Invisibility cloak on way after sonar breakthrough

High-tech 'metamaterials' can make objects invisible to sonar, scientists have found. It's a step towards the ultimate camouflage, which could one day allow people to disappear entirely.

Scientists have made a major advance in cloaking technology by creating a special coating which makes things invisible to sonar. Used by submarines and warships, sonar works by sending out pulses of sound waves, which reflect back off objects in the same way as light waves. By listening to the reflected sound, computers can 'see' whatever objects that sound has bounced off.

But by coating objects in specially designed plastic sheeting, say scientists in the latest issue of the journal Physical Review Letters, it's possible to change the rules of the game. When sound waves hit an object that has been cloaked in this way, they bend instead of bouncing, sliding smoothly round the outside of the object and continuing on their way.

Already, this technology could have important applications. In naval warfare, surface ships detect submarines using sonar. During World War I, before sonar had been invented, German submarines were undetectable beneath the waves. Now, if this latest sonic cloaking technology can be miniaturised and improved, submarines could once again become effectively invisible.

But that's just the beginning. After all, the same principles that allow us to bend sound waves could one day bend light waves in the same manner. Already, researchers have found ways to bend certain wavelengths of light, but only on very small scales. Scientists are optimistic, however, that they will soon expand the range of wavelengths they can bend, and that the 'metamaterials' (very thin sheets of specially shaped polymers) they rely on will become cheaper and easier to manufacture.

If that happens, we could one day see the first real Harry Potter style invisibility cloaks. In military terms, that would be a huge advance – the US army is already funding much of the research in this area, following up on their successful work on 'stealth' technology, which makes aircraft invisible to radar.

Vanishing virtue

Of course, effective cloaking wouldn't just be exciting for spies and soldiers. People have dreamt of invisibility for thousands of years. Indeed, for the Ancient Greeks, it was the basis for one of the most interesting moral questions of classical philosophy.

What would happen, asks a young man in Plato's Republic, if anyone could become invisible? Surely, someone who could do whatever they wanted without fear of being detected would immediately abandon the rules of conventional morality.

Not so, replies the philosopher Socrates. Truly virtuous people don't act morally for the sake of their reputation, but for the sake of virtue itself.

You Decide

  1. Invisibility often appears in pop culture as a superpower. What superpower would you choose? Why?
  2. Why do people act morally? Is it because they want to or because they fear others will disapprove of them if they don't.


  1. Write fictional account of one day in a world where someone or everyone has the power of invisibility.
  2. Do some further research into camouflage, how it works and why it matters. Present your findings to the class, with some pictures if possible.

Some People Say...

“If everyone could be invisible, society would break down.”

What do you think?

Q & A

How might invisibility work?
We see things when light bounces off them and into our eyes. So the first step is to stop light reflecting off things.
Then what?
If something just absorbed all light, we'd see a dark area where that thing should be, which wouldn't be much good for invisibility. True invisibility means we would see straight through something, as though looking at a pane of glass.
But light couldn't pass through something thick like a human being.
Indeed not. So the trick is to bend the light around something. That's where metamaterials come in: they can refract light in such a way that light from behind something is bent round it and appears in front of it. That's probably as close as we can get to real invisibility.

Word Watch

Invented to detect submarines under the ocean surface, sonar sensors emit loud pings and then listen for echoes coming back off hard objects under the water.
Scientific research is published in scientific journals after being reviewed and checked by other scientists. Some journals are more prestigious than others, but generally if a research paper has been published it will have passed a certain standard of quality.
Sound (and light, although it gets a bit complicated) travels through air or water in the same way that waves travel over the sea. The distance between the peaks of the waves is called the 'wavelength', and defines the pitch of the sound.
Radar works like sonar, by sending out 'pings' and listening for echoes. In this case, however, the pings are not sound but radio waves.
Classical philosophy
the first Western philosophers were Ancient Greeks, whose thought has been a huge influence on later civilisation. The most famous are Plato, Socrates and Aristotle, who all lived in the 5th and 4th Centuries BC.

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