5 ms·
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/mi
by notfish 4y ago
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/blackbody_calculator/blackbody.php https://www.spectralcalc.com/blackbody_calculator/blackbody....
- deleted 4y ago[deleted]
- Sharlin 4y agoA 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.
- gnulinux 4y agoWhat if you're in a pitch-black dark room of mirrors? Would it make it more likely notice the other person through photons?
- Sharlin 4y agoSo 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.
- notfish 4y agoWe 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.
- bigbluedots 4y agoComments like yours are one of the reasons I love HN. Thank you!
- de6u99er 4y agoWhat if the room was made out of perfect mirrors?
- ASalazarMX 4y agoIt'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.
- dylan604 4y ago>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.
- qwezxcrty 4y agoNo, 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
- devindotcom 4y ago>Assuming a spherical isotropically radiating human ...in a vacuum, of course!
- ASalazarMX 4y agoIn a perfectly dark room, isolated from cosmic rays, at zero Kelvin.
- _yb2s 4y agomy home office setup
- Sharlin 4y agoOf course.
- ask_b123 4y agoDo we have to account for blink rate?
- Someone 4y agoI don’t understand the physics, but clicking “Calculate” produces a graph with x axis between 8 and 12 μm. Isn’t that 8,000 to 12,000 nm and thus outside of visible range for humans (400 to 800 nm)? Decreasing the lower limit to zero shows things drop of rapidly near the visible range for humans. Or do I have to subscribe and interpret the text file version?
- fractallyte 4y agoI added a relevant comment elsewhere on this page: https://news.ycombinator.com/item?id=34457309 https://news.ycombinator.com/item?id=34457309
- reef84_ 4y agoWhy “nonzero”? That’s already explicit.
- eternauta3k 4y agoDoes an infrared photon have enough energy to stimulate a rod?
- thesimonlee 4y agoDefinitely. 20 years ago when homes were not littered with LEDs all over, I would wake in the night to total blackness. I could still find my way around the house just able to see based on what is I suppose a noise floor of ambient temperature. Go into the kitchen & behold the stove top emitting 'bright' white light, from I suppose a temperature of around 30degC /90F. Obviously everything is a blackbody, but those photons surely can't be 'single' visible ones.
- yetanotherloser 4y agoGosh. I used to have pretty good night vision and recognise what you mean about "see based on the noise floor" - but I never had an experience like seeing the stovetop heat. Remarkable. I wonder how much variation there is between people? Unfortunately mine's faded with age so I don't think it's worth my trying to see if I can see that myself now...
- Luc 4y agoDid you consider you were seeing (very low amounts of) visible light? Temperature had nothing to do with it.
- deleted 4y ago[deleted]
- eternauta3k 4y agoIs it possible that your house was illuminated by ultrashort infrared laser pulses? https://www.pnas.org/doi/full/10.1073/pnas.1410162111 https://www.pnas.org/doi/full/10.1073/pnas.1410162111
- Maursault 4y agoLuminous beings are we, not this crude matter.