New York Times seeks to connect concerning transformation optics and invisibility cloaking
DOI: 10.1063/PT.4.0138
‘Duke University has developed a working invisibility cloak,’ mock-reported satirist Stephen Colbert in the rollicking, unpredictable headline litany that begins his Comedy Central fake news show. ‘Now the Blue Devils quidditch team will be unstoppable!’
With that reference to the sport of wizards and witches on flying broomsticks in the Harry Potter children’s novels and movies, Colbert was exploiting a science-fiction extrapolation of the physics. The actual news was also headlined recently by BBC , Discovery News , Science Daily , Wired UK , the Huffington Post , and other media—now including the New York Times Sunday commentary ‘Hiding in plain sight ’ by Duke research engineers David R. Smith and Nathan Landy.
Physics Today Online, citing BBC’s report, summarized the science :
One of the inventors of ‘transformation optics’ has taken another step forward in the development of structures that can redirect light, hiding the objects behind them. David Smith of Duke University and his colleagues created a diamond-shaped structure that eliminates some of the imperfections of previous invisibility cloaks. The device was able to perfectly hide a 7.5-cm-diameter, 1-cm-tall cylinder from detection by microwaves. However, the cloak only worked from one direction. Microwaves from any other direction could see the cylinder. Because of the wavelength differences between microwaves and visible light, this doesn’t make invisibility to sight any more promising, but hiding objects from microwaves could be useful for the military and telecommunications.
The Times editors hyped the conjectural science-fiction possibilities by inventing a callout that, at a minimum, misleads: ‘How do you make something invisible? Easy—bend all the light around it.’ Editors use callouts in part to inform those who just skim past an article.
For actual readers of the article’s text, though, Smith and Landy use the science-fiction possibilities only to frame and explain the news. They begin with a dissection of magicians’ visual deceptions, which brings them to the scientific ‘recipe for a bit of magic that humans (and mythical humans) have sought, from the time of Plato to the age of Harry Potter: invisibility.’ They have learned, they report, how to ‘one-up’ magic with science by changing light’s trajectory without mirrors:
We do it with the science of materials—designing a ‘cloak’ that can make light curve around an object, and then emerge just as if it had passed in a straight line through space. (Think of it like water flowing past a rock in a stream.)
The phenomenon is indeed supernatural. That’s because nature doesn’t appear to offer any materials that can accomplish this feat. The reason is that light has both electric and magnetic components—and to make it swerve around an object, one has to redirect both of these very different components and have them sync up immediately after the detour. That’s impossible to do with metals, fabrics or any other traditional materials.
But research findings over the past decade have shown us how to develop artificially structured ‘metamaterials'—in which tiny electrical circuits serve as the building blocks in much the same way that atoms and molecules provide the structure of natural substances.
By changing the geometry and other parameters of those circuits, we can give these materials properties beyond what nature offers, letting us simultaneously manipulate both the electric and magnetic aspects of light in striking harmony.
This year, with one such metamaterial, we built the world’s first invisibility cloak capable of managing both components of light.
Then they stipulate what’s obscured in Colbert’s whimsy and the Times editors’ callout: ‘There is a catch, admittedly. Our cloak works only on microwaves, not on visible light. And humans don’t ‘see’ microwaves in the first place.’
The authors go on to mention potential microwave payoffs. They stipulate that ‘tricky technological barriers,’ including a four-orders-of-magnitude wavelength difference, make actual invisibility to eyesight at best a distant prospect. Their commentary makes clear what the website for Duke’s Center for Metamaterials and Integrated Plasmonics puts this way : ‘It may be a while before our quidditch team reaps the benefits.’
An additional word about underlying research publications:
When Smith and Landy mention that this year, using a metamaterial, they ‘built the world’s first invisibility cloak capable of managing both components of light,’ they’re referring to research reported in the recent Nature Materials article ‘A full-parameter unidirectional metamaterial cloak for microwaves .’ Even that report begins by invoking science fiction: ‘Invisibility is a notion that has long captivated the popular imagination.’ But it quickly switches, citing a pair of Science research reports from 2006, the year when, it says, ‘invisibility became a practical matter for the scientific community as well, with the suggestion that artificially structured metamaterials could enable a new electromagnetic design paradigm, now termed transformation optics.’ The Science articles are ‘Controlling electromagnetic fields ’ and ‘Metamaterial electromagnetic cloak at microwave frequencies .’
Steven T. Corneliussen, a media analyst for the American Institute of Physics, monitors three national newspapers, the weeklies Nature and Science, and occasionally other publications. He has published op-eds in the Washington Post and other newspapers, has written for NASA’s history program, and is a science writer at a particle-accelerator laboratory.