Daniel Radcliffe as Harry Potter

New Delhi, Nov. 20: Two European physicists today unveiled a new blueprint for cloaks of invisibility that they say will push an idea featured in the Harry Potter series and other works of fiction closer to reality.

Researchers Ulf Leonhardt and Tomas Tyc have outlined a pencil-and-paper plan to overcome what appeared an insurmountable challenge in the quest for invisibility that became legitimate science about two years ago.

Since 2006, independent research groups in Europe and the US have shown that a certain class of artificial materials could make things appear invisible by directing light waves to curve around them like water flowing around a rock.

Until now, proposals for invisibility required materials with special properties that bend light, but managed to do that only to narrow bands, or specific colours, of light. This meant only partial cloaking — the object remained visible.

Now, Leonhardt, a German physicist at the National University of Singapore, and Tyc from the Masaryk University in the Czech Republic have shown it may be possible to bend all colours of light around objects by exploiting the curvature of space.

Drawing on a geometrical idea of curved space, the scientists have shown that light passing naturally through curved space raises the possibility of broadband cloaking and appears to make achieving invisibility easier. Leonhardt and Tyc presented their strategy in the journal Science today.

“Invisibility has become possible in principle. Now, it is only a matter of will and money to make invisibility possible,” said Leonhardt.

Scientists at Duke University in the US were among the first to experimentally demonstrate invisibility in 2006. They had constructed a cloak of light-bending materials that worked only on microwaves, but not on visible light.

In August this year, a team from University of California, Berkeley, also reported creating materials that bend light in unusual ways. But such attempts were impractical for true invisibility because they worked on a single wavelength, or colour.

“In curved space, light is naturally bent — so it doesn’t take that much effort to guide light around hidden objects,” Leonhardt told The Telegraph. “Curved space is the more natural, gentler version of invisibility,” he added.

“This is an improvement over existing ideas. It appears to relax the stringent requirements on materials needed for invisibility,” said S. Anantha Ramakrishna, an IIT Kanpur physicist who had worked with John Pendry at Imperial College, London. Pendry had collaborated with the Duke team to produce the first cloaking device. “But we’ll still need specialised materials that react to light in a certain way. There is still a long way to go for invisibility,” Ramakrishna said.

Scientists also point out that the curved space strategy for invisibility will not be foolproof. Measurements on the light would reveal subtle signatures of a curved path, and thus give away the presence of a cloaking device.

“As always, perfection is not practical, and practical things are not perfect,” Leonhardt said. He said implementing these ideas will require fairly sophisticated materials. “But it may be within reach of existing technology.”