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Re:Can a Human See a Single Photon? by Sharlin on Friday January 20, 2023 @12:04PM (#34456109)
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 human, the probability of hitting a pupil from any distance is thus pretty unlikely.

Re:Can a Human See a Single Photon? by notfish on Friday January 20, 2023 @12:33PM (#34456560)
We probably need to get more precise for a real answer.

The number I’m getting is about 2 photons/minute per steradian; a steradian has solid area 1m^2 at 1m away. With fully dilated pupils (8mmish) you get an area of pi x 2 x r^2 = 50mm^2, which gives us a rate of about .15 photons/day.

So… Maybe. If you’re very lucky. It’d be interesting to do the same math for a room temp object to see if you’re above the noise floor at all or if this is completely impossible, but I should go do my actual job instead of letting myself get nerdsniped by this.

Re:Can a Human See a Single Photon? by gnulinux on Friday January 20, 2023 @12:16PM (#34456320)
What if you're in a pitch-black dark room of mirrors? Would it make it more likely notice the other person through photons?
Re:Can a Human See a Single Photon? by Sharlin on Friday January 20, 2023 @12:39PM (#34456657)
So you can probably fit three to five one-bounce reflections in your field of view. Then there’s the “infinite” number of higher-order reflections, but given that the probability for a photon to be absorbed rather than reflected is maybe 5% every time it hits a mirror, the additional reflections don’t really contribute that much beyond maybe 20 bounces. So I guess the odds could improve to something like 1/10,000 as a really rough guesstimate.
Re:Can a Human See a Single Photon? by bigbluedots on Friday January 20, 2023 @01:13PM (#34457212)
Comments like yours are one of the reasons I love HN. Thank you!
Re:Can a Human See a Single Photon? by de6u99er on Friday January 20, 2023 @01:21PM (#34457346)
What if the room was made out of perfect mirrors?
Re:Can a Human See a Single Photon? by ASalazarMX on Friday January 20, 2023 @02:06PM (#34458099)
It's still more likely to be reabsorbed by other part of the body than the other's retinas. Wonder if anyone will dare to do the math.
Re:Can a Human See a Single Photon? by dylan604 on Friday January 20, 2023 @02:34PM (#34458521)
>Wonder if anyone will dare to do the math.

Warning! Madness this way lies.

I'm thinking back to the movie Real Genius during one of the montage scenes where they're cramming for finals in a common area when one student just stands up from his material and starts screaming in madness before fleeing. Everyone else, just behaves as if this is normal as someone takes the now vacant place at the table.

That guy screaming in madness? That's me after just thinking of doing the math without even grabbing a pencil.

Re:Can a Human See a Single Photon? by qwezxcrty on Friday January 20, 2023 @05:17PM (#34460848)
No, this will not help. Thermodynamic law forbids this.

Otherwise one can create a machine concentrating all the thermal radiation of one black object at temperature T1, onto another perfectly white object also at T1 with a tiny black hole, heat up the second and then violate the second law of thermodynamics.

Keyword for further Googling: etendue

Re:Can a Human See a Single Photon? by devindotcom on Friday January 20, 2023 @01:58PM (#34457950)
>Assuming a spherical isotropically radiating human

...in a vacuum, of course!

Re:Can a Human See a Single Photon? by ASalazarMX on Friday January 20, 2023 @02:03PM (#34458040)
In a perfectly dark room, isolated from cosmic rays, at zero Kelvin.
Re:Can a Human See a Single Photon? by UniverseHacker on Friday January 20, 2023 @06:41PM (#34461813)
my home office setup
Re:Can a Human See a Single Photon? by Sharlin on Friday January 20, 2023 @03:22PM (#34459291)
Of course.
Re:Can a Human See a Single Photon? by ask_b123 on Friday January 20, 2023 @02:04PM (#34458068)
Do we have to account for blink rate?