# Punching a Hole in Time

This latest item of science news leaves me wondering just how much of it is hype and how much is real, so I’m pushing it out into a couple of skeptic communities to see what folks think. Here is the claim …

### First Demonstration of Time Cloaking

Physicists have created a “hole in time” using the temporal equivalent of an invisibility cloak.

Moti Fridman and buddies, at Cornell University in Ithaca, claim that they have designed and built a cloak that hides events in time.

Time cloaking is possible because of a kind of duality between space and time in electromagnetic theory. In particular, the diffraction of a beam of light in space is mathematically equivalent to the temporal propagation of light through a dispersive medium. In other words, diffraction and dispersion are symmetric in spacetime.

That immediately leads to an interesting idea. Just as its easy to make a lens that focuses light in space using diffraction, so it is possible to use dispersion to make a lens that focuses in time.

Such a time-lens can be made using an electro-optic modulator, for example, and has a variety of familiar properties. “This time-lens can, for example, magnify or compress in time,” say Fridman and co.

This magnifying and compressing in time is important.

The trick to building a temporal cloak is to place two time-lenses in series and then send a beam of light through them. The first compresses the light in time while the second decompresses it again.

But this leaves a gap. For short period, there is a kind of hole in time in which any event is unrecorded.

So to an observer, the light coming out of the second time-lens appears undistorted, as if no event has occurred.

In effect, the space between the two lenses is a kind of spatio-temporal cloak that deletes changes that occur in short periods of time.

The device has some limitations. The Cornell time cloak lasts only for 110 nanoseconds–that’s not long. And Fridman and co say the best it can achieve will be 120 microseconds.

OK, so thats the claim. You can read the full article that I cut and pasted the above from here on the MIT Technology Review. It is the Physics arXiv blog no less, not the Daily Mail, so I’m tempted to give it credibility.

Now for some more links …

• Here is a link to the actual peer-reviewed paper, and yes they really are talking about temporal cloaking, not just spatial cloaking.
• Here is a link to a write-up within Science Now, and yes they are also talking about a “time lens”

Also, McCall, Paul Kinsler of Imperial College London, and colleagues proposed the idea of a spacetime cloak in the February Journal of Optics. Their comment on this is as follows:

“I am very pleased to see that our concept of the spacetime cloak has been realized experimentally,” McCall says. Kinsler notes that the Cornell experiment “is much easier to implement than was our proposed optical experiment and can generate much bigger time gaps.”

If it is all true and not simply a bit of hype to sex up some interesting light refraction, then it truly is fascinating, and yes, before you say it, I’ve no idea what practical use it could ever have, and suspect the authors of the paper also have no idea. That however should not be a reason to dismiss it, for once upon a time lasers had no real practical application either and yet that technology is now pervasive.

The turn of phrase deployed implies the manipulation of time itself, but reading what they have actually done suggests to me that all they are doing is to bend light in order to hide a particular instance or event. In other words, they are not bending time itself around space, rather, bending light in time and space. So what it appears to be is a blotter of the recording, rather than a preventer of the passage of time, but even so it still makes it interesting, but a long way off Dr Who mode.

Still, I’d be really interested if some more knowledgeable skeptical reader can point out any critique of all this, or has perhaps some additional thoughts on it.

Suggested applications (tongue in cheek)

• Small holes in time may provide major financial firms, just what they need to manipulate markets by inserting or deleting “real time” transactions
• This may also provide a place for the Catholic Church to dump all their rogue priests.
• How about conducting the Philadelphia Experiment for real … requires one US warship and some expendable crew
• Required … one cat, preferably owned by a chap called Schrödinger, for a game of hide and seek
• Revisit the concept of the Indian rope trick
• A place to dump all the time we have wasted reading Cr*p on the Internet

OK, so what do you make of this? If you have got any serious thoughts, or alternatively a crazy suggestion on how to apply it, drop a comment either into the blog, or into the forum where the link to the blog was posted.