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.

[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 ).

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.

[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.

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.

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.