Human eyes can detect single photons?

[Auto-Didact]

I'm not sure where this thread belongs; it is essentially a topic at the intersection between quantum optics, human physiology and even psychology, but I will focus more or less on the implications for quantum physics, so I just opted for this subforum.

There is a recent article over Scientific American titled The Human Eye Could Help Test Quantum Mechanics. It is an intriguing piece based on a recent arxiv preprint:

Holmes et al. 2018, Testing the limits of human vision with quantum states of light: past, present, and future experiments

The human eye contains millions of rod photoreceptor cells, and each one is a single-photon detector. Whether people can actually see a single photon, which requires the rod signal to propagate through the rest of the noisy visual system and be perceived in the brain, has been the subject of research for nearly 100 years. Early experiments hinted that people could see just a few photons, but classical light sources are poor tools for answering these questions. Single-photon sources have opened up a new area of vision research, providing the best evidence yet that humans can indeed see single photons, and could even be used to test quantum effects through the visual system. We discuss our program to study the lower limits of human vision with a heralded single-photon source based on spontaneous parametric downconversion, and present two proposed experiments to explore quantum effects through the visual system: testing the perception of superposition states, and using a human observer as a detector in a Bell test.

The newer experimental evidence that the preprint refers to is described by another article over at Nature titled: People can sense single photons:

Experiment suggests that humans are capable of perceiving even the feeblest flash of light.

People can detect flashes of light as feeble as a single photon, an experiment has demonstrated — a finding that seems to conclude a 70-year quest to test the limits of human vision.

The study, published in Nature Communications on 19 July, “finally answers a long-standing question about whether humans can see single photons — they can!” says Paul Kwiat, a quantum optics researcher at the University of Illinois at Urbana–Champaign. The techniques used in the study also open up ways of testing how quantum properties — such as the ability of photons to be in two places at the same time — affect biology, he adds.

“The most amazing thing is that it’s not like seeing light. It’s almost a feeling, at the threshold of imagination,” says Alipasha Vaziri, a physicist at the Rockefeller University in New York City, who led the work and tried out the experience himself.

These ideas indeed go back a century to Poincaré (in The Foundations of Science), and later to Feynman (in his Lectures), who both spoke extensively on this subject, as well as to many others since.

In any case, it is absolutely intriguing to think to what extent such research might help on shedding some much needed light on problems in the foundations of QM; the capability of replacing a measuring apparatus directly with a human being would surely be a paradigmatic shift in QM research. It goes without saying that it would be absolutely unbelievable if such research could end up resolving the measurement problem in QM.

 

[Nugatory]

the capability of replacing a measuring apparatus directly with a human being would surely be a paradigmatic shift in QM research.

Why would it matter whether a photon is detected by an interaction with a biological molecule and then the initial energy is amplified by electrochemical processes in a nervous system, instead of being detected by more traditional detectors?

It goes without saying that it would be absolutely unbelievable if such research could end up resolving the measurement problem in QM.

Well yes, I do agree that that would be absolutely unbelievable...

 

[DaveC426913]

I recall some astronauts kept seeing occasional strange flashes. Scientists eventually deduced that they were seeing Cosmic Rays (or was it Gamma) directly interacting with the optical receptors.

 

[Auto-Didact]

Why would it matter whether a photon is detected by an interaction with a biological molecule and then the initial energy is amplified by electrochemical processes in a nervous system, instead of being detected by more traditional detectors?

W.r.t. physics, there are two reasons:
1) In biophysics, this might lead to the capability to do experiments which biologists have never been able to even envision. Until even as short as a decade ago, non-trivial quantum biology was generally seen as quite literally impossible.
2) In QM, as the authors speculate, there is a possibility that it could lead to a new line of experiments which might actually end up resolving longstanding problems.

Well yes, I do agree that that would be absolutely unbelievable...

The whole idea is somewhat reminiscent of Deutsch's argument of using AI to test the MWI.

 

[DaveC426913]

W.r.t. physics, there are two reasons:
1) In biophysics, this might lead to the capability to do experiments which biologists have never been able to even envision.
2) In QM, as the authors speculate, there is a possibility that it could lead to a new line of experiments which might actually end up resolving longstanding problems.

Maybe I'm missing something but how does it change anything that we can see something directly, that we can otherwise see with assistive technology?
Similarly, if we could see bacteria with our naked eyes, would that be better than using a microscope?

Are you perhaps thinking of the antiquated QM idea that an observer must be a conscious mind? Because that's been pretty well debunked.

 

[Nugatory]

W.r.t. physics, there are two reasons:
1) In biophysics, this might lead to the capability to do experiments which biologists have never been able to even envision. Until even as short as a decade ago, non-trivial quantum biology was generally seen as quite literally impossible.

That's a weaker and much more plausible claim than "... surely lead to a paradigmatic shift".

Are you perhaps thinking of the antiquated QM idea that an observer must be a conscious mind? Because that's been pretty well debunked.

To be fair, the authors explicitly deny any interest in that issue.

 

[Auto-Didact]

Are you perhaps thinking of the antiquated QM idea that an observer must be a conscious mind?

No.

Direct experiments simply bring with them more information than do indirect experiments, and potentially bring with them new ways of thinking as well.

I'm more interested in how such novel viewpoints might end up eventually favoring one interpretation over another, e.g. in the spirit that Elitzur argues here regarding Aharanov's two state vector formalism (TSVF) versus standard QM.

 

[Auto-Didact]

That's a weaker and much more plausible claim than "... surely lead to a paradigmatic shift".

Maybe I'm letting my suspicions get the better of me, but I think an actual "democratization" of QM into the direct experiential realm of regular people could easily lead to a profound shift regarding how society - and therefore also how scientists - generally views, thinks about (and funds) the subject.

 

[black hole 123]

i disagree with the consciousness/collapse thing. even if somehow u need a human eye to see the photons to cause collapse, the eye is a mechanical device, consciousness whatever it is, is only observing the electrical pattern in the brain not what the eye sees. Nugatory put it succintly, the eye is no different from a machine detector. you see with ur brain not with ur eyes.

 

[pinball1970]

No.

Direct experiments simply bring with them more information than do indirect experiments, and potentially bring with them new ways of thinking as well.

I'm more interested in how such novel viewpoints might end up eventually favoring one interpretation over another, e.g. in the spirit that Elitzur argues here regarding Aharanov's two state vector formalism (TSVF) versus standard QM.

What eye would you one use for these types of studies is mentioned as a possible issue/variable.

An old eye? Young? male or female?

A colourist?

Circadian rhythms could play a part, menstrual cycle?

I supposed if you used a big enough sample size the errors could be reduced.

It would be very interesting setting such an experiment up.

 

[Auto-Didact]

You are seeing it the wrong way around: the concept of averaging for one kind of 'general human eye' in order to experiment with is completely mistaken and goes directly against the proven empirical methodology of the last century of medical science. Practically nothing in human physiology is averaged in this manner, not even simple measures like height or age.

What would need to be done in order to carry out the experiments properly is to classify groups based on similar ocular characteristics and overall general characteristics, both constant/periodic and otherwise, such as those which you have layed out above. Each such group would need adequate sample sizes in order to say anything meaningful.

In other words, there will be an average curve for adult men, another for adult women, another for infants, for children, for teens, for elders, for healthy, morbid, multimorbid, and so on. Each class will be an arm to be sampled and studied adequately, i.e. through a double-blind randomized controlled trial; this is the only way to get to the bottom of things.

Then the outcomes of tests of individuals within such arms with potentially differentiating ocular characteristics should be compared among each other and over the arms with those of similar ocular characteristics. In this manner all eye types - both typical and atypical - can be identified, their prior probabilities discovered, and carefully experimented with.

This would then automatically lead to a catalogue of 'eye types' for which the experiment might need to be tuned differently. It is highly likely the eyes within a single type will show a greater degree of homogeneity with regard to a particular experimental set up and outcome than eyes from a different type.

Just carelessly averaging over all eyes would have concealed this and likely lead to a higher than necessary amount of false negatives. Personally, I'm particularly interested in whether or not there would be any marked differences in the outcomes of those with certain types of blindness, forms of dementia and psychiatric morbidity in comparison with the healthy population.

 

[ZapperZ]

I must say that I don't quite understand the brouhaha here.

First of all, it is not new that the human eye can detect single photons. This has been known for quite some time.

However, why is this different than having single-photon detectors? We already have those. Many phototubes are already sensitive to single-photons. And not only that, I've already mentioned why the human eye is, in fact, a rather poor light detector when compared to the many photodetectors that we currently have.

So I don't get this.

Zz.

 

[Auto-Didact]

However, why is this different than having single-photon detectors?

Human eyes are not LTI-solid state devices, neither are they connected to a green or red light which show the results of the experiment.

Human eye/brain systems are essentially a highly complicated form of coupled soft matter detectors with a host of secondary and tertiary nonlinear couplings. Unless you can write down an explicit typical Hamiltonian for this coupled system without some crazy simplifying assumptions and then prove it won't differ from regular solid state devices, this is an intriguing scientific experiment.

Even if you could do that, I really see no good reason why one should assume a priori that there are no differences whatsoever to be found on either the physical, the biological side or both sides with regard to these experiments.

 

[ZapperZ]

Human eyes are not LTI-solid state devices, neither are they connected to a green or red light which show the results of the experiment.

Human eye/brain systems are essentially a highly complicated form of coupled soft matter detectors with a host of secondary and tertiary nonlinear couplings. Unless you can write down an explicit typical Hamiltonian for this coupled system without some crazy simplifying assumptions and then prove it won't differ from regular solid state devices.

Even if you could do that, I really see no good reason why one should assume a priori that there are no differences whatsoever to be found on either the physical, the biological side or both sides with regard to these experiments.

But what you are saying here makes it an even WORSE detector! It has way too many complications, so much so that now, the detector becomes an issue. And we haven't even talked about the human optical illusions yet!

As experimentalist, the LAST thing want is a detector that detracts from what I'm trying to measure. The more complicated the measuring device is, the more things can go wrong, and the more one can question the outcome. It is why still use old-fashioned phototubes to detect the Cerenkov light in neutrino experiments, and why Hamamatsu still makes them!

Zz.

 

[Auto-Didact]

But what you are saying here makes it an even WORSE detector! It has way too many complications, so much so that now, the detector becomes an issue. And we haven't even talked about the human optical illusions yet!

As experimentalist, the LAST thing want is a detector that detracts from what I'm trying to measure. The more complicated the measuring device is, the more things can go wrong, and the more one can question the outcome.

It all depends on what the goal of the experiment - not necessarily that of the experimenter - is. Outside of the theoretical implections, I see this as more of a challenge to a new line of experimental biophysicists than anything else.

Moreover, if as I say it did end up leading to an accurate medical test for distinguishing extremely difficult to signal phenomena such as dementia and psychiatric symptoms, such a thing could be a medical gold mine.

 

[ZapperZ]

Moreover, if as I say it did end up leading to an accurate medical test for distinguishing extremely difficult to signal phenomena such as dementia and psychiatric symptoms, such a thing could be a medical gold mine.

And I do not see how it does, considering that it can't even be a good detector for simple experiments. You now take something that can't be used for straight-forward experiments, and using it for a more complex system. How reliable is the result?

Zz.

 

[Auto-Didact]

You now take something that can't be used for straight-forward experiments, and using it for a more complex system. How reliable is the result?

The accuracy and reliability of the results of a tool is dependent on the diagnostic skills of the utilizer. A single good physician can achieve more with his bare hands, eyes and ears than a hundred very smart regular people with advanced apparatuses and no proper medical experience; this experiment is carried out every day: it is called medical school.

The full validity of a tool can only be judged by careful experimentation i.e. RCT, not by the a priori suppositions of scientists based on their experiences with making and using tools.

 

[ZapperZ]

The accuracy and reliability of the results of a tool is dependent on the diagnostic skills of the utilizer. A single good physician can achieve more with his bare hands, eyes and ears than a hundred very smart regular people with advanced apparatuses and no proper medical experience; this experiment is carried out every day: it is called medical school.

The full validity of a tool can only be judged by careful experimentation i.e. RCT, not by the a priori suppositions of scientists based on their experiences with making and using tools.

I never said anything about medical diagnostics. I simply questioned the validity of a result if that result can be affected by so many other external factors. It is why we measure the signal-to-noise ratio of a photodetector, because a noisy detector can easily provide false data. You do not want your detector affecting the result!

The first post in this thread that you created had all to do with quantum measurements in a physics experiment! You brought it up, and that is what I'm addressing.

Zz.

 

[Auto-Didact]

I never said anything about medical diagnostics. I simply questioned the validity of a result if that result can be affected by so many other external factors. It is why we measure the signal-to-noise ratio of a photodetector, because a noisy detector can easily provide false data. You do not want your detector affecting the result!

The scientific study of (medical) diagnostics is exactly the study of how a 'valid' detector, optimally tuned or otherwise, interferes with the outcome of using the tool. This can be formalized using mathematical systems theory.

The first post in this thread that you created had all to do with quantum measurements in a physics experiment! You brought it up, and that is what I'm addressing.

I originally posted this in the biology subforum, because this seems like an instance of non-trivial quantum biology which warrants further investigation.

But yes, the physics side is also definitely interesting, more so from a theoretical stance than an experimental stance, because it implies that experimental QM still works despite all the complications added over regular LTI solid state detectors.

However, seeing there have already been experiments carried out I'm far more interested in expanding the experiments in the manner I explained in posts #7 and #11 than in discussing beforehand why such experiment might fail: those reasons are usually obvious to anyone who knows anything about QM.

Of course, I'd also love to discuss and learn from experts here on what parts of the experiments carried out so far as described in the paper may or may not be questionable and for which specific reasons. I think critically assessing and citing those questionable bits of the paper is only fair towards the researchers.

 

[Swamp Thing]

Two people, arms outstretched, one north-south, one east-west. A dumbbell in each hand. Voila, a human gravitational wave detector.