So why can't invisible people see?

[Dr.Epic]

So I'm basically writing a story where the protagonist has the ability to turn invisible, and I want this to be somewhat scientifically accurate (as accurate as a story about someone who can turn invisible can be). I vaguely remember reading somewhere that were people actually able to turn invisible, they couldn't see, but I forget the exact scientific reason why. Something about how light needs to pass through the eye or something. I forget. I just need the scientific explanation why. You can go into as much detail in your explanation by the way. You can just give me a brief explanation in a sentence or two or write a few paragraphs. It wouldn't hurt to know more about this phenomena.

Thanks.

[Xondoure]

Basically eyes are lenses for observing light, and in order to do so the light needs to interact with them. If all of the light is going through or being warped around them without reflecting off of them, then the light isn't interacting with the retina and the brain would receive no signals.

[Dr.Epic]

Basically eyes are lenses for observing light, and in order to do so the light needs to interact with them. If all of the light is going through or being warped around them without reflecting off of them, then the light isn't interacting with the retina and the brain would receive no signals.

Thank you. That is very useful to me.

[Xondoure]

Thank you. That is very useful to me.

No problem. :smallsmile:

[Heliomance]

Alternatively, if they're invisible by bending light so it goes around them rather than through them, then no light is entering their eye, so they still can't see.

[Eldan]

The lenses aren't the problem.

The cone and rod cells in the back of the eye contain pigments that get excited when light hits them. If the light were to simply go through them, no excitement, no nerve signal.

Imagine the film in a camera. If it was totally translucent, the light couldn't interact with it, and couldn't make a picture.

[Brother Oni]

I believe this is mentioned in Ghost In The Shell with the thermoptic camouflage technology, where people equipped with the gear have external sensors so they can see what's going on around them.

The issue of not bumping into things while invisible (since you can no longer see your body) was addressed by extended intensive training in using the gear. The fact that the vast majority of the users were full body cyborgs or it was installed on fully autonomous AI assisted vehicles was probably not coincidental.

[factotum]

The lenses aren't the problem.

They would still *be* a problem, though, because if the light rays passing through the lens aren't focused as they normally would be you'll not get much of an image for the rods and cones to deal with, even if they *were* working!

[The Succubus]

I once tried to write a short story about an invisible spy. He was hopeless at subterfuge - everyone could see right through him. =/

[Heliomance]

I believe this is mentioned in Ghost In The Shell with the thermoptic camouflage technology, where people equipped with the gear have external sensors so they can see what's going on around them.

The issue of not bumping into things while invisible (since you can no longer see your body) was addressed by extended intensive training in using the gear. The fact that the vast majority of the users were full body cyborgs or it was installed on fully autonomous AI assisted vehicles was probably not coincidental.

Not bumping into things (as long as you can see the things to avoid) really wouldn't be much of a problem. It wouldn't matter if you can't see your own body, we have this neat sense called proprioception, which lets us know where our body is even if we can't see it. An easy test of this is to touch your own ear. You should be able to get it first time, even though it's impossible (without the aid of a mirror) to see your ear.

[The Succubus]

Proprioception is also one of the critical systems that make up your sense of balance as well. The other two are vision and the ear's vestibular system.

/the more you know

[Yora]

The easiest solution is to be only invisible to visible light and some other kinds of electomagnetic radiation, but being able to see in other spectrums. But that means one wouldn't be invisible to other people who have the same ability either.
Generally, shorter wave lengths can distinguish finer details, so ultraviolet or x-ray would be peferable to going beyond infrared. Infrared devices are so common that one would have to be invisible to them as well and at even longer wave lengths vision might be more difficult to get into sharp focus.

[Brother Oni]

Not bumping into things (as long as you can see the things to avoid) really wouldn't be much of a problem. It wouldn't matter if you can't see your own body, we have this neat sense called proprioception, which lets us know where our body is even if we can't see it. An easy test of this is to touch your own ear. You should be able to get it first time, even though it's impossible (without the aid of a mirror) to see your ear.

I'm fully aware of the existence of this sense, but I contend there is a difference between not falling over your own legs and your legs falling over something else.

As a little test, put a cup of tea on the desk in front of you. Stare at it until you're 100% sure where it is, then close your eyes and try and pick it up by the handle.
I'd be surprised if you get it perfectly first time and not end up having to adjust your grip because you're slightly off.

Now apply this to complex physical actions and situations like being in a firefight, where such errors in spatial awareness are compounded and can be critical to your survival. Going in without training in being invisible would be extremely foolish.

[Heliomance]

I'm fully aware of the existence of this sense, but I contend there is a difference between not falling over your own legs and your legs falling over something else.

As a little test, put a cup of tea on the desk in front of you. Stare at it until you're 100% sure where it is, then close your eyes and try and pick it up by the handle.
I'd be surprised if you get it perfectly first time and not end up having to adjust your grip because you're slightly off.

Now apply this to complex physical actions and situations like being in a firefight, where such errors in spatial awareness are compounded and can be critical to your survival. Going in without training in being invisible would be extremely foolish.
It's not the same, though, because you're then denying yourself real-time visual information on the cup. In the situation where the only thing you can't see is your own body, you can cross-reference vision and proprioception for greater accuracy.

Incidentally, I did just manage to perfectly pick up a bottle of water with my eyes closed.

[Brother Oni]

It's not the same, though, because you're then denying yourself real-time visual information on the cup. In the situation where the only thing you can't see is your own body, you can cross-reference vision and proprioception for greater accuracy.

Oh I agree it's not quite the same, but short of actual invisibility, there's no way of actually seeing who's right.
In your example, I don't see how you can cross reference a visual sense with an invisible object without the object somehow interacting with the environment and hence giving a marker for where it is. By making it a static test throughout, you don't need real-time visual information for your body sense to act on.

I think the bone of contention we're having is that I believe you're over-estimating the accuracy of proprioception, but I see no way of proving or disproving that without quite rigourous testing, since as a very individualised sense, people's abilities differ.

For example, I could have trouble accurately touching the tip of my tragus quickly (the cartilage bit at the front of the ear) consistantly without training, whereas you could do it innately. It doesn't really prove or disprove anything about the accuracy of proprioception except that we're different (and I'm a bit of a butter fingers :smalltongue:).



Incidentally, I did just manage to perfectly pick up a bottle of water with my eyes closed.

Hence why I specified the handle of a cup of tea, which has a smaller target area than a bottle of water and hence more likely to indicate accuracy issues. :smalltongue:

[Heliomance]

Surely the easiest and most accurate test of proprioception is to make the object you're touching also part of your own body. Close your eyes and try to touch your fingertips together. I'm generally accurate to within under a centimetre, though that does admittedly drop if I'm moving faster.

[Brother Oni]

Surely the easiest and most accurate test of proprioception is to make the object you're touching also part of your own body. Close your eyes and try to touch your fingertips together. I'm generally accurate to within under a centimetre, though that does admittedly drop if I'm moving faster.

Ah, but I could argue that you're biasing the test as you have two frames of reference. We also haven't defined the speed at which we're trying to touch our fingertips together, neither have we set the starting distance, how many practice goes you have, or whether repeated attempts influence later results due to conditioning.

Rigourous testing is a pain in the arse as there's nearly always something you've forgotten. :smallsigh:

However you've mentioned that you're generally accurate to within 1cm, which suggests that there's a margin of error.
Given that this is a relatively simple physical action under stress-free conditions, could I not claim that with more complex actions in a stressful environment, this margin of error can be compounded, to the point that combat effectiveness could be noticably affected, thus warranting the need for specialised training?

For normal walking and talking, the error wouldn't be an issue. In situations where large unpleasant individuals are attempting to make the rest of your life short and painful, I think it could be.

[Grey_Wolf_c]

Rigourous testing is a pain in the arse as there's nearly always something you've forgotten. :smallsigh:

The test you suggested, and the others being performed also seem to be testing something other than the matter under discussion originally.

Now, I have no answer one way or the other, but the question was: can someone who cannot see his own body move accurately through an environment he can see. I think we can all agree to eliminate conscious individuals that depend on sight from the test (i.e. other people that might bump into you).

Can this experiment be achieved without invisibility? I don't see why not. 90% of the time we ignore our own bodies when moving about. Most of the time we only depend on seeing our manipulation appendages (i.e. hands) when interacting. But we don't look down at our feet to walk.

Testing suggestion:
Equipment: skiing glasses with plastic extension that prevents the wearer from seeing anything bellow a certain angle (say, 45 degrees under the horizontal), possibly with some arm movement restriction to prevent him from placing his hands in his field of vision. Some restriction to neck movement may be necessary to prevent the subject from looking down.

Have a person run an obstacle course and see how well he performs. Control subject will wear same glasses but with extension made of clear plastic.

Ten of each type of subject should give reasonably deep reference data pools.

Yours,

Grey Wolf

[Ravens_cry]

If you are able to be a little less invisible in small areas, night vision goggles that work by enhancing existing light could be useful.

[Lord_Gareth]

If you are able to be a little less invisible in small areas, night vision goggles that work by enhancing existing light could be useful.

In H.G. Wells' The Invisible Man, the title character was still partially-visible in his eyes and this was used both as an explanation for how he saw (albeit kinda badly IIRC) and as a method for the book's actual protagonist to detect him for some righteous ass-whipping.

[noparlpf]

So I'm basically writing a story where the protagonist has the ability to turn invisible, and I want this to be somewhat scientifically accurate (as accurate as a story about someone who can turn invisible can be). I vaguely remember reading somewhere that were people actually able to turn invisible, they couldn't see, but I forget the exact scientific reason why. Something about how light needs to pass through the eye or something. I forget. I just need the scientific explanation why. You can go into as much detail in your explanation by the way. You can just give me a brief explanation in a sentence or two or write a few paragraphs. It wouldn't hurt to know more about this phenomena.

Thanks.

Seems like I'm a bit late. Like people have said, if one is invisible because light is completely passing through them with no interactions with them at all, then a) the lens cannot focus light to the fovea, and b) the photoreceptors won't work because they need photons to interact with them for them to do their things. If light somehow "bends" around them, then again, no light is interacting with the lenses or photoreceptors.

[Ravens_cry]

In H.G. Wells' The Invisible Man, the title character was still partially-visible in his eyes and this was used both as an explanation for how he saw (albeit kinda badly IIRC) and as a method for the book's actual protagonist to detect him for some righteous ass-whipping.

Yeah, I actually have that book. Not a bad example if you are willing to accept the premise as stated rather than trying to rationalize the process.

[Melayl]

In order for an invisible person to see, their corneas, lenses and retinas would all need to be visible. Light must interact with all three for sight to occur, and that can't happen if they're invisible.

[Ravens_cry]

In order for an invisible person to see, their corneas, lenses and retinas would all need to be visible. Light must interact with all three for sight to occur, and that can't happen if they're invisible.
Which is why photomultiplier night vision goggles would be useful as you could make them much more transparent than if you were trying to see with just Maek 1 eyeballs

[Heliomance]

With the "bend light around me" version, a system could presumably be engineered to redirect enough light to see by into the eyeballs, and compensate with the other light hitting the body. Net result: A very slight, probably pretty much imperceptible, darkening of the area with the invisible person in.

[Socratov]

well, actually, it depends on the method of becoming invisible.

As previously mentioned, when you bend the light around you won't see (as if you created a cilinder redirecting the light around you so people can't see you. if the protagonist becomes invisible by an extreme form of camouflage (which some japanese scientist seems to have pulled off in some degree) you can still see because the light actually hits you but you pretend to be exactly like your background.

But basically it depends on the question: will the light reach my eyes or not. yes->I can see, no-> I can't

off topic: I always though invisibility was rather idiotic, I liked Hithchiker's guide to the galaxy's Somebody Else's Problem field better becuase of the sheer simplicity of it. Why spend resources on becoming really invisible if you can make people think they don't want to notice you or that you are not important enough to be noticed. Plus it would help make so many *jedi handwave* jokes

[Morph Bark]

The easiest solution is to be only invisible to visible light and some other kinds of electomagnetic radiation, but being able to see in other spectrums. But that means one wouldn't be invisible to other people who have the same ability either.
Generally, shorter wave lengths can distinguish finer details, so ultraviolet or x-ray would be peferable to going beyond infrared. Infrared devices are so common that one would have to be invisible to them as well and at even longer wave lengths vision might be more difficult to get into sharp focus.

That sounds like a good clarification of how people who'd be on some "spirit plane" overlapping with the real world could see one another without being seen by normal people.

Other ways to avoid the "can't see while invisible" stuff: their invisibility is either a result of very effective camouflage (like in that one James Bond film where a car goes invisible by putting the images of what's behind it on its front and vice versa) or by making the invisibility basically a psychically-induced illusion and thus they are still visible to electronics and such.

[The Succubus]

The other way to get around it would be through some form of occular implant that stimulates the optic nerves directly, similar to a cochlear implant for ears.

[Eldan]

But that implant would have to detect light too, in some way. So it would have to be visible.

[The Succubus]

Unless it operated on an derivative of light, such as heat or infrared. Or, it could use echo location and translate it into something the optic nerve sees as light. I vaguely recall this idea was in a prototype stage somewhere in the world.

[lesser_minion]

The other way to get around it would be through some form of occular implant that stimulates the optic nerves directly, similar to a cochlear implant for ears.

Whatever parts you use to see would have to be visible themselves. A camera and an ocular implant might be less noticeable than a pair of floating eyeballs, but it would still need to interact with light in order to let you see, so it would still be theoretically visible.

The main point of interest is that this is theoretical -- just because something is visible, it doesn't mean that it will be seen.

[noparlpf]

Unless it operated on an derivative of light, such as heat or infrared. Or, it could use echo location and translate it into something the optic nerve sees as light. I vaguely recall this idea was in a prototype stage somewhere in the world.

I saw something about that somewhere. I think the planned model does use a camera, but it should be possible (in twenty years (http://xkcd.com/678/)) to design a machine that uses echolocation and ties in to the brain's visual system to provide a black-and-white "image" of the area, providing depth perception either through triangulation by two such receivers, or by measuring the distance from the receiver. The main issue is learning how to see 360 degrees. Might be disorienting for someone who grew up with 180 degree binocular vision, like most humans.
Alternatively, you could just learn how to echolocate stuff yourself like these guys (http://en.wikipedia.org/wiki/Human_echolocation#Notable_individuals_who_employ_ echolocation).

[Togath]

How effective would something simply copying an image of what would be there is the person it’s hiding wasn't?, like the camouflage thing mentioned by a few other people. The only downside that comes to mind would be dusts or liquids(but anything that makes you invisible has those as a flaw) and that your shadow would still be there(it might also slightly distort the appearance of the area).

[noparlpf]

How effective would something simply copying an image of what would be there is the person it’s hiding wasn't?, like the camouflage thing mentioned by a few other people. The only downside that comes to mind would be dusts or liquids(but anything that makes you invisible has those as a flaw) and that your shadow would still be there(it might also slightly distort the appearance of the area).

I think that's what's being developed in real life as the most plausible method of advanced camouflage.

[Ravens_cry]

I think that's what's being developed in real life as the most plausible method of advanced camouflage.
The trouble I have heard so far is that anyone who can see in other frequencies (such as through thermal imaging) they stand out quite strongly.
The whole 'bending light around you' has been done with microwaves in the lab using meta-materials to a certain extent, but we are a long way from doing that with visible light.

[Togath]

Aye, the alternate detection methods are the main problem with the uber camouflage method, though if you could come up with way to take out your enemy's thermal imaging and such it might work better(though you would need to come up with a way to do so without breaking whatever is providing your camouflage, and your enemy would probably be more cautious, though they would have to locate you with sight, which could probably overcome the downside of letting them know your there, unless they just started some sort of constant barrage, though no weapon come to mind which could achieve one for more then about a minute)

[Socratov]

Aye, the alternate detection methods are the main problem with the uber camouflage method, though if you could come up with way to take out your enemy's thermal imaging and such it might work better(though you would need to come up with a way to do so without breaking whatever is providing your camouflage, and your enemy would probably be more cautious, though they would have to locate you with sight, which could probably overcome the downside of letting them know your there, unless they just started some sort of constant barrage, though no weapon come to mind which could achieve one for more then about a minute)

well, invisible!= undetectable

You would still be detected by traces, smell, hearing, pressure sensing, heat signature, etc. The shadow would depend on the way invisibility is achieved.

[Absol197]

So, what I wanted to post has mostly been covered, but I wanted to get this down anyways, as a sort of collection of all the different ways of achieving invisibility, their effectiveness, and the invisible person's ability to see.

There are five main methods to achieve invisibility:

Camouflage Invisibility
The easiest method, the one that we're most familiar with, and the one with the most real-world examples. Most people wouldn't consider this "real" invisibility, but it is nonetheless a very effective means of remaining unseen. Animals have been employing this method for milennia to keep themselves alive, so there must be something to it, right?

Basically, this method boils down to having your physical appearance mimic that of your surroundings. Whether that's from wearing clothes designed to blend in, or by changing your skin color and patterns to match.

The Downsides: Compared to the other forms of invisibility, this one has many downsides. Firstly, as mentioned above, you're not actually invisible, just very well disguised. You still cast a shadow, your shape can be distinguished, and your disguise is only effective from certian angles. You also need to either keep still, or move very slowly. Your disguise is also limited in that it provides only a general blending - it cannot display exactly what is behind you. If your backdrop is very specific, or changes rapidly, you'll be much easier to spot. Also, if you're using clothes or other static apperati to become "invisible," your options for where your technique is effective are limited.

If you're using an adaptive camouflage, whether biological, mechanical, or supernatural in nature, would allow you to move quicker and have a greater range of backdrops to hide behind.

Can You See?: Yes, you can! Light is not prevented from reaching your eyes, and so your vision will be unhindered. however, in most cases, your eyes will not match the environment you're trying to hide in, and so might break the illusion and give you away.

Transparent Invisibility
The one that, I believe, most people assume when considering invisibility, transparent invisibility means that light simply is not disturbed by your presence, and so you cannot be seen.

There are examples of transparent invisibility in the real world (or near enough), only most of them do not involve living things. Glass, water, and other substances are nearly transparent. They do, however, still refract light, which creates a distortion effect that is noticeable.

The degree of transparency determines how invisible you are: a low transparency means you would appear as see-through, but still be visible. Your transparency would be different than how much you refract light, however, and you would still be detectable (although difficult to pin down) by the distortions you create, if you refract the light passing through you. "Perfect" invisibility with this method requires 100% transparency and no refraction.

The Downsides: The main downside comes with the aforementioned refraction. If you refract light, the distortions would give away your position. Additionally, since we get a fair amount of our external heat from light striking our bodies, being transparent would get very cold very quickly!

Can you See?: This depends. If your transparency is less than 100%, then yes, you can see. However, your vision would be restricted, almost as if it were much darker than normal, as only a fraction of the light you would normally see would reach your eyes. With perfect transparency, even if you refract light, you would not be able to see.

Distortion Invisibility
Also known as the "Invisible Girl" method, this type of invisibility involves bending the light around the invisible subject, and then bending them back into position after they've passed, creating a pocket around the subject. There are very few examples of this in nature, but we've been able to bend light for a while, so a device that could create this effect could be theoretically possible, if not necessarily practical.

Unlike transparency, distortion invisibility doesn't involve to what degree you're invisible. Instead, it requires you to think about how large an area whatever is creating the distortion needs in order to bend the light around you effectively. the larger the area, the less power would be needed, but the further from you a potential observer can be before they notice something is wrong. If the field is not big enough, you would become invisible at the edges, and more and more visible (in a hazy and distorted fashion) the closer to the center of your image, from the ponit of view of the observer.

The Downsides: The major downside of distortion invisibility is that the distortion field must exist outside of you. Therefore, once a potential observer approaches to near the field, they would start to notice that something is amiss. When they proceed within the field (if they can), they would become effecitvely invisible as well (and if, they had any light sources, would be able to see you).

Additionally, the same considerations to heat as in transparent invisibility must be taken into consideration.

Can you see?: Yes and no. The distortion moves outside light around you. None reaches your eyes, so you would not be able to see outside the distortion field. Light sources inside the field would allow you to see inside the field. However, this could be risky - depending on how the field works, that light might be able to escape, giving away your presence.

Projection Invisibility
Projection invisibility is how most of our current "invisibility" attempts work. In effect, the light that strikes the object to be made invisible is recorded, and then a matching beam of light is projected from the other side of the object, creating the illusion that the object doesn't exist.

There are no examples of this in nature that I am aware of.

The Downsides: For a device that prodices this effect, to achieve the best invisibility possible, there would need to be a matrix of sensors and projectors covering the surface of the entire object, which is technologically challenging. Additionally, because the sensors would not be able to project, and the projectors would not be able to sense, the projected images would be low-quality, potentially giving away the presence of the object. A supernatural verison of this effect, however, would have no such limitation, and could theoretically proceed upwards to perfect invisibility.

Can You See?: Yes! At least, probably. A large object, such as a car or other vehicle that you could be inside could be rigged to project the images gathered both inside as well as out the opposite side, allowing you to see the same image that observers on the other side could. An outfit that comes equipped with a helmet or visor could also project a similar image. With a supernatual effect, the light is still striking your eyes (and being re-projected out the back of your head), so you would be able to see normally.

Phantasmal Invisibility
The only version in which light is not actually being manipulated, phantasmal invisibility is entirely supernatural. You use a psychic illusion to convince observers that you aren't there.

There are two main versions of this kind of invisibility: in the first, you convince the observer that you are uninteresting and boring, or else supposed to be there and innocuous, and so they ignore you. The second has you trick the observer into not seeing you at all.

In the first version, you could even manipulate objects in plain sight of observers without alerting them, as long as you do not draw undue attention to yourself. In the second, such things would likely alert them, although if you can trick their mind to think that you aren't there, you can probably also trick them into thinking the objects haven't moved.

The additional benefit of this method is that you could extend it to other senses beyond sight. You could become inaudible, unsmellable, and potentially intangible, as well as invisible, because the entire effect is in the minds of the observers.

The Downsides: In either case, you would still be observable by inanimate observers, such as cameras. If you are using the ability to make yourself boring and uninteresting, performing actions that break that illusion could result in the effect ending. With psychically-induced invisibility, such things would not break the effect, but still might alert observers that something is amiss.

Can You See?: Yes! No light is being manipulated, so you can see perfectly normally.

[Asta Kask]

Oh I agree it's not quite the same, but short of actual invisibility, there's no way of actually seeing who's right.
In your example, I don't see how you can cross reference a visual sense with an invisible object without the object somehow interacting with the environment and hence giving a marker for where it is. By making it a static test throughout, you don't need real-time visual information for your body sense to act on.

Blind people do quite well, don't they?

[Xondoure]

Projection Invisibility
Projection invisibility is how most of our current "invisibility" attempts work. In effect, the light that strikes the object to be made invisible is recorded, and then a matching beam of light is projected from the other side of the object, creating the illusion that the object doesn't exist.

There are no examples of this in nature that I am aware of.

The Downsides: For a device that prodices this effect, to achieve the best invisibility possible, there would need to be a matrix of sensors and projectors covering the surface of the entire object, which is technologically challenging. Additionally, because the sensors would not be able to project, and the projectors would not be able to sense, the projected images would be low-quality, potentially giving away the presence of the object. A supernatural verison of this effect, however, would have no such limitation, and could theoretically proceed upwards to perfect invisibility.

Can You See?: Yes! At least, probably. A large object, such as a car or other vehicle that you could be inside could be rigged to project the images gathered both inside as well as out the opposite side, allowing you to see the same image that observers on the other side could. An outfit that comes equipped with a helmet or visor could also project a similar image. With a supernatual effect, the light is still striking your eyes (and being re-projected out the back of your head), so you would be able to see normally.

See Cuttlefish. They're pretty awesome.

[Absol197]

See Cuttlefish. They're pretty awesome.

Do they actually project light, or do they simply alter the pigments of their skin? I haven't been able to read up on the matter as of yet, so I don't know. If they alter their pigments, then it would be camouflage, but if they're actually projecting light, then you'd be right, and I'd be even more amazed at what nature can do!

[Eldan]

A bit of both. Some are bioluminescent, but I don't think they use that for camouflage. I'll have a look at it.

[Xondoure]

Do they actually project light, or do they simply alter the pigments of their skin? I haven't been able to read up on the matter as of yet, so I don't know. If they alter their pigments, then it would be camouflage, but if they're actually projecting light, then you'd be right, and I'd be even more amazed at what nature can do!

A bit of both. http://news.nationalgeographic.com/news/2008/08/080608-cuttlefish-camouflage-missions_2.html

Edit: Basically they reflect light (so it falls under camouflage) but they're using the background to adjust the disguise in much the same way as projection invisibility would theoretically work.

[Absol197]

A bit of both. http://news.nationalgeographic.com/news/2008/08/080608-cuttlefish-camouflage-missions_2.html

Edit: Basically they reflect light (so it falls under camouflage) but they're using the background to adjust the disguise in much the same way as projection invisibility would theoretically work.

So it's a super-advanced form of camouflage. That is really awesome!

[Ravens_cry]

So it's a super-advanced form of camouflage. That is really awesome!
It's actually better that it doesn't project light unless the background it was trying to replicate also projected light.

[noparlpf]

It's actually better that it doesn't project light unless the background it was trying to replicate also projected light.

Yeah. Creating light as well as reflecting ambient light means that it will appear more visible than the background. Altering its pigments to match the background is much more effective.

[Absol197]

It's actually better that it doesn't project light unless the background it was trying to replicate also projected light.

Well, the idea behind projection invisibility (at least in the pecfect sense) is that the subject absorbs 100% of any beam of light striking it (so none is reflected back into the environment), and then projects a different beam, with the same intensity and frequency (so, same brightness and color), and possibly polarity, out from their body on the same path that the original beam was taking, essentially making it look like the beam was uninterrupted.

That's the kind of light projection I was asking about with regards to the cuttlefish. I wasn't saying it should turn itself into a floodlight, that would draw predators to it really quick. Just negate it's "shadow," as it were.

[noparlpf]

Well, the idea behind projection invisibility (at least in the pecfect sense) is that the subject absorbs 100% of any beam of light striking it (so none is reflected back into the environment), and then projects a different beam, with the same intensity and frequency (so, same brightness and color), and possibly polarity, out from their body on the same path that the original beam was taking, essentially making it look like the beam was uninterrupted.

That's the kind of light projection I was asking about with regards to the cuttlefish. I wasn't saying it should turn itself into a floodlight, that would draw predators to it really quick. Just negate it's "shadow," as it were.

That sounds way more complicated than just reflecting light in the same way the stuff behind you would.

[Absol197]

That sounds way more complicated than just reflecting light in the same way the stuff behind you would.

It is, which is why true invisibility hasn't been invented yet, either by humans or by nature.

The original claim, however, was that cuttlefish used a form of projection invisibility. I was trying to confirm if that was true, or if they simply used a very sophisticated, very adaptive form of camouflage. It seems that the answer is that they use camouflage.

I originally asked if they actually projected light because that's a requirement for using projection invisibility. Obviously, the answer is, "No." At least for the purpose of avoiding detection.

[Xondoure]

Well, the idea behind projection invisibility (at least in the pecfect sense) is that the subject absorbs 100% of any beam of light striking it (so none is reflected back into the environment), and then projects a different beam, with the same intensity and frequency (so, same brightness and color), and possibly polarity, out from their body on the same path that the original beam was taking, essentially making it look like the beam was uninterrupted.

That's the kind of light projection I was asking about with regards to the cuttlefish. I wasn't saying it should turn itself into a floodlight, that would draw predators to it really quick. Just negate it's "shadow," as it were.

But that still leaves light bouncing off of you from the projection side... So I'm not sure how it would work.

[Absol197]

But that still leaves light bouncing off of you from the projection side... So I'm not sure how it would work.

Perfect projection invisibility would be 100% absorption across the subject's entire surface, meaning there would be no reflection at all, only the projected light.

But I'm not sure if this is still a productive line of discussion...

[noparlpf]

Perfect projection invisibility would be 100% absorption across the subject's entire surface, meaning there would be no reflection at all, only the projected light.

But I'm not sure if this is still a productive line of discussion...

So you have to be a black hole? I don't think anything else quite absorbs 100% of photons, but I have no idea. The issue there being your projection wouldn't escape either.

[Absol197]

So you have to be a black hole? I don't think anything else quite absorbs 100% of photons, but I have no idea. The issue there being your projection wouldn't escape either.

:smallsigh: 100% absorption would be the perfect example. I know it's not physically possible - it would need to be some sort of supernatural ability. It's a method by which someone could become invisible, and yet still see, which is what Dr. Epic was originally asking about - his character can turn invisible, so he wanted to know why one could or couldn't see while invisible.

Obviously, there are many physical barriers to true projection invisibility: no material absorbs 100% of light, no currently known organism can project light from every single square nanometer of its body of a perfect wavelength and intensity; very few have skin (not to mention hair, eyes, etc.) that are capable of both absorbing and determining what the color and intensity of striking light is; there are many, many issues. But, with supernatural abilities, liek the one mentioned in Dr. Epic's OP, it is theoretically possible, so I was explaining how it could work (again, in theory).

[factotum]

Absorbing all inbound light wouldn't make you *invisible*, though--it would make you very, very black. Useful maybe late at night, not so much on the high street at high noon!

[Heliomance]

That's why with projective invisibility, the absorption is combined with re-emitting the light on the other side.

[Xondoure]

That's why with projective invisibility, the absorption is combined with re-emitting the light on the other side.

I'm not sure it's possible to have a surface that absorbs all light hitting it while projecting the light it wishes.

But as Absol said, it's a possibility for magical settings.

[Absol197]

Absorbing all inbound light wouldn't make you *invisible*, though--it would make you very, very black. Useful maybe late at night, not so much on the high street at high noon!

:smallsigh:


That's why with projective invisibility, the absorption is combined with re-emitting the light on the other side.

Thank you! I thought I mentioned this enough that...


I'm not sure it's possible to have a surface that absorbs all light hitting it while projecting the light it wishes.

...Supernatural ability. That's what this entire thread was created to discuss, and I've mentioned it several times.

Okay, I think I'm done. Sorry if I got snippy, but I apparently wasn't being as clear as I thought I was.

[noparlpf]

Absorbing all inbound light wouldn't make you *invisible*, though--it would make you very, very black. Useful maybe late at night, not so much on the high street at high noon!

Eh, even at night dark blues are better than blacks. Especially perfect black.


I'm not sure it's possible to have a surface that absorbs all light hitting it while projecting the light it wishes.

But as Absol said, it's a possibility for magical settings.

Well, magic.

[Xondoure]

...Supernatural ability. That's what this entire thread was created to discuss, and I've mentioned it several times.

Okay, I think I'm done. Sorry if I got snippy, but I apparently wasn't being as clear as I thought I was.

:smallconfused:


But as Absol said, it's a possibility for magical settings.

So yeah, I mentioned that...

[Triscuitable]

While you're all being very effective in contributing to the topic, I'd like to bring us on a quick tangent. A recent Red Vs. Blue PSA featured everyone's favorite idiot Caboose being subject to being turned invisible. As it turned out, he couldn't sleep because he could see through his eyelids.

Anyways, carry on.

[noparlpf]

While you're all being very effective in contributing to the topic, I'd like to bring us on a quick tangent. A recent Red Vs. Blue PSA featured everyone's favorite idiot Caboose being subject to being turned invisible. As it turned out, he couldn't sleep because he could see through his eyelids.

Anyways, carry on.

Wasn't that mentioned in Wells' "The Invisible Man"?

[Xondoure]

While you're all being very effective in contributing to the topic, I'd like to bring us on a quick tangent. A recent Red Vs. Blue PSA featured everyone's favorite idiot Caboose being subject to being turned invisible. As it turned out, he couldn't sleep because he could see through his eyelids.

Anyways, carry on.

You'd think he'd get one of those sleeping masks or something.

[Ravens_cry]

You'd think he'd get one of those sleeping masks or something.
Or even just find a really dark place to sleep, or make one. Your eyelids are so thin that some light seeps through anyway; enough that you can tell the position of a light source with your eyes closed.

[Triscuitable]

Wasn't that mentioned in Wells' "The Invisible Man"?

I wouldn't be surprised.


You'd think he'd get one of those sleeping masks or something.

I believe that was part of the joke.

[noparlpf]

Or even just find a really dark place to sleep, or make one. Your eyelids are so thin that some light seeps through anyway; enough that you can tell the position of a light source with your eyes closed.

It's actually really frustrating. I'm just shy of hypersensitive to several sorts of sensory stimuli, so even with newspapers taped across my windows, the tiny bits of light leaking in around the edges, under my door, and from my digital clock (I decided the light was preferable to the ticking of an analog clock; supposedly people acclimatise to that, that even being the specific example my Bio prof. gave, but I don't) bother me and make it harder to fall asleep. It doesn't help that the college seems to want the campus lit up like noon all bloody night.

[Absol197]

While you're all being very effective in contributing to the topic, I'd like to bring us on a quick tangent. A recent Red Vs. Blue PSA featured everyone's favorite idiot Caboose being subject to being turned invisible. As it turned out, he couldn't sleep because he could see through his eyelids.

Anyways, carry on.

Hmm...If this was transparent invisibility, this wouldn't be a problem, as he wouldn't be able to see in the first place (unless his eyes didn't become invisible, in which case there would be two points where he could be potentially seen still).

If he was using projection invisibility, this wouldn't be a problem, either, because the light would be stopped by his eyelids normally.

All in all, I love Red vs. Blue, and I'm more than willing to let this slide in the name of funnies. But it's not accurate as far as what would happen if someone could actually gain a method of true invisibility.