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Can invisible technology make Harry Potter disappear?

Here, however, we encounter a bit of frustration. Microwave light can't detect anything smaller than its wavelength—about an inch—such as metamaterials. But people don't see in microwaves; we see colors with much smaller wavelengths, on the scale of nanometers. So concealing an object from human vision would require metamaterials dramatically smaller than their present size.

The problem gets worse. For light to travel around the cloak and resume its original path, it must, for a brief instant, move faster than the speed of light. Scientists can achieve this boost along a single light frequency, but the system breaks down when several colors are involved. So, while it might be possible to mask some yellow in young Potter's striped scarf, the red would regrettably remain.

Finally, diverting light around a cloak takes precise placement of metamaterials. That's fine if we want to disguise a stationary object, but makes it extremely hard to keep a moving object invisible—a problem given how quickly those books fly off the shelf.

So we're faced with an unfortunate Catch-22 (a book we'd never dare cloak): We can hope that invisible technology becomes more efficient, but if it does, we must accept the inevitable science articles making reference to you know who.

The real Wishful Thinker behind this column was engineer David R. Smith of Duke University, whose greatest act of invisibility might be the way he circumvents the question of when we'll have a fully operational cloak.

Have an idea that should be thought about wishfully? Send it to jaffee@si.edu.

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