The invisibility cloak

By Marcus Wilson 22/03/2010

Yes, the headline writers are at it again, talking about those crazy scientists designing invisibility cloaks. As usual, the articles I’ve seen in the papers (e.g. the front page of The Waikato Times) and popular internet sites are high in ‘Harry Potter’ and ‘Star Trek’ and low in science.

Research into this kind of thing is not new, but it has lept forward recently with development of ‘meta-materials’, particularly those with negative refractive index. Refraction is what causes a stick to look bent when you put it in water. Negative refractive index materials, amongst other things, bend the light the ‘wrong’ way when the light hits them. They can be used to steer light in otherwise unavailable directions. That’s what you need to do if you want to hide an object – you want the light coming from one side of it to somehow work its way around the object and leave again from the other side as if the object had not been there. I heard a great talk on meta-materials by John Pendry, one of the key players in this field, at the Australian Institute of Physics conference at the end of 2008.

There’s a huge range of potential applications – though of course an invisibility cloak is perhaps the most exciting for your average person in the street.  In this case what has been cloaked is a bump (not a particularly large one, mind you) on piece of gold. A ‘cloak’, has been placed over the bump, and the effect of the cloak is that light reflects off it in the same manner as it would if the surface were flat. A far cry from hiding an entire Romulan armada, but a significant step forward nonetheless.

A reasonable summary of the gold bump experiment is on the PhysicsWorld site, , though, in my opinion, it doesn’t go into huge detail. For that you’ll need to go to the original article in the journal Science, , which you will probably have to pay for.

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