Reality is getting even less trustworthy.
Imagine if you could “cloak” an event, make it disappear in time. It’s one thing to make an object (a space) invisible, a concept now a reality courtesy of “metamaterials,” but another to make an event disappear, though the event cloak (space-time cloak) idea uses similar ideas of gaming particles of light to create an illusion of perception. A pair of physicists, Martin McCall and Paul Kinsler, explore this idea in this month’s Physics World.
Both space and space–time cloaks use a general method called “transformation optics”, whereby cloak designers decide what route they want light to take before calculating what sort of material the light should pass through to achieve that aim. The point is that light rays travel along paths that can be mathematically altered – for example from straight lines to curves.
By tweaking the paths of light particles, you’re able to curve them around an object, hiding it. Cloaking an event is a bit different, however. The light isn’t curved, space-time is. (Think of time as a space that can be bent and shaped by fiddling with the speed of light.) Imagine if you had a room in which light traveled slower than its top speed, which is basically any room that isn’t a total vacuum. To create the cloak, you would need to speed the light up from the period before the event—my dog shitting in the neighbor’s garden, say—and then you would need to slow the light down for the period of time after the event.
In doing so, you’re leaving a dark gap of time in the middle that escapes perception.
Now imagine that during the moment of darkness, a safe-cracker enters the scene and steals the money, being careful to close the safe door before he leaves or a dog entering the scene and shitting in the scene. With the safe-cracker gone, the process of speeding up and slowing down the light is reversed, leading to an apparently untouched, uniform illumination being reconstituted. As far as the light reaching the surveillance cameras is concerned, everything looks the same as it did beforehand, with the safe door firmly shut. The dark interval when the safe was cracked has literally been edited out of visible history.
See? It’s so easy. You just slow down light from the future. OK? I suppose the problem is in thinking that “after the event” is the future. By screwing around with space-time, you can make the time post-event not the future. “. . .time is as much a coordinate as space,” McCall and Kinsler remind us. So: speeding light up, and then slowing it down bends space-time and leaves the gap.
What we would need is a set of parallel metamaterial layers, each containing an array of tiny metallic elements, the conduction electrons in which would interact with light in a way that could be easily controlled. Such tiny elements, or “meta-atoms”, are the usual way of building up the metamaterials used in ordinary spatial cloaks, but what we need is a more adaptable interaction.
The catch is this that with our currently-only-imagined metameterials, you could only get a fraction of nanosecond of cloaking. Which is bad for nefarious plots, but maybe eventually good for computing, insofar as you could create an “interrupt-without-interrupt” function. The duo imagines a space-time cloaking system in a lab within a few years.
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