A Cloaking Device? Scientists Gain Ground on Science Fiction

By Charles Petit, Science News

Ulf Leonhardt is riding high these days, with a new award from the Royal Society of Great Britain to further develop his ideas on how to make things in plain sight disappear.

Born in East Germany and now occupying the theoretical physics chair at Scotland’s University of St. Andrews, Leonhardt is among the leaders of the worldwide race to realize an old dream of science fiction: cloaking devices. They would steer light or other electromagnetic waves around them like water around a stone in a smooth stream, leaving nary a ripple of difference in the flow. Such things, letting light swish past like a boxer ducking every punch, would be invisible.

Cloaking device is a common term in technical literature. It also deliberately evokes myth and popular fiction. Allusions include the Romulan technology that first amazed TV viewers of the old Star Trek in the episode “Balance of Terror,” when hostile Bird of Prey fighting vessels just disappeared, poof. One finds cloaking in J.K. Rowling’s novels about the young wizard Harry Potter with his invisibility cape. Farther back, H.G. Wells’ novel The Invisible Man (and the movie of the same name, along with its sequel The Invisible Woman) toyed with much the same idea. J.R.R. Tolkien assigned similar power to The One Ring in his tales of hobbits. Inspiration for the ring apparently came from way back — the magical ring that the shepherd Gyges recovered from an earthquake-spawned chasm in Plato’s The Republic. 

Leonhardt’s role in the cloaking field’s rise to respectability did not get off to an encouraging start. The details of his initial frustration and eventual triumph illustrate the swiftness with which the field entered the mainstream — even surprising some experts. “I began my work at a time when invisibility was not fashionable at all,” he says. That was about a decade ago. After years of quiet work with a few colleagues, he wrote a paper titled “Optical conformal mapping.” The abstract’s first words come right to the point: “An invisibility device should guide light around an object as if nothing were there.”

In 2005 he sent the paper to Nature, which rejected it, and to Nature Physics. Editors at Nature Physics, Leonhardt recalls, took just two days to reject the paper as well. So, he says, he sent it to Science. There, it lasted two weeks before the heave-ho. In early 2006 he tried again, this time with Physical Review Letters, or PRL. Another no-go. One reviewer said the mathematics, while classical (the calculations refer to Maxwell’s and Newton’s equations of light and to other mathematical constructs credited to such titans as Fermat, Lagrange, Euler, Descartes, Euclid, Kepler, Einstein and Feynman), did not offer enough new physics. Ouch.

But it was another PRL reviewer’s rebuke that opened Leonhardt’s eyes wide. It said he was not alone. The assessment, routinely shared with Leonhardt, indicated that the reviewer had been to two meetings in the previous months “in which John Pendry discussed his group’s efforts on the same issue, calling it a cloaking device or their Hogwarts project in reference to the cloak of invisibility associated with the Harry Potter series.” Pendry and his colleagues, the assessment added, “supposedly have filed a patent related to this work.” Hence, the anonymous reviewer declared, the work was not new and did not merit publication in PRL.

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