On 12/4/2012 9:14 PM, Craig Weinberg wrote:


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." -http://physicsworld.com/cws/article/news/2005/mar/02/new-look-for-classic-experiment


I looked at the paper. It doesn't show the detector arrangement, but from the description I don't see that it can obtain which-way and no-which-way for the *same* electron.





    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.

But if they don't detect the direction of the photon with sufficient resolution then they won't act as erasers of the interference pattern.




    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?

'It knows' because you have to select out the photon detections corresponding the ones whose partner went in the detector eye in order to see the interference.




    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.

I don't see any jargon. It's just that real experiments are messier and have more details to explain than thought experiments.

Brent

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.

Craig


    Brent

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