Why is Space a Vacuum

[Atrocities]

Why is Space a Vacuum

Forgive this obviously stupid question but I really do not understand this. Why is space a vacuum? How is it a vacuum? Is everything being sucked into something creating a vacuum? I am serious, I honestly do not understand the principle, albeit I am sure, a simple one.

Say you open an oxygen tank in space, the pressure in the tank is far greater than the pressure out side of it so yes, the gas will escape. But what happens to it afterward? Does it form an oxygen bubble or simply dissipate? If it dissipates, where does it dissipate to?

Could someone please explain the concept of vacuum of space for me? I would enjoy reading it.

[Phoenix-D]

Space is a vaccum because there is little to nothing -there-. Vaccum is just lack of pressure. Nothing there, nothing to exert pressure..

Given enough time and nothing external to stop it, gas will expand to fill any available space. In the case of your oxygen bottle, that amounts to the entire UNIVERSE. So the pressure is very low even when there is something there.

[narf poit chez BOOM]

i think what you are asking is, does the air exert presure on the container or does the vacuum actually suck?

i would say that the air exerts presure becuase there is 'nothing' in space to suck, although i have wondered about this to. i mean, how come nobody seems to wonder about this?

so, Phoenix-D, why does it exert pressure?

[ January 28, 2004, 03:37: Message edited by: narf poit chez BOOM ]

[Phoenix-D]

The air exerts the pressure. Or tries to.

[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.