by Jeff Hecht

Ray guns! Death rays!

The terms conjure images of the golden era of space adventurers—Buck Rogers, Flash Gordon. But in truth, future weapons have been a crucial aspect of science fiction since H. G. Wells armed his Martian invaders in War of the Worlds with heat rays that ignited everything in their path.

Wells concocted his future weapon by combining the idea of searchlights with infrared technology, but scientists at the time were already working with all sorts of new radiation—X rays and gamma rays. By the 1920s a few of them, notably Nikola Tesla in the U.S. and Harry Grindell Matthews in Britain, made the somewhat dubious claim that, indeed, a death ray could be built. Pulp science-fiction readers may have willingly suspended their disbelief, but top scientists certainly didn’t, and after World War II, a high-level review panel proclaimed death rays to be an impossibility.

And unfortunately, the killjoys were right. Even nuclear radiation doesn’t kill instantly on contact.

Just 15 years later, however, the first laser fired bright pulses of red light, and popular science writers began envisioning applications for “The Incredible Laser”—applications ranging from eye surgery to laser cannons. But real scientists were, once again, more skeptical. So skeptical that laser pioneer and future Nobel laureate Arthur Schawlow posted an “Incredible Laser” article from the Sunday supplement This Week on his laboratory door at Stanford along with the note: “For credible lasers, see inside.” Needless to say, nothing inside was anything like the wildly overenthusiastic—although nominally factual—newspaper piece.

Half a century later, though, the landscape has changed again. We certainly have the laser eye surgery part down and, surprisingly, we’ve even come a bit closer to the cannons as Northrop Grumman demonstrated last year by firing a 100-kilowatt laser beam steadily for more than five minutes. That’s an impressive achievement by laser standards. The bad news, though, is that this laser doesn’t come in a pretty, prêt-a-porter-sized package.

No, for one thing, this laser has no beam-directing optics, so it can’t target. A bit of a drawback for a weapon. It also has never been operated outside the controlled environment of a laboratory, draws 500 kilowatts of electricity, and is rather inconveniently housed in a shiny metal box about the size of six McMansion-sized refrigerators. Even Godzilla would have a hard time lifting that.

So the question of the day is this: In this age of microminiaturization and nanotechnology, why don’t we have laser pistols, damn it?

Blame this one on the laws of physics.

Lasers don’t generate energy; they convert energy from other sources into light, and in the process, much of the input energy is lost as heat, hampering the amount of damage it can inflict. And what about a power source? Batteries wouldn’t work. A laser gun drawing the 5000 watts of power needed to produce a kilowatt of laser light would need more than a 30-ampere, 120-volt line could deliver, and again, that sort of beam wouldn’t do much damage.

Now, what makes old-fashioned bullets deadly is their momentum. The explosion of gunpowder in a .45-caliber pistol propels the bullet out of the barrel with only 500 joules of energy and the bullet’s momentum keeps it going when it hits a soft target, so it rips through flesh, often with deadly consequences.

Laser light, however, can cause damage only by delivering energy that heats the target. So, say, zapping a mosquito would be no problem—if you could get it to stay still. People, however, are much bigger, and usually try to get out of the way if they feel parts of themselves burning. So in order to kill a human (or an alien) as convincingly as a bullet does, the laser would have to burn a hole through their body by vaporizing tissue, and at the cellular level, that means evaporating water.

As you might recall from 7th grade science, our bodies are mostly made up of water, and evaporating enough of it to make the kind of through-the-body hole we’re talking about would take about 50,000 joules. Now, that’s only about 100-times more energy than the bullet carries. But because the evaporating water would block the beam and dissipate its energy, it would actually take many times more energy than that to truly finish the job.

Lasers may not be able to kill, but they can cause blindness by burning the eye’s light-sensitive retina. However, staring at the sun can do the same, and, sorry folks, the Geneva Convention has been modified to ban blinding lasers. Staring at the sun like an idiot, however? Still allowed. (And, sadly, wouldn’t even get you a Darwin Award these days.)

One thing lasers can do effectively is destroy important military targets, such as rockets, artillery shells, or robotic aircraft which carry fuel or explosives. No evaporating water to interfere there. Just point and track. The laser energy heats the target until it ruptures the fuel tank, or heats the explosive to its ignition temperature and boom! There goes the Death Star. Or, somewhat more mundanely, bang goes the unexploded bomblet lying in an Afghan battlefield before it can kill somebody, a thing that’s actually been done.

Bottom line, however? Lasers just aren’t cut out for killing people.

Still, we do love our sidearms, and if our 25th century heroes and villains aren’t going to be strapping on nifty ray guns or clunky blasters or cellphone-sized phasers, then what sort of weapons could we realistically expect the 25th century to provide?

Well, one possibility would be to adapt a concept originally conceived during the Reagan era “Star Wars” program called “Brilliant Pebbles.” Back then, “Star Wars” researchers were studying a variety of far-out laser weapon ideas, cool stuff like orbiting laser battle stations and X-ray lasers powered by nuclear bombs. But they also looked at slightly less spectacular weapons prospects such as firing high-speed projectiles that would destroy nuclear warheads with the energy of their impact. In other words, hitting a bullet with a bullet.

The idea was called “Smart Rocks,” projectiles that, when fired, could home-in on their targets. Lowell Wood of the Lawrence Livermore National Laboratory then expanded the idea, proposing to use advances in computer technology to build a fleet of satellite-based “Brilliant Pebbles” with sophisticated guidance systems, although, in truth, his “pebbles” were really watermelon-sized missiles.

While that project was shelved after the Cold War ended, the technology trends that inspired Wood have endured and evolved. Computer chips have continued to shrink in size and increase in power, and the sensors needed to recognize targets and guide missiles have likewise become more powerful. So instead of ray guns, why not shrink those watermelon-sized missiles designed for patrolling outer space down to the size of the pebbles they were originally named for and fire them from portable weapons?

The resulting “Brilliant Bullet” would be much more than a lead slug. And much cooler. For instance, it would probably contain a nano-scale propulsion system to guide it along its course and an imaging sensor to photograph people and compare them to an image of the target stored in its memory. (Or, even better, some way to match the person’s genome with that of the target.) It might even unfold wings after emerging from the barrel.

But of course a really “Brilliant Bullet” wouldn’t even require a gun. It could be made larger, the size of a ball-point pen, say, with lightweight wings and a tiny engine that would push it silently through the air. It could be coated with an optical metamaterial, science’s version of an invisibility cloak that bent light around it, making the bullet itself almost impossible to see. It would flicker past people fast enough that they would catch only a ripple in the air, but would move slowly enough to check each person in the area to identify the target. Once it had, it would then ignite its propellant, accelerate to lethal velocity and, bango, good night Seattle. Not as satisfying as firing a gun, maybe, but it would certainly be more accurate. And more deadly.

So, fledgling evil overlords take heart, laser guns may not be possible or practical, but other deadly options are in the works, and the future looks bright for conquest. Optical metamaterials are real. Unmanned aerial vehicles are real. And as for brilliant bullets? Who knows how long before they’re real as well.

All we can say is watch out, Buck Rogers, cause we’re gunning for you.

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