Scientists Make Item Invisible to Microwaves

Vicissidude writes "A team of American and British researchers has made a cloak of invisibility. In their experiment the scientists used microwaves to try and detect a copper cylinder. Like light and radar waves, microwaves bounce off objects making them visible and creating a shadow, though it has to be detected with instruments. If you can hide something from microwaves, you can hide it from radar and visible light. In effect the device, made of metamaterials — engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials — channels the microwaves around the object being hidden. When water flows around a rock, co-author David R. Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock. The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow."

I know a recently-shampooed poodle

[Anonymous Coward]

...that would love to be invisible to microwaves.

Re:

[jalvear]

Yes, I know a few hot dogs in my fridge that would like to be invisible to microwaves.

Why should Harry Potter have all the fun?

[the Gray Mouser]

The article mentions that doing the same thing to light waves should be possible.

How long do you think till you can pick up a Cloak of Invisiblity at your local MegaMart?

Quite some time.

[AltGrendel]

This was already addressed to some degree in the SciFi book "The Last Mortal Man". The reasoning for making them illegal was that the criminal element used them to evade law enforcement. I'm sure the DHS would have alot to say about this.

Re:

[the Gray Mouser]

Ok, on a serious note then:

How long till we see military issue suits? They wouldn't have to be perfect to be a big help to infantry in medium cover terrain.

Of course, almost anything military gets a civilian version eventually, so we're back where I started.

Re:Quite some time.

[Rei]

And the biggest beneficiary of infantry invisibility suits? Guerilla fighters.

Sure, they won't get them right away. But you better believe that they'll try to capture them, and any state sponsors that they have immediately try and produce or otherwise acquire them. Big armies, trying to cloak things like tanks driving down the stret, will have a much harder job at it than fighters simply hiding themselves and their RPG, already in the shadows or buildings. Not to mention things like pressure or vibration-triggered mines/IEDs won't be affected, which also benefits guerilla fighters on their own turf.

Re:Quite some time.

[c6gunner]

It just means that organized combat would evolve to take advantage of them also. Ever since WW2 we've been moving to smaller and smaller units working as independent organizations, then re-combining to carry out more complex tasks. With the introduction of cloaking technology you'd see the extreme end of that. 4-8 man squads operating independently on foot and light vehicles, hunting down guerrillas the same way the currently hunt us. Biggest obstacle to us doing that NOW is that we're so easy to identify. If we could have small units operating all over a city, totally invisible to anyone...well, good luck trying to plant IED's, or even gathering at your buddy Ahmed's house to discuss tomorrow's plan of attack.

Re:

[iluvcapra]

The way you describe it, military cloaks of invisibility would seem to be plainly illegal under the Hague Conventions [yale.edu], supposing that killing an enemy while you are invisible translates as a "treacherous act," by Article 23. Also if you engaged in combat under a Cloak you would be necessarily trading in your protections under GC1 and 3.

Re:

[c6gunner]

Nonsense. Well, the Hague convention art. 23 bit is nonsense anyway. You could argue that we already "kill treacherously" because we employ camouflage, snipers, artillery, landmines, etc. Any such argument would be just plain silly though. The treachery part of the Hague conventions refers more to things like poisoning, or getting your prostitutes to "distract" them while you sneak up and slit their throats (sound unlikely? think about how old these conventions are). As to the GC, you're absolutely ri

Re:

[toddbu]

The reasoning for making them illegal was that the criminal element used them to evade law enforcement.

This assumes, of course, that the criminal element (or anyone else for that matter) will be able to use the cloaks successfully. Think about how hard it would be to rob a bank. If you're wearing the cloak then how does the teller know that you're there demanding money? Perhaps you just want to cloak the getaway car. How do you find it back when you're done with the job? Even if you remembered where

Re:Quite some time.

[Rei]

That's silly. The teller can hear you.

Even if there was no "on-off" button on this, it would be trivially easy to "make" one. Paint water colors on all or part of the object that you can wash off. Tape on visible objects. Put a cover over it. Etc. This assumes that the cloak *itself* isn't flexible, allowing you to take that on or off.

Also, I doubt it'll be perfect invisibility. Even if, to the naked eye it appears perfect, I doubt it would to custom goggles analyzing the scene. Surely there are some wavelengths that it won't work on (from the sound of it, you need to customize a layer of this for a *specific* wavelength). Or the polarity could be thrown off. Or all sorts of other things.

Re:Quite some time.

[XenoRyet]

The real issue, and the major downside to a cloak of this nature, is how do you see where you're going while you are wearing it?

If it's diverting all the light around you, there's no light to get in and hit your eye so you can see.

The solution would be much more complex than the basic cloak. You'd have to let some light in, but make sure it didn't get back out again. I can see that being problimatic.

Re:

[beyowulf]

I suppose they'd have to make the cloak invisible to the visible spectrum and provide goggles to see the non-visible(Infared, UV) spectrum.

Re:

[gutnor]

You only need 2 little holes of 5 mm and you have all the lights needed for your eyes. Considering the likely imperfection of the invisibility suit, it is likely that when you can spot the holes, you are already close enough to detect the wearer.

Not only that

[phorm]

But a moving object is still traceable, as it will physically disturb the environment around it. A human will trample vegetation, break branches, or leave footprints etc. A tank will leave track prints, stir up a whole lot of dust, and many other such things.

So this technology would be most useful for hiding static vehicles/persons, or perhaps even moreso for hiding buildings (think, a whole, semi-invisible bunker).

I wonder how it would affect sound waves as well. Perhaps sonar would pick up things that

Re:

[JasonTik]

You'd have to let some light in, but make sure it didn't get back out again.

This would be devastating to the cloaking effect if the same wavelengths were let in that you were trying to cloak against. Your cloak would make the area it covers darker by not passing all light.

If you were trying to cloak against visible, you would have to use microwave or something else to look at things with to avoid this.

Re:Quite some time.

[borawjm]

The real issue, and the major downside to a cloak of this nature, is how do you see where you're going while you are wearing it?

Use your feelings, you must

Re:

[AikonMGB]

It occurs to me now (after the fact, of course) that said blind person would have far less fun in said ladies' washroom...

Re:

[CmdrGravy]

I'm sure any relatively non moronic criminal would quickly work out how to maximise the benefits of being totally invisible and avoid the risks you have mentioned. For example if you were invisible you wouldn't need to ask the teller anything, just follow someone into the secure area of the bank, hang around for a while seeing where all the keys etc are kept and then wander into the vault stuff as much cash as you can carry under your invisibility cloak and wander out again. I don't see why you'd need a get

Re:

[ichigo 2.0]

This would be solved by using IR cameras, or even pressure sensors.

Re:

[drinkypoo]

But they can unlimber the beanbag gun and fire several projectiles through the door that mysteriously opens by itself...

Re:Why should Harry Potter have all the fun?

[thermopile]

I was on a selection committee for DARPA to look into this stuff a few years ago.

Negative Index of refraction Materials (NIMs), metamaterials, or whatever you want to call them, are relatively easy to make in the microwave region, since the wavelengths are on the order of centimeters. Thus, using a special arrangement of rings, loops, and wires, you can craft a lattice-like material that exhibits negative refraction. Technically, it has a negative magnetic permeability (mu) and negative permittivity (epsilon).

This has all kinds of weird implications. The group velocity is still in the forward direction, but the phase velocity goes in reverse. Evanescent waves propogate, not die off. Perfect lenses can be made. Measurements LESS than the wavelength of light can be taken. There was a list of implications in the August issue of Scientific American, I believe.

Anyhow, this works great at the ~cm scale. Visible light is hard as hell: the scale there is on the order of nanometers. And the copper or silver or tungsten wires used to make the metamaterials have MISERABLE magnetic losses at these small scales, so mu is no longer negative. The energy no longer propagates in the medium. As of three years ago, there were no promising candidates for solving this problem. There was an outside hack at using carbon nanotubes -- which may or may not maintain their permeability down to small scales -- but it was a long shot at best. Arranging the little guys would have been devilishly difficult.

Glad to see that Pendry, who's been in this field almost as long as Veselago, is still making good strides. Even if they can't get to the visible wavelength, NIM's have spectacular applications for microwave antennae.

Re:

[avirrey]

I'm not as smart as thermopile, but I will say that the definition of 'invisible' for the most part should be limited to the human visual range. While this may be the ultimate goal the truth is that our 'detection' of a massive range of frequencies across the spectrum is so advanced, that anyone hiding behind a 'vision inhibiting' cloak could still be detected by other methods. Again, I'm not a hard-core physicist, but I would assume if you do some sort of city-sweep with X-rays you should be able to pick u

As an optics tool...

[Wilson_6500]

My first thought is, naturally, how can we apply this to masers? If you could "switch" this material's negative index of refraction very quickly--say, through physical deformation with a piezoelectric transducer, which should interrupt the properties of the lattice--wouldn't you have yourself a very nice solution for generating short pulses? Put one of these right before the output coupler and switch it at a high rate, and you have your pulsed maser.

Re:

[shafty023]

But when you walk to the aisle with all of the cloaks how will you find them

Re:

[turgid]

How long do you think till you can pick up a Cloak of Invisiblity at your local MegaMart?

Maybe you can already, but I've never seen one myself.

hmm,

[joe 155]

I'm unsure about the water claim, although it is true that you can't tell the difference that doesn't mean that it's not different, the water has been moved all over the shop, but it looks like it hasn't been affected.

Other than that if they make something invisable from visable light then it wouldn't be able to see anything, so a person would be blind or a bot would be virtually impossible to navigate, because you couldn't see it or track it...

Still, very interesting idea.

Just talking...

[nathan s]

..from my ass, so to speak, but I imagine you could leave certain frequencies uncloaked, enough to slip in, say, remote video from a drone flying nearby or surveillance cameras in the area or GPS satellites in the case of bots. Perhaps a super-advanced version could shift cloaked frequencies on the fly in order to prevent jamming/detection of the video source even. I dunno, if this works in the first place it seems like there should be ways around the "blindness."

Re:

[Daniel_Staal]

I'd say the simplest is just to make a few small holes in the cloak. If they are small enough they will be overlooked. Attach a small camera to the hole, and you've got a good chance of a wide field of view with a dust-mote sized hole.

Re:

[MightyYar]

Just think of the military uses. All you have to do is convince your enemy to use this on the roof of all their sensitive laboratories.

sigh

[geekoid]

clearly, you would make goggles that can filter from a non visible part of the light. Like IR.

Re:

[UbuntuDupe]

Other than that if they make something invisable from visable light then it wouldn't be able to see anything, so a person would be blind or a bot would be virtually impossible to navigate, because you couldn't see it or track it...

Interesting story -- one time in German class, we encountered the word "unsichtbar" (roughly, "unsightable"), and I was called upon to guess what it means. I guessed, incorrectly, "blind". (which oddly enough is also spelled "blind" in German.) The teacher then said that no, it

Re:

[grommit]

I'm unsure about the water claim, although it is true that you can't tell the difference that doesn't mean that it's not different, the water has been moved all over the shop, but it looks like it hasn't been affected.

Exactly. 10, 20, 30 years from now we may have the processing power and precise enough monitoring equipment to look at a river and say if there is a rock a mile upstream or not.

I think the point is to make the item not necessarily invisible but blend it in with the background noise to the poi

Moo

[Chacham]

FTA:

A team of American and British researchers has made a Cloak of Invisibility. Well, OK, it's not perfect. Yet. But it's a start, and it did a pretty good job of hiding a copper cylinder.

So, we'll just just change his name to Harry Copper.

This title is absurd. Invisibilty?

The research is very kewl though, and i hope it progresses. But why not lay off the stupid titles, and produce results based on kewlness or usefulness, instead of what can be termed with a popular buzzword. Information Technology is bad enough from its buzzword infusion. Must we destroy legitamte research/discoveries as well?

Re:Moo

[twostar]

someone using the term "kewl" is complaining about buzzwords?

*Ring* Hello?
Hi, this is the Pot calling. Is the Kettle in?

Yay for TV Dinners

[Odin_Tiger]

This will allow for more variety in TV Dinner desserts, because they can just shield it so only the stuff that needs to get nuked will get nuked. w00t!

Re:

[theantipop]

This will allow for more variety in TV Dinner desserts, because they can just shield it so only the stuff that needs to get nuked will get nuked. w00t!

I don't know what kind of desserts you eat, but mine do not include "engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials". Sounds like some expensive and, uh, tasty ice cream.

You know you are a fat geek when...

[B5_geek]

You know you are a fat geek when...
    the first thing that came to your mind when reading this summary was:

"Oh cool, no more burnt and undercooked mini-pizzas!"

I really should go outside more often.

To boldly go ..

[slashbob22]

.. where no man has gone before.

They may be onto something.

Bah!

[Clazzy]

They could've posted a pict...

Oh, wait. Never mind!

Picture here!

[thepotoo]

Pictures are now live at http://www.microwavecloakingpicture.com/ [microwavec...icture.com].

Amazing stuff.

Re:Picture here!

[ichigo 2.0]

The site seems to be cloaked from the HTTP spectrum.

Obvious?

[bigberk]

Girls locker room. Too obvious? Those lucky copper cylinders! I want to hear everything!

Re:

[dan828]

I really hope the you are still in Jr. High.

perhaps not but...

[StressGuy]

people who sell talcum powder might just have a new market...followed by paintball gun manufacturers.

TERRIBLE NEWS!

[abscissa]

What!! This is awful!! It means my microwave item-detecting device, which I walk around with to detect objects and random items, will now be obsolete!!

Color me dubious

[Ancient_Hacker]

Sounds mighty fishy.

You might be able to channel some energy around an object, but:

• There's no way to effectively pass an image through. You can't detect that the light is hitting at a 43 degree angle, therefore you have to pass that photon through and emit it from the other side at the same angle.
• Detecting, moving, and reemitting the light loses a certain and irreducible percentage of the light, so the "invisible" image is always going to appear darker.
• Doing this from every possible angle of source

Re:

[UbuntuDupe]

True, but to dismiss something like this because it's still possible to detect the cloaked object would be in error. Think about the camoflauge gear militaries already use. You can still see them. HOWEVER, if you're not looking carefully enough, it's a lot easier to miss them in certain environments. The point of cloaking or camoflauge is not to make you undetectable, but to make it require more resources to detect you, just like the point of encryption is not to make the data unreadable to others but to

Re:

[compro01]

but the thing is, you don't need to be completely invisible. you just need to be invisible enough to not be noticed. traditional camouflage works in the exact same manner, in that they can see you, but they don't notice you.

  combine that with this and you've got even better camouflage and they'll notice you even less often.

I have a perfect cloaking material right here...

[thrill12]

...in my home.
Only funny thing about it is.... I can't find it.

I bet if I could find it though, I'd win the Nobel prize.

meta-materials

[lgw]

If you can hide something from microwaves, you can hide it from radar and visible light.

I don't think this follows, at least when we're talking about metamaterials [wikipedia.org]. So far no one has invented metamaterials for optical wavelengths, as metamaterials rely on complex structure that's somewhat wavelength specific. It's easier to play "fool the photon" with microwaves (because of the longer wavelength) or X-rays (because of the higher energy) than it is with visible light. (Xiang Zhang's experiments in extending near-field effects of visible light are a very different mechanism, and are lumpedin with metamaterials simply for lack of a better term.)

Re:

[Anonymous Coward]

Actually that's not true. Metamaterials *have* been invented that work in the visible (although at the red end of the spectrum where wavelengths are longer) and there have been metamaterials which work in the near-IR for some time now. You are absolutely correct that fooling a microwave is easier, however fooling X-rays will be enormously difficult - x-rays have wavelengths on the order of the spacing between atoms in a solid, hence creating nanostructures with a "repeat unit" on this order is virtually imp

Was Anyone Else Thinking...

[Banner]

Romulan Bird of Prey? (Or equally, the small Klingon ships also armed with the cloaking device?).

Sorry, grew up on waaaay too much startrek :-)

Re:Was Anyone Else Thinking...

[angelasmark]

You obviously didn't grow up on too much star trek. Any true trekkie would know that its a Romulan Warbird and a Klingon Bird of Prey...

Re:Was Anyone Else Thinking...

[OfficialReverendStev]

You obviously didn't either. Somebody bring me the learnin' stick. You're both technically right. The Romulan Bird-of-Prey (from TOS, small white-ish ship with the bird painted on the bottom) did have a cloaking device, as did the Klingon (and Romulan) D-7 Battlecruiser. In the TNG era the Romulan Warbird (big and green) and the contemporary Klingon ships (Bird-of-Prey and Vor'Cha). Now, go play. I have a phaser to polish.

Re:

[gstoddart]

Romulan Bird of Prey? (Or equally, the small Klingon ships also armed with the cloaking device?).

Don't the Klingon Warbird's all have cloaking as well? Or is that all after TOS? I seem to remember several episodes where Klingon battle cruisers de-cloaked at (in)opportune moments.

Cheers

"In effect the device, made of metamaterials..."

[FirmWarez]

Ah, so the ship is the cloaking device! So much for putting on pointy ears and stealing it.

Has anyone seen David Smith? I searched the lab...

[Wonderkid]

Apparently, he had an accident with the targetting mechanism.

Backpack of Invisibility?

[Doc Ruby]

I'll go out on a limb on a series of "ifs" (and maybe a bag of physics naivetes), but let's say we perfect this manner of imperceptibly "derefracting" light. And let's say we also complete the ambitious work identifying and manipulating gravitons, still hypothetical. Could we "cloak" spaces and matter from any interaction with our universe, not just electromagnetic? Maybe the Stong and Weak Forces would remain for interaction, but practically, outside the tiny diameter of a nucleus, could anyone notice?

Could a "gravity cloak" create subspaces operating as independent universes? Could we contain matter too highly interactive for current use safely? Like a tiny black hole conveniently near a device it's powering, or a pair coupled into a wormhole for "faster than light" travel through custom-folded space? Vast amounts of stuff crammed into pocketsized spaces.

Maybe the old playground philosphers choosing between "teleportation or invisibility superpowers" will finally have a lab to figure out which is really better.

Re:

[cHALiTO]

Yay! magical bag of holding!

or maybe I can finally go around carrying tons of cash (if I had any), a saint-bernard, 3 drinks, a fishing pole, a monkey, a shovel, and loads of pirate-wannabe stuff? excellent!

Re:

[Lord Ender]

Could we "cloak" spaces and matter from any interaction with our universe, not just electromagnetic?

It's already been done. But you don't even have to cloak gravitons. What do you think all that dark matter is? It's intersolar sprawl, and the aliens use the cloaking so that we don't keep bothering them, asking for technology.

Stealth Ship

[rlp]

Sounds like a better version of stealth. I recall reading that an early attempt at a stealth ship did TOO good of a job of dispersing microwaves (compared to background reflection of empty ocean) and showed up as a moving 'hole' on surface radar screens. Assuming that this technology could be applied to bending light around an object, it would need to do so without creating obvious distortions.

Re:

[LWATCDR]

Yep I see it as more use for stealth aircraft, ships, and other vehicles. While microwaves are really just a different color of light the difference is the wavelengths may make optical invisibility using this method impractical. Makes a good headline though.

Microwaves? That's nothing!

[Dark Paladin]

The majority of slashdot readers have been invisible to human women for *years* now.

Wake me up when scientists can do *that*.

Re:

[Slightly Askew]

Already done. Scientests have been invisible to human women long before slashdot was even conceived

I have a cheaper way to do this

[WillAffleckUW]

I make myself invisible to microwaves by unplugging them, or turning off the lights.

Sneaky little buggers, always watching you and beeping at you to take your dinner or coffee out ...

Comment removed

[account_deleted]

Comment removed based on user account deletion

What about radiation from the object?

[MrHops]

Seems to me, even given perfect invisibility, that the object in question would radiate energy all by itself.

Do some spectranalysis, and you immediately know something fishy is going on. (Copper won't radiate like the ground, for example)

Watch out for that "next step," it's a doozy.

[dpbsmith]

"The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow."

Right, and my "overunity" (perpetual motion) device has an calculated energy output equal to 100.1% of its input. But due to a few minor engineering losses that reduce the output, the current working model only produces 99.9% of the input.

The next step is to go for that last 0.2%. I did this work very quickly ... and that led to a devic

Co-author with last name "Smith" - is he a Doctor?

[Damek]

Cloaking devices are nice and all, but wake me when they've started work on a Chameleon Circuit.

Actual invisibility is useless

[mark-t]

If you bend the lightwaves around yourself so that they can continue moving past you, what light waves can enter your eyes, exactly? You'd be in pitch darkness, unable to see a damn thing because the light can't get to you because it's being bent around you. If you choose to allow some light through so you can see, then other people would see blackness there because there's light that's not getting reflected by anything... again, useless.

Re:Actual invisibility is useless

[DrKyle]

There's this thing called a pinhole camera, it's a relatively new advance. By allowing this pinhole of light in with the proper equipment just enough light could be absorbed to allow the user to navigate. Of course there would be a visible pinhole floating in space, but could you reliably pick it out at a distance of more than a few feet?

The failure of moderation

[mcrbids]

There's this thing called a pinhole camera, it's a relatively new advance.

And, folks, here's a case indicating the limits of moderation by the unwashed masses. A pinhole camera [wikipedia.org] is the very oldest type of camera. Having no lens, it can be made with a box and (gasp!) a nail. It is known to have been known about by the Chinese somewhere in the 5th century B.C, and Aristotle in 4th century B.C. [photo.net] Oh, how a small bit of research in widely available knowledge could have saved the parent poster from looking like

Whooooosh!

[djeca]

There's this thing called sarcasm, it's a relatively new advance. By stating a clearly false proposition in the proper tone of voice a touch of humour can be added while still conveying to the reader the intended meaning. Of course on the Internet the tone of voice can be lost, but what sort of moron would fail to realise this?

Article From May

[mugnyte]

  the wires posted this one recently, but the science article came out in May. Old news?

It's the first time we _know_ it's been done

[Catmeat]

But for something with such obvious military applications, I wonder if they have really been beaten to the punch by 10 years by some deep black Skunkworks research team, courtesy of about 2 orders of magnitude more funding.

After all, the F-117 first flew in 1977 - it's 30 year old technology. I bet they've not been sitting on their hands since then.

WTF

[hurfy]

Is the world coming to an end?

Zonk's title is actually more accurate than the original !

hehe, sounds interesting but a bit overhyped. Seems like a long way from a 2-dimensional version to 3. I am not even sure what one would see using 2 dimensional version, how do you hide 2 of 3?? Would not that leave only a line, but with no width you can't see the line, but then it would be complete but its not so.....

Pictures

[debrain]

Does anyone have any pictures?? What's it look like? What would we see?

finally!

[Gospodin]

I'll be able to heat up my Chef Boy-R-Dee without taking it out of the can!

A Cloaking Device?

[Ltar]

This is a violation of the Treaty of Algeron, the romulan empire will not stand idly by and watch as you disturb the delicate peace between our peoples! Hand over your research and all of your devices to Romulan high command at once, or they will be taken from you.

They're making this WAAAAAAAAY too complicated.

[frogstar_robot]

Just paint the copper cylinder pink and turn on a cheap and simple Somebody Else's Problem Field.......

Research has been delayed

[Hoi Polloi]

They are still looking for the prototype. It is around here somewhere...

A visible light version already exists...

[Dave21212]

There's a photo of it here [lowes.com]. It's sitting there in the middle of the table (actually, just a little to the left of the middle).

Seriously though, how funny would that demo be... "I've created this material lattice that re-directs visible light such that nobody can ever see it ! oh wait, I had it here somewhere... D'oh !"

Basically, neat trick for radar/MW, lousy for visible light. Why even go there ?

The big limitation

[Beryllium Sphere(tm)]

>The cloaking has to be designed for specific bandwidths of radiation.

You can use lots of different frequencies for radar. This is so cool it must have lots of uses but a cloaking device doesn't seem to be among them.

Vulcan-level tech?

[cnerd2025]

"from the on-our-way-to-vulcan-level-tech dept."

Goodness, Zonk, don't you know anything?! The Vulcans didn't use cloaking devices; the Romulans and Klingons did (as well as some rogue Federation types)! I was about to say "your geek license has been revoked", but decided against it. Thanks for posting the link to this article.

Re:

[ScaryFroMan]

Technically, Romulans are Vulcan.

Water doesn't reflect off objects?

[RomulusNR]

When water flows around a rock, Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock.

Is that even true? It seems to me that the flow pattern of two identical channels, one with a rock and one without, would differ in a way that would be detectable downstream -- at least if you knew what it was supposed to look like without a rock.

Say goodbye to airport security

[Com2Kid]

Make one of these that works for X-Rays.

Wrap a gun in it, put in carry on bags.

Pass right on through the machine, nothing noticed.

Two words

[Guysmiley777]

Multispectral sensors. While you may be able to fool some of the wavelengths all of the time and you may be able to fool all of the wavelengths some of the time, you'll never be able to fool all of the wavelengths all of the time.

Repost?

[BobSutan]

Correct me if I'm wrong, but wasn't this already posted back in May 06 [slashdot.org]? So what's different with this story?

Re:

[pontifier]

That was just the idea, now they've actualy built one.

Pasisve radar

[MoogMan]

Is it still detectable with passive radar methods?

Briefly, a passive radar system will monitor the background radar/microwave "noise" that gets emitted by hot objects, radio masts and the like. If they detect a lack of signal in a specific area, then logically that means something is deflecting or absorbing the microwaves.

Well, I have to say

[ScrewMaster]

that having only read the summary this seems genuinely cool. Of course, it's also genuinely scary, but that's the price of progress I suppose.

Re:

[wyldeling]

Both follow the path of least resistance. It just happens that most of the time light follows a straight line. A mirage [wikipedia.org] is an example of when light doesn't follow a straight line.

Re:bad analogy

[zippthorne]

fluids follow the path of least resistance. Light follows the path of least time.

Fermat's principle

[Anonymous Coward]

To expand: light following the path of least time is known as Fermat's principle [wikipedia.org]. Fermat's principle can in turn be derived from Feynman's path integral formulation of quantum mechanics [wikipedia.org]; it is related to [wikipedia.org] the principle of least action [wikipedia.org]. Feynman's book QED: The Strange Theory of Light and Matter has a lay derivation of Fermat's principle from path integrals (due to constructive superposition of quantum phase differences).

Re:

[wyldeling]

Point. Let me clarify. Mathematically, they are the same thing. The principle of least action applies in both cases, just the path the minimizes the particular Lagrangian (T - V) [wikipedia.org] (or Hamiltonian (T + V) [wikipedia.org], if you prefer) differs depending on the potential energy. (Both methods are applications of the Calculus of Variations [wolfram.com]. ) Either way, it is a minimization problem and the same techniques apply. So, as far as I'm concerned, they tend to blend together.

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[Rob T Firefly]

Drama. It's the scientific law all plot devices must follow.

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[Vicissidude]

That's straight from the article. Take it up with RANDOLPH E. SCHMID, AP Science Writer.

Grammar Nazi

[dosun88888]

You didn't point out a single spelling mistake in the original post. You're certainly not the Definition Nazi.