A metamaterial is as out-of-this-world as it sounds. Physicists, material scientists and engineers are coming together in this new, exciting field in order to create new materials that could be used to create invisibility. Imagine owning Harry Potter’s invisibility cloak: it’s not as impossible as you might think!
Now it will still be a while before invisibility cloaks as we think of them are possible. Take a look at this image:
What does it remind you of? A wheel, maybe a K’Nex piece, a zoomed-in picture of a roll of cassette tape?
Well, this is actually the first ‘cloaking device’. It deflects microwaves (light with a longer wavelength than the light we can see, the same ones that are used in your home microwave) around anything placed in the centre. In theory, if you put a (small) cup of tea in the centre and placed the whole thing in the microwave, nothing would happen to the tea, as the microwaves would go right round it.
Pretty cool or what? The metamaterial itself is made by creating ‘fake atoms’ – engineering tiny bits of material, each as small as an atom, which act as the ‘atoms’ in the material. Because the properties of each bit can be chosen very specifically, it’s then possible to change the characteristics of the material to suit your purposes. In this case, the materials are engineered to have slightly different refractive indices – the property which defines the speed light travels through a material – so that light can be directed around the object in the centre.
You might be getting confused at this point – the speed of light is supposed to be a constant! But this isn’t the case. We know that in a vacuum, the light travels at a certain speed (the number everyone learns, 300,000,000 metres per second). But depending on the material it’s travelling through – air, water, or metamaterial – the light can speed up or slow down relative to its previous speed. For example, light speeds up when it passes from water to air, which is why things on the bottom of a pool always look closer than they actually are. (Try putting a spoon in a glass of water and looking at it from different angles.)
The scientists have a lot of work to do, though, before they can get to the stage of bending visible light to create invisibility we really can’t see – and then they’ll have yet more work to do on making the cloaks flexible.
But who knows – maybe in 15 years’ time, hide-and-seek will get a whole lot more interesting…