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Torch light in space

  1. Jan 10, 2009 #1
    Is it true to say, in space (or in vaccum), you wouldn't be able to see the torch light, unless you point it to your eyes?
  2. jcsd
  3. Jan 10, 2009 #2

    Doc Al

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    Staff: Mentor

    Since there would be nothing for the light to reflect off of, that would be correct.
  4. Jan 10, 2009 #3

    Lol. That makes more sense. Thanks for the translation
    Last edited: Jan 10, 2009
  5. Jan 10, 2009 #4
    I believe he means a torch in the British sense, which is known to Americans as a Flashlight.
  6. Jan 10, 2009 #5
    Thank you. :blushing:
  7. Jan 10, 2009 #6
    Good point. We don't "see" light. Light is the means by which we see other objects. However a terminology problem arises when light from a light source is entering directly into you eyes without first reflecting off of something else. If we continue the logic of the term "see" then "seeing light" should only apply to a situation where light from source A reflects off light from source B allowing us to "see" light from source B. That's fiction.

    However, looking directly into a light source is an undeniable light-eye interaction. You're doing it right now. If we don't "see" light, then are you unable to "see" most of your computer screen? If, on the other hand, we propose that all we ever "see" is light, then how are we aware of the objects all around us?

    It's opening a can of words. Better to just accept the fact that the verb "to see" can be applied alternately to the illuminated and the illuminant, depending on the context, despite the dissonant logic.
  8. Jan 11, 2009 #7
    This post was way too philosophical, I think. We see when photons hit the eyeball. We don't see light from a flashlight in space because there are no particles for photons to bounce off of, so if it's not pointing towards the eyes those photons will never reach the eyeball.
  9. Jan 11, 2009 #8
    It was worth it for the line :"It's opening a can of words." You watch: in a year everyone will be saying that.
  10. Jan 11, 2009 #9
    But the reflector is itself a photon emitter-photons are absorbed from the source and some regenerated as the reflected photons
  11. Jan 11, 2009 #10
    Then my question becomes: to what extent can we consider all visible objects to be photon emitters?
  12. Jan 11, 2009 #11
    Now isn't that what dark matter comes down to? What potential object within the universe fails to serve as a photon emitter, which is the fundamental question of the MACHO-hunters (which had been discredited by a majority of physicists)

    Tough question, which I highly doubt anyone knows the answer to (at the moment)
  13. Jan 12, 2009 #12
    A possible way to answer zoobyshoes question is in terms of energy supply and conversions.The torch bulb is continually being supplied by a relatively large amount energy input all the time while the battery lasts whilst the supply to the reflector originates from the torch bulb and is very much smaller by comparison.
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