Invisibility For Dummies
|The proof of concept demonstration of a 'cloaking' device has a lot of people interested in how this technology works and what it means for the military, industry and, most likely, peeping Toms. I am here to help.|
First, there are a few concepts. These are always the most difficult things to get people to agree on but if I don't make this simple enough that at least some wiseacre tells me I oversimplified, I did not do my job.
The important concept is that light, as physicists define it, is at multiple frequencies across a spectrum. That's why we have colors. In the picture below, there are frequencies and wavelengths for common items such as TVs, radios, microwaves, and the Gamma-Bomb that created The Incredible Hulk.
So far, the 'cloak' they have constructed only works in the microwave spectrum. You can see by the chart that this is outside the visiblity range for humans. Light that we can see has a higher frequency and a much smaller wavelength.
The next issue is the material. To make this work, they had to create "metamaterials" ... and those aren't found in nature. The New Scientist Tech article didn't go into detail about the material properties that made this work so I will. Metamaterials have electrical and magnetic properties that have a different index of refraction than normal materials. In other words, you see them differently because their electromagnetic properties are different.
How does that affect light? Maxwell discovered the complex relationship between electricity and magnetism and how they propagate at the speed of light. Snell's Law, or the "right-hand rule," tells us that magnetism curls around a wire in the direction of your fingers when you point your thumb in the direction of the current flow. According to the right-hand rule, light will always bend that way because of positive electrical permeability and magnetic permittivity.
Metamaterials, with their exotic properties, have negative permeability or permittivity, so they bend light away from what you normally expect. If you position them correctly, you can use this negative refraction to make light focus to a point. If I can prevent that electromagnetic energy from entering a region, light will "flow" around an object in the region, undistorted. Since the object won't reflect light, you won't see it and it will cast no shadow.
This all sounds great, so why aren't we out there zapping Klingons with it?
1) So far it only works in the microwave region. The optical region has much smaller wavelengths so for this to work the metamaterials have to be in the nano-size range. We have no way to make them that small yet.
2) It's still single frequency. This is a much more difficult problem. Looking at the chart above you can see the visible spectrum covers a lot of ground. We need variable-index-of-refraction materials that can accommodate all frequencies and wavelengths and that will take a lot more work. Those don't exist yet.
This is going to happen in our lifetimes. We haven't quite gotten a handle on light yet because it's both a particle and a wave and that's a pesky issue to resolve in lots of other ways. But we're making progress. Most likely, the answers will come by not treating light as the source of the problem but as the by-product.