Transcript for Paul Kinsler on Space-Time Holes

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Jim Fleming: This Hour we're talking about disappearing. But what about literally disappearing, and becoming invisible?

Harry Potter’s invisibility cloak is closer to reality than you think. In 2006 researchers at DUKE created the first device that could cloak an object in two dimensions.

In 2010 in Germany researchers went one step further, and produced a 3D cloak. It was small, very, very small, but it worked.

Now, optical physicists at the Imperial College in London have created the blueprints for the perfect hiding place: a hole carved out of space-time.

Paul Kinsler, one of the study’s authors, explained to Steve Paulson what they did:

Paul Kinsler: There were two types of cloaking device. For the last five years or so, people have been very interested in cloaking objects, so if you have something sitting on the table, a cup of coffee, for example, you could place a cloaking device around it and all the light would be bent around your cup of coffee and seamlessly re-integrated on the far sides, so no one could say that the cup of coffee was there” the device would make it invisible.

What we’ve done actually is something a little bit different. We’ve tried to cloak an event so if someone spilled the coffee, for example, we could put a cloak around there and you would see the coffee beforehand, and the coffee would come afterwards, but you couldn't see the time actually, that the coffee was spilled.

Steve Paulson: So, how long could you make something disappear?

Paul Kinsler: Well, unfortunately not very long. What you can do is controlled very much by the speed of light, which is very fast. For example, it takes about 8 minutes for light to get from the Sun to the Earth. So as a general rule if I wanted to make an event cloak that cloaks something for 8 minutes, I would need something as big as that distance, from the Sun to the Earth. So we’re not going to be able to cover the 8 minutes, unfortunately, but we could for example easily do a micro-second or something, which is a long time to a computer, even if not for us.

Steve Paulson: Let me see if I can understand what you’re doing here: it sounds like you’re actually creating a void in space-time, where there is no light. Is that right?

Paul Kinsler: Yeah. We’re creating a dark spot, and the idea of this is without illumination, there’s nothing to light up what happens, and therefore, no one will be able to see it.

Steve Paulson: So you’re actually  But I mean it’s not just time you’re dealing with, and it’s not just space, you’re dealing with both space and time and you’re creating, kind of, an empty space, in there.

Paul Kinsler: Yeah. That’s right. If I go back, sort of, to the traditional cloaks, if you like, which cloak objects, you can imagine for example like if they’re on a highway, multi-laned highway, with a stream of cars. OK? And the idea of an object cloak is that maybe there’s a traffic island or an obstruction on one of the lanes. And the traffic’s all steered, nice and evenly, around the object and joins itself back together afterwards. And once it’s done that, there’s a nice, even flow of traffic again, and now we can tell from the flow of traffic that there was an obstruction there.

What we will do is a little bit different. We need to control things in time, because we want to hide something that occurs at exactly five o’clock for example. So what we need to do, we need to speed some of the light up, and slow some of it down. So if I go back to the analogy with the highway, we want to sort of speed the leading cars up and slow the trailing ones down, and of course, that’s leaves the gap in the traffic, which, of course, is a gap in the photons that make up the light, so that's a dark spot.

Steve Paulson: So, you’re manipulating the light. That's what’s you’re doing.

Paul Kinsler: We're manipulating the light. We're speeding some of it up, and slowing some of it down.

Steve Paulson: I have to say that kind of sounds like the Star Trek transporter. Those people, you know, who go into the transporter room and are beamed down to another planet instantaneously.

Paul Kinsler: Well, it would look a bit like this. For example when you’re cloaked you could, in principle, drive very far or if you can make a cloak big enough and so an observer would see you in a place at a moment and in another place the next moment.

But in fact [xx] light from the transporter you’re beamed from one place to another. With air-cloak, it would look like you were beamed instantly, from one place to another, but in fact you’d have to do a lot of work between the two locations. So it turns the [xx] appears, it’s an illusion, it’s not really a transporter.

Steve Paulson: I'm struck by the language that you’re using.

You’re talking about a cloak, an invisibility cloak, and of course this conjures Harry Potter.

Which comes first? Harry Potter and the invisibility cloak, or the scientific efforts to do this.

Paul Kinsler: Well, of course there are many instances where invisibility is being used in literature over the past centuries.

I grew up reading Tolkien’s “Lord of The Rings”, in which of course the invisibility and [xx] was Star Trek, and the cloak of the Star ships.

So, in fiction it has arrived a lot sooner then in science. The scientific attempts were serious attempt were quite recent [xx] five years ago or so.

Steve Paulson: O course radio interviewers like me would consider of this [xx] and would ask if you were a SF writer or a [xx] writer, could you imagine a possible scenario, or a plot would use this invisibility cloak in a way that would be more or less scientifically accurate?

Paul Kinsler: Well, you can make the space-time cloak directional. So in the event of somebody standing in front of the cloak, somebody standing behind the cloak for example the event proceeding normally so that you can have two observer who [xx] honest about the signals are coming into them and what they observe, but they are going to disagree.

Of course you get that, two people disagree about almost anything you like, that's something that offers rich possibilities I think [xx] the fiction writers.

Steve Paulson: So in reality is all about perception.

Paul Kinsler: Well, yes indeed. We only know what comes into our senses when it reaches us. So we can't really tell what's happening at the other side of the room we have to infer it from the xx of each of them but almost anything could happen to the light [xx] arise before it got to us.

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Jim Fleming: Paul Kinsler is an optical physicist at the Imperial College in London. Steve Paulson spoke with him.