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Creating a Perfectly Black Material

6 Answers
Could we use nano-technology to create a perfect black body? Ok lets make it "easy", the material only needs to have no emission in the visible band of the spectrum. Incident, visible, infra-red, ultraviolet etc can be absorbed but not re-emitted at visible wavelengths. Are there any constraints of physics which make this impossible?
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Okay Points27 allow me to preface my answer with the following statement, which I know to be both paradoxical and recursive (but aside from this I stand by my statement). "Nothing can be deemed impossible, with the single exception being - deeming something impossible." It is true because we will likely never know everything, and even if we do, there is no way to know that we know everything! Again I realize it's logically a bit recursive as an explanation. But this appears to be the way of things.

That said, I believe that it would not be possible to use ANY type of technology, or find a naturally occurring entity or process that produces a perfectly black material (material as in some type of matter).

Let me qualify that by explaining that to be perfectly black there would necessarily be zero possibility of a photon emission from the material (which usually follows photon absorption in matter). Quantum physics eliminates zero probabilities no matter which way you look at it. And while I file myself under the skeptical category in the "quantum arena" generally speaking, it unquestionably has provided a theoretic framework that has produced "correct" answers to such questions. Correct, meaning not that they are necessarily "real" but that they are backed by experimental evidence. So I concede fully that quantum physics is a wonderful tool of prediction for certain areas of physics. This type of question is no exception.

Now, when you amended the question to narrow the spectrum of photon wavelengths that may be emitted to the visible spectrum, the question is not as easy to answer (even though I realize your alteration was made to simplify it instead of make it more difficult)!

Since energy in quantum physics, is fundamentally confined to specific sized "packets" or magnitudes, I would expect to one day be able to find something that has an emission spectra that is somehow (maybe through man-made alterations) is above the normal visible spectra at it's lowest energy level. But due to the probability aspect of quantum physics, this by no means guarantees that the emission would no be altered by quantum uncertainty. That which provides a opportunity seems to be the same that breaks it to pieces. There could be no 100% black is what I'm saying, if quantum theory is fundamentally not a flawed discipline.

A black hole comes to mind, which I would expand to include a perfect vacuum for many of the same reasons (although they are not the color of a physicality, i.e. matter, but rather a process) should be perfectly black (provided nothing is behind it), but there again is a nagging quantum physics problem. There can be no such space, since background energy (a.k.a. vacuum energy) constantly produces particle-pairs which are subsequently annihilated. But are capable of absorbing/emitting photons, thus not perfectly black.

In the end, "not perfectly black", means "not black", period.

This means that based on currently accepted scientific theory, is my opinion that perfectly black material could not be produced by man or as a natural phenomenon. Possibly if there was an infinitely expanding "edge" to our universe and you could hypothetically ?keep up? with it and stare directly at it, it MIGHT appear black. But that is not a real concept that is believed to even exist! (You would be more likely to find it riding on a Unicorn/Pegasus-hybrid at superluminal speed, looking at a blackness from yesterday!) Still, I'll defer to my original quotation above.
Points27 ...

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Another carbon allotrope known as diamond is not black, although since it is clear most people would immediately rush to the conclusion that they look nothing like black. I however only say they are not black because when you find a flat surface you can see a sudden reflection of white light flash in you eyes. The nature of being clear doesn?t rule out blackness as a reflective quality, it only speaks to the transmittance of light through the substance from behind. (just a side note.)

I believe you could darken a substance by altering it's macroscopic topology to be less smooth and scatter more light, however this does not "define" darker or blacker substances really. It can lead to them in most cases, It can also lead to other effects like iridescence depending on the specifics of the material and it's reflective qualities.

The atomic structure can also be very important. Many crystalline substances (I'm especially speaking about the metals) have electrons in their outer shell that delocalize in the solid crystal form and lead to the characteristic metallic effect. The same metal in an amorphous form is often black (however not always black, this depends on the electron configuration). I would say far less lustrous are the amorphous metals than their crystalline counterparts.

So I believe it's a combination of the macroscopic topology and the electron configuration of a particular atom that contribute to it's blackness.

I suppose it could be improved upon if the topology can be altered by nanotechnologies (ironically most involve carbon allotropes like graphene)! As to the electron makeup of the substance, it would require changing it to a degree I believe to be beyond the nano-tech capability unless it was simply to change the element somehow! Beyond that I can't speak intelligently about the blackness changes to an element that remains the same element after the changes are made.

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In physics a "black body" is an object which has reached an equilibrium temperature and has the characteristic "black body" radiation. The radiation was finally described quantum mechanically (Plack's Law) and necessitated the introduction of Planck's constant. The black body is a perfect absorber and a perfect emitter of radiation.

Your question is can this body be just a perfect absorber without any emissions. Of necessity (Conservation of Energy) such a body would heat up and not maintain a constant temperature. Nevertheless, at least for a while, it could absorb energy and heat up slowly, so that it would not "glow" in the dark, depending on its reflectivity and its specific heat. As with acoustic baffles, it is possible to design a geometry such that reflected radiation (light) bounces around inside the object and cannot get out in a simple manner. The radiation is eventually absorbed and heats the material. The idea would be to have many, many reflections giving the material the opportunity to absorb the scattered radiation. This property should be possible with any material, even highly reflective ones, since there are multiple opportunities for absorption.

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I'm not an expert however I doubt this would be possible as if all the energy from all wavelengths is absorbed a huge amount of energy would store up very quickly and either melt the substance or sufficiently change it's molecular structure to allow re-emmision. However if some method was created to allow the transform the energy into something other than heat such as sound it could work? Either way any stable material would require some way of getting rid of excess energy.

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Ok , it looks as if my criterion was a bit stringent to say the least!
Can we at least improve "blackness" by manipulating matter using nano-technology or changing the topology of the surface to improve blackness. What makes a black material such as soot not perfectly absorbtive? Is amorphous carbon black because of its surface topology, its atomic structure or a combination of both? (probably the latter as graphite is not black)

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As far as I know with my limited physics knowledge, there are no laws which state that objects must reflect some of the energy it has absorbed, even if it is not visible to the human eye. WIth that backing, it would definitely be possible to create a perfect black body, which not only absorbs all visible light, but also all energy. Hmm thinking about it more makes the object sound like a black hole!

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