Invisibility cloaks captured the public imagination in the Harry Potter movies - but the science to create one is still some way away. Warner Brothers via IMDb
For science!

Researchers unveil 'invisibility cloak' big enough to cover a human

Researchers have combined tanks of water and mirrors to make a pretty decent system for hiding a human.

RESEARCHERS HAVE UNVEILED a Harry Potter-style invisibility cloak system which is big enough to disguise an adult human.

The team at the University of Rochester in New York have pioneered a system which they admit is bafflingly simple: setting up tanks of water and mirrors which perfectly carry light around an object, leaving it invisible to those standing in front of it.

The experiment in ‘transformation optics’explained by the Technology Review, basically exploits a principle called ‘Snell’s Law’ – which describes how images are skewed when viewed through water.

By putting an item between two mirrored tanks of water, each of them bent into an ‘L’ shape, it’s possible to redirect light so that the object in between is totally cloaked:

Its creators admit that there’s little ‘new’ technology in their technique – and that it only works if someone is standing directly in front of the two tanks of water.

They have, at least, successfully determined how something as simple as water and mirrors can be used to disguise large objects almost perfectly.

It’s the size aspect that’s particularly important: in their paper, the writers say:

The point we wish to emphasize is not the novelty but the ease of scaling to nearly arbitrary size.

If you want to disguise something even larger, all you would need is a larger mirror and some larger tanks of water, they say.

An image from the team’s experiments, showing how a chair can be nearly perfectly disguised by a tank of water in front of it.

Anyone hoping to use the cloak to slip around Hogwarts or Diagon Alley unnoticed will be disappointed, however: the elaborate setup means the system is not very portable. The search for a more portable system continues.

The ‘holy grail’ of an invisibility system is one which can capture all frequencies of light and ‘absorb’ or deflect them so that an object behind it is shielded. Any success at this technique has been limited to tiny objects with little practical application.

Read: Thermal cloaking could make objects ‘invisible’ to heat

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