![]() It’s sometimes said that there are only two real magic tricks in the entire repertoire: making things vanish, and making them appear. The cloak emerged from research on a new class of materials known as optical metamaterials, which can defy the normal laws of optics. It was a specialty of the stage magician, dating back to the earliest accounts of sleight-of-hand in Roman times, when prestidigitators performed a variant of the old balls-and-cups trick in which the balls seemed to vanish from one place and reappear in another. Invisibility is a magical idea, and for many centuries the only way we have been able to achieve it is with magic. But how was I to describe, let alone explain, this complicated arrangement of prisms, mirrors, screens and, um, pandas … and to make it sound fabulous?Ī novice witnessing this piece of physics magic could be forgiven for thinking she was being hoodwinked-as if she’d been ushered into a circus sideshow to see “wonders” that are all too obviously monkey torsos crudely stitched onto fish tails. It’s hard enough trying to convey any sort of invisibility trick on the radio. The air of farce was compounded by the fact that I was witnessing all of this for a radio documentary. So “invisibility” here meant failing to reveal something that was already hidden. But when the prisms became apparently transparent, the sliver should have come into view obscuring part of the panda’s reflection. It was masked by their mirrored rear surface when the switch was off. What was actually being hidden in there? Well you see, there was a little sliver of metal inserted behind the calcite prisms. The action was taking place inside the plastic box set up in the corner. I’d seen this kind of kit before it’s like a gigantic Erector set. We were in the Metamaterials Laboratory of the university’s physics department -a room dominated by a huge steel “optics table,” in which all manner of lenses and mirrors had been positioned to send laser beams along carefully arranged routes. What, then, had vanished? Well, it’s complicated. When my host, Jensen Li-a very smart young Chinese physicist from the University of Birmingham in England-hit the switch, the light now appeared to travel in a straight line right through the prisms, despite their mirrored facets, and was reflected off the mirror behind them and through the viewing screen to reach my eye. They blocked the reflection in the mirror because they had mirror-coated rear faces themselves, off which the light from the panda bounced out of my line of sight. I knew that the cloak itself would not be some fabulous garment, but would pretty much resemble what it was: small prisms of transparent crystal made from a mineral called calcite. ![]() ![]() Was it as underwhelming as it sounds? I hadn’t arrived with high expectations, because I knew enough about these “cloaks” not to anticipate something out of Harry Potter. ![]() I knew enough about these “cloaks” not to anticipate something out of Harry Potter. This, I had to admit, was a strange sort of invisibility. When the switch was flipped “on,” that missing part sprang back into view, as though the prisms had become wholly transparent. The reflection had a chunk missing where a couple of small triangular prisms, glued back to back and placed in front of the mirror, obscured the view. I was told to look through a viewing screen, through which I saw, in a gold-tinted mirror, the slightly distorted reflection of a toy panda. It was housed in a Plexiglass box, and there was an on-off switch on the side. Well, this invisibility cloak certainly wasn’t like that. We all know what invisibility is, don’t we? Now you see it, now you don’t. I’ve written a whole book about invisibility-its myths, magic, and technology-but never before had I seen in the flesh one of the new devices that promise to make things vanish. Just before Christmas I finally got to see an invisibility cloak.
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