A couple of years ago, a number of physicists made international news (some descriptions here and here) by proposing that “cloaking devices” were theoretically possible to construct. Two papers appeared consecutively in Science Magazine in May 2006, one by U. Leonhardt of the University of St Andrews, Scotland (Science 23 June 2006: Vol. 312. no. 5781, pp. 1777 – 1780), and the other by J.B. Pendry of Imperial College, London and D. Schurig and D.R. Smith of Duke University (Science 23 June 2006: Vol. 312. no. 5781, pp. 1780 – 1782). Both papers describe how, with the proper materials, one could create devices which ‘guide’ light around a central core region without distortion, effectively making the cloak, and whatever sits in the core, invisible. This idea is illustrated by the figure below, from the Pendry paper, which shows how light rays could be guided around the core:
These papers have generated so much interest that it is fair to say that they have created their own subfield of optical science, what one might call ‘invisibility physics’, and numerous research groups are busy concocting their own invisibility schemes or attempting to construct a Leonhardt/Pendry-style device.
It is interesting to note, however, that the study of objects which are in some sense ‘invisible’ is not really new, and in fact there is a century-long history of scientists studying objects which may be considered, one way or another, undetectable.
I happen to know a lot about the history of such objects, so I thought I’d start yet another long-running series of posts, this one on invisibility physics. We start today with a discussion of what may be the first paper of this type, written by none other than the remarkable physicist Paul Ehrenfest.
Skulls in the Stars 
