Event cloaking


It’s just possible you haven’t heard yet that the final Harry Potter movie, Harry Potter and the Deathly Hallows Part 2, has just been released…although if that’s the case you’re probably also living on another planet and aren’t reading this at all.

Harry Potter, boy wizard, makes very good use, over the course of the books and movies that bear his name, of an invisibility cloak. No such thing exists in our everyday world, of course, because his cloak is magic. Also (sorry to break it to you), Harry Potter is not real.

But as Arthur C. Clarke famously said (and I’ve repeated more than once in these columns), “Any sufficiently advanced technology is indistinguishable from magic.” And these days, technology is getting very close to magic indeed.

So close, in fact, that not only are invisibility cloaks theoretically possible (and have even been demonstrated on a very small scale), scientists now think it might be possible to create an “event cloak,” which would hide, not just objects, but entire events from view.

No magic wands are required. Just some really, really fancy engineering, as Richard A. Lovett reports in a recent article for National Geographic News.

Paul Kinsler, a physicist at Imperial College London, came up with the idea with colleagues Martin McCall and Alberto Favaro.

Real-life invisibility cloaks bend light around an object, routing an image of what is behind it to the front of it, in effect hiding it from sight.

The event cloak, however, would use special materials filled with metallic arrays that could actually adjust the speed of the light passing through it.

The scientists use the example of a thief trying to break into a safe. The cloak would slow down light coming into the robbery scene while the safecracker was working; then, once the robbery had been completed, the process would be reversed, and the slowed light would be allowed to race forward again. If you stitch the “before” and “after” light seamlessly together, to an observer it would seem that one instant the safe was closed tight, and the next it had been ransacked.

Lovett quotes “invisibility researcher” (and don’t we live in a great age when you can actually identify someone as an “invisibility researcher”?) Ulf Leonhardt, a physicist at the University of St. Andrews, as saying an event cloak is “an interesting idea and great fun,” although Steve Cumme,r a “cloaking specialist” (ditto what I said about “invisibility researcher,” only now with extra Star Trek cachet!) from Duke University cautions that actually making such a cloak would be “really, really challenging.”

Well, duh.

The problem is, we don’t have any way to control the speed of light on a large scale with the precision the event cloak would require. We can do it inside a fiber optic cable, however: the speed of a signal can be varied by a few percent by changing the intensity of the light. So in theory, you could hide an event occurring inside a fiber optic cable—such as a signal moving from “on” to “off.” We might be able to demonstrate that within a few years…but there are some big buts.

Apparently cloaking an event lasting more than a few femtoseconds (a femtosecond is one millionth of a nanosecond) would require an immensely powerful laser in a laboratory setting.

On the other hand, you can take it out of the laboratory and reduce the power required—and increase the length of the event that can be cloaked—by using a miles-long cable, just like the ones telecommunications companies already use. The duration of the event you can hide depends on how long you can delay the light, and the longer the cable, the longer the delay you get from slowing the speed of light the same percentage.

So, if you’re planning to do something you don’t want anyone to know about—like, steal something from a vault in Gringott’s, for instance—how long will you have to wait until your event cloak is ready?

Let’s put it this way: don’t hold your breath. As Lovett notes, “The materials needed for speeding and slowing light have yet to be invented.”

But just knowing it’s possible is half the battle. Once you have the theory, the rest is just engineering.

No magic required!

Permanent link to this article: https://edwardwillett.com/2011/07/event-cloaking/

1 comment

  1. I think you missed the most potent example of event cloaking – we could now skip our birthday, should we wish to remain the same age 🙂

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