Science, Fiction, Life

Could Cloaking Devices Work?

By now, you have probably seen the absolutely epic Starcraft 2: Ghosts of the Past trailer. If not, take a look at this, and pay particular attention to the depiction of Sarah Kerrigan’s cloaking device at about 11 seconds in:

[youtube=http://www.youtube.com/watch?v=C_E83GfWM-A&w=574&h=346]

Cloaking is common in science fiction: Star Trek pioneered it with the Romulans, and other popular franchises like Star Wars and Predator and Halo have used it. And of course in Starcraft and Starcraft 2 both the Terrans and the Protoss have a whole variety of cloaked units. But could it really work? You may be surprised to learn that the answer is yes!

Obviously, this sort of technology would be extremely useful for the military, so they are funding research into technologies that could make it a reality. There are basically two ways that you could achieve “cloaking”. The first way would be to actually divert light around the cloaked object, so that it appears not to be there.

An example of the path that parallel light rays would take around a cloaked sphere.

This requires some really bizarre optical properties because the light needs to bend away from the object and then back. All natural materials have a positive index of refraction, which is a value that indicates how much a material bends light. To divert light around an object, you need material with a variable index of refraction, and it needs to be negative at some point.

Researchers have managed to create “metamaterials” with optical properties that allow them to “cloak” objects, but the technology is still in its infancy. In 2006, the first example managed to divert microwaves around a metal cylinder. Microwaves are easier than visible light because they have a much large wavelength: centimeters instead of nanometers. Metamaterials are typically made of narrowly spaced repeating lattice, and they only work on wavelengths larger than the spacing of the lattice. It is much easier to make a lattice smaller than a centimeter than it is to make one smaller than a nanometer!

This is the metamaterial that was used to "cloak" a metal cylinder in microwaves.

More recently, infrared light was diverted around a “bump” in a gold sheet so that the sheet appeared to be flat, and many research teams are working on metamaterials that work on shorter wavelengths and over broader wavelength ranges.

The other way to “cloak” something is a bit more intuitive, and doesn’t require such exotic materials. This method is called “active camouflage” and works by projecting an image of the object’s background on the front.

This laptop's background is demonstrating the principle behind active camoflage.

The trick with active camoflage is to have the object you’re trying to hide covered in small unobtrusive cameras that can observe the surroundings and in some sort of screen that can project the appropriate colors. Researchers at the University of Tokyo have made an “external” active camouflage device which uses a video camera to view the background and a projector to project it on the object being hidden, but so far nothing even close to the cloaking devices in Starcraft has been produced.

Using a specialized camera and projector, this cloak appears transparent, but not from all angles, since the image is projected onto the jacket from near where the viewer is standing.

Interestingly, some of the best examples of active camouflage in the real world are found in nature. Chameleons typically just change their overall color, but octopuses and cuttlefish are underwater masters of disguise, rapidly changing their color and even their texture as they move over different surfaces. It’s not active camouflage in the truest sense of the word because they don’t usually reproduce an exact image of their background, but they can mimic the appearance well enough that they might as well be cloaked. Take a look at this video to see what I mean. The octopus is essentially invisible until the diver scares it and it flees:
[youtube=http://www.youtube.com/watch?v=SCgtYWUybIE&w=480&h=385]

So, technology for cloaking devices is still very primitive, but it’s not totally science fiction. There really are lots of scientists working on developing the necessary materials, and they’re making progress! Perhaps surprisingly, the best example of cloaking in the real world comes not from high-tech labs but from nature. In the StarCraft universe, considering that they have technology like faster-than-light travel, I’m willing to believe that the Terrans and the Protoss also have enough know-how to play with optics and create reliable broad-band cloaking devices. And even though creatures on Earth really do have what amounts to active camouflage, I’m sure glad the Zerg don’t have similar talents!

6 Comments

  1. Joseph

    An interesting thing about the way octopuses and squid achieve their camouflage is that, I’m pretty sure, they have cells full of dye that they can expand and contract at will to make them visible or not. They are essentially covered with pixels in a few colors. This is exactly the way an e-ink display works!

    I think my favorite thing about all these “cloaking” technologies is that, if you think about it, when in use they would produce pretty much the same distortion effects that we see in video games. Science imitating art imitating life, huh?

  2. Kevin

    I hadn’t seen that trailer. Awesome! Are you getting your copy tomorrow?

    • Ryan

      Yeah, if that trailer were for a movie, it would be a blockbuster. The dialogue was cliche, but man, it *looks* so good!

      Not sure when my copy is arriving… but probably in the next few days at least.

  3. restaurant city money hack

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  4. scishark

    Apparently they can apply the cloak in 3D (as opposed to 2D shown here) + in optical wavelengths,

    http://www.scishark.com/2011/04/cloaking/

  5. Kyle

    can a person use magnetic energy to bend light?

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