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The part that seems the most dubious to me is the "choice": > 2. It is possible to make free choices, or at least, statistically random choices. I don't see w

The part that seems the most dubious to me is the "choice": > 2. It is possible to make free choices, or at least, statistically random choices. I don't see what would be really compelling in that. If it's false it would just mean that our actions are all kind of mechanistically decided by other events, and that does not shock me. Other point: > 1. When someone observes an event happening, it really happened. What if it really happened in the reality of the observer (and maybe not in other realities)? What is meant by "reality"? Some insight is to be gained by precising what we call the reality, in relation to the corpus of all the observations in what we believe is our universe.

coliveira 6y ago
The main problem of quantum interpretation is the supposed, artificial, distinction between observer and observed system. In a quantum world this distinction is not possible, every event capable of "observing" a system is itself part of the system, modifying it. That's why such interpretations (postulating this separation) give all kinds of strange paradoxes that are impossible to solve. In the quantum world, there is no such thing as an observer, it is just all part of the system. Consider for example the system composed of a pool table. In classical physics we can assume we can always measure the position and momentum of all balls in the table. But what would happen if measurement was not possible without big changes in position and velocity? Suddenly the whole notion of "observation" would lose its meaning, and the only way to describe the pool table is as a probabilistic mesh of balls moving around in uncertain directions.
- henearkr 6y ago
  Yes, I think you put your finger on it. As the observer is part of the system, his "reality" is as much superposed, entangled, etc., as the quantum events that compose it (himself and his observation too). That would give credit to the multiverse interpretation of quantum mechanics then. Maybe the observation process of a quantum phenomenon by a human observer is akin to the orthogonalization of a matrix: as the observer becomes entangled with the observed particle, each possible observer-eigenstate (i.e. any observer in "his reality") ends up observing an eigenstate of the observed quantum phenomenon, instead of a dirty superposition. To call it "orthogonalization of the observer-observed system" would be more descriptive than "wave-collapse", but the main difference is that the orthogonalization treats in parallel all possible outcomes, each linked to a different state (outcome) of the observer too, whereas the "collapse" view insists on the fact that the observed eigenstate is unique. And moreover, at least in mathematics, there are conditions for the orthogonalization to be possible at all, so that should be interesting.
- cmehdy 6y ago
  Even in the classical world we measure that pool table by interacting with it. If I stand next to the table and see it, it's because light hit it and then hit my eyes - but I've absorbed whatever light might have gone on its course through me as an observer and maybe hit the table again eventually (attenuated), and I also happen to emit some light myself. My body being present and warm, my breathing of air in the room, etc.. creates convection currents of air, which affect the fluid mechanics of the same volume of air that the balls are in. My brain can't really perceive much of any of that and does a lot of filtering of information, and we've designed the pool table to be something we grasp and play with easily so the relative inertia of the balls will mostly overcome all the more minor terms to take into account wrt fluid mechanics, but all of that is classical physics already. "Closed systems" might only exist conceptually.
- tsimionescu 6y ago
  Well, the problem is that the reality we observe daily is not at all like quantum reality. We know exactly where our instruments are, even though we know that they are completely stationary. There is no particle/wave duality to tennis balls. This is the origin of the problem of observation - the predictions of quantum mechanics break down at some point, and we have no idea why. In particular, this happens very clearly when our measurement instruments directly interact with a quantum system, so we call this 'the measurement problem'. Of course, we can postulate that in fact, despite all of our observations, both subjective and objective, the classical world also behaves quantically but we just can't notice it happening (e.g. the Many Worlds interpretation does this). We can also say that the quantum world does NOT in fact behave that way, but that the universe is perfectly deterministic and just set up in such a way that we can never observe events that contradict this vision of the universe (superdeterminism claims this - that for example you will always happen to choose the right dial on a measurement apparatus to observe entanglement, but that there is no fundamental reason why that should happen - it could theoretically happen otherwise, but in this universe, ever since the big bang, it has been decided that at some point you will set that dial in the particular way that will make you observe the entanglement result). There are other theories that postulate that quantum mechanics is in fact deterministic, but very hard to predict, but there are non-local effects (deBroglie-Bohm pilot wave theory is such an example). We can also ignore the whole hope of trying to understand all this, and simply use the math if and when we need it to predict particle phenomena.
tsimionescu 6y ago
You may say that it's not surprising, but in fact all statistical-style reasoning relies on it. If the universe is superdeterministic, than no kind of statistical reasoning makes any sense, since everything is already set in stone, there is no probability to any event, it has either happened already or will never happen. Since there is no freedom or even randomness, there are no statistically independent events or measurements.
- elwell 6y ago
  > no kind of statistical reasoning makes any sense Probabilities are useful when you don't have perfect knowledge. But yes, they are an illusion. In truth, every event has a 100% chance of happening. And things that didn't happen aren't real events, they just seemed to be possible, but we were wrong.
  - tsimionescu 6y ago
    Sure, but please stop requiring clinical trials for new medicine, as they have no more relevance than throwing a coin. Oh, and stop throwing coins, as the result is correlated with the future decision which you will take anyway. In general, all of modern science, starting with quantum mechanics, depends on the idea that statistical independence exists. To truly abandon this idea, we would abandon almost all of the mathematical apparatus that has given us QM and all experimental observations of QM.
    - elwell 6y ago
      No principal investigator of a clinical trial has perfect knowledge of the current state of reality, nor the means to calculate subsequent states. Therefore statistics are very useful.
      - tsimionescu 6y ago
        They may or may not have perfect knowledge, but if they don't have free will or any ability to randomly choose participants, then there is no reason to trust that the patients they choose are not correlated to the medicine they are testing, such that all of the patients they chose will have the maximum response possible to the medicine, with the least amount of side effects.

coliveira 6y ago

The main problem of quantum interpretation is the supposed, artificial, distinction between observer and observed system. In a quantum world this distinction is not possible, every event capable of "observing" a system is itself part of the system, modifying it. That's why such interpretations (postulating this separation) give all kinds of strange paradoxes that are impossible to solve. In the quantum world, there is no such thing as an observer, it is just all part of the system. Consider for example the system composed of a pool table. In classical physics we can assume we can always measure the position and momentum of all balls in the table. But what would happen if measurement was not possible without big changes in position and velocity? Suddenly the whole notion of "observation" would lose its meaning, and the only way to describe the pool table is as a probabilistic mesh of balls moving around in uncertain directions.

henearkr 6y ago
Yes, I think you put your finger on it. As the observer is part of the system, his "reality" is as much superposed, entangled, etc., as the quantum events that compose it (himself and his observation too). That would give credit to the multiverse interpretation of quantum mechanics then. Maybe the observation process of a quantum phenomenon by a human observer is akin to the orthogonalization of a matrix: as the observer becomes entangled with the observed particle, each possible observer-eigenstate (i.e. any observer in "his reality") ends up observing an eigenstate of the observed quantum phenomenon, instead of a dirty superposition. To call it "orthogonalization of the observer-observed system" would be more descriptive than "wave-collapse", but the main difference is that the orthogonalization treats in parallel all possible outcomes, each linked to a different state (outcome) of the observer too, whereas the "collapse" view insists on the fact that the observed eigenstate is unique. And moreover, at least in mathematics, there are conditions for the orthogonalization to be possible at all, so that should be interesting.
cmehdy 6y ago
Even in the classical world we measure that pool table by interacting with it. If I stand next to the table and see it, it's because light hit it and then hit my eyes - but I've absorbed whatever light might have gone on its course through me as an observer and maybe hit the table again eventually (attenuated), and I also happen to emit some light myself. My body being present and warm, my breathing of air in the room, etc.. creates convection currents of air, which affect the fluid mechanics of the same volume of air that the balls are in. My brain can't really perceive much of any of that and does a lot of filtering of information, and we've designed the pool table to be something we grasp and play with easily so the relative inertia of the balls will mostly overcome all the more minor terms to take into account wrt fluid mechanics, but all of that is classical physics already. "Closed systems" might only exist conceptually.
tsimionescu 6y ago
Well, the problem is that the reality we observe daily is not at all like quantum reality. We know exactly where our instruments are, even though we know that they are completely stationary. There is no particle/wave duality to tennis balls. This is the origin of the problem of observation - the predictions of quantum mechanics break down at some point, and we have no idea why. In particular, this happens very clearly when our measurement instruments directly interact with a quantum system, so we call this 'the measurement problem'. Of course, we can postulate that in fact, despite all of our observations, both subjective and objective, the classical world also behaves quantically but we just can't notice it happening (e.g. the Many Worlds interpretation does this). We can also say that the quantum world does NOT in fact behave that way, but that the universe is perfectly deterministic and just set up in such a way that we can never observe events that contradict this vision of the universe (superdeterminism claims this - that for example you will always happen to choose the right dial on a measurement apparatus to observe entanglement, but that there is no fundamental reason why that should happen - it could theoretically happen otherwise, but in this universe, ever since the big bang, it has been decided that at some point you will set that dial in the particular way that will make you observe the entanglement result). There are other theories that postulate that quantum mechanics is in fact deterministic, but very hard to predict, but there are non-local effects (deBroglie-Bohm pilot wave theory is such an example). We can also ignore the whole hope of trying to understand all this, and simply use the math if and when we need it to predict particle phenomena.

tsimionescu 6y ago

You may say that it's not surprising, but in fact all statistical-style reasoning relies on it. If the universe is superdeterministic, than no kind of statistical reasoning makes any sense, since everything is already set in stone, there is no probability to any event, it has either happened already or will never happen. Since there is no freedom or even randomness, there are no statistically independent events or measurements.

elwell 6y ago
> no kind of statistical reasoning makes any sense Probabilities are useful when you don't have perfect knowledge. But yes, they are an illusion. In truth, every event has a 100% chance of happening. And things that didn't happen aren't real events, they just seemed to be possible, but we were wrong.
- tsimionescu 6y ago
  Sure, but please stop requiring clinical trials for new medicine, as they have no more relevance than throwing a coin. Oh, and stop throwing coins, as the result is correlated with the future decision which you will take anyway. In general, all of modern science, starting with quantum mechanics, depends on the idea that statistical independence exists. To truly abandon this idea, we would abandon almost all of the mathematical apparatus that has given us QM and all experimental observations of QM.
  - elwell 6y ago
    No principal investigator of a clinical trial has perfect knowledge of the current state of reality, nor the means to calculate subsequent states. Therefore statistics are very useful.
    - tsimionescu 6y ago
      They may or may not have perfect knowledge, but if they don't have free will or any ability to randomly choose participants, then there is no reason to trust that the patients they choose are not correlated to the medicine they are testing, such that all of the patients they chose will have the maximum response possible to the medicine, with the least amount of side effects.