Star Wars has a lot to answer for when it comes to science. Take its laser beams, which look like dashes drawn on the negative and sound like a synth effect.
Science isn’t what Star Wars was about…but still, that’s sooooo wrong. As for the sound effect – I have to confess I put a lot of time into getting a Moog synthesiser to imitate it.
The actual sound is some foley dude hitting a taut steel wire with a hammer.
The science is clear.
1. A laser is a beam of coherent light, not a dash; and light beams are visible only if they are reflected along the way – for instance, by fog, where droplets of water scatter and attenuate the beam. That’s why nightclubs spew smoke around their lasers. The best instance I saw was in Efteling, the Dutch amusement park. It’s possible, in some circumstance, to see a laser beam in clear air, thanks to Rayleigh scattering, which I explained last week. Rayleigh scattering is inversely proportional to wavelength, so it works best with blue or green lasers; and it is also angle-dependent. In vacuum, the laser’s totally invisible (no “tracer fire” from your “space fighter”…sorry…)
I should add that all this is true only if the laser operates in a frequency visible to the human eye. Because electromagnetic radiation (light) gets more energetic at shorter wavelengths, if I was designing one, I’d want it to fire in ultraviolet or higher. You can’t see it…but you’ll get the world’s worst sunburn (at really short wavelengths, gamma frequencies, the beam would generate, secondarily, a pretty blue glow visible to us, in air…but I digress…)
2. Laser beams move at light speed. If you see it, it’s already hit you. Yet Star Wars “lasers” move so slowly they can be dodged. Besides, if I had the tech to build a Death Star, I think I’d have the tech to make any gun hit first time, every time (though there’s no drama in that).
3. Laser beams are silent in vacuum. But even in air, the energy isn’t usually enough to accelerate air molecules fast enough to create a shock wave. Really powerful lasers are audible because they DO create that shock wave – which we hear as a ‘crack’ or ‘bang’.
4. As Winch Chung points out on his website, a laser gun won’t look like a Mauser C96 with bits glued on (Han Solo’s gun). It’ll look like a camera. We’re dealing with light here! Needless to say, Robert Heinlein worked that out way back; the Wormface ‘blue light’ ray guns in Have Spacesuit, Will Travel (1958) were described as cameras for good reason.
5. Star Wars blasters seemed able to burn through Imperial Stormtrooper armour and still have enough energy to demolish the Jango Fett clone inside (Tem Morrison – a Kiwi actor!) Generously, let’s suppose each laser has a battery with the capacity of a laptop’s – say 7 ampere hours, but half the size so it fits in the stock.
Let’s say the armour was titanium alloy, 5mm thick. Those Star Wars ‘pew’ bolts seemed to last a quarter of a second. A handy online laser calculator tells me that to burn through that armour in 0.25 second you need a 100 kW ‘pew’. Oh, and the clone has to stand still. Then you have to burn through the clone himself, which can be done with a 1 kilowatt ‘pew’ creating a 2 cm wide hole through his body. Maybe it’ll kill him. (The science tells me that strobing the laser would work better, but hey, this is galaxy long ago and far away, right?)
Can the battery do it? Let’s suppose a power-in-to-light-out efficiency in the gun (‘slope efficiency’) of 70%, better than any current laser. To get a 101 kW beam you’ll need an input of 145 kW. Now let’s suppose the battery in the laser runs at a standard 14.8 volts DC, can be technomagically deep-discharged without shorting, and can technomagically deliver all its power in a few stupendous blats without melting (the laws of chemistry and physics tell me otherwise, but hey…this is a galaxy long ago, etc etc… )
With 7 ampere hours you’ll have 103.6 watt-hours or 372,960 watt-seconds, meaning the battery can supply that 145,000 watt output for 2.57 seconds (at a draw of 9,797.2 amperes). Cool, you’re in. Ten shots, roughly, before the battery’s out. Strong to start with, feeble at the end. PEW! Pew! Pew… pew…. fizzle….
Or not. To do that I had to make assumptions about battery discharge that don’t meet the laws of physics. And there is one other point. The physics of electrical transmission tell me a current draw of 9,797 amperes on a 14.8 volt system requires copper wires 2.83 cm thick to carry it, giving you a scale for the rest of the laser. Then there’s that input-output inefficiency. The energy difference goes into the laser gun itself. You might not get burned if the stock’s insulated. Maybe.
All this said – well, yes, it was done to make a great story, and the original Star Wars of 1977 was. But it was so influential it defined ‘lasers’ for us…in ways they’re not. Grrrrrr.
Do you have any pet irritations about the Hollywood-isation of science?
Copyright © Matthew Wright 2013