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?
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.
Does this diminish their efficiency with the gases pushing in all directions instead of all “pushing back”?
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.
At 0:51 of this video, you can see the effects of a nuclear weapon detonated at an altitude of 300 miles (Operation Argus). Makes a very good shock wave; if it hit you, I’m betting you would hear something, if only briefly.
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.
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)
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.
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
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
Kubrick almost put a depiction of this in 2001 A Space Odyssey, but decided it wouldn’t look realistic enough.
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)
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.
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.
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?
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?
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?
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.
They are smoke streamers used to track the explosion shockwave: Nuclear test streamers - Everything2.com
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.
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.