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bunchberry@lemmy.world ⁨8⁩ ⁨hours⁩ ago

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. 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.
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.

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bitcrafter@programming.dev ⁨6⁩ ⁨hours⁩ ago
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”?
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- bunchberry@lemmy.world ⁨5⁩ ⁨hours⁩ ago
  Entanglement is just a mathematical property of the theory. If it is sufficient to explain measurement then there is not anything particularly unique about MWI since you can employ this explanation within anything. You also say I missed your point by repeating exactly what I said.
  
  You’re the one giving this bullet point list as if you are debunking all of my points one-by-one. If you agree there is nothing especially “more local” about MWI than any other interpretation then why not just ignore that point and move on?
  
  A relative state is not an entangled state. Again you need to read the papers I linked. We are talking about observer-dependence in the sense of how the velocity of a train in Galilean relativity can be said to have a different value simultaneously for two different observers. I drew the direct comparison here in order to explain that in my first comment. This isn’t about special relativity or general relativity, but about “relativity” in a more abstract sense of things which are only meaningfully defined as a relational property between systems. The quantum state observer A assigns to a system can be different from the quantum state observer B assigns to the system (see the Wigner’s friend thought experiment). The quantum state in quantum mechanics is clearly relative in this sense, and to claim there is a universal quantum state requires an additional leap which is never mathematically justified.
  
  Please for the love of god just scroll up and read what I actually wrote in that first post and respond to it. Or don’t. You clearly seem to be entirely uninterested in a serious conversation. I assume you have an emotional attachment to MWI without even having read Everett’s papers and getting too defensive that you refuse to engage seriously in anything I say, so I am ending this conversation here.
  
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  - bitcrafter@programming.dev ⁨4⁩ ⁨hours⁩ ago
    
    I assume you have an emotional attachment to MWI without even having read Everett’s papers and getting too defensive that you refuse to engage seriously in anything I say, so I am ending this conversation here.
    
    Uhh, okay. Like, you were the one who felt the need to go on the attack here, but if you need to stop for your mental health than so be it. 🙂
    
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