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Coincidence About Vision on Earth

  1. Jul 28, 2005 #1
    Our sun eminates electromagnetic radiation over an enormous range of frequencies. Radiation curves (energy@wavelength) resemble bell curves, and highly accurate measurements have shown that the peak of the sun's radiation curve is in the visible light range. This is not a coincidence, it is exactly what we would expect according to the Theory of Evolution.

    This observation explains why visible light was chosen from the broad spectrum of EM frequencies. But there is another equally compelling reason that we "chose" visible light, and that is where we find our coincidence: Water is transparent to visible light.

    All life on earth is surrounded by water in either liquid or vapor form. Having vision in the microwave or radio spectrum (on earth) would mean that everything would be about as clear as antartica on a bad day (when the water goes opaque for us).

    We could use this coincidence to asses the likelihood of intelligent life on other planets in the galaxy (Max output of the star corresponds to a spectrum for which the planets main enviroments are transparent. I don't know if we can tell what gases are present on distant planets.)

    It is arguable that intelligent life could exist without vision, but I think that the universe is too brutal for it to evolve to an intelligent stage. It is also concievable that humans could have evolved vision in the visible range even if it was not the peak of the suns spectral curve.

    My apologies if these ideas are considered basic, I have never thought much about astrobiology before.
  2. jcsd
  3. Jul 28, 2005 #2
    Why would you say it's not a coincidence that the sun emits light we can see, but then flip flop and state that water being transparent is. After all isn't all life supposed to have started in the water? What about air also being transparent?
  4. Jul 28, 2005 #3


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    It might make it easier to see the connection if you recognize that sensory input organs evolved BECAUSE there was data available to receive and interpret.

    If the oceans were a poor conductor of light, then critters would receive little input from the world around them through that channel (eg. no shadows of predators passing overhead). Without an input that makes a dramatic impact on survival, those senses would not be strongly driven to evolve.

    None of that of course alters your main point, which is that using this info might help us find life.
  5. Jul 28, 2005 #4
    You're pointing out two good reasons why any creatures who happened to be born with vision in the range we call "visible" light, would have an advantage over those who didn't, and who would therefore more likely tp pass their genes on. I'll buy it.
    Blindness for a human means the inability to sense important large and small scale features of the environment when not in direct tactile contact with them. So for an intelligent alien life form the requirement wouldn't have to be that they be sensitive to any particular frequency of light, but that they have some sensory means of assessing the important features of their environment. I recently heard about a fish that lives in the muddy Nile which "sees" by producing a large electric field and sensing how nearby objects change that field.
  6. Jul 28, 2005 #5
    The coincidence is that both of these things happened in the same place, independent of one another!

    There are a limited number of ways of assessing the enviroment, senses. We are already equiped to detect EM waves, pressure waves, contact forces and we also have limited particle detection.

    Of these, EM waves are king. They are the most abundant thing in the universe, and they carry more information faster then anything else. Some fish turning itself in to a dipole/multimeter is not equivalent to vision, which I stress is the optimal data transfer medium in the universe.
  7. Jul 29, 2005 #6


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    It is very logical to project a selection bias for vision within the local EM spectrum. But that does not vary enough to be a huge factor for any main sequence star. There are also other issues. 'Eyes' that could 'see' with any useful degree of resolution at radio frequencies would be enormous. And organic molecules [an important ingredient in evolving 'eyes'] do not last long when exposed to short wavelength [e.g., UV, gamma rays] radiation.
    Last edited: Jul 29, 2005
  8. Jul 29, 2005 #7
    They are "king" if you have access to them, yes. But if, as you reasoned, intelligence depends on not being blind, there are still important ways not to be blind on a planet whose atmosphere isn't transparent to the visible spectrum. I agree that transparency is vital, but there are other ways to attain it that amount to not being blind.
    On such a planet the dipole/multimeter creatures would be favored and each mutation in which this ability became more sophisticated would be favored. The kind of information available from this kind of sense depends both on the sophistication of the instrumentation and how the brain of such a creature processes it. All such non-visible-light senses, echolocation in bats and dolphins, for example, are probably, in principle, enough to gather the kind of information needed to not be blind.

    There is a point after which "intelligence" is no longer dependent on the information you have at your disposal, but how you analyze it. This separates us from all the other creatures on earth who can use visble light to gather info about the environment. On a non-transparent to visible light planet, the beings could be both non-blind and have the same chances as we did of developing the ability to process and analyze the information they can gather that we do.

    The question becomes: At what point in the evolution of their ability to process and analyze information to well call them "intelligent"?

    I think the reasoning of your Opening Post is very good and the notion of looking for planets whose main environments are transparent to the maximum output of its star for intelligent life is novel and worth exploring. People usually point to all kinds of other criteria, either taking this one for granted, or not having thought of it. I agree it is a good reason to rule planets in. I'm not sure it tells us what remaining planets we can confidently rule out.
  9. Jul 29, 2005 #8


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    I have a hard time seeing how these are independent. Also, it is worth noting that solid water is not transparent and it is the dominant form in which water appears in the solar system.

    For every star there will be ranges of distances where water will tend to vaporize, take liquid form or be solid. Water is composed of sub-iron elements which are common throughout the universe under any reasonable baryogenesis scheme. The notion that a sun with a particular spectrum will have liquid and vaporous water on a body somewhere in its solar system is hardly that coincidental.
  10. Aug 4, 2005 #9
    Let's not forget also that eyes specialize by species depending on the need.

    Mosquitos see infrared.
  11. Aug 4, 2005 #10


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    Flowers radiate in ultraviolet, so the visible spectrum for bees, wasps, etc. extends in that direction as well. And things like frogs see only lines of various angles and movement.

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