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Science Technology

Fatal Flaw Discovered In Invisibility Cloaks 255

KentuckyFC writes "Carpet cloaks took the world by storm last year because they were the first devices to hide objects at optical frequencies. The idea is that a thin layer of dielectric material placed on a surface can make light look as if it is reflecting off the original surface. In other words, the layer is invisible and anything embedded within it is invisible too. This trick is like hiding something under a carpet, hence the name. Carpet cloaks are relatively easy to make because the dielectric material does not need to be specially constructed to steer light in special ways; physicists call this an isotropic material. Now a group at MIT has shown that isotropic carpet cloaks have a fatal flaw. When viewed at an angle, the carpets don't hide objects at all. Instead, they simply shift their position by about the same distance as they are high. So when viewed from an angle of 45 degrees, an object 0.2 units high is shifted to one side by a distance of 0.15 units, says the team. That's a serious limitation for carpet cloaks."
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Fatal Flaw Discovered In Invisibility Cloaks

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  • bummer (Score:2, Insightful)

    by Anonymous Coward
  • Wrong Cloak (Score:5, Insightful)

    by LaminatorX ( 410794 ) <sabotage&praecantator,com> on Monday April 19, 2010 @05:03PM (#31902122) Homepage

    So what they're saying is it's more of a Cloak of Displacement? While less stealthy, I think that's actually better odds of avoiding the hit than the penalty for attacking an invisible opponent.

  • I guess? (Score:4, Insightful)

    by Monkeedude1212 ( 1560403 ) on Monday April 19, 2010 @05:03PM (#31902124) Journal

    Yeah - you aren't invisible, but wouldn't that still make the tracking missile miss you?

    • If it's optically tracked, sure. You might be out of luck if the operator is using IR.

    • That's what I'm saying. Shifting the apparent location of a target is almost as good.
    • Re:I guess? (Score:5, Interesting)

      by Arancaytar ( 966377 ) <arancaytar.ilyaran@gmail.com> on Monday April 19, 2010 @05:30PM (#31902462) Homepage

      Depends on the size of the missile...

      • I think you'll find it's less about the size of the missile and more about the yield of the warhead.

        One of the advantages to 10+ Mton nuclear warheads, is that you don't need to be very precise

        • Re: (Score:3, Informative)

          by Khyber ( 864651 )

          No, it's about the size of the missile. The warhead is always listed in pounds but the potential is always listed in kinetic energy.

          For example, the BrahMos has 32 times the kinetic energy of the Tomahawk, despite having a warhead 3/5 the size. It is by far much more destructive than our Tomahawk because of its higher mass and higher velocity capability.

    • Maybe so but a broad spray of shrapnel and bullets won't. Even rain could defeat a cloak unless the rain goes right through it without resistence.

    • Two words. Splash. Damage.
      • Two words. Splash. Damage.

        That's four words.

        Or were you saying that "Two words" is two words? Seems like a bit of a tautology, though maybe not for the reason you'd think...

    • Re: (Score:2, Insightful)

      by BitZtream ( 692029 )

      Not if it realizes you're likely behind a cloak and just adjusts itself with some nifty math.

      But ... that was my first thought as well.

      Okay, so I'm not invisible, but you still don't actually know where I'm at so its close enough for a lot of neat things.

      I suspect however, that much like in the fantasy of StarTrek (sorry to burst some of your bubbles :) and root kit detection, theres always a way to detect the target, but knowing the right way to look for it is half the battle.

      In general, Stealth aircraft j

  • by jornak ( 1377831 ) on Monday April 19, 2010 @05:04PM (#31902136)

    I'm sure a carpet cloak like this would have military applications, and in a desert environment like the Middle East, people aren't going to notice you unless they're close to you.

    A sniper on a ridge covered with one of these babies is still going to do the job.

    • So if I understand this right TFA says that these cloaks just render something as appearing where it isn't rather than completely invisible when viewed from various angles?

      If so that's still got the possibility of being pretty bloody useful.

      • by mwvdlee ( 775178 )

        At least it could hide things from satelites, since they don't look down at any significant angle.

        • They do look down at significant angles. This is why you have to hide stuff you don't want seen whenever the spy satellite is over the horizon, not just when its over head. The operators get to decide when to use fuel (or bleep off a flywheel) to reorient a satellite.
    • by Fred_A ( 10934 )

      I'm sure a carpet cloak like this would have military applications

      Sure, if you have soldiers the size of a pinhead.

      But then, remember that all the jihadists have to do is move sideways a bit and "ha ha, we can see your pinhead, you silly infidel !"

  • Soo.... (Score:4, Insightful)

    by Some.Net(Guy) ( 1733146 ) on Monday April 19, 2010 @05:05PM (#31902150) Homepage
    When they were creating these cloaks, they didn't think to look at it from other angles than just straight on? Seriously? That's the equivalent of "it works on my machine."
    • Re:Soo.... (Score:5, Insightful)

      by e2d2 ( 115622 ) on Monday April 19, 2010 @05:12PM (#31902262)

      They're making things invisible. It's kind of hard. So cut them a break? It's not like it's been done before and they just half-assed it after all.

    • Re: (Score:2, Insightful)

      by BitZtream ( 692029 )

      Well, they probably did and really knew about it for a long time, but geeks being geeks, these minor details probably didn't come out because they were so proud of what they had accomplished, and rightfully so. Even a cloak that works head on is freaking impressive to the point of becoming magic. I know they are just wave guides, but its still freaking impressive.

      With that in mind, someone comes a long and notices it a long time later and points it out and the scientists are like 'yea well, we haven't got

  • Finally!!! (Score:4, Funny)

    by Locke2005 ( 849178 ) on Monday April 19, 2010 @05:06PM (#31902164)
    At last, my sig is actually appropriate for a slashdot story!
  • by Anonymous Coward on Monday April 19, 2010 @05:06PM (#31902178)

    You could bump into the invisible object.

  • Props to Soulskill (Score:3, Insightful)

    by magsol ( 1406749 ) on Monday April 19, 2010 @05:11PM (#31902240) Journal
    ...for making a Wing Commander reference (from the books, not the horrific movie that by coincidence has the same name) in the "department" byline for this story.
    • ...for making a Wing Commander reference (from the books, not the horrific movie that by coincidence has the same name) in the "department" byline for this story.

      Wow, given the implied Scottish accent in "you-cannae-fire-while-cloaked", I actually would have thought that was a reference to Scotty from Star Trek.

      Apparently, I'd have been wrong. Of course, one can argue that any Scottish accent in Sci Fi after Scotty is, by definition, an homage to the great engineer -- and, for purposes of discussion, I bel

    • There were Wing Commander books? I'm only familiar with the Wing Commander video games that were the basis for the movie.

  • Pictures (Score:4, Informative)

    by brianleb321 ( 1331523 ) on Monday April 19, 2010 @05:12PM (#31902260)
    I demand more pictures of invisibility cloaks in articles about invisibility cloaks. Theory be damned.
  • but will the cloaks still work when shaped like small* spheres?

    *small where you are almost looking radial from any direction

  • What happens... (Score:2, Interesting)

    by d1r3lnd ( 1743112 )
    What happens when you layer them? I mean, if you overlap a bunch of these invisibility carpets, what would you end up looking at?
  • Shoot to miss (Score:4, Interesting)

    by Mr. Foogle ( 253554 ) <brian.dunbar@NoSPAm.gmail.com> on Monday April 19, 2010 @05:17PM (#31902318) Homepage

    So when viewed from an angle of 45 degrees, an object 0.2 units high is shifted to one side by a distance of 0.15 units, says the team. That's a serious limitation for carpet cloaks.

    Maybe. But it would be a great way for soldiers to conceal themselves from aimed rifle fire.

    • Re: (Score:2, Insightful)

      by PinkFreud ( 51474 )

      That might work. A 6 ft soldier would appear to be displaced by about 4.5', if that ratio holds.

    • So what if you took two of them and overlapped them at 45 degree angles? I realize that's not quite descriptive enough to clarify my line of thought, so let me elaborate:

      Say I have a cube covered by this thing. When looking at it from a 45 degree angle, I see the cube displaced.

      So what if I then take another slightly-larger carpet cloak and prop it up 45 degrees off-axis such that when I look at this outer cloak straight-on, I see "through" the outer cloak, and when I look at it at 45 degrees, I see
    • Couldn't they just use two cloaks placed at the appropriate angles in relation to each other?

  • guess I'll have to postpone that trip to Mordor.
  • Disappointing (Score:4, Interesting)

    by Mursk ( 928595 ) on Monday April 19, 2010 @05:23PM (#31902380)
    I don't know about you, but when I hear the phrase "fatal flaw," I really expect something a little more, I don't know... hilarious.
  • When I take two steps to the right, all of a sudden all I see are AC posts modded down to -1. It appears the Slashdot moderation system is angle-dependent! I'm sure to win the Nobel for this.
  • by eegad ( 588763 )

    It took a team from MIT to walk to the side of the object, look at the object and report that the object could be seen? I think this cloak managed to hide something other than the object....

  • by Posting=!Working ( 197779 ) on Monday April 19, 2010 @05:36PM (#31902534)

    I mean, I know we all understand it, but if you're giving an example, why use unitless decimals when you can use integers and tangible concepts? Why not just say it would displace a 4 meter tall truck by 3 meters instead of 0.2 units tall object by 0.15 units?

  • in a theoretical device, i have been theoretically impressed

  • You will still get pushed off the subway platform by the crowd, or hit by a bus that doesn't see you!
  • 1. Roll up the carpet.
    2. Put the object in a carpet, then put the carpeted object in another, slightly angled carpet, then put THAT into yet another slightly more angled carpet, and that entire batch into still yet another, even more slightly angled carpet, etc, until all angles are covered.

  • Remember the "Wonder Woman - Invisible Man - Superman Encounter"?

    I'll pass on the cloak in any event, thanks.

  • For all the talk of cloaking technologies I hear around here, this is the first I've heard of this one. Sure, I'm not an expert in the field, but if this "took the world by storm" last year, I'm surprised no news stories ever reached me.

    Most suspicious, though, are the references to this as a technology for which practical devices have been built. The effect described in TFA is something you could see empirically if you had a working model; you don't need someone to draw a diagram showing the course of a

  • of circumstances where any viewpoint other than roughly straight on is impractical - for example looking at someone through a tunnel, or someone a long way off through a telescope where to get any viewpoint from a significantly different angle would take a lot of walking. Presumably it works just fine then.
  • rotating mirror mount?

  • ... Although, if TFA is to be believed, it won't appear to be.
  • ... wouldn't these "invisibility cloaks" be easily defeated with thermal detection equipment?

  • The displacement isn't as useful as everyone thinks. Anything that is wider than it is tall will still get hit by any shot that's near center or to the correct side of the displacement, and some shots that would have missed will be hits. Actually anything whose height to width ratio is 4:3 or lower will still get hit. That covers a lot of the military equipment you'd want to hide - tanks, planes, ships, most buildings, most vehicles, anyone not standing up, etc.

Neutrinos have bad breadth.