41–50 of 142 posts
Question in the title -> No. 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.
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…
The visible light spectrum corresponds to photons with energies of roughly 1.6 to 3.4 electron volts. That's a non-trivial amount of energy, enough to break the weaker bonds in many kinds of molecules.
In comparison, our environment is awash in huge numbers of thermal infrared photons, with energies on the order of 0.025 eV. But each of these photons has much less than 1/100th the effectiveness when it comes to interacting with atomic bonds.
As for the photopigments themselves, you can think of them kind of like atomic-scale mousetraps. Once a photosensitive molecule has been put into a highly energetic state, it only takes a tiny stimulus to make it release that energy, eventually leading to a much larger nerve impulse. Biological photosensors have been optimized by evolution to take advantage of this effect.
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…
If you were constantly bombarded with atoms at the same energy level (1.5-3.5eV), you would notice them as well. This just occurs less frequently (unless you are on fire).
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…
Similarly surpising, large cities can be seen from orbit if you know where to look.
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?
Earlier quoted context omitted.
It is true you can taste protons. Whether you can taste a single one, I'm not sure, nor even how to test it. Fun video by Steve Mould on the subject: https://www.youtube.com/watch?v=FSYE1T5d9jc
I’m convinced you cannot taste single protons. Water self ionizes, so there will always be acidic species (H+, H3O+, …) way way above the concentration of single molecules. https://en.wikipedia.org/wiki/Self-ionization_of_water
What is the comparison to modern camera sensors nowadays? Can they detect single photons?
Yes, modern CMOS image sensors have quantum efficiencies of more than 80 %, and modern CCDs are well above 90 %. This depends on wave length, particularly in the NIR spectrum. This means that 80 or 90 % of the incident photons are converted into electrons. This number does not include photons being reflected from the surface of the sensor or the filter stack on top. There's also SPADs "single photon avalanche diodes"…
For detecting single photons, you need really high in-sensor amplification. Options include SPADs or photomultipliers if you don't need an image, or image intensifier tubes (used in night vision) if you do need an image. Semiconductor cameras that use IIT-like operational principles are in development now, undergoing testing for next-gen (digital) night vision.
Earlier quoted context omitted.
It’s cool our brains have that as a heuristic for whatever reason. Wonder if you could train yourself to see 1-3?
If you tune up your sensitivity to 1-3 photons, you'll probably find a maddening TV white noise overlaid on your vision.
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.
Would be fun to see if it’s possible to set up the experiment as a double slit. Would humans sense an interference pattern? Is the back of an eye a sufficient observer? :)
It definitely is. The retina "measures" photon positions, which is why you see images. Observation is just interaction, no need to consider whether A can observe B. If they interact, some kind of observation takes place.
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?
Most of the effects of LSD (patterns etc) are actually pretty well understood. It's probably caused by a stable geometric pattern generated by a reaction-diffusion process in your visual cortex. https://plus.maths.org/content/uncoiling-spiral-maths-and-ha...
Related to your question (although minus drugs) - I very recently figured out how to "turn off" shot noise suppression in my visual processing. I woke up a few months ago and was struggling to understand something I was looking at in the room (it was a low-contrast scene with confusing shadows) and something clicked, and all of a sudden I could see the shot noise from my eyes. Very bizarre! I can now detect it just by paying close attention in moderately dim conditions.