Cloak of Invisability

[Vader]

Looks like it will happen soone rather than later is this a good thing or a bad thing?

See it herehttp://www.msnbc.msn.com/id/15329396/
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Duct tape is like the force they both have a light side and a dark side and they bind the universe together.

[Hitchhiker]

Ooh, force fields!

[wordcross]

for those who are more scientifically curious:

http://www.eetimes.com/news/latest/showArticle.jhtml?articleID=193400671
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Has anyone really been far even as decided to use even go want to do look more like?

[GH]

I'm struggling with the concept here. The article claims that the microwaves "flow" around the cloaked area like water, and that visible light would do the same. But for that to happen, for some light to be "transported around" the cloaked area (by whatever a "metamaterial" is) and rejoin the "stream" of light on the other side, wouldn't the "transported" light have to travel faster than the undisturbed light? I get how some water can travel faster than other water, but how could some of the light travel faster than the speed of light?

[wordcross]

untrue. It could "flow" like water, it would just not get to the other side of the object as fast as the light that doesn't "flow."

Obviously this could be detected by highly specialized machines in laboratories and such, but there would be no noticeable difference to most detection devices or to the human eye,
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Has anyone really been far even as decided to use even go want to do look more like?

[Lepton*]

I haven't looked into it, but I imagine that this could be accomplished (in visible light) by constructing a material that, due to the correct gradient in the index of refraction, would act like an open-sided fibre-optic cable. Hmm, interesting, although I am not sure about potential portability.

[Samadhi]

Only some minor components and my Bird of Prey will be ready to fly. Have at thee Federation!
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Jack_Ian]

I answered "yes".
It's definitely good or bad.

[Chuck]

I answered "yes" because I'd rather have the government make something invisible than shoot me for seeing it.

[GH]

[extro...*]

[Samadhi]

You do know how fast light travels don't you?

Edit: extro beat me to it
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Lepton*]

GH is right, though. It's the same principle that lets me see that a glass has water in it or that pair of eyeglasses is missing a lens. This technology will make things transparent but making them truly invisible will require the device to remove ALL optical effects... I don't know if that is even possible. The eye is sneaky.

[Samadhi]

Your analogies aren't quite right. You're conflating different principles. In the first example you're talking about something inside a glass that refracts light, in the second you're talking about a piece of glass that is designed to refract light. Something can be perfectly transparent, but still refract light.

Even if it were "fake" glasses with non-refracting lenses, you'd still be able to detect them. But that's because most glass, like the glass in your typical window, reflects about 5% of the light that hits it. Even high grade glass used in specialized optics reflects around 1%. If a piece of glass did not reflect any light and did not refract any light, you wouldn't see it.

But, as I said, refraction/reflection is not the principle we're talking about here. This is more akin to (there's a term, but I forget what it is) our threshhold for detecting separate images. When we watch a movie, we perceive it as smooth motion, but it's really just a set of still images shown at rapid speed. This speed (IIRC it's around 20 frames per second) is FAR less than the millisecond of difference (IE 1000 frames per minute) that would occur if light had to wrap around something even the size of Disneyland. We clearly would not see the difference.
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Lepton*]

1. Assume that we are working in regular air with an index of refraction very close to n=1.
2. If this cloaking device channels the light around the centre then this channeled light must - between hitting and being re-emited by the cloak - travel slower than it would in the air.
3. Thus, the cloak will have an index of refraction n = c/v greater than that of regular air, as a bulk (although it may certainly be very complicated).
4. Therefore the cloak will refract light.
5. As Samadhi implies, if an object refracts light, then it can be seen.

I *think* it's reasonable to treat the cloak as a bulk body of non-unity index of refraction. Your thoughts?

[wordcross]

[Bicho the Inhaler]

[Samadhi]

I see what Lepton is trying to say with 2<=>3. But he's wrong. If a light ray enters and exits by the same angle, it can not have experienced refraction. (see the formula for refraction)
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Coyote]

I can't say that GH and Lepton are right (in regards to being able to detect the cloaked object), but I won't dismiss the possibility. The human eye and brain are wired to be very sensitive to changes in stimuli, even when those stimuli would normally fall below the threshold of perception.

Experiment: Find an area of ground that's lit with direct sunlight, with one patch also lit by reflected sunlight from a hinged window. Ideally, the ground should be unevenly colored (to add some extra 'noise' into the equation) and the window should be dirty around the edges (to eliminate any sharp border between the reflected light-patch and the surrounding area).

Normally it would be impossible to detect exactly where the reflected patch is, even if you know just where to look. But if someone opens the window, the patch becomes instantly visible. It also would be seen if someone were to pass their hand back and forth in front of the window.

Conjecture: If the cloaked object were in motion, or objects behind it were in motion, the brain would detect a subtle change in the stimuli. The change may fall so far below the threshold that you wouldn't even consciously be aware of it (unlike the window example), but you would still have a nagging sense that something wasn't quite 'right' with what you were looking at.

[Samadhi]

[Coyote]

When I say 'I can't say', that's not to say I 'can't', per se. There's an implied 'with certainty' in there. That goes without saying.

[extro...*]

[Bicho the Inhaler]

Coyote, I suspect that you're right, if only because it's impossible to actually build something perfectly. The theory may be perfect, but the implementation almost certainly wouldn't be. Regardless, it's still a huge milestone in technology that will change the world. The Predator was a hell of a lot more dangerous when he was invisible, even though you could see him move if you looked in his direction.

[Bicho the Inhaler]

One more thing: if you are inside a cloak that is working, the world is as invisible to you as you are to the world. You can't even communicate with the outside world. (Obviously: since all electromagnetic waves from outside the cloak are going around you, none are reaching your eyes or any instrument you are holding.) However, I *think* this should be surmountable in practice by weakening the cloak a little to permit a small amount of radiation to travel between you and the outside, preferably only through a tiny aperture. Then you could still be hidden well enough that nobody would see you, but you would be able to see.

[Samadhi]

Yeah, I messed up. Even perfect glass (no reflection) would be detectable by refraction. If the light enters and exits at the same angle, it will still be offset because it traveled at a different angle while in the glass. If the glass somehow had the same index of refraction as air, then it would be invisible. I've seen this done with glass/water and it's pretty cool.
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Lepton*]

White corn syrup and a fairly common laboratory glass (pyrex?) have the same index of refraction which is useful for the same experiment as Samadhi describes in the last post.

I'll try to explain a bit better why I think that the cloak will act as an optical body.

[Lepton*]

Oh right, it's not corn syrup but Wesson Oil (whatever that is). You can fill a glass with the oil and drop a Pyrex beaker into the glass and you won't be able to see the Pyrex. Pretty nifty, imho.

[Samadhi]

Yes, precisely.
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Bicho the Inhaler]

Lepton - yeah, I don't know about that, either. Somebody actually brought that up at the lecture, and the speaker didn't seem to know the answer. But surely this is a commonly observable phenomenon. What does this "decoherence" look like? Increased glare or something?

[Samadhi]

I think L is just trying to make a term for the phenomenon. I.E. If you wrap light rays around your body, you're decoherant. There's got to be a better term though.
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[Lepton]

Coherence is a property that is unique to the light coming from lasers. You can think of it as the wavepeaks lining up. Other than lasers, almost all the light we experience is decoherent. So I'm not sure that the decoherency will be detectable. Maybe this was a poor line of reasoning. Oh, I don't know.

Bicho, I'm a bit concerned to hear that you live off canola oil.

[Coyote*]

I guess that explains why no one pays attention to me when I'm incoherent. I'm invisible!

[Samadhi]

But does Coyote* = Coyote ^-1 ?
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[worm]

[Mr Stoofer]

What's the argument that this could be a bad thing?

[V*]

Haven't you seen The Invisible Man?!?!?!??!

[CzarJ]

(pa-dum ching!)....

[extro...*]