Why is Space a Vacuum

[narf poit chez BOOM]

why?

[Atrocities]

Since space is so expansive, endless really, we could never hope to fill it with anything that we can breath.

So if oxygen occurs on our planet, whey does it now occur naturally in space?

How do we over come the obvious danagers that make space space? I have read about things like cosmic winds, megnetic storms and microscopic particle currents and such, so space is not devoid of gasses and such. Just look at a nebula. They are not dispersed into nothingness to fill the void, so if a nebula can exsist as a nebula, a collection of gasses, why can there not be a oxygen Nebula?

[Phoenix-D]

There could be an oxygen nebula. Of course, the pressure there would still be far too low to support human life, to say nothing of the tempature.

Oxygen occurs naturally wherever it collects due to gravity, or where it is created by fusion reactions (or supernova)

EDIT: air exerts the pressure because its a bunch of N2 and O2 molecules bouncing around. Those hitting the container are what creates the effect we call pressure.

[ January 28, 2004, 03:49: Message edited by: Phoenix-D ]

[Fyron]

When molecules move and collide with something, they exert force on it, transfering some kinetic energy. This is what pressure is, a measure of the average force that the matter is exerting upon a surface, an object, a probe, etc.

[ January 28, 2004, 03:49: Message edited by: Imperator Fyron ]

[Will]

The gas itself is exerting the pressure, as seen from a macroscopic scale. What's really happening is all the little gas molecules are moving about randomly, bouncing off each other, etc. There is almost no matter in the surrounding volume to resist the expansion, the 'bubble' will spread out rather quickly.

Think of the air molecules as little balls in a room, bouncing around. Now, if you removed most of the energy loss from collisions, gravity, and air resistance, the balls would mimic the behavior of air molecules (eg, toss a ball at the wall, it will bounce back with nearly the same speed, bounce off the opposite wall, and continue back and forth for a length of time). Now, if you think of the same thing only take away all the walls, you will have the situation of escaped gas in space. The only thing that might keep molecules in the same volume are the molecules themselves (eg, molecule in the 'center' starts moving out, but hits another molecule, and is sent back towards the center). But the probability of such collisions are small, so the gas spreads out.

The reason that there can be a concentration of air around the Earth is the gravity holding it down. So on Earth, the forces of gravity act like a spherical 'wall' containing the gas molecules.

Naturally occuring gasses in space are due to gasses being lost by planets and stars. So with the above example, Earth has a 'wall' blocking off escaped gasses, but it has 'holes', where any molecule gaining enough force can break through and escape into space. Same with stars, only molecules are helped along by the fact that stars are really just explosions being held in by gravity.

Nebulae are gas clouds, yes, but they also contain several stars inside. The combined forces of the gravity of these stars and of the cloud itself allows it to stay together. Theoretically, there could be an oxygen nebula, but it is highly improbable that it would consist of largely oxygen. There would also be hydrogen, helium, lithium, berelium, boron, carbon, etc, etc. The gasses would also not be at the correct pressure to breathe, if that's what you're wondering.

--edit: a much longer-winded Version of what they said...

[ January 28, 2004, 04:04: Message edited by: Will ]

[Suicide Junkie]

The amount of matter in the universe is just very small compared to its volume.
On the order of 10^-28 kg per cubic meter.
The mass of a proton is 1.67 x 10^-27.

Now, most of the mass is also concentrated in stars, planets and whatnot, so the matter left to spread over deep space is even less.
Interplanetary space has a bit more than deep space, mot not too much.

-----

The oxygen molecules from your tank are all travelling quite fast in random directions, and since there are no longer any walls to hold them in, the random motions cause them to spread out quite quickly. Gravity will deflect them somewhat towards the nearby large bodies, but the velocity of those oxygen molecules is surprisingly high.

After they rapidly leave your immediate vicinity, they'll spread out around the solar system and the concentration drops to undetectable levels again.

A kilogram of oxygen has 2x10^25 molecules, but a cubic AU (radius of earth's orbit) has 3x10^33 cubic meters in it.
Evenly spaced and at orbital speeds, you'd bump into those lost molecules rarely enough to count each meeting.

[Renegade 13]

Gases such as oxygen exist in nebula's due to the nova's or supernova's that created the nebula's. During the final years of a star's life, progressively 'heavier' elements are combined via fusion to create even more, "heavier" elements. That is to say, at first hydrogen is fused to form helium. Then, once the hydrogen supply becomes a little short, the helium at the core of the star begins to fuse together to form other elements. Through this chain of events, the "heavy" elements are formed, elements like oxygen, lithium, etc.

So when the star goes nova, those elements are dispersed into interstellar space, forming a nebula. However, these nebulae are constantly expanding due to the forces that created them in the first place. So eventually, the elements that form them are dispersed until the elements are spread as evenly as possible.

So basically, what a vacuum is is all the atoms that form the universe trying to spread themselves as evenly as possible throughout the universe, trying to create a uniform pressure. So the gas escaping from the tank is simply trying to equalize its internal pressure with the pressure of space. However, the pressure of space is very low, and space is so huge, so the tank becomes virtually empty, except for a few molecules that remain.

Also, gravity does overcome the drive to equalize pressure on both large and small scales. Planets on the small scale, and galaxies on the large. And galaxy clusters and superclusters if you want to go that far.

But I've probably confused you enough already, so I'll stop there.