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Gillianren
2006-Feb-24, 08:52 PM
In a move I now deeply regret, I gave my boyfriend the complete series of The Flash for Valentine's Day. It is, for the record, not a very good show. (The husband of the woman who runs our local comic book shop knows a guy who worked on it, and that guy agrees that it wasn't a good show!)

So there's an episode wherein a character can turn invisible using the relatively (ha!) workable expedient of bending visible light around himself. Leaving aside that I don't know how in God's name you'd do that with 1990 technology, here's my question: They detect him using infrared. Correct me if I'm wrong, here--that's the point of the thread, after all!--but wouldn't the fact that visible light is bent around him do things to the infrared, making that not a way to detect him?

TheBlackCat
2006-Feb-24, 09:03 PM
Well, if it is active infra-red, then yes. However, passive infra-red, which is emitted by his own body, might be able to get through. It depends on whether the effect is one-way or bidirectional. Personally I would think that something that causes light to bend around something would cause light coming from either direction to bend. This would cause any infra-red that is emitted by his body to curve around and go right back towards his body from the other side. This would mean the only modes of energy transfer would be convection and conduction through the air. His temperature would increase until these modes of energy transfer increase enough to compensate for the lack of ratiative energy transfer.

However, this issue is not really important. Since his body is hotter than the ambient temperature, thermal energy will be conducted and convected away from his body into the surrounding air. This means the temperature of the air directly outside of the invisibility field will be noticably different from ambient temperature (assuming a pretty close-fitting invisibility field), making him detectable by passive thermal sensors. They do not have to actually see him, him heating up matter nearby would be just as detectable.

If they were using active infra-red, though, they would have no chance. Honestly they are much better off using ultrasound imaging or passive sonic sensors.

The real problem I have with those sorts of invisibility systems is what happens when the invisibility field reaches the ground? At the very least you should have some sort of noticable effect where his feet touch the ground, and thus where the invisibility field must intersect the ground, leaving some area with who knows what sort of distortion (black footprints?).

I did develop an idea for frequency-specific cloaking system based on worm holes, but of course it uses worm holes so it is not really possible.

Swift
2006-Feb-24, 09:47 PM
The only kind of way I could explain the light being bent differently for visible versus infrared is that in some optical materials, the index of refraction (how much the light is "bent" when it enters the material) is dependent on wavelength. Depending on how this character bends light, maybe their bending is dependent on wavelength. I would imagine it would not be that they bent visible light, but not infrared, but that because of this wavelength dependence their bending would not be as "perfect" and you would detect them as some sort of visible distortion.

Gillianren
2006-Feb-25, 04:33 AM
Thanks. I mean, I can't really talk to my boyfriend about this (he doesn't want to hear it from me, since I'm perfectly capable of ignoring things like this if I actually like the source material), and he wouldn't be able to answer it anyway, so he'd just (wisely) dismiss it as me grousing for the sake of grousing. I mean, I could complain about the writing, but that's too subjective.

Enzp
2006-Feb-25, 05:52 AM
Sometimes the premise is just stupid and we are left to just enjoy the ride - or not. Even if his body could bend light around itself, the paths would not all be the same, so there would be phase cancellations and other distortions, and how would you avoid that watery effect they use on TV shows - or like Predator for that matter. OK for a walk in the forest, but no good for standing in front of you in the living room.

Humots
2006-Feb-25, 06:56 PM
One problem is: if visible light is being bent around a person, then how is that person able to see anything? No visible light is getting through. One possibility is that the invisible man has some kind of gadget that enables him to see in non-visible wavelengths. Then of course the same gadget would enable others to see him.

H. G. Wells ignored this problem in his classic story, though IIRC it has been suggested that he was aware of it and other drawbacks. Probably he couldn't think of a solution and just ignored it in order to write the story.

In his short story The Lady Vanishes (http://www.geocities.com/firstspeaker.geo/short/sheffield_charles.html) scientist and SF writer Charles Sheffield describes how a working "Invisibility Cloak" could be made, and its limits.

His idea was along the lines of super-chemoflage: a suit that displays a duplicate of the background behind a person. There are obvious problems and limits. The suit would have to work from any angle, while the hidden person was in motion, and without any delay.

In real life, any or all of these could be difficult or impossible to achieve. That doesn't mean that such a suit would be useless, just that it would only be useful under certain conditions. Like, you're invisible as long as you don't move, or as long as you stand against a background so that you can only be seen from one angle. Being an invisible lurker could be very useful.

Gillianren
2006-Feb-25, 07:44 PM
Well, yes, and I did point that out. The fact is, I suppose, that if one is going to believe that a lightning-induced lab accident created a superfast human, we should accept the invisibility thing and that it somehow mysteriously doesn't make the guy blind as well. (Come to that, how did the guy get struck by lightning through a window in what wasn't nearly the tallest building in the area, nor even--as far as I can tell--the top floor?)

DonM435
2006-Feb-27, 02:11 AM
One problem is: if visible light is being bent around a person, then how is that person able to see anything? No visible light is getting through. One possibility is that the invisible man has some kind of gadget that enables him to see in non-visible wavelengths. Then of course the same gadget would enable others to see him.

H. G. Wells ignored this problem in his classic story, though IIRC it has been suggested that he was aware of it and other drawbacks. Probably he couldn't think of a solution and just ignored it in order to write the story.
. . .

Wells' Invisible Man didn't bend light around himself -- he just bleached his tissues to transparency. Of course, with transparent retinae he'd be just as blind.

Donnie B.
2006-Feb-28, 01:29 AM
(Come to that, how did the guy get struck by lightning through a window in what wasn't nearly the tallest building in the area, nor even--as far as I can tell--the top floor?)Just lucky, I guess... :D

Daniel H.
2006-Feb-28, 01:54 AM
One problem is: if visible light is being bent around a person, then how is that person able to see anything? No visible light is getting through.

Ironically, the only time I can recall someone paying attention to this problem was in a series of fantasy novels. When a wizard used his magic to make a light bending shield to make himself invisible, it left him navigating primarily by sound and feel.

porky26030
2006-Feb-28, 06:15 AM
There's one more that I can remember: Timothy Zahn's first Star Wars series, bugger me if I remember the title of it, though.

The remnants of the Imperial Fleet obtain a cloaking device with the same drawbacks, and try to solve it by using the "predictor," presumably an algorithmic computer, to fire blindly through the cloaking field at where they think the enemy is. It ends up not being very effective, and they resort to using a dark Jedi instead.

Later in the series, they put cloaking devices on asteroids and put them in orbit around a planet as a terror tactic. They can only be detected by some sort of gravity/mass detector thingy, which I thought sounded pretty plausible... at least, as plausible as a universe with telekinetic mindreaders and cloaking devices can be.

Van Rijn
2006-Mar-01, 01:08 AM
One problem is: if visible light is being bent around a person, then how is that person able to see anything? No visible light is getting through. One possibility is that the invisible man has some kind of gadget that enables him to see in non-visible wavelengths. Then of course the same gadget would enable others to see him.


Other possibilities: Leave small holes for the pupils or let a little light through and use light amplifiers.



In real life, any or all of these could be difficult or impossible to achieve. That doesn't mean that such a suit would be useless, just that it would only be useful under certain conditions. Like, you're invisible as long as you don't move, or as long as you stand against a background so that you can only be seen from one angle. Being an invisible lurker could be very useful.


Yes, its surprising how good regular camouflage can be in the proper setting with someone who knows how to use it (don't move too fast, don't make noise, keep to cover as much as possible, etc.). I could easily see where "smart" or adaptive camouflage could be very useful. It wouldn't need to be quite at the "predator" level to still do amazing things.

I've also thought that someone might want to temporarily stop their temperature signature. They could wear a regulated "cool suit" with a tank of liquid nitrogen (or whatever) to keep their surface at a computer controlled ambient temperature for a limited time.

Doe, John
2006-Mar-01, 02:16 AM
I've also thought that someone might want to temporarily stop their temperature signature. They could wear a regulated "cool suit" with a tank of liquid nitrogen (or whatever) to keep their surface at a computer controlled ambient temperature for a limited time.

I saw that in a commercial. This good looking female spy type was trying to evade heat sensing security 'bots so she stripped down and covered her whole body with the anti-perspirant product being hyped.


hey, made me stop surfing for a sec. . .