Is an invisibility cloak really possible?

This is a really cool guest blog by the awesome Jonny Brooks!

Have you had a moment so embarrassing that you just wanted the ground to swallow you up? Or you’ve ever wanted to sneak into a room where you know your boss or teacher is talking about you, just so you know what they really say about you? At times like these it would be so handy to have an invisibility cloak just like Harry Potter so no one would ever know you were there.

Well this is what scientists around the world are trying to do right now.

Figure 1: Harry Potter and his awesome invisibility cloak........... that you can't see
Figure 1: Harry Potter and his awesome invisibility cloak……….. that you can’t see

How does it work?

To be invisible you have to make sure that no one can see you. Obvious right? But that’s not the only thing (otherwise hiding behind the door would make you “invisible”). In addition to not being able to see you, the tricky part is also making sure that the person can see what’s behind you. This creates the illusion that people can see straight through the invisible object.

This can be done in several ways, although two of the most common methods are by transformation-optics cloaking and optical camouflage:

transformation-optics cloaking – This method makes use of materials known as metamaterials. These metamaterials are engineered so they exhibit properties that have not yet been found in nature. Built correctly, these materials allow us to bend light around an object making the object invisible and also making sure people can see what’s behind you.

Figure 2: Bending light around an object
Figure 2: Bending light around an object

optical camouflage – This is one of the simpler methods of making an object invisible. Take an object that you want to make invisible (like a human for example) and put a camera on the back of the object. This camera records the images behind the object. If that camera is connected to a video feed in front of the object, then you can project the images of the camera onto the object, creating the illusion that you can see right through it.

Are we close?

Good question. I guess the answer is “kind of”.  Transformation-optics cloaking was one of the first successful demonstration of the method in 2006, but it only worked with microwaves. This means that if our eyes were able to see microwaves, then we would have an invisibility cloak. Unfortunately this isn’t the case. Our eyes see visible light.

Not only that, but many of the methods used to make objects invisible scatter more light, at a different part of the light spectrum, than the object that they were trying to hide. For example, if you had a cloak that made an object invisible to red light, it may actually be scattering lots of blue light. Therefore it may be invisible to red light but if you shine blue light at it, then the object was probably more obvious than it was before.

Despite this, new methods of cloaking are being developed that use electricity to make an object appear invisible. These have the benefit that the device will not scatter light over a broad range of the light spectrum. However, much more research is needed before we have something that truly works for visible light.

So in short, it’ll be a very long while before we have a true Harry Potter style invisibility cloak, but we are making progress. For now, we’ll just have to keep dreaming.

Thanks for writing for Sparkly Science Jonny!

Give him a follow on twitter @Jonny_CBB and check out the work he does at the University of Oxford

xxx

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