What force keeps the vacuum of space contained?

  • 3 Replies

0 Members and 1 Guest are viewing this topic.


Offline Steve

  • First timers
  • *
  • 1
    • View Profile
What force keeps the vacuum of space contained?
« on: 10/03/2011 13:30:03 »
Steve asked the Naked Scientists:
What force keeps the vacuum of space contained?

What do you think?
« Last Edit: 10/03/2011 13:30:03 by _system »


Offline burning

  • Full Member
  • ***
  • 71
    • View Profile
What force keeps the vacuum of space contained?
« Reply #1 on: 10/03/2011 15:48:09 »
I'm not entirely sure what you mean, but I'll give it a stab.

First off, although it may sound a bit pedantic, a vacuum is an absence of material, so it really can't be "contained."  A vacuum is maintained by preventing matter from leaking into the volume that has been evacuated.  It's also important to remember that a vacuum does not itself exert a force pulling things into it.  What we colloquially call suction is really due to the fact that a relatively evacuated region exerts less force on matter than a relatively occupied region does (the force in question being the cumulative effect of numerous interatomic or intermolecular collisions), so matter between two such regions gets a net push toward the vacuum.

Now the main places for matter to leak into space from is large dense object, i.e. stars and planets, and I'm guessing that you might be trying to ask what prevents something like Earth's atmosphere from being "sucked" (or more properly pushed) into the vacuum of outer space.  If this is your point, the short answer is gravity.  While the net effect of collisions might be to push the molecules of the atmosphere away from Earth, gravity exerts a counteracting pull. 

If we look at the problem more closely, gravity doesn't fully succeed in keeping the atmosphere down.  A certain small fraction of molecules inevitably get a large enough kick (or enough small unbalanced kicks) to exceed the escape velocity of Earth.  Eventually any planet will lose enough of its atmosphere that its surface will for all practical purposes be in vacuum.  The key word is eventually.  I don't happen to know the figures for how long this will take, but when you consider how long this planet has had a breathable atmosphere, you can figure that this won't change on a time scale we need to worry about.


Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • 12350
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
What force keeps the vacuum of space contained?
« Reply #2 on: 10/03/2011 17:21:11 »
I'm not sure it is a 'force'? Burning gave a splendid example on the borders existing macroscopically. If you look at it from a QM level the question seems to become what it is that makes 'matter', like the air we breath and the earth we stand upon. A atom is some 99 percent vacuum if I remember right, and that :) is weird ::)).

Looked at this way you will find that vacuum seems to be the most abundant property of SpaceTime. But gravity, absolutely gravity, and 'time' maybe? When you look at something of the size of a atom, everything become fuzzy. Heisenberg's uncertainty principle (HUP) interface with reality and makes matter something where we never can pinpoint their particles absolutely. If I understand it rightly(?) Feynman's 'many paths' is a alternative to HUP in where the 'indeterminacy' instead becomes alternative paths, all taken by a particle in a interaction, but only the one having the highest probability making it all the way to our reality. And so we meet the question of 'times arrow' and how that express itself in a QM perspective? And if that is right? But macroscopically, which after all is where we 'live' and 'observe' normally, Burning gave you "the truth, the absolute truth, and nothing but the truth, so help me" eh, Einstein :)

And I'm pretty sure of that.
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."


Offline syhprum

  • Neilep Level Member
  • ******
  • 3931
    • View Profile
What force keeps the vacuum of space contained?
« Reply #3 on: 10/03/2011 19:31:16 »
There was an interesting article in the SCIENTIFIC AMERICAN recently on how planets lose their atmospheres, I will try and find a reference.

« Last Edit: 10/03/2011 19:33:19 by syhprum »