3 ms·

I'm becoming more of a fan of Everett. Wave collapse feels like nonsense, and requires arbitrary notions of "observers". I don't fully grasp the ramifications o

I'm becoming more of a fan of Everett. Wave collapse feels like nonsense, and requires arbitrary notions of "observers". I don't fully grasp the ramifications of the Many Worlds interpretation, but if it means reality is deterministic, I'll take it.

FakeComments 7y ago
I personally vote for seeing if you can patch TQFTs to be more Bohmian, and thus introduce non-local variables. We know non-locality happens: Copenhagen’s non-determinism is an extraneous assumption.
TheOtherHobbes 7y ago
MWI feels like nonsense to me. The problem is that it's unbounded. It's not just about specific measured quantum events, because that begs the question about how and where and why universes branch off. Without that foundation, it becomes about all possible quantum events. Literally. Any moving particle that has a chance to decay may decay at any time, spawning a universe. And some of those spawned interactions will lead to other spawned interactions... Somehow you have to get the Born Rule from a number of possible interactions that is so big it reduces the number of particles in the universe to an insignificant rounding error. Assuming this number is even countable (up for debate) there must be universes in which quantum physics doesn't appear to work as it does here. You can't just assume that somehow you get the right answer with a nice converging integral. Because the complete list of possible MWI universes includes a very small - but not zero - number where consistently unlikely interactions are the norm, so they operate with the "wrong" laws - for example neutrons that refuse to decay, or gluons that stay permanently glued. Which being the case, we don't know whether this universe is a probabilistic freak and the "real" laws are different to the ones we see here. Maybe our Born Rule is the freak, and most universes operate differently. With MWI, there's no way to tell. And so on for other issues. MWI is best left to science fiction plot lines. I really can't see it making sense as either falsifiable science or consistent philosophy.
- eigenspace 7y ago
  This is a very common misunderstanding based on the sloppy way people tend to explain Many Worlds. In the Many Worlds picture, branching of wave functions isn’t built into the basic postulates of QM. Not every quantum event results in branching. Branching an emergent property of large systems. Consider the following: * I have a qbit in a superposition for 0 and 1 * I as a large, hot, wet macroscopic system interact with that qbit in such a way that my future behaviour depends on the state of that qbit (say if I measure it to be 1 I shoot myself and if I get 0 I go for a walk) If I try to measure the qbit, I become entangled with it. According to unitary evolution, my wave function would be an entangled superposition of the two events. However, for macroscopic systems entanglement and superpositions are basically meaningless. I couldn’t do an interferometry experiment on my body that would determine if I’m in a entangled state so a many worlds person would say that the wave function of be unvierse has effectively branched into two parts that never very little overlap or influence on each other. —————————————————— Maybe this analogy will help: If I have a cup of water and we look at it on a macroscopic scale, there’s a very clear difference between the liquid and the air above it. There’s a division. However, if you zoom in, that division becomes very fuzzy. There’s a region near the waters surface where air molecules and water molecules freely mix and interact and there’s actually a somewhat smooth crossover between the air and water. So the phase separation between a cup of water and the air above it isn’t a fundamental part of the rules of physics. It’s just an emergent behaviour like the branching of the wave function.
  - millstone 7y ago
    Right. The problem of interpretation arises when the qbit has value 0 with probability 75%, and value 1 with probability 25%. In what sense can the universe be said to have branched into two, yet the probabilities are not evenly divided? What can probability even mean if both branches are in some sense realized - is one branch 3x as "real" as the other?
    - eigenspace 7y ago
      Again, I’d say you’re misunderstanding the point. The branches aren’t a real thing in quantum mechanics. They’re just a particular way of looking at the wave function of the universe. In the evolution of the wave function, it sometimes will ‘split’ into two parts that are essentially independent of each other and may have different amplitudes associated with them. These amplitudes may be shown to correspond to the (square root of the) probability of finding yourself in one branch or another. However, if you knew about the entire wavefunction as an outside godly observer to the universe might, then there’d be no point in speaking of ‘branches’.
magicalhippo 7y ago
> Wave collapse feels like nonsense, requires arbitrary notions of "observers". There's recently been a long thread over on PhysicsForums[1] about the Wiegner's friend experiment[2]. The thread was kicked off by this[3] paper detailing a realization of the experiment, in which the authors conclude "this result lends considerable strength to interpretations of quantum theory already set in an observer-dependent framework and demands for revision of those which are not." Then again as far as I can see MWI doesn't come out victorious, "one way to accommodate our result is by proclaiming that “facts of the world” can only be established by a privileged observer—e.g., one that would have access to the “global wavefunction” in the many worlds interpretation". Then again I haven't studied QM so what do I know. Fun to think about while on the bus tho! [1]: https://www.physicsforums.com/threads/a-realization-of-a-basic-wigners-friend-type-experiment.968181/ https://www.physicsforums.com/threads/a-realization-of-a-bas... [2]: https://en.wikipedia.org/wiki/Wigner%27s_friend https://en.wikipedia.org/wiki/Wigner%27s_friend [3]: https://arxiv.org/abs/1902.05080 https://arxiv.org/abs/1902.05080

FakeComments 7y ago

I personally vote for seeing if you can patch TQFTs to be more Bohmian, and thus introduce non-local variables. We know non-locality happens: Copenhagen’s non-determinism is an extraneous assumption.

TheOtherHobbes 7y ago

MWI feels like nonsense to me. The problem is that it's unbounded. It's not just about specific measured quantum events, because that begs the question about how and where and why universes branch off. Without that foundation, it becomes about all possible quantum events. Literally. Any moving particle that has a chance to decay may decay at any time, spawning a universe. And some of those spawned interactions will lead to other spawned interactions... Somehow you have to get the Born Rule from a number of possible interactions that is so big it reduces the number of particles in the universe to an insignificant rounding error. Assuming this number is even countable (up for debate) there must be universes in which quantum physics doesn't appear to work as it does here. You can't just assume that somehow you get the right answer with a nice converging integral. Because the complete list of possible MWI universes includes a very small - but not zero - number where consistently unlikely interactions are the norm, so they operate with the "wrong" laws - for example neutrons that refuse to decay, or gluons that stay permanently glued. Which being the case, we don't know whether this universe is a probabilistic freak and the "real" laws are different to the ones we see here. Maybe our Born Rule is the freak, and most universes operate differently. With MWI, there's no way to tell. And so on for other issues. MWI is best left to science fiction plot lines. I really can't see it making sense as either falsifiable science or consistent philosophy.

eigenspace 7y ago
This is a very common misunderstanding based on the sloppy way people tend to explain Many Worlds. In the Many Worlds picture, branching of wave functions isn’t built into the basic postulates of QM. Not every quantum event results in branching. Branching an emergent property of large systems. Consider the following: * I have a qbit in a superposition for 0 and 1 * I as a large, hot, wet macroscopic system interact with that qbit in such a way that my future behaviour depends on the state of that qbit (say if I measure it to be 1 I shoot myself and if I get 0 I go for a walk) If I try to measure the qbit, I become entangled with it. According to unitary evolution, my wave function would be an entangled superposition of the two events. However, for macroscopic systems entanglement and superpositions are basically meaningless. I couldn’t do an interferometry experiment on my body that would determine if I’m in a entangled state so a many worlds person would say that the wave function of be unvierse has effectively branched into two parts that never very little overlap or influence on each other. —————————————————— Maybe this analogy will help: If I have a cup of water and we look at it on a macroscopic scale, there’s a very clear difference between the liquid and the air above it. There’s a division. However, if you zoom in, that division becomes very fuzzy. There’s a region near the waters surface where air molecules and water molecules freely mix and interact and there’s actually a somewhat smooth crossover between the air and water. So the phase separation between a cup of water and the air above it isn’t a fundamental part of the rules of physics. It’s just an emergent behaviour like the branching of the wave function.
- millstone 7y ago
  Right. The problem of interpretation arises when the qbit has value 0 with probability 75%, and value 1 with probability 25%. In what sense can the universe be said to have branched into two, yet the probabilities are not evenly divided? What can probability even mean if both branches are in some sense realized - is one branch 3x as "real" as the other?
  - eigenspace 7y ago
    Again, I’d say you’re misunderstanding the point. The branches aren’t a real thing in quantum mechanics. They’re just a particular way of looking at the wave function of the universe. In the evolution of the wave function, it sometimes will ‘split’ into two parts that are essentially independent of each other and may have different amplitudes associated with them. These amplitudes may be shown to correspond to the (square root of the) probability of finding yourself in one branch or another. However, if you knew about the entire wavefunction as an outside godly observer to the universe might, then there’d be no point in speaking of ‘branches’.

magicalhippo 7y ago

> Wave collapse feels like nonsense, requires arbitrary notions of "observers". There's recently been a long thread over on PhysicsForums[1] about the Wiegner's friend experiment[2]. The thread was kicked off by this[3] paper detailing a realization of the experiment, in which the authors conclude "this result lends considerable strength to interpretations of quantum theory already set in an observer-dependent framework and demands for revision of those which are not." Then again as far as I can see MWI doesn't come out victorious, "one way to accommodate our result is by proclaiming that “facts of the world” can only be established by a privileged observer—e.g., one that would have access to the “global wavefunction” in the many worlds interpretation". Then again I haven't studied QM so what do I know. Fun to think about while on the bus tho! [1]: https://www.physicsforums.com/threads/a-realization-of-a-basic-wigners-friend-type-experiment.968181/ https://www.physicsforums.com/threads/a-realization-of-a-bas... [2]: https://en.wikipedia.org/wiki/Wigner%27s_friend https://en.wikipedia.org/wiki/Wigner%27s_friend [3]: https://arxiv.org/abs/1902.05080 https://arxiv.org/abs/1902.05080