Comment by inlineint | Hacker News Reader

Comment by inlineint | Hacker News Reader

The statement about detecting a single photon by an eye is new (and possibly contradictory), but detection of a very few number of photons by human eye is not a new thing. Cherenkov radiation[1] was discovered by observing a very small number of photons (actually only a few of them) in short time interval by eyes.

The experiments were conducted this way because there were no sensitive enough photodetectors in 1930s, so the eyes were the most sensitive available tool for this kind of experiments. Eyes of a physicist were prepared to the experiments by being in complete darkness for a few hours before the measurements. Description of the experimental procedure can be found here[2].

[1] https://en.wikipedia.org/wiki/Cherenkov_radiation

[2] http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c....

It isn't even completely new. Its hard to Google how that this paper is new, but the claim has been made decaden ago. https://en.m.wikipedia.org/wiki/Absolute_threshold#Vision:

"1972 Sakitt conducted an experiment that combined elements of signal detection and threshold theory. Two key elements of the study were a high tolerance for false positives and a multiple-choice option on deciding whether or not a light was seen. In the classic studies described above, the tolerance for false positives was so low that threshold was biased upward. Based on statistical analysis of a large number of trials, 6 photons each absorbed by one rod near-simultaneously looked "very bright," 5 photons looked "bright," 4 photons "a moderate light," 3 photons "a dim light." Two observers were able to see 2 photons as "slightly doubtful if a light was seen." One observer saw a single photon as "very doubtful if a light was seen." Zero photons were seen as "did not see anything."

One thing to note is that these experiments are hard to do. Dark adaptation (https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Dark_adapta...) takes a long time; some researchers claim it continues for up to 24 hours (sorry, can't find a reference)

That means sitting in the absolute dark for hours (you will not want to do a few short experiments, as that means dark adapting more times). It's not like you can easily repeat this with Rens of people.

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