[extropy-chat] Is Many Worlds testable?

scerir scerir at libero.it
Fri Dec 29 00:36:27 UTC 2006

>>I've got the impression that Deutsch thinks
>>that the knowledge of the 'which way', or the consciousness
>>of the knowledge of the 'which way', or the possibility
>>of knowledge of the 'which way' the particle took,
>>erases the interference pattern. Well, this is not
>>true. It is not 100% true. It is only partially true.

> My lay understanding is the third option above. The very 
> *possibility* of decohering the superposed states causes the 
> splitting.

Yes, what is relevant is the mere possibility (of knowledge).
Vaguely reminiscent of the Aristotle-Heisenberg 'potentia'.

"In an experiment the state reflects not what is actually
known about the system, but rather what is knowable,
in principle, with the help of auxiliary measurements
that do not disturb the original experiment. By focusing
on what is knowable in principle, and treating what is known
as largely irrelevant, one completely avoids the
anthropomorphism and any reference to consciousness that
some physicists have tried to inject into quantum mechanics."
- Leonard Mandel (Rev.Mod.Phys.,1999,p.S-274)

Note also that QM isn't just nonlocal but also 'contextual'.
John Bell, i.e., writes in 1966 that "It was tacitly
assumed that measurement of an observable must yield
the same value independently of what other [compatible]
measurements may be made simultaneously [....] There
is no apriori reason to believe that the results
should be the same. The result of an observation
may reasonably depend not only on the state of the 
system (including hidden variables) but also on
the complete disposition of the apparatus [...]".

> This is very strange, especially when it can be 
> subsequently erased. (I think Cramer's story helps 
> deal with this.) 

Nice put (maybe).

> But what do you mean by "partially true"? 
> Thin and unconvincing fringes? :)

Exactly. There is a smooth transition between
the particlelike and the wavelike behaviour
of a photon. The smooth transition depends
on the specific setup you use, its symmetry, etc.
The common saying that we can have a blob pattern *or* 
the interference pattern, depending on the knowledge
or unknowledge of the 'welcher weg', is completely
wrong. There is a smooth transition in the pattern
and in the knowledge. It is called Greenberger-Ya'sin-
Englert relation.

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