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Can't imagine something that is colorless

  1. Aug 10, 2004 #1
    I can't imagine something that is colorless. Even clear is color. Is the starry nights contrasting black totally made from stars that are so red-shifted they appear black? If this isn't true, than what makes space black? Without the red-shifted stars, what color would it be? Still black? White? Colorless?... What is colorless? Does such exist?
  2. jcsd
  3. Aug 10, 2004 #2
    Black is the absence of colour.
  4. Aug 10, 2004 #3
    To see a color light must bounce onto something that has a color (which means does not absorb all light) and that light (or light directly from the emitter) must reach at least one of your eyes. If there's nothing there that emits or bounces light you won't see any light which will result in blackness/darkness (which is the reason some black portions of space are black). Stars might be invisible when the distance is so great that the light particles are so scattered that the light intensity is too low to be able to see with the naked eye.

    I think the only colorless thing the way you mean colorless (as in it doesn't alter the lighting that bounces off it) is a mirror.
  5. Aug 11, 2004 #4

    When there is truly an absence of color the receptors in your eye are at rest. When at rest, the eye sends out signals at a steady and slow rate which corresponds to a color we call dark grey. When one's eye perceives black it supresses this rate or shuts it off. Therefor the perception of black creates a definite change in the eye receptors which means that black is a ture and genuine color on its own.

    black is a color
  6. Aug 11, 2004 #5
    From my understanding:

    The absence of any light, therefore the absence of colour, is black. I’m not talking about looking at a black surface among other coloured surfaces. I’m talking about being in a complete light free environment. There are only a few such places naturally occurring on Earth. One is at the bottom of the ocean, and a few others are in some caves. I’ve been to one such cave, which I believe was in Tennessee. During a tour, we entered one ‘room’ and the tour guide explained how dark it naturally was in that room. He then turned off the lights. It was pitch black, however, after several moments I did notice very faint pulses of grey.

    So to me, this means that the absence of colour IS black, however after a while our eyes, due to the photoreceptors going mad trying to find a light source to focus on, perceive it as dark grey.
  7. Aug 14, 2004 #6

    When the lights were shut off in the cave you percieved black because light was still reflecting around the cave. After a while, you started to notice the color dark grey because some of the light was leaving the room. If you had stayed in the cave long enough it would have been completly dark grey. Thus meaning that when you percieved black, you were not in complete absence of light because you saw black.
  8. Aug 14, 2004 #7


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    Uh.. this is the most illucid description I've ever seen.

    First, the human visual system is not a particularly good scientific detector. The visual system is quite imaginative, and often begins making up colors and shapes for you when the eyes are seeing nothing at all. Your brain has a variety of groups of neurons that act to detect specific angles of lines, or specific curves. When no information at all is presented to them, they will occasionally emit false positives, and you'll think you're seeing something.

    The total absence of any (visible) photons would be called, by any scientist, black. The inside of a cave is not really completely light-tight, but it's probably light-tight enough that the light levels inside are below the threshold needed to stimulate your eyes.

    As far as the light taking its time on moseying out the door, that idea is preposterous. Light travels at 300,000 kilometers per second. Even if the cave's walls are rather reflective, it wouldn't take long at all (picoseconds or less) for essentially every visible photon in the room to be absorbed by the walls in a 100-foot wide cave. Why don't you do that calculation?

    - Warren
  9. Aug 14, 2004 #8
    As tree penguin said, to see a colour, light muse bounce off something that has that colour. For example, if you have an orange t shirt, you see it as orange because when light (of all wavelengths in the visible spectrum) shines on it, the t shirt absorbs most of the wavelengths except for the wavelength corresponding to orange which it reflects. So if something is of a colour 'X', it means it absorbs all wavelengths except the wavelength corresponding to colour 'X'.

    Now if you call something colourless, I think it means that the light hitting that something is not absorbed (not a single visible-light wavelength of it). For example, clear glass is a material you could call colourless. The glass does not absorb any specific wavelengths. It transmits most (some of the light is reflected) of the light that hits it. But it does not selection of what wavelengths is transmitted as no wavelengths is absorbed.

    I hope this makes sense!

    As for seeing dark as grey, it's an interesting fact but as chroot explained, scientifically, black means zero photons. There is a difference between what is there and what our senses perceive to be there.

    lvlastermind, you said it yourself:

  10. Aug 15, 2004 #9


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    We live in a fairly colorless universe. That is to say color isn't something that exists in the physical universe outside of the mind. In other words, the phenomena of color is exclusively a property of the mind, and isn't directly related to the objects we perceive. Stars don't posses color, nor does the night sky or anything else.

    Color is also not directly a property of light either. It is true that light is usually the cause of the processes in the brain which are interpreted as various colors, but that's not the point. The eye receives light of various wavelengths, and sends this data encoded via and electrical signal to the brain. The processing of this signal is what we perceive as color, and isn't something out there.

    So in answer to the question: than what makes space black? is that space isn't black at all. By default, black is the color we see, even in complete darkness. When light from certain regions of the sky reach the retina, we perceive different colors in spatial arrangements that correspond to the light from the sky. In the case of the night sky, most of the sky appears black because light is reaching us from a minority of it's regions.
  11. Aug 15, 2004 #10


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    You start to notice the color dark grey because your pupils are dialating so they can take in more light. Thus, you go from being unable to see (black) to being able to see a dim light.

    Furthermore, your ability to see light is much more sensitive than your ability to see color. That is why you see shades of grey when the light is very dim.
  12. Aug 16, 2004 #11
    Glass is a pretty poor example of "colorless" as you can in fact see it. Gases like nitrogen and oxygen are a couple of things that spring to mind as being "colorless". Funny that no one has brought that up yet, but sometimes the things most obvious are the most easily overlooked?
  13. Aug 16, 2004 #12
    Thanks for pointing that out. In fact I chose glass as an example because it is an easier example to explain how light goes through undisturbed.

    And yes the most obvious things are the most easily overlooked! The really colourless stuff is stuff our eyes can't detect because light goes through it undisturbed.
  14. Aug 16, 2004 #13
    Good Point! I hadn't thought of that although this is something I learnt at high school! :smile:
  15. Aug 16, 2004 #14
    Ok, you shine a bundle of full spectrum light a an object the color you see is the light reflected by the object.
    In other words, if you shine light at that object, yet filterout the color you saw with a bundle of full spectrum light, the object should appear black?
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