The silly science of Star Wars – why lasers don’t go pew pew

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.

'That's no moon'. Wait - yes it is. It's Mimas, orbiting Saturn.
‘That’s no moon’. Wait – yes it is. It’s Mimas, orbiting Saturn.

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.

The worn out ribbon pitch-controller on my Micromoog. Apparently Bob Moog invented that device for Beach Boys keyboard player Brian Wilson.
Part of the control panel on my Micromoog. Ready to go ‘Pew! Pew!’.

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


15 thoughts on “The silly science of Star Wars – why lasers don’t go pew pew

  1. But Matt…it was in the script! Now you’ve gone and ruined a perfectly good movie by giving me reason to think it never happened…a Long time ago…in ..a..galax…oh forget it! 😉

    My pet Hollywood peev is that all cars burst into flames and explode after they crash. I would need a computer to count the number of car accidents I responded to during my time working an ambulance.In reality I saw one accident related fire and NO explosions. I did see numerous people paralyzed for life because a would be do-gooder pulled a victim from the wreckage thinking that the car would explode ‘like on TV’. The problem being that when they moved the hapless victim, the victim’s spinal cord was cut by crushed vertebrate. Sorry, That one struck close to home. *steps down from soapbox*

    1. I think they did the ‘Hollywood exploding car’ on Mythbusters – and, of course, cars are deliberately designed NOT to burst into flames, still less explode. Curiously, though, one of New Zealand’s top historians was killed nine years ago when his car hit a tree and burned (no explosion, of course) – but as you say, even firing is very rare, and this accident was unusual in that sense.

      It must have been horrendous to see some of those accidents, especially the outcomes of misguided help. I’ve had only one experience of it, when my wife and I were first on the scene of a fatal one-car accident (I saw it spin into a tree about 200 yards ahead of me). We were swiftly joined by other rescuers and what got me was (a) they started doing stupid things, and (b) drew others into that – a follow-my-leader effort to pointlessness that achieved nothing for the woman inside the car. She was beyond help anyway, but nobody knew that just then.

  2. Now you’re just being mean. Next thing you’re going to tell us a warp drive’s impossible, you cannot swing over a snake pit using a bull whip, and there’s not a guy in a blue police box who travels through space and time protecting Earth from aliens. I’m not even going to ask what you think about Santa Clause! 😉

    Regarding Hollowood-isations of science, not necessarily an irritation but something I’ve wondered about: Films like Ironman and Transformers have these machines that can morph, shifting components around so Ironman’s faceplate can retract into his helmet or Optimus Prime can turn from a fourteen-wheeler into a three-storey robot. I always wonder where do all the parts fit. A solid object can’t change its volume, and you’ll need an insane amount of servos to move all those parts around.

    Speaking of the Transformers, I reckon it’s safe to say Optimus weighs in at a few tons, yet his limbs move as fast as any human’s. Aside from that it would require incredibly powerful motors with unimaginable torque to move his limbs that fast, won’t the momentum of his arm during a punch be so great that the arm would simply tear itself off at some point?

    1. Curiously, I have a post written for next week on the physics of giant mechs – I was thinking ‘Pacific Rim’ rather than ‘Transformers’ but it’s much of a muchness…and you’re absolutely right about the practicalities.

      Apropos that blue police phone box – I wish I had one. Anything that’s bigger on the inside than the outside and can travel anywhere through time and space gets my vote…:-)

  3. Actually, I remember reading that the blasters weren’t lasers but plasma bolts. Charged gas. That would make more sense than light.
    Now phasers on the other hand are part laser and part particle beam. 🙂

    1. Plasma bolts would make more sense:

      …on the other hand, I’m not sure the original film-makers concieved of it to this detail… 🙂

      I first saw the use of the word ‘blaster’ in Asimov’s SF – ‘The Caves of Steel’, and that may well be one of the earliest uses, not sure. Later he worked out a possible science behind it, conceptualising it as a microwave projector with (sensibly) a limited number of shots, but able to be ‘turned down’ to produce a weaker beam for longer.

  4. I read somewhere that the laser sound effect was created by hammering on a certain type of electrical chord (hopefully not plugged in and connected to sensitive equipment at the time). I think they just thought it sounded cool. So goes Hollywood science. 😉

  5. What?! Why would you go and try to find actual science in Science FICTION?! I’m going to go curl up with my Star Wars (the trilogy) and forget everything you just said.

    *I cut you with my light-saber Woosh! Wooonnng!*

      1. Ni! Ni! Sorry, mixed up with another movie there…OK, lightsabres. I figure they’re the sort of sound you’d get, for instance, if you recorded the hum of two Selsyn film projector motors on idle, mixed that with a recording of the wave-form induced in a microphone held behind the yoke of a CRT, then played the whole composite back and re-recorded it via a microphone whipped back and forth in front of the speaker so as to get a good doppler for that distinctive ‘whom whom’ sound.. It’s true – you don’t think I’d make this up do you?.

  6. I’m with Dennis; I can’t tell you how many times my patients argued with me because I did not do it like they did on TV. I’d answer either, “Probably because I’m not trying to kill you.” or “But I’m a Real Nurse and know what I’m doing.” I know there are some things that cannot be done correctly on TV or they would injure the actor, e.g., CPR and checking the jugular pulse. Those dramatic needles scare even me. You do not hold down a patient having a seizure. I watched an episode of reality ER where the doctor hollered for them to do that and everyone standing around the stretcher grabbed a limb! Also, you know longer put anything in their mouth to stop them from swallowing their tongue. They’ve proven that doesn’t happen even during the worst seizure.
    I’m planning on doing a blog about TV medicine with all those quirky, oddball stuff they do. I probably should have it ready for next week.
    As far as Star Wars and all the other movies, I love the effects and wondered if some of them were possible. I know because of Start Wars some brainy nerd (no offense intended; I have my own brainy nerds in my family and I love them all dearly) looked at what was on the screen and said “What if…”. The imaginative things we see on TV and in movies can lead to real life inventions.
    I love how some of those effects were spelled in the responses. Since I’m now an author, those things strike my fancy.

    1. They were pretty cool sound effects – the guy who did them, I believe, was Ben Burtt. The coolest part, for me, was the way he used ‘found sounds’ – the real world noises he could discover around him – to create the effects. It gave them a depth and realism that just wouldn’t have happened if he’d done them any other way.

      Look forward to seeing your blog. It’s amazing how much the ‘Hollywoodisation’ of events affects our perception of them – even our notion of what is ‘right’. Whereas in reality they’re geared for visual spectacle and to efficiently convey emotion and story. Real life is never so in-your-face dramatic.I rail about movie physics a bit, partly because it’s an excuse to outline the real thing (which I find fun and cool anyway) – but it’s a worry when medical procedures get the same treatment and people believe it’s the way things are meant to be done.

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