On 9/18/2011 4:32 PM, Darren New wrote:
> On 9/18/2011 15:31, Patrick Elliott wrote:
>> Well.. Yes and no. The quantum eraser "changes the conditions" withing
>> that
>> D time frame, such that the transition to a state is interrupted, by
>> inserting a new set of conditions that allow for the prior quantum state.
>
> Right.
>
>> Since the transition never took place, no state change happened.
>
> Right. Indeed, that's the point of the experiment. That it is *not* the
> case that the particle went through one slit or the other or both.
>
> You said
>  > A real cat would already invalidate the experiment, as would anything
> else you might use, like a sheet of radiation sensitive material
>
> But that's clearly not the case, if what you're measuring is whether the
> particle went through one slit or the other or both or neither.
>
> Other than that, you're pushing the analogy too far for me to track what
> you're talking about.
>
What I am saying is that, in the case of the quantum eraser, you are 
rigging things so that the event doesn't happen, or a different one 
does. I think the confusion here is where the "observation" takes place, 
and where the measurement does. In this case you have sort of decoupled 
them. You are creating an "observer", which is affected by the particle, 
and in turn begins collapsing its state, then you introduce a new 
"observer", which either erases the result, or changes it to something 
else, then you "measure" what happened as a result. The term "observer" 
becomes more ambiguous in this case. A proper term would have been 
"interactor", i.e., the thing that alters the state. The confusion 
arises in that a) that isn't really a word, and b) they opted for the 
misleading term "observer", when talking about how the state collapses. 
In reality, the measurement doesn't have to happen when the first 
observation takes place. It may not even be possible to measure that 
interaction at all, save as a consequence of it having happened. Q.E.D. 
Whether you measure the system or not, doesn't effect if something 
happened, since measurement and interaction/observation are rarely 
simultaneous, in *any* experiment, nor is the act of measuring critical 
to the result.

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