Above, A Basic Demonstration of Optical Cloaking. Cloaking is a term for hiding an object from view at specific frequencies, but evidently one can cloak things DIY-style with four mirrors and their precise placement.

So before reading further, how is the illusion above happening? Any guesses?

Professor of Physics at the University of Rochester John Howell and his 14 year-old son Benjamin built three uni-directional optical cloaking devices with everyday materials. For around $150, they put together “one made of Plexiglass and water, another of inexpensive lenses, and a third constructed using ordinary mirrors.” The video demonstration above shows one of the devices and two of his sons… sometimes. 

What might this small feat of optical engineering be used for? Since it’s uni-directional it has limitations, but in theory, it could hide satellites orbiting Earth. You can read more about how Professor Howell’s devices work in the videos notes, here on arXiv.org, or on MIT Technology Review.

There are also a few more videos with mirrors in the archives.

Thanks, @AmebaCuriosa.