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Can a Human See a Single Photon? (1996)

math.ucr.edu

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Re: Can a Human See a Single Photon? (1996)

#81

Post by bigbluedots »

Sharlin wrote: post #71
notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

Comments like yours are one of the reasons I love HN. Thank you!

Re: Can a Human See a Single Photon? (1996)

#82

Post by fractallyte »

This is a snippet from Scientific American, October 1993, 50 and 100 years ago:

October 1893: "It now does not seem improbable that, when by the power of thought an image is evoked, a distant reflex action, no matter how weak, is exerted upon certain ends of the visual nerves, and, therefore, upon the retina. Helmholtz has shown that the fundi of the eyes are themselves luminous, and he was able to see, in total darkness, the movement of his arm by the light of his own eyes. This is one of the most remarkable experiments recorded in the history of science, and probably only a few men could satisfactorily repeat it, for it is very likely that the luminosity of the eyes is associated with uncommon activity of the brain and great imaginative power. It is fluorescence of brain action, as it were." --Nikola Tesla, in a paper read before the Franklin Institute

Can anyone - uh - shed some light on it?

Re: Can a Human See a Single Photon? (1996)

#83

Post by fractallyte »

notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

I added a relevant comment elsewhere on this page: https://news.ycombinator.com/item?id=34457309

Re: Can a Human See a Single Photon? (1996)

#84

Post by de6u99er »

Sharlin wrote: post #71
notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

A bit more than just “some” luck needed for one of those photons to be emitted straight into the other person’s pupil! The angular diameter of a human pupil (~5 mm) at a distance of ~2 m is about 0.2 degrees, taking the small angle approximation. So the area of the pupil is maybe 0.04 square degrees, or around one millionth of a full solid angle (~41,000 square degrees). Assuming a spherical isotropically radiating h…

What if the room was made out of perfect mirrors?

Re: Can a Human See a Single Photon? (1996)

#85

Post by VLM »

pavlov wrote: post #9
superposeur wrote: post #6

I’ve been aware of this fact as Feynman points it out in the course of the lectures, but find it totally nuts — there is some sense of scale I’m missing. Matter consists of discrete chunks, atoms, but these chunks are so infinitesimal and numerous that there is no question of seeing them and any effect involving a handful of them is far, far below the human scale. Light also comes in chunks, and the number of these c…

Maybe seeing in the dark is simply so valuable that evolution has created extremely light-sensitive eyes for many species? If there was a molecule whose detection in tiny amounts would give a species a competitive edge, we might have noses capable of detecting 5-molecule amounts of this substance.

photography perspective: Lets say hunting (any species) is most effective when the hunter has a wide field of view from a small pupil. So any hunting carnivore animal, will hunt better under non-ideal light if their pupils are smaller, which requires more sensitive eyes.

Higher sensitivity should lead to wider range of sharp focus, that should lead to more hunting success, more dinners, then more descendants.

I suppose on the prey side being able to see the wolf later during sunset should result in becoming the wolf's dinner less often leading to generally more descendants.

Re: Can a Human See a Single Photon? (1996)

#86

Post by moloch-hai »

mlindner wrote: post #55
LastTrain wrote: post #45

Earlier quoted context omitted.

It is too bad the risks (criminal) are so high, LSD is an interesting enough experience that is worth trying at least once.

As someone who's never taken LSD and have talked to people who have, the number of times people express irreversible changes in how they think about things just from trying things once makes me think that it is not a very good idea to even try once. A chemical that causes irreversible random brain chemistry changes from a single use sounds like damage has happened and the user simply interprets that damage as an impr…

Any profound experience (and many a mundane one) causes permanent change. We call that "memory".

But people who are borderline schizophrenic should never do LSD. They may tip into full-on psychosis. They should, however, take MDMA, and experience quiet, maybe for the first time.

Re: Can a Human See a Single Photon? (1996)

#87

Post by kstrauser »

photochemsyn wrote: post #64
lebubule wrote: post #15

Recent experiments have put the claim to test Overview https://www.nature.com/articles/nature.2016.20282 The actual work https://www.nature.com/articles/ncomms12172 > Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance.

Interesting study, though if you look at the results 'significantly above chance' looks to be 0.60 +/- .05, which is indeed better than 0.50 but not what anyone could call reliable detection. I wonder if trained owls could detect single photons, or if their night vision is based on just having much larger lenses that collect more light? It seems that all rods in retinas are activated by single-photon-absorption, it's…

Owl eyes have really cool adaptations (see https://abcbirds.org/blog/owl-eyes/). If we can somewhat detect single photons, it seems very likely owls could do it much more repeatably.

Re: Can a Human See a Single Photon? (1996)

#88

Post by moistly »

gameshot911 wrote: post #80

Another cool fact is that the human eye can see individual cells! [1] In this example it's a white blood cell, but the eye can also see human ovums as well. I was convinced this was the case as a kid, but no one ever believed me! [1] https://www.wikiwand.com/en/Blue_field_entoptic_phenomenon

There are single-cell organisms up to an inch or so in diameter. https://en.m.wikipedia.org/wiki/Valonia_ventricosa

There are even visible bacteria! https://www.science.org/content/article/largest-bacterium-ev...

Re: Can a Human See a Single Photon? (1996)

#89

Post by reef84_ »

notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

Why “nonzero”? That’s already explicit.

Re: Can a Human See a Single Photon? (1996)

#90

Post by eternauta3k »

notfish wrote: post #65

This fun fact gets even more fun when you consider that a human radiates a nonzero amount of visible light via blackbody radiation - on the order of a photon/minute - which means that in theory, with some luck, in an otherwise cold and completely dark room, two humans might be able to notice each other through vision alone. You can check my math here if you want to convince yourself: https://www.spectralcalc.com/blac…

Does an infrared photon have enough energy to stimulate a rod?
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