
People can sense single photons - mathgenius
http://www.nature.com/news/people-can-sense-single-photons-1.20282
======
white-flame
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
Probably at this stage it's all about reducing the noise. I'm not sure what
that means, maybe cooling your eyeballs?

~~~
milcron
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-
foun...](https://www.quantamagazine.org/20160712-hyperuniformity-found-in-
birds-math-and-physics/)

~~~
beefield
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)

~~~
ravar
If you take the 2d Fourier transform of the sequence and the low frequency
components go to zero the point process is hyper uniform [1] . Poison disk
noise has this property but is generally slow to generate.

[1]
[http://arxiv.org/pdf/1408.4645v1.pdf](http://arxiv.org/pdf/1408.4645v1.pdf)

------
Thrender
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
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?

------
IIAOPSW
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!

~~~
Immortalin
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)

~~~
Cerium
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.

~~~
ajuc
That book is awesome sci-fi for so many reasons.

------
cantrevealname
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...](https://www.reddit.com/r/IAmA/comments/4tgsaz/iama_i_built_a_fusion_reactor_in_my_bedroom_ama/d5hbr6r)

~~~
taneq
Likewise similar, "cosmic ray visual phenomena":
[https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena](https://en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena)

------
inlineint
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....](http://iopscience.iop.org/article/10.3367/UFNe.0179.200911c.1161/pdf)

~~~
Someone
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_adapta...](https://en.m.wikipedia.org/wiki/Adaptation_\(eye\)#Dark_adaptation))
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.

------
srtjstjsj
> 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.

~~~
Noseshine
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.

------
kirrent
"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?

------
runeks
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.

~~~
danarlow
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-
co...](http://www.andor.com/learning-academy/ccd,-emccd-and-iccd-comparisons-
difference-between-the-sensors)

~~~
runeks
That's pretty cool! Would you happen to know how many photons it takes to
activate the average consumer CCD?

------
jkot
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.

------
blazespin
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.

------
retrogradeorbit
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.

------
Quai
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
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
> \- 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?

~~~
VLM
OP is kidding, I can identify the first statement as the pre-quantum
ultraviolet catastrophe argument where everything warmer than absolute zero
should emit one single honkin big gamma ray and drop back to absolute zero,
whereas in practice blackbody radiation doesn't go to infinity with short
wavelengths but goes to a peak (for example "red hot steel")

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.

~~~
T0T0R0
Who are you, and how did you find me???

(...and it's _Schrödinger 's_ Cat)

------
ACow_Adonis
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...

~~~
suchow
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
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.sp0...](http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1979.sp012716/abstract?cited-
by=yes&288/1/613) 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.

------
lagudragu
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.

~~~
suchow
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).

~~~
suchow
I have a slight correction to my earlier comment, in which I said "Using this
design, a bias that systematically selects one response more often than the
other will lead to performance below chance." A bias of this kind will drive
performance closer to chance. Performance that is significantly below chance
would be evidence that observers _can_ see single photons, but that they have
the response labels reversed in their minds.

------
TheRealPomax
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.

------
tintor
Tested on 3 people only.

~~~
cespare
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.

------
hmate9
I knew I just felt something brush against me

------
Hydraulix989
People can hear single frequencies too

~~~
1_listerine_pls
A photon is not a frequency.

~~~
cee_el2
But both the sound the frequency of which we hear and the photon which we
sense.. are waves

~~~
noobermin
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.

~~~
1_listerine_pls
Unrelated question,

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](http://i.imgur.com/RdWRpnHl.png)

Do you think it would be feasible? I am not a physicist.

~~~
noobermin
So, I am more on the plasma side than the laser side, unfortunately, so get a
second opinion :) but I'm not sure it would. First of all, when talking about
_heating_ , you're mainly relying on dielectric heating[0], which depends on
the dipole moment (perhaps) and polarizability of the things you're looking
at. The wavelength might play a role but the idea is dielectric heating is a
classical phenomenon, not quantum. I'm don't want to misunderstand your idea,
but it sounds like you are applying intuition from QM regarding a material's
absorption spectrum, which is,obv., quantum and thus selecting regarding
wavelength. Dielectric heating will affect both species regardless given if
both can be polarized leading to heating.

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](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...](http://pubs.rsc.org/en/content/articlelanding/1998/cs/a827213z#!divAbstract)

~~~
1_listerine_pls
Thank for the answer.

\- 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.

