# For Science!From Blasters to Phasers: How Close Are We to Laser Guns?

CJ Miozzi | 28 May 2014 20:05
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### Projectile Speed

In both movies and video games, we find examples of humans dodging bolts without the aid of supernatural abilities or bionic augmentations. This arguably renders bolts inferior to beams and even bullets for most anti-personnel purposes, and calls into question the science behind the projectile.

If the projectile is a laser, then it is traveling at light speed and cannot be dodged. If the projectile is a stream of accelerated particles, which is the most common explanation for such weapons, then it is merely traveling at roughly 670 million miles per hour. Barring any form of Force powers or other magical hokum, it doesn't matter how fast your reflexes are - you aren't dodging that.

But maybe we want to argue that the bolts aren't actually being dodged, that the characters are instead dodging before the trigger is pulled. Fine, but then how do we explain the visual depiction of a bolt flying across the movie screen?

Movies traditionally play at 24 frames per second, and in order for a viewer to determine the direction of a blaster bolt, that bolt must be visible in at least two consecutive frames: one frame to serve as a reference, the next to suggest the movement. Modern rifles have a muzzle velocity of more than 3,900 ft/s, meaning a bullet would travel 3,900 feet in 24 frames, or 163 feet per frame - that's greater than the length of half a football field. Even a humble Beretta pistol has a muzzle velocity of 1,250 ft/s, or 52 feet per frame.

Add to that the fact that the human eye can only process 10 to 12 separate images per second and we realize that we would actually need a minimum of about 3-4 frames for the human eye to process the direction the bolt is traveling in. That means that by the time your eye can register the movement of a Beretta bullet, it has moved at least 100 feet. Most fight scenes don't take place on such scales.

What about long corridors and perspective shots? Doesn't that put that 100 feet figure into the realm of plausibility? If it were a glowing Beretta bullet, maybe. But we're talking about accelerated particles traveling at almost one million ft/s, or over 7,500 miles per frame. That's over twice the length of the continental United States.

The conclusion is obvious: not only would a realistic bolt be moving too fast to dodge, it would also be moving too fast to be seen.

### Projectile Appearance and Noise

Now, there is one saving grace for the blaster. Modern militaries make use of tracer rounds, which are bullets that include a pyrotechnic charge that leaves a visible trail. If you watch footage of tracers in action, you'd swear you're seeing a blaster bolt.

If we concede that a blaster bolt is something that cannot be dodged, and the visual effect is simply the trail left by some form of tracer that is perhaps even latent to the bolt itself, then we have redeemed the bolt into the realm of plausibility. However, the implication is that your target would be dead before you saw the bolt, which would simply be a "ghost" of the actual projectile.

What about laser beams? Shouldn't lasers be invisible?

To answer that, we need to clarify what we are seeing when we "see" lasers. A laser consists of concentrated photons, or particles of light. We don't "see" light; we see the physical objects that light illuminates. When you direct a laser pointer at a wall, you see a red dot on the wall because the beam of photons is being concentrated on that spot. Point the laser through fog, and you'll be able to see some of the beam because the photons are illuminating the fog particles in its path.

Whether we "see" a laser beam or not depends on three factors. The first is the wavelength of light the laser emits - many military lasers used for tracking are in the infrared range, invisible to the human eye. Regardless of other factors, infrared and ultraviolet lasers are inherently invisible to us. Green lasers happen to be the most visible to us simply because our eyes are most sensitive to that wavelength of light. The second factor is the number of particles in the air the photons have to bounce off of - the greater the number of particles, the greater the visibility of the beam. Lastly, the strength of the laser also matters. Even in the absence of fog, a powerful enough green laser beam will be visible to us by reflecting off individual air molecules.

What this means is that a weapons-grade laser could either be visible or invisible; the decision is up to the designer. An invisible laser seems to be the perfect stealth weapon for a sniper, who can steadily aim through a scope from an incredible distance and not have to compensate for wind or ballistics. However, as a sidearm, having a visible laser may be beneficial to aiming.

But what about the noise? Would we hear the distinct pew pew popularized in fiction?

Likely not, but we would hear something. The machinery that operates high-powered lasers, their power source, and their cooling equipment, will make noise, generally a low humming or buzzing. Likewise, a particle accelerator would also generate similar noise as the magnets hum with electrical current.

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