sides are just correlated with each other because both subsystems (both socks) were prepared that way earlier. * Granted, the issue of entanglement is actually slightly more complicated since a sock being either red or blue is not quite the same as the sock being in a superposition of both colors, i.e. being red and blue at the same time. But this difference just boils down to the fact that, in (the Copenhagen interpretation of) quantum mechanics there are measurements whose outcome is non-deterministic and superpositions just encode this very fact (together with complementary observables that allow us to distinguish between pure eigenstates and superpositions in the first place. Without complementary variables we would never see a difference between the two.) So, for instance, in entanglement experiments one often prepares two particles in a superposition of eigenstates of the spin-z operator and then proceeds to measure the particles' spin with respect to another axis. It turns out that the results of both measurements will be random but correlated. Will you able to explain the results using the sock analogy? No, because the socks are entirely classical, in particular deterministic, and there are no complementary variables such as spin x and spin z (e.g. the color of the socks has nothing to do with it being made from cotton or wool and both properties are defined independently). Will you now need non-locality, though? Still no, you just needed to add non-determinism in the form of complementary variables to your theory. So, put differently, if your theory of quantum mechanics is non-deterministic, then it can very well be local. Only if it is deterministic, it must be non-local (see, for instance, Bohmian mechanics). So, while you could have both, indeterminism and non-locality, at the same time, you certainly don't need both and, in fact, in the standard (Copenhagen) interpretation of quantum mechanics we don't have both. I think the missunderstanding that the Copenhagen interpretation is both non-deterministic and non-local originates from the idea that we imagine the wave function to collapse upon measurement and this collapse to propagate faster-than-light from one entangled particle to the other. But the collapse of the wave function is not just not compatible with special relativity but it is also not compatible with the unitary time evolution of quantum mechanics, so we should consider it merely a tool for us instead of something that is actually happening. What matters at the end of the day are expectation values of measurements and for that you don't need the collapse of the wave function or non-locality at any point.
- abdullahkhalids 10y ago
  1. The philosophical basis of our physical theories is a very well studied problem. The reason you don't see it in common parlance is that most of us, even most professional physicists, are not qualified to talk about these issues in detail. For stuff you have not seen, you need to dig deeper into literature. Its all there - I am not qualified to point to a good resource. 2. Physicists are always happy to consider all sorts of theories. Problem is that any new theory must also retrodict all known experimental results as well as make new predictions. The reason you don't see better theories than QM is that we physicists have failed to be creative enough to think of a theory that is better than QM at prediciting experimental results. When we do, or when you tell us a precisely defined mathematical model of reality that is better than QM at predicting reality, we will throw away QM like a burning brand and hop onto the philosophical bandwagon of the new theory.
  - mablap 10y ago
    you don't see it in common parlance I think one of the factors for that is the fact that most high-level scientists learn to be cautious about the claims they make. You're much more likely so hear a layman make strong claims about X or Y than you are to hear the same from a PhD physicst, on average. What a lot of people who didn't go through the grinder of Academia seem not to understand, is that when one says "I don't know", it doesn't mean "I know nothing about this". If I say "I don't know", chances are I could discuss the subject at length, but my comprehension is not satisfactory to answer the question on a deep level, or I don't really grok the subject enough to feel confident to give my opinion. This is less present in laymen and can lead to some friction in discussions.

SomeStupidPoint 10y ago

But as I understand it, this is because of technical lock-in: physicists had to choose between non-locality and indeterminism, chose indeterminism, got forced in to non-locality for other reasons, and never went back to re-examine the model, because it was getting decent computational results, and it would be a lot of work to rebuild. I've never seen a solid argument for indeterminism being anything but an extraneous assumption in QM. Entanglement (and other behaviors at low temperature) necessitates non-locality, which means the most parsimonious model would also use that, rather than indeterminism, to resolve Bell's inequality. So is there any reason besides "it predicts good enough" and "technical lockin" to keep using models with indeterminism? (Physics actually seems a hodgepodge of random philosophical assumptions no one bothered to ever review because they're deep in the model. Not unlike code suffering from code rot.)

malkarouri 10y ago
(Physics actually seems a hodgepodge of random philosophical assumptions no one bothered to ever review because they're deep in the model. Not unlike code suffering from code rot.) This..
codethief 10y ago
Entanglement doesn't require non-locality.
- SomeStupidPoint 10y ago
  Does it not? Can you explain how entanglement works as an entirely local phenomenon?
  - codethief 10y ago
    (Sorry for replying so late, I hope you'll still see this.) Well, the situation of entanglement is not really* different from the following one: Imagine you have two pairs of socks, a red pair and a blue pair. Now, certainly you only wear a red (blue) sock on your left foot iff you wear one of the same color on your right foot, right? So, consider the measurement of your left sock's color by pulling up the leg of your pants and looking at your sock. If it is red, you can be 100% sure you will measure your right sock to be "red" as well, and, similarly, if it is blue you will measure blue on the right, too. Now, in order to explain this phenomenon, do you need faster-than-light travel of your left sock's color to your right sock at any point? No. The results of the color measurements on both sides are just correlated with each other because both subsystems (both socks) were prepared that way earlier. * Granted, the issue of entanglement is actually slightly more complicated since a sock being either red or blue is not quite the same as the sock being in a superposition of both colors, i.e. being red and blue at the same time. But this difference just boils down to the fact that, in (the Copenhagen interpretation of) quantum mechanics there are measurements whose outcome is non-deterministic and superpositions just encode this very fact (together with complementary observables that allow us to distinguish between pure eigenstates and superpositions in the first place. Without complementary variables we would never see a difference between the two.) So, for instance, in entanglement experiments one often prepares two particles in a superposition of eigenstates of the spin-z operator and then proceeds to measure the particles' spin with respect to another axis. It turns out that the results of both measurements will be random but correlated. Will you able to explain the results using the sock analogy? No, because the socks are entirely classical, in particular deterministic, and there are no complementary variables such as spin x and spin z (e.g. the color of the socks has nothing to do with it being made from cotton or wool and both properties are defined independently). Will you now need non-locality, though? Still no, you just needed to add non-determinism in the form of complementary variables to your theory. So, put differently, if your theory of quantum mechanics is non-deterministic, then it can very well be local. Only if it is deterministic, it must be non-local (see, for instance, Bohmian mechanics). So, while you could have both, indeterminism and non-locality, at the same time, you certainly don't need both and, in fact, in the standard (Copenhagen) interpretation of quantum mechanics we don't have both. I think the missunderstanding that the Copenhagen interpretation is both non-deterministic and non-local originates from the idea that we imagine the wave function to collapse upon measurement and this collapse to propagate faster-than-light from one entangled particle to the other. But the collapse of the wave function is not just not compatible with special relativity but it is also not compatible with the unitary time evolution of quantum mechanics, so we should consider it merely a tool for us instead of something that is actually happening. What matters at the end of the day are expectation values of measurements and for that you don't need the collapse of the wave function or non-locality at any point.
abdullahkhalids 10y ago
1. The philosophical basis of our physical theories is a very well studied problem. The reason you don't see it in common parlance is that most of us, even most professional physicists, are not qualified to talk about these issues in detail. For stuff you have not seen, you need to dig deeper into literature. Its all there - I am not qualified to point to a good resource. 2. Physicists are always happy to consider all sorts of theories. Problem is that any new theory must also retrodict all known experimental results as well as make new predictions. The reason you don't see better theories than QM is that we physicists have failed to be creative enough to think of a theory that is better than QM at prediciting experimental results. When we do, or when you tell us a precisely defined mathematical model of reality that is better than QM at predicting reality, we will throw away QM like a burning brand and hop onto the philosophical bandwagon of the new theory.
- mablap 10y ago
  you don't see it in common parlance I think one of the factors for that is the fact that most high-level scientists learn to be cautious about the claims they make. You're much more likely so hear a layman make strong claims about X or Y than you are to hear the same from a PhD physicst, on average. What a lot of people who didn't go through the grinder of Academia seem not to understand, is that when one says "I don't know", it doesn't mean "I know nothing about this". If I say "I don't know", chances are I could discuss the subject at length, but my comprehension is not satisfactory to answer the question on a deep level, or I don't really grok the subject enough to feel confident to give my opinion. This is less present in laymen and can lead to some friction in discussions.