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joomes
2002-Jun-28, 06:46 PM
Hello,

I only recently watched this movie and apart from the problem of "invisibility" itself a couple of more practical questions came to my mind.

How much/What can/would an invisible person actually see?

Assuming invisibility means there is no interaction with em-waves whatsoever (I mean the usual effects, not gravity, ...) or even only between these 'visible' 400-800 nm the retina would not be able to 'catch' any light.

So would he just see a black nothing? (That's when I gave up my dreams of x-ray vision /phpBB/images/smiles/icon_wink.gif

And even if this would still somehow happen how could he focus? (So the 'nothing' would be blurry /phpBB/images/smiles/icon_wink.gif

And even if this would still somehow happen weren't there some kind of mirror image from the world behind his head? (So there should better be a mirror behind or in front of him.)

What if he left from a dark cave at daytime: If he could somehow adapt to the change of brightness (and avoid looking into the sun), would he then see the door's mirror image?

Assuming he was only invisible between 400 and 800 nm one could still find him on infraed. So, what if he were invisible there, too. What would happen to his body temperature? Since he cannot emit IR or -which is the same here- he cannot absorb IR would he start freezing or overheating or one of these?

Could I give him an electric shock? If he were wet?

Chip
2002-Jun-28, 07:12 PM
[quote]
On 2002-06-28 14:46, joomes wrote:
"...And even if this would still somehow happen weren't there some kind of mirror image from the world behind his head? (So there should better be a mirror behind or in front of him.)"

Chip:
In the movie Predator, (1987), the alien "hunter" pursuing the soldiers has an interesting invisibility suit or armor. The suit appears to acquire visual elements within the creature's vicinity, and adapt them as an electronic covering or on suit projection, causing the creature to blend into the surroundings. This invisibility sort of "reflects" the surroundings, but much more efficiently than a mirror. Therefore, it's not really invisibility, but rather a very sophisticated camouflage. (Those predatory aliens are sure clever!) However, if the alien hunter moves or runs, it can be seen as a vague moving shape. The suit also "shorts out" when the creature enters water and he can be seen for a while. The creature sees in infrared and cannot detect the hero if he (hero) is cold or covered with mud. The alien's invisibility suit may be effected by temperature rather than the water itself. Nevertheless, the Pentagon would pay a lot for a camouflage outfit like that! /phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Chip on 2002-06-28 15:14 ]</font>

SeanF
2002-Jun-28, 07:28 PM
On 2002-06-28 14:46, joomes wrote:
How much/What can/would an invisible person actually see?

Assuming invisibility means there is no interaction with em-waves whatsoever (I mean the usual effects, not gravity, ...) or even only between these 'visible' 400-800 nm the retina would not be able to 'catch' any light.



And yet not only could the character still see in the movie, but there's one scene where we (via an infrared monitor) watch him reach into a cage and pick up an invisible dog without having to feel around for it. In other words, not only can he still see, he can see things "normal" people can't!

Either that, or it was just a mistake on the movie-makers' part . . . /phpBB/images/smiles/icon_wink.gif



_________________
SeanF

<font size=-1>[ This Message was edited by: SeanF on 2002-06-28 15:28 ]</font>

xriso
2002-Jun-29, 07:42 AM
I recall some mumbo-jumbo about his matter "phasing out" or something to that effect. I suppose he could see if the real dimension somehow "copies" all its EM into the phased dimension, but the phased does not copy back visible light (so he is invisible). I believe that this solves numerous problems (he can still pick up stuff, punch people, wear clothes, etc.), but it is rather arbitrary.

Silas
2002-Jun-30, 09:12 PM
The lens of the eye is a miracle of biology; it is completely transparent, yet living tissue. (The liquid inside the eye is transparent, but not living, per se; it is merely a substance, like tears or blood plasma, that is secreted but is not living.)

One big problem with a transparent living tissue: how does it receive nutrition from the blood stream? You can't have capillaries running through it; they would cloud the vision. Instead, blood simply diffuses through it, one of the few instances of diffusion in mammalian circulation.

(Some have suggested that REM sleep -- Rapid Eye Movement -- is useful in that, by shaking things up, it helps the blood move around, just like shaking a fruit-at-the-bottom yogurt cup to move the fruit bits all through the mixture.)

The lens of the eye heals very slowly when injured...

If we could, somehow, persuade all the living cells of the body to become transparent, you'd still have a bright purple circulatory system and a lovely pink skeletal system completely visible. You'd also have a nasty bolus of digestive material collected in the large intestine (ew!) and a papery outer covering of dead skin cells (ew!) Oh, yes, and the lungs would be clearly outlined in mucus. (ew!)

And, as we've known since H.G. Wells, the "power" of invisibility wouldn't be worth a darned thing: you'd leave footprints, your breath would be visible in a cold room, your body heat would still be detected, and anything you want to carry with you -- a weapon or a sheaf of secret papers -- would betray you by appearing to bob along in midair.

Wells himself, in a bit of whimsy, demolished the notion in his story, "The Kingdom of the Blind," in which a sighted man finds himself in a land of people who are all blind from birth. He imagines, foolishly, that he can deceive them without effort...and is brought to a very rude awakening.

High-tech invisibility -- a la Star Trek cloaking devices, or our merely real-world "stealth technology" -- is another fettle of kish.

Silas

David Hall
2002-Jun-30, 09:36 PM
On 2002-06-30 17:12, Silas wrote:

And, as we've known since H.G. Wells, the "power" of invisibility wouldn't be worth a darned thing: you'd leave footprints, (etc...)

Not to mention the necessity of walking around 'au naturel'. Especially in the winter. Brrr... /phpBB/images/smiles/icon_eek.gif /phpBB/images/smiles/icon_wink.gif /phpBB/images/smiles/icon_razz.gif

beskeptical
2002-Jun-30, 10:32 PM
On 2002-06-28 15:28, SeanF wrote:
And yet not only could the character still see in the movie, but there's one scene where we (via an infrared monitor) watch him reach into a cage and pick up an invisible dog without having to feel around for it. In other words, not only can he still see, he can see things "normal" people can't!

Either that, or it was just a mistake on the movie-makers' part . . . /phpBB/images/smiles/icon_wink.gif
______________
SeanF


Infrared vision would be seeing radient energy waves that are out of the human eye range. Lots of animals have vision and hearing that is out of the human's range of perception.

I thought Predator came close to realistic (except the human triumphed /phpBB/images/smiles/icon_rolleyes.gif ). I understand the US military is looking into a camouflage suit that digitalizes the visual data on one side of the suit and projects it on to the opposite side.

I have no idea how far along the concept is to being a usable invention.