aptain, the Suliban ship has vanished."
In the UPN series Enterprise, technology from the 24th century is being sent back in time to the 22nd, so that Suliban criminals can alter the course of history under the direction of shadowy future commanders in a "temporal Cold War." In addition to genetic enhancements that give them a chameleon's power to blend in with their surroundings, the Suliban use a "cloaking device," possibly of Romulan origin, that is capable of rendering whole starships invisible.
Militarily speaking, if you want your stuff to be difficult to spot and neutralize, any sort of camouflage is useful. Even a green cloth thrown over the top can make a truck or person hard to recognize, and the right pattern of colors and textures can really blend an object into the background. This trick is even more important if your plans—whether nefarious or noble—require an element of surprise. But, believe it or not, cloaking devices do not have to be shipped back from the 24th century. We have them—or something like them—already.
The simplest form of camouflage is darkness. When there's less light bouncing around, it's easier to sneak in and out of trouble without being seen. Sneaky types can even enhance the darkness by wearing black clothing. You might not expect such a crude trick to be effective—especially against non-black backgrounds—but anyone who's ever witnessed a candlelight ninja attack at their local Renaissance fair knows differently. Black objects drink in ambient light, fading into the shadows around them. It's not that they can't be seen, it's that they don't look like anything threatening. In poor light, the outline of a moving ninja simply confuses the eye, and the visible slit of flesh around his face can easily be mistaken for a fluttering insect. This is also why we have stealth aircraft, which absorb radar waves rather than reflecting them. In color terms they are radar-black, and return no more echo than a bird or bug.
Invisible armies can be seen on the horizon
Of course, with a bright spotlight shining directly on them, the ninja and the stealth bomber are easily seen. An even cheaper way to catch them is by occultation, or shadow: putting faint light sources behind them and watching for any flickers. On a cloudless night, even the stars can give an aircraft away as it passes in front of them, one by one. Of course, in outer space, there are stars all around, and few clouds or other obstacles to hide behind. If you want to stay hidden, you need a better trick than a can of black paint.
How about making your spaceship out of glass? Its stealth will benefit from any transparent material which passes the starlight through rather than blocking or reflecting it. Unfortunately, materials like glass and especially diamond will refract, distorting the image behind them and also, at certain angles, reflecting part of the light and splitting the rest into rainbows. This "chandelier effect" might still be better for most purposes than a coat of black, and the appearance would only improve if new materials were discovered that had a very low index of refraction. But a spaceship—or any other sort of vehicle—presumably needs people and equipment inside of it. In a glass hull, these would stand out like the proverbial sore thumbs.
"Captain, why are all those people sitting in empty space, zooming toward us on an attack profile?"
Still, it's possible to achieve cheap, crude invisibility through simple video technology: make the entire surface of the vehicle both a video camera and a video projector. Every part of the exterior displays an image of the light shining on the opposite side, including full visual reproduction of the sky, ground, buildings and whatever else might be around. A chameleon can blend colors and even patterns, but it can't reproduce motion, or fine details such as text, and it certainly can't match light and shadow effects. But a video screen easily can.
This is known as "electro-optical camouflage," and is featured to humorous effect in the Sony Pictures movie I Spy, and chillingly in John McTiernan's 1987 classic Predator. In the real world, this effect has been known and used at least since World War II, when Britain's Royal Air Force placed floodlights on the wings of antisubmarine aircraft to blend them into the daytime sky. And today, in the United States, there are strong indications that both industry and government are pursuing this technology in earnest.
It's estimated that an M-1 battle tank could be rendered semi-invisible for about $10 million; all you'd really need are some ruggedized LCD screens, half a dozen digital cameras, some wiring and some lights. It doesn't sound all that hard, so you can safely assume the military has already tried it, and probably even deployed it on the battlefield under the additional camouflage of Top Secret classification. One of Boeing's recently declassified stealth aircraft is also rumored to have chameleon powers, and the airplane's name, the Bird of Prey, may in fact be an homage to Star Trek's stealthy Romulans and Klingons.
Suliban thieves are wasting their time travel
The cloaking illusion would be far from perfect—a moving tank or plane would look like a boxy distortion in the air, especially if its video screens were dirty or damaged. But it would be enormously better than the simple paint splatters we use today. And with the capability to display 3-D holographic images as well as flat ones, high-resolution display technologies such as quantum dots could possibly make the camouflage even more convincing in the future.
Defeating sonar would be more difficult, but naval submarines today are coated with vibration-dampening (acoustically black) materials. For active suppression, microphones and speakers are used to detect vibration, and generate canceling waves that are 180 degrees out of phase with the original wave. If you've ever jumped on a trampoline with another person and felt them "steal your bounce," then you're already familiar with canceling waves and their effects.
Noise-canceling systems can already be found in hearing protectors, helicopter engines and high-end audio equipment. It's conceivable that sound-canceling equipment could be incorporated into vehicles or even clothing to suppress constant, repetitive or slowly changing sounds. (For what it's worth, this idea was the basis for my first science-fiction story, published in 1987.) Of course, in space, no one can hear you scream, or reflect your sonar pings back to you. In a vacuum, there is no noise to suppress.
Anyway, this all goes to show how chowderheaded the Suliban really are. They could be stealing their cloaking technology from the 21st century (say, the Smithsonian Institute or even an old Encyclopedia Britannica) and saving themselves the temporal headache. Still, their antics are fun to watch. And now it is my turn to disappear, at least until next month. Poof!
Wil McCarthy is a rocket guidance engineer, robot designer, science-fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots, and some other "really cool stuff" he can't tell us about. His short fiction has graced the pages of Analog, Asimov's, Science Fiction Age and other major publications, and his novel-length works include Aggressor Six, the New York Times notable Bloom and The Collapsium.
