A Cloak of Invisibility?

August 15, 2008

Considering that I’ve co-authored two books on popular culture (2004’s Poplorica and 2006’s OOPS!, available in remainder bins everywhere!), it’s a bit embarrassing to admit that I don’t really know that much about the Harry Potter phenomenon. A while back, I wandered into a Borders bookstore and found myself surrounded by a tumultuous horde — whole families — clad in billowy robes, scarves and neckties, all awaiting the midnight release of the latest of J.K. Rowling’s almost preternaturally best-selling novels. The idea crossed my mind: What if this costuming tie-in concept caught on, and Borders started insisting that all customers dress up like fictional personages in the books that they wanted to purchase? It was a discomforting thought for someone who had come in search of a copy of John Burdett’s Bangkok 8, a detective thriller set in Thailand that prominently features transsexual Thai cabaret performers known as katooeys. Now, they probably make sequined gowns in extra-large, but where would I find a pair of size 11-and-a-half spike-heeled pumps?

But once again, I digress. The relevant Harry Potter connection here is a garment that’s not so much a fashion statement as it is an ingenious device: the Cloak of Invisibility. Here’s an explanation of the cloak, which I got from an article in Wikipedia:

According to the legend, the Cloak of Invisibility has the power to shield the wearer from being seen by Death. It is a true invisibility cloak, in the sense of being able to completely shield the wearer from sight, and cannot be worn out by time or spells. Other typical invisibility cloaks described in the books, which are sometimes woven from the hair of a beast known as the Demiguise, can become opaque with age and are vulnerable to being penetrated by various spells.

Granted, the cloak has a few imperfections — snakes can somehow sense people who are under it, and there’s some sort of spell with a fancy-schmancy Latin name that allows the eyes to penetrate its protection as well. (See, I am catching on a bit.) But for the most part, the Cloak of Invisibility is a pretty nifty bit of camouflage

That’s why in the non-wizard real world, researchers have been working to develop an effective cloaking technology.

One early approach has been to use augmented reality — that is, additional data artificially added to sensory input — to create an illusion that will fool observers. As this 2005 article from HowStuffWorks.com explains, this sort of optical camouflage requires an elaborate setup. A wireless video camera behind the cloak-wearer captures the background view and transmits it to a computer, which modifies the image to correct the perspective and then projects it into a special type of half-silver, half-transparent mirror called a beam splitter or combiner, which reflects the modified image onto the reflective surface of the cloak while also allowing ordinary light from behind the observer to filter through as well. If it’s too tough to grasp the written explanation, here’s a YouTube video in which Japanese researchers demonstrate the technology.

As you can see, this approach might be effective, provided that you have several assistants, ample time to set up the equipment, and are trying to hide from someone with the visual acuity of, say, Mr. Magoo.

However, researchers also are developing another invisibility method that so far shows great promise. This sort of cloaking would use metamaterials — man-made composites in which the material's tiny structures are engineered to have special electromagnetic properties — to cause light to flow around an object or person, rather than being reflected. In 2006, Duke University researchers demonstrated a cloaking device that rerouted microwave radiation around an object in this manner. The following year, Purdue University scientists, using calculations by British physicists, came up with a theoretical design  for an invisibility cloak with a surface that would consist of a cylindrical array of nano needles that would bend light, though only one particular frequency at a time. And new papers in Science and Nature by University of California-Berkeley professor Xiang Zhang and colleagues describe experiments in which the researchers were able to make light flow around cloaked objects. (As I write this, the papers aren’t yet up on the Web, but here’s an Associated Press article describing the research.)

It’s not hard to imagine how cloaking technology would be useful in real-life situations. Soldiers could sneak through enemy lines undetected. Spies could conduct surveillance right out in the open. Britney Spears could even stop at Starbucks to use the restroom without being mobbed by paparazzi. The possibilities seem endless. Of course, if cloaking technology became widely available, terrorists, drug smugglers, shoplifters and reporters for the National Enquirer might find uses for it as well. So what do you think? Should scientists endeavor to create a real-life Cloak of Invisibility? Or is this something that we should leave to fictional wizards? Express your opinion below.

Comments

[Astroboy]

FIRST!!!!!!!!

[Caffeine Driven Stress Magnet]

Great! ...now I can vacuum the living room in the nude, without having to close the drapes.

[Lola]

How many years will it take to get an invisibility cloak on the consumer market?

[Mothra]

I would love to have it, so I could get into situations where I don't have access and be the fly on the wall.

[Eight Year Old]

Id like the power to be invisible. I would sneak up on people and do stuff secretly.

[Wizard]

I can't believe you haven't read the Harry Potter books.

[Michael Phelps is God]

I like it better when you write about global warming.

[Chris Croker]

LEAVE BRITNEY ALONE!!! Look at all she's been through! Can't you see that she needs to be invisible?!

[Shawn]

If Britney Spears was invisible, we'd all be a lot better off.

[Brian]

>Great! ...now I can vacuum the living room in the nude, without having to close the drapes.

Except that you will be "wearing" your cloak of invisibility! :)

[Bill]

Good point!

[Man or Metaman?]

Metamerials are really amazing, especially considering that they've only been around since 2001. From the Secrets of the Metamaterials blog http://io9.com/5036183/secrets-of-the-metamaterials-that-will-make-you-invisible Here's the best explanation I've seen of how this invisibility thing could work:

Controlling the way light rays bounce off of and move through objects is no easy feat, but that's exactly what Berkeley's metamaterials do. All naturally-occurring materials have a positive refractive index. As light waves travel from one medium to another, the difference in the refractive index between the two will cause the light wave to bend at a certain angle. Consider what happens when you stick a straw into a glass of water — the straw appears to bend or break as it enters the water. What you're seeing is the way light bends as it moves from the air (which has a refractive index of about 1) and water (which has a refractive index of about 1.33). The light is still propagating forward, but it's made a slight turn, and so your eyes see a bendy straw.

In the case of negative refraction, the light waves behave much more oddly, as you can see in the above image by UC Berkeley's Jason Valentine and Robert Lee. Valentine explained to me that in negative refraction, a light ray no longer appears to be propagating forward — when it bends, it bends backward. The energy flow of the wave still moves in its forward direction, but the electric and magnetic components of the light ray seem to be traveling in reverse. They've turned far more drastically than they would in the natural phenomenon of positive refraction. So instead of seeing a bendy straw, once the metamaterial is combined with other light-bending tech, you'd see a straw that seemed to disappear.

In order to manipulate light at this level, you have to manipulate the structure of the material it's hitting at an extremely small scale. That's where metamaterials come in. Metamaterials negatively refract waves of visible light because they're woven out of materials smaller than the wavelengths of that light. If you think of a metamaterial as a piece of cloth, the "threads" in that make it up are somewhere between 400 and 700 nanometers in size. As fabrication techniques for such metamaterials have grown more and more advanced, this nanoscale structural manipulation has become possible, and UC Berkeley's team has used it to full advantage.

[Skeptic]

Now, THAT actually sounds possible to do.

[Yianna]

It can definitely serve for a good purpose (crossing enemy lines), but I'm sure there would be those who use the advance for harm for example crime.