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Does light reach every single part of space?

  1. Apr 6, 2015 #1
    We all know that light is photons (massless particles) travelling in waves in straight lines. My doubt is: photons are emitted by circular objects, which means that there are some angles between waves, which means that photons don't reach every single part of the space...
  2. jcsd
  3. Apr 6, 2015 #2


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    I really have no idea what you mean by "angles between waves" or why you think that means "photons don't reach every single part of space"?
  4. Apr 6, 2015 #3
    Ok sorry, maybe i wasn' t so clear...
    Photons are emitted by round objects and travel through a straight line; there must be a distance of space between those lines and since they come from a round object there bust be a part of space where light doesn't arrive. I linked an image just for rendering the concept.

  5. Apr 6, 2015 #4


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    A light wave from a point source travels in a circle (actually, in 3 dimensions, a sphere) centered on the point. The lines you show are only a few of the infinite number of radii of such a circle (or sphere).
  6. Apr 6, 2015 #5
    I know that but an object which is light-years far from the one emitting the photons, may doesn't receive any of them!
  7. Apr 6, 2015 #6
    Photons can be understood as particles, but also they can be understood as waves, (in an electromagnetic field).
    If you throw a rock in to a pond it produces waves.
    The waves spread out until they are too small to be seen, but they spread in a continuous, and even way, no gaps where the wave is absent.
  8. Apr 6, 2015 #7
    Interesting answare! But i still don't understand how a finite number of waves spreading out from a round object can reach every single part of space...
  9. Apr 6, 2015 #8
    For most light sources, the intensity drops off with distance, because the light energy is spread out over a larger area. You are correct that an object far from the source may not receive any photons from the source, because as the intensity drops, the rate of photons drops, and the probability of getting a photon is lower. The actual number of photons hitting the target is random. This has nothing to do with spaces between angles since angles are dense and have no spaces between them, and simply has to do with probability.
  10. Apr 6, 2015 #9
    It's not intuitive how light works. At your level, you will simply have to accept that light travels as a wave which is infinitely divisible, but the wave only have a certain probability of interacting with a target, and only in clumps of energy and momentum, which we refer to as photons. If you are looking for an intuitive description, you won't find one.
  11. Apr 6, 2015 #10
    Thanks for answering. You know, I love physics because is all logic and I think it is all related to logic and intuitive stuff... Anyway, do you have any official source where I can read what you said? Like a book or something else...
  12. Apr 6, 2015 #11


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    We had almost exactly the same thread a few months ago. You may find some of the answers on how dense the barrage of photons we are receiving is and how small the "gaps", if they can still be called "gaps" when they are so small, are:

    There are objects in space that we can take pictures of (using the Hubble Space Telescope) that are so dim and far away that a big telescope only captures a few photons per second from them, so you might say there are "gaps" between the rays from such objects. But those objects are on the other side of the visible universe from us. There is nowhere in the universe far enough away from galaxies that it isn't awash with light.
  13. Apr 9, 2015 #12
    But that means that: Yes! There are Gaps! I read the other article and I realized how dense they are, but it doesn't mean there are no gaps...
  14. Apr 9, 2015 #13
    There aren't gaps in the wavefunction. There are just gaps in where the photons actually happen to be measured. Do you know what a wavefunction is? In other words, the photon has a probability of being emitted in any direction, with no gaps, but the actual photon is emitted in one direction randomly, so yeah there are gaps, but it has nothing to do with gaps in angles.
  15. Apr 9, 2015 #14
    Thanks for answering, but I don't really understand what you mean... You said that there are no gaps in the wavefunction, but we know that each photon travels in a wave and you said that they fallow "random" directions, but that means that between a wave and another there is a gap!
  16. Apr 9, 2015 #15
    Yeah, you kinda need to study quantum mechanics for a while. It's not easy to explain.
  17. Apr 9, 2015 #16
    Try, please. I don't think there is any kind of physics not-understandable by human logic...
  18. Apr 9, 2015 #17
    As we get further from the light source, the probabiltiy of actually detecting a photon becomes less.
    However that probability exists to the same degree at every point in space that is the same distance from the source.
    There are no point in space where the probability is zero, hence the wave is everywhere, regardless of where a photon was actually seen,
    Over time and averaged out, every point of space at the same distance from source will 'see' photons at a rate consistent with the probability of seeing photons at that distance.
  19. Apr 9, 2015 #18
    Ok I think I got what you said. That means that all the waves we use (like radio waves for example) travel in all directions just like mechanical waves in water?
  20. Apr 9, 2015 #19
  21. Apr 9, 2015 #20
    Ok thanks, Does anybody know the equation that relates the distance traveled by the waves to the probability of finding a photon at that point?
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