Saibal wrote
> [...] it's not appropriate to fix up the theory by introducing notions 
from the macroscopic domain that should in principle follow from the 
fundamental dynamics at the micro-level. [...]

Brent wrote
> The notion of "result" and "measurement" are not introduced, they are 
fundamental to knowledge.  They are exactly where MWI gets into trouble. 

If there is a disagreement, we should take care to clarify what is it 
about. A putative reductionist view accepts a theory as fundamental, 
perhaps along with some constraints on initial conditions, and claims that 
"observer", "result", and "measurement" will emerge. Right?

I think that this cannot work, because there is some unavoidable 
approximation in the translation from "a quantum state of a part of the 
world" to "this quasi-solid apparatus, observer, and environment (which may 
be part of the observer)". With conventional QM, we express this 
approximation as the very-very small probability of the apparatus 
quantum-tunneling through the floor, and so on. With a MWI, I do not see 
how we can formulate this approximation from the reductionist point of view.

So there is a dualism: The supposedly fundamental theory applies to an 
imagined, objective world, and it also applies to the world of our 
experience. There is a connection of course, because if the latter were 
untrue then we could have no clue about the validity of the theory in the 
objective world. A key notion here is workability of the theory: that it 
tolerates the impossibility of infinite precision, so it works in both 

Brent continued
> [...] By saying there is no result of an experiment it muddles the 
concept of probability.

Although I have seen proposals for introducing probability in a MWI (Zurek, 
Vaidman, John K. Clark), they cannot refer to the notion of aleatory 
probability, involving randomisation, as when one shuffles a deck of cards 
or shakes and rolls dice. On the other hand, conventional QM does assume 
that dice are rolled, and so the requisite randomisation is supposedly 
introduced, and we can speak of probability proper. Where is the 
randomisation in a MWI? (A rhetorical question.) So, there is no 
probability (strictly speaking) in a MWI. We can only identify 
something-like-probability; I have posted about this subject in a recent 

George K.

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