I’ve spent a lot of time on this blog talking about the optics of invisibility, both hypothetical and actual. Though a number of forms of invisibility have been considered in both science and fiction for over a hundred years, the study of the subject really exploded in 2006 with the publication of two theoretical papers introducing designs for “invisibility cloaks.”
The principle behind one of these cloaks is illustrated below, taken from the original paper by Pendry, Schurig and Smith. The cloak guides light around the central region and sending it along its original path, like water flowing around a boulder in a stream. The lines in the illustration represent rays of light being deflected and returned to their original trajectories.
The device is passive; it “works its magic” by virtue of the materials it is built out of, and guides light around the hidden region by what amounts to refraction.
It is fun to talk about the unusual implications of optical invisibility, but it is hard to show it! Cloaks are complicated, and there are relatively few experimental realizations to date — and those that do exist are not easily reproducible without a lot of resources.
Fortunately, there exists a simple trick, suggested by my colleagues*, that can be used to demonstrate the principle of cloaking in a striking way! I assembled a version of this trick myself for use in a recent popular talk on invisibility physics that I gave; a short video of it is shown below.
A finger placed behind the device is readily visible, but a finger placed within the cloak vanishes!
For about $50, you too can make your own “cloaking device”, albeit an oversimplified and crude one! Let’s take a look at how it is done.
Skulls in the Stars 