No such thing as explosions in outer space? Just implosions?

[Iamme]

Heard this from a caller on the Bill O'Reilly radio show moments ago. They are talking about the new Star Wars movie coming out. Bill thinks this will set the new box office record? This caller says that he has watched past Star Wars and it bothers him that the effects are wrong because he said that things *implode* in outer space; not *explode*.

This makes no sense to me. We can look at solar flares on the sun. They are driven outward (at least initially), in what i have seen on film. Also, isn't rocket propulsion an outward force, in outer space?

Is anyone here in the know about this?

 

[drkitten]

Heard this from a caller on the Bill O'Reilly radio show moments ago. They are talking about the new Star Wars movie coming out. Bill thinks this will set the new box office record? This caller says that he has watched past Star Wars and it bothers him that the effects are wrong because he said that things *implode* in outer space; not *explode*.

Is anyone here in the know about this?

The caller is simply incorrect. That may be putting it a little mildly.

If you need a more authoritative statement about how things can explode, consider the following description from NASA about the Apollo 13 incident:

The Apollo 13 malfunction was caused by an explosion and rupture of oxygen tank no. 2 in the service module. The explosion ruptured a line or damaged a valve in the no. 1 oxygen tank, causing it to lose oxygen rapidly. The service module bay no.4 cover was blown off. All oxygen stores were lost within about 3 hours, along with loss of water, electrical power, and use of the propulsion system.

 

[Ladewig]

One would do well to take everything heard on any of O'Reilly's programs (from the host, from guests, from callers) with a very big grain of salt.

[cough]Paris Business Review[/cough]

 

[Jeff Corey]

My guess is that the person may have heard the fact that we would not hear explosions in space because there is no medium to transmit sound and morphed that into "There are no explosions in space."
And if somebody identified as a scientist said it on TV, it must be true.

 

[Ziggurat]

It's partly a matter of what you mean. On earth, in a typical explosion, you have a shockwave of compressed gas that expands outwards at the speed of sound. In space (or any other vaccuum environment), without an existing atmosphere, you CANNOT maintain a shockwave pressure front. Gas will expand freely - if it encounters an object, it may exert pressure, but since there is no shock front, it will be more like a wind than an impact. So you can get things flying apart, but you don't get a blast front.

You certainly can have explosions within contained vessels which then rupture the vessels, as happened on Apollo 13. Solar flares start from a non-vaccum environment, but the gas plumes they create do not have shockwave pressure fronts.

As for the starwars movies, well, the caller is half right. There's no reason for implosions to be any more common in space than anywhere else (and in fact the only place I'd expect them to be the norm is deep sea conditions and the like, where external pressure is very high, not zero). But the billowing fireballs and clouds of smoke of the first movies really was quite fake. Any gas produced in a vaccuum is just going to diffuse away, it won't roil upwards in that mushroom cloud-like style characteristic of rising hot gas in an atmosphere. And the particulate matter from any "explosion" won't slow down as it expands, because there's no air drag on it (with the possible exception of Alderan exploding, where gravitational energy would try to suck it back together). So in that sense, the caller is quite correct that the explosions in the first starwars movies are obviously done in an atmosphere, and don't look like what you'd get in space.

 

[Red Siegfried]

One would do well to take everything heard on any of O'Reilly's programs (from the host, from guests, from callers) with a very big grain of salt.

[cough]Paris Business Review[/cough]

I heard that in outer space, they're are not loofahs, they're actually all falafels.

But yeah, I think he must have heard somewhere that explosions don't make any sound in space and got confused. Damn Star Wars movies for not being realistic anyhow.

Now let's get into a debate about what shape explosions take in outer space. I had a friend told me that all explosions in space are perfectly round. I essentially said that he was correct except for the word "all." It depends quite a bit on what it is that's exploding.

 

[jmercer]

He was probably confused over what happens with deep-sea vehicles.

Shape of explosions? Tell your friend s/he's wrong about the spherical explosion.

It's not impossible to have a spherical explosion in space, but it would have to be planned. Here's the deal - the "shape" of an explosion has to do with many, many factors - but gravity and air pressure are two that don't matter much at all. Some of the factors have to do with the speed of burn during the explosion; the evenness of the burn rates throughout the explosion; density of the explosive material (does it vary? Is it the same?); the shape of the material and/or enclosure; how the explosive material was detonated, and so forth.

To have a perfectly spherical explosion accidently would be quite an amazing thing.

 

[Art Vandelay]

I don't see how there could be an implosion in space. Doesn't that require pressure?

Most flames are spherical, since the fuel collects into a sphere.

Something that is unrealistic in Star Wars is how there's an explosion, and we see and hear it at the same time. At the distances involved in these battles, light would arrive much quicker than sound.

 

[MRC_Hans]

The lack of sound speed delay is more or less universal to all movies. I have no idea why.

The explosion of Alderan in SW is particularly silly: This is an entire inhabited planet, so it must be more or less Earth-sized. Even given that some weapon could impart enough energy in a single shot toblow up a planet (without the recoil sending the Death Star into the next solar system, or tearing it apart ), the shock waves would need many hours to travel across the planet, and the actual disintegration would take days.

Explosions can happen in space, although as noted, they behave differently. Implosions, OTOH, are impossible. An implosion happens when a vaccum or (relative) low pressure is filled suddenly with surrounding medium, and since there is no surrounding medium in space...

Hans

 

[MRC_Hans]

Just to nitpick, I do think it is possible to hear explosions in space. Take a look at the picture here; this is a very large explosion in space, but the effect is largely scaleable. When an explosion occurs in space, a shell of gas will be expanding away from it at a constant or slightly accelerating speed (due to the pressure in the shell itself), and within this shell, the pressure will be higher than in the surrounding space, so when this shell passes you, or the hull of your spaceship, it will influence it mechanically. If the pressure gradient is high enough, it might even cause damage, and at least it is entirely possible that you will hear it.

Hans

 

[Vagabond]

What bothers me far more than the unrealistic explosions in space is what I call crackerbox physics. They have to be able to have combat in space, without actually killing the main characters of the movie/show so they institute what I call crackerbox physics. This enables the inside of the ship to take damage without the outside taking any and venting the entire ship into space thus killing all your main characters. However, I call it crackerbox physics because it makes about as much sense as hitting a box of crackers with a rubber mallet and breaking all the crackers but leaving the box intact. If you throw enough force/energy at the box to break the crackers the box has to break first. I understand why they do this but it's totally unrealistic.

 

[MRC_Hans]

Crackerbox physics:
Well, yes and no. Obviously, if you are to build a fighting spaceship, you will go to A LOT of trouble to build it so it can stay pressurized, even in the face of consideral damage. Unless you take the perhaps obvious course of letting the crew don spacesuits and actually depressurize the hull when making ready for battle. However, that will leave you very vulnerable to surprise attacks. And surprise attacks have been all the rage for as long as wars have been fought .

So just as 20th century warplanes have self-sealing fuel tanks that can have bullets pass straight through them without spilling much fuel, I suppose it is conceivable that XXXXth century space warships could have self-sealing hulls that might take a lot of damage and stay pressurized.

Hans

 

[Ladewig]

Just to nitpick, I do think it is possible to hear explosions in space. Take a look at the picture here; this is a very large explosion in space, but the effect is largely scaleable. When an explosion occurs in space, a shell of gas will be expanding away from it at a constant or slightly accelerating speed (due to the pressure in the shell itself), and within this shell, the pressure will be higher than in the surrounding space, so when this shell passes you, or the hull of your spaceship, it will influence it mechanically. If the pressure gradient is high enough, it might even cause damage, and at least it is entirely possible that you will hear it.

Hans

Wouldn't there have to be very specific conditions: one is close to the target ship, the target ship is very large, and the target ship actually explodes? And even then it would never "sound" like the explosions one hears in space movies.

 

[rwguinn]

Wouldn't there have to be very specific conditions: one is close to the target ship, the target ship is very large, and the target ship actually explodes? And even then it would never "sound" like the explosions one hears in space movies.

Well, yes. The pressure will change with distance in an inverse cubic relationship. And the "sound" (pressure wave, if you prefer) would not be what they show in the movie.This is entirely true.
But!\
How many people would wait in line for a month to see a movie where all the true action occurred in dead silence? or takes 3 weeks to happen? Artistic license can be a good thing...

 

[Ziggurat]

Just to nitpick, I do think it is possible to hear explosions in space. Take a look at the picture here; this is a very large explosion in space, but the effect is largely scaleable. When an explosion occurs in space, a shell of gas will be expanding away from it at a constant or slightly accelerating speed (due to the pressure in the shell itself), and within this shell, the pressure will be higher than in the surrounding space, so when this shell passes you, or the hull of your spaceship, it will influence it mechanically. If the pressure gradient is high enough, it might even cause damage, and at least it is entirely possible that you will hear it.

Hans

Actually, it isn't scalable, at least not arbitrarily. In the case of that stellar explosion, the length scales are so huge that the surrounding space is not, in effect, a vacuum. A mean free path for a particle of gas of one mile, for example, is basically a perfect vacuum for human length scales, but not for stellar length scales . The expanding gas shell from the nova encounters stationary gas around it, and gets slowed down until it forms a pressure shockwave. But the pressure in this shockwave is actually going to be very small, and the shock front spread out over a very large distance (relative to people). On a more human length scale, if the mean free path for gas is very large, then when the initial explosion occurs, you get a distribution of velocities for your expanding gas. The fast particles zoom off very quickly, the slower particles more slowly, and everything just spreads out. Without enough surrounding gas to slow down the fast particles, you can't form a shockwave pressure front. The mean free path for your gas particles must be much smaller than the length scale of your explosion in order to form a shock wave.

 

[Vagabond]

Crackerbox physics:
Well, yes and no. Obviously, if you are to build a fighting spaceship, you will go to A LOT of trouble to build it so it can stay pressurized, even in the face of consideral damage. Unless you take the perhaps obvious course of letting the crew don spacesuits and actually depressurize the hull when making ready for battle. However, that will leave you very vulnerable to surprise attacks. And surprise attacks have been all the rage for as long as wars have been fought .

So just as 20th century warplanes have self-sealing fuel tanks that can have bullets pass straight through them without spilling much fuel, I suppose it is conceivable that XXXXth century space warships could have self-sealing hulls that might take a lot of damage and stay pressurized.

Hans

Well, in sci fi you can do anything but my point was they blow the crap out of the inside of the ship, they have stuff flying all around and people getting killed without breaking the outer hull. In order to do significant damage to the inside you are going to have to do more than significant damage to the outside first.

 

[dann]

My guess is that the person may have heard the fact that we would not hear explosions in space because there is no medium to transmit sound and morphed that into "There are no explosions in space."

Or he may have been thinking of the implosions that result in black holes.

 

[Art Vandelay]

This enables the inside of the ship to take damage without the outside taking any and venting the entire ship into space thus killing all your main characters.

What's really silly is that apparently, in the future ships will be designed to make it clear that the outside is taking damage by having all the control panels explode. In Star Trek, the consoles keep spewing sparks, and it doesn't make any sense.

rwguinn

The pressure will change with distance in an inverse cubic relationship.

How many people would wait in line for a month to see a movie where all the true action occurred in dead silence?

True. And in reality, one wouldn't really be able to see the ships, either, since there isn't any ambient lighting in space. If you're near a star, half would be lit, but the shadows would be completely dark.

 

[Alkatran]

Do you guys realise how much star wars would suck if all the sound effects weren't there (or even delayed)? Give the guys a break...

And yes, I also find it odd why people in the future don't depressurize their ships. If you're pressurized, small holes become massive gaping holes.

The star trek panel sparks bother me, too. Who the hell designed that thing? The enemy shoots at the ships and 20 people get fried because the console they're at decides to explode "OH NO! UNDER ATTACK! SELF DESTRUCT!"

 

[MRC_Hans]

I found a site once, dedicated to explaining the technicalities of the Star Wars universe. Their explanations for the explosion sounds and the sound of passing ships actuall made a bit of sense: The sounds are generated by the ship's radar (or whatever) system to make it easier for the crew to orient themselves in the complex 3d battlefield. Modern fighter projects are actually looking into the same thing: Augmenting the pilot's perception by including audible cues.

They did not explain why Emperial Storm-troopers cannot hit the broad side of a planet, even if it stands still, however.

Hans