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> that makes a strong implication towards a many world interpretation You say that like it's a shortcoming. :) There are many who take the (very reasonable) p

by tbabb 5y ago

> that makes a strong implication towards a many world interpretation You say that like it's a shortcoming. :) There are many who take the (very reasonable) position that the many worlds interpretation is the most epistemologically parsimonious one. Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantum mechanics completely unchanged. The "worlds" arise naturally as more and more particles in the environment become entangled with the measured system, and "wave function collapse" turns out to be the predicted observation of an observer who is themselves made out of quantum states. The only difference between many worlds and the "standard" Copenhagen interpretation is that Copenhagen adds that, at some point, the entanglement process stops, and a bunch of states in the wave function disappear. And it doesn't specify how, or why, or how to calculate when it will happen. Those that advocate for many worlds would point out that this extra epistemological burden is questionable, given that the correct prediction is made without it.

danbruc 5y ago
Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantum mechanics completely unchanged. Yes, it gets rid of the collapse postulate, but no, it actually introduces many worlds. You can wiggle a bit around, claim that prior to the wave function collapse there are also many worlds in Copenhagen or whatnot, but in the end many worlds makes a metaphysical claim that two cats exist, one dead, one alive while Copenhagen claims only one cat exists in the end.
- tbabb 5y ago
  it actually introduces many worlds No, this is the misunderstanding that I'm talking about. The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed. Before the measurement/entanglement, the system and environment are independent, and can be written (|0> + |1>) ⊗ (|0> + |1>). After the entanglement, the wave function of the universe can no longer be factored that way, and the system and environment are in a joint state of |00> + |11>. The |00> and the |11> are the multiple "worlds", they show up— in both interpretations— whether you want them to be there or not. Copenhagen doesn't want them to be there, so it says that one of the |00> or |11> goes away... at some point... because [waves hands and mumbles]. Many worlds merely declines to do this, and that is legitimately the only difference between the two.
  - danbruc 5y ago
    The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed. The many worlds are in the entangled state but then the collapse postulate reduces them to one world. If you remove the collapse postulate you put them back in. And sure, the collapse postulate is an awful solution breaking unitary evolution and you have every right to reject it, but that does not change the fact that many world introduces - or at least not removes - additional worlds that are not there in Copenhagen.
    - tbabb 5y ago
      The distinction between "adding" and "removing" a postulate is an important, non-arbitrary one. The "worlds" are there in both theories; Copenhagen adds a new phenomenon (non-unitary evolution) which makes some of them disappear at unspecified times. The "worlds" are direct consequences of suppositions shared with Copenhagen. Many worlds has N postulates, Copenhagen has no fewer than N+1. One theory is a strict subset of the other's premises. It is not at all accurate to say that many worlds is the one that "introduces" suppositions.
      - danbruc 5y ago
        I think it is not as simple as counting the number of postulates. The ultimate arbiter is physical reality and that decides whether removing or adding postulates is what brings you into agreement. The fact that the quantum state in some equation before wave function collapse looks like many worlds say nothing whether you should take this at face value or whether you are missing an additional postulate that gives you only one world. If you argue that the collapse postulate is stupid because it is non-unitary and therefore in conflict with experimental evidence, then sure, I totally agree with this. But just because it is an additional postulate it does not per se make many worlds the better theory. Relativity without the constant speed of light is also a theory with one fewer postulate but it of course in much worse agreement with reality. The problem with the interpretations is that we are currently unable to distinguish them experimentally which unfortunately adds much more personal preferences to the discussion then there should be.
feoren 5y ago
My understanding is that "Wave function collapse" is an artifact of one of the many possible ways of describing quantum mechanics mathematically. There's really nothing to remove, is there?
- dragonwriter 5y ago
  > My understanding is that "Wave function collapse" is an artifact of one of the many possible ways of describing quantum mechanics mathematically. The contention seems to be that the Copenhagen interpretation elevates wave function collapse from mathematical artifact to real phenomenon.
  - feoren 5y ago
    Sure, but the Copenhagen interpretation is basically rejected as absurdist and is unnecessary for the exact same reason. It's also trying to give a physical explanation for an artifact of one of the many mathematical representations of quantum mechanics. Schrödinger's Cat is a reductio ad-absurditum to disprove the Copenhagen interpretation!
nwallin 5y ago
The problem with interjecting an implication that many worlds is true (regardless of how persuasive the arguments in its favor are) into a layperson's explanation of why quantum entanglement doesn't permit FTL communication are threefold: 1. It doesn't have anything to do with the topic at hand. It is, at best, a distraction. 2. It is impossible to design an experiment which is capable of distinguishing between a universe where many worlds is the correct interpretation of quantum mechanics or a universe where Copenhagen is the correct interpretation. Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. We simply do not have the tools to arrive at the truth of the matter. 3. You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics. I'm not sure if anyone's started talking about De Broglie–Bohm theory yet, but it'll... oops I just did. I say this as someone for whom many worlds feels truthier.
- tbabb 5y ago
  > It doesn't have anything to do with the topic at hand. To the contrary, it provides an intuitive model that produces correct predictions. That is inherently valuable and extremely relevant. > Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. Strongly disagree— See further discussion[1] under my original post for support. > You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics Not wrong >_> [1] https://news.ycombinator.com/item?id=27900738 https://news.ycombinator.com/item?id=27900738
  - nwallin 5y ago
    > it provides an intuitive model Uh. No. It definitely -- definitely -- doesn't do that. Many worlds, for all its many virtues, gives us "There's another dimension where you -- you -- are Batman!" Because that's what the phrase "many worlds" means to most people. > > Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. > Strongly disagree— See further discussion[1] under my original post for support. So in that discussion, you made the argument: > Both models agree with observation— any measurement we make will not contradict either "empty garage" or "undetectable dragon". ...which is literally the argument people make when they're arguing Jesus vs Mohamed. It's just that nobody agrees on which holy being is the empty garage and which one is the undetectable dragon. > Not wrong >_> Woooo! I won an argument on the internet!!

by tbabb 5y ago

danbruc 5y ago

Contrary to some misunderstandings of it, it doesn't "add" extra worlds; it removes the concept of "wave function collapse", and leaves all the other known laws of quantum mechanics completely unchanged. Yes, it gets rid of the collapse postulate, but no, it actually introduces many worlds. You can wiggle a bit around, claim that prior to the wave function collapse there are also many worlds in Copenhagen or whatnot, but in the end many worlds makes a metaphysical claim that two cats exist, one dead, one alive while Copenhagen claims only one cat exists in the end.

tbabb 5y ago
it actually introduces many worlds No, this is the misunderstanding that I'm talking about. The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed. Before the measurement/entanglement, the system and environment are independent, and can be written (|0> + |1>) ⊗ (|0> + |1>). After the entanglement, the wave function of the universe can no longer be factored that way, and the system and environment are in a joint state of |00> + |11>. The |00> and the |11> are the multiple "worlds", they show up— in both interpretations— whether you want them to be there or not. Copenhagen doesn't want them to be there, so it says that one of the |00> or |11> goes away... at some point... because [waves hands and mumbles]. Many worlds merely declines to do this, and that is legitimately the only difference between the two.
- danbruc 5y ago
  The extra "worlds" follow directly and exclusively from the existence of the various basis states in a wave function, and the laws of entanglement. No other postulates are needed. The many worlds are in the entangled state but then the collapse postulate reduces them to one world. If you remove the collapse postulate you put them back in. And sure, the collapse postulate is an awful solution breaking unitary evolution and you have every right to reject it, but that does not change the fact that many world introduces - or at least not removes - additional worlds that are not there in Copenhagen.
  - tbabb 5y ago
    The distinction between "adding" and "removing" a postulate is an important, non-arbitrary one. The "worlds" are there in both theories; Copenhagen adds a new phenomenon (non-unitary evolution) which makes some of them disappear at unspecified times. The "worlds" are direct consequences of suppositions shared with Copenhagen. Many worlds has N postulates, Copenhagen has no fewer than N+1. One theory is a strict subset of the other's premises. It is not at all accurate to say that many worlds is the one that "introduces" suppositions.
    - danbruc 5y ago
      I think it is not as simple as counting the number of postulates. The ultimate arbiter is physical reality and that decides whether removing or adding postulates is what brings you into agreement. The fact that the quantum state in some equation before wave function collapse looks like many worlds say nothing whether you should take this at face value or whether you are missing an additional postulate that gives you only one world. If you argue that the collapse postulate is stupid because it is non-unitary and therefore in conflict with experimental evidence, then sure, I totally agree with this. But just because it is an additional postulate it does not per se make many worlds the better theory. Relativity without the constant speed of light is also a theory with one fewer postulate but it of course in much worse agreement with reality. The problem with the interpretations is that we are currently unable to distinguish them experimentally which unfortunately adds much more personal preferences to the discussion then there should be.

feoren 5y ago

My understanding is that "Wave function collapse" is an artifact of one of the many possible ways of describing quantum mechanics mathematically. There's really nothing to remove, is there?

dragonwriter 5y ago
> My understanding is that "Wave function collapse" is an artifact of one of the many possible ways of describing quantum mechanics mathematically. The contention seems to be that the Copenhagen interpretation elevates wave function collapse from mathematical artifact to real phenomenon.
- feoren 5y ago
  Sure, but the Copenhagen interpretation is basically rejected as absurdist and is unnecessary for the exact same reason. It's also trying to give a physical explanation for an artifact of one of the many mathematical representations of quantum mechanics. Schrödinger's Cat is a reductio ad-absurditum to disprove the Copenhagen interpretation!

nwallin 5y ago

The problem with interjecting an implication that many worlds is true (regardless of how persuasive the arguments in its favor are) into a layperson's explanation of why quantum entanglement doesn't permit FTL communication are threefold: 1. It doesn't have anything to do with the topic at hand. It is, at best, a distraction. 2. It is impossible to design an experiment which is capable of distinguishing between a universe where many worlds is the correct interpretation of quantum mechanics or a universe where Copenhagen is the correct interpretation. Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. We simply do not have the tools to arrive at the truth of the matter. 3. You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics. I'm not sure if anyone's started talking about De Broglie–Bohm theory yet, but it'll... oops I just did. I say this as someone for whom many worlds feels truthier.

tbabb 5y ago
> It doesn't have anything to do with the topic at hand. To the contrary, it provides an intuitive model that produces correct predictions. That is inherently valuable and extremely relevant. > Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. Strongly disagree— See further discussion[1] under my original post for support. > You guarantee that everybody is going to stop discussing entanglement+FTL communication and will start arguing about interpretations of quantum mechanics Not wrong >_> [1] https://news.ycombinator.com/item?id=27900738 https://news.ycombinator.com/item?id=27900738
- nwallin 5y ago
  > it provides an intuitive model Uh. No. It definitely -- definitely -- doesn't do that. Many worlds, for all its many virtues, gives us "There's another dimension where you -- you -- are Batman!" Because that's what the phrase "many worlds" means to most people. > > Arguing about Copenhagen vs many worlds is literally no different than arguing about Jesus vs Mohamed. > Strongly disagree— See further discussion[1] under my original post for support. So in that discussion, you made the argument: > Both models agree with observation— any measurement we make will not contradict either "empty garage" or "undetectable dragon". ...which is literally the argument people make when they're arguing Jesus vs Mohamed. It's just that nobody agrees on which holy being is the empty garage and which one is the undetectable dragon. > Not wrong >_> Woooo! I won an argument on the internet!!