People can sense single photons
nature.com
nature.com
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.
https://www.quantamagazine.org/20160712-hyperuniformity-foun...
Agree, it's not a digital system so there is always some noise, just like you can never get perfect silence in terms of sensory perception. Your brain has also a way to project some kind of images in your mind even when you don't see anything in complete darkness, so it's far from just being the detection of photons.
That's a little different because your body produces lots of noises which are only perceivable in the absence of other background noises, eg when inside an anechoic chamber[1].
The more photons you simulate/see, the less grainy it gets.
Of course, the human eye has no concept of "frames", so it's not easy to directly compare the two.
http://www.corpshumain.ca/en/images/Retine_couches_couleur_(...
Note that the light comes from the TOP and passes through all those layers before hitting the photosensitive one!
So - at the Earth's surface, even on a very dark night, I think you would be receiving far, far too many photons for them to each register as a sort of noise blob. More likely it is the natural noise of your nervous system as it does all the things that cells need to do and produces the slight visible side effect that's more pronounced in darkness and low contrast.
Edit: Also, since I remember this coming up in my neuro classes, this has been shown in less rigorous experimentation before:
http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.h...
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?
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!
Probably wouldn't tell us much about the characteristics of the light either.
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.
Someone should do the math, perhaps in the right country
it is cheaper to use mass indentured labor than
electronics.
They also tend to be good at making cheap electronics.
That occurred to me as well as I read that article. It certainly raises some interesting questions about potential observations and wavefunction collapse.
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.
Anyway there was an article on Ars recently about directly observing entanglement, so it's kind of already been done.
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...
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
[2] http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c....
"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_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.
For "high-confidence", that's a massive false-positive rate.
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.
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?
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.
"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."
[1] http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-co...
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.
"An ideal single-photon source has yet to be created." 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
- 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?
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?
What I can't identify by name is the philosophical arguments in the other statements.
I'm about 90% sure one is a metaphysical Copenhagen interpretation of QM (You've heard of Heisenberg's lucky cat?) but I'm not as certain as the UV catastrophe analogy. Depends how you read it, I guess.
(...and it's Schrödinger's Cat)
If what you say is true then we should have seen a signal from it long ago.
The definition of an _ideal_ source is "that it should be on-demand, efficient, robust and easy to implement." It seems fragile, inefficient and difficult to implement sources have been invented multiple times.
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...
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.
"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.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.
It's been known for a while that humans can detect <SMALLNUM> of photons. I think people have looked at the fine structure of a rod and determined that it should have very high quantum efficiency. Finally, direct measurements of the electrical activity of individual (isolated) rod cells suggests that they do respond to single photons.
However, the intact retina has some "normalization" circuitry, which might wash out the signal from a single rod. Even if it makes it out of the eye, the signal has to pass through a lot of cortical processing before the subject consciously perceives it, so these results are a little surprising. However, there is some data suggesting that rats can detect the activity of a single cell in somatosensory cortex (Houwelling and Brect, 2007)[1], so it seems possible.
In summary, it doesn't seem totally outlandish based on what we already knew but...replications are good.
[1] http://www.nature.com/nature/journal/v451/n7174/full/nature0...
- 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.
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).
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).
Taking the following from the paper:(http://www.nature.com/ncomms/2016/160719/ncomms12172/full/nc...):
Averaging across subjects’ responses and ratings from a total of 30,767 trials, 2,420 single-photon events passed post-selection and we found the averaged probability of correct response to be 0.516±0.010 (P=0.0545; Fig. 2a).
Edit: Having (quickly) read the paper, it does seem the psychology of the volunteers was taken into proper consideration, I stand corrected:
Before collecting data, subjects were extensively trained using a classical light source with photon number between 1 and 15 photons at the cornea (Supplementary Fig. 4a). The improved performance with experience is clearly and quantitatively visible (Supplementary Fig. 4b,c). Subjects typically required 6–8 sessions, performing one session a day, to reach their optimal performance level (Supplementary Fig. 4b,c). Each session took~2 h, when including dark adaption.
During data acquisition, each subject went through up to 20 sessions. Still this high amount of sessions was not enough to obtain statistically significant performance for individual subjects, and therefore we pooled the data together to increase significance (Fig. 2a–d). As subject’s sensitivity and criteria used to assign the confidence ratings might vary in psychophysics trials28, we aimed to minimize or normalize possible factors causing variability to achieve maximum sensitivity and similarity across subjects by using extensive training of the subjects and using our 2AFC paradigm.
Additionally, the research does have interesting observations:
Surprisingly, a strong dependence on the temporal separation of the two events was observed peaking at ~3.5 s, with a decay time on the order of seconds (Fig. 2c). Such a long timescale phenomenon represents more than an order of magnitude disparity with the known integration time of the visual system4. This result directly shows that the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ~5 s time interval.
Thus, consistent with both observations, we suggest that the detection of a single photon – or equally a photon-like noise event (that is, spontaneous isomerization) – temporarily increases the effective gain of the visual system under extreme low-light conditions, such that a second temporally coinciding photon (or photon-like noise event) can be behaviourally detected with a higher probability.
It's not uncommon when you have a cool idea you want to test that doesn't rely on naive subjects and it would take longer to get permission to & recruit outside volunteers -- just grab a few people from around the lab and try it out.
I was in his undergrad quantum physics (for engineers) course at the time.
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"
I want to heat some micro particles in an heterogeneous mixture. However, they need to be heated with precision so that the other components of the mixture don't get melted. So, I was thinking in getting a laser to do that. The laser would need to have a wavelength that targets only the component that I want to heat.
picture I drew http://i.imgur.com/RdWRpnHl.png
Do you think it would be feasible? I am not a physicist.
Now, say one is more polarizable than the other and so is heated first. However, a more important consideration here is that this is a heterogeneous mixture, so I think what is more likely is heat will be even distributed between the species. You're essentially trying to achieve a non-equilibrium state (high temp in one species and not the other) when one species is on top of the other! On shorter time scales, the more polarizable/polarized stuff might be "heated" first but that heat will eventually move to the other species from collisions leading to equal heating.
So it all depends. Will your target species be heated to melting before that heat transfers to other stuff? This does depend on the coupling of the laser energy to the particles but it also depends on the time scale it takes to melt too and the collision frequency between target species and other species. So, as you see, it depends specifically on the materials you're thinking of, which you could probably look up.
Honestly, you could try something much simpler, like just choosing species based on their melting point. Obviously, your question seemed to imply that they melt at similar melting points and you make to make species A melt before species B. If you just choose species with diff species with diff melting points, you don't even need a laser, just a heat bath.
[0] https://en.wikipedia.org/wiki/Dielectric_heating
This might be helpful if you want to learn what effect material properties has on effectiveness of dielectric heating. First google scholar result :)
[1] http://pubs.rsc.org/en/content/articlelanding/1998/cs/a82721...
- Will your target species be heated to melting before that heat transfers to other stuff? = That's the plan, the heat will propagate so I want to apply just enough heat to minimize the amount of heat transferred. They have different melting points: around 50C in difference.
Likewise, the minimum amount of light you can see is not measured in terms of frequency.
In other words, higher frequency does not mean more light or sound.
So, his analogy does not make sense at all.
The correct analogue for sound would be "people can hear single phonons".