11 ms·

People can sense single photons

194 points by mathgenius 10y ago

IIAOPSW 10y ago
You know how cool this is?! It should be possible to set up an experiment with entangled photons and use your eyes as the detector. We could literally see quantum mechanical behavior with our own eyes! Pardon my crudeness but how fucking cool is that!
- markcerqueira 10y ago
  Just tried this experiment at home! Felt about one photon in my left eye and two in my right in one minute!! :D
  - nsxwolf 10y ago
    What's your source of single photons?
    - markcerqueira 10y ago
      Forgot the margin of error! +/- 2 photons!!! :D :D :D
    - VLM 10y ago
      A quarter century ago we used a well characterized laser at a known power level that given a very precise wavelength and total power results in a very precise number of photons per second, like on the order of somethingE15 photons per second. From what I remember of filters neutral density transmission is log, so its pretty easy with a laser power meter to prove a ND2.0 outputs 1e-2 of input photons and turns the remainder of photons into heat or reflects them. Show an easily measurable somethingE15/sec photons out of a laser and the meter will read 1% power. Now you can buy neutral density filters of all kinds of measurable density. And filters stack, 1% of 1% is what you'd expect, not something crazy like average or RMS or whatever. So my numbers above might be all messed up but conceptually it boiled down to create a "normal scale human brightness" fountain of a knowable number of photons per second and filter it such that theoretically about one sneaks thru every second or once in awhile or whatever. Unfortunately we didn't have time to fool around with looking at it. From memory, I think we used it as some kind of quantum proof lab. So part one is diffraction patterns prove photons totally are definitely waves, and part two of the lab was this really sensitive photometer (essentially a geiger counter for photons) shows that each light photon is a distinct and countable bullet. And look, varying the density of the filter stack has no effect on the energy of each photon bullet it merely affects the rate at which they arrive isn't quantum mechanics spooky and wonderful? If that wasn't what we did with it, it probably should have been, or at least from memory I think that's pretty close to what we did. I suppose in the modern era lasers are a lot more powerful so you would need a better filter and rather than the weird vacuum tube photon sensor you'd just use a COTS solar panel and measure the single electrons produced by the single photons (within solar panel efficiency correction factor etc) You know whats really fun to do with quantum mechanics, is do a dual slit diffraction graph with a source that's like 1 photon per second so you know the apparatus only has one photon in flight at any given time. Rather than doing the two parts of my undergrad lab separately, do them together. In my infinite spare time that would be fun to build at home. I would imagine it would take a long time to gather the data, perfect for home amateur scientist types. I know what that graph looks like, and it freaks people out every time.
      - nsxwolf 10y ago
        I only understood a tiny bit of what you said, but I do get freaked out by the double slit experiment with single photons. It's like the photon is interfering with versions of itself in alternate universes.
- Immortalin 10y ago
  Can this be used for neutrino detection? Instead of ice + light sensor, you use sweatshop + human. Someone should do the math, perhaps in the right country it is cheaper to use mass indentured labor than electronics. (This is just a thought experiment, I am not supporting sweatshops)
  - flukus 10y ago
    I think the mental pressures from confining people into completely dark rooms underground for hours on end might produce some false positives. Probably wouldn't tell us much about the characteristics of the light either.
    - dalke 10y ago
      We've done it before. Geiger and Marsden were the first to observe what is now often called the Rutherford gold foil experiment, https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experim... . They used a microscope to look at the flashes of fluorescent light created after the alpha particle scatters from the foil. (We could repeat this experiment in upper-level physics lab class. The teacher said it takes about 20 minutes for the eye to become sensitive enough to see flashes. He said then that the eye could see a single photon. Looking around now, I confirmed that papers of the time only said that was needed no more than 10 quanta.) So while there may be some false positives, it's not high enough to make it useless.
  - antognini 10y ago
    I seem to remember doing a similar problem in an order of magnitude astrophysics class I took. We calculated that there were good odds that at least one person on the planet detected a neutrino from Tycho's supernova when it interacted with the vitreous body of the eyeball. (This is from memory, so don't quote me on it --- I may have remembered the sign wrong!)
  - Cerium 10y ago
    This concept is explored in Neal Stephenson's Anathem. To avoid spoilers, I will be vague. One of the orders in the novel runs such an experiment. They have many people watching a pool or water or ice, and they independently record flashes they may see. If everyone sees the same thing, then they have captured a neutrino.
- StanislavPetrov 10y ago
  >We could literally see quantum mechanical behavior with our own eyes! That occurred to me as well as I read that article. It certainly raises some interesting questions about potential observations and wavefunction collapse.
- noobermin 10y ago
  Just to note, they do hint at that in the end of the article, so you bet your socks scientists are thinking about it. It certainly was one of the first thing that entered my mind.
- grondilu 10y ago
  If you see anything it would mean that the photon had been entangled with your retina, your visual nerve and your brain. All those being macroscopic objects, you could not see any quantum behavior. I'm not sure what would you expect to see anyway. A photon in two places at once? That's not how it works. The wave function tells you where a particle can be detected, and that can be in several places, but in the end it is only actually detected in only one of those places.
- IshKebab 10y ago
  They couldn't reliably detect single photons. Being able to see one in every thousand single photons would still count as being able to see them. Anyway there was an article on Ars recently about directly observing entanglement, so it's kind of already been done.
- biswaroop 10y ago
  A lot of the tests of single-photon entanglement require coincidence measurements: being able to detect if two photons arrived at the same time. I'm not sure how fast the human brain would be for these kinds of measurements. People usually use FPGA-based amplifiers with fast photodiodes.
- tim333 10y ago
  Yeah I was thinking cool, you could use cinema 3d specs for the polarizers and just need a source of entangled photons. The latter seems tricky though - all the sources I could find are infrared or lower frequency and so wouldn't be visible. Some info here http://physics.stackexchange.com/questions/172159/what-laser-and-bbo-are-needed-to-create-entangled-laser-streams http://physics.stackexchange.com/questions/172159/what-laser...
Hydraulix989 10y ago
People can hear single frequencies too
- 1_listerine_pls 10y ago
  A photon is not a frequency.
  - cee_el2 10y ago
    But both the sound the frequency of which we hear and the photon which we sense.. are waves
    - antoineMoPa 10y ago
      Wave vs particle all over again
      - ccozan 10y ago
        But we don't "see" imdividual photons. The cell reacts to a chemical reaction/ absorbtion in the photopigment, thus dependent of the energy of the photon, which is directly related to the frequency of the wave duality of that photon.
        function_seven 10y ago
        > The cell reacts to a chemical reaction/ absorbtion in the photopigment, thus dependent of the energy of the photon, which is directly related to the frequency of the wave duality of that photon. This is what we call "seeing" :) This is like saying the atoms in your fingertip never "touch" the elevator button's atoms. Instead, a strong oppositional force develops when the atoms in your skin get close to the atoms in the button. While true, that's exactly what we call "touching"
    - noobermin 10y ago
      Look, I'm in laser plasma physics, and people conflate photons and monochromatic plane waves in my field all the fucking time. Even worse, they conflate plasma waves with phonons * shudder * . There is similar mathematics that describe both but conceptually they are different things.
kirrent 10y ago
"Some physicists have suggested that such experiments could test whether a superposition of two states could survive in a person's sensory system, and perhaps be perceived in the brain." This sentence surprises me. I would have thought that maintaining coherence during the interaction with someone's eyes would be impossible. Does anyone know anything in more detail about this part?
Thrender 10y ago
What's sticking out to me is that they definitely showed individuals can detect a single photon in some sense, but they did so statistically-- No individual was ever confident that any single event happened. There's something really philosophically fascinating going on here that I can't quite articulate. It's like, did some people really see single photons? Or did the group collectively see a photon packet?
- ccvannorman 10y ago
  Why don't you conduct another experiment with paramaters to answer that question, thus observing and collapsing the possibility space of distributed photon wave collapse observations into a single reality state?
- deleted 10y ago
  [deleted]
white-flame 10y ago
If you pay close attention in very low level light situations, you'll notice that what you do see (or at least what I see) is actually reminiscent of the RGB graininess of low level light photographs. That graininess is to my understanding caused by the variation of the number of photons hitting that portion of the receptors, which is unnoticeable when flooded with quadjillions of them in decent lighting. So this is a nice semi-expected result in this experiment, though it does seem to be near the limit of default human perception. I wonder how well somebody could train themselves to notice single-photon events, much like musicians can notice tiny audio events and variations.
- Thrender 10y ago
  Probably at this stage it's all about reducing the noise. I'm not sure what that means, maybe cooling your eyeballs?
  - 50CNT 10y ago
    I'm not a medical professional, but I believe that would impede their function. Eyelids weren't designed to clear off frost.
    - baq 10y ago
      they're designed to not freeze in the first place: see all the people who've been to the poles and retained sight.
  - milcron 10y ago
    Related - this was on HN just the other day. Birds have a "hyperuniform" distribution of rods and cones which is superior to our own. https://www.quantamagazine.org/20160712-hyperuniformity-found-in-birds-math-and-physics/ https://www.quantamagazine.org/20160712-hyperuniformity-foun...
    - beefield 10y ago
      Sorry for being lazy and not doing proper research, but maybe someone knows this right away. Is Sobol sequence hyperuniform? If not, is there an algorithm you can use to generate hyperuniform random variables? (Basically I am thinking that it could make Monte Carlo simulation in some circumstances a bit more effective)
cantrevealname 10y ago
In a related vein, the kid who built a fusion reactor in his bedroom--which was on the HN front page the other day--had a fascinating comment about visualizing a single neutron: Q: How does one detect fast neutrons? A: Neutron bubble dosimeter. It is basically a tube full of gel suspending small drops of a special liquid. If a fast neutron strikes one of these droplets, the drop vaporizes and turns into a visible bubble. It still amazes me that a single neutron has enough energy to make its presence known to my naked eye.[1] [1] https://www.reddit.com/r/IAmA/comments/4tgsaz/iama_i_built_a_fusion_reactor_in_my_bedroom_ama/d5hbr6r https://www.reddit.com/r/IAmA/comments/4tgsaz/iama_i_built_a...
- taneq 10y ago
  Likewise similar, "cosmic ray visual phenomena": https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena
srtjstjsj 10y ago
> Considering only the answers with the high-confidence R3 rating, we found that the probability of providing the correct response was significantly elevated compared with all responses (0.60±0.03, P=0.0010), For "high-confidence", that's a massive false-positive rate.
- frozenport 10y ago
  Nice catch, these error bars are enough to call bullshit on the whole thing.
- Noseshine 10y ago
  You misunderstand and subsequently misrepresent the whole experiment and paper. Nobody but headliners (people only reading the headline) and overexcitable readers even tries to make this about "we can reliably detect single photon events". Yes that's what the headline seems to say. The detection is clearly much better than chance. This is about exploring the absolute lower limit of human perception. It is not about "we can 'see' single photons", even though that's not even wrong - we sort-of can, the experiment shows we have a chance higher than random. On that low level it isn't about absolutes but about statistics. I'm really disappointed in the comments here, the first time I saw this - was it on HN too not that many days ago? - comments were a lot better. Do't use a tabloid-paper interpretation and do read the actual paper too, as always headlines are useless.
blazespin 10y ago
A lovely thought, but how do we know they didn't just sense some vibration caused by an electrical surge in the machine firing the photon.
inlineint 10y ago
The statement about detecting a single photon by an eye is new (and possibly contradictory), but detection of a very few number of photons by human eye is not a new thing. Cherenkov radiation[1] was discovered by observing a very small number of photons (actually only a few of them) in short time interval by eyes. The experiments were conducted this way because there were no sensitive enough photodetectors in 1930s, so the eyes were the most sensitive available tool for this kind of experiments. Eyes of a physicist were prepared to the experiments by being in complete darkness for a few hours before the measurements. Description of the experimental procedure can be found here[2]. [1] https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation [2] http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c.1161/pdf http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c....
- Someone 10y ago
  It isn't even completely new. Its hard to Google how that this paper is new, but the claim has been made decaden ago. https://en.m.wikipedia.org/wiki/Absolute_threshold#Vision https://en.m.wikipedia.org/wiki/Absolute_threshold#Vision: "1972 Sakitt conducted an experiment that combined elements of signal detection and threshold theory. Two key elements of the study were a high tolerance for false positives and a multiple-choice option on deciding whether or not a light was seen. In the classic studies described above, the tolerance for false positives was so low that threshold was biased upward. Based on statistical analysis of a large number of trials, 6 photons each absorbed by one rod near-simultaneously looked "very bright," 5 photons looked "bright," 4 photons "a moderate light," 3 photons "a dim light." Two observers were able to see 2 photons as "slightly doubtful if a light was seen." One observer saw a single photon as "very doubtful if a light was seen." Zero photons were seen as "did not see anything." One thing to note is that these experiments are hard to do. Dark adaptation (https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Dark_adaptation https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Dark_adapta...) takes a long time; some researchers claim it continues for up to 24 hours (sorry, can't find a reference) That means sitting in the absolute dark for hours (you will not want to do a few short experiments, as that means dark adapting more times). It's not like you can easily repeat this with Rens of people.
ACow_Adonis 10y ago
Am I the only HN reader whose bullshit detector has gone off and, admittedly without reading the study at this stage (I will attempt to do so when I get home), thinks this has all the hallmarks of future non-reproducible results? A photon? Really? Extraordinary claims require extraordinary evidence...and to me that's a pretty extraordinary claim. And yet when I read the report it sounds like a probability based argument from a group of 3? ESP trials all over again anyone? I mean, as scientists, I feel we should be cynical/skeptical...
- noobermin 10y ago
  You can also see it this way: There exist (∃) some detectors which are also human males. These three males have been statistically proven to detect single hit photons at a rate greater than chance. Yes, you are right, this doesn't suggest all humans or even most humans (discounting the blind and individuals with poor sight) can detect single photons, but they certainly have characterized these three individuals.
- suchow 10y ago
  It's reasonable to be skeptical, but it is even more reasonable to evaluate a peer-reviewed publication in one of the most rigorous subfields of psychology (sensation & perception) after having read at least its abstract, ideally the whole paper.
  - dalke 10y ago
    Especially when papers before it have established that at most only a few photons were needed for perception. The very first line is: "Landmark experiments by Hecht and colleagues in the 1940s established that dark-adapted human subjects are capable of reporting light signals as low as a few photons (~5–7)." Looking around, http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1979.sp012716/abstract?cited-by=yes&288/1/613 http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1979.sp0... is a 1979 paper showing that a toad retina can respond to a single photon. The claim from this new paper doesn't seem that extraordinary given what's been known for decades.
- mattkrause 10y ago
jkot 10y ago
I am in skywatcher group, we travel to Atacama desert... One of the experiments we did was determining maximal visual magnitude. My friend was able to see 8.1 magnitude star with 90% probability. We counted stars in triangles, 2nd person prepared maps and validated results.
Quai 10y ago
The BS-factor is high on this one.. "An ideal single-photon source has yet to be created." https://en.wikipedia.org/wiki/Single-photon_source https://en.wikipedia.org/wiki/Single-photon_source Still, detection of single particles has been hinted to during the Apollo program; https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena
- T0T0R0 10y ago
  Rationale for disbelief: - Ambient human body temperature is a constant source of noise as infrared photons. - In a dark, cold environment the human body is radiating a constant shower of photons in a limited spectrum. Interference patterns could augment paths and energies of photons in flight. - A human might simply guess at sensations and produce statistical anomalies that we want to believe in. - A guessing human might intuitively gain an understanding of implicit tells in the detection process, and notice cues from the researchers, and interpret behavioral signals to provide affirmative responses to stimuli. - How many photons can an individual simply think into existence by willful thought? Who's to say that the test subjects aren't detecting psychic brain waves from the researchers, by way of Vulcan mind melds and subsequent "remote viewing" events? ...after all, photons are tiny.
  - theon144 10y ago
    > - Ambient human body temperature is a > constant source of noise as infrared > photons. Which are outside of the visible range, and wouldn't interfere with the experiment, assuming they used visible range photons (the article doesn't mention this, but why would they not). > - A human might simply guess at sensations > and produce statistical anomalies that we > want to believe in. Isn't literally any study susceptible to this? Besides: "Still, participants were able to answer correctly more frequently than would be expected if they had guessed at random — and their confidence level was higher when they were right." suggests this wasn't an one-off anomaly. (Although N=3 nonetheles...) > - A guessing human might intuitively gain > an understanding of implicit tells in the > detection process, and notice cues from > the researchers, and interpret behavioral > signals to provide affirmative responses > to stimuli. I think the researchers might have heard of the double-blind method. > - How many photons can an individual simply > think into existence by willful thought? > Who's to say that the test subjects aren't > detecting psychic brain waves from the > researchers, by way of Vulcan mind melds > and subsequent "remote viewing" events? I might be missing a joke?
retrogradeorbit 10y ago
This reminds me of F. Alton Everest's notes in "The Master Handbook of Acoustics" that the threshold of hearing lies coincident with the SPL of Brownian motion of air particles on the ear drum... except this is with respect to light.
tintor 10y ago
Tested on 3 people only.
- cespare 10y ago
  I don't count that against this study -- it isn't about determining the effects of a drug or something like that. If we can show that there exists one person that can detect a single photon in a statistically significant way (vs random guessing), that still seems like a fascinating result.
lagudragu 10y ago
I'm honestly a bit surprised that such an article is placed in Nature, as there seem to be a couple questionable details in the article regarding the experiment: - Only 3 volunteers on which the experiment has been tested - The volunteers were left "in total darkness for around 40 minutes" before the actual experiment - "In many cases, they got it wrong; this is to be expected, given that more than 90% of photons that enter the front of the eye never even reach a rod cell, because they are absorbed or reflected by other parts of the eye. Still, participants were able to answer correctly more frequently than would be expected if they had guessed at random and their confidence level was higher when they were right." - The three volunteers sat through a total of more than 2,400 trials in which a single photon was emitted (and many more in which it was not). - That high volume of testing, the researchers say, gives them strong statistical evidence of single-photon detection - The participants had to say on which occasion they thought they saw a photon, and how confident they were (on a scale of 1 to 3) about their sighting. In summation, they put 3 volunteers for 40 minutes in total darkness, then performed more than 2400 trials in total (i assume 1000+ trials per person, taking into account the tests in which no photon was emmitted). "Many" times the volunteers guessed wrong, but when they guessed right they were pretty confident of it (using a rather simplistic scale of 1-3). What I'm seeing with this experiment is a result which is more confirmed due to psychological bias rather than actual results by putting these volunteers in a straining test. How would you, as a volunteer react, if you were left in the darkness for such a long test duration and would asked over a 1000 times whether you have seen a flash. Edit: After having read the actual paper on the methodology, I do retract my comment.
- Retr0spectrum 10y ago
  I haven't read the full paper, so this is only speculation. I expect they would have counted the number of times the volunteers claimed to have seen a photon, both when a photon was emitted, and when they only said that one was emitted. If the detection rate is significantly higher for "real" emissions than for the "fake" emissions, then you can draw a statistically significant conclusion (aside from the fact that there were only 3 test subjects).
- suchow 10y ago
  In the typical psychophysical study on perceptual thresholds, participants are given a two-alternative forced-choice test: a stimulus (here, a photon) is placed in one of two intervals at random, and the participant guesses which interval had the photon. Using this design, a bias that systematically selects one response more often than the other will lead to performance below chance. Finding that performance is significantly better than chance is evidence that the observer can detect a single photon. Demonstrating that performance is reliably above chance requires many trials because the level of performance is close to chance. Compare this to a yes/no design, where a bias can create the appearance of an ability to detect a single photon where there is none. The reason for waiting 40 minutes is that the eye and brain adapt to darkness. If this experiment were performed outside in daylight, it would be impossible to detect a difference of 1 photon. Only when the observer sits in a room without light can the brain adapt and have its greatest sensitivity to light. Finally, note that the logic of this study is an existence proof that people can detect single photons. Selecting three normal observers and finding that all of them have this capability is reasonable evidence that most normal observers can do the same, unless you have some specific reason to believe that these observers are unrepresentative of the population (as the researcher in the press release did re gender differences).
hmate9 10y ago
I knew I just felt something brush against me
TheRealPomax 10y ago
Of course the real test here will be a duplication study, but with more than three test subjects. The selection bias in the study as performed is essentially unacceptably huge.
runeks 10y ago
If the eye can detect a single photon, it must mean that the triggering system in the human eye, which starts the electrical signal that carries the visual information to the brain, needs less energy than a photon contains to be triggered. That's pretty amazing to me. How many photons does a CCD chip need to change one pixel from pitch black? A billion? 1e20? I'm curious to know. If we could figure out how this triggering system works, we could build amazing stuff. Probably more than really good camera chips.
- mtreis86 10y ago
  From https://en.wikipedia.org/wiki/Rod_cell https://en.wikipedia.org/wiki/Rod_cell "Activation of a single unit of rhodopsin, the photosensitive pigment in rods, can lead to a large reaction in the cell because the signal is amplified. Once activated, rhodopsin can activate hundreds of transducin molecules, each of which in turn activates a phosphodiesterase molecule, which can break down over a thousand cGMP molecules per second (Kandel et al. 2000). Thus, rods can have a large response to a small amount of light."
- danarlow 10y ago
  Electron multiplying CCD cameras can respond to single photons with > 90% quantum efficiency [1] -- that's better than rhodopsin. (I use one on a semi-daily basis.) To take advantage of that sensitivity you need to cool the sensor to -80°C so that thermal noise doesn't swamp your signal, but obviously you can't do that with your eyes. [1] http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-comparisons-difference-between-the-sensors http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-co...
  - runeks 10y ago
    That's pretty cool! Would you happen to know how many photons it takes to activate the average consumer CCD?

194 points by mathgenius 10y ago

You know how cool this is?! It should be possible to set up an experiment with entangled photons and use your eyes as the detector. We could literally see quantum mechanical behavior with our own eyes! Pardon my crudeness but how fucking cool is that!

markcerqueira 10y ago
Just tried this experiment at home! Felt about one photon in my left eye and two in my right in one minute!! :D
- nsxwolf 10y ago
  What's your source of single photons?
  - markcerqueira 10y ago
    Forgot the margin of error! +/- 2 photons!!! :D :D :D
  - VLM 10y ago
    A quarter century ago we used a well characterized laser at a known power level that given a very precise wavelength and total power results in a very precise number of photons per second, like on the order of somethingE15 photons per second. From what I remember of filters neutral density transmission is log, so its pretty easy with a laser power meter to prove a ND2.0 outputs 1e-2 of input photons and turns the remainder of photons into heat or reflects them. Show an easily measurable somethingE15/sec photons out of a laser and the meter will read 1% power. Now you can buy neutral density filters of all kinds of measurable density. And filters stack, 1% of 1% is what you'd expect, not something crazy like average or RMS or whatever. So my numbers above might be all messed up but conceptually it boiled down to create a "normal scale human brightness" fountain of a knowable number of photons per second and filter it such that theoretically about one sneaks thru every second or once in awhile or whatever. Unfortunately we didn't have time to fool around with looking at it. From memory, I think we used it as some kind of quantum proof lab. So part one is diffraction patterns prove photons totally are definitely waves, and part two of the lab was this really sensitive photometer (essentially a geiger counter for photons) shows that each light photon is a distinct and countable bullet. And look, varying the density of the filter stack has no effect on the energy of each photon bullet it merely affects the rate at which they arrive isn't quantum mechanics spooky and wonderful? If that wasn't what we did with it, it probably should have been, or at least from memory I think that's pretty close to what we did. I suppose in the modern era lasers are a lot more powerful so you would need a better filter and rather than the weird vacuum tube photon sensor you'd just use a COTS solar panel and measure the single electrons produced by the single photons (within solar panel efficiency correction factor etc) You know whats really fun to do with quantum mechanics, is do a dual slit diffraction graph with a source that's like 1 photon per second so you know the apparatus only has one photon in flight at any given time. Rather than doing the two parts of my undergrad lab separately, do them together. In my infinite spare time that would be fun to build at home. I would imagine it would take a long time to gather the data, perfect for home amateur scientist types. I know what that graph looks like, and it freaks people out every time.
    - nsxwolf 10y ago
      I only understood a tiny bit of what you said, but I do get freaked out by the double slit experiment with single photons. It's like the photon is interfering with versions of itself in alternate universes.
Immortalin 10y ago
Can this be used for neutrino detection? Instead of ice + light sensor, you use sweatshop + human. Someone should do the math, perhaps in the right country it is cheaper to use mass indentured labor than electronics. (This is just a thought experiment, I am not supporting sweatshops)
- flukus 10y ago
  I think the mental pressures from confining people into completely dark rooms underground for hours on end might produce some false positives. Probably wouldn't tell us much about the characteristics of the light either.
  - dalke 10y ago
    We've done it before. Geiger and Marsden were the first to observe what is now often called the Rutherford gold foil experiment, https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experiment https://en.wikipedia.org/wiki/Geiger%E2%80%93Marsden_experim... . They used a microscope to look at the flashes of fluorescent light created after the alpha particle scatters from the foil. (We could repeat this experiment in upper-level physics lab class. The teacher said it takes about 20 minutes for the eye to become sensitive enough to see flashes. He said then that the eye could see a single photon. Looking around now, I confirmed that papers of the time only said that was needed no more than 10 quanta.) So while there may be some false positives, it's not high enough to make it useless.
- antognini 10y ago
  I seem to remember doing a similar problem in an order of magnitude astrophysics class I took. We calculated that there were good odds that at least one person on the planet detected a neutrino from Tycho's supernova when it interacted with the vitreous body of the eyeball. (This is from memory, so don't quote me on it --- I may have remembered the sign wrong!)
- Cerium 10y ago
  This concept is explored in Neal Stephenson's Anathem. To avoid spoilers, I will be vague. One of the orders in the novel runs such an experiment. They have many people watching a pool or water or ice, and they independently record flashes they may see. If everyone sees the same thing, then they have captured a neutrino.
StanislavPetrov 10y ago
>We could literally see quantum mechanical behavior with our own eyes! That occurred to me as well as I read that article. It certainly raises some interesting questions about potential observations and wavefunction collapse.
noobermin 10y ago
Just to note, they do hint at that in the end of the article, so you bet your socks scientists are thinking about it. It certainly was one of the first thing that entered my mind.
grondilu 10y ago
If you see anything it would mean that the photon had been entangled with your retina, your visual nerve and your brain. All those being macroscopic objects, you could not see any quantum behavior. I'm not sure what would you expect to see anyway. A photon in two places at once? That's not how it works. The wave function tells you where a particle can be detected, and that can be in several places, but in the end it is only actually detected in only one of those places.
IshKebab 10y ago
They couldn't reliably detect single photons. Being able to see one in every thousand single photons would still count as being able to see them. Anyway there was an article on Ars recently about directly observing entanglement, so it's kind of already been done.
biswaroop 10y ago
A lot of the tests of single-photon entanglement require coincidence measurements: being able to detect if two photons arrived at the same time. I'm not sure how fast the human brain would be for these kinds of measurements. People usually use FPGA-based amplifiers with fast photodiodes.
tim333 10y ago
Yeah I was thinking cool, you could use cinema 3d specs for the polarizers and just need a source of entangled photons. The latter seems tricky though - all the sources I could find are infrared or lower frequency and so wouldn't be visible. Some info here http://physics.stackexchange.com/questions/172159/what-laser-and-bbo-are-needed-to-create-entangled-laser-streams http://physics.stackexchange.com/questions/172159/what-laser...

Hydraulix989 10y ago

People can hear single frequencies too

1_listerine_pls 10y ago
A photon is not a frequency.
- cee_el2 10y ago
  But both the sound the frequency of which we hear and the photon which we sense.. are waves
  - antoineMoPa 10y ago
    Wave vs particle all over again
    - ccozan 10y ago
      But we don't "see" imdividual photons. The cell reacts to a chemical reaction/ absorbtion in the photopigment, thus dependent of the energy of the photon, which is directly related to the frequency of the wave duality of that photon.
      - function_seven 10y ago
        > The cell reacts to a chemical reaction/ absorbtion in the photopigment, thus dependent of the energy of the photon, which is directly related to the frequency of the wave duality of that photon. This is what we call "seeing" :) This is like saying the atoms in your fingertip never "touch" the elevator button's atoms. Instead, a strong oppositional force develops when the atoms in your skin get close to the atoms in the button. While true, that's exactly what we call "touching"
  - noobermin 10y ago
    Look, I'm in laser plasma physics, and people conflate photons and monochromatic plane waves in my field all the fucking time. Even worse, they conflate plasma waves with phonons * shudder * . There is similar mathematics that describe both but conceptually they are different things.

kirrent 10y ago

"Some physicists have suggested that such experiments could test whether a superposition of two states could survive in a person's sensory system, and perhaps be perceived in the brain." This sentence surprises me. I would have thought that maintaining coherence during the interaction with someone's eyes would be impossible. Does anyone know anything in more detail about this part?

Thrender 10y ago

What's sticking out to me is that they definitely showed individuals can detect a single photon in some sense, but they did so statistically-- No individual was ever confident that any single event happened. There's something really philosophically fascinating going on here that I can't quite articulate. It's like, did some people really see single photons? Or did the group collectively see a photon packet?

ccvannorman 10y ago
Why don't you conduct another experiment with paramaters to answer that question, thus observing and collapsing the possibility space of distributed photon wave collapse observations into a single reality state?
deleted 10y ago
[deleted]

white-flame 10y ago

If you pay close attention in very low level light situations, you'll notice that what you do see (or at least what I see) is actually reminiscent of the RGB graininess of low level light photographs. That graininess is to my understanding caused by the variation of the number of photons hitting that portion of the receptors, which is unnoticeable when flooded with quadjillions of them in decent lighting. So this is a nice semi-expected result in this experiment, though it does seem to be near the limit of default human perception. I wonder how well somebody could train themselves to notice single-photon events, much like musicians can notice tiny audio events and variations.

Thrender 10y ago
Probably at this stage it's all about reducing the noise. I'm not sure what that means, maybe cooling your eyeballs?
- 50CNT 10y ago
  I'm not a medical professional, but I believe that would impede their function. Eyelids weren't designed to clear off frost.
  - baq 10y ago
    they're designed to not freeze in the first place: see all the people who've been to the poles and retained sight.
- milcron 10y ago
  Related - this was on HN just the other day. Birds have a "hyperuniform" distribution of rods and cones which is superior to our own. https://www.quantamagazine.org/20160712-hyperuniformity-found-in-birds-math-and-physics/ https://www.quantamagazine.org/20160712-hyperuniformity-foun...
  - beefield 10y ago
    Sorry for being lazy and not doing proper research, but maybe someone knows this right away. Is Sobol sequence hyperuniform? If not, is there an algorithm you can use to generate hyperuniform random variables? (Basically I am thinking that it could make Monte Carlo simulation in some circumstances a bit more effective)

cantrevealname 10y ago

In a related vein, the kid who built a fusion reactor in his bedroom--which was on the HN front page the other day--had a fascinating comment about visualizing a single neutron: Q: How does one detect fast neutrons? A: Neutron bubble dosimeter. It is basically a tube full of gel suspending small drops of a special liquid. If a fast neutron strikes one of these droplets, the drop vaporizes and turns into a visible bubble. It still amazes me that a single neutron has enough energy to make its presence known to my naked eye.[1] [1] https://www.reddit.com/r/IAmA/comments/4tgsaz/iama_i_built_a_fusion_reactor_in_my_bedroom_ama/d5hbr6r https://www.reddit.com/r/IAmA/comments/4tgsaz/iama_i_built_a...

taneq 10y ago
Likewise similar, "cosmic ray visual phenomena": https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena

srtjstjsj 10y ago

> Considering only the answers with the high-confidence R3 rating, we found that the probability of providing the correct response was significantly elevated compared with all responses (0.60±0.03, P=0.0010), For "high-confidence", that's a massive false-positive rate.

frozenport 10y ago
Nice catch, these error bars are enough to call bullshit on the whole thing.
Noseshine 10y ago
You misunderstand and subsequently misrepresent the whole experiment and paper. Nobody but headliners (people only reading the headline) and overexcitable readers even tries to make this about "we can reliably detect single photon events". Yes that's what the headline seems to say. The detection is clearly much better than chance. This is about exploring the absolute lower limit of human perception. It is not about "we can 'see' single photons", even though that's not even wrong - we sort-of can, the experiment shows we have a chance higher than random. On that low level it isn't about absolutes but about statistics. I'm really disappointed in the comments here, the first time I saw this - was it on HN too not that many days ago? - comments were a lot better. Do't use a tabloid-paper interpretation and do read the actual paper too, as always headlines are useless.

blazespin 10y ago

A lovely thought, but how do we know they didn't just sense some vibration caused by an electrical surge in the machine firing the photon.

inlineint 10y ago

The statement about detecting a single photon by an eye is new (and possibly contradictory), but detection of a very few number of photons by human eye is not a new thing. Cherenkov radiation[1] was discovered by observing a very small number of photons (actually only a few of them) in short time interval by eyes. The experiments were conducted this way because there were no sensitive enough photodetectors in 1930s, so the eyes were the most sensitive available tool for this kind of experiments. Eyes of a physicist were prepared to the experiments by being in complete darkness for a few hours before the measurements. Description of the experimental procedure can be found here[2]. [1] https://en.wikipedia.org/wiki/Cherenkov_radiation https://en.wikipedia.org/wiki/Cherenkov_radiation [2] http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c.1161/pdf http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c....

Someone 10y ago
It isn't even completely new. Its hard to Google how that this paper is new, but the claim has been made decaden ago. https://en.m.wikipedia.org/wiki/Absolute_threshold#Vision https://en.m.wikipedia.org/wiki/Absolute_threshold#Vision: "1972 Sakitt conducted an experiment that combined elements of signal detection and threshold theory. Two key elements of the study were a high tolerance for false positives and a multiple-choice option on deciding whether or not a light was seen. In the classic studies described above, the tolerance for false positives was so low that threshold was biased upward. Based on statistical analysis of a large number of trials, 6 photons each absorbed by one rod near-simultaneously looked "very bright," 5 photons looked "bright," 4 photons "a moderate light," 3 photons "a dim light." Two observers were able to see 2 photons as "slightly doubtful if a light was seen." One observer saw a single photon as "very doubtful if a light was seen." Zero photons were seen as "did not see anything." One thing to note is that these experiments are hard to do. Dark adaptation (https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Dark_adaptation https://en.m.wikipedia.org/wiki/Adaptation_(eye)#Dark_adapta...) takes a long time; some researchers claim it continues for up to 24 hours (sorry, can't find a reference) That means sitting in the absolute dark for hours (you will not want to do a few short experiments, as that means dark adapting more times). It's not like you can easily repeat this with Rens of people.

ACow_Adonis 10y ago

Am I the only HN reader whose bullshit detector has gone off and, admittedly without reading the study at this stage (I will attempt to do so when I get home), thinks this has all the hallmarks of future non-reproducible results? A photon? Really? Extraordinary claims require extraordinary evidence...and to me that's a pretty extraordinary claim. And yet when I read the report it sounds like a probability based argument from a group of 3? ESP trials all over again anyone? I mean, as scientists, I feel we should be cynical/skeptical...

noobermin 10y ago
You can also see it this way: There exist (∃) some detectors which are also human males. These three males have been statistically proven to detect single hit photons at a rate greater than chance. Yes, you are right, this doesn't suggest all humans or even most humans (discounting the blind and individuals with poor sight) can detect single photons, but they certainly have characterized these three individuals.
suchow 10y ago
It's reasonable to be skeptical, but it is even more reasonable to evaluate a peer-reviewed publication in one of the most rigorous subfields of psychology (sensation & perception) after having read at least its abstract, ideally the whole paper.
- dalke 10y ago
  Especially when papers before it have established that at most only a few photons were needed for perception. The very first line is: "Landmark experiments by Hecht and colleagues in the 1940s established that dark-adapted human subjects are capable of reporting light signals as low as a few photons (~5–7)." Looking around, http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1979.sp012716/abstract?cited-by=yes&288/1/613 http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1979.sp0... is a 1979 paper showing that a toad retina can respond to a single photon. The claim from this new paper doesn't seem that extraordinary given what's been known for decades.
mattkrause 10y ago

jkot 10y ago

I am in skywatcher group, we travel to Atacama desert... One of the experiments we did was determining maximal visual magnitude. My friend was able to see 8.1 magnitude star with 90% probability. We counted stars in triangles, 2nd person prepared maps and validated results.

Quai 10y ago

The BS-factor is high on this one.. "An ideal single-photon source has yet to be created." https://en.wikipedia.org/wiki/Single-photon_source https://en.wikipedia.org/wiki/Single-photon_source Still, detection of single particles has been hinted to during the Apollo program; https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena

T0T0R0 10y ago
Rationale for disbelief: - Ambient human body temperature is a constant source of noise as infrared photons. - In a dark, cold environment the human body is radiating a constant shower of photons in a limited spectrum. Interference patterns could augment paths and energies of photons in flight. - A human might simply guess at sensations and produce statistical anomalies that we want to believe in. - A guessing human might intuitively gain an understanding of implicit tells in the detection process, and notice cues from the researchers, and interpret behavioral signals to provide affirmative responses to stimuli. - How many photons can an individual simply think into existence by willful thought? Who's to say that the test subjects aren't detecting psychic brain waves from the researchers, by way of Vulcan mind melds and subsequent "remote viewing" events? ...after all, photons are tiny.
- theon144 10y ago
  > - Ambient human body temperature is a > constant source of noise as infrared > photons. Which are outside of the visible range, and wouldn't interfere with the experiment, assuming they used visible range photons (the article doesn't mention this, but why would they not). > - A human might simply guess at sensations > and produce statistical anomalies that we > want to believe in. Isn't literally any study susceptible to this? Besides: "Still, participants were able to answer correctly more frequently than would be expected if they had guessed at random — and their confidence level was higher when they were right." suggests this wasn't an one-off anomaly. (Although N=3 nonetheles...) > - A guessing human might intuitively gain > an understanding of implicit tells in the > detection process, and notice cues from > the researchers, and interpret behavioral > signals to provide affirmative responses > to stimuli. I think the researchers might have heard of the double-blind method. > - How many photons can an individual simply > think into existence by willful thought? > Who's to say that the test subjects aren't > detecting psychic brain waves from the > researchers, by way of Vulcan mind melds > and subsequent "remote viewing" events? I might be missing a joke?

retrogradeorbit 10y ago

This reminds me of F. Alton Everest's notes in "The Master Handbook of Acoustics" that the threshold of hearing lies coincident with the SPL of Brownian motion of air particles on the ear drum... except this is with respect to light.

tintor 10y ago

Tested on 3 people only.

cespare 10y ago
I don't count that against this study -- it isn't about determining the effects of a drug or something like that. If we can show that there exists one person that can detect a single photon in a statistically significant way (vs random guessing), that still seems like a fascinating result.

lagudragu 10y ago

I'm honestly a bit surprised that such an article is placed in Nature, as there seem to be a couple questionable details in the article regarding the experiment: - Only 3 volunteers on which the experiment has been tested - The volunteers were left "in total darkness for around 40 minutes" before the actual experiment - "In many cases, they got it wrong; this is to be expected, given that more than 90% of photons that enter the front of the eye never even reach a rod cell, because they are absorbed or reflected by other parts of the eye. Still, participants were able to answer correctly more frequently than would be expected if they had guessed at random and their confidence level was higher when they were right." - The three volunteers sat through a total of more than 2,400 trials in which a single photon was emitted (and many more in which it was not). - That high volume of testing, the researchers say, gives them strong statistical evidence of single-photon detection - The participants had to say on which occasion they thought they saw a photon, and how confident they were (on a scale of 1 to 3) about their sighting. In summation, they put 3 volunteers for 40 minutes in total darkness, then performed more than 2400 trials in total (i assume 1000+ trials per person, taking into account the tests in which no photon was emmitted). "Many" times the volunteers guessed wrong, but when they guessed right they were pretty confident of it (using a rather simplistic scale of 1-3). What I'm seeing with this experiment is a result which is more confirmed due to psychological bias rather than actual results by putting these volunteers in a straining test. How would you, as a volunteer react, if you were left in the darkness for such a long test duration and would asked over a 1000 times whether you have seen a flash. Edit: After having read the actual paper on the methodology, I do retract my comment.

Retr0spectrum 10y ago
I haven't read the full paper, so this is only speculation. I expect they would have counted the number of times the volunteers claimed to have seen a photon, both when a photon was emitted, and when they only said that one was emitted. If the detection rate is significantly higher for "real" emissions than for the "fake" emissions, then you can draw a statistically significant conclusion (aside from the fact that there were only 3 test subjects).
suchow 10y ago
In the typical psychophysical study on perceptual thresholds, participants are given a two-alternative forced-choice test: a stimulus (here, a photon) is placed in one of two intervals at random, and the participant guesses which interval had the photon. Using this design, a bias that systematically selects one response more often than the other will lead to performance below chance. Finding that performance is significantly better than chance is evidence that the observer can detect a single photon. Demonstrating that performance is reliably above chance requires many trials because the level of performance is close to chance. Compare this to a yes/no design, where a bias can create the appearance of an ability to detect a single photon where there is none. The reason for waiting 40 minutes is that the eye and brain adapt to darkness. If this experiment were performed outside in daylight, it would be impossible to detect a difference of 1 photon. Only when the observer sits in a room without light can the brain adapt and have its greatest sensitivity to light. Finally, note that the logic of this study is an existence proof that people can detect single photons. Selecting three normal observers and finding that all of them have this capability is reasonable evidence that most normal observers can do the same, unless you have some specific reason to believe that these observers are unrepresentative of the population (as the researcher in the press release did re gender differences).

hmate9 10y ago

I knew I just felt something brush against me

TheRealPomax 10y ago

Of course the real test here will be a duplication study, but with more than three test subjects. The selection bias in the study as performed is essentially unacceptably huge.

runeks 10y ago

If the eye can detect a single photon, it must mean that the triggering system in the human eye, which starts the electrical signal that carries the visual information to the brain, needs less energy than a photon contains to be triggered. That's pretty amazing to me. How many photons does a CCD chip need to change one pixel from pitch black? A billion? 1e20? I'm curious to know. If we could figure out how this triggering system works, we could build amazing stuff. Probably more than really good camera chips.

mtreis86 10y ago
From https://en.wikipedia.org/wiki/Rod_cell https://en.wikipedia.org/wiki/Rod_cell "Activation of a single unit of rhodopsin, the photosensitive pigment in rods, can lead to a large reaction in the cell because the signal is amplified. Once activated, rhodopsin can activate hundreds of transducin molecules, each of which in turn activates a phosphodiesterase molecule, which can break down over a thousand cGMP molecules per second (Kandel et al. 2000). Thus, rods can have a large response to a small amount of light."
danarlow 10y ago
Electron multiplying CCD cameras can respond to single photons with > 90% quantum efficiency [1] -- that's better than rhodopsin. (I use one on a semi-daily basis.) To take advantage of that sensitivity you need to cool the sensor to -80°C so that thermal noise doesn't swamp your signal, but obviously you can't do that with your eyes. [1] http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-comparisons-difference-between-the-sensors http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-co...
- runeks 10y ago
  That's pretty cool! Would you happen to know how many photons it takes to activate the average consumer CCD?