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B Can we see radio waves or other invisible waves with our eyes?

  1. Oct 25, 2018 #1
    There are many electromagnetic waves. Some of them are visible while other are invisible. Can we see those invisible electromagnetic waves?
    How
    Please give with scientific reason.
     
  2. jcsd
  3. Oct 25, 2018 #2
    Before getting into scientific reasons, there is an issue of definition.
    By definition, invisible EM waves cannot be seen.

    That aside, there are two main reasons that invisible EMs are invisible:
    1) the photoelectric effect: https://en.wikipedia.org/wiki/Photoelectric_effect
    Longer EM waves cannot trigger the electron changes in the rods and cone of our retina.
    They simply do not pack the energy to do this.
    2) the transparency of our eye lens and the liquid in our eyes:
    In general, transparent materials are transparent in the visible spectrum - with no guarantees for other wavelength. In particular, the water in out eyes is very transparent to visible light, but will block most microwave radiation.
    3) focus:
    Different wavelengths are focused differently by the materials in our irises. Those materials are "designed" for visible light. While looking at the violet light coming from black-light bulbs or bug zappers, you may have noticed that the bulbs look blurry. This is because when you get to the edge of the visible light spectrum, especially the high end (UV), our eyes do not focus these wavelength onto the retina very well.

    There is another way of interpreting your question. Since the eyes work as "designed", why haven't they adapted to other wavelengths.
    That answer is:
    * On the surface of planet Earth, day light includes lots of visible light.
    * Visible light is on the border of "ionizing radiation", so an eye that focused UV onto its retina would then need to accommodate the destructive aspects of UV radiation on proteins.
    * In the kind of scenes that mammals developed in (last 100M years), near IR does provide some additional information not available in visible light. For example, if you cut a plant from its roots, it will lighten in the near IR long before there is any visible change in the leaves. Apparently for humans and our predecessors, this additional information was not enough to develop another set of cone cells on the retina. But, compared to most other animals, we do really well with our color vision. The point is that there is a trade-off between gaining additional useful sensory information and the "use" of evolutionary development.
     
    Last edited: Oct 25, 2018
  4. Oct 25, 2018 #3
    I had no much concept about photoelectric effect.
    Thank you for your answer.
    But i was eager to know if there was any possibility to see invisible EM waves.
     
  5. Oct 25, 2018 #4
    Absolutely.
    Almost all close-circuit TV cameras will see well into the infrared.
    Astronomers use special antenna and imaging devices to collect information from all sort of EM.
     
  6. Oct 25, 2018 #5

    russ_watters

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    A significant fraction of the astronomy photos you see are not taken in visible light. I'd go so far as to say most that look like "visible" light photos are at least providing extra infrared. Then there are many that are exclusively false-color radio wave photos.
     
  7. Oct 25, 2018 #6
    I must mention that we also have a sensitivity to infra-red, but not with our eyes. You may locate a heat source by eg differential heating on your face or hands. Technically, it is 'sensing' rather than the narrower definition of 'seeing', but many snakes have heat-sensitive 'pits' on their heads which provide enough resolution for effective strikes...

    IIRC, bees and other pollinating insects have vision which extends into the near-ultraviolet. Flowers often have bright markings in that spectral range to announce themselves and guide approach.

    FWIW, people who had traditional cataract operations were able to see near-UV. I've read that such were deployed on coast-watch in hope of spotting WW2 submarines signalling to spies ashore...
     
  8. Oct 25, 2018 #7

    ZapperZ

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    Your question doesn't make much sense. By definition "invisible" means it is not visible using our human eyes. So why are you insisting on wanting to see it?

    Now, if you are asking if we are able to detect these invisible EM waves, then the answer is yes. That is how we knew of the presence of a wide range of EM spectrum beyond the visible range.

    So what are you really asking for here? Think a little bit.

    Zz.
     
  9. Oct 25, 2018 #8
    Very beautiful detailed and informative reply. Thanks
     
  10. Oct 28, 2018 #9

    Nugatory

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    A long digression about what is and is not a polite reply has been removed from this thread.

    Please, everyone, if you encounter a post that you believe is rude or otherwise inconsistent with the Physics Forums rules.... don't engage the offender yourself, report it and let the mentors deal with it.
     
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