So, What is a “Temporal Cloak”, Anyway?

Over at Skulls in the Stars (for Jonathan H and via Zite):

This week, the experimental realization* of a “space-time cloak” or “temporal cloak” by researchers at Cornell University has made national news. This novel device differs from the “invisibility cloaks” discussed previously on this blog in that it hides temporal events, not spatial objects. Loosely speaking, this has also been referred to as a “history editor”. Naturally, the discussion of “cloaking” has again brought out references to “Harry Potter cloaks” and other dramatic imagery; the reality is much more mundane, but still fascinating — and an amazing achievement. Let’s take a look at what was done, what was not done — and why it’s quite cool!

First, let’s get rid of some misconceptions that the terminology naturally brings to mind. The terms “space-time cloak” and “history editor” make it sound like the device is ripping a hole in the fabric of space-time itself — like a time machine equipped with a big eraser! This is definitely not what is happening here! There is no manipulation of time itself, but rather a manipulation of a beam of light to hide something that the light would otherwise detect.

It is difficult to come up with a simple analogy to explain what is really going on, but let us imagine a beam of light as a long moving train of hanging curtains, as illustrated below:

We might imagine that these curtains are at an assembly line and have recently been dyed, and are still wet (I told you, analogies for this phenomenon are tough!). We want to pass objects from one side of the curtains to another, but any attempt to simply push an object between them will mess up the dye and leave a mark.