Dumb astrophysics question

[scribble]

Thinking about allt he video games and movies where stuff blows up in space:

Obviously there's no atmosphere, we all know in space, no one can hear you scream (or explode).

But I'm curious about the shockwave from a blast. How does that work in a vacuum? Would there be none? Would the energy be carried solely by fragments of whatever blew up?

I know, dumb question, but I'm not sure of the answer.

 

[Monketi Ghost]

It's the luminiferous aether. When something in space explodes, it pushes against the aether, which builds up push power.

Sometimes, a large explosion causes sub-aether "space"slides, which give rise to the little-studied phenomenon known as Aether-Tsunamis, predicted by Einstein's unpublished Total Revision of Relativity and quantum mechanics.

(I suppose I really don't have to add a smiley to this.)

 

[BillyJoe]

Would the energy be carried solely by fragments of whatever blew up?

I'll go out on a limb and answer yes.

Anybody got a saw?

 

[Crossbow]

Without an atmosphere, an exploding object could not form a shock-wave, thus one would not have to worry about this effect.

However, without an atmosphere or gravity, there would be nothing to slow down shrapnel from the explosion, thus one would have to worry about this sort of thing much more so than on terra firma.

I hope this helps!

 

[wipeout]

If whatever blew up in space had a lot of gas in it then you'd feel a shockwave from the gas as the expanding sphere of it centered on the explosion passed you by.

So if someone blew up something like a spacestation, there's a shockwave if there was air in it and there's no shockwave if there wasn't.

 

[Crossbow]

If whatever blew up in space had a lot of gas in it then you'd feel a shockwave from the gas as the expanding sphere of it centered on the explosion passed you by.

So if someone blew up something like a spacestation, there's a shockwave if there was air in it and there's no shockwave if there wasn't.

Possibly, but it would take a great deal of gas and/or require the distance between the source and the target to be very short.

The volume of a spherical container increases with the cube of the radius, therefore (assuming all other things being equal), if the radius is doubled, then the volume increases by a factor of eight which means the pressure will drop by a factor of eight. Further, in the case of space, there would also be a very, very substantial temperature drop which would serve to further decrease the pressure.

Therefore, if one was dealing with a spacecraft designed for us human types (say like the Shuttle), it would be pressured at just about one atmosphere, thus if the hull were suddenly ruptured, the effects of the shockwave would be about nil within 50 meters.

 

[Ziggurat]

You can get gas expanding outwards from an explosion in space, sure. But for the case of, say, a space station exploding (or even just a conventional explosive, which generates lots of high-pressure gas), without an atmosphere, it wouldn't be exactly a shockwave. On earth, you get a shockwave because the expanding gas wants to expand faster than the speed of sound, but it can't, because there's air in the way, so it builds up a pressure front that moves at the speed of sound, which is your shockwave. Without your atmosphere, nothing is limiting the speed of the escaping gas, it'll fly away as fast as it wants, and it won't stay high pressure because it can always just disperse. So you'd probably get something more like a super-fast gust of wind, but not a shockwave (the distinction being no single front of super-high pressure).

But yeah, watch out for the shrapnel.

 

[wipeout]

I suspect you will still get a shockwave in space because the gas was compressed during the blast and the molecules are now all moving outwards and away from each other. I'm guessing the molecules' random motion gets "reset" as the molecules get squished together into almost purely outwards motion.

If you were moving outwards with the molecules you'd notice almost no pressure or temperature from them, but an object stationary relative to the explosion that was struck by them would notice a sudden pressure and temperature increase, hence a shockwave.

That's my theory anyway. And yes, it would have to big a big explosion and fairly close by, but the question was about movies and videogames...

On a similar topic, anyone notice what is funny about the idea in movies and TV that spaceships can see the craft but "it's not in range yet" for laser beams or the like?

 

[scribble]

Thanks for the answers! That's what I thought - I'd considered the possibility of air escaping form a station carrying a shockwave, but I assumed that it wouldn't carry very well.

I've been kicking around the idea of writing a space game based on realistic physics for a while, but this is one angle that hadn't occured to me until recently.

 

[Beausoleil]

I think it's a question of scale - space isn't really "empty" after all. Off the top of my head i can think of supernova ejecta impacting adjacent molecular clouds and accretion disks as examples of places where shock is important in astrophysics.

 

[wipeout]

Best movie example of a shockwave like the kind I'm suggesting might exist is when Jupiter becomes a sun at the end of the film 2010.