On Tuesday, December 4, 2012 1:51:55 PM UTC-5, Brent wrote:
>
>  On 12/4/2012 8:29 AM, John Clark wrote: 
>
> On Mon, Dec 3, 2012 at 3:26 PM, meekerdb <meek...@verizon.net<javascript:>
> > wrote:
>  
>>
>> > That's where you're wrong; read the paper more carefully.  If you 
>> record the which-way the interference is lost. [...] The interference 
>> pattern occurs *only* if the which way information is *erased*
>>
>
> Nope, you've got it exactly precisely backwards yet again. I quote from
>
>   
> http://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment:<http://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment>
>  
>  
> " If the experimenters know which slit it goes through, the photon will 
> behave as a particle. If they do not know which slit it goes through, the 
> photon will behave as if it were a wave when it is given an opportunity to 
> interfere with itself. "
>  
>
> That's why you need to read the technical papers instead of Wikipedia.  
> The above is correct when there are just photons going through one pair of 
> slits.  But in the Delayed Quantum Eraser experiment there are *two* 
> entangled photons one of which goes through slits and one of which *could 
> be detected and give which-way information*.  The point is that if it is 
> not detected (flys off to infinity, absorbed in the wall,...) the 
> interference pattern is still destroyed.  To maintain the pattern the 
> information in the entangled photon has to be *erased* - that's the 
> function of the lens.  
>
> Loss of the interference isn't because "they do not know"; it's a 
> consequence of the information being "out there" - and being absorbed in a 
> wall still leaves it "out there".  This is even clearer in the buckyball 
> Young's slits experiment, quant-ph/0402146v1.  The interference pattern is 
> lost when the buckyballs are hot enough that their IR radiation is 
> sufficient to localize them to the slit spacing - even though nobody ever 
> observes or detects the IR photons.
>
> All those below fail to consider the relevant case too; they assume all 
> cases in which no experimenter measures which-way are equivalent.  They 
> ignore the possibility that "the environment" may measure which-way but no 
> person does.
>
> Brent
>

It's confusing. Can you simplify it?

One photon heads toward the slits.
One entangled photon heads toward the detector. (They are both entangled 
with each other, but I assume you mean one pair of entangled photons, not 
two pairs.)

Is there a detector on the slits too?

It seems like the point of the experiment is that the interference pattern 
only shows up when the ability to discern which-way is not available - 
which seems to me to support observer-principle type interpretations.

Certainly I don't see any suggestion that there is a such thing as 
'information' which is independent of some kind of sense receptivity. To 
the contrary:

Time 6. Upon accessing the information gathered by the Coincidence Circuit, 
> we the observer are shocked to learn that the pattern shown by the 
> positions registered at D0 at Time 2 *depends entirely* on the 
> information *gathered* later at Time 4 and available to us at the 
> conclusion of the experiment. 
> The position of a photon at detector D0 has been registered and scanned. 
> Yet the actual position of the photon arriving at D0 *will be at one 
> place if we later learn* more information; and the actual position will 
> be at another place if we do 
> not.-http://www.bottomlayer.com/bottom/kim-scully/kim-scully-web.htm
>

I intentionally bolded the terms where the true nature of quantum is 
revealed - with the capacity to detect, 'learn', 'gather', i.e. to become 
informed through a sensory-motor event within the matter which makes up a 
physical instrument (including, but not limited to, human eyes, brains, 
etc).

Physics is sensory-motor participation. Nothing more and nothing less. 
There is no such thing as 'information'.

Craig

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