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Question about visible light properties.

  1. Jul 24, 2009 #1
    Why are we unable to see light except if we are looking at the light source or a source that is reflecting the light?

    For example; say we set up a powerful laser but we cannot see the origin or the end point. The a vacuum is produced in the room to remove all possible particles that might reflect the laser's light. We switch the laser on but we cannot see the beam of light passing from one point to the other.

    You cant really say that its because the particles are so small because if you take into account a lightsource like the sun, the light radiation and packets of quanta pretty much saturate anything in direct lines from the source (or anything reflecting the source).

    So I guess the more appropriate question is why cant we quanta in transit?
  2. jcsd
  3. Jul 24, 2009 #2


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    It's because light travels in a straight line.
  4. Jul 24, 2009 #3


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    You may be thinking of how we can see ordinary particles when they are on the move. That is becasue ordinary particles reflect or emit light i.e. photons.

    Photons do not reflect or emit photons.
  5. Jul 24, 2009 #4
    As has been pointed out, becase light goes in a straight line and if the laser is pointed at a wall (and the wall is not reflected) and there is no dust or such to scatter the light in all directons then not a single photon MEETS OUR EYE. And we see things when photons his our eyes.
  6. Jul 24, 2009 #5
    Okay I get it. I feel a bit dumb. Photons dont emit light, they are the light, so we dont see it unless the photon hits our eyes, I get it.
  7. Jul 24, 2009 #6


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    Don't feel dumb. Having someone get a question answered to their satisfaction is a very rare and gratifying thing for many of us. Ask more!
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