First, working in terms of decoherence is significantly simpler than worrying about whether something has been measured or not at every single step of the evolution of a system, because I have observed that when people do the latter they tend to get headaches contemplating the meaning of the “quantum eraser” when there is no need to. Second, you actually can observe Born’s rule in action by modeling the evolution of a system with an experimenter performing measurements and watching it emerge from the calculation.
The only way that the two sides of the EPR pair know that they agree or disagree is by communicating with each other and comparing results, which can only happen through local interactions.
I have no idea what you even mean by this. What makes the (terribly named) Many Worlds Interpretation nice is precisely that you can just treat everything as a wave function, with parts that might be entangled in ways you don’t know about (i.e., decoherence, modeled via density matrices).
The fact that you are even making this claim is why I have trouble taking the rest of your comment seriously at all, because I specifically said, “However, it is important to understand that the concept of branches is just a visualization; it is nothing inherent to the theory, and when things get even slightly more complicated than the situation I have described, they do not meaningfully exist at all.”
Not sure what this first point means. To describe decoherence you need something like density matrix notation or Liouville notation which is mathematically much more complicated. For example, a qubit’s state vector grows by 2^N, but if you represent it in Liouville notation then the vector grows by 4^N. It is far more mathematically complicated as a description, but I don’t really see why that matters anyways as it’s not like I reject such notation. Your second point also agrees with me. We know the Born rule is real because we can observe real outcomes on measurement devices, something which MWI denies exists and something you will go on to deny in your point #4
This is also true in Copenhagen. Again, if that’s your criterion for locality then Copenhagen is also local.
I think you should read Everett’s papers “‘Relative State’ Formulation of Quantum Mechanics” and “The Theory of the Universal Wave Function” to see the difference between wavefunctions defined in a relative sense vs a universal sense. You will encounter this with any paper on the topic. I’m a bit surprised you genuinely have never heard of the concept of the universal wavefunction yet are defending MWI?
That quotation does not come one iota close to even having the air of giving the impression of loosely responding to what I wrote. You are not seriously engaging with what I wrote at all. You denying the physical existence of real-world discrete outcomes is exactly what I am criticizing, so just quoting yourself denying it is only confirming my point.
A simpler way of stating my point is that entanglement is sufficient to understand measurement, and more importantly, what phenomena are “measurement-like” and which aren’t. Also, you missed my point regarding the Born rule. You can write down a mathematical model of an experimenter repeating an experiment and recording their measurements, turn the crank, and see the probabilities predicted by the Born rule fall out, without any experiment ever having taken place.
I am confused, then, about what we are supposedly even arguing about here. (Are you sure you are even arguing with me, rather than someone else?)
I did some searching and I think that what you are calling “relative states” is an older term for what we now call “entangled states”. Being entangled with another system implies (by definition) that there is a greater system containing you and the other system, and so on, which is how you end up with a universal system that contains everything. However, we do not actually believe that reality is dictated by quantum mechanics but by quantum field theory, which is manifestly built on top of special relativity and posits a single field for each kind of particle for the entire Universe, and describes the microscopic behavior so well that it is absurd. Of course, the next step is figuring out how to reconcile this with general relativity, but that isn’t something Copenhagen helps you out with either.
First you criticize the way that I talked about branches, which I only mentioned briefly as a sort of crude visualization and explicitly called out as being such. Now you are claiming that I am “denying the physical existence of real-world discrete outcomes”?
First, working in terms of decoherence is significantly simpler than worrying about whether something has been measured or not at every single step of the evolution of a system, because I have observed that when people do the latter they tend to get headaches contemplating the meaning of the “quantum eraser” when there is no need to. Second, you actually can observe Born’s rule in action by modeling the evolution of a system with an experimenter performing measurements and watching it emerge from the calculation.
The only way that the two sides of the EPR pair know that they agree or disagree is by communicating with each other and comparing results, which can only happen through local interactions.
I have no idea what you even mean by this. What makes the (terribly named) Many Worlds Interpretation nice is precisely that you can just treat everything as a wave function, with parts that might be entangled in ways you don’t know about (i.e., decoherence, modeled via density matrices).
The fact that you are even making this claim is why I have trouble taking the rest of your comment seriously at all, because I specifically said, “However, it is important to understand that the concept of branches is just a visualization; it is nothing inherent to the theory, and when things get even slightly more complicated than the situation I have described, they do not meaningfully exist at all.”
A simpler way of stating my point is that entanglement is sufficient to understand measurement, and more importantly, what phenomena are “measurement-like” and which aren’t. Also, you missed my point regarding the Born rule. You can write down a mathematical model of an experimenter repeating an experiment and recording their measurements, turn the crank, and see the probabilities predicted by the Born rule fall out, without any experiment ever having taken place.
I am confused, then, about what we are supposedly even arguing about here. (Are you sure you are even arguing with me, rather than someone else?)
I did some searching and I think that what you are calling “relative states” is an older term for what we now call “entangled states”. Being entangled with another system implies (by definition) that there is a greater system containing you and the other system, and so on, which is how you end up with a universal system that contains everything. However, we do not actually believe that reality is dictated by quantum mechanics but by quantum field theory, which is manifestly built on top of special relativity and posits a single field for each kind of particle for the entire Universe, and describes the microscopic behavior so well that it is absurd. Of course, the next step is figuring out how to reconcile this with general relativity, but that isn’t something Copenhagen helps you out with either.
First you criticize the way that I talked about branches, which I only mentioned briefly as a sort of crude visualization and explicitly called out as being such. Now you are claiming that I am “denying the physical existence of real-world discrete outcomes”?