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The Military Science Technology

How To See Through an Invisibility Cloak 201

AMESN writes "Ways to bend light around objects and render them invisible are becoming a major field of scientific study and gaining ground. While no actual invisibility cloak exists yet, researchers are also theorizing on how to beat the perfect cloak."
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How To See Through an Invisibility Cloak

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  • rain (Score:5, Insightful)

    by wizardforce ( 1005805 ) on Saturday December 05, 2009 @06:41PM (#30338958) Journal

    No invisibility cloak can hide the fact that it's still a solid object. That or utilize various frequencies of EM as it would be extremely difficult to defeat radar + infared + visible + UV all at the same time.

  • by unitron ( 5733 ) on Saturday December 05, 2009 @06:50PM (#30339014) Homepage Journal

    If you can, it's not perfect.

    The real problem isn't detecting it. It's knowing that you need to be trying to detect it in the first place, and approximately when and in what area.

  • Why worry? (Score:4, Insightful)

    by gmuslera ( 3436 ) on Saturday December 05, 2009 @07:00PM (#30339114) Homepage Journal
    A perfect invisibility cloak is also a perfect blindness cloak. Unless you make i.e. missiles or bullets (dodge that, Neo!) with it, things with a predefined target, could be somewhat useless for most interesting uses. The imperfect are the useful ones.
  • by sopssa ( 1498795 ) * <> on Saturday December 05, 2009 @07:00PM (#30339120) Journal

    I am not sure why people are being so slow to accept this.

    Because nothing in world has to be 100% perfect. It just has to work good enough. And maybe later there will be new discoveries that will improve it. That's how technology and science has always worked.

    Sure, there will always be ways to get around the invisibility cloak, just like people have ways to get around DRM. But it doesn't make it completely useless or non-working technology.

  • Invisibility (Score:5, Insightful)

    by NoobixCube ( 1133473 ) on Saturday December 05, 2009 @07:05PM (#30339164) Journal

    An "invisibility cloak" these days doesn't just necessarily apply to the visible light spectrum. The cloak could be a thermal or radar "invisibility" cloak, leaving an object perfectly visible to the naked eye, but invisible on other scans. Penetrating thermal invisibility cloaks might end up more important, because camouflage can take care of visible light from overhead, it's the thermal that's the giveaway.

  • Re:rain (Score:4, Insightful)

    by Penguinisto ( 415985 ) on Saturday December 05, 2009 @07:05PM (#30339168) Journal

    Exactly. Even the vaunted "stealth" technologies of the 1980's and '90s were engineered only towards a certain set of frequencies.

    This 'invisibility cloak' could be defeated as easily as using a video camera with "night shot" built in (basically, an infrared emitter on the camera body sends out IR, and the lens picks that up, making it a bit more active than simply taking in whatever it sees). The cloak blocks the IR, so it'll either shine with the reflected waves or will show up as a shadow.

    Other ways to defeat it? Talcum powder or other particulates (like rain ferinstance).

    'course, I doubt that they could make such a "cloak" anyway, at least insofar as it would still show movement. So unless their 'spy' is really good at standing still, he's still liable to be noticed.

  • by Bigjeff5 ( 1143585 ) on Saturday December 05, 2009 @07:48PM (#30339522)

    Stealth technology, like that used in the B-2 bomber, F-117 nighthawk, and similar aircraft, was never about bending light around the plane. Because RADAR is an active detection technology - that is, it projects radio waves of a particular frequency and waits for a reflection - it was always about reducing the angles at which the radar would reflect.

    Plain old metal, no matter how you coat it, is like a pristine mirror for radio waves (the black color was simply because they only ever intended the planes to fly at night, so the original camoflage pattern was useless). A rounded surface, like that on most planes, will reflect RADAR signals coming from nearly any direction and at least part of the signal will be sent back to the RADAR. That's how RADAR is designed to work. To get around this, you need to minimize round surfaces so that very little, if any signal at all is returned to the RADAR. On-coming RADAR gets bounced up and down, and only a small portion of the radar signal from below gets sent back. They end up looking like large birds - a far cry from massive bombers.

    Light is harder, because we distinguish between multiple frequencies of light, so many materials difuse light, and we don't rely on a source projected directly from our own bodies to see. So for this we need to get light to bend around an object to cloak it.

  • by Pyrion ( 525584 ) * on Saturday December 05, 2009 @07:53PM (#30339552) Homepage

    This has always been something that's bothered me about Star Trek. It's well-established that "cloaked" objects, including people, still exist as solid matter and therefore displace whatever space they're occupying. I would think a foolproof means of tracking cloaked objects would simply be to concentrate on whatever it is they're displacing, and look for the telltale starship/person-shaped contour of gaps of nothingness where displacement is occurring. Take the interior decks of a Federation starship for example - authorized moving displacements signifying crew (tagged by their commbadges) if they simply ever thought to track the density and movement of the air they're pumping into each and every deck. Space is much the same way - it's not a perfect vacuum, and you can't tell me that Federation sensors aren't powerful enough to pick up damn near everything in their immediate surroundings.

    This also bothered me in Stargate: Atlantis the multiple times Atlantis was cloaked to hide it from orbiting Wraith vessels. They know what Atlantis looks like, can't they just scan the ocean's surface and look for the telltale snowflake shape of water displaced by the city?

    Point is: a cloaked object in a perfect vacuum (absence of everything) would be impossible to track using displacement, but a perfect vacuum exists only in hypothesis. Cloaked objects are always going to have to displace something, so rather than trying to pick up the cloaked object directly, why not concentrate on what you can see and look for gaps which shouldn't be there?

  • Let's keep it real (Score:3, Insightful)

    by Ancient_Hacker ( 751168 ) on Saturday December 05, 2009 @08:26PM (#30339764)

    We're getting a bit too excited here. If you read TFA you'll realize how limited this thing is. Many of these designs can only work at one frequency, usually microwave, in one direction, over a very small area, in 2D, and with considerable scattering and attenuation.

    That's a heck of a long way from a usable cloaking device. The problems of scattering and attenuation are going to be particularly intractable.

    It's unlikely that every one of the many shortcomings can each be improved by the needed factor of 100 or so.

  • by Idiomatick ( 976696 ) on Saturday December 05, 2009 @09:51PM (#30340302)
    I imagine throwing a stone at something you don't know is there to find it would be quite the feat.
  • by physburn ( 1095481 ) on Sunday December 06, 2009 @01:25AM (#30341302) Homepage Journal
    That wouldn't prove cloaking impossible, it would require that a cloaking screen be powered in some way so that the dissipation of energy from the power source makes up for the extra entropy gained by the refracted light. Marl's proof can't apply that negative refraction is impossible for all frequencies, because we've have experimentally seen negative refraction at specific frequencies, including optical frequencies []. What he disproved must a unpowered clock that operates over all frequencies at the same time.

    When it comes to use electrons to see cloaked items, there is science fiction and computer game presidence. In Alien vs Predator, the switching to Electric vision, the Alien can easily see a cloaked Predator.


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