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>Except to explain our everyday experience of a single classical world. Which the parent says is explained via decoherence. Why do you feel that decoherence do

>Except to explain our everyday experience of a single classical world. Which the parent says is explained via decoherence. Why do you feel that decoherence does not account for the observed phenomenon?

pdonis 6y ago
> Which the parent says is explained via decoherence. It isn't. To take a simple example, suppose we measure the spin of a single spin-1/2 particle that is in a state such that there is a 50-50 chance of either possible result. Decoherence can explain why the total system--particle plus measuring device plus observer plus environment--ends up in a superposition of "particle with spin up, measuring device measures spin up, observer observes spin up" and "particle with spin down, measuring device measures spin down, observer observes spin down"--in other words, why the interference terms between those two alternatives go away. But decoherence cannot explain why only one of those two results actually occurs.
- wnoise 6y ago
  Who says that only one of those two results actually occurs? Only one is observed, which is a rather different thing.
  - pdonis 6y ago
    If you subscribe to an interpretation like the MWI, then yes, you would say both results occur, not just one. But you aren't basing that on decoherence; you're basing that on your chosen interpretation. Decoherence, by itself, is equally consistent with a collapse interpretation that says only one result actually occurs.
    - rcxdude 6y ago
      It is based on decoherence: no extra assumptions are required to derive the MWI, and you need arbitrary assumptions to get any other interpretation.
      - pdonis 6y ago
        > It is based on decoherence MWI is consistent with decoherence, but the choice of MWI vs. other interpretations is not based on decoherence; it can't be, because decoherence is consistent with all QM interpretations, not just the MWI, so decoherence can't possibly be the basis for choosing any one QM interpretation. > no extra assumptions are required to derive the MWI Yes, there are; you have to assume the Born rule. Various attempts have been made to derive the Born rule in the context of the MWI, but none of them have gained general acceptance as having been successful.
lisper 6y ago
> Which the parent says is explained via decoherence No, that's not what the parent says. The parent says: "The idea that quantum mechanics stops working at macroscopic scales is totally unnecessary..." which is true, with the one exception that I noted: > Except to explain our everyday experience of a SINGLE classical world [emphasis added] You can get from QM to multiple worlds without any ad hoc assumptions, but you cannot get to a SINGLE classical world that way. You have to give up either linearity or superposition.
- sideshowb 6y ago
  The necessary emphasis in the above sentence is OUR EXPERIENCE. If you can accept multiple worlds then you can accept the other ones are populated by different yous each of whom experiences a single world, namely the one they are in
  - lisper 6y ago
    It is actually much more complicated than that. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...

pdonis 6y ago

> Which the parent says is explained via decoherence. It isn't. To take a simple example, suppose we measure the spin of a single spin-1/2 particle that is in a state such that there is a 50-50 chance of either possible result. Decoherence can explain why the total system--particle plus measuring device plus observer plus environment--ends up in a superposition of "particle with spin up, measuring device measures spin up, observer observes spin up" and "particle with spin down, measuring device measures spin down, observer observes spin down"--in other words, why the interference terms between those two alternatives go away. But decoherence cannot explain why only one of those two results actually occurs.

wnoise 6y ago
Who says that only one of those two results actually occurs? Only one is observed, which is a rather different thing.
- pdonis 6y ago
  If you subscribe to an interpretation like the MWI, then yes, you would say both results occur, not just one. But you aren't basing that on decoherence; you're basing that on your chosen interpretation. Decoherence, by itself, is equally consistent with a collapse interpretation that says only one result actually occurs.
  - rcxdude 6y ago
    It is based on decoherence: no extra assumptions are required to derive the MWI, and you need arbitrary assumptions to get any other interpretation.
    - pdonis 6y ago
      > It is based on decoherence MWI is consistent with decoherence, but the choice of MWI vs. other interpretations is not based on decoherence; it can't be, because decoherence is consistent with all QM interpretations, not just the MWI, so decoherence can't possibly be the basis for choosing any one QM interpretation. > no extra assumptions are required to derive the MWI Yes, there are; you have to assume the Born rule. Various attempts have been made to derive the Born rule in the context of the MWI, but none of them have gained general acceptance as having been successful.

lisper 6y ago

> Which the parent says is explained via decoherence No, that's not what the parent says. The parent says: "The idea that quantum mechanics stops working at macroscopic scales is totally unnecessary..." which is true, with the one exception that I noted: > Except to explain our everyday experience of a SINGLE classical world [emphasis added] You can get from QM to multiple worlds without any ad hoc assumptions, but you cannot get to a SINGLE classical world that way. You have to give up either linearity or superposition.

sideshowb 6y ago
The necessary emphasis in the above sentence is OUR EXPERIENCE. If you can accept multiple worlds then you can accept the other ones are populated by different yous each of whom experiences a single world, namely the one they are in
- lisper 6y ago
  It is actually much more complicated than that. http://blog.rongarret.info/2019/07/the-trouble-with-many-worlds.html http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...