Now you see it, now you don't
Most of us will have dreamed of having an "invisibility cloak" - a garment that would let us slip from sight, or even spy on others with impunity.
Now scientists in Singapore have unveiled new technology that has been used to make a kitten and a goldfish "disappear".
A video of experiments carried out at Nanyang Technological University shows a "cloak" made of thin panels of glass, suspended in a bowl of water. Plants in the bowl are clearly visible through the cloak, but when a goldfish enters the cloak it disappears from view. Further footage shows the lower half of a kitten disappearing as it steps inside a cloak placed on a table.
The scientists have improved on earlier cloaks, which worked only with polarised light or microwaves. Although the devices are still fairly primitive, the hexagonal cloak used to conceal the goldfish can hide objects from six different directions. It could potentially be used in the security, surveillance and entertainment sectors.
The idea of an item of clothing that makes the wearer invisible has been around for thousands of years. Harry Potter inherits an invisibility cloak in the books by J.K. Rowling. But millennia earlier, in Greek mythology, the gods gave Perseus, the son of Zeus, a magical helmet that rendered him invisible, to help him in his task of slaying the Gorgon Medusa. Homer's The Iliad refers to Athena, goddess of wisdom and military victory, and patron of Athens, using the same helmet during the Trojan War.
So is reality catching up with mythology? The science of invisibility, also known as transformation optics, first drew international attention in 2006, when Sir John Pendry from Imperial College London described how it would be possible to bend light around objects. Pendry says that the latest development is a "genuine step forward".
The experiments in Singapore were led by Baile Zhang, an assistant professor of physics and applied physics, who showed off a tiny invisibility cloak at a TED conference in February. Using a box of calcite - a cheap and abundant mineral that bends light - he made a rolled up piece of paper that had been submerged in oil vanish.
The science involved in these experiments will be challenging for young students. But you could use it to introduce them to the Greek and Roman gods, or to stage a role play based on who they would most like to disappear.
- Why do some young children - and many animals - think that if they cannot see you, you cannot see them?
- Who or what would you like to disappear and why?
- How does some darkened glass allow people on the inside to look out but prevent those on the outside from looking in?
- Why does the eye sometimes play tricks on us? Get students to consider three- dimensional images and films, and then look at the same subjects in two dimensions. What are the differences?
- What would you do if you were given an invisibility cloak for a day?