Two weeks ago, the Wire reported on a new material, developed by scientists at the University of St Andrews, that might one day be used to create an invisibility cloak. Now comes the news that a different material, using the same scientific principles, could also be possible--except this material could render an object invisible in time as well as space.
Zeeya Merali at Nature explains:
The ideal space–time cloak — the theory behind which is published in the Journal of Optics today — would be an upgraded version of the 'invisibility cloak' that was first proposed in 2006... Such standard invisibility cloaks are made from metamaterials — substances with a complex internal structure that allows them to channel light around objects like water flowing around a rock in a river... "I realized that it may be possible to use metamaterials to bend light rays in both space and time, not just in space," says Martin McCall, an optical physicist at Imperial College London who led the team behind the new proposal. "This would add a new dimension to the invisibility cloak — literally." The key feature of the proposed space–time cloak is that its refractive index — the optical property that governs the speed of light within a material — is continually changed, pulling light rays apart in time.
So what does this mean? Essentially, Merali says, it means physicists have sketched out a design for a material that could bend light into the past. To borrow a metaphor from McCall: Throw an ordinary invisibility cloak over a safe, and it looks like the safe has vanished. Throw a time-warping invisibility cloak over the safe, and even if you break into the safe, what an observer will see is the safe as it existed in the past--ordinary and unmolested.