So why can't invisible people see?

[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) 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.

[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

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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

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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

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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

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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

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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

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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/n...issions_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/n...issions_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.

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!

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.

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.