McCall and his colleagues have calculated the precise properties of the metamaterial needed to build a space–time cloak that would be perfectly invisible, and there are fundamental problems that prevent it from being constructed. The theoretical calculations work only in a vacuum, and to create a space–time void of even a few minutes would require a cloak bigger than Earth because of the space required to recombine the accelerated leading edge and slowed trailing edge of the light wave. Worst of all, the theory requires the metamaterial to boost light rays beyond the fundamental speed of light."Space–time cloak could hide events"
Undeterred, the team has designed a less efficient version to be built from optical fibres – inside which light can be accelerated and slowed without breaking the fundamental speed limit. Lasers would be used to control the fibres' refractive indices, opening and closing the temporal void. The fibre-optic cloak could hide events only from observers standing directly ahead of the oncoming light waves, and it could not fully block all reflections from light travelling through the cloak while it is turned on, so some light might bleed out. A distant observer looking down the optical fibre would not spot the hidden event, but they would notice the background light getting brighter and dimmer. McCall hopes that a fibre-optic cloak creating a space–time void around 30 centimetres long, to hide actions taking place over a few nanoseconds, could be built within the next year.
David Pescovitz is Boing Boing's co-editor/managing partner. He's also a research director at Institute for the Future. On Instagram, he's @pesco.