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So it seems that quantum particles do not "choose" their state until observed. I've heard this multiple times now, including in this article (demonstrated by th

So it seems that quantum particles do not "choose" their state until observed. I've heard this multiple times now, including in this article (demonstrated by the 33 sticks analogy). I'm curious, has any research been done on HOW they "choose" their state when observed? I imagine it is pretty difficult (if not impossible) to analyze this, but is there any insight of the factors that make a quantum particle choose its state? Or is the prevalent theory that it is completely random? PD: I find this topic fascinating.

n4r9 8y ago
This is basically where interpretations of quantum mechanics come into play. The maths/experiments alone don't tell you much. There are only a few things we can be sure of, e.g. the particle is not choosing a locally determined, pre-existing value as in classical mechanics. What you believe after that comes down to which "comforting illusion" you are most willing to ditch.
- posterboy 8y ago
  > the particle is not choosing a locally determined, pre-existing value as in classical mechanics Translation: The value of to entangled measurements does not allow inference of a value back in time. > What you believe after that comes down to which "comforting illusion" you are most willing to ditch. You should drop the illusion that even 1% reading here understand enough relativity theory to even understand the problem. I don't. I took a few crash courses on physics and they tried to teach the double slit experiment to us in the second semester. Of course they had to cut it short and call it "magic". Of course even scientists parrot popular science when explaining only the difficulties they face, not the exact physics, I guess. All this local hidden variable stuff seems like a version of Laplace's demon. Well of course you don't have enough data. There could always be another hidden variable. But instead QC takes a statistical approach like thermodynamics, ignoring single states and looking at, ironically speaking, the bigger picture. > What you believe after that comes down to which "comforting illusion" you are most willing to ditch. There's no illusion to ditch. You start with a null hypothesis, so the problem is which null hypothesis to fall back on. To ditch a hypothesis you need to understand the experiments in question and the math. The philosphy is an after thought to rationalize the results, but it doesn't matter much to e.g. the material scientists doing the field work, and vice versa, the level of precision of these measurements is so far removed from our every day understanding that it really has no bearing on Multiverse Theories and all that popular nonsense. By the way, non-local hidden variables have not been ruled out. Where's the difference, distance (ie. locality) might just be a matter of more than 4 dimensions?! Maybe I misunderstand. Different question. Why is time always the independent variable? I think the problem is that people like things linear, first order, because I have a huge problem imagining differential equations, recursion and what not, even OEDs, not to mention PDEs.
  - n4r9 8y ago
    You don't need to understand even special relativity to learn about Bell's theorem. It's just about measurement settings and local influence. You're correct that non-local hidden variable theories are still plausible. Bohmian mechanics is the prominent example. In this case "locality" is the comfortable illusion that you drop. In Copenhagen it is a kind of realism. In Many Worlds it is the notion that an observation leads to a single result. There's no clear way to determine which of these is more like a "null hypothesis" than the others, so what tends to happen is that people gravitate towards one or another based on which of the illusions they're more okay with dropping. It would be nice to be able to discriminate between interpretations based on experiment, and a little work has been done on this, but we're not really anywhere near there yet.
    - posterboy 8y ago
      I wrote under the impression that locality would rely on a notion of space-time. wiki/Local_realism says as much. That then is one notion to knock down. The null hypothesis here would be non-locality. Unifying that with GR is the big problem, I hear, especially regarding gravity.
      - n4r9 8y ago
        Without some notion of space-time you could not have a meaningful notion of locality, therefore Bell's Theorem is a non-issue. But you don't need a relativistic space-time for Bell's Theorem, any space-time in which physical influences travel at a bounded speed will suffice. Bell's Theorem does, however, create an uneasy tension between quantum theory and special relativity. Tim Maudlin writes quite a good book about this called "Quantum Non-Locality and Relativity".
joe_the_user 8y ago
So it seems that quantum particles do not "choose" their state until observed. I've heard this multiple times now, including in this article (demonstrated by the 33 sticks analogy). As I understand it (and correct me if I'm wrong), the particles give different distributions depending on how they are observed and these distributions vary in fashion distinction from how they would vary if there were underlying classical distribution involved - this gives "quantum logic".
sleepyams 8y ago
I think the insight is that there isn't really a built-in mechanism in particles for making choices, it's more that through experimentation we are _imposing_ a structure that forces a choice in an attempt to extract information. But we find that even when we force the system to make a choice, we get effectively no information and this appears to us to be a sort of complete randomness. I interpret Conway's idea (in part III) to be that this is not a structural randomness, but rather randomness only in response to structure that _we_ impose during an experiment (e.g. determining spin), and that this is similar to our free will which is not structured (if you subscribe that that theory). EDIT: I feel like I should clarify: at play here is the question of how mechanistic the universe is. If we accept that the universe is mechanistic, then we are forced into a position where we have to say (if we wish to avoid determinism) that there is such a thing as a "completely random" mechanism, and furthermore we have to effectively absolve free will of any structural restrictions by requiring that it is somehow part of our vitality as humans (call this mind-body dualism or whatever -- there is a long history of this debate). Obviously this is all beyond physics, but it is important to realize what assumptions we are implicitly requiring in order to discuss randomness and free will in this case.
Viliam1234 8y ago
> I'm curious, has any research been done on HOW they "choose" their state when observed? They do not. There is no "particle choosing", ever. What happens instead is that you (the observer) are also composed of particles. This is something that people are kinda willing to admit, but afterwards they deny the logical consequence... that the particles that create you can also be in more than one state at the same time. What happens instead is "entanglement", which means that certain options of one particle become connected to certain options of another particle. All options continue to exist, but only some of the relations between different particles exist. Specifically, when observe the particle, the option "particle going left" becomes entangled with the option (remember, you are also a system of particles) "you see the particle going left"; and analogically, the option "particle going right" becomes entangled with the option "you see the particle going right". Now each version of you observe one specific outcome... and can ask themselves 'what made the particle choose this specific outcome?' But there was no choice; it's just that the other movement of the particle is entangled with a different version of you. Yes, parallel worlds -- the true shocking discovery of the quantum physics. Actually, all physicists admit that parallel worlds exist on the microscopic scale, the only controversy is that half of them say "and it's the same on the macroscopic scale, too", while the other half goes "I can't believe in macroscopic parallel worlds, therefore there must be a magical thing called 'quantum collapse' which makes this madness stop before it gets too large". (The belief in quantum collapse in unfalsifiable, because no matter how large system of particles existing in parallel configuration you build, the possible counter-argument goes "but if you make it even larger, then it will finally collapse". And this goalpost can be pushed indefinitely.) Unlike in science fiction, the parallel worlds of quantum physics have the property that the more they differ, the less they can interact. If they only differ in position of one particle (one world where the particle goes left, another where it goes right, but everything else is exactly the same), there is a lot of interaction. But if they differ in hundreds of particles, the interaction is almost zero. The disappointing part is that you can never observe the parallel universe directly, because - again - you are composed of particles; even your very act of thinking means moving millions of particles in your brain around... so just the fact that you noticed a particle moving left has put millions of particles in your brain in a different position than if you would have noticed the particle moving right. The problems with thinking about quantum physics arise when we imagine that the microscopic scale is just like the macroscopic scale, only smaller. ("Particles are like oranges, only smaller, duh. Actually, they are more like waves on the lake. Anyway, must be the former or the latter, because those are the only options I am familiar with.") When instead, the macro scale is a statistical aggregate of the micro scale, so we can't observe e.g. things that get cancelled out by other things. Instead of trying to fit the micro scale into our everyday experience, the proper way is to study the micro scale by its own laws, such as probabilities being expressed by complex numbers, and then think how could our everyday experience arise from this, i.e. again, what laws would then govern huge systems of particles, such as ourselves.

n4r9 8y ago

This is basically where interpretations of quantum mechanics come into play. The maths/experiments alone don't tell you much. There are only a few things we can be sure of, e.g. the particle is not choosing a locally determined, pre-existing value as in classical mechanics. What you believe after that comes down to which "comforting illusion" you are most willing to ditch.

posterboy 8y ago
> the particle is not choosing a locally determined, pre-existing value as in classical mechanics Translation: The value of to entangled measurements does not allow inference of a value back in time. > What you believe after that comes down to which "comforting illusion" you are most willing to ditch. You should drop the illusion that even 1% reading here understand enough relativity theory to even understand the problem. I don't. I took a few crash courses on physics and they tried to teach the double slit experiment to us in the second semester. Of course they had to cut it short and call it "magic". Of course even scientists parrot popular science when explaining only the difficulties they face, not the exact physics, I guess. All this local hidden variable stuff seems like a version of Laplace's demon. Well of course you don't have enough data. There could always be another hidden variable. But instead QC takes a statistical approach like thermodynamics, ignoring single states and looking at, ironically speaking, the bigger picture. > What you believe after that comes down to which "comforting illusion" you are most willing to ditch. There's no illusion to ditch. You start with a null hypothesis, so the problem is which null hypothesis to fall back on. To ditch a hypothesis you need to understand the experiments in question and the math. The philosphy is an after thought to rationalize the results, but it doesn't matter much to e.g. the material scientists doing the field work, and vice versa, the level of precision of these measurements is so far removed from our every day understanding that it really has no bearing on Multiverse Theories and all that popular nonsense. By the way, non-local hidden variables have not been ruled out. Where's the difference, distance (ie. locality) might just be a matter of more than 4 dimensions?! Maybe I misunderstand. Different question. Why is time always the independent variable? I think the problem is that people like things linear, first order, because I have a huge problem imagining differential equations, recursion and what not, even OEDs, not to mention PDEs.
- n4r9 8y ago
  You don't need to understand even special relativity to learn about Bell's theorem. It's just about measurement settings and local influence. You're correct that non-local hidden variable theories are still plausible. Bohmian mechanics is the prominent example. In this case "locality" is the comfortable illusion that you drop. In Copenhagen it is a kind of realism. In Many Worlds it is the notion that an observation leads to a single result. There's no clear way to determine which of these is more like a "null hypothesis" than the others, so what tends to happen is that people gravitate towards one or another based on which of the illusions they're more okay with dropping. It would be nice to be able to discriminate between interpretations based on experiment, and a little work has been done on this, but we're not really anywhere near there yet.
  - posterboy 8y ago
    I wrote under the impression that locality would rely on a notion of space-time. wiki/Local_realism says as much. That then is one notion to knock down. The null hypothesis here would be non-locality. Unifying that with GR is the big problem, I hear, especially regarding gravity.
    - n4r9 8y ago
      Without some notion of space-time you could not have a meaningful notion of locality, therefore Bell's Theorem is a non-issue. But you don't need a relativistic space-time for Bell's Theorem, any space-time in which physical influences travel at a bounded speed will suffice. Bell's Theorem does, however, create an uneasy tension between quantum theory and special relativity. Tim Maudlin writes quite a good book about this called "Quantum Non-Locality and Relativity".

joe_the_user 8y ago

So it seems that quantum particles do not "choose" their state until observed. I've heard this multiple times now, including in this article (demonstrated by the 33 sticks analogy). As I understand it (and correct me if I'm wrong), the particles give different distributions depending on how they are observed and these distributions vary in fashion distinction from how they would vary if there were underlying classical distribution involved - this gives "quantum logic".

sleepyams 8y ago

I think the insight is that there isn't really a built-in mechanism in particles for making choices, it's more that through experimentation we are _imposing_ a structure that forces a choice in an attempt to extract information. But we find that even when we force the system to make a choice, we get effectively no information and this appears to us to be a sort of complete randomness. I interpret Conway's idea (in part III) to be that this is not a structural randomness, but rather randomness only in response to structure that _we_ impose during an experiment (e.g. determining spin), and that this is similar to our free will which is not structured (if you subscribe that that theory). EDIT: I feel like I should clarify: at play here is the question of how mechanistic the universe is. If we accept that the universe is mechanistic, then we are forced into a position where we have to say (if we wish to avoid determinism) that there is such a thing as a "completely random" mechanism, and furthermore we have to effectively absolve free will of any structural restrictions by requiring that it is somehow part of our vitality as humans (call this mind-body dualism or whatever -- there is a long history of this debate). Obviously this is all beyond physics, but it is important to realize what assumptions we are implicitly requiring in order to discuss randomness and free will in this case.

Viliam1234 8y ago

> I'm curious, has any research been done on HOW they "choose" their state when observed? They do not. There is no "particle choosing", ever. What happens instead is that you (the observer) are also composed of particles. This is something that people are kinda willing to admit, but afterwards they deny the logical consequence... that the particles that create you can also be in more than one state at the same time. What happens instead is "entanglement", which means that certain options of one particle become connected to certain options of another particle. All options continue to exist, but only some of the relations between different particles exist. Specifically, when observe the particle, the option "particle going left" becomes entangled with the option (remember, you are also a system of particles) "you see the particle going left"; and analogically, the option "particle going right" becomes entangled with the option "you see the particle going right". Now each version of you observe one specific outcome... and can ask themselves 'what made the particle choose this specific outcome?' But there was no choice; it's just that the other movement of the particle is entangled with a different version of you. Yes, parallel worlds -- the true shocking discovery of the quantum physics. Actually, all physicists admit that parallel worlds exist on the microscopic scale, the only controversy is that half of them say "and it's the same on the macroscopic scale, too", while the other half goes "I can't believe in macroscopic parallel worlds, therefore there must be a magical thing called 'quantum collapse' which makes this madness stop before it gets too large". (The belief in quantum collapse in unfalsifiable, because no matter how large system of particles existing in parallel configuration you build, the possible counter-argument goes "but if you make it even larger, then it will finally collapse". And this goalpost can be pushed indefinitely.) Unlike in science fiction, the parallel worlds of quantum physics have the property that the more they differ, the less they can interact. If they only differ in position of one particle (one world where the particle goes left, another where it goes right, but everything else is exactly the same), there is a lot of interaction. But if they differ in hundreds of particles, the interaction is almost zero. The disappointing part is that you can never observe the parallel universe directly, because - again - you are composed of particles; even your very act of thinking means moving millions of particles in your brain around... so just the fact that you noticed a particle moving left has put millions of particles in your brain in a different position than if you would have noticed the particle moving right. The problems with thinking about quantum physics arise when we imagine that the microscopic scale is just like the macroscopic scale, only smaller. ("Particles are like oranges, only smaller, duh. Actually, they are more like waves on the lake. Anyway, must be the former or the latter, because those are the only options I am familiar with.") When instead, the macro scale is a statistical aggregate of the micro scale, so we can't observe e.g. things that get cancelled out by other things. Instead of trying to fit the micro scale into our everyday experience, the proper way is to study the micro scale by its own laws, such as probabilities being expressed by complex numbers, and then think how could our everyday experience arise from this, i.e. again, what laws would then govern huge systems of particles, such as ourselves.