On 9/16/2011 14:11, Warp wrote:
>    Now, how does the football (or atom, or particle) "know" that what those
> emitted particles hit is not "measurement"?

Well, that is indeed the fundamental problem exposed by Schrodinger's cat.

> measurement device that can tell the difference?

It doesn't matter if it hits a measuring device. It only matters if you look 
at the measurement.

>    Or is it the *interaction* between the traveling object and the particles
> that hit it (or which it emits), particles that *could* be used to measure
> which slit the object went through, that makes the difference?

No, because you can take the measurement as to which way it went, *then* 
erase that measurement after the particle has already hit the sensor, and 
you will or won't get interference depending on whether you don't or do 
erase the measurement after the fact.

https://secure.wikimedia.org/wikipedia/en/wiki/Quantum_erasure

https://secure.wikimedia.org/wikipedia/en/wiki/Delayed_choice_quantum_eraser

It's not a question of whether it goes thru one slit or two, or whether you 
interfere with it or not at that time. It's (weirdly enough) a question of 
whether you know what the answer was supposed to be.

Remember, tho, that each particle lands in exactly one place. One particle 
doesn't give an interference pattern like one wave would. Each particle in 
the two-slit experiment is just more or less likely to hit different places 
on the screen, but each hits at only one place.

-- 
Darren New, San Diego CA, USA (PST)
   How come I never get only one kudo?

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