# The vacuum of space and Sci Fi sfx **URL:** \ **Category:** Factual Questions\ **Created:** [June 27, 2009, 8:34pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197 "2009-06-27T20:34:58Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![mswas](https://avatars.discourse-cdn.com/v4/letter/m/e99b99/32.png) [@mswas](https://boards.straightdope.com/u/mswas)\ **Post date:** [June 27, 2009, 8:34pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/1 "2009-06-27T20:34:58Z")
So in Sci Fi movies they often have the sounds of battle, a la Star Wars. When I play Eve Online I’ll pass by explosions of people fighting and such. So my question is this, to what level will a vacuum insulate an explosion? Could you setoff a nuke nearby and not be hit by a shockwave? How does that work? ---
**Author:** ![Hyperelastic](https://avatars.discourse-cdn.com/v4/letter/h/a3d4f5/32.png) [@Hyperelastic](https://boards.straightdope.com/u/Hyperelastic)\ **Post date:** [June 27, 2009, 9:27pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/2 "2009-06-27T21:27:20Z")
This is an interesting question. Sound is transmitted by compression waves in the ambient medium, so there cannot be any sound in a vacuum. But sound could be carried by gases expanding from the explosion itself. A nuclear explosion doesn’t release much in the way of gases (I don’t think - not an expert), so you probably wouldn’t get much of a shockwave in space, but you would feel the effects of the radiated energy and electromagnetic pulse. A conventional (chemical) explosion does release quite a bit of gas, but probably not enough to carry sound. Unless you were in the immediate vicinity of the explosion, you probably wouldn’t hear a thing. A related issue is how rocket exhausts are animated in space movies. They usually show the narrow, blowtorchlike exhaust you see from a rocket when it lifts off, but in reality, when a rocket is above the atmosphere, the exhaust expands to a very wide fan immediately upon exiting the nozzle, because there’s no atmospheric pressure holding it into the familiar torchlike shape. You can see this in in-flight videos available on YouTube. ---
**Author:** ![Sapo](https://avatars.discourse-cdn.com/v4/letter/s/ec9cab/32.png) [@Sapo](https://boards.straightdope.com/u/Sapo)\ **Post date:** [June 27, 2009, 9:41pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/3 "2009-06-27T21:41:01Z")
> [@Hyperelastic](#): > > [W]hen a rocket is above the atmosphere, the exhaust expands to a very wide fan immediately upon exiting the nozzle, because there’s no atmospheric pressure holding it into the familiar torchlike shape. Does this diminish their efficiency with the gases pushing in all directions instead of all “pushing back”? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 27, 2009, 10:18pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/4 "2009-06-27T22:18:53Z")
> [@mswas](#): > > So in Sci Fi movies they often have the sounds of battle, a la Star Wars. When I play Eve Online I’ll pass by explosions of people fighting and such. > > So my question is this, to what level will a vacuum insulate an explosion? Could you setoff a nuke nearby and not be hit by a shockwave? How does that work? I’m pretty sure that if you were within a few tens miles of a nuke explosion in a vacuum, you would hear it - at least you would hear the sound of the outer layer of your spacesuit suddenly vaporizing. Also, without the atmosphere to attenuate them, you would get a lethal dose of Neutrons and X-Rays much farther away. How far, I have no idea. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [June 27, 2009, 10:52pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/5 "2009-06-27T22:52:20Z")
At [0:51 of this video](http://video.google.com/videoplay?docid=689628960191060384&ei=GKFGSry0FMb5lQeSmZSoBw&q=%22nukes+in+space%22&hl=en), you can see the effects of a nuclear weapon detonated at an altitude of 300 miles (_[Operation Argus](http://en.wikipedia.org/wiki/Operation_Argus)_). Makes a very good shock wave; if it hit you, I’m betting you would hear something, if only briefly. ---
**Author:** ![dracoi](https://avatars.discourse-cdn.com/v4/letter/d/90db22/32.png) [@dracoi](https://boards.straightdope.com/u/dracoi)\ **Post date:** [June 27, 2009, 10:52pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/6 "2009-06-27T22:52:39Z")
Nukes do form quite a bit of gas, since the temperatures they produce vaporize everything - uranium, hydrogen, steel, etc. So depending on size and type, you’d have a couple hundred kg of vaporized material expanding at pretty high speed. My guess is that the material would spread out too quickly for you to hear much - if you’re close enough to hear it, the radiation probably killed you. There would be no real shockwave. Other types of explosions might be more audible, but the mechanics of the explosion are still totally different from in Earth. Air and water help to carry explosive energy away (sound or shock waves) and that’s why explosives can be deadly at longer ranges. In space, the dynamite produces a shell of vaporized material and fragments; unless you’re very close in, it’ll be like getting hit by a handful of hot sand or a puff of smoke. And those are probably better examples for what an explosion in space would sound like - maybe a little wind or rattling, but probably not a rushing blast. ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [June 27, 2009, 11:04pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/7 "2009-06-27T23:04:56Z")
> [@Sapo](#): > > Does this diminish their efficiency with the gases pushing in all directions instead of all “pushing back”? I wouldn’t think so. Each particle of gas would on average have a certain velocity ‘backwards’ as of the moment it leaves the nozzle. That, really, is more or less the moment that Newton’s third law of motion takes effect. And the exhaust will continue to have that average ‘backwards velocity’ even as the random side-to-side vectors, and pressure effects of the gas particles bouncing off each other, cause the exhaust to rapidly spread out ‘in all directions’ (except not so much forward towards the rocket) ---
**Author:** ![HorseloverFat](https://avatars.discourse-cdn.com/v4/letter/h/8e8cbc/32.png) [@HorseloverFat](https://boards.straightdope.com/u/HorseloverFat)\ **Post date:** [June 27, 2009, 11:42pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/8 "2009-06-27T23:42:36Z")
I dont see how any shockwave is possible. What medium are you sending the shock through exactly? Sound needs to travel through a medium. There is no medium in space. A nuclear explosion would be 100% silent unless some mass it ejects hits your spaceship. If we could hear anything via interstellar space then we’d be deafened by supernovas by now. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [June 28, 2009, 12:00am UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/9 "2009-06-28T00:00:34Z")
> [@Sapo](#): > > Does this diminish their efficiency with the gases pushing in all directions instead of all “pushing back”? No, in fact the opposite is true; rockets are (slightly) more efficient in vacuum than they are in atmosphere. To intuit this consider that in an atmosphere the ambient pressure is pushing against the back of the nozzle (and other parts of the rocket, but we can ignore that for the purposes of this discussion). The exhaust imparts forward momentum by two mechanisms; the subtraction of its axial rearward velocity (as measured at the nozzle exit plane) from the moment balance (Newton’s Third Law) and the forward components of pressure from thermodynamic expansion of hot exhaust gases past the nozzle throat pushing at the angled or belled walls of the nozzle. When in atmosphere both of those effects are somewhat retarded; pressure slows the momentum of the gas particles and it reduces the pressure differential on the nozzle. Of course, because of this, you can cut down (truncate) a nozzle used in atmosphere to prevent underexpansion of the plume, and in fact you want to do this because underexpansion can lead to undue compressive structural loads on the nozzle and flow instabilities that can choke the flow through the throat. For a nozzle used in vacuum in which the plume expands more radially as described by **Hyperelastic** , you want a larger and longer nozzle to fully develop expansion. However, this all requires extra weight, and the addition from thermodynamic expansion of exhaust is relatively minor compared to the momentum transfer (especially solid propellent motors with large molecular weight products), and so most space propulsion system are designed with a somewhat overexpanded plume to reduce nozzle inertia and improve TVA response. Some types of really high exhaust velocity thrusters like ion thrusters don’t really bother with a proper nozzle cone at all; the emitter is designed to limit the cone angle. Stranger ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [June 28, 2009, 12:50am UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/10 "2009-06-28T00:50:45Z")
Nuclear blasts in space certainly will have a significant impact on things nearby – the blast, after all, is sending things outward at great velocity. Even the photons and subatomic particles it sends out have considerable pressure (Ulam proposed using the pressure from the A-bomb trigger to effect compression of material for the H-bomb, after all). It’s not as if, there being no air, you could be near an atomic blast and be perfectly safe – even if it weren’t for the fierce flux of gamma rays and particles that would vaporeize you. After all, if there _weren’t_ a huge blast wave, no opne would have proposed using the blasts from nuclear devices to propel spacecraft in **Project Orion** > **[Project Orion (nuclear propulsion)](https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion))** > > Project Orion was a study conducted in the 1950s and 1960s by the United States Air Force, DARPA, and NASA into the viability of a nuclear pulse spaceship that would be directly propelled by a series of atomic explosions behind the craft. Early versions of the vehicle were proposed to take off from the ground; later versions were presented for use only in space. The design effort took place at General Atomics in San Diego, and supporters included Wernher von Braun, who issued a whi Physicist S... Kubrick almost put a depiction of this in **2001 A Space Odyssey** , but decided it wouldn’t look realistic enough. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [June 28, 2009, 1:54am UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/11 "2009-06-28T01:54:45Z")
> [@CalMeacham](#): > > After all, if there _weren’t_ a huge blast wave, no opne would have proposed using the blasts from nuclear devices to propel spacecraft in **Project Orion** Orion would have made use of atmospheric blast waves for the initial launch phase, but once it was out of the atmosphere it would have relied on ‘shaped’ nuclear charges. The shaped charges would have had a thick plate of teflon or some other substance, oriented toward the pusher plate at the back of Orion. The shaping of the nuclear blast would direct the majority of the radiation through the teflon and toward the Orion pusher plate. The teflon (and the bomb casing, etc.) would be ionized by the radiation and the directed plasma jet would smack against the back of the ship. Without the shaping of the charge and the extra block of ionizable mass, the explosion would not have transmitted much force to the pusher plate. The difference between a ‘regular’ nuke and an Orion nuke is like the difference between a brick of C4, and a block of C4 formed into a HEAT round or Explosively Formed Penetrator.([Youtube video of Krakatoa shaped charge device)](http://www.youtube.com/watch?v=pSxh_j26UJI&feature=related) ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 28, 2009, 2:35am UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/12 "2009-06-28T02:35:04Z")
> [@Hyperelastic](#): > > …but you would feel the effects of the radiated energy and electromagnetic pulse. the EMP is an effect of the interaction between the nuclear detonation, the earth’s atmosphere, and the earth’s magnetic field. In the absence of the latter two, [an EMP would not be expected.](http://en.wikipedia.org/wiki/Electromagnetic_pulse#Generation_of_nuclear_EMP) ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [June 28, 2009, 3:27am UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/13 "2009-06-28T03:27:29Z")
> [@](#): > > The shaped charges would have had a thick plate of teflon or some other substance, oriented toward the pusher plate at the back of Orion. The shaping of the nuclear blast would direct the majority of the radiation through the teflon and toward the Orion pusher plate. The teflon (and the bomb casing, etc.) would be ionized by the radiation and the directed plasma jet would smack against the back of the ship. Without the shaping of the charge and the extra block of ionizable mass, the explosion would not have transmitted much force to the pusher plate. Exactly – but it was not supposed to be in direct contact with the “pusher plate” – material and particles from the device were going to be “blown toward” the pushed plate and provide oomph. ---
**Author:** ![runcible\_spoon](https://avatars.discourse-cdn.com/v4/letter/r/9fc29f/32.png) [@runcible\_spoon](https://boards.straightdope.com/u/runcible_spoon)\ **Post date:** [June 28, 2009, 3:19pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/14 "2009-06-28T15:19:17Z")
So, if nukes are going to be less destructive (by some amount that I have no idea how to figure out), what about conventional explosives? Presumably at least some of the issues are going to be the same, but are they mitigated by the gases released? For that matter, how much gas can a conventional explosive release, anyhow? ---
**Author:** ![Cillasi](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@Cillasi](https://boards.straightdope.com/u/Cillasi)\ **Post date:** [June 28, 2009, 3:57pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/15 "2009-06-28T15:57:28Z")
Bypassing all the scientific stuff, Sci-fi movies and Eve Online would be REALLY, REALLY boring if you couldn’t hear anything. On the other hand, too much sound would defy your ability to to suspend belief. From inside your own spaceship, it seems logical that you would hear the sound of your own guns and the sounds of ammunition hitting your ship, but not much of anything else. Isn’t there a similar problem with colors in space? > [@mswas](#): > > So in Sci Fi movies they often have the sounds of battle, a la Star Wars. When I play Eve Online I’ll pass by explosions of people fighting and such. > > So my question is this, to what level will a vacuum insulate an explosion? Could you setoff a nuke nearby and not be hit by a shockwave? How does that work? ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [June 28, 2009, 4:20pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/16 "2009-06-28T16:20:23Z")
> [@Fear\_Itself](#): > > At [0:51 of this video](http://video.google.com/videoplay?docid=689628960191060384&ei=GKFGSry0FMb5lQeSmZSoBw&q=%22nukes+in+space%22&hl=en), you can see the effects of a nuclear weapon detonated at an altitude of 300 miles (_[Operation Argus](http://en.wikipedia.org/wiki/Operation_Argus)_). Makes a very good shock wave; if it hit you, I’m betting you would hear something, if only briefly. At 7:50 in that video they show a nuclear explosion on the ground, and a number of crossing parallel smoke trails from the sky to the ground are visible to the right of the blast. Anyone know what they are? ---
**Author:** ![mswas](https://avatars.discourse-cdn.com/v4/letter/m/e99b99/32.png) [@mswas](https://boards.straightdope.com/u/mswas)\ **Post date:** [June 28, 2009, 4:30pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/17 "2009-06-28T16:30:19Z")
> [@Cillasi](#): > > Bypassing all the scientific stuff, Sci-fi movies and Eve Online would be REALLY, REALLY boring if you couldn’t hear anything. On the other hand, too much sound would defy your ability to to suspend belief. > > From inside your own spaceship, it seems logical that you would hear the sound of your own guns and the sounds of ammunition hitting your ship, but not much of anything else. > > Isn’t there a similar problem with colors in space? Most people when they play Eve turn sound effects off, so I think most people are cool with the idea that they are in the silent void of space. I’m just curious to what degree you’d actually hear or feel the explosions in a battle around you. In the game you are actually kilometers away from your enemies, and from different angles you can and cannot hear the battle sounds. Sometimes flying near someone else in battle you can hear their battle. I was wondering if there would be any point where the explosion is powerful enough to rattle your ship. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 28, 2009, 4:43pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/18 "2009-06-28T16:43:52Z")
> [@Patch](#): > > At 7:50 in that video they show a nuclear explosion on the ground, and a number of crossing parallel smoke trails from the sky to the ground are visible to the right of the blast. Anyone know what they are? They are smoke streamers used to track the explosion shockwave: [http://everything2.com/title/Nuclear%2520test%2520streamers](http://everything2.com/title/Nuclear%2520test%2520streamers) ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [June 28, 2009, 5:08pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/19 "2009-06-28T17:08:54Z")
Going back to the movies, and somewhat off-topic, are _terrestrial_ explosions depicted realistically? IANA explosives expert, but I’d say no. Where’s the delay or distortion of sound with distance? Or echoing? And explosions always seem to sound the same regardless of the bomb type, scale, or what material is near the explosion site: I suspect that these things should make a big difference. Movie makers make up physics generally that will be the least distracting to the “plot” of such films. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [June 28, 2009, 5:40pm UTC](https://boards.straightdope.com/t/the-vacuum-of-space-and-sci-fi-sfx/501197/20 "2009-06-28T17:40:33Z")
> [@HorseloverFat](#): > > I dont see how any shockwave is possible. What medium are you sending the shock through exactly? Sound needs to travel through a medium. There is no medium in space. There is a medium, just not a very dense one. Space is filled with charged gas molecules that interact though that charge; objects moving through space produce a shockwave. You can’t hear it because the medium is far too thin, but it exists. So in that sense there is sound of a sort in space; spaceships, satellites and even the Moon produce shockwaves that could be translated into audible sound if you liked.