Can two people see the same photon? Announcing the arrival of Valued Associate #679: Cesar...

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Can two people see the same photon?



Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 23, 2019 at 23:30 UTC (7:30pm US/Eastern)
2019 Moderator Election Q&A - Question CollectionHow far back can you trace a photon?Photon absorption and SightWhere did all the photon energy go?Same photon or different photon?How are we MEASURING (not computing) the energy of a single photon?Clarification on the Properties of a PhotonCan a photon cross the event horizon from the perspective of an outside observer?Why can't the light from a candle light the whole of a dark room?Dark room lightsDo Photons Ever Form Just Two Lines In Slit Experiments?












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In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments?










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  • $begingroup$
    You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
    $endgroup$
    – Mayou36
    6 hours ago
















6












$begingroup$


In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments?










share|cite|improve this question











$endgroup$












  • $begingroup$
    You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
    $endgroup$
    – Mayou36
    6 hours ago














6












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In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments?










share|cite|improve this question











$endgroup$




In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments?







photons elementary-particles






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edited 33 mins ago









Andrew Morton

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asked 15 hours ago









fangzhang mnmfangzhang mnm

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  • $begingroup$
    You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
    $endgroup$
    – Mayou36
    6 hours ago


















  • $begingroup$
    You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
    $endgroup$
    – Mayou36
    6 hours ago
















$begingroup$
You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
$endgroup$
– Mayou36
6 hours ago




$begingroup$
You should specify your question: are you asking from a purely physical point of view e.g. are you interested to know whether a single photon (forget about a candle and only a single photon!) can be detected by two different "sensors", which eyes in principle are, or rather on the full world realistic question including the energy needed to trigger something in our brain?
$endgroup$
– Mayou36
6 hours ago










6 Answers
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Seeing = detecting photons that happen to interact with your retina.



You can't see photons when they are just travelling nearby. Take lasers for example. When someone is using laser pointer, the only reason you see the beam is that photons collide with dust and air particles and therefore their direction is changed. For example into your eye. Otherwise you wouldn't see anything.



It isn't possible for two people to see the same photon.






share|cite|improve this answer











$endgroup$









  • 3




    $begingroup$
    Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
    $endgroup$
    – Michael Angelo
    11 hours ago








  • 1




    $begingroup$
    @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
    $endgroup$
    – aaaaaa
    10 hours ago








  • 1




    $begingroup$
    Interesting. I stand corrected.
    $endgroup$
    – Andrej
    10 hours ago



















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In theory, in the most perversely contrieved case, and if you are willing to cheat a bit, it would be possible. In any half-reasonable, realistic setting, the answer is a clear, definite "No". Indeed, people cannot even see single photons at all (contrary to urban myths).



How does seeing a photon work? The photon has to hit your eye, specifically one of the billion rhodopsin molecules in one of the several-million retinal cells, then something-something, and then a nerve impulse maybe, if some conditions hold goes through the roughly-one-million ganglion network in the retina, and maybe makes it to the brain. Maybe. And maybe the visual cortex makes something of it.

The "maybe" part and the fact that a single cell has billions of G-proteins going active and inactive every second, and that there's a continuous flow of cGMP up and down is the reason why you cannot really see a single photon. That just isn't reasonably possible, if anything it's placebo effect or mere suggestion.



So what's that something-something mentioned previously? The photon flips the cis-bond at position 11 in retinal to trans. Which, well, takes energy, and absorbs the photon.
This triggers a typical G-protein cascade, with alpha subunit going off and blah blah, resulting in production of cGMP at the end. If the cGMP concentration goes above some threshold, and if the cell isn't currently refractive, then the cell fires an AP. That's a big "maybe". Then comes something-something ganglion cells, which is the other big "maybe" part above.



The photon is "gone" after that. No second person could possibly see it.



Now of course, no absorption is perfect, there's an absorption maximum for each type of rhodopsin, and even at that it isn't 100%. Outside the maximum, the absorption is far from 100%. Which means that the photon is emitted again, and it could, in theory, in the most improbable case, hit another person's eye, why not. But of course we have to cheat a bit here because it strictly isn't the same photon.

Unless we are willing to cheat, the answer must therefore be "not possible".






share|cite|improve this answer









$endgroup$









  • 3




    $begingroup$
    Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
    $endgroup$
    – jamesqf
    8 hours ago










  • $begingroup$
    The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
    $endgroup$
    – Zizy Archer
    3 hours ago



















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Somehow the exchange of energy between all objects must take place. It was found that this process takes place through the emission and absorption of photons (initially called energy quanta).



Photons are indivisible particles, they do not loose or gain inner energy during their life. The detection of a photon is possible only through the absorption of this photon.



Theoretically, it is possible to obtain information about an absorbed photon by observing secondary emitted photons with lower energy (and longer wavelength).



If you think of a laser beam that you have seen from the side, dust particles in the air are responsible. They reflect the laser light and you can see the beam. Of course, the photons reflected from the dust into the eyes do not arrive at the laser target.






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    $begingroup$

    Candles do not give off single photons. Preparing light sources that can emit single photons is tricky.



    The photon contains "one photon" (some small quantity of electronvolts) of energy. The energy in a photon is directly propotional to its frequency, so two photons of the same "color" have the same energy. The process of absorbing a photon transduces "one photon" of energy from the electromagnetic field to the detector. Consequently, if either human detects the photon, there is no energy left to be detected by the other human.



    In "Direct detection of a single photon by humans", J.N. Tinsley et al. directly measure the event of conscious detection of single photons. Subjects in that experiment




    • did (barely) better than chance (51.6% (p=0.0545)) correctly identifying photon present and photon absent events) when observer confidence in event was excluded and

    • did better than chance (60.0% (p=0.001)) when confidence was included.


    Interestingly, "the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ∼5 s time interval. Averaging across all trials that had a preceding detection within a 10-s time window, the probability of correct response was found to be 0.56±0.03 (P=0.02)."



    Of course, not every photon that strikes the retina is transduced. "Based on the efficiency of the signal arm and the visual system, we estimate that in ∼6% of all post-selected events an actual light-induced signal was generated ..." So we expect to see improvements over random chance in the neighborhood of 6%, and all numbers reported above are in that neighborhood.






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      Candles emit huge numbers of photons per second, and humans can't reliably detect single photons, so let's simplify your experiment to the bare essentials.



      In the middle, we have an atom that we can excite (by firing a photon at it). Shortly after we excite this atom, it emits a single photon with a spherically symmetric radiation pattern, that is, there's an equal probability of detecting the photon in any direction. This is a standard example of an atom scattering a photon.



      Now we place several identical photon detectors around our emitter atom, in various directions. After the photon is emitted, one of our detectors may detect it. Or the photon may miss all of our detectors and collide with something else.



      We can model this as a spherical bubble centred on the emitter atom, expanding at the speed of light. When the bubble reaches a detector atom, that atom may detect the photon. When that happens, the bubble disappears, like a pin bursting a soap bubble. No other detector can detect the same photon (not even another detector at the exact same distance), all of the photon's energy was absorbed by the detector that was activated.






      share|cite|improve this answer











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      • $begingroup$
        I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
        $endgroup$
        – Eric Towers
        11 hours ago






      • 2




        $begingroup$
        "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
        $endgroup$
        – Andy Ray
        7 hours ago










      • $begingroup$
        @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
        $endgroup$
        – PM 2Ring
        3 hours ago



















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      To see a photon, it must be absorbed by a molecule in the retina [1]. The photon then no longer exists, so it is not available to be seen by another person.



      [1] Mammalia retinas can respond to single photons






      share|cite|improve this answer








      New contributor




      Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






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        6 Answers
        6






        active

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        6 Answers
        6






        active

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        active

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        12












        $begingroup$

        Seeing = detecting photons that happen to interact with your retina.



        You can't see photons when they are just travelling nearby. Take lasers for example. When someone is using laser pointer, the only reason you see the beam is that photons collide with dust and air particles and therefore their direction is changed. For example into your eye. Otherwise you wouldn't see anything.



        It isn't possible for two people to see the same photon.






        share|cite|improve this answer











        $endgroup$









        • 3




          $begingroup$
          Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
          $endgroup$
          – Michael Angelo
          11 hours ago








        • 1




          $begingroup$
          @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
          $endgroup$
          – aaaaaa
          10 hours ago








        • 1




          $begingroup$
          Interesting. I stand corrected.
          $endgroup$
          – Andrej
          10 hours ago
















        12












        $begingroup$

        Seeing = detecting photons that happen to interact with your retina.



        You can't see photons when they are just travelling nearby. Take lasers for example. When someone is using laser pointer, the only reason you see the beam is that photons collide with dust and air particles and therefore their direction is changed. For example into your eye. Otherwise you wouldn't see anything.



        It isn't possible for two people to see the same photon.






        share|cite|improve this answer











        $endgroup$









        • 3




          $begingroup$
          Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
          $endgroup$
          – Michael Angelo
          11 hours ago








        • 1




          $begingroup$
          @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
          $endgroup$
          – aaaaaa
          10 hours ago








        • 1




          $begingroup$
          Interesting. I stand corrected.
          $endgroup$
          – Andrej
          10 hours ago














        12












        12








        12





        $begingroup$

        Seeing = detecting photons that happen to interact with your retina.



        You can't see photons when they are just travelling nearby. Take lasers for example. When someone is using laser pointer, the only reason you see the beam is that photons collide with dust and air particles and therefore their direction is changed. For example into your eye. Otherwise you wouldn't see anything.



        It isn't possible for two people to see the same photon.






        share|cite|improve this answer











        $endgroup$



        Seeing = detecting photons that happen to interact with your retina.



        You can't see photons when they are just travelling nearby. Take lasers for example. When someone is using laser pointer, the only reason you see the beam is that photons collide with dust and air particles and therefore their direction is changed. For example into your eye. Otherwise you wouldn't see anything.



        It isn't possible for two people to see the same photon.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited 10 hours ago

























        answered 12 hours ago









        AndrejAndrej

        1507




        1507








        • 3




          $begingroup$
          Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
          $endgroup$
          – Michael Angelo
          11 hours ago








        • 1




          $begingroup$
          @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
          $endgroup$
          – aaaaaa
          10 hours ago








        • 1




          $begingroup$
          Interesting. I stand corrected.
          $endgroup$
          – Andrej
          10 hours ago














        • 3




          $begingroup$
          Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
          $endgroup$
          – Michael Angelo
          11 hours ago








        • 1




          $begingroup$
          @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
          $endgroup$
          – aaaaaa
          10 hours ago








        • 1




          $begingroup$
          Interesting. I stand corrected.
          $endgroup$
          – Andrej
          10 hours ago








        3




        3




        $begingroup$
        Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
        $endgroup$
        – Michael Angelo
        11 hours ago






        $begingroup$
        Actually the human eye can detect a single photon. nature.com/news/people-can-sense-single-photons-1.20282
        $endgroup$
        – Michael Angelo
        11 hours ago






        1




        1




        $begingroup$
        @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
        $endgroup$
        – aaaaaa
        10 hours ago






        $begingroup$
        @MichaelAngelo i remember that paper. Result is like 10% above 50-50 discrimination :-) But yes, human eye is very sensitive. Last (paragraph) is factually incorrect
        $endgroup$
        – aaaaaa
        10 hours ago






        1




        1




        $begingroup$
        Interesting. I stand corrected.
        $endgroup$
        – Andrej
        10 hours ago




        $begingroup$
        Interesting. I stand corrected.
        $endgroup$
        – Andrej
        10 hours ago











        4












        $begingroup$

        In theory, in the most perversely contrieved case, and if you are willing to cheat a bit, it would be possible. In any half-reasonable, realistic setting, the answer is a clear, definite "No". Indeed, people cannot even see single photons at all (contrary to urban myths).



        How does seeing a photon work? The photon has to hit your eye, specifically one of the billion rhodopsin molecules in one of the several-million retinal cells, then something-something, and then a nerve impulse maybe, if some conditions hold goes through the roughly-one-million ganglion network in the retina, and maybe makes it to the brain. Maybe. And maybe the visual cortex makes something of it.

        The "maybe" part and the fact that a single cell has billions of G-proteins going active and inactive every second, and that there's a continuous flow of cGMP up and down is the reason why you cannot really see a single photon. That just isn't reasonably possible, if anything it's placebo effect or mere suggestion.



        So what's that something-something mentioned previously? The photon flips the cis-bond at position 11 in retinal to trans. Which, well, takes energy, and absorbs the photon.
        This triggers a typical G-protein cascade, with alpha subunit going off and blah blah, resulting in production of cGMP at the end. If the cGMP concentration goes above some threshold, and if the cell isn't currently refractive, then the cell fires an AP. That's a big "maybe". Then comes something-something ganglion cells, which is the other big "maybe" part above.



        The photon is "gone" after that. No second person could possibly see it.



        Now of course, no absorption is perfect, there's an absorption maximum for each type of rhodopsin, and even at that it isn't 100%. Outside the maximum, the absorption is far from 100%. Which means that the photon is emitted again, and it could, in theory, in the most improbable case, hit another person's eye, why not. But of course we have to cheat a bit here because it strictly isn't the same photon.

        Unless we are willing to cheat, the answer must therefore be "not possible".






        share|cite|improve this answer









        $endgroup$









        • 3




          $begingroup$
          Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
          $endgroup$
          – jamesqf
          8 hours ago










        • $begingroup$
          The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
          $endgroup$
          – Zizy Archer
          3 hours ago
















        4












        $begingroup$

        In theory, in the most perversely contrieved case, and if you are willing to cheat a bit, it would be possible. In any half-reasonable, realistic setting, the answer is a clear, definite "No". Indeed, people cannot even see single photons at all (contrary to urban myths).



        How does seeing a photon work? The photon has to hit your eye, specifically one of the billion rhodopsin molecules in one of the several-million retinal cells, then something-something, and then a nerve impulse maybe, if some conditions hold goes through the roughly-one-million ganglion network in the retina, and maybe makes it to the brain. Maybe. And maybe the visual cortex makes something of it.

        The "maybe" part and the fact that a single cell has billions of G-proteins going active and inactive every second, and that there's a continuous flow of cGMP up and down is the reason why you cannot really see a single photon. That just isn't reasonably possible, if anything it's placebo effect or mere suggestion.



        So what's that something-something mentioned previously? The photon flips the cis-bond at position 11 in retinal to trans. Which, well, takes energy, and absorbs the photon.
        This triggers a typical G-protein cascade, with alpha subunit going off and blah blah, resulting in production of cGMP at the end. If the cGMP concentration goes above some threshold, and if the cell isn't currently refractive, then the cell fires an AP. That's a big "maybe". Then comes something-something ganglion cells, which is the other big "maybe" part above.



        The photon is "gone" after that. No second person could possibly see it.



        Now of course, no absorption is perfect, there's an absorption maximum for each type of rhodopsin, and even at that it isn't 100%. Outside the maximum, the absorption is far from 100%. Which means that the photon is emitted again, and it could, in theory, in the most improbable case, hit another person's eye, why not. But of course we have to cheat a bit here because it strictly isn't the same photon.

        Unless we are willing to cheat, the answer must therefore be "not possible".






        share|cite|improve this answer









        $endgroup$









        • 3




          $begingroup$
          Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
          $endgroup$
          – jamesqf
          8 hours ago










        • $begingroup$
          The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
          $endgroup$
          – Zizy Archer
          3 hours ago














        4












        4








        4





        $begingroup$

        In theory, in the most perversely contrieved case, and if you are willing to cheat a bit, it would be possible. In any half-reasonable, realistic setting, the answer is a clear, definite "No". Indeed, people cannot even see single photons at all (contrary to urban myths).



        How does seeing a photon work? The photon has to hit your eye, specifically one of the billion rhodopsin molecules in one of the several-million retinal cells, then something-something, and then a nerve impulse maybe, if some conditions hold goes through the roughly-one-million ganglion network in the retina, and maybe makes it to the brain. Maybe. And maybe the visual cortex makes something of it.

        The "maybe" part and the fact that a single cell has billions of G-proteins going active and inactive every second, and that there's a continuous flow of cGMP up and down is the reason why you cannot really see a single photon. That just isn't reasonably possible, if anything it's placebo effect or mere suggestion.



        So what's that something-something mentioned previously? The photon flips the cis-bond at position 11 in retinal to trans. Which, well, takes energy, and absorbs the photon.
        This triggers a typical G-protein cascade, with alpha subunit going off and blah blah, resulting in production of cGMP at the end. If the cGMP concentration goes above some threshold, and if the cell isn't currently refractive, then the cell fires an AP. That's a big "maybe". Then comes something-something ganglion cells, which is the other big "maybe" part above.



        The photon is "gone" after that. No second person could possibly see it.



        Now of course, no absorption is perfect, there's an absorption maximum for each type of rhodopsin, and even at that it isn't 100%. Outside the maximum, the absorption is far from 100%. Which means that the photon is emitted again, and it could, in theory, in the most improbable case, hit another person's eye, why not. But of course we have to cheat a bit here because it strictly isn't the same photon.

        Unless we are willing to cheat, the answer must therefore be "not possible".






        share|cite|improve this answer









        $endgroup$



        In theory, in the most perversely contrieved case, and if you are willing to cheat a bit, it would be possible. In any half-reasonable, realistic setting, the answer is a clear, definite "No". Indeed, people cannot even see single photons at all (contrary to urban myths).



        How does seeing a photon work? The photon has to hit your eye, specifically one of the billion rhodopsin molecules in one of the several-million retinal cells, then something-something, and then a nerve impulse maybe, if some conditions hold goes through the roughly-one-million ganglion network in the retina, and maybe makes it to the brain. Maybe. And maybe the visual cortex makes something of it.

        The "maybe" part and the fact that a single cell has billions of G-proteins going active and inactive every second, and that there's a continuous flow of cGMP up and down is the reason why you cannot really see a single photon. That just isn't reasonably possible, if anything it's placebo effect or mere suggestion.



        So what's that something-something mentioned previously? The photon flips the cis-bond at position 11 in retinal to trans. Which, well, takes energy, and absorbs the photon.
        This triggers a typical G-protein cascade, with alpha subunit going off and blah blah, resulting in production of cGMP at the end. If the cGMP concentration goes above some threshold, and if the cell isn't currently refractive, then the cell fires an AP. That's a big "maybe". Then comes something-something ganglion cells, which is the other big "maybe" part above.



        The photon is "gone" after that. No second person could possibly see it.



        Now of course, no absorption is perfect, there's an absorption maximum for each type of rhodopsin, and even at that it isn't 100%. Outside the maximum, the absorption is far from 100%. Which means that the photon is emitted again, and it could, in theory, in the most improbable case, hit another person's eye, why not. But of course we have to cheat a bit here because it strictly isn't the same photon.

        Unless we are willing to cheat, the answer must therefore be "not possible".







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered 10 hours ago









        DamonDamon

        24315




        24315








        • 3




          $begingroup$
          Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
          $endgroup$
          – jamesqf
          8 hours ago










        • $begingroup$
          The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
          $endgroup$
          – Zizy Archer
          3 hours ago














        • 3




          $begingroup$
          Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
          $endgroup$
          – jamesqf
          8 hours ago










        • $begingroup$
          The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
          $endgroup$
          – Zizy Archer
          3 hours ago








        3




        3




        $begingroup$
        Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
        $endgroup$
        – jamesqf
        8 hours ago




        $begingroup$
        Re "the photon is emitted again", is the emitted photon in any sense the SAME photon? I don't think so: the original photon is gone, and a new one is created.
        $endgroup$
        – jamesqf
        8 hours ago












        $begingroup$
        The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
        $endgroup$
        – Zizy Archer
        3 hours ago




        $begingroup$
        The photon is absorbed or not, so these absorption maxima are irrelevant here - even at 100% absorption you still have re-emission. @jamesqf Assuming same energy, I would consider it to be the same. Is the original photon also gone after its polarization changes? Or after it gets reflected/refracted? Or even after it travels in free space?
        $endgroup$
        – Zizy Archer
        3 hours ago











        2












        $begingroup$

        Somehow the exchange of energy between all objects must take place. It was found that this process takes place through the emission and absorption of photons (initially called energy quanta).



        Photons are indivisible particles, they do not loose or gain inner energy during their life. The detection of a photon is possible only through the absorption of this photon.



        Theoretically, it is possible to obtain information about an absorbed photon by observing secondary emitted photons with lower energy (and longer wavelength).



        If you think of a laser beam that you have seen from the side, dust particles in the air are responsible. They reflect the laser light and you can see the beam. Of course, the photons reflected from the dust into the eyes do not arrive at the laser target.






        share|cite|improve this answer









        $endgroup$


















          2












          $begingroup$

          Somehow the exchange of energy between all objects must take place. It was found that this process takes place through the emission and absorption of photons (initially called energy quanta).



          Photons are indivisible particles, they do not loose or gain inner energy during their life. The detection of a photon is possible only through the absorption of this photon.



          Theoretically, it is possible to obtain information about an absorbed photon by observing secondary emitted photons with lower energy (and longer wavelength).



          If you think of a laser beam that you have seen from the side, dust particles in the air are responsible. They reflect the laser light and you can see the beam. Of course, the photons reflected from the dust into the eyes do not arrive at the laser target.






          share|cite|improve this answer









          $endgroup$
















            2












            2








            2





            $begingroup$

            Somehow the exchange of energy between all objects must take place. It was found that this process takes place through the emission and absorption of photons (initially called energy quanta).



            Photons are indivisible particles, they do not loose or gain inner energy during their life. The detection of a photon is possible only through the absorption of this photon.



            Theoretically, it is possible to obtain information about an absorbed photon by observing secondary emitted photons with lower energy (and longer wavelength).



            If you think of a laser beam that you have seen from the side, dust particles in the air are responsible. They reflect the laser light and you can see the beam. Of course, the photons reflected from the dust into the eyes do not arrive at the laser target.






            share|cite|improve this answer









            $endgroup$



            Somehow the exchange of energy between all objects must take place. It was found that this process takes place through the emission and absorption of photons (initially called energy quanta).



            Photons are indivisible particles, they do not loose or gain inner energy during their life. The detection of a photon is possible only through the absorption of this photon.



            Theoretically, it is possible to obtain information about an absorbed photon by observing secondary emitted photons with lower energy (and longer wavelength).



            If you think of a laser beam that you have seen from the side, dust particles in the air are responsible. They reflect the laser light and you can see the beam. Of course, the photons reflected from the dust into the eyes do not arrive at the laser target.







            share|cite|improve this answer












            share|cite|improve this answer



            share|cite|improve this answer










            answered 12 hours ago









            HolgerFiedlerHolgerFiedler

            4,44531238




            4,44531238























                2












                $begingroup$

                Candles do not give off single photons. Preparing light sources that can emit single photons is tricky.



                The photon contains "one photon" (some small quantity of electronvolts) of energy. The energy in a photon is directly propotional to its frequency, so two photons of the same "color" have the same energy. The process of absorbing a photon transduces "one photon" of energy from the electromagnetic field to the detector. Consequently, if either human detects the photon, there is no energy left to be detected by the other human.



                In "Direct detection of a single photon by humans", J.N. Tinsley et al. directly measure the event of conscious detection of single photons. Subjects in that experiment




                • did (barely) better than chance (51.6% (p=0.0545)) correctly identifying photon present and photon absent events) when observer confidence in event was excluded and

                • did better than chance (60.0% (p=0.001)) when confidence was included.


                Interestingly, "the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ∼5 s time interval. Averaging across all trials that had a preceding detection within a 10-s time window, the probability of correct response was found to be 0.56±0.03 (P=0.02)."



                Of course, not every photon that strikes the retina is transduced. "Based on the efficiency of the signal arm and the visual system, we estimate that in ∼6% of all post-selected events an actual light-induced signal was generated ..." So we expect to see improvements over random chance in the neighborhood of 6%, and all numbers reported above are in that neighborhood.






                share|cite|improve this answer









                $endgroup$


















                  2












                  $begingroup$

                  Candles do not give off single photons. Preparing light sources that can emit single photons is tricky.



                  The photon contains "one photon" (some small quantity of electronvolts) of energy. The energy in a photon is directly propotional to its frequency, so two photons of the same "color" have the same energy. The process of absorbing a photon transduces "one photon" of energy from the electromagnetic field to the detector. Consequently, if either human detects the photon, there is no energy left to be detected by the other human.



                  In "Direct detection of a single photon by humans", J.N. Tinsley et al. directly measure the event of conscious detection of single photons. Subjects in that experiment




                  • did (barely) better than chance (51.6% (p=0.0545)) correctly identifying photon present and photon absent events) when observer confidence in event was excluded and

                  • did better than chance (60.0% (p=0.001)) when confidence was included.


                  Interestingly, "the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ∼5 s time interval. Averaging across all trials that had a preceding detection within a 10-s time window, the probability of correct response was found to be 0.56±0.03 (P=0.02)."



                  Of course, not every photon that strikes the retina is transduced. "Based on the efficiency of the signal arm and the visual system, we estimate that in ∼6% of all post-selected events an actual light-induced signal was generated ..." So we expect to see improvements over random chance in the neighborhood of 6%, and all numbers reported above are in that neighborhood.






                  share|cite|improve this answer









                  $endgroup$
















                    2












                    2








                    2





                    $begingroup$

                    Candles do not give off single photons. Preparing light sources that can emit single photons is tricky.



                    The photon contains "one photon" (some small quantity of electronvolts) of energy. The energy in a photon is directly propotional to its frequency, so two photons of the same "color" have the same energy. The process of absorbing a photon transduces "one photon" of energy from the electromagnetic field to the detector. Consequently, if either human detects the photon, there is no energy left to be detected by the other human.



                    In "Direct detection of a single photon by humans", J.N. Tinsley et al. directly measure the event of conscious detection of single photons. Subjects in that experiment




                    • did (barely) better than chance (51.6% (p=0.0545)) correctly identifying photon present and photon absent events) when observer confidence in event was excluded and

                    • did better than chance (60.0% (p=0.001)) when confidence was included.


                    Interestingly, "the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ∼5 s time interval. Averaging across all trials that had a preceding detection within a 10-s time window, the probability of correct response was found to be 0.56±0.03 (P=0.02)."



                    Of course, not every photon that strikes the retina is transduced. "Based on the efficiency of the signal arm and the visual system, we estimate that in ∼6% of all post-selected events an actual light-induced signal was generated ..." So we expect to see improvements over random chance in the neighborhood of 6%, and all numbers reported above are in that neighborhood.






                    share|cite|improve this answer









                    $endgroup$



                    Candles do not give off single photons. Preparing light sources that can emit single photons is tricky.



                    The photon contains "one photon" (some small quantity of electronvolts) of energy. The energy in a photon is directly propotional to its frequency, so two photons of the same "color" have the same energy. The process of absorbing a photon transduces "one photon" of energy from the electromagnetic field to the detector. Consequently, if either human detects the photon, there is no energy left to be detected by the other human.



                    In "Direct detection of a single photon by humans", J.N. Tinsley et al. directly measure the event of conscious detection of single photons. Subjects in that experiment




                    • did (barely) better than chance (51.6% (p=0.0545)) correctly identifying photon present and photon absent events) when observer confidence in event was excluded and

                    • did better than chance (60.0% (p=0.001)) when confidence was included.


                    Interestingly, "the probability of correctly reporting a single photon is highly enhanced by the presence of an earlier photon within ∼5 s time interval. Averaging across all trials that had a preceding detection within a 10-s time window, the probability of correct response was found to be 0.56±0.03 (P=0.02)."



                    Of course, not every photon that strikes the retina is transduced. "Based on the efficiency of the signal arm and the visual system, we estimate that in ∼6% of all post-selected events an actual light-induced signal was generated ..." So we expect to see improvements over random chance in the neighborhood of 6%, and all numbers reported above are in that neighborhood.







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered 11 hours ago









                    Eric TowersEric Towers

                    1,14958




                    1,14958























                        2












                        $begingroup$

                        Candles emit huge numbers of photons per second, and humans can't reliably detect single photons, so let's simplify your experiment to the bare essentials.



                        In the middle, we have an atom that we can excite (by firing a photon at it). Shortly after we excite this atom, it emits a single photon with a spherically symmetric radiation pattern, that is, there's an equal probability of detecting the photon in any direction. This is a standard example of an atom scattering a photon.



                        Now we place several identical photon detectors around our emitter atom, in various directions. After the photon is emitted, one of our detectors may detect it. Or the photon may miss all of our detectors and collide with something else.



                        We can model this as a spherical bubble centred on the emitter atom, expanding at the speed of light. When the bubble reaches a detector atom, that atom may detect the photon. When that happens, the bubble disappears, like a pin bursting a soap bubble. No other detector can detect the same photon (not even another detector at the exact same distance), all of the photon's energy was absorbed by the detector that was activated.






                        share|cite|improve this answer











                        $endgroup$













                        • $begingroup$
                          I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                          $endgroup$
                          – Eric Towers
                          11 hours ago






                        • 2




                          $begingroup$
                          "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                          $endgroup$
                          – Andy Ray
                          7 hours ago










                        • $begingroup$
                          @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                          $endgroup$
                          – PM 2Ring
                          3 hours ago
















                        2












                        $begingroup$

                        Candles emit huge numbers of photons per second, and humans can't reliably detect single photons, so let's simplify your experiment to the bare essentials.



                        In the middle, we have an atom that we can excite (by firing a photon at it). Shortly after we excite this atom, it emits a single photon with a spherically symmetric radiation pattern, that is, there's an equal probability of detecting the photon in any direction. This is a standard example of an atom scattering a photon.



                        Now we place several identical photon detectors around our emitter atom, in various directions. After the photon is emitted, one of our detectors may detect it. Or the photon may miss all of our detectors and collide with something else.



                        We can model this as a spherical bubble centred on the emitter atom, expanding at the speed of light. When the bubble reaches a detector atom, that atom may detect the photon. When that happens, the bubble disappears, like a pin bursting a soap bubble. No other detector can detect the same photon (not even another detector at the exact same distance), all of the photon's energy was absorbed by the detector that was activated.






                        share|cite|improve this answer











                        $endgroup$













                        • $begingroup$
                          I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                          $endgroup$
                          – Eric Towers
                          11 hours ago






                        • 2




                          $begingroup$
                          "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                          $endgroup$
                          – Andy Ray
                          7 hours ago










                        • $begingroup$
                          @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                          $endgroup$
                          – PM 2Ring
                          3 hours ago














                        2












                        2








                        2





                        $begingroup$

                        Candles emit huge numbers of photons per second, and humans can't reliably detect single photons, so let's simplify your experiment to the bare essentials.



                        In the middle, we have an atom that we can excite (by firing a photon at it). Shortly after we excite this atom, it emits a single photon with a spherically symmetric radiation pattern, that is, there's an equal probability of detecting the photon in any direction. This is a standard example of an atom scattering a photon.



                        Now we place several identical photon detectors around our emitter atom, in various directions. After the photon is emitted, one of our detectors may detect it. Or the photon may miss all of our detectors and collide with something else.



                        We can model this as a spherical bubble centred on the emitter atom, expanding at the speed of light. When the bubble reaches a detector atom, that atom may detect the photon. When that happens, the bubble disappears, like a pin bursting a soap bubble. No other detector can detect the same photon (not even another detector at the exact same distance), all of the photon's energy was absorbed by the detector that was activated.






                        share|cite|improve this answer











                        $endgroup$



                        Candles emit huge numbers of photons per second, and humans can't reliably detect single photons, so let's simplify your experiment to the bare essentials.



                        In the middle, we have an atom that we can excite (by firing a photon at it). Shortly after we excite this atom, it emits a single photon with a spherically symmetric radiation pattern, that is, there's an equal probability of detecting the photon in any direction. This is a standard example of an atom scattering a photon.



                        Now we place several identical photon detectors around our emitter atom, in various directions. After the photon is emitted, one of our detectors may detect it. Or the photon may miss all of our detectors and collide with something else.



                        We can model this as a spherical bubble centred on the emitter atom, expanding at the speed of light. When the bubble reaches a detector atom, that atom may detect the photon. When that happens, the bubble disappears, like a pin bursting a soap bubble. No other detector can detect the same photon (not even another detector at the exact same distance), all of the photon's energy was absorbed by the detector that was activated.







                        share|cite|improve this answer














                        share|cite|improve this answer



                        share|cite|improve this answer








                        edited 3 hours ago

























                        answered 11 hours ago









                        PM 2RingPM 2Ring

                        3,70121123




                        3,70121123












                        • $begingroup$
                          I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                          $endgroup$
                          – Eric Towers
                          11 hours ago






                        • 2




                          $begingroup$
                          "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                          $endgroup$
                          – Andy Ray
                          7 hours ago










                        • $begingroup$
                          @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                          $endgroup$
                          – PM 2Ring
                          3 hours ago


















                        • $begingroup$
                          I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                          $endgroup$
                          – Eric Towers
                          11 hours ago






                        • 2




                          $begingroup$
                          "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                          $endgroup$
                          – Andy Ray
                          7 hours ago










                        • $begingroup$
                          @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                          $endgroup$
                          – PM 2Ring
                          3 hours ago
















                        $begingroup$
                        I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                        $endgroup$
                        – Eric Towers
                        11 hours ago




                        $begingroup$
                        I've read Gibbs 1996 article claiming that humans cannot see single photons. I've also read Tinsley et al.'s 2016 Direct detection of a single photon by humans where single photon stimulation is measured to result in better than chance conscious observation of single photons. I tend to believe the measurement over the "reasonable story".
                        $endgroup$
                        – Eric Towers
                        11 hours ago




                        2




                        2




                        $begingroup$
                        "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                        $endgroup$
                        – Andy Ray
                        7 hours ago




                        $begingroup$
                        "Candles don't work like that" is condescending non-helpful. You understood the sentiment but wanted to show off, and this doesn't add anything to the better answers already posted.
                        $endgroup$
                        – Andy Ray
                        7 hours ago












                        $begingroup$
                        @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                        $endgroup$
                        – PM 2Ring
                        3 hours ago




                        $begingroup$
                        @Andy I had no intention to be condescending when I wrote my answer. I'm not trying to belittle the OP, I'm simply stating facts, and providing a model (the bubble), which they might find helpful.
                        $endgroup$
                        – PM 2Ring
                        3 hours ago











                        0












                        $begingroup$

                        To see a photon, it must be absorbed by a molecule in the retina [1]. The photon then no longer exists, so it is not available to be seen by another person.



                        [1] Mammalia retinas can respond to single photons






                        share|cite|improve this answer








                        New contributor




                        Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                        Check out our Code of Conduct.






                        $endgroup$


















                          0












                          $begingroup$

                          To see a photon, it must be absorbed by a molecule in the retina [1]. The photon then no longer exists, so it is not available to be seen by another person.



                          [1] Mammalia retinas can respond to single photons






                          share|cite|improve this answer








                          New contributor




                          Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                          Check out our Code of Conduct.






                          $endgroup$
















                            0












                            0








                            0





                            $begingroup$

                            To see a photon, it must be absorbed by a molecule in the retina [1]. The photon then no longer exists, so it is not available to be seen by another person.



                            [1] Mammalia retinas can respond to single photons






                            share|cite|improve this answer








                            New contributor




                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.






                            $endgroup$



                            To see a photon, it must be absorbed by a molecule in the retina [1]. The photon then no longer exists, so it is not available to be seen by another person.



                            [1] Mammalia retinas can respond to single photons







                            share|cite|improve this answer








                            New contributor




                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.









                            share|cite|improve this answer



                            share|cite|improve this answer






                            New contributor




                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.









                            answered 2 hours ago









                            Andrew MortonAndrew Morton

                            1055




                            1055




                            New contributor




                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.





                            New contributor





                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.






                            Andrew Morton is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
                            Check out our Code of Conduct.






























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