Physics Question?

[kevin11951]

Gas: Expands to fit its container

The Universe: Infinite space & time

So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?

I have been thinking about this for a week, and nobody i know, knows.

[zmjjmz]

Gas: Expands to fit its container

The Universe: Infinite space & time

So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?

I have been thinking about this for a week, and nobody i know, knows.

I believe it would be drawn towards whatever object has the most gravitational influence.

[Ocxic]

the gas will expand indefinitely, or until and outside force affects it in some way.

[vandorjw]

1) You will not get an infinite amount of gas.
===> Matter cannot be created nor destroyed.

2) Gas only fills the container because it tries to be as far away as possible from other gas molecules to attain the lowest possible energy.
====> So I would assume in space that gas would continue to drift apart until repulsion and attraction force is equal.

(They won't go infinitely apart)

---------------
Actually, I don't know any of this for certain, but I assume that the relations that electrons have between each other is the similar to atoms.

F(r) = K Q1 Q2 /R^2 = F(a) = k M1 M2 / R^2
F(r) - F(a) = 0 (equilibrium)

F(r) = Force repulsion. (I assume both atoms had same charge(
K = some constant.
Q = Charge

F(a) = Force attraction
k = Some other constant.
M = Mass of the objects/ atoms

R = distance between objects.

(Do not cancel the R^2, even though it exists on both sides, because there will be one abs(R) for which this equation hold. If you cancel the R)

Like I said before, I don't actually know for sure, but this is what I think.

Cheers - CC7

[CholericKoala]

^^ above post got it right with the first sentence.

1st law of thermodynamics: Matter cannot be created or destroyed

So the gas molecules only get farther apart. It would disipate in space.

[GrouchoMarx]

Gas expands to fill a space because of entropy. Entropy is not really a force however, it is merely a measure of statistical likelihood. For example, there are more ways for a gas to fill the entire room than there are for it to fill just half the room. So you are statistically more likely to see the room evenly filled, than to see just one side filled. A low entropy state is a statistically unlikely state, and so next time you make an observation, chances are that you will see a higher entropy state: a state of higher likelihood. Hence, entropy tends to increase, and that's why gases expand to fill volumes. Now, the problem is that entropy is only mathematically defined for a system in equilibrium. This means that you need a volume. If your volume is infinite, there is no sense of equilibrium, and you cannot define entropy. Therefore, the theory for the expansion of a gas, which is based on entropy, breaks down in infinite space.

(Anyone?)

[vandorjw]

"Therefore, the theory for the expansion of a gas, which is based on entropy, breaks down in infinite space"

- Are you saying that gas doesn't expand in space?
- Or that space is not infinite?
- Or that all our ideas are statistically, very likely to be wrong.

cheers - cc7

[Jackp90]

I believe it would be drawn towards whatever object has the most gravitational influence.

kinda like the formation of our sun and solar system

[GrouchoMarx]

"Therefore, the theory for the expansion of a gas, which is based on entropy, breaks down in infinite space"

- Are you saying that gas doesn't expand in space?
- Or that space is not infinite?
- Or that all our ideas are statistically, very likely to be wrong.

cheers - cc7

I guess I'm saying that the theory for the expansion of a gas, which is based on the theory of entropy, which is based on statistics, is mathematically defined for a finite volume (as best as I can remember). I'm not sure how to apply the mathematics to an infinite volume.

[rudihawk]

The gas molecules will just get further and further apart...

[CholericKoala]

The gas molecules will just get further and further apart....

[Barrucadu]

Why are you assuming the universe is infinite?

[jsmidt]

Gas: Expands to fit its container

The Universe: Infinite space & time

So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?

I have been thinking about this for a week, and nobody i know, knows.

Okay:

1. The universe is not infinite in space and time. Our universe is only 13.7 billion years old. (It is possible that our universe inflated off the side of a pre-existing universe (http://en.wikipedia.org/wiki/Cosmic_inflation), however this is speculative, though I believe most theoretical cosmologists believe it (http://arxiv.org/abs/0705.0164).)

2. As for space, we live on the surface of a 4 dimensional manifold. This makes space finite too. The common analogy is: think of a universe trapped on the surface of a balloon. As the balloon inflates all the galaxies on the surface get further from each other. Well, now think of our universe as the 3d surface of a 4d balloon. (The analogy isn't perfect, but is pretty good.)

3. As for the gas: gravity does pull it to massive objects. Star formation happens as gas gravitationally collapses. But assuming no gravity, and that the gas tried to fill the universe like it does a room, it turns out the universe is expanding too fast. It can't ever traverse the whole thing. Pretend you were standing on the surface of the balloon. You can only move at the speed of light. The circumference of the balloon actually grows faster as it expands than you can traverse the balloon so you lose. :)

4. Again, the correct answer is gravity pulls it into massive objects. (Eventually, assuming your gas isn't outside the light cone (http://en.wikipedia.org/wiki/Light_cone) of other massive objects.)

Again, the balloon analogy isn't perfect, but unless you are worried about really technical details, it's good enough.

[CholericKoala]

And we dont even fully understand gravity either, so its hard to use gravity as a variable.

[PrimoTurbo]

Basically we do not know anything, when we try to figure out even the most simplest thing like gas expanding we realize we don't have 100% positive answer because we can only speculate about the nature of the universe at the point in our development.

[lisati]

"Therefore, the theory for the expansion of a gas, which is based on entropy, breaks down in infinite space"

- Are you saying that gas doesn't expand in space?
- Or that space is not infinite?
- Or that all our ideas are statistically, very likely to be wrong.

cheers - cc7
Perhaps the limits of the "container" that we know about are a special case that needs modification when applied to something on a larger scale like the universe.

And we dont even fully understand gravity either, so its hard to use gravity as a variable.

Another one: the square root of -1 doesn't have much meaning when applied to some things (e.g. working out the change you should get after you buy the groceries), but the idea behind it can be a useful stepping stone towards providing useful results in other areas (e.g. electrical engineering). Anyway, isn't it true that gravity is a myth, the earth sucks? (Enough said?)

[samjh]

Gas: Expands to fit its containerCareful. Volume increases, but concentration decreases in proportion to the volume.


The Universe: Infinite space & timeAgain, be careful how you word your ideas. The universe is not infinite. According to modern astrophysics theory, the universe is expanding. The upper limit of this expansion is yet unknown, if it exists at all.


So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?The atoms or molecules that make up the gas will increase their distance from each other due to entropy. As I stated before, the volume of gas will increase, and concentration will proportionately decrease. Therefore the gas simply dissipates until its concentration becomes negligible.


I have been thinking about this for a week, and nobody i know, knows.That's because the complete state and future behaviour of the universe is not within human knowledge.

[gn2]

So what happens when you release a gas in space, where does it go~

Wherever gravity takes it.

[gn2]

And we dont even fully understand gravity either, so its hard to use gravity as a variable.

Gravity is a constant.
All mass has gravity.

[bruce89]

In other words, life's too short too worry about gas (unless you're a swamp dragon).

[CholericKoala]

Gravity is a constant.
All mass has gravity.

Yet we dont know what causes gravity. Gravity is a constant only because we havent come across something that thwarts it yet. How does mass have gravity? What causes it?

[halovivek]

if you want know full details about this please read this link. (http://www.archive.org/stream/originalsanskrit03muir/originalsanskrit03muir_djvu.txt)

[gn2]

How does mass have gravity? What causes it?

That's one of life's great mysteries, right up there with such conundrums as what does God look like....?

[CholericKoala]

That's one of life's great mysteries, right up there with such conundrums as what does God look like....?

A lion and a lamb ;)

[Thelasko]

A common misconception is that space is empty. This isn't true. Hydrogen gas has filled outer space, only it's density is extremely low. From Wikipedia: (http://en.wikipedia.org/wiki/Perfect_vacuum#Outer_space)

But no vacuum is truly perfect, not even in interstellar space where there are still a few hydrogen atoms per cubic centimeter.
On this scale, gravity comes into play. Atoms begin to bunch up due to gravity and form clusters of mass. These clusters of mass, having more gravity, gather more atoms. The cycle continues until the force of gravity is so strong that it overcomes the electromagnetic force between protons and the atoms begin to fuse together. This is how stars are born.

Here on Earth, gravity doesn't come into play like it does on an astronomical scale. Therefore your teacher didn't teach you this exception to the rule (yet).

Whenever I try to understand how a gas works, I think of this model. (http://en.wikipedia.org/wiki/Image:Translational_motion.gif)

[blazemore]

We've already got gas released in space... it hangs around planets and stuff, and burns to be stars. It's attracted by gravity.

[CholericKoala]

Interesting though that the second law of thermodynamics states that things always tend towards disorder.

[Thelasko]

And we dont even fully understand gravity either, so its hard to use gravity as a variable.

We may not know what gravity is (but we're getting close (http://en.wikipedia.org/wiki/Higgs_boson)), but we still know how it behaves. (http://en.wikipedia.org/wiki/Gravitational_constant) In this instance, that is all that matters.

This question can be answered with classic Newtonian theories of gravity and doesn't even cross into the area of general relativity, let alone the few anomalies (http://en.wikipedia.org/wiki/Gravity#Anomalies_and_discrepancies) that can't be explained by our current models. If modern science didn't have an answer to this question, we would never be able to put humans into orbit, and return them safely. (http://en.wikipedia.org/wiki/Atmospheric_reentry)

[ReddogOne]

Gas: Expands to fit its container

This is a rule that applies to gas in a closed system and ignores gravity and other forces!


The Universe: Infinite space & time

So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?

Space is not a container and it has gravity and other forces!

(However Gas that has not been trapped by gravity would float away forever, because its not in a container, and as for the universe its only as big as the stuff in it)

[mintochris]

So much amateur physics in this thread!

the gas would expand until it's internal pressure (ie expansion due to random movement) was balanced by it's gravitational self-attraction.
What do you think jupiter, saturn and uranus are if not clouds of gas? What about a nebula?
Oh, and by the way, on cosmic(gravitational) scales entropy tends towards disorder by clumping, not spreading. It's a common misconception.

[blazemore]

Interesting though that the second law of thermodynamics states that things always tend towards disorder.

What? No it doesn't. If anything, it's the opposite. In a nutshell, all it states is that heat cannot transfer from one body to a hotter body.
Basically, if you have a 50C bit of metal and a 70C bit of metal, and put them together, then (in a vacuum and discounting radiation) they would both eventually reach 60C.

[lisati]

What? No it doesn't. If anything, it's the opposite. In a nutshell, all it states is that heat cannot transfer from one body to a hotter body.
Basically, if you have a 50C bit of metal and a 70C bit of metal, and put them together, then (in a vacuum and discounting radiation) they would both eventually reach 60C.

This reminds me of a tale I once heard: in a nutshell it stated that if you had your head in a hot oven, and feet in a cold freezer, on average, you'd probably be at a more reasonable temperature.

[diwas]

Gas: Expands to fit its container

The Universe: Infinite space & time

So what happens when you release a gas in space, where does it go, if space is infinite, and gas always expands to fit its container?

I have been thinking about this for a week, and nobody i know, knows.
Well i think the gas molecules will remain intact due to their own force of gravitation attracting each other, if no other force is applied. So it wont expand, rather be close together.
F=(G*m*n)/r^2

[ghindo]

It depends a lot on the temperature of the gas.

[diwas]

It depends a lot on the temperature of the gas.
Yes. True.

[Thelasko]

It depends a lot on the temperature of the gas.

A very nice post. Temperature is related to the kinetic energy of particles. When a particle has at least enough kinetic energy as gravitational potential energy, it can reach escape velocity (http://en.wikipedia.org/wiki/Escape_velocity).

Therefore, cooler particles will cluster together more than hotter ones.

OP may be interested to know that engineers clump liquids and gasses together as fluids (http://en.wikipedia.org/wiki/Fluid). We then categorize fluids by compressibility (http://en.wikipedia.org/wiki/Compressibility) instead of the ability to fill a given volume. Liquids tend to be difficult to compress compared to gasses.

[gn2]

Basically, if you have a 50C bit of metal and a 70C bit of metal, and put them together, then (in a vacuum and discounting radiation) they would both eventually reach 60C.

Only if both pieces of metal have the same mass...?