One of the many magical objects in the Harry Potter series is the cloak of invisibility, which can render its wearer completely transparent. Sounds like fantasy, but there are researchers who are actually working on trying to develop such an object. One of them is UNC Charlotte physics professor Greg Gbur. We visited his office to get a better understanding of his work.
Gbur: Physicists are really working toward making things that are in principle perfectly invisible, but we are a long way from actually doing that and there are a lot challenges along the way to make it actually happen.
Terry: How do you develop an invisible cloak, can you explain it to me? And keep in mind, I know next to nothing about physics.
Gbur: Actually, the earliest designs – which are relatively recent from 2006 – really involve constructing sort of a transparent device which has optical properties that guide light around a central region and send it on its way as if it didn’t encounter anything at all. The classic example used is that it guides light around the central cloaked region like water going around a boulder in a stream.
Terry: Ok, let me see if I understand this. The light itself is not actually hitting the object directly, so we can’t see it?
Gbur: Yeah, it’s not hitting the object being cloaked. It hits the cloak structure. The cloak is made out of solid material as well, but it’s made out of a transparent material that in principle, if it’s designed correctly, won’t reflect light or absorb light. It will just guide the light around and send it on its way.
Terry: What’s the difference between that and camouflage?
Gbur: That’s a good question. In camouflage, you’re usually trying to disguise something as part of the background. So you want to make something look as much like the background as possible so you don’t recognize it. The idea of an invisibility cloak – and again I say in principle because it’s not clear how well we’ll ever be to do this – but in principle a cloak is not something you would be able to see at all from any direction of observation.
Terry: What do you envision the use of this being. I’m guessing it goes beyond playing practical jokes?
Gbur: Yeah, there are actually a number of reasons. Obviously, people in the military and so forth are interested in that. Another use that has come along is actually protecting things. If you can protect things or hide things from light waves, you can also hide things from other types of waves, like earthquake waves and water waves. People have actually talked about and are thinking about designing underground structures that would guide earthquake waves around a building. Or guide water waves around an offshore platform or buoy and protect it from damaging storm waves.
Terry: As you said before, we’re still a long ways away from actually making things invisible as you’re describing. But where is it now? Has anything been made invisible? What’s the status?
Gbur: There’s been a lot more progress than one would have thought at first. When the first papers came out in 2006, I immediately thought it was going to be years before we saw progress experimentally. Well a paper came out that same year where someone had demonstrated at least the principle of using this cloaking design to guide waves around an object. And since then there have been a lot of very clever designs, experimental designs showing that in principle this is possible. Now in practice, even though we can kind of crudely demonstrate it, we’re a long ways away from having things be really hidden.
Terry: How long have you been working on all this?
Gbur: That’s a nice question because I kind of say I’m a hipster invisibility physicist because I was doing this long before it was cool.
Terry: Is it cool?
Gbur: Nowadays, it’s very cool. It’s become a very hot research topic and there’s a lot of work out there. It’s hard to keep up. I actually got my PhD in 2001 doing research on very crude, early concepts of invisibility. Nothing like what’s being done now. So I’ve been playing catch up ever since and working to keep up with all the new developments.
Terry: What would you do if you had an invisibility cloak?
Gbur: That’s an interesting question. I’m not sure. I’m going to give a nice answer and say I’d probably use it in the many ways described in terms of protecting or shielding objects instead of sneaking around.
Terry: You could be a superhero here in Charlotte?
Gbur: That’s true. I wouldn’t mind that.
Terry: Dr. Gbur, thanks for your time.
Gbur: Thank you very much.
See a cloaking device make a cat disappear here.