On 10/8/2019 5:47 PM, Bruce Kellett wrote:
On Wed, Oct 9, 2019 at 11:42 AM 'Brent Meeker' via Everything List <everything-list@googlegroups.com <mailto:everything-list@googlegroups.com>> wrote:On 10/8/2019 5:07 PM, Bruce Kellett wrote:On Wed, Oct 9, 2019 at 10:24 AM 'Brent Meeker' via Everything List <everything-list@googlegroups.com <mailto:everything-list@googlegroups.com>> wrote: On 10/8/2019 2:59 PM, Philip Thrift wrote:That sounds reasonable. Indeed, it is reasonable. It is just as reasonable as the measurement postulate. In fact, it is logically entirely equivalent to the measurement postulate.It's not clear here what "logically" equivalent means. It is instrumentally equivalent...which is why it's an interpretation and not a different theory (as GRW is). It's different from the measurement postulate in that the measurement postulate says the wave function instantaneously changes to match the observed measured value. MWI says those other measured values obtain in other orthogonal subspaces of the Hilbert space and you are only observing one. Those are not "logically" the same. What do you mean by "logically equivalent"? It seems to me that if two assumptions fulfil the same explanatory role -- they are functionally equivalent -- then it is sensible to call them "logically equivalent". They fulfil the same logical role in the argument.I mean X=>Y and Y=>X. But MWI entails some things that CI doesn't and vice versa. In the C60 buckyball experiment CI doesn't give a very satisfactory account, because it doesn't have a good definition of "measure". MWI introduced the idea of decoherence to fulfill that role without actually requiring a human observer.That explanation of "measurement" is every bit as available to the CI theorist as to the Everettian theorist. As Peter Woit pointed out a while back, there is not much different between Everett and Copenhagen. Both can work with "its quantum all the way down", and develop the same understanding of "measurement". There is nothing particularly "many worlds" in the notion of decoherence.
But at some point where MWI says we can ignore the other "worlds", CI says the wf collapses...implying collapse is a physical process. I actually like the QBist idea that collapse is just something we do to our world description.
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