超级隐形衣：可以隐形于时空之中

简单来讲，隐形衣理论如下：用一块特殊的凹透镜来将光线折射开来，让其中一部分光子加速，另一部分减速。随后在较远处放下第二块凹透镜，这块凹透镜可以将光子的速度重新调整成一致的。那么在镜片外的人看来，两片镜片中间什么都没有。

虽然在这个时空隐形区域什么都看不见，但是如果真的想靠它来当怪盗的话，行动速度不得不快一些——即是是康奈尔大学实验装置的最好记录，也只有120纳秒。

//这篇文章很……晦涩。看英文原文的钢笔压力很大。大家随便看看吧，不能理解？无所谓，这世界上又少了一个怪盗。

Some People Talk About Space-Time Invisibility Cloaks. At Cornell, They Built One

We’ve written previously about the theoretical possibility of “event cloaks”--metamaterial space-time devices that could theoretically conceal an entire event in time from the view of an outsider. Well, while some bright minds were just talking about bending space-time to their whims, a team at Cornell was doing it. And it works. For 110 nanoseconds.

There’s a more thorough explanation of this notion in our previous coverage, but briefly this is the idea: basically, you need two time-lenses--lenses that can compress and decompress light in time. This is actually possible to do using an electro-optic modulator (what, you don’t have one?). Basically, using two of these modulators you would slow down or compress the light traveling through the first lens, and then set up a second lens downrange from the first that would decompress, or accelerate, the incoming photons from the first lens.

Got that? Refer to this handy gif, courtesy of some blokes working on a similar idea at Imperial College London:

Paul Kinsler, Imperial College London

Think of the photons like steadily flowing traffic on a highway. If you slow the traffic at a point upstream, you create a gap. You can cross the highway through the gap and then accelerate that traffic to catch up to the traffic ahead, closing the gap. To someone further downstream, the gap is not there--to that observer, the gap might as well have never existed because there’s no evidence of it.

During that gap, whatever occurs goes unrecorded. But, as we noted above, you’d have to be pretty quick were you to use such a device to pull some kind of shenanigans. The current device the Cornell gents have built creates a 110 nanosecond event gap, and they concede that the best it could achieve is 120 microseconds. But, as KFC notes at Technology Review, rarely is anything final in cutting edge theoretical physics.

Details at arXiv.

[Technology Review]http://www.popsci.com/technology/article/2011-07/some-people-talk-about-time-cloaks-cornell-they-built-one