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Do photons carry information?

  1. Aug 12, 2011 #1
    I was wondering, well basically if photons carry information about themselves that is interpreted by our brain?
    I ask because I was thinking about things like color and distance. Correct me if i'm wrong but we see different colors because of the way the molecules or elements that make up an object absorb and reflect light, right?
    And I was wondering about how we percieve distance as well, when a photon bounces off of an object and reaches us does it carry information that our brain interprets about the makeup and distance of the object that it bounced off of?
  2. jcsd
  3. Aug 12, 2011 #2


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    Interesting questions.
    I'm almost sure that distance is something humans "learn" when they are babies.
    Basically there's no difference between a photon that comes from a far star with a photon that comes from your hand, it's the brain that learned that stars are far that make yourself "think" that stars are indeed far.
    Stars might be a bad example though, if nobody tells you how far they are, you're unlikely to figure out yourself and you might think they are "glued" on the sky at a ridiculously close distance.
    What I'm saying is that a baby under 1 year old has absolutely no idea how far are objects from him until he learns to grab object with his arms.
    In that sense, photons do not contain any information if they come from far away or they were just created and reached your retina.
  4. Aug 13, 2011 #3


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    Photons only have intrinsic properties such as wavelength, spin, polarization, ETC. The term information has a wide variety of meanings and gets into other areas such as perception, consciousness, representation, ETC. In my opinion a single photon does not carry information. It is our interpretation of the results of a measurement that conveys information, if that makes any sense.
  5. Aug 13, 2011 #4


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    yes, a photon carries physical information (the kind of information that a Maxwellian demon could harvest energy from, given a random distribution of such photons). This has been demonstrated qualitatively in a lab following Leo Szilard's protocol:


    Information heat engine: converting information to energy by feedback control
    Shoichi Toyabe, Takahiro Sagawa, Masahito Ueda, Eiro Muneyuki, Masaki Sano
    Nature Physics 6, 988–992 (2010) doi:10.1038/nphys1821

    Anything that can occupy more than one state (and that's all matter) carries information. Moving between states requires an energy exchange. No consciousness necessary.

    Humans are very sophisticated Maxwellian demons, but the Earth has all kinds of non-living Maxwellian systems (lightning is an excellent example, given the preceding process of charge separation)

    There's also excellent examples of non-living sorting systems in the study of self-organization:

  6. Aug 13, 2011 #5
    Absorbed part doesn't play a role in determining the color of an object. It's the reflected part that carries information about the object which photons bounce from. It originates from the molecular structure for a homogeneous monolayer medium. For multilayer mediums each layer contributes to the reflected part of the beam.

    Human vision is a very complex mechanism, different structures are responsible for color/distance and edge detection. From a macroscopic point of view distance is related to the intensity of the reflected part but in daily life we try to determine distance/size of an object by comparing the current corresponding data perceived by our vision system to some previously earned experience and try to make an approximation.
  7. Aug 13, 2011 #6


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    I notice that Drakkith says "no, a photon does not carry information" and Pythagorean immediately says "yes, a photon does carry information"! I suspect it is a difference in interpretation of the word "information". To me, "information" is "interpreted data". A photon carries data, not information- our brains do the interpreting.
  8. Aug 13, 2011 #7
    Imagine human eye is a matrix with 5.10^6 elements and each element can be perceived as a pixel. Optical waves interacting with vision cells (rods and cones, which are actually the pixels themselves) will have different amplitude/frequency/phases thus induce different waveforms at the electrical level. Our brain interprets these electrical signals and tries to match patterns of same/similar waveforms in the previously earned experiences.Depending on the output of this process a decision will be made by the individual.

    Photons carry the data only, this data becomes the information after a decision about it is made.
  9. Aug 13, 2011 #8


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    Yeah, I think so. I'm using the physical definition, not the more common laymen definition. I'm also considering my http://en.wikipedia.org/wiki/Neuroethology" [Broken] experience.

    From an evolutionary point of view, biological systems are physical systems just like any other. We have a much more sophisticated way of interpreting and storing information, but a photon in one state will interact with an electron differently than a photon in another state. The information was in the photon independent of humans and the electron is able to "interpret" the nature of the photon and react accordingly. Humans also "interpret" but we do so through a neuroethological chain of events.

    That is, we can store representations of our encounter with the information in the past, and weigh it's emotional significance (which is, in general trend, tied to our survival, but may contain prediction errors if our history was biased towards particular kinds of events) which factors into our "according reaction".

    Many systems throughout the universe show a variably complex way of reacting to information, from the electron's straightforward reaction to a biological systems history-weighted reactions.
    Last edited by a moderator: May 5, 2017
  10. Aug 13, 2011 #9
    I'm interpreting the word "information" as indicated by the context of the question. Namely, do photons carry some kind of information that tells us about our surroundings (color, distance, etc.)?

    Yes and no. You are right about color. Photons each have a frequency, which is basically color.

    But your basic mistake is to assume that the information is contained in single photons. Actually, most of the information is contained in the pattern that ALL the photons coming into your eyes form. They form shapes, lines, and patterns, and your brain has tricks to know which shape is on top of which other shape, perspective, the relative brightness of each surface, A gradual change from light to dark on a surface indicates that it is curved with respect to the light source. That tells your brain what kind of shape the object has. Artists exploit these kind of tricks do produce and image that looks 3-d on a 2-d surface. A drawing is basically a kind of optical illusion that tricks the brain.

    As far as distance goes, a photon doesn't show how far it has traveled, but the number of photons will diminish with distance from a light source (lower intensity--each photon at a given frequency carries the same energy, so there must be less of them). That's one clue that your brain can use for detecting distances, but it's only one clue among many that your brain will use to judge how far away something is. As far as your brain is concerned, lightness or darkness is all relative. If you look at a lump of coal in a bright light, it's not going to be as dark as a snowball in the dark, but the snowball still looks white in the dark because its darkness is judged relative to the rest of the scene.

    So, basically, if you want to understand vision, it may be more helpful to think of it as a psychology question than a physics question. It's also helpful to imagine trying to design/program a robot that can interpret what they see. Of course, physics underlies everything, but sometimes it can be impractical to pursue psychology to the point where it becomes physics. It's quite an undertaking, to say the least.
  11. Aug 14, 2011 #10


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    We aren't really the best at predicting distances (, I think shading and Euclidian cubic assumption is mostly where our distance estimations come from. According to Ramachandran, it's because we have learned about parallel walls, not so much that we were born with the assumption, but this isn't an article, just a video by a pop neurologist, so I don't know how well that question is really investigated:

    The Ames Room Illusion
    Last edited by a moderator: Sep 25, 2014
  12. Aug 16, 2011 #11
    If photons don't carry information, then why do we watch television? As relevant to human vision, each photon carries only a color (frequency) and a location in space and time (only to a limited degree of accuracy because of the uncertainty principle). Vision occurs when we observe the color and location on our retina of many photons over time, and extract distance and object information from the relationship between the photon impacts. In summary, a single photon carries only color and location data, and any other properties of the environment must be deduced indirectly by comparing many received photons.
  13. Aug 16, 2011 #12
    If particle nature of a photon is considered, it carries much more data than just colour etc.
  14. Aug 16, 2011 #13
    Good information and discussion. There is some confusion about the word information. Obviously a photon doesnt carry information the we would think of it. But surely it carries information nonetheless. Or data, or whatever you wanna call it to understand it.
    When we see a color it is because the photons are behaving in a manner that allows us to percieve characteristics about them. So that is an exchange of information. Yes our brain interprets it but it interprets it the way nature intended, we didnt make our eyes or our brain. Although I guess all particles carry information. Right?
  15. Aug 16, 2011 #14
    - A photon can carry binary information, right handed spin can be denoted 1 and left handed spin can be denoted 0 (or vice versa)

    -A photon can carry positive real number valued data, its wavelength

    This is based on information, in the strict technical sense, being a sequence of characters that record and/or send a message.
  16. Aug 16, 2011 #15


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    I'm not sure what else can really be said other than Yes/No, photons carry/don't carry information depending on your definition of information.
  17. Aug 17, 2011 #16
    I'll throw my hat in...

    We're able to control photons to carry information - (i.e. fiber optics)

    They 'tell' us their origins (i.e. gamma spectroscopy)

    We can 'send' it and ask it for information (i.e. Bragg's law)

    A single photon probably is useless. But the OP asked, Photon(s). So i think the answer is yes.
  18. Aug 17, 2011 #17


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    A single photon can tell you two things: its energy and when it arrives (the Heisenberg uncertainty principle implies a limit to the accuracy of the two but we can ignore that for this discussion, I think).
    Using more photons, we can transport more information by modulating the rate of arrival or the energy of the photons (amplitude or frequency modulation, in radio terms or, perhaps the varying reflectivity of a piece of paper with writing / pictures on it). Increasing the numbers of photons used gives a disproportional increase in the amount of information which can be transported because we are basically dealing with permutations of possible states - involving the Factorial operator and that produces very big numbers very quickly.
    Talking more practically, there is the added factor of signal to noise ratio which also limits the amount of information that can be transported in any system because noise will interfere with the accuracy of actual measurement.

    Brillian clip, btw, of the self organising dipoles. Really fun and almost 'ideal'.
  19. Aug 18, 2011 #18
    "A single photon can tell you two things: its energy and when it arrives"

    Can we not get polarization data/information from it?
  20. Aug 18, 2011 #19


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    In principle, perhaps, but it would be the same as for directional information. They would both need contributions from many photons, I think.
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