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The Details:
We have ways to generate light and direct it with our own technology. Humans have had the ability to do this for even longer. Within the last number of decades, we have begun understanding what light is and how it works, how photons are generated, etc.

I have imagined a magical system in which it is possible to create and/or project/direct light. There is also the ability to do so with "darkness," which will be defined as a localised absence of any sort of illumination in this question. However, while light would shine from a source, one might be able to "direct" the darkness as if it were a fluid. As an example, if you are familiar with Avatar: The Last Airbender, something akin to water-bending comes to mind, though it need not be as "solid"--or perhaps tangible is the better word?

Never thought I would call liquid water 'solid'...

The Question:
Is there a way to describe this projected "physical" darkness, taking into account real science and by taking grossly large liberties with any physical limits, in a "scientific" manner? I would rather it not involve any matter to physically block the light, but if it is handled well it would work. There aren't any limitations presently in the magical system, apart from there not being infinite energy (which may be the major limiting factor here, for all I know). You may assume that annihilating a city/continent/planet/star with the power requirements is not an issue, nor are localised absolute-zero (or supernovae-like) temperatures, if your answer requires them.

Note that this does not need to conserve energy (or, I guess by extension, mass) as the effect will only persist as long as it is controlled, and any energy not in the world already will enter, be used, and promptly exit. Picture it like a sink, or a black hole sucking stuff in as a "white hole" spits stuff out.

My thoughts:

  • Looking at such a darkness, one might see only blackness as no light would bounce off. I can imagine it being a very strange thing to see, as it will likely have no perceivable depth. Perhaps it would look perfectly 2-D in a 3-D world? (Note: Vantablack)
  • With a strong EM waves, light can be "bent" in an terribly small way, but I fear the other effects that a sufficiently powerful EM wave would have on any matter it passes through.
  • I may need to come up with a completely different way to explain this, stepping almost completely outside of the realm of physics.
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  • $\begingroup$ Hope you don't mind the tag edits. . . $\endgroup$ – HDE 226868 Nov 18 '14 at 21:39
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    $\begingroup$ I don't know if this makes sense, but maybe it could be made of matter that resists changes in Electromagnetic fields. So when light passes through it, severely diminishes the amplitude of the photons. It would work similarly to how electromagnetic induction always resists a change of magnetic flux. $\endgroup$ – overactor Nov 19 '14 at 7:16
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    $\begingroup$ You might want to be intrested in a google search for "blackest black" $\endgroup$ – PlasmaHH Nov 19 '14 at 10:53
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    $\begingroup$ @PlasmaHH That's essentially the effect I was hoping for, and serves as a good way to explain what one might see. Thanks! $\endgroup$ – Crabgor Nov 19 '14 at 13:31
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    $\begingroup$ relevant: A demonstration at MIT of actually making light disappear by adding more light that cancels out the original waves: youtube.com/watch?v=RRi4dv9KgCg A very interesting side effect is that it effectively reverses the direction of light! as in, whatever would be lighting up the area would get brighter as it reabsorbs the energy that would have gone into the dark spot. $\endgroup$ – John Meacham Nov 20 '14 at 5:12

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We appear to be talking about a substance that behaves as if it was a fluid and is directable by human consciousness, and has the property of being dark.

I would say that this "magical fluid" would be completely intangible in a physical sense, capable of being interacted with only by the powers of the mind.

As for what the darkness is, we must consider the possibilities that:

  • The darkness is a region of space around which light is bent - this would account for darkness within the region, but it would be more or less invisible from the outside. Hence, not a viable option

  • The darkness is a region of space that absorbs light - This would mean that the region would appear completely black, as any light that would otherwise have passed through the region from an object to an observer's eyes would not arrive. In addition, such a region would cast a shadow, as light from the dominant light sources would not pass through the region.

  • The darkness does not actually involve any lack of light - the space it occupies is simply seen as something black. Such a darkness would not cast a shadow, as light would pass through it, it would just be seen as darkness by optical sensors such as eyes and cameras.

Of these three options, the first is not practical, and the third is interesting but not as useful as the second.

The second option, where light is absorbed in a region of space, is the most interesting, and will be the subject of the remainder of this answer.

Since we might want to keep the law of conservation of mass and energy, we could postulate that the magic creating this light-absorbing darkness is changing the energy from the light that intersects its volume of effect to some other form.

This could be a change in the nature of the energy - perhaps the light is being changed to sound, so the darkness field would have an audible presence, the sound emitted being related to the frequencies of light being converted. Light outside the human visual range would be converted to sound outside the human auditory range, so IR & lower frequencies would be converted to subsonic sounds, and UV and higher frequencies would be converted to ultrasonic sounds.

This could also be an energy to mass conversion. Since the amounts of light energy are relatively low, we're talking about adding a few atoms or subatomic particles to the atmosphere inside the darkness volume.

A combination of these two effects is also possible.

So, we have a light-energy absorbing volume of space. The effects of coming into contact with such an effect would be literally chilling - IR emitted from the air and other substances would be absorbed and converted, and no external radiated heat would be able to penetrate the region. This would result in a rapid loss of heat from any substance in the area of effect.

Such an effect could be readily weaponised, and a hollow shell of darkness could conceal things within it without them freezing, though there may need to be vision slits, and there would be a tell-tale frost/mist around the edges.

As to how such an effect is created, and why it is manipulated like a fluid, as opposed to simply appearing at the place it is needed, we could propose the existence of a class of particles with non-zero mass, generated by the minds of magicians (or psionicists), that I will call Psions. There would have to be a number of different kinds, some capable of interacting with other Psions to create different types of Psion or others simply negating different Psions. Each type of Psion would have its own effects, one of which would be the darkness field effect. Others may exist that attract certain types of matter, or catalyse certain chemical reactions.

Since these Psions are created by and are directable by the mind and body of a magician, they must travel from the caster's body to the place where they are needed. The speed with which they travel and can be manipulated depends on the strength of the caster's mind. If any physical movements are involved, they could simply be a focus for the mind or it could be that the areas of the mind that control the movement of Psions also control bodily movement.

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  • $\begingroup$ I didn't specify in the question that we were necessarily conserving energy or mass, but since you did, +1. Perhaps that was an error in my part that could use some clarification. $\endgroup$ – Crabgor Nov 18 '14 at 22:41
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    $\begingroup$ @Cragor, Psuedo-scientifically was mentioned, and we might as well change as little as possible... $\endgroup$ – Monty Wild Nov 18 '14 at 22:59
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    $\begingroup$ +1 for also exploring the consequences of the light-absorbing. $\endgroup$ – celtschk Nov 18 '14 at 23:00
  • $\begingroup$ Whdy not just affect visible light only? $\endgroup$ – John Dvorak Nov 19 '14 at 10:18
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    $\begingroup$ @Cragor most ordinary matter interacts with photons on a per-energy basis. If the difference between the ground state and an excited state of an electron in an orbit is the same as the incoming photon energy, the photon gets absorbed and the electron gets excited. This is how colors work in real life. $\endgroup$ – John Dvorak Nov 19 '14 at 13:40
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Since light is the presence of a thing (photons), and darkness the absence of that thing, to "project" darkness you have to rid the area being projected of that thing.

I can think of three possible ways, of varying degrees of scientific plausibility (starting at "low" and going downhill from there):

Anti-photons (Edit: Apparently there's no such thing. Drat!)

Just as your flashlight can project photons, your "darklight" could project anti-photons. These would interact with photons by annihilating them, and would have the nifty narrative property of being able to be overpowered by a stronger light (which in turn could be overpowered by a stronger "dark").

The problem here is that antimatter annihilations release massive amounts of energy, as literally the entire mass of both particle and anti-particle are instantly turned into energy (okay, not literally literally...). Photons (and, consequently, anti-photons) don't have a lot of mass, but there's enough of them in the beam of a flashlight that it's going to get very messy.

An observer on the outside would see only darkness (well, maybe, I'm not actually sure what annihilating photons with anti-photons looks like), while an observer inside the area would... well, I'm pretty sure they'd simply be cooked alive by the energy being released, if not blasted apart outright. Probably far more destructive than you want in any case.

Phase-shifted photons

Photons are not just particles; they're also waves. This means that we can "cancel them out" with a wave that is phase-shifted by 180 degrees: when the light wave reaches its peak, the "dark wave" is at its trough, and vice-versa. Since wave forms are additive, this will give you a net result of zero light.

Unfortunately, I know of no way to generate a single phase-shifted waveform like this, let alone adaptively generate them for all the colors currently visible in a given area you're trying to project them into. If you ignore that, though, this is quite simply -- and quite literally -- just canceling out the light in the area. Probably the most straightforward means of projecting darkness, really.

Assuming you can perfectly match your projected waveform with the ambient one, and vary it across different parts of the area since there's going to be different colors passing through different parts, especially when viewed from different angles, observers inside and out will simply see darkness. Anything less than absolute perfection will allow glimpses of colors and/or flashes of light.

Repelling photons

If we imagine that photons have a charge, then an opposite charge would, of course, repel them, in exactly the same way of trying to push two "south" poles of a pair of magnets together.

Of course, if this were an EM charge, then as you note there's quite a few side effects to consider. But if the charge is of some other form of energy (hey, there's magic anyway, so why not?), then we could much more easily project a directed charged field that would repel photons with minimal side effects.

Interestingly, an observer inside this field would see total darkness, except that any light source with them would work (albeit with some weird streaking/stretching effects, and likely only directly away from the center of the field); an observer outside the field, however, would see the surface as a big mirror, likely with some blurring going on as photons get turned around at different points rather than bouncing off a solid mirror.

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    $\begingroup$ There's no such thing as anti-photons - they are their own antiparticle. Great idea for canceling out, though, so +1. $\endgroup$ – HDE 226868 Nov 18 '14 at 21:39
  • $\begingroup$ So a photon plus a photon already annihilate one another? Huh, I had no idea! $\endgroup$ – Kromey Nov 18 '14 at 21:41
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    $\begingroup$ The idea of a particle and its antoparticle annihilating into "pure energy", although often read, is actually wrong. For example, when an electron and a positron (anti-electron) annihilate, the result is either two or three photons, depending on whether the electron and positron had spin zero (roughly: antiparallel spin) or spin one (roughly: parallel spin). In principle they could also produce a neutrino-antineutrino pair, but that's more rare because that involves the weak interaction, which is, as its name already says, weak. $\endgroup$ – celtschk Nov 18 '14 at 22:43
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    $\begingroup$ @Cragor They have no "rest mass", but that's not the same thing as "no mass", especially since you can't bring a photon to rest anyway. Once again physics is hurting my brain! $\endgroup$ – Kromey Nov 18 '14 at 22:44
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    $\begingroup$ @Kromey: The concept of a "relativistic mass" is outdated, because it tends to confuse more than it helps. Using the term "mass" only in the modern way (in old terms: "rest mass" or, better, "invariant mass", because the only relation to being at rest is has is that for a particle at rest it is equal to the "relativistic mass" of that particle) makes your brain hurt less. The mass of a particle is simply $m=\sqrt{E^2/c^4-p^2/c^2}$ which is well defined for any particle, no matter whether you can put it at rest or not. For photons, you have $E=pc$ which implies $m=0$. $\endgroup$ – celtschk Nov 18 '14 at 22:50
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Bending or somehow repelling light wouldn't work. Light isn't a property of an area of space, it's something traveling through said area. As such, such measures would only change its direction, meaning light will still seemingly originate from or pass through this area.

It can however be used if it's acceptable that it's still visible from, say, a single direction. Imagine some magic field that redirects all photons inside it straight upwards. From any other angle, it would look pitch black as no photons arrive from that direction. From above however, it would be considerably brighter as the light from all other directions is basically summed up into a single bright beam.

In order to be truly black from any angle, some way to ensure that none of the light entering the field leaves it, at least none of the visible light. Such a thing exists in reality: a black hole. However, assuming that no matter is involved in or affected by this field, that obviously isn't viable. One could instead imagine other alternatives: changing the frequencies of light passing through it to be beyond the human spectrum, use some magic wormhole that redirects light to some far-off place or another dimension, convert it into magical energy and route it to your own "mana", turn the light into heat (not sure how quickly the air would heat up from that tbh), just destroying it (if conservation of energy isn't your thing) or somehow cancel it out with something else.

Or maybe just say "a wizard did it"? :)

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  • $\begingroup$ For my purposes, "a wizard did it" is the usual idea, but later on I will most likely need a reasonable explanation, which will then turn into "a wizard did it" for simplicity if people don't care. :P Interesting ideas. I'd hate to be on the receiving end of a bunch of tiny singularities, I must admit. $\endgroup$ – Crabgor Nov 18 '14 at 22:26
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My idea is for something similar to dark matter - but exactly its opposite. I can't call it anti-dark matter, because antimatter is completely different. So for now I'll call it krad matter. Oh, the lengths I go to in order to create names!

Dark matter does not interact via the electromagnetic force. This has some interesting side effects, the most important of which is that dark matter cannot emit photons - that's why it's "dark" (Note: For the non-physics-buffs out there, photons are the bosons that carry the electromagnetic force.). Essentially, dark matter doesn't emit light, which is why we can't see it. (For anyone interested, dark matter can be detected by its gravitational effects on other objects - such as its effect on the galactic rotation curve.)

Krad matter would have to be just the opposite - it interacts strongly with the electromagnetic force, and thus absorbs a lot of photons. Normally, it would have all the properties of dark matter, such as density and concentration. But (and here's where we give science a break) perhaps the person controlling it could summon up a lot of it, therefore absorbing all the light in the region.


In response to the (insightful) comments below by Cragor and Oldcat:

Okay, so the dark matter comparison has some flaws. I tried to ignore them and keep this almost entirely science-based, but I realized there's no way to do this well, so I'll abandon that strategy for this last bit. Although it's actually still based on science.

The trouble lies in the krad matter's absorption of photons. There's going to be energy transfer, and that means the matter is going to heat up, thereby radiating heat. That's a problem. The solution lies in quarks. Quarks are confined within hadrons - they can never escape. Add more energy, and you end up producing more quarks (and the same number of anti-quarks). They same principle could be at work here. Add energy to a particle of this matter, and a new particle is created.

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  • $\begingroup$ I did look up dark matter/energy during my research, and tossed it away. This is altogether different, and a very interesting take on things. I am also operating on the assumption that dark matter doesn't BLOCK light either, though I don't recall ever seeing that shown anywhere. Is that completely incorrect? $\endgroup$ – Crabgor Nov 18 '14 at 22:23
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    $\begingroup$ If dark matter blocked light, it would gain energy by doing so and eventually get hot enough to radiate that same light outward. $\endgroup$ – Oldcat Nov 19 '14 at 0:47
  • $\begingroup$ @oldcat Good point. Edit made. $\endgroup$ – HDE 226868 Nov 19 '14 at 0:58
  • $\begingroup$ With respect to the edits, the energy is then released (in some form or another, is there a rule to this or can it be anything?) when the quark-antiquark pairs recombine? Just so I know if I'm understanding fully. $\endgroup$ – Crabgor Nov 19 '14 at 17:30
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    $\begingroup$ @Cragor Yes, it is released when the quarks in a meson annihilate, which would produce photons (nice catch). I suppose you could avoid this by simply not carrying the analogy so far - that is, saying that these particles cannot annihilate one another (and so don't obey particle conservation laws). $\endgroup$ – HDE 226868 Nov 19 '14 at 18:28
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One thing not forbidden under our current understanding of physics is the stretching of space-time. You could have a machine, etc. that systematically "stretches out" space-time in the affected regions to an arbitrarily large degree. All light in the region would be stretched out as well, turning to low-energy radio waves, basically invisible. (The same process has distorted light from the Big Bang to invisible microwave radiation.)

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There are a couple of things that spring to mind for me:

Unlight is a place

Perhaps magic is a way of interacting with other places - possibly consciousness is an intersection of different planes or dimensions already ( or possible worlds, if you want to use quantums as your magic today ) and what a magician can do is to extend that intersection into the world around them, so if they want to conjure heat they can open up the intersection with a dimension filled with heat or a place in their own dimension - there's loads of ways you could play this concept.

Working with this model a magician who wanted to create your barrier of darkness would effectively open a doorway that sent the light somewhere else - so inexplicably in the dark corner of a dark dimension, there is suddenly a bright light as all the light that was going between two locations in the magician's world is sent there instead.

For a good take on the magic as parallel places concept you could read the Malazan Book Of The Fallen stories.

Darkness is an element

I am currently reading an excellent book where, as characters travel between different empires they are literally under different skies- the sun and moons change as they move between different domains. It hasn't been explained yet and it doesn't really matter if it never is because it just provides a compelling setting for the story to take place. A bit of weirdness can be interesting in its own right- making darkness into a thing that has some kind of physical existence aside from being the absence of light would be a good way to remind the reader that they are in a different world now.

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From a different era : Flann o'Brien, fills his book "The Third Policeman" with footnotes regarding the famous philosopher de Selby, often from the Commentaries by Le Fournier.

One such footnote reads:

It is not clear whether de Selby had heard of this (that winds have colours) but he suggests [Garcia, p.12] that night, far from being caused by the commonly accepted theory of planetary movements, was due to the accumulation of 'black air' produced by certain volcanic activities of which he does not treat in detail. See also p.79 and 945, Country Album. Le Fournier's comment [ in Homme u Dieu) is interesting. " On ne saura jamais jusqu'a quel point de Selby futcause de la Grande Guerre, mais, sans aucun doute, ses theories excentriques - specialement celle que nuit n'est pas un phenomene de nature, mais dans l'atmosphere un etat malsain amene par un industrialisme cupide et sans pitie - auraient l'effet de produire un trouble profond dans les masses.'

So there you have it - de Selby's theory is that darkness is caused by "accretions of black air".

There are enough authoritative references in there that one should not challenge the truth of this theory without making the effort to chase them up. Oh, and no cheating with online translators, please!

So it is possible that Flann o'Brien was as far ahead of his time on Dark Matter as he was on the Atomic Theory.

Unfortunately the book never quite adequately establishes who de Selby and Le Fournier are. Presumably if one lived closer to that time, this would be self evident.

And yet, there are skeptics. Black air, it turns out,

is highly combustible, enormous masses of it being instantly consumed by the smallest flame, even an electrical luminance isolated in a vacuum. 'This', Bassett observes, 'seems to be an attempt to protect the theory from the shock it can be dealt simply by striking matches, and may be taken as the final proof that the great brain was out of gear.'

de Selby himself, it is reported, experimented with bottling this substance - of course, in black glass bottles. Perhaps these could be used as grenades, when it is time to make a sharp and unobserved exit?

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  • $\begingroup$ Fortunately, I do speak french to (mostly) understand the quote there. :P Quite interesting. I'll probably look into it more later today. $\endgroup$ – Crabgor Nov 20 '14 at 16:21
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From a scientific point of view, anything that interacts with photons will also interact with ordinary matter through electromagnetic interaction. Since you probably don't want to destroy the atoms by accumulating darkness, this hypothetical substance should consist of particles that are uncharged (otherwise, since it isn't normal matter and thus is not stopped from entering atoms by the Pauli principle, it would significantly alter the field inside atoms, and thus effectively destroy any material it comes into contact with), but have an electromagnetic dipole moment that allows it to absorb electromagnetic radiation, that is, light (OK, in principle an electric dipole moment, if strong enough, probably could also significantly disturb atoms, but maybe one could make is small enough … or simply paper over that problem). Also, for it to effectively absorb light, you want it to have another interaction which allows them to quickly lose energy. That interaction could be yet another field which only interacts with your "darkness fluid" but not with ordinary matter (you could even claim it to be an interaction with dark energy). To form a fluid, you also want those particles to be fermions (so the Pauli principle disallows all of them to be in the same place).

The effect would then be that the particles absorb light (through their electric dipole moment), and then emit the energy over the dark channel (dark energy or other "dark field").

If the effect should be temporary, you can make the particles unstable; then the effect would only remain until those particles decayed.

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You could have a look at electromagnetic induction. When the electromagnetic field through a surface surrounded by a conductor changes, this will generate an electric current which in turn generates a magnetic field that resists this change. In the case of a superconductor, the generated field will be precisely strong enough to stop the change completely.

Since light is electromagnetic radiation, we can imagine a substance which similarly manages to partially or fully cancels out all light that passes through it by generating electromagnetic fields opposite to the waves of the light.

severe speculation:

It seems like what you'd need to achieve this is a bunch of charged particles that are able to move without resistance. A massless charged particle seems ideal here. Sadly, since it is massless, it would be unable to not move at the speed of light. If they move around in a confined space randomly, they would create an incredibly strong and chaotic electromagnetic field. Though you could just invoke quantum mechanics and claim they move in all directions at the same time (much like particles with mass at rest bounce off the higgs field in all directions at the same time) and therefor create no net electromagnetic field. Another problem becomes simply containing these particles, and this is a big one. You'll have to use electromagnetism to keep these particles together and this will likely be just as difficult as what the particles are doing for you (canceling the light). But could possibly be more straightforward. (Maybe a rather simple, if powerful electromagnetic field would be enough to turn any particle headed out of the confined space around.)

what would this achieve?

Well, since these particles can only cancel out light within their volume, light would be able to pass through it largely unchanged. However, inside the substance all light would be entirely canceled out. which means that it would be pitch black.

So the way to use it is to surround your enemies with it (or just their heads) and though you will still be perfectly able to see them, all they would see is darkness.

some possible side effects

This would interact with all electromagnetic fields, including that of the earth, so if you move this substance it would generate a field to resist this change. Since this resists all change in electromagnetic fields, it is possible that brains and nerves in general stop working within this substance. I'm not sure how to solve this one without some serious handwaving.

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This is a very late answer, but I feel that it should be addressed.

Many answers here revolve around the idea that darkness is the absence of photons. While that is true, light and "visibility" is entirely dependant on the observer. Why not have a gaseous material that has a very large extinction coefficient. You're not destroying photons in a medium, just absorbing them. Or have a gas with a large refractive index, distorting the light as it enters the medium. The light isn't destroyed, it's just slowed to the point where the wavelength would shift into infrared, which would be black to an observer of the visible spectrum. All of this is possible in modern science, and it seems a lot less complex than a majority of the other answers here.

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  • $\begingroup$ I'm not sure on the refraction part... care to elaborate more on that? I seem to recall that when light refracts in a medium, and then exits that medium, it also "refracts back." If we see something through a window, for example. $\endgroup$ – Crabgor Nov 19 '14 at 18:52
  • $\begingroup$ This is the gist of my answer. $\endgroup$ – HDE 226868 Nov 19 '14 at 19:13
  • $\begingroup$ @Cragor Sorry, I was under the impression that someone would be inside said "darkness," hence refraction. This link gives a detailed view of a complex refraction index. $\endgroup$ – user3334871 Nov 19 '14 at 20:27
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I'd be thinking of two possiblities. The equivalent of 'noise cancelling' applied to light. If you take a sound wave, invert it and play it back then it'll cancel out.

It's fairly easy - you take a microphone swap the outputs and feed it into a speaker.

This only works though, if the sound wave hits your microphone before the speaker. So for a noise cancelling headset - I can have the 'external noise' hit my microphone, and be 'cancelled' before it got to my ear.

With light, you'd be creating an interference pattern - some bits would be dark, but other bits would be brighter because your interference would be constructive rather than destructive.

Otherwise, I'd be thinking in terms of fog or smoke - some miniscule but absorbent particles in the air that make 'darkness' by virtue of their light absorbtion. But what you do have is an intriguing phenomenon where the speed of light is reduced in different substances - by slowing down light particles you get an 'optic boom' in the form of cherenkov radiation. Maybe your light is slowed down very slightly by this effect, causing two alternate - interfering - light paths.

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An admittedly quick and pretty soft answer...

  1. Find a way of creating entangled pairs of the photons coming from the area. Keep hold of these.

  2. Alter the frequency of your photons, reducing it until it's outside of the visible light spectrum.

Hey presto, the light coming from the area is no longer visible!

Provided you can accomplish step one, you could even conceivably do the rest technologically. Entanglement stretches across spacetime - you could have the necessary processes carried out later in a facility, and have them happen now. In theory.

http://www.extremetech.com/extreme/156673-the-first-quantum-entanglement-of-photons-through-space-and-time

http://www.nist.gov/cnst/photons_101310.cfm

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protected by HDE 226868 Nov 21 '14 at 0:50

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