> The idea that quantum mechanics stops working at macroscopic scales is totally unnecessary
Except to explain our everyday experience of a single classical world. Then something in QM has to give.
Except to explain our everyday experience of a single classical world. Then something in QM has to give.
Which the parent says is explained via decoherence. Why do you feel that decoherence does not account for the observed phenomenon?
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.
http://blog.rongarret.info/2019/07/the-trouble-with-many-wor...
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.
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.
Epicycles did work for the solar system. But the modern solution was much simpler.