15 ms·

Can a Human See a Single Photon? (1996)

195 points by adenadel 9y ago

deleted 9y ago
[deleted]
tristanj 9y ago
Article is from 1996. Another study was done last year and they also found humans can probably see single photons, though the study is limited as its sample size is n=3. https://www.nature.com/news/people-can-sense-single-photons-1.20282 https://www.nature.com/news/people-can-sense-single-photons-...
- laretluval 9y ago
  They ran each subject for 2400 trials. Was that decided in advance? This really needs a registered replication.
- pharrington 9y ago
  That Nature article and the OP are in complete agreement. Neither say humans can visually experience single photons.
- tdaltonc 9y ago
  A low subject count is a big problem in a lot of psych studies, but much less so in psychophysics. They typically do thousands of trials on each subject and the variance between subjects is usually extremely small.
- ekianjo 9y ago
  > can probably see single photons Photons don't exist in the first place. Science has moved on and modern models don't assume the existence of actual particles. It's only electromagnetic waves.
  - guftagu 9y ago
    How do the waves have inertia then? We know for a fact that photons exert force in the surface they strike
  - swiley 9y ago
    That's not quite right, They still come in descrete packets. It makes sense to call these photons and I've been told it's better to just think of them using statistics rather than to use something like waves or particals. Not that I understand quantum mechanics.
  - fiatjaf 9y ago
    "Science has moved", "Photons don't exist". How do you live with that?
  - colanderman 9y ago
    Ok, tell that to the Standard Model. [1] Like it or not, in modern physics, "photon" refers to a particular type of discrete lump of momentum and energy. It is a thing you can definitely have one of. [1] https://en.wikipedia.org/wiki/Standard_Model https://en.wikipedia.org/wiki/Standard_Model
    - ekianjo 9y ago
      Then its not a particle with zero mass as often defined.
- mattkrause 9y ago
  That's not the actual paper. This is: https://www.nature.com/articles/ncomms12172 https://www.nature.com/articles/ncomms12172
dang 9y ago
Discussed in 2008: https://news.ycombinator.com/item?id=299724 https://news.ycombinator.com/item?id=299724.
baking 9y ago
There is a well known (I heard about it in the late 70's) problem with these types of experiments. The assumption is that if the subjects' "guesses" statistically match the assumed hit rate of photons then there must be a cause and effect. This experiments seems to make no attempt to eliminate the possibility that this is completely random.
- sgk284 9y ago
  All of human reasoning and understanding comes from matching our observations statistically with potential causes. You may heat up a tea kettle a thousand times with a flame and conclude that the flame is heating the tea kettle, but perhaps every time the flame was too small and too far and it was in fact another source of energy hitting it from the environment warming it. Our understanding of the world comes from substantial enough correlation that it moves into the realm of cause-and-effect. Though admittedly we often assume this too quickly.
  - deleted 9y ago
    [deleted]
  - baking 9y ago
    But you have to be able to have a control. I heard Barbara Sakitt speak around 1976-77. She was the author of the widely cited "Counting Every Quantum" (1972) and she basically said that her original methodology was flawed. Unfortunately, no one cites her later work and I don't have access to the full text of "Information received from unseen lights" (1976) which I think was the paper she was presenting.
- deleted 9y ago
  [deleted]
- joeyo 9y ago
  > This experiments seems to make no attempt to eliminate > the possibility that this is completely random. Psychophysicists use two-alternate forced-choice experiments precisely to eliminate the possibility of the result being "completely random". Indeed, for this experimental design it---given sufficient trials---is quite easy to do hypothesis testing and compute confidence intervals for the hypothesis that the subjects can perform the task better than chance. You are correct, of course, that this doesn't prove that they see the photons. Maybe the experimental apparatus was poorly made and accidentally a noise when the photons were flashed. Or maybe someone cheated and told them which trials the photons would be delivered. Or perhaps they simply have ESP. But the one thing that we can easily have confidence about is when an effect differs from random chance.
m3kw9 9y ago
Very nice write up on the experiment
looki 9y ago
> However, 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. If we could consciously see single photons we would experience too much visual "noise" in very low light, so this filter is a necessary adaptation, not a weakness. Wonder if this is related to what I experience. Visual snow - basically seeing static in your vision, especially at night. I sometimes don't notice it for weeks, but then I just pick up on it again and can't stop noticing. It's still hard for me to believe that it's not normal, given that it happens with any camera ever built, but apparently not many people experience it.
- GuiA 9y ago
  Interesting - are you stating that not many people experience the snow, or not many people don’t go for weeks without noticing? I’ve always experienced it, and remember playing as a kid squinting my eyes really hard to make random colors and patterns appear (the latter often looking like a grey 3D grid deforming over time)
  - deleted 9y ago
    [deleted]
- AdamJacobMuller 9y ago
  I see this. I always assumed everyone did...
- cordite 9y ago
  I thought it was an artifact of how our vision system works, not input to that system.
- dieterrams 9y ago
  It's likely that what you're noticing is an artifact of how visual perception works. Even in pitch dark, your brain is still trying to do pattern matching, and because that process of pattern matching results in what we 'see', you are unlikely to perceive perfect darkness.
- 9y ago
sillysaurus3 9y ago
Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you even noticing? Example: https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif The fact that colors influence colors around them means that there are far more than 256^3 viewable colors: the spatial axis is like a fourth channel. Another fun one: If you take a paper plate and poke a hole in it, then take a toothpick and stick it in front of the hole, from the bottom, pointing upwards.... Then it'll look like it's coming down from the top! It's very hard to explain in words, but basically it's a pinhole camera, so everything appears upside-down. Your brain tries to compensate and flips it right side up, but it can't quite do that with the toothpick-hole scenario. So when you push the toothpick up from the bottom, it looks like it's coming down from the top. Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. A fun puzzle is, how do you see an individual pixel? Can you think of any common object that would help you do this? (No magnifying lenses, for example, and using a phone is sort of cheating.) Answer below. ... Answer: pluck a hair out of your head and put it on your screen. The line along the edge of the hair will turn into a stairstep pattern, which is just another way of saying you can see individual pixels.
- tbabb 9y ago
  Perhaps a nitpick, but 256^3 doesn't really represent anything about human perception-- it's just how we store colors in computer memory. The human eye can perceive a far wider range of colors than any screen can (currently) represent. It's just as valid (and probably more accurate) to use floating point to store color (rather than bytes), and in many high-fidelity applications this is actually how it's done. The bit about colors "looking different" in different contexts also isn't really an "extra axis". The example you give is just your brain (attempting to) separate out the illumination from the scene colors. The range of actual colors you can perceive isn't increased by this. Fundamentally human color perception is three-dimensional, because humans have three classes of color receptors on their retinas. There are also rods in the retina (the cells that are color-insensitive and detect only brightness), and in principle they could inform color perception, but this does not seem to be the case-- the intensity of light only shifts things around in the original three-dimensional space. There are also a very, very few people (women only) with genetic mutations that give them four different color receptors in their retina. However, there is no evidence that their brains can take advantage of this extra information and allow them to perceive an extra "axis" of color. It is much more likely that the "mutant" receptors are lumped in with the stimulus of one of the others, which will shift their perception of color, but not expand it. In short: There are three axes of color perception. Optical illusions don't change that.
jankotek 9y ago
Under ideal conditions human can see 9th magnitude stars. We tried under real sky, and got 8.1 magnitude stars at 80% probability. Not sure how it translates to photon counts.
jankotek 9y ago
Humans can see single gamma photons, even with closed eyes :-)
- cocoablazing 9y ago
  https://www.orau.org/ptp/articlesstories/invisiblelight.htm https://www.orau.org/ptp/articlesstories/invisiblelight.htm
akashakya 9y ago
If you like the these kind of writeups, You might like the parent post, which have many such intresting articles from the Usenet Physics FAQ. http://math.ucr.edu/home/baez/physics/index.html http://math.ucr.edu/home/baez/physics/index.html
- gciruelos 9y ago
  john baez is a brilliant guy. and also he's the cousin of joan baez, which makes me appreciate both of them even more.
tudorw 9y ago
an aside, but an interesting one, Biophotons... was new to me, https://www.ncbi.nlm.nih.gov/pubmed/?term=biophoton https://www.ncbi.nlm.nih.gov/pubmed/?term=biophoton
z3t4 9y ago
When we are able to guess, eg not have to be 100% accurate - all our sensors become super human.
splittingTimes 9y ago
Let me up the ante, not only can we detect single photons. A pioneering study at the interface of biology and physics found, that isolated rod photoreceptors of frogs are sensitive to differences in the light sources statistical properties, e.g coherent (laser) vs thermal (sun, light-bulb) vs sub-poissonian (resonance fluorescence of quantum dots) light statistics: "Measurement of Photon Statistics with Live Photoreceptor Cells" (2012) [1] "The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions" It seems Lorentz hypothesis in 1911 was right, that the boundaries of our perception are set by basic laws of physics, and that we reach the limits of what is possible. === [1] [pdf] https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.109.113601 https://physics.aps.org/featured-article-pdf/10.1103/PhysRev...
- theoh 9y ago
  I can't find what this Lorentz hypothesis of 1911 is, but surely you are claiming too much. Physical entities can detect X-rays, but humans haven't evolved that ability (except, recently, externally/collectively). The idea that our perceptual apparatus is optimal, rather than a contingent product of a particular evolutionary path, is easy to refute -- but maybe that isn't what you mean by "reach[ing] the limits of what is possible."
  - mromanuk 9y ago
    We can reach maximum optimization of wathever physical property we use. For example our brain and it super efficiency vs a super computer.
    - bhaak 9y ago
      But humans had millions of years to evolve. The computer is only 70 years old. Give it 100 years and we will make it as efficient as a human brain, possibly even better. Evolution is a slow process. Non sentient trial and error. We beat that in time easily.
  - 9y ago
appleflaxen 9y ago
I would never have guessed this result, because it seems like a vast overoptimization for light detection: in what circumstances would a human being need to see a single photon? And if those circumstances are rare, then what is the cost (in fitness, energy, etc) that we pay to maintain that ability?
- baking 9y ago
  Rods can respond to individual photons, that is pretty much accepted. The issue is what can we perceive. The first nerve synapse screens out about 50% of isolated photons (ones that are not correlated from other rods) which has been estimated from modeling. Which means that some of those singular photons are getting through (perceived) and can be isolated from the background noise through careful experiments. I don't think we evolved to see single photons, but that we evolved to be very sensitive to light while reducing the noise and that sweet spot means that we can quite possibly, under ideal conditions, see individual photons slightly more than we think we see non-existent photons.

195 points by adenadel 9y ago

deleted 9y ago

[deleted]

Article is from 1996. Another study was done last year and they also found humans can probably see single photons, though the study is limited as its sample size is n=3. https://www.nature.com/news/people-can-sense-single-photons-1.20282 https://www.nature.com/news/people-can-sense-single-photons-...

laretluval 9y ago
They ran each subject for 2400 trials. Was that decided in advance? This really needs a registered replication.
pharrington 9y ago
That Nature article and the OP are in complete agreement. Neither say humans can visually experience single photons.
tdaltonc 9y ago
A low subject count is a big problem in a lot of psych studies, but much less so in psychophysics. They typically do thousands of trials on each subject and the variance between subjects is usually extremely small.
ekianjo 9y ago
> can probably see single photons Photons don't exist in the first place. Science has moved on and modern models don't assume the existence of actual particles. It's only electromagnetic waves.
- guftagu 9y ago
  How do the waves have inertia then? We know for a fact that photons exert force in the surface they strike
- swiley 9y ago
  That's not quite right, They still come in descrete packets. It makes sense to call these photons and I've been told it's better to just think of them using statistics rather than to use something like waves or particals. Not that I understand quantum mechanics.
- fiatjaf 9y ago
  "Science has moved", "Photons don't exist". How do you live with that?
- colanderman 9y ago
  Ok, tell that to the Standard Model. [1] Like it or not, in modern physics, "photon" refers to a particular type of discrete lump of momentum and energy. It is a thing you can definitely have one of. [1] https://en.wikipedia.org/wiki/Standard_Model https://en.wikipedia.org/wiki/Standard_Model
  - ekianjo 9y ago
    Then its not a particle with zero mass as often defined.
mattkrause 9y ago
That's not the actual paper. This is: https://www.nature.com/articles/ncomms12172 https://www.nature.com/articles/ncomms12172

dang 9y ago

Discussed in 2008: https://news.ycombinator.com/item?id=299724 https://news.ycombinator.com/item?id=299724.

baking 9y ago

There is a well known (I heard about it in the late 70's) problem with these types of experiments. The assumption is that if the subjects' "guesses" statistically match the assumed hit rate of photons then there must be a cause and effect. This experiments seems to make no attempt to eliminate the possibility that this is completely random.

sgk284 9y ago
All of human reasoning and understanding comes from matching our observations statistically with potential causes. You may heat up a tea kettle a thousand times with a flame and conclude that the flame is heating the tea kettle, but perhaps every time the flame was too small and too far and it was in fact another source of energy hitting it from the environment warming it. Our understanding of the world comes from substantial enough correlation that it moves into the realm of cause-and-effect. Though admittedly we often assume this too quickly.
- deleted 9y ago
  [deleted]
- baking 9y ago
  But you have to be able to have a control. I heard Barbara Sakitt speak around 1976-77. She was the author of the widely cited "Counting Every Quantum" (1972) and she basically said that her original methodology was flawed. Unfortunately, no one cites her later work and I don't have access to the full text of "Information received from unseen lights" (1976) which I think was the paper she was presenting.
deleted 9y ago
[deleted]
joeyo 9y ago
> This experiments seems to make no attempt to eliminate > the possibility that this is completely random. Psychophysicists use two-alternate forced-choice experiments precisely to eliminate the possibility of the result being "completely random". Indeed, for this experimental design it---given sufficient trials---is quite easy to do hypothesis testing and compute confidence intervals for the hypothesis that the subjects can perform the task better than chance. You are correct, of course, that this doesn't prove that they see the photons. Maybe the experimental apparatus was poorly made and accidentally a noise when the photons were flashed. Or maybe someone cheated and told them which trials the photons would be delivered. Or perhaps they simply have ESP. But the one thing that we can easily have confidence about is when an effect differs from random chance.

m3kw9 9y ago

Very nice write up on the experiment

looki 9y ago

> However, 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. If we could consciously see single photons we would experience too much visual "noise" in very low light, so this filter is a necessary adaptation, not a weakness. Wonder if this is related to what I experience. Visual snow - basically seeing static in your vision, especially at night. I sometimes don't notice it for weeks, but then I just pick up on it again and can't stop noticing. It's still hard for me to believe that it's not normal, given that it happens with any camera ever built, but apparently not many people experience it.

GuiA 9y ago
Interesting - are you stating that not many people experience the snow, or not many people don’t go for weeks without noticing? I’ve always experienced it, and remember playing as a kid squinting my eyes really hard to make random colors and patterns appear (the latter often looking like a grey 3D grid deforming over time)
- deleted 9y ago
  [deleted]
AdamJacobMuller 9y ago
I see this. I always assumed everyone did...
cordite 9y ago
I thought it was an artifact of how our vision system works, not input to that system.
dieterrams 9y ago
It's likely that what you're noticing is an artifact of how visual perception works. Even in pitch dark, your brain is still trying to do pattern matching, and because that process of pattern matching results in what we 'see', you are unlikely to perceive perfect darkness.
9y ago

sillysaurus3 9y ago

Would there be any interest in a series I've been thinking of putting together about all the fantastically counterintuitive ways your eye fools you without you even noticing? Example: https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif https://media.giphy.com/media/3o7btPOMufN5FziFWg/giphy.gif The fact that colors influence colors around them means that there are far more than 256^3 viewable colors: the spatial axis is like a fourth channel. Another fun one: If you take a paper plate and poke a hole in it, then take a toothpick and stick it in front of the hole, from the bottom, pointing upwards.... Then it'll look like it's coming down from the top! It's very hard to explain in words, but basically it's a pinhole camera, so everything appears upside-down. Your brain tries to compensate and flips it right side up, but it can't quite do that with the toothpick-hole scenario. So when you push the toothpick up from the bottom, it looks like it's coming down from the top. Lastly: https://i.imgur.com/epXYhJd.png https://i.imgur.com/epXYhJd.png If you cover up the top half of the image, the bottom looks gray. But the strawberries look red. A fun puzzle is, how do you see an individual pixel? Can you think of any common object that would help you do this? (No magnifying lenses, for example, and using a phone is sort of cheating.) Answer below. ... Answer: pluck a hair out of your head and put it on your screen. The line along the edge of the hair will turn into a stairstep pattern, which is just another way of saying you can see individual pixels.

tbabb 9y ago
Perhaps a nitpick, but 256^3 doesn't really represent anything about human perception-- it's just how we store colors in computer memory. The human eye can perceive a far wider range of colors than any screen can (currently) represent. It's just as valid (and probably more accurate) to use floating point to store color (rather than bytes), and in many high-fidelity applications this is actually how it's done. The bit about colors "looking different" in different contexts also isn't really an "extra axis". The example you give is just your brain (attempting to) separate out the illumination from the scene colors. The range of actual colors you can perceive isn't increased by this. Fundamentally human color perception is three-dimensional, because humans have three classes of color receptors on their retinas. There are also rods in the retina (the cells that are color-insensitive and detect only brightness), and in principle they could inform color perception, but this does not seem to be the case-- the intensity of light only shifts things around in the original three-dimensional space. There are also a very, very few people (women only) with genetic mutations that give them four different color receptors in their retina. However, there is no evidence that their brains can take advantage of this extra information and allow them to perceive an extra "axis" of color. It is much more likely that the "mutant" receptors are lumped in with the stimulus of one of the others, which will shift their perception of color, but not expand it. In short: There are three axes of color perception. Optical illusions don't change that.

jankotek 9y ago

Under ideal conditions human can see 9th magnitude stars. We tried under real sky, and got 8.1 magnitude stars at 80% probability. Not sure how it translates to photon counts.

jankotek 9y ago

Humans can see single gamma photons, even with closed eyes :-)

cocoablazing 9y ago
https://www.orau.org/ptp/articlesstories/invisiblelight.htm https://www.orau.org/ptp/articlesstories/invisiblelight.htm

akashakya 9y ago

If you like the these kind of writeups, You might like the parent post, which have many such intresting articles from the Usenet Physics FAQ. http://math.ucr.edu/home/baez/physics/index.html http://math.ucr.edu/home/baez/physics/index.html

gciruelos 9y ago
john baez is a brilliant guy. and also he's the cousin of joan baez, which makes me appreciate both of them even more.

tudorw 9y ago

an aside, but an interesting one, Biophotons... was new to me, https://www.ncbi.nlm.nih.gov/pubmed/?term=biophoton https://www.ncbi.nlm.nih.gov/pubmed/?term=biophoton

z3t4 9y ago

When we are able to guess, eg not have to be 100% accurate - all our sensors become super human.

splittingTimes 9y ago

Let me up the ante, not only can we detect single photons. A pioneering study at the interface of biology and physics found, that isolated rod photoreceptors of frogs are sensitive to differences in the light sources statistical properties, e.g coherent (laser) vs thermal (sun, light-bulb) vs sub-poissonian (resonance fluorescence of quantum dots) light statistics: "Measurement of Photon Statistics with Live Photoreceptor Cells" (2012) [1] "The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions" It seems Lorentz hypothesis in 1911 was right, that the boundaries of our perception are set by basic laws of physics, and that we reach the limits of what is possible. === [1] [pdf] https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.109.113601 https://physics.aps.org/featured-article-pdf/10.1103/PhysRev...

theoh 9y ago
I can't find what this Lorentz hypothesis of 1911 is, but surely you are claiming too much. Physical entities can detect X-rays, but humans haven't evolved that ability (except, recently, externally/collectively). The idea that our perceptual apparatus is optimal, rather than a contingent product of a particular evolutionary path, is easy to refute -- but maybe that isn't what you mean by "reach[ing] the limits of what is possible."
- mromanuk 9y ago
  We can reach maximum optimization of wathever physical property we use. For example our brain and it super efficiency vs a super computer.
  - bhaak 9y ago
    But humans had millions of years to evolve. The computer is only 70 years old. Give it 100 years and we will make it as efficient as a human brain, possibly even better. Evolution is a slow process. Non sentient trial and error. We beat that in time easily.
- 9y ago

appleflaxen 9y ago

I would never have guessed this result, because it seems like a vast overoptimization for light detection: in what circumstances would a human being need to see a single photon? And if those circumstances are rare, then what is the cost (in fitness, energy, etc) that we pay to maintain that ability?

baking 9y ago
Rods can respond to individual photons, that is pretty much accepted. The issue is what can we perceive. The first nerve synapse screens out about 50% of isolated photons (ones that are not correlated from other rods) which has been estimated from modeling. Which means that some of those singular photons are getting through (perceived) and can be isolated from the background noise through careful experiments. I don't think we evolved to see single photons, but that we evolved to be very sensitive to light while reducing the noise and that sweet spot means that we can quite possibly, under ideal conditions, see individual photons slightly more than we think we see non-existent photons.