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Why do we see black objects? Colors of objects are formed when the spectrum of that color is reflected. Example Green objects are green because they reflect the green spectrum of light, red objects are red because they reflect red spectrum of the visible light and white objects because they reflect all the visible spectrum of light. When an object absorbs all the visible spectrum of light, it becomes black. But if nothing is reflected from the object, shouldn't it be invisible instead of black?

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  • $\begingroup$ simply, it's not a perfect black object ... $\endgroup$ – user46925 Jan 12 '16 at 16:37
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    $\begingroup$ Black is the color we perceive in the absence of light, so it should indeed be black. To make something invisible you have to make it completely transparent - so that light behind the object can pass through it and into your eyes. However a perfect absorber would absorb any light hitting it from behind, and so not be invisible. Real objects aren't perfect absorbers, hence you can still see their texture. $\endgroup$ – Judge Jan 12 '16 at 16:47
  • $\begingroup$ I think the answers given so far misinterpret the intention of the OP's question. I don't think he want's to know how black an object can be, but rather why can't we see through it. The comment by @Judge answers this. $\endgroup$ – pela Jan 12 '16 at 19:16
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I wrote an earlier answer to the question: "Is true black possible?" which addresses some of the points you mention. It includes this image of "the blackest substance known":

enter image description here

In particular, most "black" objects have a small amount of reflectivity, from which you can deduce clues about their shape. But the sample of really black material which I show is SO black that it looks like there is a hole in space - you can't see any shape in the surface, and it does indeed look "invisible" in the sense that you don't really see the object, you see a "hole". But you don't see what is behind the hole: black is not the same as "transparent", and the black object absorbs all photons. It's not actually possible to make a material that is black in one direction and transparent in the other - there's a simple argument to be made that such a material would violate the laws of thermodynamics. Instead, in this world we're stuck with the "reciprocity theorem" that tells us that blackness is a two-way street.

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Even if a perfectly black object reflects no visible light, we can still distinguish its shape from a non-black background. Most real-life black objects are just much darker than the surroundings, not perfectly black.

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Black is entirely a construct of your brain, created internally to fill in a spatial region in which you eyes detect no appreciable level of photon emissions. That may sound a bit surprising, but try this: Imagine red, then green, then blue. You could do it, right? Well, no photons were involved there either. Black is the same idea, since it too is something created in your brain without any photons from your eyes. Black is just a bit more vivid because it is directly linked into your external perception systems as a way to fill in those gaps.

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I will address the "see" part.

Why do we see black objects? Colors of objects are formed when the spectrum of that color is reflected. Example Green objects are green because they reflect the green spectrum of light, red objects are red because they reflect red spectrum of the visible light and white objects because they reflect all the visible spectrum of light.

This is only partially true. We "see" the spectrum colors because the retina of the eye responds to the frequency. But at the same time the retina and the brain have a system that builds up colors from combinations of frequencies, even two frequencies are enough to produce color perception in the brain.

Thus one can have the black of the other answers, no reflected frequencies, but one can create a black paint that gives the same perception from the three primary colors. The eye perceives "black" from the confluence of the reflected frequencies.

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As long as there is a discontinuity in the index of refraction ( real or imaginary parts) then there will be a reflection from the "black" object. How your eye-brain perceives it is a different matter..

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  1. A related question is, why do we see white?

From a physics perspective you are correct, we should not see the object. We should see a hole, a complete absence, like looking into the face of a shadow rider or a dementor.

However, from a biological and neuroscientific perspective, we autocorrect. The limited light is detected by the super sensitive rods on the edge of our retina, limited information gets sent via ganglion and bipolar cells, down the optic nerve, through the thalamus and lands in the visual cortex near the back of your neck. This is where we create the virtual object which "pops out", at which point, your interpretation/version of what exists deviates from what actually exists. An interesting experiment would be to take a photo (as the one above) and look to the photo and then to the real object side by side, although your brain may also compensate for the photo and pop out an object!

The retinal rods and visual cortex (occipital lobe) also explain why we only see in black and white in low light.

  1. Neuroscience aside, I wanted to provide a second answer.

I was actually interested in your questions on brane theory and faster than light travel but it seems that these don't conform to flat earth theory so were closed and unanswerable :) On brane theory, I would guess yes, different fundamental laws, simply from analogy with air versus ocean. If you walk on the beach you create constructs of sand, you walk to the ocean bio-dome and "cross over", then you are underwater and everything changes. Dimensions must exist and perhaps facilitate the electron jumping lobes in the p-orbital, the "cross over" must be a common surface but the other side would be largely independently governed.

On the faster than light, there was a good "faster than light" wikipedia entry. I would guess that yes, time would reverse but not in the "back to the future" sense. As with the 'why do we see black?' question, I would anticipate biology to act independently to physics and so time reversal is not the secret to eternal youth and once a cause has had an effect, it would not reverse. Further, I'm not sure relativity or newtonian physics would apply anyway, so if you want to travel across the universe, perhaps instead, you would be better off seeking out schrodinger's errant pets and missing electrons in your higher dimension.

Stay curious. xx

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  • $\begingroup$ You should give links to the closed questions you are addressing. Otherwise the second part of your answer is a nonsequitur $\endgroup$ – anna v Jan 20 '16 at 5:19
  • $\begingroup$ Good call, thanks, links to question 1 and question 2 $\endgroup$ – Isobella Lines Jan 20 '16 at 9:45
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We don't actually see light itself. We see objects which emit, reflect, absorb or refract light. Where the light strikes our retina and which cone is triggered allows the brain to create images because of contrast. This visual representation of reality is what we see. Because we have binocular vision this image appears 3 dimensional. Of all the species on the planet, ours is the closest to objective reality but we only actually see about 1% of the universe.

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  • $\begingroup$ Light is the only thing we see. That's why television and computer screens can work. The stuff we see on a screen is not there. It's just light. $\endgroup$ – David Hammen Mar 26 '17 at 23:48
  • $\begingroup$ You are not seeing light. The source of that light is a diode. This is what you see. Each diode emits a different wavelength of light. $\endgroup$ – zane scheepers Mar 27 '17 at 10:37

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