**Next message:**E. Shaun Russell: "Re: ginagram"**Previous message:**Chen Yixiong, Eric: "Global Mind Link NOT totalitarian collective"**In reply to:**scerir: "HUMOUR: quantum head job"**Next in thread:**David Hodgson: "RE: TECH: Quantum Head Job"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

scerir wrote:

*>
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*> A single particle is prepared in a (weird) superposition.
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*> The superposition consists in being in three boxes.
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*>
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*> The initial state is |psi_1>
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*> |psi_1> = 3 ^ (-1/2) ( |A> + |B> + |C> )
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*>
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*> and the final state is |psi_2>
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*> |psi_2> = 3 ^ (-1/2) ( |A> + |B> - |C> )
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*>
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*> where A, B and C are the three boxes.
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*>
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*> If you search, in the intermediate time, in the box A
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*> you'll find the particle. Otherwise the state would be
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*> |psi_huh> = 2 ^ (-1/2) ( |B> + |C> ) which is forbidden
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*> being orthogonal to the final state.
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*>
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*> If you search, in intermediate time, in the box B
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*> you'll find the particle. Otherwise the state would be
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*> |psi_hoh> = 2 ^ (-1/2) ( |A> + |C> ) which is forbidden
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*> being orthogonal to the final state.
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*>
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*> Then the single particle is in the box A (searching in A)
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*> and in the box B (searching in B).
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*>
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*> What about searching in A *and* B? I don't know.
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*> And it's too late now. And QM is a nasty trick.
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I can't tell whether or not this is a serious description of quantum

physics, but I'm guessing that this is actually one of those transparently

flawed thought experiments - the reason being that if this is true, it's

obviously easy to build a quantum ansible. Send box A to London, send box

B to Boston. London chooses whether or not to perform a measurement at

4:00 and Boston measures at 4:01. If London measures, Boston will never

find the particle; if London does not measure, Boston will always find the

particle.

The flaw, I think, is that any measurement of A collapses the complete

state - if the particle is not found in A, that does not just eliminate

the portion of the particle's position function which was in A; it

collapses the state completely. So if the measurement shows the particle

is not in box A, the resulting quantum state is either 1 * |B> or 1 * |C>

- not 2 ^ (-1/2) ( |B> + |C> ). Thus, the particle is not forced to be in

A.

-- -- -- -- --

Eliezer S. Yudkowsky http://singinst.org/

Research Fellow, Singularity Institute for Artificial Intelligence

**Next message:**E. Shaun Russell: "Re: ginagram"**Previous message:**Chen Yixiong, Eric: "Global Mind Link NOT totalitarian collective"**In reply to:**scerir: "HUMOUR: quantum head job"**Next in thread:**David Hodgson: "RE: TECH: Quantum Head Job"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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