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The main problem of quantum interpretation is the supposed, artificial, distinction between observer and observed system. In a quantum world this distinction is

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.

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.