
 Can a Human See a Single Photon? - hhm
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html
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mechanical_fish
Which brings me to one of my favorite physicist stories ever. From Richard
Rhodes' _The Making of the Atomic Bomb_ , page 47, describing the 1907 work of
Ernest Rutherford and Hans Geiger:

"There was a way to make individual alpha particles visible using zinc
sulfide... A small glass plate coated with zinc sulfide and bombarded with
alpha particles briefly fluoresced at the point where each particle struck, a
phenomenon known as "scintillation" from the Greek word for spark. Under a
microscope the faint scintillations in the zinc sulfide could be individually
distinguished and counted. The method was tedious in the extreme. It required
sitting for at least thirty minutes in a dark room to adapt the eyes, then
taking counting turns of only a minute at a time -- the change signaled by a
timer that rang a bell -- because focusing the eyes consistently on a small,
dim screen was impossible for much longer than that. Even through the
microscope the scintillations hovered at the edge of visibility; a counter who
expected the experiment to produce a certain number of scintillations
sometimes unintentionally saw imaginary flashes."

Thank god they invented the photomultiplier before I arrived on the scene.

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hhm
How could they tell there were imaginary flashes? It seems like a private
experiment, you can't check it. (Maybe there were not expected flashes at all
and they saw some anyway?)

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mechanical_fish
Well, I left out the next sentence of the book, in which Geiger builds an
electronic counter (perhaps you've heard of it? :) and uses it to cross-check
the humans.

According to the book, after using the counter to confirm that properly
trained and rested humans were as accurate as the electronics, the next step
was _to put the electronic counter away_ because the humans could also give
you spatial information: They could not only tell you that a flash had
happened, but could tell you where it was in the visual field. Multichannel
PMTs or (god bless 'em) chilled semiconductor-based multi-element low-noise
photodetectors were still dozens of years in the future...

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hhm
Thank you! Your posts are always very good reading :)

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porfirion
I wonder if it's in any way related to visual snow phenomenon[1].

[1] <http://en.wikipedia.org/wiki/Visual_snow>

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AndyKelley
Hey cool, I was wondering if that was only me, and if it had a name.

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time_management
I think it happens to everyone in small amounts. Low blood pressure seems to
be a common culprit for me. If I get super-relaxed, like after a yoga class or
a good workout, I can actually see my heartbeat. It's weird, and it was
unsettling until I figured out what it was.

A close friend of mine has HPPD, and although I can't speak directly from
experience on that, it seems to me that much of HPPD is an anxiety reaction to
normal visual phenomena that most people grow used to and filter, but for
which people can develop hypersensitivity and then become convinced that
something is wrong. (This would be much like how, during the onset of a severe
panic attack, especially in a person who has never had one before, normal
semi-liminal physical sensations morph into "evidence" of impending
doom/insanity.)

