WASHINGTON — Invisibility cloaks seem to be an enduring staple of science fiction and fantasy. When I was growing up, this was most evident in "Star Trek." For the last decade or so, it's been Harry Potter. The allure is not surprising — I expect that everyone has had a fantasy, at some time or another, about being invisible. Whether the motivation is to get a free peep show or escape out of, or into, dangerous situations, the freedom offered by disappearing into the background is compelling. The real question, of course, is: Will it ever be possible?
Alas, no. In the first place, even if you could be invisible, it wouldn't be all it is cracked up to be. It is a simple law of physics that interactions are two-way streets, so if you are invisible because nothing interacts with you, then alas, you wouldn't be able to see — your retina would not intercept light. So there goes all the fun.
But more important, perhaps, the particles that make us up do interact with electromagnetic radiation — which means that while we can camouflage objects, we cannot make them transparent to all forms of radiation. We might hide them in the microwave, or infrared, or even the visible part of the spectrum by exploiting the wave nature of light, either causing the waves to bend around objects or by causing waves that scatter off the object to interfere with each other, effectively canceling each other out. But since this technological wizardry is usually tailored to the wavelength in question, then waves of vastly different wavelengths, like X-rays, for example, might still scatter off of them.
Nevertheless, since I first wrote "The Physics of Star Trek" in 1995, the lure of invisibility cloaks has continued to motivate creative scientists, and several remarkable advances have taken place in finding new ways to literally make objects invisible, at least to certain frequencies of radiation. When announcing new research in this field, shrewd communications officials from universities and laboratories have, over the last several years, taken to referring to Harry Potter in their press releases announcing cloaks for buildings, shields for microscopic objects, and more. In recent weeks, the University of Texas-Austin generated lots of headlines with this press release.