Recent experiments have put the claim to test<p>Overview
<a href="https://www.nature.com/articles/nature.2016.20282" rel="nofollow">https://www.nature.com/articles/nature.2016.20282</a><p>The actual work
<a href="https://www.nature.com/articles/ncomms12172" rel="nofollow">https://www.nature.com/articles/ncomms12172</a><p>> Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance.
On a related note, you can hear sounds that displace your eardrums on the order of an atomic diameter. At least that is something I heard years ago, a quick search turned up this StackExchange question [1] so there may be some truth to this, I did however not read the answers too carefully. They actually seems to suggest that the threshold is even quite a bit smaller which makes me somewhat cautious of the claim, but then again you are essentially integrating over really many atoms in your eardrum getting displaced together.<p>[1] <a href="https://physics.stackexchange.com/questions/147826/how-much-air-needs-to-be-displaced-to-generate-an-audible-sound" rel="nofollow">https://physics.stackexchange.com/questions/147826/how-much-...</a>
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.<p>You can check my math here if you want to convince yourself:
<a href="https://www.spectralcalc.com/blackbody_calculator/blackbody.php" rel="nofollow">https://www.spectralcalc.com/blackbody_calculator/blackbody....</a>
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.<p>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.<p>Light also comes in chunks, and the number of these chunks should be comparable to number of atoms since, e.g every single atomic transition generates a photon. Actually they should be far <i>more</i> numerous as they are massless and easily created, destroyed.<p>Yet, somehow, they are not far below the human scale of detection — as few as 5 (!) results in a perceivable flash.<p>What am I missing here? (Obviously this boils down to a numeric estimation and the numbers are what they are — my question is why do the numbers wind up even remotely in the human ballpark.)
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.<p>I was convinced this was the case as a kid, but no one ever believed me!<p>[1] <a href="https://www.wikiwand.com/en/Blue_field_entoptic_phenomenon" rel="nofollow">https://www.wikiwand.com/en/Blue_field_entoptic_phenomenon</a>
This is a snippet from Scientific American, October 1993, <i>50 and 100 years ago:</i><p><i>October 1893:</i> "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 <i>see</i>, 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<p>Can anyone - uh - shed some light on it?
Genuine question: I’ve never taken LSD, but could some of its purported visual effects be explained as seeing photons via a depressed neurological filter?
If you look carefully, you can see a little bit of noise in very low lighting, probably because of the small number of photons. However, the amount of noise you see with your eyes is orders of magnitude less than the camera in your phone picks up. Camera technology is still well behind biological cameras. To get similar performance you’d probably have to cool the ccd with liquid nitrogen.
As a layman in modern physics, I struggle to understand the shape and size of a photon as a wave. As far as I understand, e.g double slit experiment would implicate that the size of a single photon wave would be clearly macroscopic in nature. Is there any text available that would discuss this without a need of Ph.D in physics?
> sensors in the retina can respond to a single photon. But neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms<p>Like an activation function in artificial neural networks
Question in the title -> No.<p>TL/DR: No, we cant. The retina itself can respond to a single photon, but we are not retinas. Instead, the eye filters out this low light sensitivity lest we go crazy with the resulting visual noise at night.
This reminds me; if I look at a red LED in the dark, my eyes seem to add a purple shape around it, kinda like an infinity symbol. Does this happen to anyone else?
its an interesting space to try and inspire engineering from biology, a quick search says eagles have the best eyesight<p>i just saw a video about a dog's nose being used for particle detection in crime scenes, i'm wondering if there's already been, or when there will be work on recreating the basis of an eye as a detector<p>or if maybe this has already been subverted by lens manufacturing
It's amazing what happens in an eye: retinal (C₂₀H₂₈O), an aldehyde of Vitamin A, exists in two forms: all-trans-retinal gets hit by photos, flips and becomes 13-cis retinal (simplifying slightly). If enough photons are involved, the info gets transmitted to the train. If the photons were in a particular constellation, we see a "rectangle" or "circle"; quite a miracle if you think about it.
There's a fun way you can try seeing individual photons yourself! With a Nuclear Spinthariscope, somewhat popularized in this XKCD comic
<a href="https://xkcd.com/2568/" rel="nofollow">https://xkcd.com/2568/</a><p>You can buy them for about $50 from some science education sites. It's quite a conversation starter, as long as you're ready to sit in the dark for 15 minutes.