We see things using light, of course, namely as light scatters on an object. Using materials with a negative index of refraction, experiments have been able to create an 'invisibility cloak' for objects, which is certainly exciting. The downside is they are not in the visible range so Romulans are not going to be invading Earth any time soon.
We've also written about an invisibility cloak for time before but that was a mathematical extension of a physical process - because light normally slows down as it enters a material it is theoretical to locally manipulate the speed of light so that some parts speed up and others slow down so rather than being curved in space, the leading half of the light speeds up and arrives before an event, while the trailing half is made to lag behind and arrives too late. The result is that for a brief period the event is not illuminated and escapes detection.
The researchers pre-publishing this week have manipulated light in a fiber-optic cable using that theoretical process. Some of the light passing through a split-time lens speeds up and some slows down and when the waves come back together it arrives at its destination with no record of that 'gap' in time. The event is invisible in time.
Their invisibility cloak for time lasted for 15 trillionths of a second, which was enough time for them to register that their pulse of light were cloaked in the time domain.
Schematics of the temporal cloak using a pair of split time-lenses (STL). The STL's are used to create a temporal 'hole' in a probe beam such that any temporal or spectral changes caused by an event within this hole do not occur. Thefigure is oriented such that the probe light is described by horizontal lines, and lines at different orientations represent different wavelengths. D denotes the magnitude of the total negative or positive group-velocity dispersion.
It isn't perfect, thanks to third-order dispersion, so longer periods of time (by simply using a longer cable) will not work until the kinks are worked out. The single-mode fiber has a length of, at most, 50 Km before scattering is too much - which means a temporal gap of just over a microsecond.
Citation: Moti Fridman, Alessandro Farsi, Yoshitomo Okawachi, Alexander L. Gaeta, 'Demonstration of temporal cloaking', arXiv:1107.2062v1
More on invisibility:
Meta-Flex: Your Future Invisibility Cloak?
Like Your New Invisibility Cloak? The Chinese Have Already Cracked It
Plasmonics Advance Yields 2-D 'Invisibility' Cloak
Invisibility Cloak Gets A Nanomaterial Boost
Mathematics Of Cloaking: New Analysis Improves Methods To Render Objects Invisible
Invisibility Advance - 3D Cloaking Metamaterial In Optical Range Created
Research into Metamaterials May Pave the Road to Invisibility
First Tunable Electromagnetic 'Gateway' Acts Like A 'Hidden Portal'