Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The invisible people

  1. Feb 5, 2006 #1
    Can an invisible person see? Please explain for me. Thanks
  2. jcsd
  3. Feb 7, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    I've reinstated this thread because I don't think it is quite as non-sensical as ZapperZ thought! I interpret it as "suppose there were some people who were invisible or used some kind of mechanism to make them invisible- could they see?"

    Let me answer in reverse form. To "see" something means that light from that object enters your eye and is absorbed by your retina. Someone standing behind you would, at the very least, see dark spots where that light was absorbed so you couldn't be truly invisible.
  4. Feb 7, 2006 #3


    User Avatar
    Science Advisor

    If the method used to cause invisibility employed the bending of light around the subect so that the light could continue as though it had never been interupted, then true invisibility could be achieved. Given this conition, the invisible individual (which just happens to be a lot of fun to say!) would not be able to see.

    However, in order for vision to occur, light need only reach the eye. So, bending all the light around a person except that which enters the eye would yeild a very close approximation of invisibility, without any loss of visibility (if that majes any sense).
  5. Feb 8, 2006 #4


    User Avatar
    Science Advisor
    Homework Helper

    Light is visible if the wavelength falls in the visible spectrum. You could have,say, infra-red sensors and UP-convert it to visible light (like those night-watchers). You'd still be invisible to the eye.
    Last edited: Feb 8, 2006
  6. Feb 8, 2006 #5


    User Avatar
    Gold Member

    Interesting approach, Galileo. I assume then that your refractory (or whatever) apparatus would selectively pass IR and not visible wavelengths to the interior of the device. Could work.
  7. Feb 8, 2006 #6
    My first thought was also to say that the invisible person could not see since all incident light would go right through. But this transparency is a static method of being invisible. And since we are speaking of rather improbably conditions here, how about a dynamic method of being invisible instead? Light is indeed absorbed by the invisible body so the subject can see, but then it is dynamically re-emitted on the other side the same way it came in. This subject could be invisible but still able to see because it actually processes all incident light.
  8. Feb 9, 2006 #7


    User Avatar
    Science Advisor
    Gold Member

    There would have to be a time delay between absorption and re-emission. In principle, this delay could be detected and so, arguably, the subject would not be truly invisible.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: The invisible people
  1. Complete Invisibility (Replies: 7)

  2. Invisibility Update (Replies: 6)

  3. Why is air invisible? (Replies: 2)