Spacetime Invisibility

Yesterday, I was linked to by Warren Kinsella's blog. That lead to an extra 250 or so visitors than I normally get each day. I don't expect many (or, really, any) repeat visits - but it was still pretty cool. Even if I did call Mr. Kinsella a hack. (For the record, I meant it in the nicest possible way, just to highlight how big a deal it is that he's speaking out against Iggy's policy on Afghanistan.

If any of you did come back after yesterday - welcome! I really wasn't expecting that, but it's neat having you back.

Anyway, for today's topic... I thought this was pretty cool, so I figured I'd share: Theoretical Spacetime Invisibility Cloaks.

The basic idea is surprisingly simple. We see things because our eyes are able to interpret information from visible light. That light travels at, obviously enough, the speed of light, which means we see things once light has traveled from them to our eyes. Technically speaking, we never see anything the exact instant happens - there's always a time lag between the object and when we see it.

This is fairly well-known for anyone with an interest in astronomy. The Moon is one light-second away, the Sun a little over eight light-minutes away, the nearest star 4.3 light-years away, the nearest galaxy , and so on. There are time lags on even everyday distances, however impossibly slight. For something a meter away, we see it as it was about 1/300,000,000th of a second ago.

Here's how you use that information to build a spacetime cloak. All those times are for the speed of light in a vacuum, but light can slow down depending on what material it passes through. Researchers have slowed down light to as little as 38 miles per hour by sending it through a special, super-dense form of matter. And it's through carefully slowing down and speeding up light that we can create a temporal void.

Let's say you're standing a mile away from an observer. You start slowly decreasing the speed of the light traveling towards the observer so that it's only traveling at 60 miles per hour, or a mile per minute. Since you're slowing the light down gradually, the observer won't be able to perceive the change. Once the light has reached 60 miles per hour, the observer is now seeing you as you were one minute ago. You've now created a one minute spacetime corridor. You've now got a minute to do whatever you want without the observer having any idea what you're up to.