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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