From: dseeman@novell.com (Daniel Seeman)
Newsgroups: sci.physics
Subject: Re: photon 'detectors' - how reliable?
Date: 25 Jan 93 18:03:02 GMT
Organization: Novell Inc., San Jose, Califonia

In article <1993Jan23.232914.19166@lynx.dac.northeastern.edu> mkagalen@lynx.dac.northeastern.edu (michael kagalenko) writes:
>In article <1993Jan21.162025.23220@novell.com> dseeman@novell.com (Daniel Seeman) writes:
>>In article <wwadge.727584610@csr> wwadge@csr.UVic.CA (Bill  Wadge) writes:
>>>I was browsing through one of the many 'pop' physics books,
>>>where they are describing one of the stock quantum mechanics
>>>experiments, and noticed something along the lines of
>>>
>>> .. towards a detector which records every photon ..
>>>
>>>Is this possible? Can one really build a device so sensitive that it will
>>>detect 100% reliably every photon that enters it, and never
>>>go off by accident?
>>>
>>>Seems unlikely, but then I'm not a physicist ...
>>>
>>It is not unlikely at all.  Do this experiment:
>>
>>Enclose yourself in a room with a light that is controlled by a dim switch.  Dim
>>the light until you can barely see your hand.  Then, look at the bulb.  At this
>>point, your eye is detecting every photon that is comming your way (from the
>>bulb).  True, the eye is pretty unique in that its design is ---well pretty
>>good.  Apparently our designer (nature,evolution, god---arguably all are one in
>>the same) was quite "skilled."  However, there are other devices (natural and
>>man-made) that have the same (and better) efficiency.
>>
>>One thing that may help you consider this is that a light bulb emits photons in
>>all directions (except down into the socket---the metal circuit casing stops the
>>photons).  But you only see the ones that are directly along your line of sight.
>>All other photons in the room are detected or felt by something else (like the
>>walls of the room heat slightly etc...).  So, you do not (nor does any other
>>singular detector) see ALL the photons emitted by a light source unless that 
>>source is directing all its photons toward the detector.  When you look at it
>>in that "light---pun intended" these detectors do not seem so awesome.
>>
>>Hope this helps...
>>^^^^^^^^^^^^^
>>dks.
>
>
>Vain hope, since what you're saying is wrong.

Is this description *ABSOLUTELY* correct to the last photon? You are correct, no
it is not.  Your eye suffers from inefficiencies too.  But I put this out to
show that detectors are in use today that are sufficiently efficient.  And to
that extent, the exercise is not wrong.  

I discussed this matter with 
Scott Chase and he feels that I (and my optometrist) should be a bit more
precise with these statements.  Only *PERFECT* eyes under *IDEAL* conditions
would be *CAPABLE* of reacting to significantly high percentage (we discussed
efficiencies over %80 or so) of incident photons.  

Why don't you ask your optometrist?  Be sure to set up the experiment for her so
she knows what your are "looking" for.  I would be interested in what she says.
But at least one reputable optometrist thinks the efficiency we discuss is
at least plausible (maybe not probable though).  Also the person at school who
taught me this simple exercise is a pretty good reference too.  Certainly he 
was not counting beans at the time but rather was trying to illustrate a point.
That is what I was trying to do too (eg. there are some very efficient detectors
in use today and they are not necessarily "high-tech" mechanical solutions).

dks.