Prototype invisibility cloak can ‘bend’ light
Scientists in Singapore have developed a basic invisibility cloak, capable of completely hiding small objects. A human sized version may not be too far off, but what would we do with it?
The demonstration film, newly released by scientists at the Nanyang Technological University in Singapore, is impressive. A cat walks towards a yellow butterfly flying in the background. It enters what looks like a glass box – but although the background with its butterfly remains visible, the cat disappears.
Although it looks simple, this box is the most advanced invisibility device in the world today. Its sides are made out of metamaterials – sheets of highly complex, precisely structured metal that defy the ordinary rules of optics. In this case, these metamaterial sheets are making light bend.
Vision is the primary human sense. Our eyes detect light bouncing off objects in the world and create images of the space around us. But when light hits the metamaterial walls of the invisibility box, it does not bounce. Instead, it bends, flowing round the box and then keeping on going as if there was nothing there at all.
Naturally, military leaders will be fascinated by this latest breakthrough. Crude cloaking devices for tanks or planes could be a huge advantage on the battlefield if they could be produced on the right scale – and at the right cost.
But for the rest of us, the disappearing cat could stir more sinister ambitions: what if we could one day make a human being truly invisible?
It is an idea that has long appealed to writers of fantasy or science fiction. J. K. Rowling gave Harry Potter a cloak of invisibility that allowed him to have wild adventures through the dark corridors of Hogwarts. Invisibility was the gift of the Ring of Power in J. R. R. Tolkien’s Lord of the Rings. Two and a half thousand years ago, the Ancient Greek writer Herodotus told a similar story of a shepherd who found a ring of invisibility in a cave, then used it to seduce a queen and kill her husband, becoming a mighty king.
For the moment, however, such fantasies will have to wait. The Singaporean invisibility box is clumsy, expensive, imperfect and only works from certain angles. Anyone who tried to roam Hogwarts or any other inhabited place in one of these would not remain undiscovered for long.
The walls have eyes
Some will think this is rather a pity. Having a real invisibility cloak would endow amazing powers. You could go anywhere; do anything; eavesdrop on any conversation. Nowhere in the world would be off limits.
That all sounds fine, critics will reply, so long as you are the one who is invisible. The problem with invisibility cloaks is what happens when everyone else gets one too. All privacy would disappear. You could never be sure you were away from prying eyes. In a world of invisible watchers, you might always be under observation.
- Is it wrong to watch people if they do not know you are there?
- If no one could see you, do you think you would still behave according to the rules of morality?
- What would you do with a ring of invisibility? Write down your top three ideas, then compare notes with your class. What sorts of thing were the most popular?
- Write a short science fiction story set ten years after the invention of the first true invisibility cloak. Explain how society has changed.
Some People Say...
“Bring on the invisibility cloaks. I have nothing to hide!”
What do you think?
Q & A
- This all sounds terribly far fetched!
- Maybe, but in a way, the argument about watchers and being watched is one of the most important debates in the world today. You will have heard all the recent news about the NSA in America snooping on emails and mobile phone calls.
- What does that have to do with it?
- Most internet users now operate on the assumption that everything they do online can be tracked by Facebook, Google, the government, Chinese hackers or someone else. The internet is like a world full of invisibility cloaks: you never know when someone is watching.
- Indeed. You could make the internet more private. On the other hand, as a citizen or even a spy, you might want to see if, for example, terrorists are online plotting an attack. Then a virtual invisibility cloak is quite useful.
- Primary human sense
- Humans have excellent vision, comparatively speaking. Our highly evolved visual processing systems are thought to be one of the reasons why we have such large brains. Unlike most mammals, we can pick up three wavelengths of light (red, green and blue) rather than two, giving us a much broader range of colour vision. Non-mammals, however, can do even better. The mantis shrimp, for example, can see not two or three different wavelengths of light, but sixteen.
- Ring of Power
- Tolkien’s ring, no doubt inspired by the ring in Herodotus, could make its wearer invisible by pulling them into a shadow world, inhabited by wraiths. It also gradually corrupted the wearer’s soul, a vivid metaphor for worries about the damaging moral effects of invisibility.
- Herodotus was a greek historian who lived in Halicarnassus, in modern Turkey, in the fifth century BC. His story of the ring of invisibility became a favourite with ancient philosophers like Plato, who used it to ask questions about the nature of morality. Some thought humans only behaved well because people could see them. Others thought morality came from within, and that even an invisible man would behave well. The argument is still going on today.