Question about Space!

**technishn08** · October 31, 2007, 05:46 PM

Ok, so here it goes. What would happen if you had a giant canister of oxygen in space, and you opened it, releasing the oxygen. Would the oxygen stay "clumped" together? Because for some reason, I think of space as sort of like a cell. Again, I don't know why, but I have some notion that everything in the Universe is simply trying to get to equilibrium. IF that is the case, would the oxygen just expand to create "even" coverage? Then I think, that has to be impossible is space is infinite. It would just keep expanding and growing ever thinner... I don't know lol. I was just thinking of this for no real reason at all.

**David Deas** · October 31, 2007, 05:52 PM

I have a question that goes with his. Astronauts fart. So if I farted in space would that fart like continue to orbit the Earth forever?

**Juvenal** · November 01, 2007, 01:00 PM

Originally Posted by David Deas

I have a question that goes with his. Astronauts fart. So if I farted in space would that fart like continue to orbit the Earth forever?

I have had a fascinating time learning about modern space suits.

I think the emission is likely to continue to accompany the astronaut until they take their diaper off after they desuit (yuck).

Theoretically the emission could leave the suit via the vents at the feet and elbows, but if it can get that far it might well have already been caught by the CO₂ scrubber.

As for orbiting the Earth forever, well this is unlikely to happen since most astronauts don't go any higher than low earth orbit. As viewers of Star Trek know well, all low orbits decay within 40 minutes (or even quicker if the spaceship develops a problem with its warp drive).

**Thanatos** · October 31, 2007, 05:57 PM

No, because gas wants to escape from itself.

**Spurius** · October 31, 2007, 06:34 PM

Originally Posted by Thanatos

No, because gas wants to escape from itself.

Especially fart gas. It auto-obnoxious and -repelling, and under the right circumstances can even exceed the speed of the expanding universe.

Yes gases tend to spread out forever, although of course things like gravity will try to counter it briefly. Even Earth loses hydrogen gas because it escapes the gravity well, and is gone for good. Is basically the same reason why Mars has not surface waters - Mars is too light.

**GORE** · November 01, 2007, 11:44 AM

the oxygen particles will repel eachother, but each particle has its own gravity aswel which is far less than the repelling force. to overcome this it would take a truely massive amount of particles; a nebula which will then form a star.

so the oxygen would disperse, but not evenly across space, as once the particle is a short distance away there is no longer any interaction.

**chris_uk_83** · November 01, 2007, 11:44 AM

Yep, agreed with Spurius. Gas particles will always move away from each other on average. The process is called diffusion and always happens.

**Spurius** · November 01, 2007, 01:11 PM

Next question will ofcourse be - then howcome galaxies formed in the first place, if the initial universe was mainly hydrogen and helium, both the shizz in lightweight and diffusive gases.

How can gravity overcome diffusion when it's still ALL a gas.

Anyone?

**Juvenal** · November 01, 2007, 01:42 PM

Originally Posted by Spurius

How can gravity overcome diffusion when it's still ALL a gas.

I presume everyone knows this already, so I am risking egg-on-face here...

Diffusion is caused by short range effects (molecules colliding and repulsion of electron shells). Gravity is a long range force (strength proportional to inverse square of distance), so if you have a sufficient quantity of gas, and the gas is cold enough (reducing the repulsive effect of the collisions) then gravity can cause randomly occuring local regions of slightly higher density to start to accumulate.

Once this gets going it is self perpetuating. Clumps swallow other clumps and get bigger. Since angular momentum of incoming material is preserved, you would expect the clumps to acquire spin as they got bigger and for smaller clumps to end up orbiting the bigger ones.

Eventually you end up with all locally available gas swept up by a system of orbiting bodies.

Other processes and effects that I don't have time to go into here might eventually result in the formation of me and my computer.

I seem to recall that there are theories that the presence of dark matter may have assisted this process during galaxy formation.

**Spurius** · November 01, 2007, 05:17 PM

Originally Posted by Juvenal

and the gas is cold enough

Yep, that sort of sums it up nicely. Any sufficiently cooler region should become a haven for gravity to kick in.

This means of course temperature in the initial gascloud after the big bang was not 100% evenly spread, or we wouldn't even be here, maybe.

Which I think stilll shows in the CMB:

**chris_uk_83** · November 01, 2007, 04:58 PM

^^seconded^^

**chris_uk_83** · November 02, 2007, 02:03 PM

That's nice, reference a picture of the Cosmic Microwave Background so people know that you're really clever

**Thanatos** · November 02, 2007, 02:57 PM

Originally Posted by chris_uk_83

That's nice, reference a picture of the Cosmic Microwave Background so people know that you're really clever

If you also say that you're a graduate student with a major in either Atmospheric Sciences or in Astronomy, you get more internet points too.

**Spurius** · November 02, 2007, 03:32 PM

Originally Posted by chris_uk_83

That's nice, reference a picture of the Cosmic Microwave Background so people know that you're really clever

Well, I was going to post this one, so people don't take me too seriously

**Simetrical** · November 04, 2007, 05:51 PM

Originally Posted by Juvenal

As for orbiting the Earth forever, well this is unlikely to happen since most astronauts don't go any higher than low earth orbit. As viewers of Star Trek know well, all low orbits decay within 40 minutes (or even quicker if the spaceship develops a problem with its warp drive).

If you're not clear of the atmosphere, yeah. Otherwise you're good for a long time, although you'll want to correct your course sometimes, probably.

Yeah, I know that wasn't a totally serious statement.

**Juvenal** · November 05, 2007, 02:50 AM

To be serious for just a few seconds...

I may be confused about the reasons for various low-orbit satellites coming down in recent years, such as Mir and Skylab. My assumption was that if you don't apply regular course corrections then the orbit eventually eventually drifts, potentially bringing part of it into higher-drag altitudes and thus leading to the infamous Star Trek "orbital decay".

I believe that Mir was actively de-orbited (i.e. by firing the motor), but I presume this was in order to exercise some control about where (or at least when) it came down.

Does anyone out there know if there is any atmospheric drag in normal low-earth orbits such as that occupied by the ISS?

**Spurius** · November 05, 2007, 08:02 AM

Originally Posted by Juvenal

Does anyone out there know if there is any atmospheric drag in normal low-earth orbits such as that occupied by the ISS?

Yes, I knew the atmosphere went up WAY above what most people assume, only a lot thinner - but not totally absent. Also the solar cycles make the atmosphere puff up every 11 years, so that adds to the drag.

http://science.nasa.gov/headlines/y2000/ast30may_1m.htm

**Simetrical** · November 06, 2007, 01:22 PM

Ah, it seems low-Earth orbits are often inside the upper stretches of the atmosphere, indeed. At least according to the Wikipedia article. Ah, well, I only learned about satellites in my physics class. Physicists don't care about silly real-world stuff like air resistance (at least not if they can avoid it).