11 Nov 2016

Now You See Me...

If you were a superhero, what power would you pick? Reading minds? Super speed? How about invisibility? That last one is a good choice. Scientists around the world are already working on ways to make everyday objects - like humans! - invisible.
It all starts with understanding light and vision. When light waves collide with the atoms in an object, the waves bounce off, or scatter. The direction of the scatter depends on the angle of the bounce. Human eyeballs detect these scattering light waves, and our brains reconstruct the shape of the original object. So, to make something invisible, all scientists have to do is make light reflect off an object the same way it would reflect if nothing was there at all.
Easy, right? Um, no.
In fact, progress on the invisibility problem didn't really begin until around 2000, when the field of metamaterials started to develop. Engineers build metamaterials out of "artificial atoms" that interact with light in very abnormal ways. These atoms allow engineers to control the way light scatters off the metamaterial with much greater precision than would be possible using naturally-exisiting materials.
Scientists have used these materials to develop several different types of invisibility cloaks, each with advantages and disadvantages. For example, objects embedded inside a spherical cloak are invisible from all sides, but only for a certain value of invisible - they can block some wavelengths of light, but not all, meaning the object blurs rather than totally disappears. Carpet cloaks, so named because they are flat, are easier to make and work on larger objects... but those objects are only invisible from one angle. If the viewer is looking at the cloak from the side instead of dead on, the object becomes visible.
Plasmonic cloaking is a new technique that combines advantages of both spherical and carpet cloaks. Rather than trying to stop light from scattering of the object, plasmonic cloaks create a matching, opposite scatter, and the two combined cancel each other out. Mantle cloaks use a variation of the same strategy, and both types offer the advantages of both spherical and carpet cloaks. However, they also share a unique downside - size. They don't work on any object that's more than a couple of wavelengths of light across.
That's not a problem, if, for example, you're the CIA and you want to hide a tiny bug or spy camera. If you're trying to hide a human, though, you've got big problems. For example, a human-sized carpet cloak would actually have be about the same size as your bedroom. Another problem is that current cloaks block light in both directions, meaning no one could see you, but you couldn't see them, either - which would make sneaking around Hogwarts at night very difficult!
Worst of all, you'd have to stay completely still. According to invisibility scientist Majid Gharghi, going from a stationary object to a moving person would be like going from simple Newtonian physics to Einstein's relativity. He told me it will likely be decades before engineers can build something that complex. Which is kind of a bummer... but on the other hand, gives you plenty of time to come up with your superhero name!
So. What superpower would YOU choose?

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