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Suppose a planet developed a peculiar form of life that was naturally invisible, but only within a 15-ft. (4.57 m) radius, by bending or refracting the majority of light around its body due to its scales, fur, or skin, but other members of its species, or similarly developed, can see through this invisibility at any range. My concept is similar to how a lens has a certain focus where an image flips, except here the image appears/disappears when the boundary is crossed.

How might such a species have developed? What chemical/material construction might this light-manipulating layer of its body be comprised of? Would this protection render the creature effectively invisible to infrared goggles or other exotic parts of the light spectrum?

This question discusses aliens that are completely invisible and indicates that they would be blind. Would the concept presented above be any more likely to allow the creature to see in the visible light spectrum? For that matter, would they see in a range of the light spectrum outside that visible to humans (which might also explain their invisibility)?

Finally, is such a creature even possible without the use of magic?

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    $\begingroup$ What do you mean by "invisible, but only within a 15 ft. radius." Do mean that observers outside that radius can see it, but once you step into that radius, it vanishes? $\endgroup$ – Cort Ammon Feb 19 '15 at 1:24
  • $\begingroup$ @CortAmmon Yes, though it technically only seems to have vanished; it is still there, just not viewable in the (human) visible light spectrum. $\endgroup$ – Frostfyre Feb 19 '15 at 2:03
  • $\begingroup$ The problem with a natural light bender is that if it was faced with 2 foes at different angles, it can't be invisible to both. $\endgroup$ – Oldcat Feb 19 '15 at 18:04
  • $\begingroup$ The Invisible Man has some pseudo-science you might want to take a look at. $\endgroup$ – Trevortni Nov 22 '16 at 23:07
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Induced Hemianopsia and visual neglect

Easy. The beast is not actually invisible, it's generating a very precisely pulsed directed-gradient magnetic field. The magnetic field it can generate has a limited range, hence the trouble it has with long distance invisibility, but when you're within range, the field interferes with precisely the correct portion of your brain, causing a phenomenon similar to hemianopsia, whereby the subject loses awareness of the existence of part of their visual field, where the inability of a person to process and perceive stimuli is not due to a lack of sensation.

To give you a vivid example, presented with a circle and asked to label it correctly with the hours of the clock on it, a person with right hemispheric hemianopsia would draw something like this:
enter image description here
Where it gets weird is that often the subject is completely unaware of the fact that part of their field of vision is missing, i.e. the person who labeled the clock would insist they did so correctly, and even become insulted if the interviewer suggested otherwise.

In baseline real-world humans, this is caused by stroke, but it is a well-known fact that the functioning of a human neural net can be disrupted with pulsed magnetic fields via transcranial magnetic stimulation.

So in other words it's not really invisible, it's just literally making you ignore the part of the world where it, and its ridiculously large teeth are located.

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    $\begingroup$ Creepy stuff, right? $\endgroup$ – Serban Tanasa Feb 19 '15 at 2:24
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    $\begingroup$ Creepy, certainly. But brilliant! I may have to re-engineer my creature in this fashion. Still, there's been some good suggestions so far. I suppose I should wait to see what else crops up. $\endgroup$ – Frostfyre Feb 19 '15 at 2:51
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    $\begingroup$ The ability for the brain to screw up on basic perception always freaked me out, now that teeth are added to the mix I won't be able to sleep for weeks! $\endgroup$ – DaaaahWhoosh Feb 19 '15 at 14:38
  • $\begingroup$ So, it has a perception filter? $\endgroup$ – KSmarts Feb 19 '15 at 16:20
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    $\begingroup$ This approach fits the "Somebody Else's Problem field" in the works of Douglas Adams, and the narrative of invisibility spells in some fantasy or roleplaying game narrative - i.e., invisibility as a mind-affecting spell that causes you to simply not acknowledge something that your eye can see perfectly well. $\endgroup$ – Peteris Feb 19 '15 at 18:07
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I would approach it from an active approach, not a passive one. A passive approach is limited by the rules of electromagnetics in air, and as 2012rcampion pointed out, there's no real way to form an image outside of 5m without forming one within 5m as well.

However, active approaches are allowed to do far more interesting things. An active approach directly emits signals with an intent of confusing its opponent. This would not be able to make it invisible, but it could make it very hard to get a bead on.

All of the active effects you would be looking at would be "threat specific." They would have to identify a threat to them, and determine how their brain works well enough to find a way to mess with it. This creature would clearly have to rely on common patterns that show up in predator species, because it could never learn how to perfectly fool each individual.

Consider two situations that show up in fiction:

  • An individual whom you are warned to never look in their eyes. If you look in their eyes, you'll get lost in them. That's when he strikes, and you wont even raise a hand against him.
  • Looking in a mirror. Suddenly, and without rhyme or reason, the image in the mirror smiles and walks off, leaving you to wonder if you were actually in the mirror, and not him, the entire time.

Both of these seem to describe a visual effect which has a marked effect on the mind of the individual. This shows that there is prior art for visual effects disorienting an individual.

Anything along these directions would cause a tremendous instinctive desire to not look at the creature. As an example, we are constantly moving our head slightly. If the creature can "change its spots" in a way to make us think we aren't moving at all, by moving its spots in the opposite direction in perfect mimicry, we start to wonder if we have any control over our own body. If it can make a good guess (based on eye-line) to what part of their body we are looking at, they could blur those spots, and make everything else sharp, making us question if we can even focus our own eyes. That one would be particularly entertaining because the best way to look at it would literally be through the corner of your eye. (It would make it hard for the creature to guess what you are looking at).

A particularly self-aware individual could comfortably negate these effects. I find this to be a feature, because I find stories that reward self-awareness particularly interesting. A self aware individual could probably even choose to exhaust the creature by tricking it into using particularly exhausting patterns and movements, while the self-aware individual just smiles back at it.

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  • $\begingroup$ This comes to mind. $\endgroup$ – Trevortni Nov 22 '16 at 23:03
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This doesn't strictly fit your concept, but it was the first thing that popped into my head and gives you many of the desired effects, so I'll post it anyway.

Consider that what we call "visible" is really just a small spectrum of light compared to the entire spectrum. So what that means is a creature could be "invisible" to another species if it is only reflective outside of that of species' visual spectrum.

Now it's hard to imagine any form of life similar to ours that's completely invisible to our visual spectrum. But what if an alien species had a smaller spectrum, or only saw in infrared/UV/x-ray? Then it seems more likely that a creature could develop that was pretty much invisible to that species - their eyes just literally can't pick them out.

I also like this because I can imagine this alien species meeting humans for the first time, and warning them about this invisible super-predator and how they need to always be super alert. And the humans are just staring at this predator as it's strolling up to the camp because it's not invisible to them, and casually shooting the thing just before it's ready to attack. And now the aliens think humans have super powers and can see invisible creatures.

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  • $\begingroup$ It would appear black, which is a perfectly normal thing. $\endgroup$ – JDługosz Feb 19 '15 at 17:30
  • $\begingroup$ Only if it absorbed all of those frequencies, not if it was transparent to them (I realize this isn't clear in my answer). $\endgroup$ – Dan Smolinske Feb 19 '15 at 17:53
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Imagine that you are 20 feet away from this creature. Since you are outside of the transition range, the creature is visible. Now, focus in on a single ray of light your eyes or cameras are receiving. Follow that ray of light back towards the creature. We can follow this ray all the way back past the transition range, until we hit whatever surface on the creature is emitting that light.

This means that in order to have the desired behavior, somehow your creature would need to be invisible (with all the associated issues), and be capable of projecting an image of itself from the transition zone. I actually asked a question on the Physics stackexchange about this sort of problem, and it seems that without some form of 'smart dust' this behavior would be impossible.

Rather I suggest that, since the invisibility is close range, it could be simulated by some other effect. For example, a form of area-effect telepathy that removes the sensation of the creature from nearby minds. (Although I question what the utility of such an adaption would be, since anything could see you coming-literally!)

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  • $\begingroup$ It's hard to hit what you can't see. Perhaps it's partly from a terror factor. Yes, you saw it coming...but where is it now? $\endgroup$ – Frostfyre Feb 19 '15 at 0:59
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    $\begingroup$ @Frostfyre I see, so it might hide normally (say using camouflage) until you approach to inspect that weird shadow, which, huh, turns out to be nothing. Then you turn around to head back to your party and it's too late. Reverse jump-scare, I like it. $\endgroup$ – 2012rcampion Feb 19 '15 at 1:06
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Rather than full invisibility I might go for highly souped-up camouflage. It seems quite plausible that a creature might have the facility for rapid colour change similar to a cephalopod and combine this with light sensitive cells such that it can change the colour on one side to match the light received on a counterpart cell on the opposite side. This would have the visual effect of a screen showing an image of the scenery behind it.

Of course, this isn't a perfect camouflage because the shape of the creature is not the shape of its background, so from certain angles it will appear as a distorted image of the background terrain. This would still be exceptionally hard to see in most cases, but evolution might well tailor it further - if the creature has a specific prey or predator it wishes to be hidden from, it may be able to align its refractive ability towards that specific creature, so that it would be effectively invisible from where they are. For this it would need stereoscopic vision in the appropriate direction, perhaps indicating chameleon-like eyes.

Interesting evolutionary considerations:

  • Predators that prey on a creature like this might well be pack hunters.
  • Evolution takes place in an ecosystem, so this camouflage would probably be limited to the range of colours visible to creatures that the species needed to hide from. Consequently it might well reach into higher or lower wavelengths than visible light, or it may ignore whole ranges of light that don't matter to colour-blind prey.
  • Distance at which it becomes truly effective depends on the distance at which it can judge the camouflage effectively - too far away ( or hiding from something else ) and it is just unusually hard to see.
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  • $\begingroup$ It's funny you mention predators, because this sounds almost exactly like what the Predator uses, albeit its cloaking ability is manufactured rather than biological. $\endgroup$ – Seth Feb 19 '15 at 16:28
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Maybe the primary sense in that ecosystem is not sight as we know it. It might be sonar, or something quite novel (see Hal Clemet). Even with electromagnetic radiation, different bands and different media can change things. Animals can be nearly transparent in water; in the twilight region fish can only be seen by their shadows against the twilight direction, so light emitting countershading makes them invisible with the complexity of image formation. IR might be blinded by heat or invisible by being cold blooded (or cooled on that side).

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It will not be possible for a such animal to develop natural way. Any such development is always arms race between predator and prey. Such perfect predator would increase population until would eliminate all prey, and died off.

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  • $\begingroup$ Not really. There are many examples of essentially predator-less adult animals (elephants), or hyper-efficient predators (sharks) that are vulnerable at early stages of development and also fight each other as adults, limiting population growth. $\endgroup$ – Serban Tanasa Feb 27 '15 at 1:56
  • $\begingroup$ Another reason why I sorta wish 'not-a-reality-check' was a feasible/legal tag candidate. They didn't ask if it was possible, but how. $\endgroup$ – Caleb Woodman Mar 18 '16 at 0:41

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