On Tuesday, December 4, 2012 6:27:42 PM UTC-5, Brent wrote:
>  On 12/4/2012 12:32 PM, Craig Weinberg wrote: 
> On Tuesday, December 4, 2012 2:52:25 PM UTC-5, Brent wrote: 
>> Kinda depends on what you mean by 'available'.  If the entangled photon 
>> is allowed to hit a wall and be absorbed, it is only 'available' to a kind 
>> of Maxwellian demon who can discern the thermal atomic motions and trace 
>> them back to get which-way infomation - but the interference pattern is 
>> destroyed anyway.  If the entangled photon is simply allowed to fly out the 
>> window and off to infinity it is 'available' many years later to an 
>> inhabitant of some extra-solar planet - and the interference pattern is 
>> destroyed in our present.  
> What if the inhabitant of the extra-solar planet catches the photon in a 
> lens just like the quantum eraser?
> The interference would be destroyed.  Note that the way the experiment 
> works (and necessarily so) is that the photons detected at the interference 
> plane have to be post-selected to pair up with those either erased or not 
> on the other leg.  So since an extra-solar observer could only catch a 
> small fraction of the photons, the interference would erased in the 
> corresponding small fraction of those hitting the interference plane.

You could look for a temporal rather than spatial interference pattern. 
That way there would be a chance that if any photons were received they 
might continue to stream for long enough:

"The latest experiment is radically different because the slits exist in 
time not space, and because the interference pattern appears when the 
number of electrons at the detector is plotted as a function of their 
energy rather than their position on a screen. The work was performed at 
the Technical University of Vienna in collaboration with physicists from 
the Max Born Institute in Berlin, the Max Planck Institute for Quantum 
Optics in Munich and the University of Sarajevo. 

Paulus and co-workers focused a train of pulses from a Ti:sapphire laser 
into a chamber containing a gas of argon atoms. The pulses were so short – 
just 5 femtoseconds – that each one contained just a few cycles of the 
electric field. 

The team was able to control the output of the laser so that all the pulses 
were identical. The researchers could, for example, ensure that each pulse 
contained two maxima of the electric field (thatis, two peaks with large 
positive values) and one minimum (a peak with a large negative value). 
There was a small probability that an atom would be ionized by one or other 
of the maxima, which therefore played the role of the slits, with the 
resulting electron being accelerated towards a detector. If the atom was 
ionized by the minimum, the electron travelled in the opposite direction 
towards a second detector. 

The team registered the arrival times of the electrons at both detectors 
and then plotted the number of electrons as a function of energy. The 
researchers observed interference fringes at the first detector because it 
was impossible to know if an electron counted by the detector was produced 
during the first or second maximum. 

There was no interference pattern at the second detector because all the 
electrons were produced at the same time at the minimum. However,when the 
phase of the laser was changed so that there was one maximum and two 
minima, interference fringes were seen at the second detector but not at 
the first. “We have complete which-way information and no which-way 
information at the same time for the same electron,” says Paulus. "It just 
depends on the direction from which we look at it."  

> What if the inhabitant naturally has eyes which function as quantum 
> erasers?
> Those wouldn't be eyes.  The eraser focuses the photons on the same spot 
> whichever slit they went through so the 'eyes' that would erase the 
> information are 'eyes' that can't resolve the slits.

Maybe more photoreceptors than eyes, but they can still discern light from 
dark, so they could be used as eyes of a sort, especially if their brain 
accumulated light-dark patterns over time...i.e. more like optical ears.

> What if the inhabitant has one eye which is a quantum eraser and one which 
> isn't?
> Depends on which one detects the photon.

Yes, that's the point. If you don't know which one, how does the 
interference pattern know?

> What if the inhabitant has a cat in a box with a cyanide capsule triggered 
> by...
> What if you read the papers yourself.

I try but find the jargon distracting. It's amazing how much clearer 
Leibniz and Einstein are to read - it seems like they are actually trying 
to explain something that they understand rather than impress a peer review 
or grant committee.


> Brent

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