> On 28 Jan 2021, at 2:49 pm, 'Brent Meeker' via Everything List
> <[email protected]> wrote:
>
>
>
> On 1/27/2021 5:11 PM, Pierz Newton-John wrote:
>> I’m not saying decoherence is reversible. I’ve corrected myself (or accepted
>> your correction) on that point. But my understanding of proposals for
>> disconfirming MWI involve extending quantum coherence to larger and larger
>> scales. Deutsch has argued that if we can get enough qubits into a quantum
>> computation, we’ve effectively “proved” MWI since “where did all that
>> information come from?".
>
> And Scott Aaronson has pointed out it all had to be in this world in order
> for interference to produce an answer.
>
That argument rests on the definition of world as a decohered branch, and
Deutsch would not accept that definition. I’m not sure if I agree with his
argument, but I’m also not necessarily convinced by that definition of “world”.
I mean, it’s perfectly good as far as it goes, but I’m not sure I’m happy with
it being marshalled as an argument in this way. If there is a world W which
contains an electron in an up/down superposition, then in the Deutsch picture,
and I would say the Everett picture in general, that means some observer in W
is unaware of which world he/she is in: the one where the electron is up or the
one where it is down. Or rather (and this is Deutsch not Everett), the stack of
worlds where it is up or the stack where it is down.The measurement leaks that
information via decoherence, and the worlds diverge irretrievably at that point.
> Brent
>
>> Other proposals similarly involve reversibility at large scales. If QM is
>> not universal, then at some scale that will prove impossible not merely due
>> to technological limits, but limits of the laws of physics. If such a limit
>> were found, that would certainly disconfirm MWI.
>
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