Cloak of Invisibility Coming Soon?

Chris writes "The idea of an "invisibility cloak" has made the leap from science fiction books to an international patent application. The "three dimensional cloaking process and apparatus" for concealing objects and people (WO 02/067196) employs photodetectors on the rear surface which are used to record the intensity and color of a source of illumination behind the object. Light emitters on the front surface then generate light beams that exactly mimic the same measured intensity, color and trajectory. The result is that an observer looking at the front of the object appears to see straight through it."

Re:Practicality?

[lburdet]

actually, it *could* work in 3-D...
follow me on this one... assuming it reproduces the light intensity it received on one side *exactly*!!

if one were to built a perfectly spherical such object, there would indeed be no trace of you... all incident rays would be propagated through the center of the sphere to the other side.
come to think of it, i don't think you'd even have a shadow, which could have given you away... a shadow is whe something "blocks" the sun's rays... thing is, the rays are blocked, but then re-created at the exact opposite of the sphere...

a wall won't be useful, but walking aroung in a bubble-boy-like sphere could work, imho

You're not an engineer, are you?

[p3d0]

Have some imagination!

• For looking straight at the object: just coat the whole thing in emitters and detectors. That's not a big fundamental problem. You don't want light reflecting off the object anyway; might as well have detectors that absorb it.
• The resolution problem can be addressed simply by increasing the resolution until it's small enough not to be noticable. Regardless, even at low resolution, it's better than normal camouflage, isn't it? (Ever seen Predator?)
• The infrared problem can be solved the same way the visible light problem is solved. Just have IR detectors and emitters. You can even to a variety of frequencies (just as with visible light) to fool various enemy equipment.

To me, a big problem would be to counter an active detection system that shines light on the object and looks for reflections. The emitters will be subject to a design trade-off between emission and absorption, and it might be hard to find a technology that does both well enough.

Doesn't seem possible.

[mborysow]

Even if this intended to be just one way. You'd have to have very little light coming from the direction of the intended person to be "blinded." This would assume that this cloak will absorb *all* (up to a point that's observable) the light that would have reflected off of it and to the observer. Well, perfect black body's just don't exist. There'll always be likely to have a reflection come off of this thing.

That's just the beginning, I don't think we're anywhere near having what's essentially an instantly recorded and rebroadcast super high resolution wrappable screen. The way, though I could be mistaken, that most light sources are created even in high definition display devices, will allow for scattering, so the image you would see where the person should be would be blurry. You'd have to get pretty close to duplicating every photon. Not nearly so accurately of course since the human eye isn't so good, but still.

Anyway, I'm just stupid. /me wanders away.

Depth perception

[Myco]

Many have already pointed out the most obvious problem -- any angle other than straight on is going to wreck the effect. But let's not forget that a human with two functional, open eyes never views an object from just one angle (unless one eye's view of the object is obstructed -- geez, picky...). Ah, the miracle of depth perception. I don't think this method is nearly sophisticated enough to compensate for all the subtle clues we get from our binocular vision. Nice try, though. I mean, I think that everyone who's considered the possibility of invisibility has come up with a scheme like this. It's nice to see it coming closer to reality, but we all know that at this stage it's too limited except for perhaps certain special circumstances. But yeah, I want one too.

Jack London's "The Shadow and the Flash"

[dpbsmith]

...is an amusing century-old story about competitive brothers who devise two different methods of achieving invisibility. It's online here [berkeley.edu].

In his fictional story, both methods have problems. The problems are more than fictional, since one of the methods relies on the nonsense supposition that since black is the absence of light, the only reason you can see something that's black is that the black isn't PERFECTLY black, and that if you could achieve perfect blackness you could achieve invisibility.

However, the method described in the parent article here is equally flawed, since it would work only for an observer placed in a specific view location. One wonders how the equipment is supposed to locate the observer; if there are several observers, how does it decide which of them should be prevented from seeing the object?

The method bears a close resemblance to Hollywood special effects processes (glass shots, matte shots, etc.) Special effects processes are notorious for having visible edge effects if not done carefully, and I'm sure this would be true of the proposed method as well.

In "The Shadow and the Flash," one invisibility cloak could be detected by a sensation of darkness and depression whenever the concealed individual was nearby; the other suffered from occasional rainbow flashes due to mismatches in the index of refraction. I'm sure that the proposed method would have similar problems.

Re:Practicality?

[Sawbones]

This color scheme is used on a certain tropical fish (though I forget it's name/species/location). It's shaded dark/black on the top and light on the bottom. Predators looking up will have a hard time locating it on the relatively bright background of the sky and predators from above won't be able to see it in the mirk below. I thought it was pretty cool when I first heard about it.

Along the lines of the whole "only works from one direction" problem for this camo. If you're not going for total image replication but rather a general brightness and hue, it seems like you could have one basically strips of mixed photo sensors and emitters paired up to similar strips on exactly oposite sides of the object. It would be a much worse match from any given direction than the technique described, but it would match at least partially from all directions.

Non-military applications...

[Hallow]

How about a house with sensors on the outside walls, and the projectors on the inside?

It would be like being outside, except the outside couldn't see or get in. And I'm sure it probably wouldn't transmit uva/uvb, so no sunburn. Imagine, no more sky windows. The ceiling could be the sky, complete with clouds. (Of course you could control the briteness, turn it off/on, etc.)

This could even replace windows in buildings you'd want more secured or where glass is a structural liability.

mimic powerful light sources nigh-impossible

[fudgefactor7]

The article explains that the photoreceptors and emitter array would copy what's behind the wielder and blast it forward. Great, but what if the object behind you is super luminous or moving very rapidly. I doubt the photoemitters could keep up with, say, the sun. Heck, they might not even be able to render Quake 3 at a decent frame rate. Not to mention the power requirements...(read any of the the "wheelbarrel" comments made by others.) Also, this idea has been thought up before. Prior Art being a concern, I (personally) would reject his patent claim.

old technology...

[LuxFX]

I've already got one of those on my digital camera.

It's neat, when I turn on the screen on the back, it's like the middle of the camera is invisible and I can see right through it!

However exactly this thing WAS described ...

[Ungrounded Lightning]

In his fictional story, both methods have problems. The problems are more than fictional, since one of the methods relies on the nonsense supposition that since black is the absence of light, the only reason you can see something that's black is that the black isn't PERFECTLY black, and that if you could achieve perfect blackness you could achieve invisibility.

And the other process was to make the subject transparent. Would work if possible but also impractical.

But a "cloak" that either records the view on one side, small patch by small patch, and reconstructs it on the other side ditto, or actually pipes the light around and re-emits it, has been used repeatedly in science fiction since the Golden Age of Campbell's editorship of Astounding/Analog magazine.

I THINK some of 'em even got the need for networking each "camera" to multiple "displays", to account for the virtual passage of light through the thickness of the cloaked space, though I don't recall any of 'em explicitly mentioning the need for the network connectivity to be dynamic, to account for a flexing body.

(I'd dig through my collection to find a few samples but it would take a while. If you want to dig through yours, start with Randall Garret.)

Now if somebody has come up with a particular WAY to pipe the light or its signal around that's worthy of a patent. But if they've just patented the idea of mimicing a transparency (light emission) or do what an octopus does (variable absorbtive color cells to mimic the surface behind), it's been described repeatedly.

An aside: One of the funnier throwaways in a fantasy novel (Too Many Magicians?) was the presentation at a magician's conference of a spell for making EVERYTHING BUT THE EYES invisible. The disadvantage of the previous spells was that they made the subject blind, because the light didn't interact with his eyes. It is easier to hide a floating pair of eyes than a whole body, and easier to be unnoticed if you aren't constantly bumping into things. B-)