From: clarke@acme.ucf.edu (Thomas Clarke)
Newsgroups: sci.physics
Subject: Quantum Observer Paradox
Date: 21 Aug 92 13:11:20 GMT
Organization: University of Central Florida

I posted the following scenario to one of the philosophy
news groups a while back, but couldn't convince them that 
there was anything paradoxical going on.

Do physicists see the same problem I see? At least a conceptual
problem?

Set up two slits which are illuminated by photons from a 
moveable light source.

Behind each slit put a coherent optical mixer with output at 3000 Hz.  
[This is a device that mixes photons with laser light in a non-linear 
crystal toproduce an electrical signal.  If all is done right the
electrical signal is an "exact" replica of the light's electromagnetic 
field, but at a lower frequency.  This might have to be done in two
steps light -> infrared -> electrical, with apparatus cooled in LHe
etc. etc., but I believe it is possible with today's technology]

Take the two electrical signals and apply them to earphones worn
by an observer.

The question is what does s'he hear as the light source is moved around.

Clearly in classical limit (lots of photons) the phase of the 
signals from the two slits vary so that she will have some perception
of changes.  Actually, if lambda-light/slit-seperation equals 
lamda-3000Hz-sound/ear-seperation (~=2) , then she should be able to point
correctly in the direction of the light.

Now as the light is dimmed, eventually we reach the single photon regime
of the classic two slit experiment.  S'he will hear something, since
h-nu of light is much greater than kT and human hearing goes down to
just above the thermal noise threshold at 3000 Hz, but what?  
Will s'he be able to localize the noises s'he hears?

If s'he can't localize in the single photon limit, then presumably
quantum coherence is destroyed by the hearing process, possibly 
at the hair cell level.

If s'he can localize in the single photon limit, then quantum coherence
is maintained in the brain at least as high as the corpus callosum.
Does h'er awareness of the localized sound then have a component of
quantum coherence?

Where does the detection take place?  Coherently in the brain 
of the observer?  Incoherently in the ears of the observer?
Elsewhere?  

What do you think?

An ASCII picture:

                              electro-optics          
       |       /|                 __           /|
     ~>       _\|        ^  .~>. |__|-         \|
  /    |     /  |        |            \|\ --> / |
o -    |     \_ |        o -      __  /|/     \_|
  \    |       /|        |  .~>. |__|-         /|
     ~>        \|        ^                     \|
       |        |      motion                 time
       
       Two Slit    <-->    An Equivalent  
             
                                                    
         __      _____      perceived |    ^
^  ..~> |__|--- / ___ \     direction |   /
|              O /o o\ O         ?    |  /
o -      __        \   |              | /
|  ..~> |__|-     \_/  |              |/______  
^            \_________|                 time
motion                   
       
       ??????equivalent????????        


--
Thomas Clarke
Institute for Simulation and Training, University of Central FL
12424 Research Parkway, Suite 300, Orlando, FL 32826
(407)658-5030, FAX: (407)658-5059, clarke@acme.ucf.edu